Food Biochemistry and Food Processing (Simpson/Food Biochemistry and Food Processing) || Non-Enzymatic Browning in Cookies, Crackers and Breakfast Cereals

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30Non-Enzymatic Browning in Cookies,

Crackers and Breakfast CerealsA.C. Soria and M. Villamiel

IntroductionNon-Enzymatic Browning Indicators

Available LysineFurosineHydroxymethylfurfural and FurfuralColourFluorescenceAcrylamideMaltulose

References

Abstract: In this chapter, the authors have attempted to collectthe main studies carried out up to 2010 on the most investigatedquality indicators in cookies, crackers and breakfast cereals. Thesecereal-based foods, mainly consumed for breakfast, constitute a veryimportant source of energy, particularly in the case of children. Forthis reason, their processing (baking or extrusion cooking) should becarefully carried out in order to keep their quality. One of the mainreactions that takes place during the processing of these cereal-basedfoods is non-enzymatic browning including Maillard reaction andcaramelisation, which might contribute to the development of colourand fluorescence. In this sense, the evaluation of chemical indicatorssuch as available lysine, furosine, hydroxymethylfurfural, furfural,acrylamide and maltulose might afford important information on theprocessing and storage conditions to which cereal-based productshave been submitted.

INTRODUCTIONCereal-based products such as cookies, crackers and breakfastcereals represent a predominant source of energy in the humandiet, especially for children consuming cereal derivatives forbreakfast meals.

Cookies, crackers and breakfast cereals can be manufacturedby means of traditional processes or by extrusion cooking. Ingeneral, during conventional treatment of flour products (usu-

ally, temperatures higher than 200◦C for several minutes), moreintense processing conditions are applied as compared to thoseused in the extrusion process (Gonzalez-Galan et al. 1991,Manzaneque Ramos 1994, Huang 1998).

Extrusion cooking is a well-established industrial technologywith a number of food applications since, in addition to theusual benefits of heat processing, extrusion has the possibility ofchanging the functional properties of food ingredients and/orof texturising them (Cheftel 1986). In the extruder, the mixtureof ingredients is subjected to intense mechanical shear throughthe action of one or two rotating screws. The cooking can occurat high temperatures (up to 250◦C), relatively short residencetimes (1–2 minutes), high pressures (up to 25 MPa), intense shearforces (100 rpm) and low moisture conditions (below 30%). Inaddition to the cooking step, cookies, crackers and breakfastcereals manufacture involves toasting and/or drying operations(Cheftel 1986, Camire and Belbez 1996, Manley 2000).

During these technological treatments, due to the elevatedtemperatures and low moisture conditions used, different chemi-cal reactions such as the non-enzymatic browning can take place.Non-enzymatic browning includes Maillard reaction (MR) andcaramelisation. The products resulting from both reactions de-pend on food composition, temperature, water activity and pH,and can occur simultaneously (Zanoni et al. 1995).

As it is known, MR occurs between reducing sugars such asglucose, fructose, lactose or maltose, and free amino groups ofamino acids or proteins (usually the ε-amino group of lysine).The MR is favoured in foods with high protein and reducingcarbohydrate content at intermediate moisture content, temper-atures above 50◦C and a pH in the range from 4 to 7. Carameli-sation depends on direct degradation of carbohydrates due toheat and it needs more drastic conditions than those of the MR.Thus, at temperatures higher than 120◦C, pH lower than 3 orhigher than 9 and very low moisture content, caramelisation isfavoured (Kroh 1994).

Food Biochemistry and Food Processing, Second Edition. Edited by Benjamin K. Simpson, Leo M.L. Nollet, Fidel Toldra, Soottawat Benjakul, Gopinadhan Paliyath and Y.H. Hui.C© 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

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30 Non-Enzymatic Browning in Cookies, Crackers and Breakfast Cereals 585

Furthermore, other chemical reactions that might take placeduring processing of these products may also affect the extent ofnon-enzymatic browning. Thus, starch and non-reducing sugarssuch as sucrose can be hydrolysed into reducing sugars thatcan later be involved in other reactions, for instance, in the MR(Camire et al. 1990).

The chemical changes that take place during the technologi-cal process used in the elaboration of this type of cereal-basedfoods contribute, to a certain extent, to their typical organolep-tic characteristics. However, important losses of lysine due tothe formation of chemically stable and nutritionally unavailablederivatives of protein-bound lysine can be observed under MRconditions (Torbatinejad et al. 2005).

