Exam 2 Flashcards
1
Q
Cultured Dairy Products
A
Cultured dairy products are products made from milk (or a standardized mix) that are coagulated primarily by decreasing the pH to the isoelectric point of casein
Basically casein gels made with or without removal of whey
2
Q
Without Removal of whey
A
Butter milk
Sour Cream
Yogurt
3
Q
With Removal of Whey
A
Cottage Cheese
Cream Cheese
Greek Yogurt
4
Q
Getting Microbs into milk
A
- Rely on natural flora
- “Back Slopping”
- Using a bit of the previous days production to inoculate the current batch
- Addition of well defined starter cultures
5
Q
Starter Culture
A
One or more strains of one or more species of desirable bacteria used to inoculate a raw or pasteurized product to start a fermentation–W. E. Sandine
6
Q
Mother Culture
A
A small volume of culture (<1L) maintained in the laboratory
7
Q
Bulk Culture
A
The larger culture used to inoculate milk to make a specific product. (0.5-5% by weight or volume)
8
Q
Mesophilic Starters
A
Optimum growth T<30°C
9
Q
Thermophilic Starters
A
Optimum growth T 47-45°C
10
Q
Defined Strain Starters
vs. Mixed Strain Starters
A
-Single strain & Multiple Strain
11
Q
Traditional” Starter Preparation(Bulk Starter)
A
Inoculum –> 1lb mother culture –(0.5lb)–> one or more intermediate cultures (50lb) –(10lb)–> Bulk culture (1000lb)
If I want to make 80,000 lb of milk into cheese, using a 1% inoculum, when do I start preparing culture?
12
Q
Dairy Starter Bacteria-LAB 1
A
Lactococcus (Streptococcus)
-Mesophilic
-Lactococcus lactis ssp. lactis
-Lactococcus lactis ssp. cremoris
-Lactococcus lactis ssp. lactis biovar.diacetylactis
Thermophilic
-Streptococcus thermophilus
Leuconostoc
-Leuconostoc mesenteroides ssp. cremoris
-Leuconostoc mesenteroides ssp. dextranicum
13
Q
Dairy Starter Bacteria-LAB 2
A
Lactobacillus
- Group I-Obligate homofermentors
- Lactobacillus delbrueckii ssp. bulgaricus
- Lactobacillus delbrueckii ssp. lactis
- Lactobacillus acidophilus
- Lactobacillus helveticus
- Group II - Facultative homofermentors
- Lactobacillus casei ssp. casei
- Lactobacillus plantarum
- Group III - Obligate heterofermentors
- Lactobacillus brevis
- Lactobacillus fermentum
- Lactobacillus kefir
14
Q
Dairy Starter Bacteria-LAB 3
A
Pediococcus
- Pediococcus pentosaceus - Pediococcus acidilactici
15
Q
Dairy Starter Bacteria-Non LAB
A
Propionibacterium
-P. freudenreichii (Swiss cheese)
-P. theonii
-P. acidipropionici
-P. jensenii
Brevibacterium linens (Lindburger cheese)
16
Q
Dairy Starter Bacteria-Molds
A
Penicillium (blue cheese)
-P. camemberti
-P. roqueforti
Others
17
Q
Genus
A
“one or more species with the same general phenotypic characteristics and which cluster together on the basis of 16s rRNA sequences” (Brenner et al 2001)
18
Q
Species
A
“a group of strains that are highly similar to each other and collectively have certain distinguishing characteristics” (Colwell et al 1995)
19
Q
Subspecies
A
“a group of strains within a species that consistently cluster on the basis of phenotypic and genotypic characteristics” (Wayne et al 1987; Brenner et al 2001)
20
Q
Strain
A
- “any culture knowingly defined from the original strain” (De Vos and Truber 2000)
- “Descendents of a single isolation in pure culture…ultimately derived from an initial single colony” (Brenner et al 2001)
21
Q
Primary Metabolic Activities of Starter Microorganisms
A
Acid Production (LAC) Protein Metabolism (PRT) Citrate Metabolism (CIT) Exopolysaccharide Production (EPS) Acetaldehyde Production (ACET) Bacteriocin Production Probiotic Function
22
Q
Acid Production (Lac)
A
The primary metabolic activity of lactic starter cultures
-Responsible for conversion of into coagulum or curd
Strains can be Lac+ or Lac-
-As we look at various phenotypes, think about what genotypes could be responsible.
