BPVI 15 Block 4 Unit 15

UNIT 15 PACKAGING, STORAGE, QUALITYATTRIBUTES AND COMMONDEFECTS OF DRIED MILKS

Structure

15.0 Objectives

15.1 Introduction

15.2 Packaging of dried milks

Bulk packaging

Retail packaging

15.3 Packaging of infant foods

15.4 Packaging of malted milk foods

15.5 Packaging of dairywhitener

15.6 Storage of dried milk

15.7 Qualityattributes of dried milks

Flavour

Colour

Physical properties

Reconstitution and instant properties

15.8 Common Defects of dried milks

Off flavours

Discolouration

Free fat

Poor solubility

Slowly dispersible particles

Sludge formation

Scum formation

Occurrence of white flecks

Scorched particles

Cakiness

Feathering

15.9 Let us sum up

15.10 Key words

15.11 Some useful books

15.12 Answers to check your Progress

15.0 OBJECTIVES

After reading this unit we should be able to:

know various ways of packaging of different dried milks.

learn storage of dried milks.61

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judge various qualityattributes of milk powders.

understand various possible defects in dried milks and the ways to avoid them.

15.1 INTRODUCTION

The keeping qualityof dried milk products during storage is of great importance toconsumer acceptance. To maintain the high qualityof the product during storage, itis necessary to prevent their organoleptic and physico-chemical deterioration.Packagingofdriedmilkproducts, therefore,assumesgreatersignificance.Thepowderpackaging room should be completely isolated to reduce the spread of powderdust.Appearance of common defects in milk powders is influenced by quality ofmilk used in production, care taken during production, handling and storage,manufacturing conditions, moisture content in the product, metallic contamination,and packaging and storage conditions.

15.2 PACKAGING OFDRIED MILKS

Milk powder packaging should be carried out in a dryatmosphere. This is becauselactose is present in glass (i.e. non-crystalline/amorphous) state in dried milks andthe dried milk in this state is very hygroscopic. If exposed to humid atmosphere, itwould readily absorb moisture, become sticky and cake in storage.

The skimmedmilk powder is packed in containers that retain product qualityduringstorage as well as result in better handling. The successful packagingof whole milkpowder involves the additional step inert gas packaging in which oxygen entrappedin the air cells of the milk powder particles is removed and thus reduce the oxygenconcentration to as low a level as possible. The oxygen permeates the walls of aircells and diffusesout until equilibrium isattained between the interior ofair cells andhead gas space in the can. Attainment of equilibrium in the gas packed cans isreached in about 5-7 days. The general procedure is to immediately remove oxygenby subjecting the product to 28” of vacuum within 24 hours of drying with finalpackaging within a few days. Less than 2% final oxygen in the headspace of thepackage is considered satisfactoryfor most storage conditions.This is accomplishedbyvacuumizing and gas packing with an inert gas. The specific procedure selectedfor gas packaging is governed by final oxygen limit desired in the package, and bythe equipment-fillingrate in relation tooxygen evacuation rate.Asper Prevention ofFoodAdulterationAct,The spray-dried milk shall be packed in nitrogen or mixtureof nitrogen and carbon dioxide in hermetically sealed containers.

i. Bulk Packaging

Traditional packaging of 25 kg milk powder, irrespective of type, has been inpolyethylene linedmulti-wallpapersacks.This typeofpackagingis themostversatileof all the packs for milk powders and it is due to this versatility that these are likelyto remain the major bulk container for milk powder. Their keyfeatures are that theyare robust, relatively low in cost and are capable of being packed at high productionrates i.e. 9 to 10 ton/hrwith modern filling/sealingequipment.Automatic dispensingmachines are readily available to dispense correct weight of powder in one bagbefore shifting the product flow into the next bag. Bags are sewn 3 to 3.5 stitchesper inch automatically or by a manually operated sewing machine suspended andcounterbalanced within easyreach of the filling area. These are convenient pack formajor end users such as recombining plants and repacking stations.

Specifications for multi-wall bags varyfrom country to country, but generallya 4-5-plybag with a minimum weight of 420 g/m2 and an inserted low-densitypolythene

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(LDPE) liner of 75 micron is considered to be adequate. Amajor improvement inthe design of the multi-wall bags is the development of a “heat sealable style.” Thishas been achieved byincorporating the polythene liner into the bagas the innermostplyduringbag manufacture.