The amount of lysine and its biological availability are mean-ingful criteria for the nutritive quality of cereals, as foodsprocessed from cereal grains are low in essential amino acidssuch as lysine and methionine (Horvatic and Eres 2002). Asthis deficiency can be further impaired by losses originated inbrowning reactions during processing, a compromise must befound where the objectives of heat treatment are reached with aminimal decrease in the nutritional quality of the food. Differentindicators based on the evaluation of the extent of non-enzymaticbrowning have proved to be useful, not only for processing con-trol, but for optimisation of operating conditions in the manu-facture of cereal-based foods (Singh et al. 2000, Gokmen et al.2008a, 2008b). Although some of the studies on cereal-basedproducts reported in this review have not been directly carriedout in cookies, crackers or breakfast cereals, they have been con-sidered here since both the manufacture and composition couldbe similar and, consequently, the same chemical reactions mightbe involved.

NON-ENZYMATIC BROWNINGINDICATORSAvailable Lysine

The determination of available lysine has been used to evalu-ate the effect of heating on the protein quality of the followingcereal-based products: pasta (Nepal-Sing and Chauhan 1989,Acquistucci and Quattrucci 1993), bread (Tsen et al. 1983,Ramırez-Jimenez et al. 2001), cereals (Fernandez-Artigas et al.1999a), cookies fortified with oilseed flours (Martinkus et al.1977) and biscuits (Singh et al. 2000).

Since extrusion cooking is a well-established technology forthe industrial elaboration of cereal-based foods, several authorshave studied the effect of the initial composition and the differentoperating conditions on lysine loss in extruded materials. Insamples of protein-enriched biscuits, Noguchi et al. (1982) foundthat the loss of reactive lysine is significant (up to 40% of theinitial value) when the extrusion cooking is carried out at hightemperature (190–210◦C) with a relatively low water content(13%). When moisture is increased to 18%, the lysine loss ismuch less pronounced or even negligible.

Noguchi et al. (1982) also studied the effect of the decreaseof pH on lysine loss in biscuits obtained by extrusion. These au-thors observed a higher lysine loss at low pH, since strong acid-

ification markedly increases starch or sucrose hydrolysis and,consequently, the formation of reducing carbohydrates. Starchhydrolysis and corresponding formation of reducing sugars wasalso proposed as the main cause of lysine loss in extruded wheatflours (Bjorck et al. 1984).

An important decrease of available lysine content (40.9–69.2%) in wheat grain processed by flaking and toasting wasobserved by McAuley et al. (1987), and they attributed theseresults to the high temperature reached during toasting. In gen-eral, extrusion cooking of cereal-based foods appears to causelysine losses that do not exceed those for other methods offood processing. In order to keep lysine losses within low levels(10–15%), it is necessary to avoid operating conditions above180◦C at water contents below 15% (even if a subsequent dryingstep is then necessary) (Cheftel 1986).

Phillips (1988) suggested that the MR is more likely to occurin expanded snack foods in which nutritional quality is not amajor factor than in other extruded foods with higher moisturecontents, if the processing conditions are controlled. Horvaticand Guterman (1997), in a study on the available lysine contentduring industrial cereal (wheat, rye, barley and oat) flake pro-duction, found that the effects of particular processing phasescan result in a significant decrease of available lysine amountsin rye and oat flakes, whereas less influence can be observed inthe case of wheat and barley flakes. Apart from the importanceof processing conditions, the results obtained by these authorsseem to indicate that the decrease of lysine availability is higherfor cereals with greater available lysine contents in total proteins.

Other important consideration is to avoid the presence of re-ducing sugars during extrusion. Lysine loss and browning aremore intense when reducing carbohydrates such as glucose, fruc-tose or lactose (added as skim milk) are added to the food mixabove 2–5% level (Cheftel et al. 1981). In agreement with theseresults, Singh et al. (2000) and Awasthi and Yadav (2000) foundhigher lysine loss and browning in traditionally elaborated bis-cuits enriched with whey or skim milk.

An investigation of the changes in available lysine contentduring industrial production of dietetic biscuits was performedby Horvatic and Eres (2002). Dough preparation did not signifi-cantly affect the available lysine content. However, after baking,a significant loss (27–47%) of available lysine was observed inthe studied biscuits. The loss of available lysine was found to besignificantly correlated with technological parameters, mainlybaking temperature/time conditions.