-There are often multiple possibilities!
23
Q
Homofermentative Metabolism
A
One primary end product from the metabolism of carbohydrate
- Lactococcus lactis ssp. lactis - Lactococcus lactis ssp. cremoris - Streptococcus thermophilus - Lactobacillus delbrueckii ssp. bulgaricus - Lactobacillus helveticus
24
Q
Heterofermentative Metabolism
A
More than one end product from the metabolism of carbohydrate
- Bifidobacteria
- Lactobacillus brevis
- Lactobacillus kefir
- Leuconostoc
25
Fermentation of Lactose to Lactic Acid
Lactose (lactose permease)--> lactose --(beta-galactosidase)--> Glucose to lactic acid w/ bi-product galactose
lactose (PEP-PTS)--> lactose-phosphate --(P-bea-galacosidase)--> Glucose to lactic acid w/ bi-product galactose-6P
26
Products of Heterofermentation
lactic acid C3H6O3
acetic acid C2H4O3
carbon dioxide CO2
ethanol C2H6O
27
Protein Metabolism (Prt)
- Milk is rich in protein but poor in low molecular weight nitrogen
- In order to grow rapidly a source of low molecular weight nitrogen is required.
- Casein --(proteinase)--> peptides --(peptidase)--> (peptides + peptidase = amino acids --> bacterial protein) or (amino acids to bacterial proteins)
Prt- low growth, but Prt+ has much higher growth
But Prt+ or Prt- with MPH has the greatest growth
28
Strains can “share” the ability to break down protein
Casein (milk protein) ---(proteinases)--> Oligopeptides--(peptideases)--> small peptides + AA
29
Citrate Metabolism (Cit)
Citrate ---> Diacetyl
30
Diacetyl Producing Strains
Lactococcus lactis ssp. lactis biovar. diacetylactis
| Leuconostoc mesenteroides ssp. cremoris
31
Acetaldehyde Strains
L. delbrueckii ssp. bulgaricus
32
Exopolysaccharide Production (EPS)
Any polysaccharide found outside the cell wall including…
Slime (loosely associated)
Capsule (more closely associated with the cell)
Operationally these are known as Exopolysaccharide or EPS
33
Characteristics of EPS of LAB
Typically neutral (non-charged) heteropolysaccharides
Large in size 1,000,000 or larger
Production is variable (among strains)
Production is “growth associated”
34
Biological Functions of EPS
```
Protection against desiccation
Protection against bacteriophage attack
Adhesive agent
Adsorption to surfaces
Concentration of nutrients
```
35
Applications for EPS-Producing Cultures
```
Enhancing body of buttermilk
Increasing viscosity of sour cream
Reducing MSNF levels in yogurts
Reducing/eliminating the need for stabilizer addition
Moisture retention in low-fat cheese
Novel applications
```
36
EPS Producing Strains
Lactococcus
Streptococcus
Lactobacillus
Leuconostoc
Note that strains vary in level and type of EPS produced
37
Bacteriocin Production
Bacteriocins are proteinaceous inhibitory substances produced by bacteria that inhibit closely related strains
Similar to antibiotics but with a limited spectrum
Can be used for “protective effect” or shelf life extension
38
Examples of Bacteriocins
Nisin
Lactococcus lactis ssp. lactis
Pediocin
Pediococcus
39
History of Yogurt
Origin in the Middle East, Turkey or Iran (circa 10,000 BC)
Praised for its healthful benefits (500 BC)
“Milk of eternal life”
1900: Dr. Ilya Metchnikoff isolated bacillus cultures for making yogurt
1925: First modern yogurt plant
1970s: increasing popularity in U.S.
