Asian Noodles (Science, Technology, and Processing) || Rice and Starch-Based Noodles

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CHAPTER 16

Rice and Starch-Based Noodles

ZHAN-HUI LU and LILIA S. COLLADO

16.1. INTRODUCTION

The term “Asian noodles” is used very broadly to describe noodle-like products fromEastern, Southeastern, or Pacific Asian countries that are made from wheat flour,rice flour, or other starch materials as the main structural ingredient (Lu and Nip2006). Rice- and starch-based noodles differ from wheat noodles in many aspects.Wheat flour and water easily form dough through appropriate mixing and kneadingtechniques that facilitate sheeting and slitting into strips or strands to produce noodles.This unique ability to form cohesive, elastic, and extensible dough is attributed togluten, the unique protein in wheat (Hoseney 1990a,b). In the absence of gluten inother starch-based raw materials, a pregelatinized starch binder must be added beforethe dough can be kneaded and extruded into threads or strings. An alternative processmay involve the pouring of a starch batter onto a cloth or metal sheet followed bysteaming, cooling, scraping, tempering, and slicing into thin strands.

These products are known as nonwheat noodles or, more appropriately, as starchnoodles. The characteristics of starch noodles are heavily dependent on the functionalproperties of the starch as it undergoes one or two heat treatments during processing(Mestres et al. 1988). The heat treatment may involve boiling or steaming thatgelatinizes the starch, and the subsequent retrogradation sets the structure of thestarch noodles (Tam et al. 2004). These products include noodle sheets, strips, andthreads from the flour and starch of cereals, and legume and root-crop starches.

Rice (Oryza sativa L.) supports more than half of the world population (FAO2007a). The Food and Agriculture Organization (FAO) of the United Nations fore-casts for global milled-rice production in 2007 stands at 426 million metric tons,which is 1% higher than 2006 (FAO 2007b). Rice is the staple food in most Asiancountries and is consumed in most households on a daily basis. There is an increasingneed for conveniently processed rice products to keep up with the fast pace of modernlifestyles. Rice noodles are the main processed food product made from rice. The

Asian Noodles: Science, Technology, and Processing, Edited by Gary G. HouCopyright C© 2010 John Wiley & Sons, Inc.

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394 RICE AND STARCH-BASED NOODLES

processing of rice into noodles provides benefits for both consumers and manufac-turers. It has a large potential market because it is served not only as a snack foodbut also as a main dish. The processing technology of rice noodles is also simplerthan the production of other starch-based noodles, such as mung bean and potatonoodles that start with the extraction of starch. The whole polished rice kernel is uti-lized completely in the finished product and this confers certain nutritional benefitsto consumers. Rice noodles generally have higher protein content than other starchnoodles. It has also been demonstrated that rice noodles provide a lower glycemicblood index when eaten by diabetic patients (Panlasigui et al. 1991, 1992). This canbe attributed to the fact that starch noodles are retrograded and are, therefore, a sourceof resistant starch (RS) (Collado et al. 2001).

Rice noodles are made by soaking rice and then milling, cooking, and kneadingit into dough and extruding it into threads or slicing the sheet into strips. The ricenoodles may then be eaten fresh; otherwise, they are dried to extend their shelf life.

Rice noodles are popularly known in China as mifen, or as mixian (thin threads)and hefen (flat strips). It is believed that noodles originated in China several thousandyears ago but that the present-day form was developed within the last 2000 years.The Chinese character for fen (starch noodles) is written with mi (rice) on the leftside as part of its written structure, indicating that it originated from rice. It is alsobelieved that fen spread from China to neighboring countries. This is supported byterms with similar sounds in these countries (Lu and Nip 2006).

A Chinese story explains how rice noodles were invented. In 214 BC, the firstemperor of the Qin Dynasty, Qin Shi Huang, sent his army to conquer southern China,where rice was the staple food. Most of the soldiers were from northern China, wherewheat noodles were the staple food. They could not adapt to daily rice meals, so awise chef tried to make noodles from rice flour in the same way that wheat flournoodles were processed, but he failed. After several trials, he understood the problemand made modifications in the process. He invented a stone mortar with a hole drilledinto the bottom. The wet rice dough was placed into the mortar and then presseddown by a wooden cork through a wooden lever. The threads were extruded from thehole and fell directly into the boiling water in a big kettle. The cooked noodles wereperceived to be very similar to wheat noodles and were well accepted by the soldiers.Later, traditional Chinese spices and herbal medicines were added to the noodle soupto prevent diseases and cure illnesses. Eventually, the meat of dead war horses wasalso added to the soup and became the earliest Guilin mifen from Guangxi Provinceof China. It is still cooked and consumed today. This noodle soup became known inmany other provinces and was called Guoqiao mixian (Guoqiao means “cross theriver”) in Yunnan Province, Changde mifen (Changde is a place name) in HunanProvince, and hefen (or shahefen) in Shahe Town, Guangdong Province (Sun 2006).The processing method for rice noodles has not changed in the different provinces,but the different flavors of the soup in each of the provinces gave distinctive characterto the otherwise bland-tasting noodles.

Starch noodles are also produced from corn (Zea mays), buckwheat (Fagopyrumesculentum), mung beans (Vigna radiata), peas (Pisum sativum), sweet potatoes(Ipomea batatas), potatoes (Solanum tuberosum), canna (Canna edulis), arrowroot


TYPES OF RICE AND STARCH-BASED NOODLES AND THEIR CONSUMPTION 395

(Maranta arundinaceae), cassava (Manihot esculenta), and yam (Amorphophalluskonjac). A portion of the substrate is gelatinized to serve as a binder for the doughor batter, which may then be extruded, sheeted, and further molded into the desiredshape. Variations in processing are made to suit the substrate and intended product.

16.2. TYPES OF RICE AND STARCH-BASED NOODLESAND THEIR CONSUMPTION

16.2.1. Types of Rice

The classification of rice varieties has changed through the years as shown in Ta-ble 16.1, but the most recent and recognized varieties are classified into four groups:Japonica, Javanica, Indica, and Scinica (Matsuzaki 1995).

Only nonglutinous Indica rice is used to produce rice noodles due to its highamylose content, which ranges from 25% to 33% (Juliano 2005). Japonica rice isseldom used for rice noodle production because of its high stickiness but it may bepartially blended with Indica rice to improve the noodle texture.

16.2.2. Types of Rice Noodles

Rice noodles (mifen) are produced in different ways in different geographic locations.According to the preparation methods for making noodles of different dimensions,noodles can be classified into two groups, qiefen and zhafen, as shown in Figure 16.1(Cheng 2000). Qie in Chinese means “slice into broad strips from a large and thinsheet” and measurements that range from 1 to 2 mm thick, 4 to 6 mm wide, and

TABLE 16.1 Classification and Characteristics of Asian Rice

Researchers Classification of Variety Groups

Kato and others(1928) Japonica Indica

Morinaga (1954) Japonica Javanica Indica

Nakagawara (1978)Japonica(Japanese Type)

Javanica(Javanese Type)

Indica(Indian Type)

Scinica(Chinese Type)

Major Characteristics(Matsuo 1952)

Shape of seed Short kernel Large kernel Long kernelShape of flag leaf Short, narrow Long, wide Long, narrowNumber of tillers Many Few ManyAwn Usually absent Usually present Usually absentShedding habit Difficult Difficult EasyPanicle length Short Long Medium

Source: Matsuzaki (1995).