The influence of storage on the lysine loss in protein-enrichedbiscuits was studied by Noguchi et al. (1982). Lysine loss wasobserved to increase when samples were stored at room temper-ature for a long period of time. Hozova et al. (1997) estimated,by measurement of lysine, the nutritional quality of amaranthbiscuits and crackers stored during 4 months under laboratoryconditions (20◦C and 62% RH). Although a slight decrease in thelevel of lysine was detected, this was not significant. However,these authors suggested that lysine degradation can continuewith prolonged storage and it is necessary to consider this factin relation to consumers and the extension of storage time.

In a survey on 20 commercially available cereal-based break-fast foods, Torbatinejad et al. (2005) stated that reactive lysine

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586 Part 5: Fruits, Vegetables, and Cereals

is a more accurate measure of unmodified lysine since total ly-sine determination often includes lysine that has reverted frommodified lysine derivatives (early Maillard products) duringacid hydrolysis. In addition to the formation of unavailable ly-sine derivatives, it has also been described that the advanceof MR as a result of processing is at least partly responsiblefor the reduction in the overall protein digestibility (Rutherfurdet al. 2006).

Furosine

The determination of furosine (ε-N-2-furoylmethyl-lysine), gen-erated from the acid hydrolysis of Amadori compounds formedduring the early stages of MR (Erbersdobler and Hupe 1991),has been used for the assessment of lysine loss in malt(Molnar-Perl et al. 1986), pasta (Resmini and Pellegrino 1991,Garcıa-Banos et al. 2004, Gallegos-Infante et al. 2010), babycereals (Guerra-Hernandez and Corzo 1996, Guerra-Hernandezet al. 1999), baby biscuits (Carratu et al. 1993), cookies(Gokmen et al. 2008a), fibre-enriched breakfast cereals(Delgado-Andrade et al. 2007), flours employed for the for-mulation of cereal-based products (Rufian-Henares et al. 2009)and bread (Ramırez-Jimenez et al. 2001, Cardenas-Ruiz et al.2004). Other 2-furoylmethyl derivatives such as the ones cor-responding to GABA (2-FM-GABA) have been, among others,suggested as indicators of the extent of the MR in different veg-etable products (Del Castillo et al. 2000, Sanz et al. 2000, 2001,Soria et al. 2009).

Furosine determination was used by Rada-Mendoza et al.(2004) to evaluate the advance of MR in commercial cookies,crackers and breakfast cereals. Furosine was detected in all anal-

ysed samples within a wide range of variation: 25–982 (in cook-ies), 163–751 (in crackers) and 87–1203 (in cereals) mg/100 gprotein. Figure 30.1 illustrates, as an example, the HPLC chro-matogram of the 2- FM-amino acids of the acid hydrolysate ofa cereal breakfast sample. Besides furosine, these authors found2-FM-GABA in samples of crackers and breakfast cereals,which was absent in most cookie samples analysed. The pres-ence of 2-FM-GABA in breakfast cereals and crackers may beattributed to the considerable amount of free GABA present inrice and corn used in their manufacture.

Recently, Delgado-Andrade et al. (2007) showed that regard-less of the protein source (i.e., type of cereal), the higher theprotein content, the higher the furosine level of breakfast cerealformulations. According to this, breakfast cereals enriched indietary fibre showed the highest content of this quality marker.Regarding the physical form of the sample, higher furosine lev-els were found in puffed cereals as compared to flakes, probablydue to the more pronounced heating during processing.

Contribution of milk components used during breakfastcereal manufacture to furosine content is still controversial(Rada-Mendoza et al. 2004, Delgado-Andrade et al. 2007).Whereas some authors partly attributed the wide variation ofthis heat-induced marker to the considerable amounts of furo-sine in dried milk (Corzo et al. 1994), others concluded thataddition of these components was not directly related to the lev-els of furosine in the product. The effect of fibre, which was nottaken into account in some of these studies, could be responsiblefor the discrepancies observed.

In cookies, furosine formation has been shown to behighly dependent on the dough formulation and baking con-ditions (Gokmen et al. 2008a). Therefore, furosine cannot be

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Figure 30.1. HPLC chromatogram of the acid hydrolysate of a breakfast cereal sample: (1) 2-furoylmethyl-GABA and (2) furosine (FromRada-Mendoza et al. 2004).