40
Definition of Yogurt 21 CFR 131.200
Culturing cream, milk or skim milk with Lactobacillus bulgaricus and Streptococcus thermophilus (LB & ST)
3.25% milkfat, 8.25% MSNF
TA >/= 0.9% lactic acid
May be heat-treated after culturing to destroy viable organisms and extend shelf-life
41
General Yogurt Categories
Firm yogurt (set-style): firm gel in a pack, normally consumed by use of a spoon
Stirred yogurt: gel has been broken, cooled and packed after coagulation
Drinkable yogurt: like stirred, but product has been homogenized and brought into a liquid form before filling
Frozen yogurt: incubated in tanks and frozen like ice cream
42
Yogurt Production Scheme
Milk selection
Dry matter standardization
Homogenization
(Deaeration)
Pasteurization
Heat treatment
Inoculation
--> flavoring, fill retail container, ferment, cool/store (SET STYLE
OR
-->ferment, break, stir/cool, fill (STIRRED STYLE)
-->ferment, break, stir/cool, homogenize, fill (DRINKABLE STYLE)
43
Mix Preparation: Non-Dairy Ingredients
```
Sweeteners
-sucrose, honey, HFCS, corn sugar, non-nutritive sweeteners
-use level varies (0-10%)
Stabilizers
-ensures texture uniformity between batches
-commonly use gelatin or modified starch
-use level <1%
-related to texture quality/defects
```
44
Mix Preparation: Standardization
Standardization of milk fat and total solids
To obtain desired gel structure, milk solids must be increased by 1-3%
Remove water by evaporation, under vacuum
Remove water by reverse osmosis
Add milk powder
45
Mix Preparation: Homogenization
Homogenize mix (~ 63°C/145°F)
First stage 2000 psi, second stage 500 psi
Break up fat globules and particulate ingredients
Often non-fat yogurt mixes are homogenized for improved texture
46
Mix Preparation: Deaeration (Optional)
```
Vacuum pressure of 12 psi, 70°C/160°F
Advantages:
increased viscosity
improved gel stability
removal of volatiles
reduction of fouling in plate heat exchangers during heating of yogurt
```
47
Mix Preparation: Heat Treatment
85-115°C (185-235°F) for 30 s - 30 min
Changes the interactions of the casein micelles
Whey proteins are denatured
whey proteins denature onto cappa-casein
produces a thicker, heavier body with better water binding capacity
Normal HTST pasteurization does not sufficiently denature the whey proteins.
48
Mix Preparation: Advantages of Heat Treatment
Denaturation of whey proteins onto casein micelles
Destruction of competitive microflora
Removes dissolved oxygen
Generates peptides
49
Setting and Inoculation
Cool to inoculation temperature (41-43°C, 106-109°F)
Add culture without over-agitation
Fermentation in a quiescent state
50
Fermentation: Culture
Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus (ST and LB)
-thermophilic (42°C, 107°F)
51
Inhibiting Factors
Inherent Inhibitors
Antibiotics
Sweeteners
Bacteriophages
52
Fermentation Temperature
ST optimum temp 38-42°C (100-107°F)
LB optimum temp 42-45°C (107-113°F)
Temperature influences fermentation profile
53
Metabolites
```
Lactic Acid
-Drop in pH, characteristic flavor
-Form from glucose by both ST & LB
Acetaldehyde
-Aroma
-Formed by LB
Diacetyl
-Butter flavor
-More ST than LB
Polysaccharides
-Consistency, especially stirred yogurt
-Both ST & LB
```
54
Fermentation
Single strain:
-ST will coagulate milk, low TA/high pH
-LB higher TA, lower pH; with initially slower growth rate and acid production
-Alone, both create unsatisfactory products
Mixed strain:
-rapid growth/acid development
-improved flavor
```
3-5 hours is typical (40-45°C)
Utilization of lactose
pH declines
Gel formation
Flavor development
Microbial enzymes
Exopolysaccharide production
```
55
Where does fermentation take place?
