Hydrocolloids trong các sản phẩm sữa nuôi cấy

Chapter Hydrocolloids in Cultured Dairy Products Joseph Klemaszewski Cultured dairy products include a wide range of product textures and flavors within the category and even sometimes across geographical regions for the same product Reasons for this range from availability of milk supply, species from which milk is obtained, shipping considerations, traditions, processing constraints, regulations, and taste preferences This chapter illustrates some examples of stabilization of cultured dairy products primarily in the North American market The cultured dairy products categories covered are cheese, buttermilk, sour cream, and yogurt Stabilization of cultured dairy products involves the interaction of ingredients including water, lipid, protein, sugars, cultures, and hydrocolloids The contributions of nonhydrocolloid ingredients, especially cultures, cannot be overlooked when formulating or troubleshooting Lactic acid bacteria produce acids, enzymes, and polysaccharides, which can positively or negatively affect texture and flavor Additionally, the conditions under which the cultures ferment result in different growth 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 cheeses like brie, queso blanco, and spreadable cream cheese to hard grating cheeses like Parmesan and Romano In the United States, hydrocolloids are not allowed in most standardized cheeses with exceptions like Hydrocolloids in Food Processing, Thomas R Laaman C 2011 Blackwell Publishing Ltd and Institute of Food Technologists 141 142 Hydrocolloids in Food Processing cottage cheese, cream cheese, pasteurized process cheese spread, and cold pack cheese food Another notable exception is nutritionally modified cheeses which allow for the addition of other ingredients if there is a benefit when replacing a macronutrient An example of this is lowfat mozzarella where fat is replaced by water alone, resulting in a soft cheese that cannot be shredded Nontraditional ingredients, like hydrocolloids, can be used to bind the water and give a texture closer to the full fat target Yogurt Yogurt consumption has increased dramatically in the United States in the last 30 years The changes in the flavor and texture of the yogurts in North America have also changed considerably over this period Traditional yogurt is made by a cup set process and does not contain added sweeteners or texturants Most of the yogurts sold in the United States today are sweeter with a smooth texture closer to pudding Products in Western Europe and some Canadian products are closer to the traditional yogurts Standards of identity in some countries, such as France, not allow for the inclusion of stabilizers in the yogurt white mass Stabilizers are allowed in yogurt marketed in the United States, per 21 CFR 131.200, when used in accordance with good manufacturing practices There are no federal standards for yogurt in Canada; however provinces may have limitations on stabilizing ingredients Fruit preparations may also contain sweeteners and stabilizing ingredients, and these may be subject 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 fruit preparations differ While most yogurts contain fruit or bulky flavor ingredients, they are not typically processed in a dairy plant and are not covered in detail in this chapter Strawberries are the most popular bulky flavor added to yogurt in North America Diced or sliced strawberries are typically processed with sweeteners, flavors, stabilizers, and optional colors The resulting fruit preparation is added to white mass at levels ranging from 10 to 20% 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 Hydrocolloids in Cultured Dairy Products 143 yogurts can be set to add the same level of bulky flavor ingredients and facilitate easier transitions to packaging other yogurt flavors All yogurt manufacturing begins with milk pasteurization Higher temperatures and longer hold times are used for yogurt production than most other cultured dairy products Continuous processing can have hold times of 1–10 minutes at 185–200◦ F Vat pasteurization at 160◦ F for 30 minutes is not uncommon, and the come-up time and cool-down time for the vats results in significant denaturation of the whey proteins The denatured protein results in a firmer yogurt texture and shorter incubation times Spoonable yogurt is made by either a cup set process or a vat set process 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 bottom yogurt The yogurt cups are then incubated until the desired pH is reached Yogurt cups are then placed in a cooler Because cup set yogurts not see significant shear until the time of consumption, coagulated proteins and culture-produced polysaccharides contribute significantly to the texture These contributions can be altered by changes in the incubation temperature, protein content of the white mass, casein to whey 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 then pumped out of the vat, and fruits are mixed with the yogurt prior to filling the cup In addition to the factors mentioned with cup set yogurt, the amount of shear in this process has a significant impact on the finished yogurt texture The viscosifying contributions from the fruit preparation are also more significant in a vat set yogurt as the fruit and sweetening matrix are dispersed throughout the yogurt In both cup set and vat set yogurt, changes to the flavor and texture occur as culture growth continues at a slow pace The majority of yogurts manufactured in the United States is Swissstyle, or stirred, stabilized with modified food starch, typically from waxy maize, and gelatin Starch is commonly used at 2–3% in vat set yogurt and at a lower level in cup set yogurts Yogurt manufacturers that want to make claims about