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considered a reliable marker of the extent of the thermal treat-ment for comparison of different products or processing plants.In these cases, the measure of lysine availability is a better indexof protein quality.

Similarly, the variable amounts of dried milk used in manu-facture of cereal-based products and the different levels of freeGABA in unprocessed cereals appear to be the major drawbackfor the use of furosine and 2-FM-GABA as suitable indicators todifferentiate between commercial cereal-based products. How-ever, in the cereal industry, where exact composition is known,measurement of 2-FM-GABA and furosine formed might beused as indicators to monitor processing conditions during themanufacture of cereal products.

Finally, the effect of the addition of common bean flour (15%and 30%) to semolina on furosine content, total phenolics andother parameters related to quality evaluation (moisture, optimalcooking time, cooking loss, water absorption capacity, colourand firmness) was determined by Gallegos-Infante et al. (2010)in spaghetti pasta obtained at different temperatures (60–80◦C).Although an increase in furosine and phenolic contents wasobserved in pasta fortified with bean flour and dried at hightemperature, further research is necessary to elucidate the actualphenolic content and the antioxidant capacity related to the MRproducts or polyphenols.

Hydroxymethylfurfural and Furfural

Hydroxymethylfurfural (HMF) and furfural are intermediateproducts in the MR, originated from the degradation in acidsolution of hexoses and pentoses, respectively (Hodge 1953,Kroh 1994).

HMF is a classic indicator of browning in several foods suchas milk (van Boekel and Zia-Ur-Rehman 1987, Morales et al.1997), juices (Lee and Nagy 1988) and honey (Jeuring andKuppers 1980, Sanz et al. 2003). HMF has also been detected inseveral cereal-based foods, including dried pasta (Acquistucciand Bassotti 1992, Resmini et al. 1993), baby cereals (Guerra-Hernandez et al. 1992, Fernandez-Artigas et al. 1999b), cookies(Ait-Ameur et al. 2006) and bread (Ramırez-Jimenez et al. 2000,Cardenas-Ruiz et al. 2004).

In a study on the effect of various sugars on the quality ofbaked cookies, furfural (in cookies elaborated with pentoses)and HMF (in cookies elaborated with hexoses) were detected(Nishibori and Kawakishi 1992). HMF has also been foundin model systems of cookies baked at 150◦C for 10 minutes(Nishibori and Kawakishi 1995, Nishibori et al. 1998).

Garcıa-Villanova et al. (1993) proposed the determination ofHMF to control the heating procedure in breakfast cereals aswell as in other cereal derivatives. Birlouez-Aragon et al. (2001)detected HMF in commercial samples of breakfast cereals (corn-flakes), in samples before and after processing using traditionalcooking and roasting, and in a model system of wheat, oats andrice with two levels of sugars submitted to extrusion. Althoughonly traces of HMF were detected in the raw material, HMFformation during extrusion increased proportionally as sugarconcentration increased. Among all the analysed samples, thehighest content of HMF was found in commercial samples.

The effect of recipe composition in terms of leavening agent(ammonium and sodium bicarbonates) and sugars (sucrose andglucose), and baking conditions (temperature and time) on HMFformation in cookies has been recently studied by Gokmen et al.(2008b). The type of leavening agent, affecting both pH of for-mulation and degradation of sugars, appeared as one of the mostimportant parameters from the viewpoint of HMF formation.Water activity, which has also been reported to be highly influ-ential on HMF formation, must reach levels lower than 0.4 forallowing a significant formation of this indicator in commercialcookies (Ait-Ameur et al. 2006).

Together with HMF and furfural, glucosylisomaltol (GIM, anintermediate product of the MR that is generated principallyfrom the reaction between maltose and glutamine) has been de-termined by HPLC as a control index of the MR development inbreakfast cereals (Rufian-Henares et al. 2006a), with the advan-tage over HMF that the MR, and not the addition of thermallydamaged ingredients, is the sole pathway of formation of GIM.

Recently, Rufian-Henares and Delgado-Andrade (2009) stud-ied the effect of digestive process on the bioaccessibility offurosine and HMF and on the antioxidant activity of corn-based breakfast cereals. Digestion allowed liberation of HMFand Amadori products (furosine) and increased the solubility ofantioxidant compounds.