For packing whole milk powder (WMP), the package is gas-flushed (nitrogen). In1991, Colby-packaging systems introduced a new filling machine for milk powdermanufactured by standard methods. “COLBYPAC-25” discharges the product ina 25 kg disposable barrier laminate bags. Machines incorporate a “Pre” or “Post-gassing” step, which extends the shelf life of milk powder, O

2is removed (pre or

post filling) and replaced with CO2or N

2. Gas-flushed packs are required to be

more sturdyand with considerably improved barrier properties so as to maintain themodified atmosphere within the package. Some markets require the milk powderto be delivered in 300 kg Bulk bins, gas-flushed. These systems require specialisedfilling/gassing/sealingequipment.

i) Bulk bin: Considerable interest in the bulk handling of milk powder has beengenerated by the increased costs of handling and transportation. Concept ofbulkbinpackagingis relativelynewand isprovingtobeofvalue tothe repackingand reprocessing plants. Following are the major types of bins:

a) Tote bin: The bins are for 800 and 1000 Kg of powder and fabricatedfromdifferentmetalsoralloys includingstainless steel. Aluminiumismostoften used by the dry milk industry, costing about one-half as much andbeing lighter than those made from stainless steel. It is well suited to theinternal transfer of powder to central packing stations. These bins areoften used as a container for shipment to industrial users. The advantagesare mainly in reduction of labour and bag costs with possiblya reductionindustproblem.Automaticconveyingequipment isavailable to fillagroupof these bins, each in succession when properly positioned. They areairtight andcanbestacked. Thebins areemptied intoahopperbyelevatingand tilting. Its major disadvantages include the high initial cost ofconstruction and the cost of returning empty bins to the milk powdermanufacturers.

b) Big bag/Bag in box: Both styles are superseding the tote bin. Theirbasicconcept is thatof a largesizedmulti-wallbagin thata largepolythenebagisfilledwithmilkpowderandclosedbytying. Thefilledbagisprotectedfrom outside influences bywoven plastics such as polypropylene or rigidtwin or triple laminated corrugated board. Theyare normally transportedon pallets and are emptied bysuction hose.Apart from potential savingsin filling and transportation costs, the relatively low cost of packs permitsthem to be exported on a nil return basis.

Check Your Progress 1

1) Why milk powders should be packed in a dry atmosphere?

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2) What additional steps are taken in packaging of whole milk powder thanskimmed milk powder?

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3) What is the traditional packaging of 25 kg milk powder and why?

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4) Describe bulk packaging of milk powder in Big bag/Bag in box.

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ii. Retail Packaging

The retail pack market is dominated by the metal can but there is increasingcompetition from a number of plastic laminates that are being formed into a varietyof pack styles.

i) Metal can: The metal can is the nearest to a complete container for milkpowder. However, apart from cost, the major drawback of the can is itstendency to rust through moisture condensation when changes in temperatureare experienced during storage and transportation. The incidence and severityof this problem has been reduced by the adoption of aluminium ends for thecans and improved lacquers for the can bodies. The can is commonlyof three-piece construction and is manufactured from electrolytic tinplate. The featuresinclude:

A cylindrical body that is either welded or soldered.

Abase that is double seamed on to the body.

A lid that is double seamed on to the bodyimmediatelyafter the vaccum/gassing cycle has been completed. Sealing compounds in lid and baseensure that the can is hermetically sealed

Equipments for semiautomatic and automatic packagingofwhole milkpowderwhich can vacuumize and N

2-pack cans, have been developed by leading

companies. Themostof themachinesused for packagingofwholemilkpowder



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operatewithgravityfeedandvibratinghopper. Thelatestmodel is acombinationofAuger and vacuum feed, which combines speed and accuracyof filling withcompact, clean and dustless packaging byvacuum method. The cans are thenfinallysealed bya double seamingoperation on an automatic closing machine.

a) Filling the cans: The cans used for milk powder packaging abroad arecommonly of 1 pound, 2.5 pound and 5 pound weights. There is also a4.5 ounce-can.Alimited number of 25 pound and 100 pound cans arealso used.

b) Vaccum packing: To confine the oxygen content in the headspace ofcan to 3% or less requires a vacuum of about 28.5 inches on a 30-inchbarometer at the time of vacuuming.

