MICR 4070 Exam 2 Study Guide

How you will sanitize/clean your plant?

PowerPoint 1: Preservation by temperatures & drying 

1. Describe the mechanism of drying preservation

a. Objectives

 Reduce or prevent growth of vegetative cells

 Prevent germination/out growth of spores  

 Prevent microbial toxin production

b. Method for reducing aw of foods

 Dehydration

 Crystallization

 Addition of solutes

c. Drying Methods

 Natural drying – sun drying

∙ Fish & other meats

 Mechanical drying – controlled – plants, fruits, veggies

∙ Spray drying - liquid food sprayed as small droplets into hot air,  causing rapid drying

How to sanitize food processing surfaces effectively?

∙ Freeze drying (lyophilization)- food rapidly frozen, and then  

exposed to a high vacumm. The frozen water is removed by  

sublimation.

o Basically water goes from solid  vapor (skips liquid phase)

o Adding water back recovers product freshness

∙ Smoking -food products are exposed to low heat and smoke  

which contains some antimicrobial components.

d. Effect of drying on microorganisms:  

 The process of drying is not lethal per se to m/o: bacteria endospores  survive, as do yeasts, molds, and many gram-negative and positive  bacteria.  We also discuss several other topics like Is desire related to sexual dysfunction?

∙ Osmophilic (probably Yeasts that are highly resistant to osmotic  pressure), halotolerant (salt tolerant), xerotolerant

What are the chemical preservatives used for food preservation?

 Most troublesome group of m/o in dried foods are the molds such as  Aspergillus glaucus group  

 Difference in dry resistance due to osmoregulatory capacities (to  maintain homeostasis with respect to water content)  

∙ Can grow at lower water activities

e. Mechanism of drying preservation

 Temperature effect

 Reducing aw below growth limit of m/o

 Extended lag time and reduced growth rate

∙ Longer shelf life  

f. fully preserved dried foods

 Dried milk powders (aw 0.2):

∙ evaporation: 140-150oC If you want to learn more check out Whose scheme was the watergate scandal?

∙ spray drying: inlet air temp. 190-250oC

∙ jet or nozzle dryer  

∙ rotary atomizer dryer,

2. Identify major types of microorganisms associated with LMF and IMF a. low-moisture foods (LMF):  

 less than 25% moisture, and water activity (aw) between 0.00 and 0.60 b. Intermediate-moisture foods (IMF):  

 15 to 50% moisture, and an aw between 0.60 and 0.85  

 jelly/jams  

PowerPoint 2: MAP & irradiation preservation 

1. Define MAP and its history

a. “The enclosure of food products in gas-barrier materials, in which the  gaseous environment has been changed to slow respiration rates, reduce  microbiological growth and retard enzymatic spoilage, with the intent of  extending shelf life”

i. Extends shelf life but does not improve the quality  

ii. Reduced O2 content, increased CO2, increased nitrogen We also discuss several other topics like Why is russia referred to as the third rome?

b. History

i. 1882 - Discovered CO2 can help meat

ii. 1889 - Antibacterial activity of CO2 established

iii. 1895 - 100% CO2 inhibited germination of mold spores

iv. 1928 - First use of MA for apples in Europe (1940 in U.S.)

v. 1938 - Beef from Australia (60%) and New Zealand (26%) shipped  under CO2 Don't forget about the age old question of Who was chosen by roosevelt as supreme commander of d-day?

vi. 1977 - 41% retail meat in U.S. vacuum packaged

2. Types of MAP

a. Controlled atmosphere packaging (CAP): replacement of air with a gas  (mixture) and maintaining continuous control of the atmosphere i. Requires sturdy packaging

ii. 2-3 combinations of a gas

iii. Sealed

b. Modified atmosphere packaging (MAP): changing the atmosphere of a  package by evacuating and back-flushing with gas or purging with a gas  mixture during packaging and sealing

i. 2-3 gasses  

ii. sealed

iii. Normally have to do 2-3 times to get desired gas mixture

c. Vacuum packaging (VP): removal of air from package and hermetically  sealing to maintain a vacuum

i. Reduce air significantly

3. Gases used in MAP

a. You must gas design a suitable gas composition for your foods

i. Normal O2 content in air is 20-25%  

ii. 78% Nitrogen

iii. .03% CO2

iv. 1% Argon  

b. Most commonly used:

i. CO2: Both bacteriostatic and fungistatic, inhibition of product  We also discuss several other topics like What were the landscapes like during mesozoic era?

respiration

ii. N2: normally a filler gas, doesn’t react with other food products;  chemical control

1. Bag of chips to prevent cracking/crumbling

iii. O2: color control, control of anaerobic pathogens We also discuss several other topics like What are the six types of hypothesis-testing?

