Average: 76.7

1. Exam 2 Average: 76.7 100 90 80 70 60 50 40 30

2. Question 1 Types of coagulants ·What types of coagulant (rennet or rennet substitutes) are available? • Calf or lamb rennet • Extract from calf or lamb stomach • Contains proteolytic enzymes: • chymosin (95%), pepsin (5%) • Rennet substitutes • Animal • Plant • Fungal protease – ex. Mucor miehei enzyme preps • Genetically engineered microorganisms – “recombinant chymosin” Dried or liquid forms http://www.wsu.edu/creamery/phototours/phototourschz.htm

3. Question 2 Heat treatment of milk Describe how the heat treatment of the milk (no heat treatment, thermization or pasteurization) impacts the microbiology and biochemistry of cheese ripening. Why would a cheese maker choose to use unpasteurized (heat-treated or raw) milk for cheese making? • Pasteurize: • 161°F (71.7°C), 15 seconds or equivalent • Required for cheeses that are not held for • >60 days at >1.7 °C • Thermization: • Heat treatment less than pasteurization • NSLAB and others can survive Cheese must be held for >60 days at >1.7 °C (FDA) • No heat treatment • Raw milk

4. Question 2 Microbiological changes: Nonstarter bacteria Nonstarter bacteria: unintentionally added bacteria that grow to high numbers in cheese. Lactobacillus, Enterococcus, Micrococcus, Pediococcus……others Starter Nonstarter LAB (NSLAB) 109 cfu/g 101 Time

5. Question 3 Sauerkraut: Microbiological Changes Explain the progression of microorganisms in a typical sauerkraut fermentation. Time

6. Question 3 Pickles: Microbiological changes NaCl inhibits L. mesenteroides – no heterolactic fermentation Time

7. Question 4 Ripening: Surface-ripened (mold) Which has the higher pH, the surface or the inside of a surface mold ripened cheese? Give two reasons for the pH difference. Penicillium camembertimold spores added to surface of cheese after pressing or added to milk before coagulation Little O2 inside cheese, so mold only grows on surface. BUT, the extracellular enzymes produced by the mold (proteases and lipases) can diffuse in to the cheese. Size affects ripening. Examples: Camembert Brie Flavor from protein, carbohydrate and lipid degradation by: • P. camembertiproteases and lipases • Milk enzymes • Coagulant • Starter culture • Nonstarter bacteria

8. Question 4 Ripening: Surface-ripened (mold), pH Changes in pH during Camembert cheese ripening • pH increases due to: • Release of ammonia by mold’s proteolytic enyzmes • Consumption of lactic acid by mold

9. Question 5 Vegetable Fermentations: Steps Why are heterolactic fermenting lactic acid bacteria undesirable in pickle fermentations? How is their growth discouraged? • Brining Addition of salt affects which organisms can grow Brining methods: Dry salting – cabbage - osmotic pressure draws water from the plant cells to make a brine Brine addition – cucumbers and olives, - add a concentrated salt solution to vegetables - final salt concentration is affected by water coming out of vegetable cells

10. Question 5 Pickles: Microbiological changes NaCl inhibits L. mesenteroides – no heterolactic fermentation Time

11. Question 5 Vegetable Fermentations: Spoilage Tissue softening – pectinolytic enzymes from yeast and molds Discoloration – pinkish color of sauerkraut - yeasts Off odors and flavors – usually from coliform growth before L.A.B become established Gaseous deterioration – Growth of heterolactic fermenters in pickle and olive fermentation - Aerobic growth of yeast + molds before conditions become anaerobic “bloaters”

12. Question 6 Some cultures do not ferment galactose Lactose Galactose in cheese Lactose Reducing sugar will react with free amino groups when heated ------Maillard browning Glucose Galactose Glycolysis Lactate- 2H+ Gal-species Gal+ alternatives Lactate- 2H+ S. thermophilus Lb. delbrueckii Gal+ derivatives Lb. helveticus

13. Question 7 Sources of proteolytic enzymes in cheese Name three sources of proteolytic enzymes that are active in all ripened cheeses and describe how they participate in casein breakdown. Coagulant Native milk enzymes pepsin, trypsin (heat sensitive and low activity at cheese pH) plasmin (heat stable and active at cheese pH) Bacteria (starter and nonstarter) cell envelope-associated protease intracellular peptidases Molds (if added)