Colour

Colour is an important characteristic of cereal-based foods and,together with texture and aroma, contributes to consumer pref-erence. Colour is another indication of the extent of MR andcaramelisation. The kinetic parameters of these reactions areextremely complex for cereal products. As a consequence, thecolouring reaction is always studied globally, without taking intoaccount individual reaction mechanisms (Chevallier et al. 2002).Colour depends both on the physico-chemical characteristics ofthe raw dough (water content, pH, reducing sugars and aminoacid content) and on the operating conditions during processing(Zanoni et al. 1995, Gokmen et al. 2008b).

Brown pigments (melanoidins) formation occurs at the ad-vanced stages of browning reactions and, although is undesir-able in milk, fruit juices and tomatoes, among other foods (DeMan 1980), it is desirable during the manufacture of cookies,crackers and breakfast cereals. Colour development has beenstudied in cereal-based foods such as baby cereals (Fernandez-Artigas et al. 1999b), bread (Ramırez-Jimenez et al. 2001), cook-ies (Kane et al. 2003, Gokmen et al. 2008b), breakfast cereals(Rufian-Henares et al. 2006b, Moreau et al. 2009) and gluten-free biscuits (Schober et al. 2003).

The formation of melanoidins and other products of the MRdarkens a food, but a darker colour is not always attributed tothe presence of these compounds, since the initial compositionof the mixture can also afford colour. In a study on the proteinnutritional value of extrusion-cooked wheat flours, Bjorck et al.(1984) determined the colour of the extruded material and founda correlation between the reflectance values and total lysinecontent of extruded wheat. As the reflectance of the raw flours

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was very different, comparison could not be made for the effectof extrusion.

Hunter ‘L’ values determined for wheat flours, commercialflaked-toasted, extruded-toasted, and extruded-puffed breakfastcereals were found to be positively correlated with availablelysine (McAuley et al. 1987). Rufian-Henares et al. (2009) con-cluded that the colour difference (�E) obtained from the CIELab parameters L∗, a∗, b∗ between toasted and untoasted sam-ples results in a reliable measurement of the visible colour pro-duction for the toasting step of different flours usually used forthe formulation of cereal-based products. During industrial bak-ing of cookies, the effect of time on colour development andother parameters (volume, structure, weight and crispness) wasstudied by Piazza and Masi (1997). The development of crisp-ness increased with time and was found to be related to theother physical processes that occur during baking. Gallagheret al. (2003) observed different colour development in the pro-duction of a functional low-fat and low-sugar biscuit, depend-ing upon the quantities of sugar and protein present. Regardingspaghetti pasta fortified with different levels of Mexican com-mon bean flour, the difference in colour was associated with theuse of common flour rather than the drying temperature assayed(Gallegos-Infante et al. 2010).

The manufacture of many breakfast cereals starts with thecooking of whole cereal grains in a rotary pressure cooker. Dur-ing this operation, the grains absorb heat and moisture, andundergo chemical (browning reactions) and physico-chemicalchanges as a consequence. The cooking stage is thought to havea key influence on the properties of the final product, such ascolour, flavour and texture. Horrobin et al. (2003) studied the in-terior and surface colour development during wheat grain steam-ing and the results obtained indicated the possible relationshipbetween the colour development and moisture uptake during thecooking process. In a study on the effects of oven humidity onfoods (bread, cakes and cookies) baked in gas convection ovens,Xue et al. (2004) observed that increased oven humidity resultsin products with lighter colour and reduced firmness.

As aforementioned, the formation of MR products and in-tense colour are responsible for the organoleptic properties ofthis type of products. Moreover, it is also important to considerthat the brown pigments formed could present some biologicalactivities. Thus, Bressa et al. (1996) observed a considerableantioxidant capacity in cookies during the first 20–30 minutesof cooking (when browning takes place). Whole grain break-fast cereals have also proved to be an important dietary sourceof antioxidants (Miller et al. 2000). Borrelli et al. (2003) stud-ied in bread and biscuits the formation of coloured compoundsand they examined the antioxidant activity and the potentialcytotoxic effects of the formed products. Summa et al. (2006)also correlated acrylamide concentration and antioxidant activitywith colour of cookies by means of a three-dimensional modelin which the three coordinates of the CIE colour space were usedas variables.

Bernussi et al. (1998) studied the effect of microwave bakingon the moisture gradient and overall quality of cookies, and theyobserved that colour did not differ significantly from that of thecontrol samples (cookies baked using the traditional process).