natural, organic, Kosher, Halal, or vegan may use alternate stabilizers if any are added Natural yogurts can be stabilized with modified starches from corn, tapioca, potato, 144 Hydrocolloids in Food Processing and/or rice These are used in the white mass in combination with hydrocolloids Commonly used hydrocolloids are pectin and locust bean gum Low methoxyl pectins are used because of their ability to form a gel at lower solids levels compared with high methoxyl pectins Gelling properties of low methoxyl pectins can be enhanced by amidation Pectin from apple and citrus are used in yogurts and the botanical source also provides differentiation to a lesser extent than amidation and degree of esterification Pectin on a yogurt label can also be from the fruit preparation, which may be a high or low methoxyl Carrageenan is used in a small number of yogurts Because of its milk protein reactivity, the level of carrageenan used is usually less than 0.1% Extracts with higher levels of ␬-carrageenan, high levels of milk protein in the white mass, and more severe heat treatments contribute to milk 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 other cultured dairy products, attention must be given to the starch source, chemistry, and processing Most of the starch used in yogurt is crosslinked 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 formation Thus yogurt made with waxy cornstarch has less syneresis and a less brittle structure Starch from dent (also called common) corn contains 25–30% amylose, with the remainder being amylopectin Modified starch from common corn is rarely used in some yogurts, and in some instances can be combined with waxy cornstarch High amylose starches contain 50% or more amylose and require heating above 212◦ F to swell and provide optimal functionality High amylose starch is not used in cultured dairy processing, as the gelatinization temperature cannot be reached using equipment common to most cultured dairy plants Tapioca starch contains 15–20% amylose and imparts a creamier texture to yogurt with less flavor masking than cornstarch However, tapioca starches are usually more expensive than cornstarches, so their use in yogurt 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 Hydrocolloids in Cultured Dairy Products 145 homogenization are sources of shear common in dairy manufacture Lactic acid bacteria lower the pH of yogurts to 4.0 or less throughout the shelf life The changes in starch, along with changes in protein interactions, are common factors in loss of viscosity and lack of smoothness in yogurt as the product reaches the end of its shelf life Freeze-thaw stability is a consideration for tube yogurts that are marketed as an alternative to frozen novelties The two types of starch modifications used in cultured dairy products are cross-linking and substitution These modifications can be used on starch regardless of botanical source and are described in 21 CFR 172.892 Substitution increases starch water holding capacity and peak viscosity, provides freeze-thaw stability, reduces syneresis, gel formation, and retrogradation, and decreases gelatinization temperature Cross-linking improves heat stability, acid stability, shear tolerance, and gelatinization temperature, but decreases peak viscosity Starches with higher levels of substitution are easier to cook out with a HTST pasteurization process and give yogurts better stability High levels of cross-linking provide more stability to homogenization, but sacrifice viscosity A starch with a lower level of cross-linking that can survive the yogurt making process intact can be used to achieve the same finished product viscosity as a starch with a higher level of crosslinking Alternatively, a higher amount of starch with a low level of cross-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 conditions on finished yogurt viscosity The low shear condition represents a process with a low or no homogenization such as nonfat yogurt An example of a very high shear condition is homogenization following vat pasteurization Under low shear conditions, a starch with a low level of cross-linking provides the highest viscosity If this starch is processed under more rigorous conditions, the starch granules are destroyed resulting in a much lower viscosity Increasing the level of cross-linking results in more intact starch granules after processing, as cross-linking limits the amount of swell in a granule Any amount of cross-linking exceeding the amount needed for the severity of the process prevents cost optimization Dairies that utilize the same starch for unhomogenized nonfat yogurt and homogenized lowfat yogurt are reducing the number of items inventoried at the expense of formula optimization Process optimization to lower the amount of shear in order to decrease Hydrocolloids in Food Processing Apparent viscosity (cP @ 50 1/s) 146 Low shear High shear Low XL Med XL High XL V High XL Level of cross-linking (XL) Figure 7.1 Effects of shear and starch cross-linking level on yogurt white mass viscosity the amount of cross-linking and stabilizer level has potential economic and flavor benefits The ability of a starch to withstand the rigors of processing is also dependent on the formulation, pasteurization time and temperature, thermal history before homogenization, substitution level, substitution chemicals, cross-linking agent, botanical source of starch, and shear from processing before and after culturing Microscopic evaluation of iodine-stained yogurt is used to determine the degree of cook and overprocessing of starch Figure 7.2 shows examples of properly cooked and overprocessed waxy maize starches Evaluation in yogurt white mass 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 widely used thickening agent in spoonable