```
Sales pack (set style)
Fermentation tanks (stirred or drinking)
Continuous pre-fermentation, main fermentation in sales pack (set style)
Continuous fermentation (stirred/drinking)
```
56
Breaking and Cooling
pH ~4.6
Rapid cooling to avoid further pH drop (<0.3 units)
product should reach 15-20°C (59-68°F) within 1½ hours
Break coagulum with agitator
After cooling, final pH ~ 4.5 with a titratable acidity of 0.9 - 1.0% lactic acid
57
Adding Fruit
```
Fruit selection
Flavors added to milk before culturing
Fruit on the bottom
Fruit blended with yogurt after culturing
Label:
“Fruit yogurt”, >/= 6% fruit
“Yogurt with fruit preparation”, 3.5 - 6%
“Yogurt with fruit flavor”, < 3.5%
```
58
Filling and Packaging
Retain the coagulum without unnecessary agitation or disturbance
Most loss of body and gel weakening occurs during transfer of the product from the fermentation tank to the filler
After filled, containers should be held for at least one day for development of texture and flavors
59
Greek Style Yogurt
Industrialized process - concentrate the skimmed or full-fat yoghurt by mechanical separators (Quark separator) or Ultra filtration (UF)
- Skim milk fermented to pH 4.60 - 4.55
4. 70 In large scale with longer waiting time before separation
- Run through a quark separator
- Target 9-10 % protein in white mass
60
Culture recommendation for Greek style yogurts
Choice depends on the technology
Separated:
Important: cultures with very low process post-acidification
-Milk base: skim milk 3.25% protein (low buffering capacity)
-Few hours at fermentation temperature before it is separated
-Lower fermentation temperature will give milder product
61
Direct set /Fortified Greek style yogurt
Feasible in smaller plants without a separator
Protein level is adjusted in a milk base
-Protein source MPC or blends of MPC and WPC
-Protein level 7.0-7.5% provides good texture
-However, developers target 10% protein as it is in separated
-End pH 4.60-4.55
Can be run as set in a cup, FOB or vat-set
If vat-set, need a strong positive pump to empty the tank and run through the smoothing valve
62
Greek Style Yogurt without whey separation
Skim or reduced fat milk-->add MPC to get 8.0-10.0% protein (higher protein usually causes powdery off notes) --> Inoculate culture (0.1 -0/2% of F-DVS) & incubate at 39 - 43oC (102-109oF) --> end at pH 4.6 stir, filter, cool and ingredients pack and store
63
Culture recommendation for Greek style yogurts
Fortified:
High texture, medium yogurt flavor, provide freshness
Important: some yogurt flavor is desired
Remember that 10% protein (high buffering capacity)
Mild cultures are too mild
64
Live & Active” Cultures
```
Requirements:
LB & ST
Active cultures at end of shelf life
Activity test
108/gram total population at time of manufacture
TA of at least 0.3% at all times
```
65
Flavor Defects & Shelf Life
```
Too acidic
Bitter
Yeasty, fruity, musty, cheesy
Insufficient acidification
Not enough characteristic flavor (less important when fruit added)
Other off-flavor
```
66
Benefits of Yogurt
FALSE!
Yogurt Starter Cultures (ST & LB) are incorporated into the normal flora of the intestines suppressing the growth of harmful (putrefactive) microbes
```
Good source of nutrients
Good source of vitamins
Relative stability and safeness
High Ca & P
Alleviation of problems associated with lactose intolerance
```
67
Bio-Yogurt
Typical flora may include L. acidophilus and genus Bifidobacterium
Considered oral probiotics
Living microorganism which, upon digestion in certain numbers, exert health benefits beyond inherent basic nutrition
68
Yogurt Trouble Shooting
```
Potential Problems
Weak body:
Synerysis:
Color migration:
Lumpy/curdy:
High acid at end of shelf-life:
Gassy:
```