1. Keeps meat products bright red

2. Possible anaerobic m/o – Clostridium botulinium

iv. CO: antioxidant and decay inhibiting

1. Debate: food industry is being pushed to use this more bc of its  effectiveness, however it is technically poisonous to humans – so its safety is being questioned

4. Characteristics of MAP

a. Polymers: 4 used (don’t need to memorize which four) but know: i. Polyethylene (PE): used very frequently

b. Factors to consider when selecting:

i. Barrier properties: permeability to various gases and water vapor ii. Machine capability: resistance to tear, possible to be heat-formed 1. “Heat formed” – make sure the material of packaging can be  

sealed without being damaged

iii. Sealing reliability: ability to seal itself and to the container

iv. Anti-fog properties: good product visibility

5. Food products used with MAP

a. MAP food products

i. Red meats: color stability, oxidation control

1. Bacon, or high fat meats/foods

ii. Fresh produce: delay fruit ripening, reduce respiration, retard softening  (2~5% O2, 8~10% CO2)

iii. Poultry: precooked products

iv. Seafood: little use

v. Prepared foods: increasing use on fresh pasta, salad, sandwiches, sous  vide

vi. Bakery products: retard the mold growth

b. Changes in meat, fish, and poultry produced by MAP storage

i. Enzymatic aging process is unaffected  

ii. Microbial spoilage: bacteriostatic activity of CO2

iii. Fat oxidation: reduced O2 levels reduce the oxidation of fats,  although oxidation can still occur at low oxygen tensions

iv. Oxidation of myoglobin: increased CO2 promotes metmyoglobin  formation and color darkening

1. Myoglobin makes red meat

c. Changes in fresh produce by MAP storage

i. Anaerobiosis created by respiration

ii. Subsequent anaerobic respiration

6. Effects of MAP on microorganisms

a. Following bacteria have relative sensitivity of m/o to MAP storage at  refrigerated temps:

i. Pseudomonas (most sensitive), Aeromonas, Bacillus, molds,  

Enterobacteriaceae, Lactobacillus, Clostridium (most resistant)

b. Inhibitory effects of carbon dioxide

i. Mechanism unknown: disrupting membrane function, enzyme  inactivation, reduction of intracellular pH

ii. Extended lag phase and generation time

iii. Reduction of total bacterial population

c. Effect of MAP on meat spoilage flora

i. Shift from G- to G+

1. b/c Aerobic spoilage m/o

ii. Prevents mold growth

d. Effect of MAP on foodborne pathogens

i. Growth inhibition:  

1. S. aureus, Salmonella, Yersinia

ii. Possible growth:

1. L. monocytogenes, Clostridia, major concern in MAP packed  

seafood  

PowerPoint 3: Chemical preservatives & sanitation 

1. Understand mechanism of organic acids as antimicrobes

1. Chemical preservatives – GRAS Standards (“generally regarded as safe”) a. Food antimicrobial agents are chemical compounds added or already  present in foods

i. Ex. In yogurt, lactic acid is already present

ii. Ex. Add ascorbic acid or salt to foods

b. Mostly bacteriostatic or fungistatic and not –cidal

c. Cellular target include the cell wall, cell membrane, metabolic enzymes,  protein synthesis, and genetic systems

d. Top 4 preservatives: all short-chain fatty acids (carbon from 2 to 6) i. Sorbates

ii. Propionates

iii. Benzoates

iv. Lactates  

2. Understand how other natural synthetic preservatives work and foods  theyre used in

a. Major Short Chain Fatty Acids

a. Benzoic Acid and benzoates (salt form of acid)

i. pKa = 4.19, optimum pH 2.5 to 4.5

1. pka is dissociation constant; when the H dissociates

ii. Antifungal agent primarily – yeast/mold

iii. Antibacterial agent for L. monocytogenes

iv. Foods: up to 0.1% in beverages, syrups, cider, margarine, olives,  pickles, soy sauce, pie