c) Nitrogen packing: It consists of drawing a high vacuum on the cans ofdried whole milk (within 1/4 inch of the barometer), then dissipating thevacuum with an inert gas such as nitrogen or carbon dioxide, and sealingthe cans.

d) Doublevaccumizing: Somemanufacturersdoublevaccumizethepowderbefore gassing. In this case, the dried milk is transferred from the sifter tolargedrums(usual capacity200pounds). Thefilleddrumsare immediatelyvacuumized. This temporary form of package is held for several hours orovernightor evenas longas48hours. After the holdingperiod, thepowderis transferred to final containers, inwhich it is againvacuumized followedbygassingand sealing.

e) Double gassing: To obtain a low level of headspace oxygen in WMP, adouble gassing technique is applied. The customary procedure is thecollection of filled cans on trays to be conveyed into the vacuum chamber.Theair is removedrapidly(60seconds)with thegaugeindicatordecreasingto 29” of vacuum. After a 2 to 5 min hold, the pressure is restored withnitrogen to 0.5 to 1.0 psi above atmospheric pressure. Nitrogen may bereplaced with a mixture of nitrogen and CO

2, the latter being restricted to

5 to 20%. After removal from the chamber, the hole in the lid of cans issoldered. Containers are held for oxygen desorption. When oxygenequilibrium has been attained in the head space, usually within a week,but at themost ten days, the cans are punctured and the vacuum treatment,pressure restored with nitrogen, and sealing steps are repeated.

ii) Sachet packs: Flexible packaginghas evolved from polyethylenebags to moresophisticated packs. Sachet pack styles vary from the simple flat pack, whichis heat-sealed around the edges to the complex free standing, block bottomform. In most cases, the sachet of milk powder is enclosed for distribution andsale inside cardboard boxes. In recent times, metallized polyester/liner low-densitypolyethylene laminateshaveemerged.SyntheticmaterialssuchasNylontend to generate static electricityduring packaging operation,which maycausefaults in vital seal areas.

A development that could well have useful application is the introduction of‘soft can’. In a fullyautomated system, a sachet is formed from a heat sealablecomposite foil and a robust carton formed around the sachet. The system thenfollows the standard filling, vacuum and gas packing practice of the metal can.As the composition of the laminate is virtuallya perfect barrier to moisture andgas, it is considered that this system could offer a suitable alternative to the can.

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Withthedevelopmentofaluminium/plasticlaminateswithconsiderablyimprovedbarrier properties, the quantity of WMP and special products in this type ofpackaging is showinga rather marked increase.Atypical composition of sachetmaterial for whole milk powder is polyester 12 micron/Al-foil 9 micron/PE 50micron. which is satisfactory in relation to oxygen transmission. Bags with 250g, 500 g and 1000 g are used. Material combinations that exclude foil arebeing used successfullyon the lower fat powders.

15.3 PACKAGING OF INFANT FOODS

Generally, infant foods are packed in metalised tin containers, which can be sealed,oxygen evacuated and filled with an inert gas.Tin containers having snap on plasticlids are now available. In order to reduce the ever increasing cost of tin containers,laminated flexible packaging material are in great use. The laminated pouches, afterpacking, inert gas injecting and sealing are then placed into individual cardboardcartons for easyhandling.

15.4 PACKAGING OF MALTED MILK FOODS

The freshlydried malted milk foods are highly hygroscopic, absorb moisture veryrapidlyand become moist, soft, stickyand unmanageable if handled and packed inordinaryatmosphere. Therefore, handlingand packaging of maltedmilk foods mustbe done in an atmosphere of controlled low humidity. Further the finished product ispackaged mostly in glass bottles with screw type metal lids or in other containersimpervious to moisture vapours.

15.5 PACKAGINGOFDAIRYWHITENER

For bulk packing, dairywhitener maybe packed similar to whole milk powder andfor retail packing, dairywhitener maybe packed similar to infant foods.

As per BIS standards (IS 12299 : 1998), for bulk packaging, the product may bepackedinquantitiesof25kginbagsoffoodgradepolyethyleneofminimumthickness0.05 mm. The bags should be properly closed by tying with a string or a rubberband and shall be subsequently encased in sacks or multi-walled kraft paper, suchas crepe kraft paper bags of not less than 80 g/m2 grade lined with Hessian clothhaving a mass of 270 g / m2and having two inner layers of plain kraft paper of notless than 80 g/m2 grade.