Rice noodles (mifen)

Cut rice noodles(qiefen)

Extruded rice noodles(zhafen)

Hefen: shahefen

Juanfen or changfen (with filling)

Fermented rice noodles

Extrusion-cooked rice noodles

FIGURE 16.1 Types of rice noodles classified by noodle-shaping methods.

around 200 mm long. Zha means “extrude into threads” that have a round shapewith a diameter ranging from 1 to 3 mm and a length ranging from 50 to 400 mm(Figure 16.2). Rice noodles are either fermented or nonfermented, but only zhafenis a typically fermented product. Fermented rice noodles are also called sour mifenbecause of their slight sour smell. This method for classifying rice noodles is favoredby researchers because it indicates the processing technology of the products.

Another convenient way to classify rice noodles in the industry is based on themoisture content and processing methods used that dictate the way products arepackaged, distributed, prepared, cooked, and consumed (Figure 16.3).

Traditionally, in China, rice noodles are also named after their place of origin suchas Shahefen made in Shahe Town, Guangdong; Guilin mifen made in Gulin, Guangxi;Changde mifen from Changde City, Hunan; and Guoqiao mixian from Yunnan. Inrecent years, some manufacturers have begun to use corn starch or other starchescombined with or in place of rice flour to make similar products, and still call them“rice noodles.” While they have similar properties, they do not have the same qualitycharacteristics of original rice noodles (Lu and Nip 2006).

16.2.3. Types of Other Starch Noodles

The variety of other starch noodles is presented in Table 16.2, which lists the crop fromwhich substrate is produced, the equivalent English names, and the countries wherethey are produced. It must be pointed out that this table presents the typical starch-noodle products to which the authors had access. It can be noted that starch noodlesare produced extensively not only in China but also in Malaysia, the Philippines,

FIGURE 16.2 Types of rice noodles.


RAW MATERIALS AND QUALITY REQUIREMENTS 397

Fresh (wet) rice noodles

Dry rice noodles

Frozen rice noodlesRice noodles (mifen)

Dried (Instant hefen, waved instant rice noodles etc.)

Instant rice noodles Fermented rice noodlesFresh (wet)

Nonfermented rice noodles

⎧⎪⎪⎪⎪⎨ ⎧⎪ ⎪⎪ ⎧⎨⎪ ⎨⎪⎪ ⎩⎩⎩

FIGURE 16.3 Types of rice noodles based on moisture content and processing methods.

Vietnam, Thailand, Korea, and Japan. And there are many more from other countriessuch as India and Pakistan. Some of these starch noodles are shown in Figure 16.4.

16.3. RAW MATERIALS AND QUALITY REQUIREMENTS

16.3.1. Rice and Other Substrates

Indica rice is commonly used because of its high amylose content, cheap price, andhigh yield. Indica rice is also classified as early Indica and late Indica accordingto their harvesting season (early Indica is harvested around August, and late Indicais harvested around October in southern China). Early Indica rice is particularlypredominant as an early-season crop. Its inferior eating and cooking qualities accountfor its lower price in the market.

TABLE 16.2 Types of Starch Noodles from Crops Other Than Rice

Crop Equivalent English NamesRegional Names of Noodles(Country)

Mung bean, pea Green bean thread noodlesVermicelliTranslucent noodlesSilver noodlesShining noodlesGlass, crystal noodlesJelly noodles

Bai fun, Sai funFen szu, Fensi (Chinese)Soo hoon, Su boon (Cantonese)Tung boon (Indonesia)Sotanghon (Philippines)Woosen (Thailand)Ban tau (Vietnam)Harusame (Japan)

Corn Corn starch noodles Luglug (Philippines)Buckwheat Buckwheat noodles Naeng myon (Korea)

Soba (Japan)Canna Canna starch noodles Mi´en, Mi´en dong (Vietnam)Sweet potato, potato Sweet potato noodles Dang myeun, Tang myun (Korea)Cassava Tapioca sticks Hu tieu bot loc (Vietnam)Arrowroot Arrowroot starch noodles Bo. t dong, Bo. t hoang tinh,

Bo. t mı tinh (Vietnam)Yam Yam noodles, devil’s

tongue noodlesShirataki, sirataki, ito konnyaku(Japan)

Source: Alden (2005).



Sweet potato noodles Corn sticks Potato noodles

Instant corn noodlesGreen bean noodles Instant rice ribbons

FIGURE 16.4 Selected starch noodles.

The rice should be aged and stored for at least 9 months before being processedinto noodles. Rice stored for more than 1 year is considered better. A small amountof late Indica rice or Japonica rice might be mixed with early Indica rice to adjustthe texture of rice noodles, but this technique depends on the technician’s experience.

The properties of rice starch, which account for around 85% of rice dry weight,strongly affect the quality of rice noodles. In the traditional cottage production,selection of rice raw material for rice noodle production is conducted by sensoryevaluation of the cooked rice. The evaluation is based on acquired knowledge andexperience of the processor. National quality standards of rice raw materials forindustrial noodle production are not presently available.

16.3.1.1. AmyloseBased on amylose content, rice is classified as waxy 0–2%, very low 2–9%, low10–20%, intermediate 20–25%, and high >25%. Many of the long-grain varietieshave higher amylose content than the short grain varieties. This difference in starchcomposition may largely be responsible for the well-known differences in cookingand eating quality of rice varieties. In China, Indica rice varieties with amylose


RAW MATERIALS AND QUALITY REQUIREMENTS 399

content higher than 22%, and in Thailand, varieties with greater than 27% amylosecontent are used in the production of rice noodles (Tungtrakul 1998). Generally, high-amylose rice varieties give high hardness, high tensile strength, and high consistency.These attributes and parameters are highly valued in noodle processing and packaging.However, this must be balanced by a low retrogradation rate and the ability to deformwithout breakage of finished noodle products.

Generally, the best substrate for starch noodles is considered to be starch fromlegumes like mung beans, which normally have more than 30% amylose content. Theeating and cooking qualities of mung bean starch noodles are usually the benchmarkfor high standards when working on experimental substrates and process parametersfor starch noodles. Aside from high tensile strength and chewiness, bean noodles arealso known for clarity and gloss not observed in other substrates. This characteristicis the reason they are referred to as transparent, glassy, or even invisible noodles.These types of noodles also have high tensile strength in both their raw and cookedforms. The pasting profile obtained from the amylograph that is characterized by highhot paste stability and high setback has been used by several researchers as screeningcriteria for evaluation of different substrates and starch modification processes forsuitability in noodle production (Lii and Chang 1981; Chang and Lii 1987; Colladoet al. 2001). Morphological properties, gel properties, and starch granular size werealso found to correlate with the textural properties of the cooked starch noodles (Chenet al. 2002, 2003; Singh et al. 2002).

16.3.1.2. ProteinProtein content is one of the indices of the nutritional value of milled rice. It canbe an indirect indicator of cooking quality because its hydrophobic nature acts asbarrier to inward water diffusion during cooking of the grain. The protein content ofmilled rice ranges from 5% to 15%. High-protein rice varieties have a harder texturethan average-protein rice (Tungtrakul 1998). Low-protein rice varieties tend to beflavorful, tender, and cohesive (Ohtsubo et al. 1993).

16.3.1.3. Fat AcidityFat acidity is one of the important rice quality indices that must be monitored duringstorage. Free fatty acids and volatiles increase during drying and storage due tohydrolytic and oxidative reactions. Free fatty acid content is higher in broken ricecompared with milled rice (41.6–45.5 mg KOH/100 g), as determined by the improvedDuncombe method (Ohtsubo et al. 1987). High-amylose milled rice contains a fatacidity value of 10.8–22.1 mg KOH/100 g. Broken rice that is known to producegood-quality rice noodles should be stored for 0.5–1 year (aged rice), and free fattyacid content should be less than 100 mg KOH/100 g.

