Hydrocolloids trong các sản phẩm sữa nuôi cấy

Highertemperatures and longer hold times are used for yogurt production thanmost other cultured dairy products.. These contributions can be altered by changes in theincubation temperatur

Hydrocolloids in Cultured Dairy Products

Joseph Klemaszewski

Cultured dairy products include a wide range of product textures andflavors within the category and even sometimes across geographicalregions for the same product Reasons for this range from availability

of milk supply, species from which milk is obtained, shipping ations, traditions, processing constraints, regulations, and taste prefer-ences This chapter illustrates some examples of stabilization of cultureddairy products primarily in the North American market The cultureddairy products categories covered are cheese, buttermilk, sour cream,and yogurt

consider-Stabilization of cultured dairy products involves the interaction ofingredients including water, lipid, protein, sugars, cultures, and hy-drocolloids The contributions of nonhydrocolloid ingredients, espe-cially cultures, cannot be overlooked when formulating or troubleshoot-ing Lactic acid bacteria produce acids, enzymes, and polysaccharides,which can positively or negatively affect texture and flavor Addition-ally, the conditions under which the cultures ferment result in differentgrowth rates and by-products These components have been the subjects

of many studies and are beyond the scope of this chapter

Texture in cheese products covers the spectrum for soft fresh cheeseslike brie, queso blanco, and spreadable cream cheese to hard gratingcheeses like Parmesan and Romano In the United States, hydrocol-loids are not allowed in most standardized cheeses with exceptions like

Hydrocolloids in Food Processing, Thomas R Laaman

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2011 Blackwell Publishing Ltd and Institute of Food Technologists

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cottage cheese, cream cheese, pasteurized process cheese spread, andcold pack cheese food Another notable exception is nutritionally mod-ified cheeses which allow for the addition of other ingredients if there

is a benefit when replacing a macronutrient An example of this is fat mozzarella where fat is replaced by water alone, resulting in a softcheese that cannot be shredded Nontraditional ingredients, like hydro-colloids, can be used to bind the water and give a texture closer to thefull fat target

Standards of identity in some countries, such as France, do not allowfor the inclusion of stabilizers in the yogurt white mass Stabilizers areallowed in yogurt marketed in the United States, per 21 CFR 131.200,when used in accordance with good manufacturing practices Thereare no federal standards for yogurt in Canada; however provinces mayhave limitations on stabilizing ingredients Fruit preparations may alsocontain sweeteners and stabilizing ingredients, and these may be sub-ject to other regulations The pH, total solids, processing conditions,and regulations for the fruit are very different from the white mass,thus the stabilization requirements as well as the regulations for fruitpreparations differ While most yogurts contain fruit or bulky flavoringredients, they are not typically processed in a dairy plant and are notcovered in detail in this chapter

Strawberries are the most popular bulky flavor added to yogurt inNorth America Diced or sliced strawberries are typically processedwith sweeteners, flavors, stabilizers, and optional colors The resultingfruit preparation is added to white mass at levels ranging from 10 to20% Some nonfruit flavorings, such as vanilla, are also incorporated

as a “vanilla fruit prep” to provide a product with a texture similar

to fruit-flavored yogurts Equipment for mixing and packaging stirred

yogurts can be set to add the same level of bulky flavor ingredients andfacilitate easier transitions to packaging other yogurt flavors.

All yogurt manufacturing begins with milk pasteurization Highertemperatures and longer hold times are used for yogurt production thanmost other cultured dairy products Continuous processing can havehold times of 1–10 minutes at 185–200◦F Vat pasteurization at 160◦Ffor 30 minutes is not uncommon, and the come-up time and cool-downtime for the vats results in significant denaturation of the whey proteins.The denatured protein results in a firmer yogurt texture and shorterincubation times

Spoonable yogurt is made by either a cup set process or a vat setprocess Cup set yogurts are made by adding inoculated white mass,which has not undergone significant fermentation Fruit may be present

in the bottom of the cup at the time of filling for a fruit on the bottomyogurt The yogurt cups are then incubated until the desired pH isreached Yogurt cups are then placed in a cooler Because cup set yogurts

do not see significant shear until the time of consumption, coagulatedproteins and culture-produced polysaccharides contribute significantly

to the texture These contributions can be altered by changes in theincubation temperature, protein content of the white mass, casein towhey protein ratio, total solids of the yogurt, culture strain selection,and stabilizing ingredients used

