Lecture 17 Part 1 Dairy Products I PDF

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Taught by Dr. Michael Miller. Information comes directly from the PowerPoint slides in lecture. Talks about yogurt, kefir, buttermilk, and sour cream and a bit of history....

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FSHN 471 17th Lecture Part 1 History of Dairy Products ● Among the oldest of fermented foods ○ Cultured dairy products have evolved on every continent ○ Mentioned in the Old Testament, Hindu sacred texts, and other ancient religious texts and writings ● Fermentation and acid formation were very important for increasing the stability of milk ○ Relied on endogenous lactic acid bacteria (LAB) ○ Without LAB, other bacteria (including pathogens) could grow ● Milk as a Substrate ○ Carbohydrate-rich and nutrient-dense composition ■ Composition of fresh cow’s milk: ● 5% lactose, 3.3% protein, and pH 6.6 – 6.7 ○ Ideal conditions for most microorganisms! Lactic Acid Bacteria and Milk ● LAB are saccharolytic and fermentative ○ Saccharolytic: Capable of hydrolyzing or breaking down a sugar molecule ○ Fermentative: Produce ATP via glycolysis; lack respiration ○ Ideally suited for milk ○ In general, LAB will out-compete other microorganisms for lactose ○ In addition, acidification will produce an inhospitable environment for would-be competitors ● Function of LAB ○ Ferment lactose to lactic acid ■ Decreases pH and reach the isoelectric point of casein ● Casein: major milk protein ● Isoelectric point: pH at which the net electrical charge of a protein is zero and the protein is at its minimum solubility ● For casein, isoelectric point is 4.6 ○ When sufficient acid has been produced to cause the pH to reach 4.6, casein precipitates and a coagulum is formed ○ The culture may also produce other small organic molecules (acetaldehyde, ethanol, diacetyl, acetic acid) ○ Relatively low amounts but important for the overall flavor profile of the product ○ The culture may also produce other compounds that contribute to the viscosity, body, and mouth feel of the product ○ The choice of LAB cultures is dictated by the product being produced Yogurt ● Yogurt constitutes >50% of the cultured dairy product market in US

● Yogurt can be made from skim, reduced-fat or whole milk ○ Use quality milk that is free of antibiotics and other inhibitory substances ● Add nonfat dry milk to increase the total solids to 12% to 15% ○ Skim milk has ~8.5% solids ○ Increase % solids by concentrating the milk by evaporation (less common) ● Other ingredients including stabilizers can be added ○ Gums and starches: Carrageenan, pectin, gelatin ● Usually, the yogurt mix is homogenized if it contains fat ○ Homogenization is unnecessary in a non-fat yogurt ○ Some producers make a unhomogenized, cream-on-the-top whole milk yogurt ● Homogenization ○ Ensures a uniform composition and stable structure throughout a product ● In US, yogurt is required to be made using pasteurized milk ● However, the yogurt mix receives a heat treatment far beyond pasteurization ○ Pasteurization = 71.7°C for 15 seconds ■ Denatures nearly all whey proteins, decreases syneresis ■ Syneresis: separation of water from the coagulated milk. Avoid by: ● Increasing milk solids & heat treatment and including stabilizers ○ Typical yogurt treatment = 85°C for 30 minutes ● Cultures ○ Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus ■ Many commercial products contain more than one strain of each organism ■ 1:1 ratio of S. thermophilus to Lactobacillus delbrueckii subsp. bulgaricus ○ Both organisms are needed to make yogurt with the desired properties ■ S. thermophilus grows initially ● Lowers pH to acceptable level for L. delbrueckii subsp. Bulgaricus ● S. thermophilus is weakly proteolytic and relies on the small pool of free amino acids in milk ○ S. thermophilus quickly uses up the available amino acids ■ L. delbrueckii subsp. bulgaricus produces a proteinase that provides amino acids for both organisms ■ Eventually, L. delbrueckii subsp. bulgaricus will produce more acid than can be tolerated by S. thermophilus ● Prevents the continual co-culture of both organisms ● To make yogurt starter cultures, the organisms are grown separately in species-specific optimum conditions, harvested and mixed in the desired ratio ● Fermentation Conditions ○ Incubated between 40°C – 45°C (thermophilic culture) ■ In general, L. delbrueckii subsp. bulgaricus has a higher temperature optima than S. thermophilus