16.3.1.4. Viscosity and Gel Consistency of Rice FlourViscosity measurements of paste or gel made from milled rice flour or starch havelong been in use for evaluating cooked rice texture (Perez and Juliano 1979).The Brabender Viscoamylography test has been the standard method for studying thepasting characteristics of starch and starch-based products. The Rapid Visco Analyzer(RVA) can provide similar information in a shorter time and with a smaller sample



size. Flour from well-aged rice will have higher viscosity than freshly harvested milledrice. Hard gel is preferred for noodle making because hard gel rice will be more stableto overcooking and will retain its form. It has been suggested that the ideal starch basefor preparing noodles is one with restricted swelling and a viscosity that remains con-stant or even increases during continued heating and shearing, indicative of good hotpaste stability (Collado et al. 2001). Stability ratio (holding viscosity/peak viscosity)is correlated to noodle firmness, rehydration (cooked weight), and swelling volume ofthe starch (Collado and Corke 1997). Setback correlates negatively with noodle ten-sile strength and extensibility. Pasting temperature shows positive correlations withnoodle hardness, tensile strength, and extensibility (Hormdok and Noomhorm 2007).

16.3.2. Water Quality

Water quality has a noticeable effect on rice noodle texture. The pH value of the watershould range from 6 to 6.5; water hardness must be less than 50 mg/kg; turbiditymust be less than 3◦; and coliform count must be less than 3 cfu/100 g. In a study,we found higher contents of Mg and K elements in nonfermented rice flour (139.0± 0.6 mg/kg of Mg, 359.6 ± 2.1 mg/kg of K) than in fermented rice flour (50.9 ±1.2 mg/kg, 75.5 ± 1.8 mg/kg) when preparing fermented rice noodles. It was alsonoticed that even 30 mM of Na+ could increase the differential scanning calorimetry(DSC) peak temperature by 1.5 ◦C of 38% w/w slurry (unpublished data). Accordingto the Hoffmeister series, Mg2+ has a much stronger effect than Na+ on thegelatinization inhibition, while K+ and Na+ have a similar effect (Levine and Slade1991). Therefore, Mg2+ needs more careful consideration because it is common andabundant in many water resources used in production systems. Water hardness hasbeen found to impact the stickiness of cooked noodles. The effects of cooking watercomposition on the stickiness of spaghetti have been studied and it was suggested thathigher stickiness was obtained in spaghetti cooked in harder water and that mineralcomposition of the water played a role in influencing the cooking quality of spaghetti(Malcolmson and Matsuo 1993; Numfor et al. 1995). However, there were no studieson the effect of water quality on rice noodles found in the literature reviewed.

Rice noodles made from neutral water (pH 7) have the highest retrogradationrate. At acidic conditions (pH 5.5), the retrogradation rate slows slightly. Noodlesprepared from water with pH 9.5 have the lowest retrogradation rate. The textureof rice noodles prepared from alkaline water (pH 10) or acidic water (pH 5.5) isimproved and the best tensile properties are achieved with acidic water (Sun 2006).

16.3.3. Additives

16.3.3.1. Modified Starches and Starches from Other SourcesAcid-modified starch is used to inhibit the starch retrogradation of products duringdistribution and storage. Corn starch is usually used to increase hardness and decreaseadhesiveness of rice noodles. It is attributed to the high amylose content of corn starch(34.4%). Edible canna (Canna edulis) is a perennial herb of the family Cannaceae,native to the Andean region of South America. This plant has large, starchy rhizomesand has been used traditionally as a staple food by the Andean people for more than


EQUIPMENT, PROCESSING, AND PRODUCT QUALITY 401

4000 years (Thitipraphunkul et al. 2003). Edible canna starches have large granulesand high amylose content, and they are used mostly for preparing transparent starchnoodles. The noodles made from edible canna starch had excellent eating qualitiessuch as high tensile strength, minimal swelling, and good transparency. Addingedible canna starch can improve the viscosity and pliability of hefen and increaseschewiness as well as transparency. Its amylose content is around 29%. Potato starchcan also improve the transparency and elasticity of hefen. The gelatinization temper-ature of potato starch is lower but its swelling power is 48 times that of corn starch.Potato starch also has slower retrogradation rate and is very effective in decreasingthe percentage of broken noodles. Chufa (Cyperus esculentus L. var. sativus Boeck.)starch can be used to improve the chewiness of hefen. Composite starches aremore effective than single starches for textural improvement of rice noodles. Arecommended formula is 5% corn starch, 2% edible canna starch, 2% potato starch,and 1% Chufa starch. This formula can increase the tensile property of hefen anddecrease the percentage of broken noodles and cooking loss significantly (Sun 2006).

16.3.3.2. Sodium ChlorideSodium chloride (NaCl) at 0.5–1% can increase the water-holding capacity of ricenoodles and inhibit the growth of microorganisms that are present as contaminants(Sun 2006).

16.3.3.3. Phosphate CompoundsPhosphate compounds (Na2HPO4·12H2O, NaH2PO4·2H2O, Na4P2O7·10H2O,Na5P3O10, (NaPO3)6, etc., 0.1–0.4%) can increase the soluble materials leakingout from starch granules, enhance the binding ability of starch molecules that tendto improve the tensile strength of noodles, and decrease the percentage of brokenstrands (Sun 2006).

16.3.3.4. Glycerin MonostearateGlycerin monostearate (0.3–0.5%) is an emulsifier often used to improve the textureof rice noodles and to inhibit the retrogradation of noodles, although the mechanismremains unclear (Sun 2006).

16.3.3.5. Plant OilPlant oil (0.5–2%) is used as a coating on the surface of rice noodles. Peanut oil isused most often. In industrial production, the oil is used for lubrication of the machineand prevention of stickiness between noodle sticks. The use of oil makes the handlingof rice noodles easier. Although adding oil cannot inhibit the starch retrogradation,the hardness of noodles tends to decrease when oil content is increased (Sun 2006).

16.4. EQUIPMENT, PROCESSING, AND PRODUCT QUALITY

This section is divided into four subsections corresponding to (1) fresh rice noo-dles, (2) dry rice noodles, (3) frozen rice noodles, and (4) instant rice noodles.Fresh rice noodles are discussed first since their basic processing is common to all



the other noodle types. Furthermore, for fresh noodles, the classification based onnoodle dimension used is qiefen and zhafen because their processing represents thetypical procedures and practices used in rice noodle manufacturing. Instant rice noo-dles are included in this section because of their emerging importance in the foodindustry.

16.4.1. Fresh Rice Noodles

Considerable amounts of fresh rice noodles are produced for the retail market, restau-rant trade, and household market, especially for breakfast. The noodles are usuallyproduced at night and then distributed to markets before dawn. The shelf life of freshrice noodles is less than 24 hours in summer and 48 hours in winter, so noodles arefresh and their mouthfeel is the best. Fresh rice noodles include qiefen (flat strip) andzhafen (round thread). The representative qiefen type of noodle is hefen (shahefen) andjuanfen, which is a rolled-noodle type with fillings inside and will not be discussedin this chapter. Zhafen includes fermented rice noodles and extrusion-cooked ricenoodles. Fermented rice noodles have a pliant, chewy texture while extrusion-cookedrice noodles have a chewy and firmer texture (Sun 2006).

16.4.1.1. Fresh HefenHefen (shahefen) are Cantonese oily rice-based noodles that are produced by prepar-ing a rice slurry from Indica rice flour, followed by steaming a thin layer of the slurryon an oil-coated stainless tray or bamboo sheet. The gelatinized fen is then foldedinto layered slabs, followed by slicing of the slabs into strips. Oily rice-based hefenis very soft and smooth in texture (Lu and Nip 2006). The characteristics of hefen areas follows:

1. Easy to serve and smooth mouthfeel. Hefen is excellent for soup dishes inwhich hefen is just placed into boiling soup and it is ready to serve. It cooks fastbecause its thickness is less than 1 mm and it has a high moisture content ofabout 70%. It is also easier to digest because of its high degree of gelatinization.