Vat set yogurts, also called stirred, are made by culturing white mass

to a target pH, then cooling and stirring the yogurt The yogurt is thenpumped out of the vat, and fruits are mixed with the yogurt prior tofilling the cup In addition to the factors mentioned with cup set yogurt,the amount of shear in this process has a significant impact on thefinished yogurt texture The viscosifying contributions from the fruitpreparation are also more significant in a vat set yogurt as the fruit andsweetening matrix are dispersed throughout the yogurt In both cup setand vat set yogurt, changes to the flavor and texture occur as culturegrowth continues at a slow pace

The majority of yogurts manufactured in the United States is style, or stirred, stabilized with modified food starch, typically fromwaxy maize, and gelatin Starch is commonly used at 2–3% in vat setyogurt and at a lower level in cup set yogurts Yogurt manufacturersthat want to make claims about natural, organic, Kosher, Halal, orvegan may use alternate stabilizers if any are added Natural yogurtscan be stabilized with modified starches from corn, tapioca, potato,

Swiss-and/or rice These are used in the white mass in combination withhydrocolloids Commonly used hydrocolloids are pectin and locust beangum Low methoxyl pectins are used because of their ability to form agel at lower solids levels compared with high methoxyl pectins Gellingproperties of low methoxyl pectins can be enhanced by amidation.Pectin from apple and citrus are used in yogurts and the botanicalsource also provides differentiation to a lesser extent than amidationand degree of esterification Pectin on a yogurt label can also be fromthe fruit preparation, which may be a high or low methoxyl.

Carrageenan is used in a small number of yogurts Because of itsmilk protein reactivity, the level of carrageenan used is usually less than0.1% Extracts with higher levels of␬-carrageenan, high levels of milkprotein in the white mass, and more severe heat treatments contribute tomilk protein reactivity Yogurts made with too much carrageenan have

a curdy texture Carrageenan is also used in some fruit preparations,more so in Europe than in North America

Because starch is widely used in North American yogurts and othercultured dairy products, attention must be given to the starch source,chemistry, and processing Most of the starch used in yogurt is cross-linked and substituted cook-up cornstarch from waxy maize hybrids.Waxy cornstarch consists of branched amylopectin with less than 1%linear amylose Amylose forms a firm brittle gel, which can expel water

as the starch undergoes retrogradation during storage Steric hindrance

of the amylopectin branches prevents retrogradation and gel tion Thus yogurt made with waxy cornstarch has less syneresis and aless brittle structure Starch from dent (also called common) corn con-tains 25–30% amylose, with the remainder being amylopectin Modifiedstarch from common corn is rarely used in some yogurts, and in some in-stances can be combined with waxy cornstarch High amylose starchescontain 50% or more amylose and require heating above 212◦F to swelland provide optimal functionality High amylose starch is not used incultured dairy processing, as the gelatinization temperature cannot bereached using equipment common to most cultured dairy plants Tapi-oca starch contains 15–20% amylose and imparts a creamier texture

forma-to yogurt with less flavor masking than cornstarch However, tapiocastarches are usually more expensive than cornstarches, so their use inyogurt is limited more by economics than functionality

Unmodified starches are limited in their ability to withstand shear,temperature abuse, acid, and freeze-thaw conditions Pasteurization and

homogenization are sources of shear common in dairy manufacture.Lactic acid bacteria lower the pH of yogurts to 4.0 or less throughoutthe shelf life The changes in starch, along with changes in protein inter-actions, are common factors in loss of viscosity and lack of smoothness

in yogurt as the product reaches the end of its shelf life Freeze-thawstability is a consideration for tube yogurts that are marketed as analternative to frozen novelties

The two types of starch modifications used in cultured dairy ucts are cross-linking and substitution These modifications can beused on starch regardless of botanical source and are described in

prod-21 CFR 172.892 Substitution increases starch water holding ity and peak viscosity, provides freeze-thaw stability, reduces syneresis,gel formation, and retrogradation, and decreases gelatinization temper-ature Cross-linking improves heat stability, acid stability, shear tol-erance, and gelatinization temperature, but decreases peak viscosity.Starches with higher levels of substitution are easier to cook out with

capac-a HTST pcapac-asteurizcapac-ation process capac-and give yogurts better stcapac-ability Highlevels of cross-linking provide more stability to homogenization, butsacrifice viscosity A starch with a lower level of cross-linking that cansurvive the yogurt making process intact can be used to achieve thesame finished product viscosity as a starch with a higher level of cross-linking Alternatively, a higher amount of starch with a low level ofcross-linking must be used to achieve the target viscosity if the starch