Broyart et al. (1998) carried out a study on the kinetics ofcolour formation during the baking of crackers in a static elec-trically heated oven. These authors observed that the darkeningstep starts when the product temperature reaches a critical valuein the range of 105–115◦C. A kinetic model was developed inorder to predict the lightness variation of the cracker surfaceusing the product temperature and moisture content variationsduring baking. The evolution of lightness appears to follow afirst-order kinetic influenced by these two parameters.

Colour development has also been included, together withother parameters (temperature, water loss, etc) in a mathematicalmodel that simulated the functioning of a continuous industrial-scale biscuit oven (Broyart and Trystram 2003).

The effect of raising agents and sugars on surface colour ofcookies was studied by Gokmen et al. (2008b).

Changes in surface colour, water activity and pH of cookieswere determined to understand the chemical mechanisms re-sponsible for HMF formation during baking of cookies fromdifferent formulations.

Fluorescence

During the advanced stages of the non-enzymatic browning,compounds with fluorescence properties are also produced. Sev-eral analytical methods based on fluorescence measurementshave been used to evaluate the extent of this reaction (Rizkallahet al. 2008, Tregoat et al. 2009, Calvarro et al. 2009). For in-stance, the FAST (fluorescence of advanced Maillard productsand soluble tryptophan) method proposed by Birlouez-Aragonet al. (1998) is based on the fluorescence ratio between MR prod-ucts and tryptophan determined when excited at 330–350 nm.This parameter is dependent on heat treatment of the productand is related to its protein nutritional loss. Thus, this method,firstly validated on milk samples, has been used in other foodsmodified by the MR such as breakfast cereals (Birlouez-Aragonet al. 2001) and rye bread (Michalska et al. 2008).

Birlouez-Aragon et al. (2001) studied the correlation betweenthe FAST index, lysine loss and HMF formation during themanufacture of breakfast cereals by extrusion and in commercialsamples. The FAST index was in good agreement with HMF for-mation. These authors also found that the relationship betweenFAST index and lysine loss indicates that, for severe treatmentsinducing lysine blockage higher than 30%, lysine loss is lessrapid than the increase in the FAST index. Thus, the fluorimetricFAST method appears to be an interesting alternative to eval-uate the nutritional damage on a great variety of cereal-basedproducts submitted to heat treatment.

Delgado-Andrade et al. (2006) determined free and total(free + linked-to-protein backbone) fluorescence intermediatecompounds (FIC) related to MR in commercial breakfast ce-reals. Levels of free and total FIC were also correlated withother well-established heat-induced markers of the extent of theMR or sugar caramelisation during cereal processing, such asHMF, furfural, GIM and furosine. Data support the usefulness ofFIC measurements as an unspecific but adequate heat-inducedmarker of the extent of thermal processing in breakfast cereals,since statistically significant correlations were found between

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FIC values and other heat-induced markers. Recently, Calvarroet al. (2009) reported a new methodology to monitor Maillard-derived fluorescent compounds (FC) in cookies by flow-injectionanalysis. Ratio between total and free FC was proposed as refer-ence for setting the limits to the appropriate range of processingand to avoid over-processing. Because of the significant correla-tion with acrylamide levels, this methodology is also proposedfor estimation of acrylamide formed in cookies.

Acrylamide

For almost 8 years now, a significant amount of research ac-tivities has focused on the mitigation of the formation of the‘probable carcinogen to human’, acrylamide (2-propenamide),in a number of fried and oven-cooked foods (IARC 1994, Jensenet al. 2008). One of the possible mechanisms involved in theacrylamide formation is the reaction between asparagine andreducing sugars such as glucose or fructose via MR (Mottramet al. 2002, Weisshaar and Gutsche 2002, Courel et al. 2009).Since asparagine is a major amino acid in cereals, the possi-ble formation of acrylamide in cereal-based foods should beconsidered.

Variable amounts of acrylamide have been found in cereal-based foods such as bread, cookies, crackers, biscuits and break-fast cereals (Yoshida et al. 2002, Ono et al. 2003, Riediker andStadler 2003, Delatour et al. 2004, Taeymans et al. 2004, Rufian-Henares et al. 2006b, Sadd et al. 2008).