2. Simple and low-cost processing method. The processing operations includewashing, soaking, grinding, steaming, cooling, and slicing. Only a few piecesof equipment, a small workplace, and only one or two workers are required.

3. Various products can be derived from hefen. Small shrimps, ginger, and shallotcan be added during production. The gelatinized slab can also be sliced intosquares instead of strips and then used as wrappers to produce juanfen andchangfen. Miscellaneous grain crops can also be used as raw materials toproduce hefen. The shelf life of hefen is only 1–2 days. It can be dried to makedried hefen or instant hefen.

The schematic diagram for fresh Cantonese hefen is presented in Figure 16.5.There is no special equipment for fresh hefen, and bigger pieces of equipment areused when production is larger scale.



Rice (early Indica)↓

Soak for 2–3 hours↓

Grind to make pulp of 18 °Bé↓

Apply a small amount of oil on canvas conveyor belt or stainless trays to coat the trays evenly

↓Pour rice slurry to form a thin layer (about 1 mm thick)

↓Steam the thin layers of rice slurry to gelatinize the starch

(100–105 °C; steam pressure, 0.25–0.35 MPa; 100–120 s)↓

Cool and slice the layered rice sheets into 1 cm wide strips

FIGURE 16.5 Typical production scheme for fresh Cantonese oily hefen. Source: Sun(2006).

In some areas, the process procedure is modified a little. Rice is cleaned andsteeped in water for 2–3 hours. Steeped rice is ground with water into a starch slurryand allowed to stand for 1–2 hours. A rotating drum touching the wet-milled riceslurry forms a film, which is then passed on to a stainless steel or cotton conveyorbelt that carries the film into a steam tunnel for gelatinization. The gelatinized sheetwith 1-mm thickness is air-dried on the moving conveyor belt, which is immersedin peanut oil. The grated conveyor belt is coated with peanut oil to reduce adhesionand give the noodles sheen and a peanut aroma. The noodles are then sliced into bigsquares and piled together. Then the noodle sheets are sliced into 1-inch wide noodlestrips with a paper cutter for the big-strip type (Tungtrakul 1998).

16.4.1.2. Fermented Rice NoodlesThe processing of fermented rice noodles is the same as for traditional extrudedrice noodles (nonfermented), except that the rice grains of nonfermented noodles aresoaked for about 3 hours while fermented rice noodles are soaked for a longer timeperiod of 2–6 days. Due to the short shelf life after production, quality standards andoperation control depend heavily on the worker’s skill (Lu et al. 2003, 2005, 2007).The process is schematically presented in Figure 16.6.

Among factories in southern China, fermentation is conducted in several steeltanks (volume 6–8 m3, depth 2–2.5 m) in plants with a seasonally dependent ambienttemperature of 10–30 ◦C. Tanks are almost completely filled with milled rice grainsand covered with a thin layer (8–15 cm) of water. The rice grains are staticallyfermented with or without a starter for 4–6 days and then wet-milled, steamed, andextruded into rice noodles (Lu et al. 2005). Nowadays, processing lines are designedto greatly improve the scale of production (Figure 16.7). An illustration of a workshopin a fermented rice noodle factory is shown in Figure 16.8. A schematic diagram ofthe processing line of fermented rice noodles is shown in Figure 16.9.



↓Wash and de-sand

↓ Grind ← adding left-over rice noodles

↓Pour rice slurry on a canvas conveyor belt and steam

in a steam tunnel (about 75% of degree of gelatinization)↓

Extrude the steamed sheet into threads↓

Cook in boiling water↓

Steam threads (over 90% of degree of gelatinization)↓

Wash and cool down↓

Slice to certain length↓

Final products

↓Soak

↓

↑Inocula preservation

↑Fermentation → Extract of inocula

Rice ← Add inocula

FIGURE 16.6 Typical production scheme for fresh fermented rice noodles. Source: Sun(2006).

FIGURE 16.7 Processing line of fermented rice noodles.



FIGURE 16.8 An illustration of a workshop for fermented rice noodles.

In Thailand, fermented rice noodles are called khanom jeen. Rice is cleaned andsteeped in water for 2–3 days. Steeped rice is washed many times and ground withwater. Water from the starch slurry is removed by draining in a cheesecloth bag orby filtration using a filter press. The starch cake is partially gelatinized by steaming.The gelatinized cake and raw starch cake are kneaded in a screw kneader. The starchball is extruded through a die into boiling water, and noodles float when cooked. The

FIGURE 16.9 Processing line for fermented rice noodle. Source: Sun (2006).



TABLE 16.3 Temperature and Duration of Soaking and Fermentation inProducing Fermented Rice Noodles

Season Winter Spring/Autumn Summer

Initial water temperature (◦C) 42–45 30–35 20–30 or roomtemperature

Soaking temperature (◦C) <10 10–25 25–35Soaking time (days) 5 4 3

Source: Sun (2006).

cooked noodles are immediately cooled with water. The fermented rice noodles aresold fresh (Tungtrakul 1998).

Descriptions of Processing Technology

fermentation Rice is soaked in tap water (1:1.4 w/w rice:water) and fermentedat room temperature for 3–4 days in summer and 5–6 days in winter. Inoculumcomes from the sinks, which contain supernatant fermented over 2 days. Soakingtemperature affects the duration of soaking time and may be varied depending onthe season of the year (Table 16.3). When warm water is used, fermentation durationcan be shortened to 1–2 days in summer and 3–4 days in winter. However, it hasbeen observed that fermentation in cold water is better because of the development ofpleasant flavor and aroma. Insufficient fermentation affects the chewiness of noodles,whereas overfermentation normally causes development of off-flavor noodles. Atthe end of fermentation, the pH value of the viscous supernatant is around 4.1 and therice grains are easily crushed with the fingers (Figure 16.10). The surfaces of the ricegrains are then washed thoroughly with tap water to remove adhering foreign matter.

adding leftover rice noodles Leftover or unsold rice noodles are used to im-prove the texture of fermented rice noodles. The leftover rice noodles are soaked for1–2 days, sliced into short sticks, and mixed with the fermented rice grains beforegrinding. About 30% of leftover rice noodles are added in Guilin mifen, and 10–20%are added in Changde mifen. The texture of Guilin mifen is a little softer than thelatter. The mechanism of improvement is not fully understood. It may serve as abinder like pregelatinized starch or texture improver.

grinding The slurry should be fine enough to pass through an 80-mesh screen.In practice, a technician places a drop of slurry on his/her back of hand and touchesit with the other fingers to determine if it has a sandy feeling or not. The moisturecontent of the slurry is maintained within the range of 50–55%. A frequentlyused grinder is shown in Figure 16.11. A schematic diagram of the thread-shapingextruder is shown in Figure 16.12.

mixing and spreading the slurry on a canvas conveyor belt and steamingto form a sheet The slurry is mixed to prevent sedimentation and the homo-geneous slurry leaks out from a narrow gap of the slurry container to a canvas



FIGURE 16.10 Fermentation sinks and foams on surface of fermented supernatant (ricegrains are sticky and easy to crush).

Grinding section

FIGURE 16.11 Grinder.