For retail packing, BIS standards (IS 12299 : 1998) specify that the product shallbe packed in nitrogen or in a mixture of nitrogen and carbon dioxide. The productshall be packed in clean and sound metal containers or in a food grade flexible packmade from a film or combination of any of the substrate made of board, paper,polyethylene,polyestermetallizedfilmoraluminiumfoil insuchawaysoas toprotectit from deterioration. In the case of the plastic material, onlyfood grade plastic shallbe used.


1) What are the merits and demerits of metal cans for retail packaging of milkpowder?

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2) Describe sachet packs for retail packaging of milk powder?

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3) Describe packaging of infant milk food.

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4) Describe packaging of malted milk foods.

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5) As per BIS standards (IS 12299 : 1998), what is the requirement of retailpacking of dairywhitener?

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15.6 STORAGE OF DRIED MILKS

To ensure maximum keeping quality, packaged milk powders should be stored in adark, cool and dried place. In most cases, simple storage in clean dry areas withproper stacking on pallets is all that should be necessary, but some of the newerlaminates mayalso require some humiditycontrol in storage. Good quality WMPwith low oxygen content can be expected to withstand room temperature storagefor 6 monthsor more without an oxidized off-flavour. Skim milkpowder has longershelf life than whole milk powder.

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15.7 QUALITYATTRIBUTES OFDRIED MILKS

Milk powders possess various organoleptic, physico-chemical and reconstitutionalproperties, whichare important to both industrial and consumeruse.Thesepropertiesare the basic elements of quality specifications for milk powders. These propertiesof the powder are affected by the milk quality, the design of the evaporator anddryer, and bythe process conditions. Duringdryingprocess, care is taken to conserveas much as possible the natural properties of the original raw milk. Qualityof driedproducts should besuch that when reconstitutedwith water, give littleor no evidenceof detrimental change compared to the original liquid products.

i. Flavour

Milk powders are expected to demonstrate a slightly sweet, clean and pleasantflavour, though other dried milk products may be expected to confirm to certainother specific requirements. Non-fat dried milk does not have rich flavour becauseof absence of fat.

ii. Colour

Milkpowdershouldbeuniformincolour, freefromforeignspecksandburntparticles.It shouldexhibit greenish white orcreamish white colour, respectivelyin buffalo andcow milk powders.

iii. Physical Properties

Particles shape: Spray dried skim milk powder particles have been found to beregular spherical or slightly oval with different surface structures, as revealed byelectron microscopy. Some particles maybe smooth, but most of them are severelywrinkled with deep surface folds and having “apple-like structure”. The internalstructure of almost everyparticle of spraydried milk powder shows a large vacuole,in which smaller globular particles are trapped.

Particle size distribution: The particle size distribution of a powder is a measureof the average particle diameter and of the spread of sizes on either side of thisaverage. However, thegeneral rule is that themean particle size(estimatedbysievingtest shouldnotbe smaller thana set size.Forexample, for instant wholemilk powder,the mean particle size suggested is 180 m with not greater than 20 % fractionabove 500 and not greater than 10%. fraction of below 125. The particle size ofpowders affect their appearance,flowability, bulk density,Dust characteristics andreconstitution .

Bulk density: Bulk density, also known as apparentor packingdensity, is a measureof the mass of milk powder that occupies a fixedvolume. It is normallyexpressed ing/ml. The bulk densityof normal spraydried powder mayvarybetween 0.5 - 0.8 g/ml.

The bulk densityof milk powder is economically, commerciallyand functionallyanimportant property.When shipping powders over long distances, the producers areinterested in high bulk density to reduce the shipping volume, since inmost cases thetransportationcostsarechargedbyvolume.Also,highbulkdensitysaves inpackagingmaterial. In some instances producers may be interested in low bulk density tosupply apparently larger amounts of powder on the retail market than that of theircompetitors.

The way, in which particles pack together also influence the bulk density. It dependson the particle size range. The wider the range of sizes, the more likelyit is that small



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particles will pack in the voids left between large particles and the higher will be thebulk density.As smaller particles containproportionatelyless occluded air than largeparticles, the removal of fine material, for instance in the manufacture of instantwhole milk powder, affects the bulk densityboth bydecreasing the average particledensity and by decreasing the number of small particles available to fill the voidsbetween the larger particles. If a powder is subjected to severe mechanical action,there maybe a breakdown of individual particles, forming more fine material anddecreasing the number of internal voids, thus increasing the bulk density.