is broken down by processing

Figure 7.1 shows the effects of cross-linking and processing tions on finished yogurt viscosity The low shear condition represents

condi-a process with condi-a low or no homogenizcondi-ation such condi-as nonfcondi-at yogurt Anexample of a very high shear condition is homogenization following vatpasteurization Under low shear conditions, a starch with a low level ofcross-linking provides the highest viscosity If this starch is processedunder more rigorous conditions, the starch granules are destroyed re-sulting in a much lower viscosity Increasing the level of cross-linkingresults in more intact starch granules after processing, as cross-linkinglimits the amount of swell in a granule Any amount of cross-linkingexceeding the amount needed for the severity of the process preventscost optimization Dairies that utilize the same starch for unhomoge-nized nonfat yogurt and homogenized lowfat yogurt are reducing thenumber of items inventoried at the expense of formula optimization.Process optimization to lower the amount of shear in order to decrease

Low XL Med XL High XL V High XL

Level of cross-linking (XL)

Low shear High shear

Figure 7.1 Effects of shear and starch cross-linking level on yogurt white mass

of iodine-stained yogurt is used to determine the degree of cook andoverprocessing of starch Figure 7.2 shows examples of properly cookedand overprocessed waxy maize starches Evaluation in yogurt whitemass is easiest prior to culturing and must be done prior to the addition

of fruit preparations that contain starch

After milk proteins, cultures, and starch, gelatin is the most widelyused thickening agent in spoonable yogurts Gelatin’s properties includethermo reversible gelling, elasticity, sheen, ease of processing, clean fla-vor release, and melting point near 95◦F Common commercial sources

of gelatin are beef hides and bones, pork skins, and fish skin Because

of its animal source, concerns about gelatin have been raised by variousgroups for suitability in vegetarian diets, Kosher and Halal certification,and infectious agents like hoof-and-mouth disease (9 CFR 94.18c) or

Figure 7.2 Micrographs of modified waxy corn starch obtained at two stages of

cooking Starch on the left is properly good and gives maximum viscosity The ple on the right is overcooked and has lower viscosity (Microscopy courtesy of A Peck—Cargill, Inc.)

sam-bovine spongiform encephalopathy (USDA 1997) Replacing gelatinhas been the target of food ingredient suppliers in a broad range of foodapplications including yogurt The wide use of gelatin in yogurt todaydemonstrates the unique benefits from this ingredient

Textural improvements in yogurt can be obtained with shear afterculturing, and the gelling properties of gelatin are well-suited for thisprocess Postculture shear is needed to incorporate fruit, and higherlevels of shear produce a smoother textured yogurt with more sheen.Since gelatin requires some time and low temperatures to set, yogurtscan be cooled for short periods of time prior to filling, without completeloss in gel structure from gelatin By contrast, starch will lose significantviscosity when sheared Another benefit of gelatin is lower back pressureduring processing than other hydrocolloids

Gelatin is available in a range of gel strengths, as measured by bloom,from 50 to 300 Use level depends on processing, bloom strength, anddesired viscosity and can range from 0.3 to 1% Excessive levels ofgelatin result in a brittle gel and a lack of smoothness

In addition to being consumed for calcium and protein, yogurts areconsumed for the digestive benefits The marketing of yogurts with

probiotic cultures and digestive benefits has been underway for sometime in Europe and Asia As this market develops in North America,companies are also increasingly marketing yogurts with dietary fibers.Most hydrocolloids are a source of dietary fiber but do not contributesignificant amounts to the diet because of their low use level In order

to qualify as a good source of fiber, a product must provide 2.5 grams

of fiber per serving In 6 ounces of yogurt, this equates to a use level of1.5–2% depending on the level of fiber in the ingredient This yogurtwould be too thick to process and package if a hydrocolloid like guargum was used Inulin or chicory fiber has been used in yogurt for severalyears by a few companies in the United States Inulin recently obtainedapproval for use in yogurt in Canada as a source of fiber that can beclaimed in product labeling Several types of inulin are commerciallyavailable with varying chain lengths Longer chain lengths impart lesssweetness and provide some creaminess and viscosity Inulin is added

to yogurt primarily for its health benefits including increased calciumabsorption and digestive health Insoluble fibers are not usually added

to yogurt white mass as they impart chalkiness

In the course of yogurt manufacture, there will be times when theproduct does not meet specifications, and troubleshooting always beginswith identifying process deviations Some common causes of texturaldefects are improper incubation temperature, wrong break at pH, omis-sion of ingredients or errors in weighing, and contaminants Enzymesand growth inhibiting contaminants, such as phage, may not be harmfulfrom a food safety standpoint but can ruin a day’s production from aneconomic standpoint Amylase can be present in a number of ingre-dients including fruits and berries, and the effects of this enzyme onstarch may not be observed until the yogurt has entered distribution.Special consideration needs to be given to unintended ingredients asnew flavors are developed with nontraditional fruits