The presence of acrylamide, together with that of other un-desirable Maillard compounds, such as furosine, HMF, car-boxymethyllysine, has been related to formulation and process-ing conditions of model systems of cookies (Courel et al. 2009)and crackers (Levine and Smith 2005). In general, baking con-ditions, the selected leavening agent and addition of asparagineto the formula were identified as the most significant sourcesof variability (including those contributing either to the for-mation or elimination) of acrylamide. In a similar approachby Rufian-Henares et al. (2006b), the relationship among lev-els of acrylamide and compositional parameters (type of cerealand protein and dietary fibre contents) of commercial break-fast cereals was shown. In addition, no significant relationshipbetween acrylamide and classical browning indicators such asHMF, furosine or coloured compounds was found in the com-mercial samples analysed. However, it could be feasible that thisrelation become significant for samples processed at industrial/

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pilot-scale under controlled formulation and processingconditions.

Sadd et al. (2008) studied different alternative mitigationstrategies to reduce acrylamide in bakery products. Whereasyeast fermentation was an effective way of reducing asparagineand hence acrylamide, amino acid addition to dough gave mod-est reduction of this contaminant. Removing ammonium-basedraising agents was also beneficial. Calcium supplementation forbinding asparagine looked promising, but interactions with otheringredients need further investigation. Lowering the dough pHreduced acrylamide, but at the expense of higher levels of otherprocess contaminants.

Alternatively, Anese et al. (2010) have recently evaluated thepossibility to remove acrylamide from previously hydrated com-mercial biscuits by vacuum treatment. Selection of suitable tem-perature, time and pressure conditions has proved to be requiredto maximise acrylamide removal while minimising its formationand effect on the sensory properties.

On the other hand, the correlation between mitigation of acry-lamide and its influence on beneficial properties of food, such asthe antioxidant activity has been scarcely studied. Summa et al.(2006) reported a strong link between the composition of thepastries and baking parameters and the genesis of acrylamide as

well as antioxidants. Therefore, suppressing the MR generallyleads not only to acrylamide mitigation but also to losses ofsubstances considered to be beneficial.

Maltulose

Besides MR, isomerisation of reducing carbohydrates may takeplace during processing of cookies, crackers and breakfast cere-als. Maltulose (Fig. 30.2), an epimerisation product of maltose,has been found in the crust of bread (Westerlund et al. 1989).Maltulose formation has also been observed during the heatingof a maltodextrin solution at high temperature (180◦C) (Krohet al. 1996). Garcıa-Banos et al. (2000, 2002) detected mal-tulose in commercial enteral products and proposed the ratiomaltose:maltulose as a heat treatment and storage indicator ofenteral formulas.

In cookies, crackers and breakfast cereals, Rada-Mendozaet al. (2004) detected maltulose (from traces to 842 mg/100 g)in all commercial samples analysed. Figure 30.3 shows the gaschromatographic profile of the trimethylsilyl oxime-derivativesof mono- and disaccharide fractions of a cookie sample. Sim-ilar patterns were obtained for crackers and breakfast cereals.The formation of maltulose depends mainly on initial maltose

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Figure 30.3. Gas chromatographic profile of the trimethylsilyl oxime-derivatives of fructose (1,2), glucose (3,4), sucrose (6), lactulose (8),lactose (9, 10), maltulose (11, 12) and maltose (13,14) of a cookie sample. Peaks 5 and 7 were the internal standards: myo-inositol andtrehalose, respectively (from Rada-Mendoza et al. 2004).

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content, pH and heat treatment intensity of the process. Sincecookies, crackers and breakfast cereal samples may contain vari-able amounts of maltose, the usefulness of maltulose as indica-tor of heat treatment might be questionable. Previous studies onthe formation of maltulose during heating of enteral formulas(Garcıa-Banos et al. 2002) pointed out that values of the ratiomaltose:maltulose were similar in samples with different mal-tose content submitted to the same heat treatment. Therefore,the ratio maltose: maltulose is an adequate parameter for com-paring samples with different initial maltose contents. Becausemaltose isomerisation increases with pH, only in samples withsimilar pH, differences in maltose: maltulose ratio can be dueto different heat processing conditions. These results, shown byRada-Mendoza et al. (2004), seem to indicate that the ratio mal-tose: maltulose can allow the differentiation among commercialcereal-based products and may serve as an indicator of the heatload during its manufacture.

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Food Biochemistry and Food Processing (Simpson/Food Biochemistry and Food Processing) || Non-Enzymatic Browning in Cookies, Crackers and Breakfast Cereals