Flowability: The flowabilityof a powder refers to the ease with which the powderparticles move with respect to one another.Flowability is one of the major functionalproperties of dried milks, with considerable implications inpackaging, metering (or,quantitative transfer) into a process vessel, etc. Based on flowability, the productmay be termed “free flowing”, “moderately cohesive” (less flowable) or “verycohesive” (least flowable). The main factors controlling flowabilityare:

Particle size distribution - cohesion or resistance to flow, of spray dried milkpowder increases with decreasing particle size

Surface texture

Milk fat is an important factor in cohesion. Increasing fat content up to 20 %increases the resistance to flow.

Pressure nozzle powders are superior in this respect to rotaryatomizer powdersand two-stage drying gives better result than single-stage drying.

Other factors improving flowabilityare:

Agglomeration

Low percentage of fines

Addition offree-flowingagents (e.g. sodiumaluminium silicate)

Addition of components by drymixing (e.g. sugar, whey powder)

Low free fat content

Low relative humidityof atmospheric air

Skim milk powder is more free-flowing than whole milk powder.With increase inwater content (e.g. > 5%), free-flowingness considerably decreases. At lowertemperature, the free-flowingness is slightlybetter.Anti-cakingagents (‘free flowingagents’ or ‘flow conditioners’) are believed to reduce interparticle forces, and assuch theyare expected to increase the bulk densityof powders and, therefore, theirflowability. Such compounds often act bypreferentiallyabsorbing moisture owingto their high moisture-holding capacity. Thus they prevent caking and minimiseflowability lossduringstorage.

iv. Reconstitution and Instant Properties

Reconstitutability refers to the ease with which a powder can be dissolved in waterand it consists wettability, sinkability, dispersibilityand rate of solution. Ideally, highrates of wettabilityand rapid solubilization with a minimum of scum remaining arerequired. The milk powder is said to have good reconstitution properties if thereconstituted liquid milk differs little or not at all from homogenized whole milkprepared fromsweet fresh milk. The solubilityof milk powders produced in moderndriers approaches 100%. For skim milk powder and whole milk powder to be

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graded as instant the values of dispersibility in percent should be above 90 and 85,respectively.

Check Your Progress - 3

1) Discuss storage of dried milks.

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2) List various important qualityparameters of milk powders.

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3) Discuss the importance of bulk densityof milk powder.

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4) How the flowabilityof milk powders can be improved?

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15.8 COMMON DEFECTS OF DRIED MILKS

Some of thecommon defects that maydevelop in dried milk products due to variousreasons are described below:

i. Off Flavours

Oxidised/ tallowy flavour: Dry whole milk and other dry high-fat milk productsundergo oxidativedeterioration (Also called tallowy).Whole milk powder with lowto medium preheat treatments (equivalent to a WPNI of about 3-5) has a greatertendency to undergo lipid oxidation, with distinctive tallowy and musty flavours,



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than powders made with higher heat treatments (equivalent to WPNI values of2.5).Chemical changes result with the addition of oxygen to the double bonds ofunsaturated glycerides, giving at first peroxides and later aldehydes, ketones etc.,which impart the unpleasant flavour. Copper and iron act as catalysts. Higherstorage temperature,higheracidity, sunlight andultraviolet irradiationpromote fasterdevelopment of oxidative deterioration.

Rancidity flavour: Rancidity is due to hydrolysis of fat through lipase enzymeleading to production of free fattyacids, like butyric acid.

Stale flavour: Stale flavours, due to carbonyl compounds, can be detected in milkpowders almost as soon as they are made. The mechanism of formation of thesecompounds maybe through the Maillard reaction, but manycompounds contributeto a stale, cardboard flavour, including oxidation by products. The defect isaccelerated by high moisture content and high temperature of storage.

Cooked flavour: Milk powders often have cooked flavour, which results fromcomponents formedduringpreheatingandpossiblyduringevaporation.Duringdrying,conditions are mostly not such that off-flavours are induced. On the contrary, aconsiderable part of the volatile sulphydryl compounds (especiallyH

2S) is removed.