The popularity of yogurt has led to an increase in the number ofproducts introduced with yogurt and new yogurt products These includenutritionally modified yogurts (light, low carb, no sugar added), dessertyogurts, aerated yogurts, yogurt dips, drinkable yogurts, and yogurtsfor children and toddlers Many of these products vary in sweetness

or fat content, and may require stabilizer adjustments to account forthe change in solids or desired texture Whipped yogurts require higherlevels of stabilizers plus a surfactant such as lactic acid esters of mono-and diglycerides to help incorporate air

Another style of yogurt in the North American market is Greek style

or strained yogurt These yogurts are high in fat and total solids and thetraditional manufacturing process includes a whey separation step Thisprocess resembles cheese production more than yogurt and stabilizersare not typically used unless a flavored product like tzatziki sauce ismade from the yogurt Yogurt and dips with a texture similar to thestrained product can be made with traditional yogurt manufacturingequipment by altering the stabilizer and processing

Drinkable Yogurt and Smoothies

Yogurt sales in the United States have increased annually for 20 yearsand now represent over half the volume of cultured products as reported

by IDFA (Rutherford 2006) In recent years the growth rate of able yogurts and smoothies has outpaced spoonable yogurt, albeit from

drink-a smdrink-aller bdrink-ase, with sdrink-ales doubling in the yedrink-ars from 2002 to 2005 Mdrink-ar-keters have blurred the differences between drinkable yogurts, yogurtsmoothies, and smoothies No standard of identity exists for smoothiesand some are based on soy or dairy proteins and may not be fermented.Since there is no requirement for the amount of yogurt in a smoothie,there is a wide variation from products that meet the standard of iden-tity for yogurt to products made with less than 2% yogurt Consumersand manufacturers can also be confused about the yogurt content in

Mar-a drinkMar-able yogurt bMar-ased on the stMar-andMar-ard of identity for yogurt (21CFR 131.200) This standard calls for a minimum of 8.25% milk solidsnonfat before the addition of bulky flavor ingredients, but no limit isspecified on how much flavoring ingredients can be added By speci-fying minimums of milk solids and milkfat after bulky flavor addition,ice cream standards of identity (21 CFR 135.110) limit the amount ofbulky flavors to 20% Therefore a manufacture adding 50% juice to ayogurt base might consider labeling the product as drinkable yogurt.The application and wording of this regulation is unclear

Drinkable yogurts also have a wide range of viscosities, flavors, andsweetness Some consumers are looking for a low-viscosity beveragewhile others are looking for something more substantial as a significantcomponent of a meal In both of these cases, as well as smoothies madewith soy or dairy proteins, the two requirements of hydrocolloids arethe same—prevent proteins from precipitating and impart the desired

viscosity Protein stabilization is dependent on heating profile, proteinsource (casein to whey ratio, soy), protein content, total solids, andviscosity It is easier to keep protein from precipitating, or fat fromcreaming, by raising viscosity This relationship is well understood anddescribed by Stoke’s law

v p = 2r2g( ρ p−ρ f)/9 µ

where v p is the particle velocity, r is the radius of the particle, g is

the gravitation acceleration, ρ p is the density of the particle, ρ f is thedensity of the continuous phase, andµis the viscosity of the continuousphase Particle suspension can be enhanced by decreasing the particleradius, altering the density of either the continuous or discontinuousphase, and increasing the viscosity In drinkable yogurt, the particlesize can be controlled by limiting protein denaturation and aggregation

by reducing the time and temperature of pasteurization Low-viscositydrinkable yogurts can be made by pasteurizing at 180◦F for 30 seconds.The primary method of controlling protein aggregation in acid yo-gurts and smoothies is the combination of high methoxyl (HM) pectin,shear, and pH Below their isoelectric point of 4.6, milk proteins have anet positive charge which increases as the pH is decreased HM pectinhas an isoelectric pH of ∼3.6 and a net negative charge above this