FIGURE 16.12 Schematic diagram of thread-shaping extruder: (1) motor, (2) small strapwheel, (3) strap, (4) big strap wheel, (5) flange, (6) jacket, (7) press bearing, (8) verticalbearing, (9) feed inlet, (10) feed tank, (11) screw, (12) cooling set, (13) water outlet, (14) block,(15) sealing, (16) square plate, (17) square aperture, (18) bolt, (19) screw edge, (20) waterinlet, (21) screw sealing, (22) bolt, (23) sealing, and (24) stand. Source: Sun (2006).

conveyor belt and forms a thin layer (2 mm). The conveyor belt goes into a steamingtunnel and the film is steamed to form a rice sheet. Steam pressure is 0.2–0.3 MPa,steaming time is 50–100 s, and the temperature is around 92–95 ◦C. The degree ofgelatinization of the rice sheet is about 70–80%.

extruding the sheet into boiling water and cooking The apertures on thescreen are the symbol for diameter, ø 1.5–1.7 mm. The extruding pressure should becontrolled to prevent noodle expansion. The threads fall down into the boiling waterand cook for 20 seconds at a temperature above 95 ◦C. A photo of the extruding andcooking process is shown in Figure 16.13.

steaming of noodles The threads are drawn out from the boiling water sinkand steamed again in another steam tunnel for full gelatinization. Steam pressure is0.1–0.2 MPa and the noodles are cooked at 100 ± 2 ◦C for 2 minutes more.

washing to cool The noodles must be cooled down immediately in cold tap waterafter steaming, and continuously washed for around 18 minutes (Figure 16.14). Themoisture of the final products is 63–68%. The yield of rice noodles is more than225%. The finished product is presented in Figure 16.15.

16.4.1.3. Extrusion-Cooked Rice NoodlesThis type of rice noodles needs a special extruder with a screw designed to per-form two functions so that the rice dough is mixed and gelatinized inside the



FIGURE 16.13 Extruding the threads into boiling water.

FIGURE 16.14 Steamed threads are cooled in tap water.



FIGURE 16.15 Fermented rice noodle products.

extruder before threads are formed (Figure 16.16). Although early Indica riceis mainly used for the production of rice noodles, Japonica rice, corn starch,or potato starch is normally added to improve the texture of the noodles. Thegeneral production flow chart of extrusion-cooked rice noodles is presented inFigure 16.17.

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FIGURE 16.16 Diagram of an extrusion-cooking extruder: (1) mixing tank, (2) drivingmechanics, (3) motor, (4) feeding screw, (5) feeding canister, (6) joint, (7) pre-gelatinizingscrew jacket, (8) pre-gelatinizing screw, (9) valve, (10) sampling valve, (11) noodle outlet,(12) extruder screw, (13) extruder jacket, (14) cooking section, (15) heating set, (16) valve,(17) feed inlet, (18) motor, (19) reducer. Source: Sun (2006).




Soak at room temperature for 2–3 h↓

Grind to pass through an 80-mesh screen↓

Mix into dough with 38–40% moisture content, some additives may be added into the water at this step

↓Gelatinize the dough and make threads with an extruder

↓Slice and cool with fans

↓Keep the noodles in a closed room for 5–12 h to increase pliability and

make separation of threads easier in the next step↓

Wash in water and separate the bound threads↓

Cook in boiling water (90–95 °C, 15 min) to further gelatinize the noodles↓

Final products

FIGURE 16.17 Generalized production scheme for extruded rice noodles. Source: Sun(2006).

16.4.2. Dry Rice Noodles

The main advantages of dehydrated products are stability and ease of handling duringtransport. There are two main types of dry rice noodles: extrusion-cooked dry ricenoodles and waved rice noodles.

16.4.2.1. Extrusion-Cooked Dry Rice Noodles (Straight Strip)This kind of rice noodles is dried and sliced into straight strips, and then wrapped inpaper in a way similar to dried wheat noodles. They have a shelf life of more than 1year, so they can be distributed over long distances. Therefore, this is the main typeof rice noodles sold in the international markets. The general production flow chartis presented in Figure 16.18.

In Thailand, the process procedure is modified. Rice is cleaned and steeped inwater for 2–3 hours. Steeped rice is ground with water into a slurry and left restingfor 1–2 hours. The starch slurry is drained in a cheesecloth bag. The starch cakeis partially gelatinized by steaming and then kneaded and extruded by a hydraulicpress into vermicelli. The vermicelli is hung on racks in an oven for drying until themoisture content is about 13% (Tungtrakul 1998).

16.4.2.2. Waved Rice NoodlesThis kind of product was previously listed as instant rice noodles but has been re-classified because of its poor rehydration and requirement of 5–10 minutes cookingtime. The general process flow chart for waved rice noodles is presented in Fig-ure 16.19. A waved rice noodle product is shown in Figure 16.20. The processing of



Rice composite (early Indica/late Indica = 7:3)↓

Wash and soak↓

Grind the rice to pass through a 60-mesh screen (dry-milling)↓

Mix into rice dough (moisture content 30–32%)↓

Extrusion-cook and form threads↓

Cool with fans after extruding↓

First retrogradation (12–24 h)↓

Steam threads to increase the degree of gelatinization (0.04MPa, 5–8 min)↓

Second retrogradation (6–10 h)↓

Wash and comb the threads to separate↓

Dry to moisture content of 13–14%↓

Slice to 18–20 cm sticks and shape the noodles into bundles or blocks↓

Package (600–800 g per package)↓

Final products

FIGURE 16.18 Generalized production flow chart for extruded dry rice noodles. Source:Sun (2006).

waved rice noodles is one of the most fully automated among all rice noodle products(Figure 16.21).

16.4.3. Frozen Rice Noodles

Fresh rice noodles are fast-frozen at −25 ◦C. The water changes to fine ice crystalsso quickly that the starch gel network is not damaged and the fresh noodle propertiescan be completely recovered after thawing. This can be attributed not only to theinhibition of starch retrogradation at −18 ◦C but also to the inhibition of growthof microorganisms that may contaminate the product during storage. The productretains its best quality even after a shelf life of 1 year. The general process flow chartis presented in Figure 16.22. Figure 16.23 shows a diagram of the freezing tunnel forfast-frozen rice noodles.

16.4.4. Instant Rice Noodles

For noodles, the term “instant” refers to convenience during consumption of product.Instant noodles are often sold with a complete seasoning packet and are ready toserve within 3–5 minutes of preparation. Good rehydration is the most important



Adjust moisture content (32–34%)↓

Mix into rice dough at controlled temperature↓

Extrude to sheet↓

Extrude to threads↓

Form waves↓

Steam (15–20 min)↓

Slice (10 cm)↓

Dry↓

Pack (75 g per package)↓

Final products

Rice↓

Wash and soak (0.5–2 h)↓

Dry-mill (60-mesh screen)↓

Add water↓

Rice↓

Wash and soak (2–4 h)↓

Wet-mill↓

Vacuum de-water↓

FIGURE 16.19 Generalized production schemes for waved rice noodles. Source: Sun(2006).

consideration in instant noodles. This is attained in wheat instant noodles by themultipore structure formed during frying. In instant rice noodles, faster rehydrationis achieved by the very thin diameter of noodles that ranges from 0.5 to 0.6 mm andby longer steaming time for complete gelatinization. Currently, there are three kindsof instant rice noodles: (a) instant rice vermicelli, (b) instant hefen, and (c), instantfresh rice noodles.

FIGURE 16.20 Waved rice noodles.


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Fresh rice noodles↓

Slice (30–40 cm)↓

Chill in cold water (0–10 °C)↓

Weigh (150–200 g per package)↓

Fast-frozen by liquid nitrogen (–35 to –25 °C, 10–30 min)↓

Coat with ice for easy separation↓

Package at < –5 °C↓

Cold storage (–21 to –18 °C, around 95% of relative humidity)

FIGURE 16.22 Generalized production scheme for fast-frozen rice noodles. Source: Sun(2006).

16.4.4.1. Instant Rice VermicelliInstant rice vermicelli is classified into two categories, extrusion-cooked instant ricevermicelli and fermented instant rice vermicelli. The general process flow charts forextrusion-cooked and fermented instant rice vermicelli are shown in Figures 16.24and 16.25, respectively.