A cooked flavour in milk powder mainly results from methyl ketones and lactonesformed byheating of the fat (they thus are almost absent in skim milk powder) andform Maillard products.

ii. Discolouration

Milk powder tends to darken during storage, turning to brown due to maillardreaction, which refers to the reaction between free amino group of protein andlactose. This is associated with old or stale off-flavour. High moisture content andhigh storage temperatureenhancebrowningdiscolouration. Spraydried milkpowderis more susceptible to age darkening and to greater intensity than roller processpowders.

iii. Free Fat

Free fat or extractable fat is the portion of the fat content of a milk powder that canbe extracted by organic solvents (e.g. carbon tetrachloride). It is expressed as apercentage either of the total fat content or of the total mass of powder. Free fatcontent of milk powders affect flowability, reconstitutability and stability of milkpowder. The factors controlling the level of free fat are:

The type of fat: Low melting fats tend to produce higher levels of free fat

Total fat content:As the total fat content increases the free fat rises progressivelyup to 20%.

Product composition: The formation of free fat is reduced bya high content ofamorphous lactose, and is increased byhigh protein content.

Gentledryingconditions: Controlled inlet air temperature,outletair temperatureand atomizer speed.

Gentle powder treatment:Avoiding pneumatic transport, low pressure-drop incyclones and effective cooling of powder by fluid bed.

The powder moisture should not be too low

Avoid lactose crystallization

Additionofemulsifier

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iv. Poor Solubility

Powders with poor or low solubilitycause sediment, which is unsightly. They canalso cause processingdifficulties and can result in poor economy, asmilk solids maybe lost as insoluble material. The sediment produced when milk powders arereconstituted ismeasured in terms of aninsolubilityindex, so, in reality, the solubilityof a powder is expressed as its degree of insolubility. Insolubility index is a measureof the extent of denaturation of the proteins in milk powder.Anydryer can in fact bemal-operated resulting in a powder with poor solubility (i.e. insolubilityindex). Theanalysis showsthe insolubles tobeaprotein/fat/mineral complex.Theproteinconsistcasein and/or denatured whey proteins.

At a given temperature, the rate of denaturation of protein in concentrated milkdoubles for every 5% increase in total solids up to about 92%. Most of thedenaturation during the drying process occurs when the concentration of total solidsisgreater than 50%.Further, it is important tonote that atornearcritical concentration(i.e. 86-88%)even atambient temperature,50% insolubilitymaybeproducedwithin10 h.

v. Slowly Dispersible Particles

These result from the surface wetting of unagglomerated very fine particles. Theformation of a gelatinous coat prevents the ingress of water and slows the rate, atwhich theparticlesdissolve. Ifnotmaintained insuspensionbyagitation, theparticlesare likely to form a sludge.

vi. Sludge Formation

Powders with poor dispersion properties can form sludges and can demand greaterenergy inputs to ensure complete solution. In an industrial or domestic context, thepresence of a sludge following the reconstitution of a milk powder is regarded as aproduct defect.

vii. Scum Formation

Scum is the layer formed on the surface of the reconstituted milk comprising of thefoam (upper layer) and the undissolved/ slowly hydrated particles (flecks) (lowerlayer).

viii. Occurrence of White Flecks

White flecks are slowly hydrated particles in lecithinated whole milk powder andare measured (in mm) as the lower layer of the scum (i.e. foam + flecks) afterreconstitution underspecified conditions. Theoccurrenceofwhite flecks isof similarorigin to insoluble sediment. Unlike insolubility, this defect can be detected visuallybut is difficult to determine quantitatively.

ix. Scorched Particles

Scorched particles are generally accepted to be a measure for any deposits in thedryingchamber(e.g.deposits in thewheeloraround thenozzlesor in theairdisperser)having been exposed to high temperatures thus getting scorched, discoloured and atthe same timeinsoluble. Contamination ofmaterial that subsequentlypasses throughand removes this material by collusion contributes to scorched particles in suchproduct. Other factors outside the dryer which contribute to scorched particles aredirt or sediment of raw milk not efficiently removed byclarification. Deposits (i.e.brown, insoluble jelly lumps) formed in the tubes of evaporator calendria alsocontribute to the scorched particles. The scorched particles are expressed as disc



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A, B, C, and D standard depending on the intensity and colour of the particles lefton the filter.

x. Cakiness

It is a tendencyof a powder to form hard lumps in bags during storage.Amorphouslactose is responsible for the tendency of milk powders to pick up moisture fromsurrounding air. Milk powder becomes stickyduring the first phase of this moistureuptake and stoned-hard at the end of this process. Final caking is caused by thecrystallization of lactose followed by the evaporation of excess moisture.

xi. Feathering

Product intended for use as whiteners in hot beverages such as coffee and tea, mustbe reasonablythermostable.The lackof thermostabilityoccursas, socalled featheringi.e. particles visible on the surface or throughout the beverage or sediment at thebottom. Atemperature of 80-85oC coupled with the low pH of coffee, and oftenhighlevelsofcalciumandmagnesiumhardnessin thewatermakesforanenvironmenthostile to milk protein stability. Proper protein standardization, appropriate heattreatment of raw milk and incorporation of phosphates and citrates as pH regulatorsand protein stabilityenhancer are suggested to improve the stabilityof milk proteins.