1. Naturally present in cranberries, cinnamon, cloves, berries,

etc

2. 0.1% is EPA limit: 1,000 microgram/mL

b. Parabens

i. Esterification of the carboxyl group of benzoic acid: methyl-,  

propyl-, and heptyl-parabens

ii. Effective range of pH: 3.0 – 8.0

iii. Antimicrobial activity proportional to the chain length of alkyl  

compounds

1. Longer the side chain, the more antimicrobial activity

2. Want them to dissolve and have strong activity so use a  

combination of short and longer chain parabens

iv. More active against molds and yeast than bacteria

v. Used in foods: baked goods, beverage, fruit products,  

jams/jellies, fermented foods  

c. Propionic Acid and propionates

i. pKa = 4.87

ii. Produced by Priopionibacterium freudenreichii subsp. Shermanii iii. Antimolds (primarily)

iv. Antibacterial agent 0.1-5% - E. coli, S. aureus, Salmonella, L.  plantarum, L. monocytogenes, proteus vulgaris

v. Foods: generally <0.4%, baked goods and cheeses

d. Sorbic acid and sorbates

i. pKa = 4.75, optimum pH <6.0

ii. antifungal agent: mold/yeast

iii. Antibacterial agent: catalas-positive bactria (aerobic m/o) and  some FDBRN pathogens

e. Acetic acid/acetates

i. pKa 4.75

ii. oldest antimicrobial agent – more effective against yeasts and  bacteria than molds

iii. Antibacterial agent: L monocytogenes, E. coli, salmonella,  pseudomonas, Yersinia

iv. Foods: baked goods, cheese, fats, oils, gravies, and sauces, and  meats

f. Lactic acid/lactates

i. 3.79 PKA, produced naturally by LAB

ii. pH control agents and flavoring

1. sanitize meat

b. Short chain fatty acids:  

a. Undissociated form:

i. Carries no charge and can pass cell wall easily

b. Lipophilic / can dissolve in fatty solutions

c. Dissociated form CAN’T get in the cell bc there is a charge d. Release of proton will reduce pH, causing intracellular pH to drop below 7 (not good for cells)

e. Cells have mechanisms

i. Consume ATP

ii. Uses ATPase to pump proton out  

c. Medium-chain fatty acids and esters

a. Primarily as surface-active or emulsifying agents due to their  amphibilic characteristics

i. Amphibilic: can dissolve in both aqueous and lipid solutions b. Most commonly used are composed of 12-16 carbons such as  monolaurin

c. Effective primarily against gram-positive bacteria and yeast d. Nitrites/Nitrates

a. Sodium nitrite (NaNO2) and nitrate (NaNO3) are used in curing  formulas for meat

i. Adds flavor, keeps color, and antimicrobial

b. Inhibit the germination of spores and outgrowth of C. botulinium c. FBP inhibited by nitrite include: S. aureus, C. perfringens, C.  sporogenes, but not enterobacteriace

d. Carcinogenic concern: nitrosamines

i. Cause of increased approach in alternatives  

e. NaCl and sugars

a. Used since ancient time

b. These chemicals exert a drying effect on both m/o and food products c. M/o of concern: halophiles, halodurics (like to grow at presence of high  salt concentration), osmophiles (grow at high sugar content),

osmodurics (survive at high sugar content – no growth or  

multiplication)

d. Used to preserve meat, fish, cakes, pie, condensed milk, fruit  preservatives

f. Lysozyme: enzyme  

a. Found in avian (bird) eggs, mammalian milk, tears

b. Optimum temperature: 55-60*C

c. Works by destruction of peptidoglycan of bacterial cell walls  i. G+ cell wall is many layers of peptidoglycan --> B-(1,4)  