The traditional drying method for instant rice vermicelli is similar to that ofinstant wheat noodles. The noodles are exposed to different temperatures, humidity,and time combinations for different functions and stages. Noodles are conditioned for30 minutes at 30 ◦C and 70% RH, sweated for 80 minutes at 40 ◦C and 85% RH, driedfor 50 minutes at 50 ◦C and 85% RH, and then the shape is finalized for 40 minutes at40 ◦C and 75% RH. Then the noodles are finished at a low temperature (temperature,30 ◦C; humidity, 60%; 70 minutes). This method has proved to decrease the ratio

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FIGURE 16.23 Freeze tunnel for fast-frozen rice noodles. Source: Sun (2006).




Wash (10–20 min)↓

Soak for 6–8 hours depending on seasons, final moisture content 26–28%↓

Grind with water to pass through a 50-mesh screen↓

De-water to 38–40% moisture content and mix with other ingredients (potato starch, corn starch, etc.)↓

Extrusion-cook and extrude to vermicelli with a single-screw extruder↓

Cool and slice↓

Retrogradation (4–12 h depending on season)↓

Steam to fully gelatinize↓

Dry to moisture content less than 13%↓

Package with soup pouches↓

Final product

FIGURE 16.24 Generalized production scheme for extrusion-cooked instant rice vermi-celli. Source: Sun (2006).

of broken noodles but is time consuming (4–5 hours). An alternative method is toremove the surface water on the noodles before drying in hot air to finalize the noodleshape and to dry out the moisture inside the noodles using a microwave. This wasfound to improve the rehydration property of noodles during cooking and to decreaseboth dried noodle breakage and surface checking.


Soak and ferment↓

Grind to slurry↓

Pour rice slurry on a canvas conveyor belt and steam in a steam tunnel (about 75% of degree of gelatinization)

↓Extrude into noodles

↓Steam the noodles (over 90% of degree of gelatinization)

↓Wash and cool

↓Dry and package

↓Final product

FIGURE 16.25 Generalized production scheme for traditional fermented instant rice ver-micelli. Source: Sun (2006).



16.4.4.2. Instant HefenThe rehydration property of instant hefen is similar to the fried instant wheat noodles.Hefen is ready to eat after being soaked in boiling water for 2–3 minutes. The thicknessof instant hefen is only 0.6–0.8 mm. The slurry used for instant hefen has a moisturecontent of 70% and it is cooked completely with a high degree of gelatinization.

The best product is obtained from rice with amylose content of about 19%. LateIndica rice is the best rice variety used but a small amount of Japonica rice is oftenadded to improve quality. Recently, corn starch, Konjak flour, modified starch, andpotato starch have been added to improve appearance, mouthfeel, and texture ofinstant hefen. A generalized production scheme for instant hefen is presented inFigure 16.26.

Slicing sheets manually is very labor intensive and produces inferior productsduring production. Automatic slicing machines are now being used along with con-tinuous retrogradation machines, which have made it easier to handle sticky noodles.Nowadays, these two pieces of equipment are often installed in the processing line of

Fine grind (pass through a 50–60-mesh screen) ← dissolved Konjak solution↓

Adjust slurry concentration (17–27 °Bé)↓

Mix↓

Spread slurry on canvas conveyor belt↓

Steam (sheet thickness 0.5–0.7 mm)↓

Coat oil↓

Cool by strong wind and pre-dry to 35–38% of moisture content↓

Retrogradation (1.5–2 h, 4 °C)↓

Slice↓

Weigh↓

Load in molder to form a shape↓

Dry to 13% of moisture content by hot air↓

Package↓

Final product

← add gelatinized paste

Rice wash and soak (1.5–2 h in summer and 2.5–3.5 h in winter)↓

Coarse grind

FIGURE 16.26 Generalized production scheme for instant hefen. Source: Sun (2006).



hefen. Due to moisture variations in different parts of the sheet, the hefen strips oftenget entangled and are also not completely homogeneous in thickness. Consequently,automatic weighing for accurate packaging is always a problem. The schematicdiagram of the processing equipment for instant hefen is presented in Figure 16.27.

16.4.4.3. Instant Fresh Rice NoodlesFresh rice noodles are a popular breakfast in South Asia and China. Because oftheir short shelf life and fast retrogradation rate, the producers usually make freshrice noodles near local markets or sell the products next to their workplaces. Freshrice noodle production is often done in small-scale operations and is labor intensive.Restaurants located far from processors are forced to cook dried products that lack thesensory attributes of fresh noodles. The scaling up of production and new developmentin the preservation technology for producing fresh-preserved instant rice noodles willresolve these problems. There are two types of instant fresh rice noodles—fermentedfresh instant rice noodles and extrusion-cooked fresh instant rice noodles.

Process Procedure of Fermented Fresh Instant Rice Noodles The processingprocedure of fermented fresh instant rice noodles is shown as Figure 16.28.

The early stage of processing is the same as fermented fresh rice noodles. Severalprocessing breakthroughs, as explained below, have led to the commercialization offresh instant noodles.

spraying amylase solution After the steamed rice sheet is cooled by blowingstrong, hot air (70 ◦C), a certain concentration (0.1–0.4%) of β-amylase solutionis sprayed on the sheet surface to inhibit starch retrogradation in the final noodleproducts during distribution and storage.

preextruding The enzyme in the rice sheet is mixed homogeneously.

incubation at constant temperature and relative humidity Enzymaticreaction is allowed to take place for 30 minutes at 70–100% of RH.

extruding to threads A single screw extruder with an aperture size of the symbolfor diameter, ø 1.2, 1.4, or 1.7 mm is used.

cooking The threads come out from the extruder and fall down into boiling waterand are cooked at 95–98 ◦C for 10–20 seconds.

steaming The cooked threads are steamed again for complete gelatinization. Steampressure of 0.08–0.1 MPa is applied and steaming is done for 110–180 seconds.

slicing Noodles are sliced to a certain length (usually 40 cm) to achieve targetweight.


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Rice ← Add inocula ↓ ↑

soak Inocula preservation ↓ ↑

Fermentation → Extract of inocula ↓

Wash and de-sand ↓ Recovered rice noodles

Grind ↓

Mix ← Add additives ↓

Spread the slurry ↓

Steam the sheet ↓

Cool by fans ↓

Spray amylase ↓

Pre-extrude ↓

Slice sheet ↓

Equilibrium ↓

Extrude to threads ↓

Cook in boiling water

Steam threads ↓

Slice↓

Wash ↓

Acid solution soak ↓

Package ↓

Metal detection ↓

Sterilization ↓

Cool ↓

First check ↓

Storage for 6 days ↓

Second check ↓

Package with seasoning pouches

↓Final products

FIGURE 16.28 Processing technology of traditional fermented fresh instant rice noodles.Source: Sun (2006).

washing in cold water The surfaces of steamed noodles will become very stickyand may stick together. High-pressure water is used to flush the threads and dispersethem.

acid soaking The pH value of noodles is lowered to 3.8–4.0 by soaking in a 1%lactic acid solution for 30–60 seconds to inhibit the growth of microorganisms duringproduct distribution and storage.

noodles packaging A retort pouch that can tolerate high pressures and tempera-tures (>100 ◦C) is used. It is made of polyethylene or nylon.

weight checking and metal checking A metal detector is used for this purpose.

sterilization A package containing 150 g of noodles is sterilized (95 ± 2 ◦C,35–40 minutes).

cooling The sterilized rice noodles are cooled by fan to around 38 ◦C.