1) How oxidized/tallowyoff-flavour is produced in milk powder?

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2) Whymilk powders turn brownish during storage?

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3) How free fat can be kept low in milk powders?

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4) List different defects that describe the poor reconstitutabilityof milk powder.

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5) What is caking in milk powders and how it is formed?

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15.9 LET US SUM UP

The keeping qualityof dried milk products during storage is of great importance toconsumer acceptance. It is necessary to prevent organoleptic and physico-chemicaland reconstitution and instant properties deterioration of the product during storage.Important physical properties of milk powders are: particles shape, particle sizedistribution,bulkdensity,andflowability, free fat contentandreconstitutionproperties(wettabilitysinkability, dispersibilityand rate of solution). Common Defectsof driedmilks are: off flavours (oxidised/tallowy, rancid, stale and cooked), discolouration,freefat,poorsolubility, slowlydispersibleparticles, sludgeformation,scumformation,occurrence of white flecks, scorched particles, cakiness and feathering. Chemicalchanges in driedmilkproducts causestaleness, oxidized flavour, hydrolytic rancidityand insolubility that are influenced by the processing treatments, moisture content,freeoxygenlevelswithin thecontainer,andstoragetemperature.However, thekeepingqualityof driedmilk products can beenhanced to a great extent byproper packaging.

Milk powder packaging should be carried out in a dry atmosphere. The type ofpackaging material used will depend on its cost, barrier properties and convenience,besides functionality. Asuitable container for dry milk should be impervious tomoisture, light, gases and insects; should be durable for handling, resistant tocorrosions,of lowcost; andberelativelyeasyto fill, seal, handleandempty.Skimmedmilk powder in domestic commercial trade is commonlypackaged in polyethylenebags inside a 4-ply Kraft paper bag. Milk powder for industrial use and storagemaybe packaged in bins, barrels, drums and bags. For retail purposes, milk powdermay be packaged in metal cans, glass jars, sachet or cartons. The retail packageshould preferably have a re-closable opening. The successful packaging of wholemilk powder involves the additional step of release of oxygen entrapped in the aircells of the milk powder particles and gas-packing with an inert gas in hermeticallysealed containers.

Handling and packaging of malted milk foods must be done in an atmosphere ofcontrolled low humidity. Further, the finished product is packaged mostly in glassbottles with screw type metal lids or in other containers impervious to moisturevapours. For bulk packing, dairy whitener may be packed similar to whole milkpowder and for retail packing, dairywhitener maybe packed similar to infant foods.



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Packaged milk powders should be stored in a dark, cool and dried place. Some ofthe newer laminates may also require some humidity control in storage. WMP isexpected to withstand room temperature storage for 6 months or more. Skim milkpowder has longer shelf life than whole milk powder.

15.10 KEY WORDS

Bulk density : is a measure of the mass of milk powder thatoccupies a fixed volume. It is normallyexpressed in g/ml.

Flowability : The flowabilityof a powder refers to the easewith which the powder particles move withrespect to one another.

Hygroscopic : Having tendency to absorb water whenexposed to humid condition.

Cakiness : It is a tendency of a powder to form hardlumps inbagsduringstorage.Lactose,presentin glass (i.e. non-crystalline/amorphous) statein dried milks, when exposed to humidatmosphere, readilyabsorb moisture, becomesticky and cake (stoned-hard) in storage.

Feathering : It refers to lack of thermostability of milkpowder that causes visible particles on thesurface, throughout or sediment at the bottomin hot tea/coffee.

15.11 SOME USEFUL BOOKS

De, S. (2001) Outlines of DairyTechnology. Oxford University Press, New Delhi.

Early, R. (1998). The Technology of Dairy Products. Blackie Academic &Professional, U.K.