Glycosidic bond

d. Effective against G+ bacteria, fungi

e. Combination with EDTA  

i. Allows for some antimicrobial activity against G- bacteria  

g. Phosphates

a. Sodium acid pyrophosphate (SAPP), tetrasodium pyrophosphate  (TSPP), sodium tripolyphosphate (STPP), sodium tetrapolyphosphate,  sodium hexametaphosphate (SHMP), and trisodium phosphate (TSP) b. Ability of polyphosphates to chelate metal ions

c. Effective against G+ bacteria than G- bacteria

d. TSP used as sanitizer in chill water for raw poultry and other raw foods h. Sulfites

a. SO2 and its salts such as K2SO3, NaHSO3, and Na2S2O5

i. R-S-S-R + SO32- -> R-S-SO3 + RS

b. Controls spoilage and fermentative yeasts and molds on fruits and fruit products, acetic acid bacteria, and malolactic bacteria  

i. Other

a. Ethylene and propylene oxide gases: fumigants in food industry i. Frozen fruits, or containers for food

b. Hydrogen peroxide (H2O2): sterilizing agent for food contact surface c. Ethanol: desiccant and denaturant

d. Ozone (O3): powerful oxidizing gas, broad germicidal activity but  unstable

j. Antibiotics/bacteriocins

a. Secondary metabolites produced by m/o that inhibit or kill a wide  spectrum of other m/o

b. Most antibiotics are  

k. Nisin

a. Produced by some strains of lactococcus lactic

b. First used in 1951 to prevent the spoilage of swiss cheese by C.  butyricum

c. Effect against G+ bacteria, primarily spore former, and is ineffective  against fungi and G- bacteria

d. Targeting cytoplasmic membrane by forming multistatic pores  e. Able to withstand high temperatures

f. Not toxic to humans  

g. Can be destroyed by human digestive enzymes

h. Doesn’t alter flavors of food

l. Lactoferrin

a. Milk & eggs

b. Iron-binding protein

i. Iron is not readily available in food

ii. Pathogens need iron for growth, so iron-binding foods make it  unavailable

m. Spices and their essential oils

a. Cloves, cinnamon, oregano, thyme, sage, and rosemary

b. Major antimicrobial component: terpenes

c. Thymol, cinnamic aldehyde, eugenol, carvacrol

n. Onions and garlic

a. Active component: allicin (diallyl thiosulfinate)

b. Inhibition of sulfhydryl-containing enzymes  

o. Phenolic compounds

a. Simple phenols and phenolic acids

b. Hydroxycinnamic acid derivatives (from cinnamon)

c. Flavonoids such as catechins and flavons, flavonols, and their  glycosides

i. Antioxidant activity

3. Link chemicals preservatives to their abilities to prevent food spoilage a. see previous bullets

4. Understand significance of sanitation program in food processing a. Stop the cycling of microorganisms

b. Product safety

c. Product quality – extend shelf life

d. Comply with govt. regulations

e. Sanitation Standards Operating Procedures (SSOPs)

i. For each processing plant, must have SSOP

ii. cGMP: General Manufacturing Procedures

iii. Describe exactly step-by-step how you will sanitize/clean your plant.  Include what sanitizers, how long, how often

5. Define no-rinse food contact surface sanitizer and non-food contact  surface sanitizer

a. No-rinse food contact surface sanitizer

i. Reduce S. aureus (G+) and E. coli (G-) by 99.99999% or 5 logs in 30  sec at 25*C

ii. In order to show efficacy, they have picked a representative m/o of  each category (G- and G+)  

iii. Must be more effective sanitizer b/c contact with food

iv. AO – C Standards

1. Grow culture to 7.5 x 10^7 CFU/mL first

b. Non-food contact surface sanitizer

i. For floors, drains, etc: surfaces that do not directly touch foods ii. Reduce above m/o by 99.9% or 3 logs in 5 min at 25*C

6. Understand how most commonly used sanitizers work, and workers  condition

*When deciding which to use, important to look at the SPECTRUM of each  chemical; the broader the better.