Rice (aged for 6 months to 1 year)↓

De-sand and wash↓

Soak↓

Grind and pass through a 60-mesh screen↓

Rice flour (or rice dough formed by wet-milling and vacuum de-watering)↓

Mix with other ingredients and adjust the moisture↓

Extrusion-cook starch and form threads↓

Retrogradation (12–24 h)↓

Cook (98 °C, 10–20 min) or steam (100–121 °C, 25–30 min)↓

Wash in cold water (0–10 °C, 15–25 min)↓

Acid soak (1.5–2% lactic acid solution, pH 3.8–4.0, 25–30 °C, 1–2 min)↓

Package↓

Sterilization (93–95 °C, 40 min)↓

Cool and check↓

Package with seasoning pouches↓

Final products

FIGURE 16.29 Diagram of processing technology of extrusion-cooked fresh instant ricenoodles. Source: Sun (2006).

storage and checking Before storage, the packages are checked for defects (mal-sealing, foreign matter, etc.). After storage at 37 ◦C for 6–7 days, products are checkedagain for spoilage.

Process Procedure of Extrusion-Cooked Fresh Instant Rice Noodles Theprocessing procedure of extrusion-cooked fresh instant rice noodles is shown in Fig-ure 16.29. The equipment for extrusion-cooked fresh instant rice noodles is presentedin Figure 16.30.

16.4.5. Product Quality Evaluation

The quality standards of rice noodles are listed in Table 16.4 (fresh-type) and Ta-ble 16.5 (dry and instant type).



FIGURE 16.30 Sterilization equipment for fresh instant rice noodles. Source: Sun (2006).

16.5. INFLUENCE OF PROCESSES ON FINISHED PRODUCT QUALITY

16.5.1. Factors Affecting Product Quality of Rice Noodles

The producer has to consider production cost, environmental issues, consumer prefer-ence, and market competition as well as appropriate formulations and practices. Thismakes it very complicated to compare quality of different types of noodle products.Table 16.6 is a summary of the major factors that could affect the quality of ricenoodles. In the manufacture of rice noodles, one or more of the following commonprocedures are applied, depending on the products.

16.5.2. Milling Methods for Rice Flour

Dry-milled rice flours contain a higher proportion of large particles compared withflours obtained from wet-milling methods. Noodles prepared from wet-milled flourgave more acceptable textural properties with slightly higher smoothness and higherdeformation. Wet-milled flour has significantly lower starch damage but exhibits ahigher retrogradation property, which is believed to be undesirable in noodle pro-cessing. The coarse flour from dry-milling gives lower peak viscosity and lowerfinal viscosity. This could be attributed to the delayed swelling of granules embed-ded in large endosperm chunks of coarse flours compared with the earlier onset ofswelling for smaller chunks or damaged individual granules in finer flours. The noo-dles prepared from dry-milled flours had a lower retrogradation rate measured by the


INFLUENCE OF PROCESSES ON FINISHED PRODUCT QUALITY 423

TABLE 16.4 Quality Evaluation of Fresh-Type Rice Noodles

Quality AttributesNonfermentedRice Noodles Fermented Rice Noodles

Physicochemical propertiesMoisture (%) 60–70 65–70Acidity (%) — 0.12–0.18pH value 6.0–8.0 3.7–4.1

Sensory propertiesAppearance Smooth surface, uniform strips or threads, no air bubbles

inside noodles, no bound stripsColor Milky white, shiny, and

translucentFermented type is a little

whiterOdor Rice aroma, no off-flavor Characteristic smell and

aroma of fermented riceproducts, with a littleacid smell

Taste Smooth, pliable, andchewy, no grittymouthfeel

Smooth mouthfeel, elasticand chewy

Cooking propertiesCooking loss (%) <8Percentage of broken

noodles (%)<9

Hygienic standardsAerobic plate count

(cfu/g)<1000

Coliform (cfu/100 g) ≤30Mold (cfu/g) ≤150Pathogenic microbes No pathogenic microbes detected

Source: Sun (2006).

TABLE 16.5 Quality Evaluation of Dry-Type and Instant Rice Noodles

Instant Rice Noodles

Quality AttributesNormal Dry-TypeRice Noodles Dry Type Fresh Type

Moisture (%) ≤14 65–70Rehydration property After being boiled for 2–4 min or soaked in

boiling water for 6–8 min, the noodles arechewy, elastic, and smooth; percentage ofbroken noodles is less than 20%

3–5 min. ofrehydration time,clear soup

Sensory properties After being cooked or rehydrated for the required time, the noodlesare chewy, elastic, and smooth

Other attributes Same as the fresh type (see Table 16.4)

Source: Sun (2006).



TABLE 16.6 Factors Affecting Product Quality of Rice Noodles

Group I IngredientsAmylose/amylopectin ratio of rice flour usedWater qualityAmount of salt usedAmount of coating oil usedTypes and amount of additional ingredients used

Group II Dough qualityRheology of doughViscosity of slurry

Group III Processing conditionsMixing of ingredientsKneading of doughSlicing actions for dough or noodle stripsSteaming temperature and durationSheeting actionsExtruding conditionsCooking conditionsDrying of final product

Source: Lu and Nip (2006).

texture profile analysis (TPA) and tensile test. The improvement of dry-milled flourfor making noodles should be done by hydrating dry flour before processing. More-over, dry-milling eliminates the cost of removal of excess water and waste treatment(Tungtrakul 1998).

16.5.3. Effects of Extrusion on Rice Noodle Quality

Extrusion speed and feeding speed are key parameters for producing high-qualityextruded rice noodles. A feeding speed that is too slow overheats the dough, causesbrown color, and forms air bubbles in the noodle structure, whereas a feeding speedthat is too fast causes insufficient cooking, poor appearance, and low tensile strength.A high screw speed is preferred for greater production efficiency. Because it has ahigher shear stress output that mixes the rice flour more homogeneously and producesmore heat, starch will gelatinize completely. Mold aperture size, shape, and numberof mold apertures also affect the texture of noodles.

16.5.4. Effects of Fermentation on Rice Noodle Quality

Lu et al. (2003) found that protein, lipid, and ash content decreased in fermentedrice flour whereas free fatty acid increased. Fermentation had little effect on the crys-talline structure of rice starch, but the ratio of the crystalline to the amorphous regionsincreased. The gelatinization temperature and the RVA peak viscosity of rice flour


INFLUENCE OF PROCESSES ON FINISHED PRODUCT QUALITY 425

decreased while the gelatinization enthalpy increased after fermentation. Fermentedrice starch granules had slight superficial corrosion (Lu et al. 2005). The chemicalanalysis of fermented rice starch suggests that the partial hydrolysis of amylopectinoccurred during the fermentation process (Lu et al. 2007). The mechanism of texturalimprovement of fermentation is not fully understood. In industrial production, insuf-ficient fermentation causes poor texture with perceptible loss of chewiness, whereasoverfermentation causes off-flavor in the noodles. It is claimed that the success offermentation is still fully dependent on the worker’s experience.

16.5.5. Other Starch Noodles

Since the wide variety of other starch noodles and their production are still consid-ered niche markets, studies on their processing and quality considerations are ratherlimited. Consequently, the information presented in this section is not as extensive asthat presented for rice noodles.

In the preparation of buckwheat noodles, the most common process involvescombining buckwheat flour and wheat flour and adding water, the amount of whichis dependent on the protein content of the flour mixture. The flour is mixed witha circular motion with gradual addition of water. The binding capacity of the flouris greatly improved by using boiling water during the initial mixing stages, whichgelatinizes the starch.

The addition of hot water to the flour has been observed in many other products.In jelly noodles made from sweet potato and potato, a batter with appropriate flowcharacteristics is required to enable smooth application on a metal plate covered withcanvas cloth to form sheets. Hot water is mixed into the moist starch by continuousstirring for the development of the right viscosity and consistency in the doughor batter. In starch noodles, smooth balls are loaded into an extruder where theyare forced through a die with a specified opening that corresponds to the noodlediameter or a viscous batter may be poured onto a metal or canvas sheet for steaming(Figure 16.31).