pH Optimal protein stabilization is obtained by culturing milk, addingpectin, and homogenizing Pectin can be added with a flavored juiceslurry, which includes pectin, juice, sweeteners, other stabilizers, andflavors that were pasteurized separately from the dairy base Protein sta-bility is highest from pH 3.8 to 4.1 and is imparted by the electrostaticinteraction of the protein and pectin combined with steric hindrance Inorder to limit acidic flavor notes manufacturer’s balance stability fromlower pH with better flavor at pH’s closer to 4.6 Most drinkable yogurtsare made at pH 4.1–4.4 Homogenization is not practical postpasteur-ization in many plants so the shear is applied by other means such asback pressure valves Air should not be incorporated as this can lead toseparation

Protein aggregate size is also dependent on the protein content andthe amount of sugar Sugar has a protective effect on proteins duringheating and fewer problems with aggregation are observed in formulaswith higher amounts of added sugars and lower total protein Formulaswith higher sugar content also have less water that needs to be stabilized

A problem related to protein aggregation is clear liquid separation This

is common in unstabilized, unsweetened yogurt formulas as the proteinaggregates and displaces water Separation is often seen in yogurt that

is not properly stabilized and processed This serum separation is less, but a consumer often thinks that separated product is spoiled Inorder to minimize the economic impact, stabilizers are added to controlsyneresis Gelatin is effective at preventing separation in drinkable yo-gurts and buttermilks Stability against separation in the white mass isalso enhanced by the use of an exopolysaccharide producing culture.The ingredients for stabilizing protein also provide viscosity Addi-tional viscosity can be added by using any hydrocolloid that will with-stand the processing and pH of the drinkable yogurt Modified foodstarch, locust bean gum, cellulose gum, carrageenan, and guar gum arecommonly used The parameters used for starch selection in drinkableyogurts are similar to spoonable yogurts as both undergo pasteurizationand homogenization Natural and organic drinkable yogurts are madewith HM pectin in combination with galactomannans (guar gum andlocust bean gum), and/or native starch Higher levels of native starchare needed compared to modified starch as the native starch is brokendown more easily by heat, shear, and acidity than a cross-linked starch.Ingredient statements of drinkable yogurts and spoonable yogurts aresimilar especially in cases where modified starch and gelatin are used

harm-in the white mass Pectharm-in can be used harm-in combharm-ination with modifiedfood starch in fruit preparations for spoonable yogurts and in the whitemass for drinkable yogurts Table 7.1 shows formula and processingdifferences for drinkable and spoonable yogurts Culture strain selectionmay or may not be the same for both types of yogurt

Smoothie formulation and processing varies widely, especially infood service operations Many of these smoothies are made on site afterthe customer orders and may include fruit, ice, soft serve frozen dessert,

a smoothie base, flavoring syrups, protein powders, vitamin and mineralpremixes, etc Some of these components may include hydrocolloidsfor viscosity or stability of one of the components such as the soft servemix Stabilization of proteins is not a concern since the product shelflife is less than 1 hour for a product sold for immediate consumption.Retail products with a longer shelf life require more stabilization, whichcan range from systems similar to those used in drinkable yogurt to athickened juice base if the product does not contain any protein

Table 7.1 Formulation and processing parameters for drinkable and spoonable

lowfat yogurts.

Spoonable Yogurt Drinkable Yogurt

0.4–0.75% HM pectin, added

to juice base Pasteurization 180–200◦F for 3–10

minutes

180–190◦F for less than

1 minute Homogenization Varies with fat content 0

psi in nonfat to 2000 psi

Varies with fat content 0 psi

in nonfat to 2000 psi Bulky flavor 5–15% high viscosity

stabilized fruit preparation

10–30% low viscosity juice with pectin added for protein stability Postculture shear Pumping with moderate

to as sweet cream buttermilk This product could be cultured, but this

in not currently practiced on a commercial scale Cultured buttermilk

is also used in baking to provide flavor, acidity, and textural ment It is also consumed as a beverage with the largest market in thesoutheastern United States In the remainder of this section, buttermilk

enhance-is used interchangeably for cultured buttermilk

Buttermilk is listed under the standard of identity for cultured milk,21CFR 131.112, and stabilizers are optional ingredients “Buttermilkfor baking” is defined in the United States milk classification pricing byits starch content, which must be in excess of 2% of the total solids in