yogurts Gelatin’s properties include thermo reversible gelling, elasticity, sheen, ease of processing, clean flavor 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 various groups for suitability in vegetarian diets, Kosher and Halal certification, and infectious agents like hoof-and-mouth disease (9 CFR 94.18c) or Hydrocolloids in Cultured Dairy Products 147 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 sample on the right is overcooked and has lower viscosity (Microscopy courtesy of A Peck—Cargill, Inc.) bovine spongiform encephalopathy (USDA 1997) Replacing gelatin has been the target of food ingredient suppliers in a broad range of food applications including yogurt The wide use of gelatin in yogurt today demonstrates the unique benefits from this ingredient Textural improvements in yogurt can be obtained with shear after culturing, and the gelling properties of gelatin are well-suited for this process Postculture shear is needed to incorporate fruit, and higher levels of shear produce a smoother textured yogurt with more sheen Since gelatin requires some time and low temperatures to set, yogurts can be cooled for short periods of time prior to filling, without complete loss in gel structure from gelatin By contrast, starch will lose significant viscosity when sheared Another benefit of gelatin is lower back pressure during 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, and desired viscosity and can range from 0.3 to 1% Excessive levels of gelatin result in a brittle gel and a lack of smoothness In addition to being consumed for calcium and protein, yogurts are consumed for the digestive benefits The marketing of yogurts with 148 Hydrocolloids in Food Processing probiotic cultures and digestive benefits has been underway for some time 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 not contribute significant 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 ounces of yogurt, this equates to a use level of 1.5–2% depending on the level of fiber in the ingredient This yogurt would be too thick to process and package if a hydrocolloid like guar gum was used Inulin or chicory fiber has been used in yogurt for several years by a few companies in the United States Inulin recently obtained approval for use in yogurt in Canada as a source of fiber that can be claimed in product labeling Several types of inulin are commercially available with varying chain lengths Longer chain lengths impart less sweetness and provide some creaminess and viscosity Inulin is added to yogurt primarily for its health benefits including increased calcium absorption 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 the product does not meet specifications, and troubleshooting always begins with identifying process deviations Some common causes of textural defects are improper incubation temperature, wrong break at pH, omission of ingredients or errors in weighing, and contaminants Enzymes and growth inhibiting contaminants, such as phage, may not be harmful from a food safety standpoint but can ruin a day’s production from an economic standpoint Amylase can be present in a number of ingredients including fruits and berries, and the effects of this enzyme on starch may not be observed until the yogurt has entered distribution Special consideration needs to be given to unintended ingredients as new flavors are developed with nontraditional fruits The popularity of yogurt has led to an increase in the number of products introduced with yogurt and new yogurt products These include nutritionally modified yogurts (light, low carb, no sugar added), dessert yogurts, aerated yogurts, yogurt dips, drinkable yogurts, and yogurts for children and toddlers Many of these products vary in sweetness or fat content, and may require stabilizer adjustments to account for the change in solids or desired texture Whipped yogurts require higher levels of stabilizers plus a surfactant such as lactic acid esters of monoand diglycerides to help incorporate air Hydrocolloids in Cultured Dairy Products 149 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 the traditional manufacturing process includes a whey separation step This process resembles cheese production more than yogurt and stabilizers are not typically used unless a flavored product like tzatziki sauce is made from the yogurt Yogurt and dips with a texture similar to the strained product can be made with traditional yogurt manufacturing equipment by altering the stabilizer and processing Drinkable Yogurt and Smoothies Yogurt sales in the United States have increased annually for 20 years and now represent over half the volume of cultured products as reported by IDFA (Rutherford 2006) In recent years the growth rate of drinkable yogurts and smoothies has outpaced spoonable yogurt, albeit from a smaller base, with sales doubling in the years from 2002 to 2005 Marketers have blurred the differences between drinkable yogurts, yogurt smoothies, and smoothies No standard of identity exists for smoothies and 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 identity for yogurt to products made with less than 2% yogurt Consumers and manufacturers can also be confused about the yogurt content in a drinkable yogurt based on the standard of identity for yogurt (21 CFR 131.200) This standard calls for a minimum of 8.25% milk solids nonfat before the addition of bulky flavor ingredients, but no limit is specified on how much flavoring ingredients can be added By specifying minimums of milk solids and milkfat after bulky flavor addition, ice cream standards of identity (21 CFR 135.110) limit the amount of bulky flavors to 20% Therefore a manufacture adding 50% juice to a yogurt 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, and sweetness Some consumers are looking