In the production of starch noodles, processes are employed to enhance retrogra-dation such as the application of low-temperature conditioning after the gelatinizationof noodle strands or sheets. Retrogradation sets the noodle structure so that the noo-dles can withstand normal cooking temperatures in soups and stir-fried dishes. Thishappens as noodles are washed in water after cooking such as in the preparation ofrice, mung bean, and sweet potato noodles. Subzero storage after cooking is a nor-mal practice in mung bean noodle preparation. It is interesting to note that in Chinathis conditioning step is attained naturally since processing of noodles is an annualactivity done during the months of October and November when the temperature inSichuan and Shandong drops to below zero at night. After the overnight conditioning,the noodles are separated and sun-dried, and the drying is further hastened by therelatively low humidity during this time of the year. In many production systemsin Asia, favorable conditions have to be provided artificially through appropriatelydesigned processing equipment and facilities to ensure consistent product quality.



Steaming starch batterMixing starch batter

Slicing noodlesStarch sheet conditioning

FIGURE 16.31 Potato starch noodle production in Changchun, People’s Republic of China(Collado and Corke 2004).

Most starch noodles are traditionally air-dried under the sun but much of commer-cial production is now dried in mechanized driers that are part of a continuous process(Figure 16.32). In the production of jelly-sheet noodles from potato and sweet potato,the gelatinized sheet is scraped and moved onto a fine wire screen conveyor that leadsto a heating cabinet, after which the sheet comes out ready for conditioning followedby slicing, drying, and packing (Collado and Corke 2004).

In the preparation of Chinese dimsum wrappers from starches, boiling water isadded to wheat and cassava starches to enable the formation of dough that canbe formed into a ball and rolled thin into a circular sheet and used to enclose thefilling; otherwise, the sheet breaks easily when folded. Dimsum wrappers are formedby carefully picking up the flattened, soft, pliable, and circular dough on which atablespoon of filling is placed, folding the wrapper 3 to 5 times on one side of thecircle, pinching it to keep the folds in place, and then sealing it tightly with anotherpinch. Steaming not only sets the wrapper shape but also cooks the vegetable andmeat filling.

For dried starch wrappers, the shape is attained when the thin starch batter ispoured into a shaped mold, normally a round shallow container. Rice spring rollwrappers usually have a delicate weave design that is picked up from the bamboo


CURRENT AND FUTURE RESEARCH TOPICS 427

Mixing dough Extruding noodles

Conditioning noodles Drying noodles

FIGURE 16.32 Sweet potato starch noodles production in Pinyin County, Shandong, Peo-ple’s Republic of China (Collado and Corke 2004).

tray on which the wrappers are molded and dried. A Vietnamese dish uses this ricepaper as a wrapper for steamed or fried spring rolls.

16.6. CURRENT AND FUTURE RESEARCH TOPICS

The processing of rice noodles is mostly done by small- and medium-scale enterprises.Many areas of quality improvement exist in commercial production. The followingresearch is proposed for future studies.

16.6.1. Inhibition of Starch Retrogradation in Final Products

Inhibition of starch retrogradation in starch-based foods is an unresolved issue in thefood industry and deserves further study. Sun (2006) reported that β-amylase had a



significant effect on the inhibition of starch retrogradation of fermented rice noodles.Further research on this subject will benefit the development of desirable sensoryproperties for instant starchy foods.

16.6.2. Mechanism of Fermentation Process Effects onFermented Rice Noodles

Lu et al. (2003, 2005, 2007) have conducted pioneering work on the effect of naturalfermentation of whole rice grains on texture improvements of fermented rice noodles.More research is needed to understand the relationship between fermentation andphysical properties of rice noodles. This will facilitate the setting of process standardsfor consistent product quality. The adaptation of fermentation technology to otherstarchy crops, such as maize and potatoes, could contribute to the added value ofthese food resources.

16.6.3. Effect of Starch Granule Structure

Amylose content is now widely recognized as the most important determinant ofrice noodle quality. However, there are also studies that show the granule structureand component, followed by the amount of leached-out amylose in the process,have significant effects on the rheological property of the starch during heating (Liiet al. 1996). It is suggested that the integrity of swollen starch granules is themajor factor determining the rheological properties of a starch paste or gel (Tsaiet al. 1997). Tsai et al. (1997) reported that the formation of gel structure wasgoverned by the rigidity of swollen granules and that the hot-water soluble com-ponent could strengthen the elasticity of the starch gel or paste. Basic research ongranule structure, molecular components of rice varieties, and their effects on physic-ochemical properties of products may lead to the development of quality indices forprocessing.

16.6.4. Starch Digestibility of Rice Noodles

Starchy foods are known to differ in the rates at which they are digested and at whichthey elicit blood glucose and insulin responses. This has been attributed to numerousfactors, including amylose content. Because of the linear structure of amylose, starchgranules rich in amylose are thought to have more extensive hydrogen bonding andhence more crystallinity in their structure than starch granules with very little amylose.Consequently, they do not swell or gelatinize as readily upon cooking and, therefore,are digested more slowly and result in lower blood glucose and insulin responsesthan those with low amylose content. For this reason, the intake of high-amylosefood, such as rice noodles, has been considered more desirable for individuals withimpaired carbohydrate and lipid metabolism. However, research on blood glucoseand insulin responses to rice with similar chemical composition but different amylosecontent has shown conflicting results (Panlasigui et al. 1991, 1992). This indicatesthat amylose content alone may not be a good predictor of starch digestion rate and


SUMMARY 429

blood glucose and insulin response to rice; the physicochemical properties of thestarch may also exert an influence. Rice noodles usually are produced from high-amylose rice varieties (>28%). We think rice noodles should be an ideal materialto elucidate the effect of physicochemical properties of rice starch on the starchdigestibility.

Starch noodles not only provide an alternative to wheat-based noodles for celiacpatients but are now considered a source of dietary fiber from retrograded starch nowrecognized as a form of resistant starch. Other forms of enzyme-resistant starchesinclude physically inaccessible starch, such as starch that is locked in plant cells,and the native granular starch in foods containing uncooked starch, chemically andthermally modified starches, and the indigestible starch fraction (Eerlingen et al. 1993)formed after heat-moisture treatment of starch such as those formed when starchnoodles are produced. Retrograded starch is left undigested until it is fermented inthe large intestine. In the past, retrograded amylose is considered to be nonnutritive;however, it has been demonstrated that amylases gradually degrade the structure.Glucose and oligosaccharides are released from retrograded starch over an extendedperiod through the normal digestive process (Wolever and Jenkins 1985). The lowdigestibility and low glycemic response from noodles imply that these foods mayhave health benefits for both normal and diabetic individuals through sustained energylevel and prolonged satiety.

16.6.5. Environmental Considerations

Wet-milling is still a traditional process in the production of rice pulp or rice flourwith a fine flour particle size; however, the large quantity of wastewater is a bigenvironmental problem. An emerging process involves the use of dry-milling tominimize the liquid waste disposal problem. It should be noted that dry-milled riceflour is not the same as wet-milled rice flour, and the quality of the final product isperceived to be of lower organoleptic quality as compared to noodles produced fromwet-milled flour. Wet-milled rice flour produces noodles with a smoother texture.Studies on techniques to improve the quality of noodles made from dry-milled riceflour are worth undertaking because the consequent lesser impact on the environmentpresents long-term benefit for the food company.

16.7. SUMMARY

The origin, history, current status, and developing trends of rice and starch-based noo-dles are presented in this chapter. The processing technology, processing parameters,and equipment of fresh (wet) rice noodles, fermented rice noodles, dry rice noodles,instant rice noodles, and other starch-based noodles are described in detail. Mean-while, the formulas and additives used in the production of starch-based noodles areintroduced. The information contained in this chapter is intended as a comprehensivereference guide for researchers, engineers, and other professionals who are interestedin starch-based noodles.



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Asian Noodles (Science, Technology, and Processing) || Rice and Starch-Based Noodles