IS 12299 : (1998) Dairywhitener - Specification (First Revision), Bureau of Indianstandards, Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi.

15.12 ANSWERS TO CHECK YOUR PROGRESS

Your answers should include the following points.


1) i. Lactose is present in glass (i.e. non-crystalline/amorphous) state.

ii. Dried milks are very hygroscopic.

iii. Readily absorb moisture, become sticky and cake in storage.

2) i. Reduce the oxygen concentration to as low a level as possible.

ii. Vacuumizing and gas-packingwith an inert gas.

3) i. Polyethylene lined multi-wall paper sacks.

ii. Most versatile, robust, relatively low in cost, being packed at highproduction rates i.e. 9 to 10 ton/hr

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iii. Convenient pack for major end users.

4) i. Both styles are superseding the tote bin.

ii. A large polythene bag is filled with milk powder and closed by tying.

iii. The filled bag is protected bywoven plastics

iv. Normally transported on pallets and are emptied by suction hose.

v. Potential savings in filling and transportation costs.

vi. The relatively low cost - exported on a nil return basis.


1) i. Nearest to a complete container for milk powder.

ii. Equipments for semi automatic and automatic packaging of whole milkpowder.

iii. High cost.

2) i. Sachet pack styles vary from the simple flat pack, which is heat-sealedaround the edges to the complex free standing, block bottom form.

ii. In most cases, the sachet of milk powder is enclosed inside cardboardboxes.

iii. Development of aluminium/plastic laminates withconsiderablyimprovedbarrier properties —- Whole milk powder bags with 250 g, 500 g and1000 g.

3) i. Generallypacked in metalised tin containers, which can be sealed, oxygenevacuated and filled with an inert gas.

ii. Tin containers havingsnap on plastic lids.

iii. The laminatedpouches,afterpacking, inertgas injectingandsealingplacedinto individual cardboard cartons for easyhandling.

4) i. Handlingandpackagingof malted milk foods in lowhumidityatmosphere

ii. Packaged mostly in glass bottles with screw type metal lids or in othercontainers impervious to moisture vapours.

5) i. Packed in nitrogen or in a mixture of nitrogen and carbon dioxide.

ii. Packed in clean and sound metal containers or in a food grade flexiblepack made from a film or combination of board, paper, polyethylene,polyester metallized filmor aluminium foil in such a wayso as to protect itfrom deterioration.

iii. Only food grade plastic shall be used.


1) i. Should be stored in a dark, cool and dried place.

ii. In most cases, simple storage in clean dryareas with proper stock control.

iii. Newer laminates mayalso require some humiditycontrol in storage.

iv. Skim milk powder has longer shelf life than whole milk powder.



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2) Flavour, colour,physicalproperties likeparticlesshape,particlesizedistribution,bulk densityand flowability, and reconstitution and instant properties

3) i. Economically, commerciallyandfunctionallyimportant.

ii. High bulk density saves in packaging material and reduces the shippingvolume and transportation costs.

4) Agglomeration, low percentage of fines, addition of free-flowing agents (e.g.sodium aluminium silicate), addition of components bydrymixing (e.g. sugar,whey powder), low free fat content, low relative humidityof atmospheric air.


1) i. Addition of oxygen to the double bonds of unsaturated glycerides, givingat first peroxides and later aldehydes, ketones etc., which impart theunpleasant oxidized/talowyoff-flavour.

ii. Copper and iron act as catalyst.

iii Higher storage temperature, higher acidity, sunlight and ultra violetirradiation promote faster development of oxidative deterioration.

2) i. Maillard reaction

ii. High moisture content and high storage temperature enhance browningdiscolouration.

iii. Spray dried milk powder is more susceptible to age darkening and togreater intensity than roller process powders.

3) Reduction of low melting fats and total fat, gentle drying conditions, avoidingpneumatic transport, lowpressure-drop in cyclones, effectivecoolingof powderbyfluid bed, avoid lactose crystallization and addition of emulsifier.

4) Poor solubility, slowlydispersible particles, sludgeformation, scum formation,occurrence of white flecks, scorched particles.

5) i. Tendency of a powder to form hard lumps in bags during storage.

ii. Amorphous lactose in milk powders picks up moisture ? Milk powderbecomes sticky and then stoned-hard ? crystallization of lactose ?evaporation of excess moisture.

Documents

BPVI 15 Block 4 Unit 15