*Also look at good cleaning properties, non-toxic/non-irritant

*Should be long lasting as far as stability (don’t want to go buy more  everyday)

*Also look at cost $$

a. Thermal Sanitizing Methods - slower

i. Steam

1. Has high penetration activity

ii. Hot water

b. Radiation Sanitizing Methods – quicker, energy costs are lower i. UV light

1. Often is better for small areas

ii. High-energy cathode

iii. Gamma rays

c. Chemical Methods – very low cost, most commonly used in food industry i. Chlorine compounds

1. Chlorine gas

a. Sodium, calcium lithium hypochlorites

b. Chemistry of chlorine in solution

Cl2 + H2O  HOCl (hypochlorous acid) + H+ + Cl 

NaOCl (sodium hypochloride aka bleach) + H2O  HOCl +  

NaOH

c. HOCl and NaOCl = oxidizing agents

d. Max concentration – 200 ppm available chlorine

e. Advantages

i. Most widely used – cheap

ii. Oxidizer with bleaching action

iii. Effective against bacteria, yeasts, fungal spores,  

mold, mildew, and some viruses

iv. Hard water tolerant

1. Water that is high in either Ca or Mg ions

v. Acts quickly

f. Disadvantages

i. Skin irritant

ii. Corrosive to many metals

iii. Unstable during storage

1. Every time the container is open, important to  

measure how much is there bc a lot is lost in  

vapor

iv. Inactivated by organic compounds

1. Proteins/lipids/etc can bind to the Cl

v. Toxic Cl2 formation if pH<4

1. Harmful upon inhalation

2. Optimum pH 6.5-7 (neutral-ish)

2. Chlorine dioxide (ClO2)

a. Gas that’s soluble in water

b. Strong oxidizing chemicals

c. More tolerant of organic matter than chlorine

d. Need on-site generation – safety risks

ii. Iodophors  

1. Iodine + surfactant + acid

a. Max conc (25 ppm) & low temp

2. Advantages

a. Broad antimicrobial activity

b. Less irritating & corrosive than chlorine

c. Stable, long shelf life

d. Effective pH range: 2-8

iii. Quats – Quaternary Ammonium Chloride Compounds

1. Ammonium compounds that consist of four organic groups linked to nitrogen atom

2. Most commonly used is benzalkonium

3. Advantages:

a. Positive charge: compatible with negative charge, reduces  activity of negative charged compounds

b. Antimicrobial activity against mold & yeast less effective  against G- bacteria and phages

i. Good for juices (molds)

c. Odorless, colorless, and non-corrosive

d. Stable to heat and in the presence of organic matter, long  shelf-life

e. Form residual antimicrobial film

f. Some detergency and soil penetration

4. Disadvantages

a. Incompatible with anionic wetting agents

i. Important to clean really well after

b. Low hard water tolerance

i. Ions in the water can deactivate  

iv. Acid-anionic sanitizers

1. Anionic surfactants + acid with a double action

a. Sanitize

b. Acid rinse – acids react with some metal ions in foods;  dissolves any kind of Calcium stones in milk  

2. Very stable, non-staining, odorless

3. Safe for use on most food handling surfaces

4. Expensive

5. Only effective at low pH levels (2-3)

v. Carboxylic acid sanitizer

1. Fatty acids + organic acids + mineral acid: sanitizer and acid  rinse

2. Disadvantages:

a. Less effective against yeasts & molds

b. pH sensitivity – optimum activity pH < 3.5

c. Temperature sensitivity, use at >55*F

d. Inactivated by cationic surfactants

i. Need to rinse very well if using carboxylic acid  

sanitizer after cationic surfactants

vi. Peroxy acid compounds

1. Newest class of sanitizer

2. Advantages

a. Strong and fast acting: oxidation

b. Broad bactericidal activity, most effective against biofilms i. Biofilms are a group of m/o that excrete  

polysaccharides to protect themselves in a large  

group. They are usually very resistant to sanitizers  

(1000x) – which is obviously problematic. They’re  

common in the medical field – heart valves, tubes,  

etc.