14. Question 8 Whey Composition Why is there more calcium in whey from an acid curd than whey from a paracaseinate curd? How does the whey differ between the two curd types? What are the two main types of whey in the U.S. and how do they differ? Fluid Acid Whey Fluid Sweet Whey 93.66% 0.25% 0.60% # 4.85% 0.50% 0.14% 93.64% 0.05% 0.54% 4.50% * 0.80% 0.47% Water Fat‡ Protein‡ Lactose Ash (minerals) Lactic acid # Whey from paracaseinate curd has caseinomacropeptide (review on next slide). * If cheese is made by acidification, lactose will be higher - ~5.0%. ‡ Some fat and protein components of whey have health benefits.

15. Question 9 Setting the milk (paracaseinate curd) Step 2: Coagulation What are the functions of the coagulant? Add coagulant. Wait 20-30 minutes. http://www.wsu.edu/creamery/phototours/phototourschz.htm • Coagulants contain proteases and serve two purposes: • Coagulate the casein micelle to form paracaseinate curd. • Participate in casein breakdown during cheese ripening • What determines the type of coagulant? • Tradition • Price and availability • Proteolysis during cheese ripening

16. Question 10 Transformation of curds (optional) Dependent on cheese variety – not all have this step Coalesce curds together to form the characteristic texture or the cheese variety Accumulation of acid and/or physical manipulations help the curds come together in a specific way Examples: Cheddaring of Cheddar cheese, stretching of Mozzarella

17. Question 10 Mozzarella Changes in structure due to stretching Figure from M. Johnson, University of Wisconsin Figure from D. McMahon, Utah State Univeristy

18. Question 10 Mozzarella Figure from M. Johnson, University of Wisconsin Extent of demineralization

19. Question 10 Cheddaring Process Curd Transformation Cheddaring = piling and repiling of matted curd blocks until desired acid level is reached

20. Question 11 Whey expulsion factors (Syneresis) Discuss the factors that affect the moisture of a cheese. What determines how much whey is removed from the curd? More whey loss Less whey loss Curd firmness Size of curd particles Acidity Heat during cooking Force during pressing

21. Question 12 Changes in micelle structure with acidification If you want a cheese with at stretchy texture, would you want more or less acid (higher or lower pH) in the curd compared to a cheese with a crumbly texture? H+ H+ H+ Increasing acidity, decreasing pH Loss of structure, pasty, gummy, brittle Pliable, elastic, stretchy Rigid, rubbery, no curd knitting Crumbly 0.95% TA pH~4.9 0.15% TA pH ~5.4

22. Cheese Ripening Question 13a See entire cheese ripening lecture notes Flavor and texture changes during ripening are caused by… • MICROBIAL POPULATION CHANGES • Starter culture bacteria • Other intentionally added bacteria, yeasts, molds • Unintentionally added microorganisms ·What is autolysis, and why is it important in cheese ripening? Where do nonstarter lactic acid bacteria (NSLAB) come from and what is their effect on cheese? CHEMICAL REACTIONS Enzymes Nonenzymatic chemical reactions How does proteolysis during ripening affect cheese flavor and texture? How are autolysis and proteolysis related? • Added enzymes • Native milk enzymes • Microbial enzymes

23. Question 13b Methods to accelerate cheese ripening See lecture notes for details on each Name one method to accelerate cheese ripening and briefly describe how it works. If you want your Cheddar cheese to ripen quickly, what attributes would you want in your starter culture (Lactococcus lactis)? What is an adjunct starter culture? Elevated ripening temperature Addition of enzymes Selection of starter cultures Attenuated or inactivated starters Adjunct starters

24. Question 14 Cheddar and camembert cheeses are very different from each another yet they are produced using the same starter culture (mesophilic) and raw material (milk). Describe factors that cause the dramatic differences in the final products. Include processing steps, microorganisms and enzymes involved in these differences. (You could do this with any of the cheeses that we discussed.) See cheese chart for details Type of curd Relative curd cutting sizes Relative cooking temperatures Pressing Salting Special features – special bacteria, molds, or enzyme; special processing steps