for a low-viscosity beverage while others are looking for something more substantial as a significant component of a meal In both of these cases, as well as smoothies made with soy or dairy proteins, the two requirements of hydrocolloids are the same—prevent proteins from precipitating and impart the desired 150 Hydrocolloids in Food Processing viscosity Protein stabilization is dependent on heating profile, protein source (casein to whey ratio, soy), protein content, total solids, and viscosity It is easier to keep protein from precipitating, or fat from creaming, by raising viscosity This relationship is well understood and described by Stoke’s law v p = 2r g(ρ p − ρ f )/9µ where vp is the particle velocity, r is the radius of the particle, g is the gravitation acceleration, ρp is the density of the particle, ρf is the density of the continuous phase, and µ is the viscosity of the continuous phase Particle suspension can be enhanced by decreasing the particle radius, altering the density of either the continuous or discontinuous phase, and increasing the viscosity In drinkable yogurt, the particle size can be controlled by limiting protein denaturation and aggregation by reducing the time and temperature of pasteurization Low-viscosity drinkable yogurts can be made by pasteurizing at 180◦ F for 30 seconds The primary method of controlling protein aggregation in acid yogurts and smoothies is the combination of high methoxyl (HM) pectin, shear, and pH Below their isoelectric point of 4.6, milk proteins have a net positive charge which increases as the pH is decreased HM pectin has an isoelectric pH of ∼3.6 and a net negative charge above this pH Optimal protein stabilization is obtained by culturing milk, adding pectin, and homogenizing Pectin can be added with a flavored juice slurry, which includes pectin, juice, sweeteners, other stabilizers, and flavors that were pasteurized separately from the dairy base Protein stability is highest from pH 3.8 to 4.1 and is imparted by the electrostatic interaction of the protein and pectin combined with steric hindrance In order to limit acidic flavor notes manufacturer’s balance stability from lower pH with better flavor at pH’s closer to 4.6 Most drinkable yogurts are made at pH 4.1–4.4 Homogenization is not practical postpasteurization in many plants so the shear is applied by other means such as back pressure valves Air should not be incorporated as this can lead to separation Protein aggregate size is also dependent on the protein content and the amount of sugar Sugar has a protective effect on proteins during heating and fewer problems with aggregation are observed in formulas with higher amounts of added sugars and lower total protein Formulas with higher sugar content also have less water that needs to be stabilized Hydrocolloids in Cultured Dairy Products 151 A problem related to protein aggregation is clear liquid separation This is common in unstabilized, unsweetened yogurt formulas as the protein aggregates and displaces water Separation is often seen in yogurt that is not properly stabilized and processed This serum separation is harmless, but a consumer often thinks that separated product is spoiled In order to minimize the economic impact, stabilizers are added to control syneresis Gelatin is effective at preventing separation in drinkable yogurts and buttermilks Stability against separation in the white mass is also enhanced by the use of an exopolysaccharide producing culture The ingredients for stabilizing protein also provide viscosity Additional viscosity can be added by using any hydrocolloid that will withstand the processing and pH of the drinkable yogurt Modified food starch, locust bean gum, cellulose gum, carrageenan, and guar gum are commonly used The parameters used for starch selection in drinkable yogurts are similar to spoonable yogurts as both undergo pasteurization and homogenization Natural and organic drinkable yogurts are made with HM pectin in combination with galactomannans (guar gum and locust bean gum), and/or native starch Higher levels of native starch are needed compared to modified starch as the native starch is broken down more easily by heat, shear, and acidity than a cross-linked starch Ingredient statements of drinkable yogurts and spoonable yogurts are similar especially in cases where modified starch and gelatin are used in the white mass Pectin can be used in combination with modified food starch in fruit preparations for spoonable yogurts and in the white mass for drinkable yogurts Table 7.1 shows formula and processing differences for drinkable and spoonable yogurts Culture strain selection may or may not be the same for both types of yogurt Smoothie formulation and processing varies widely, especially in food service operations Many of these smoothies are made on site after the customer orders and may include fruit, ice, soft serve frozen dessert, a smoothie base, flavoring syrups, protein powders, vitamin and mineral premixes, etc Some of these components may include hydrocolloids for viscosity or stability of one of the components such as the soft serve mix Stabilization of proteins is not a concern since the product shelf life is less than hour for a product sold for immediate consumption Retail products with a longer shelf life require more stabilization, which can range from systems similar to those used in drinkable yogurt to a thickened juice base if the product does not contain any protein 152 Hydrocolloids in Food Processing Table 7.1 Formulation and processing parameters for drinkable and spoonable lowfat yogurts White mass MSNF Milkfat Sweetener Modified starch Gelatin Pectin Pasteurization Homogenization Bulky flavor Postculture shear Spoonable Yogurt Drinkable Yogurt 8.25% minimum 1% 5–10% 1–3% 0.3–0.5%