c. Broader pH and temperature ranges

d. Sanitizing & acid rinse

e. Readily biodegradable into H2O, O2, and acetic acid

i. Don’t leave any harmful chemicals behind

ii. More eco friendly

d. Application methods of sanitizers

i. Spray

ii. Circulate

iii. Foam

iv. Fog

7. Differentiate b/w sanitization and disinfection

a. Sterilant/sterilize: destroy all microorganisms including bacterial spores,  viruses, and fungi

i. Ex. Steam, oxide gas

b. Disinfectant/disinfect: destroy vegetative cells on inanimate surfaces i. According to EPA, must label which m/o are being destroyed

ii. Similar to pasteurization, not sterile but reduces population  

significantly

c. Sanitizer/sanitizer: reduce microbial population to safe level

i. Used for hospitals and general purposes (swimming pools, kitchen  counters)

ii. Usually add scents

8. Explain how to sanitize food processing surfaces effectively a. 2 steps overall: cleaning & sanitizing

a. Clean surface first

i. If you don’t clean well, soil or food pieces can either physically or chemically prevent the sanitizers from working

b. Intimate contact

i. Sanitizers need to be in close contact with bacterial cells in order to use antimicrobial activity

c. Temperature

i. Increase temp, increase chemical reaction/activity

ii. In general, usually room temp to body temp

d. Concentration

i. Increase concentration, usually increases antimicrobial activity ii. But must stay within EPA limits

e. Contact Time

i. Usually also longer the better, but there is again a limit.

ii. In general, usually 1-2 minutes

f. pH

i. Control the pH; should be kept at pH that allows for best  

antimicrobial properties

g. Composition of makeup water

i. Ions, pH, etc

h. Type & number of microorganisms

i. Important to choose the right sanitizer for the specific pathogen ii. High number of m/o can “overwhelm” the sanitizer

b. General guideline for sanitizer application

a. Sanitizer applied as the final step in the cleaning program

b. Resanitize if time between completion of sanitizer program and startup EXCEEDS 4 HOURS

i. Over 4 hours allows for regrowth and multiplication of the  

existing small amounts of bacteria

PowerPoint 4: Dairy Microbiology 

Microbiology of Dairy Products 

I. Milk Components

a. Fat: flavor, aroma, and body in mature cheese

b. Protein: casein & whey proteins

i. Casein is colloidal – suspended throughout  

ii. Whey dissolves in the water after coagulating to form curd; curd is  remove and whey dissolves

c. Enzymes: lipases, proteases, and lactase

i. Can be naturally occurring or added  

d. Lactose: main sugar for start culture to grow

i. Fundamental for fermentation

e. Ash: metallic and nonmetallic components

i. This can allow some microorganisms to grow

f. Vitamins: A, D, E, K, B, & C

g. Microorganisms in milk

i. Lactic acid bacteria (LAB)

1. Lactococci (Lc)

a. Lc. delbrueckii subsp. lactis

b. Lc. lactis subsp. cremoris

2. Lactobacilli (Lb)

a. Lactobacillus casei

b. Lb. delbrueckii subsp. lactis

c. Lb. delbrueckii subsp. bulgaricus

3. Leuconostoc (Leu)

ii. Spoilage m/o in milk

1. Coliforms: Escherichia coli

a. Can come from dirty cows

2. Psychrotrophic organisms: Pseudomonas fluorescens,  

Pseudomonas fragi (producing proteolytic and lipolytic  

extracellular enzymes)

3. Microorganisms surviving pasteurization: spore formers &  

resistant G+  

iii. Pathogenic Microorganisms

1. Know these

II. Dairy Products

a. Fermented milk products

i. Butter milk, yogurt, kefir, koumiss, acidophilus milk, cheeses

b. Function of starter culture & metabolites

i. Called starter cultures because they start the fermentation process ii. Biopreserve the product due to a fermentation

iii. Enhance the perceived sensory properties of the product

iv. Improve the rheological properties (i.e., viscosity and firmness)

v. Contribute dietetic/functional properties to food

1. Anticancer, boost immune system, etc

c. Microbial species used by dairy industry

i. Traditional starter cultures (genus)

1. Gram positive, non spore formers, microaerophilic, utilize sugars, some are nutritionally fastidious (require growth factors that they

can’t synthesize by themselves)

2. Lactococcus:

3. Leuconostoc

4. Pediococcus

5. Streptococcus

6. Lactobacillus

a. 3 groups:

i. Group A: obligately homofermentative lactobacilli

ii. Group B: facultative heterofermentative lactobacilli

iii. Group C: obligately heterofermentative lactobacilli

ii. Microbial species incorporated into dairy starter cultures

1. Added into milk products in addition to starter cultures

2. