1. Dairy Fermentations (cheese)
(2:15 – 3:15)

2. We could talk all semester about:
Fermented dairy products;
Fermented vegetables;
Fermented meats
Cocoa, coffee, tea
Beer and wine
Cereal and starch products (bread)
Legumes (Natto, tempeh)
Cereal-legume mixtures (soy sauce)

3. Spoilage or beneficial?
Process
Beneficial (controlled)
Detrimental (uncontrolled)
Conversion of sugars to lactic acid
Acid flavor in fermented meats and dairy products
Sourness of fresh meats, pasteurized milk
Malty flavor (3-methylbutanal)
Malt powder
Pasteurized milk
Ropiness (exopolysaccharides)
Yogurt
Meats, milk
Acetaldehyde (product of threonine catabolism)
Yogurt (green apple flavor)
Milk
Diacetyl
Buttermilk (butter flavor)
Fresh milk
Again, discussing from standpoint of milk as this is best defined
Lb. perolens produces high levels of diacetyl.

4. General Cheese Making Steps
Raw Milk
Heat
Pasteurize/Heat
Starter culture
Inoculate with Starter and Ripen
Add Rennet and Form Coagulum
Cut Curd & Cook
Low aw
Drain Whey
Acid development
Texture Curd
Dry Salt/Brine
Salt (4%)
Form Cheeses
Store and Age

5. What is role of microbial metabolism in flavor development?
Qualifier, this is a terribly complex topic and there is much more going on than I have time to tell you
Fermentation isn’t just about preservation, but everytime you eat cheese you should be thanking microbes

6. The organisms - starters
Product
Primary acid producers
Secondary microflora
Colby, Cheddar, cottage
Lactococcus lactis
Lactobacillus adjuncts
Gouda, Edam, Havarti
L. lactis
Citrate fermenting Leuconostoc or L. lactis
Brick, Limburger
Geotrichum candidum, Brevibacterium linens, Micrococcus, Arthrobacter
Mozzarella, Provolone, Romano, Parmesan
Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus
Lactobacillus adjuncts, animal lipases (Romano and Provolone)
Swiss
Streptococcus thermophilus, Lb. delbrueckii
Propionibacterium freudenreichii subsp. shermanii
Yogurt
S. thermophilus, Lb. delbrueckii subsp. bulgaricus
None
Point being: one big difference is the microorganisms used
What happens when you add microorganisms? Lactose utilized (energy source, precursor to membrane lipids), as well as milk proteins (we’ll get to that)

7. Homofermentative lactose utilization
Lactococcus lactis
lactose
ATP
phospho-b-galactosidase
ADP
glucose
galactose-6-P
ATP
ADP
tagatose pathway
glucose-6-P
tagatose-6-P
In order to discuss these microorganisms, need to talk about the ways they utilize lactose
Embden-Meyerhoff pathway
fructose-6-P
tagatose-1,6-diP
fructose-1,6-diP
4 triose-P

8. Lactose  2 ATP + 4 lactic acid
4 triose-P
4 ADP
4 ATP
4 pyruvic acid
4 lactic acid
Homofermentative = lactose makes one end product
Recall that tricarboxylic acid cycle, one sugar molecule makes ~38 ATP; fermentation is rather inefficient process comparatively
Lactose  2 ATP + 4 lactic acid

9. Ugly figure, focus on big picture
Humans can’t make 9 amino acids; LAB used in dairy fermentations often can only make about this many
Ugly figure, focus on big picture

10. What is happening during “aging”?
Lactococcus lactis starter levels decrease
Requires fermentable carbohydrate
Becomes acid stressed
Non-starter bacteria begin to grow
Use other energy sources: citrate, amino acids, ribose and deoxyribose
More acid-tolerant than L. lactis to pH conditions (approximately 5.1)
Video from Italy describing where non-starters come from. A) Cheese making is not a sterile process especially in smaller facilities; B) Your plant

11. Organisms – non starters
Called NSLAB, as most non-starters that contribute to flavor development are lactobacilli (acid tolerant, use many of substrates left in cheese)

12. Positive flavor impacts
Acid
Primarily lactic acid from starter
Amino acids alone
Proline = sweet
Glutamic acid = meaty/brothy
Amino acid catabolism
Met  methanethiol;
Cys  H2S
Amino acids plus carbonyls
Ever wonder why, in general, raw milk cheeses have a more complex flavor? One reason is additional microflora (also pasteurization doesn’t inactivate all enzymes, doesn’t boil off feed flavors coming in with milk)
Carbonyl = carbon double bonded to an oxygen

13. methylglyoxal
glyoxal
ethanal
Griffiths et al., J. Dairy Sci. 72:

14. Defects Proteolytic-mediated bitterness Gas slits
Fruity flavors; ethanol production by non-starters, esterification with short chain fatty acids
Amino acid catabolism
Phe  benzaldehyde
Tryptophan  skatole/indole
Tyrosine  phenol
Benzaldehyde = almond
Phenol = mediciny likely

15. Important to point out that milk caseins aren’t completely degraded (if they were, we’d have cheese soup!)
Bitter peptides are those left behind

16. Heterofermentative lactose utilization
Some lactobacilli
lactose
b-galactosidase
glucose
galactose
2 glucose-6-P
ATP
ATP
ADP
ADP

17. 2 glucose-6-P
2 CO2
ADP
ATP
2 xyulose-5-P
2 triose-P
2 acetyl phosphate
acetate
2 pyruvic acid
acetaldehyde
2 lactic acid
ethanol

18. Gas slits in cheese Citrate acetate Oxaloacetate CO2 malate pyruvate
fumarate
diacetyl
succinate

19. Other microflora Adjuncts (Lactobacillus helveticus for Cougar Gold)
Can also use this to answer question: why are raw milk cheeses so much more flavorful than pasteurized?

20. Microbiological cheese controversies
60 day aging process for raw milk cheeses
7 CFR 58
Part 7 is all about agriculture; 58 specifically is grading and inspection of dairy plants; the microbial standards for raw and pasteurized milk are found in 7 CFR 58 as well.

21. Aging on wooden shelves 21 CFR 110
Not so much a controversy as a hot button issue