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● < 42°C favors S. thermophilus ● > 42°C favors L. delbrueckii subsp. bulgaricus ○ Incubation temperature influences the growth rates of the two organisms and the metabolic products they produce ■ For example, L. delbrueckii subsp. bulgaricus is capable of producing more acetaldehyde compared to S. thermophilus ○ Fermentation lasts ~4-6 hours and is stopped when the pH reaches about 4.4-4.6 ■ Lactose concentration in yogurt is often higher than that of milk due to the addition of non-fat milk solids (often >6% lactose in yogurt) Yogurt Styles ○ Cup-Style ■ Mix is inoculated with culture and is pumped immediately into cups ■ If the yogurt is to contain fruit, the fruit is added to the bottom of the cup prior to the dispensing of the mix and culture ■ Fermentation occurs in cups ■ Consumer must stir/mix to incorporate the fruit throughout the product ○ Swiss-Style ■ Fermentation occurs in a vat that is then cooled, flavorings are added, and the yogurt is pumped into containers Post-Fermentation ○ Fermentation is complete when the target acidity is reached ○ Yogurt is then quickly cooled to below 4°C ■ Cooling is required to arrest the fermentation ■ During cooling, pH continues to drop by an additional 0.2 to 0.3 pH units ○ Cup-set yogurts are carefully moved to coolers ○ Swiss style yogurts are cooled in the vat, mixed with fruit, and filled into cups Yogurt Flavor ○ The most dominant flavor of yogurt is sourness ■ due to lactic acid produced by starters ■ Most consumers detect sourness when the pH is below 5.0 ○ Other metabolic products produced by the culture can accumulate in yogurt and contribute significantly to flavor development ■ Of these, acetaldehyde is most important ● Normally present at less than 25 ppm ● Gives yogurt its characteristic tart or green apple flavor Greek Yogurt ○ Yogurt with water removed ■ Also called “yogurt cheese” ■ Makes a thicker, creamier yogurt (texture similar to sour cream) ○ May result in a yogurt with: ■ Reduced lactose (removed with the water)

■ Reduced protein (whey is removed with the water) ● Some makers actually put the whey back into the yogurt so that the resulting Greek yogurt is higher in protein than traditional yogurt (on a per ounce basis) ■ Increased concentration of solids (fat, casein, etc.) ○ Remove water from yogurt with a cheesecloth ● Soy Yogurts ○ Similar strategy as regular yogurt except soy milk replaces dairy milk ○ Problem: lactose is the primary sugar in milk whereas the primary sugars in soy milk are raffinose and stachyose ■ Traditional starter cultures can not ferment raffinose or stachyose ■ Solutions: ● Add a fermentable sugar (sucrose is often used) ● Change the starter culture (Select strains with the desired activity) ● Yogurt Drinks ○ Stirred yogurt with a low viscosity ○ Yogurt with two main changes: ■ Post-fermentation agitation and no additional milk solids or stabilizers ● Remember that non-fat yogurt typically has >12% milk solids ○ Non-fat yogurt drinks will have ~8.5% milk solids Kefir ● Very popular product in Middle East, Eastern Europe and Central Asia ○ Accounts for as much as 70% of all cultured dairy products consumed worldwide ● Traditional- Combination of yeast and LAB (~1% ethanol) ● US- LAB only (no ethanol) Cultured Buttermilk ● Acid producers ○ Homofermentative, often Lactococcus lactis sp. lactis or L. lactis sp. Cremoris ● Flavor producers ○ Heterofermentative and can ferment citric acid to diacetyl (diacetyl producers) ● Often L. lactis subsp. lactis or Leuconostoc mesenteroides subsp. Cremoris ● Sour cream: very similar to cultured buttermilk, however, cream is used instead of milk and it uses a milder heat treatment...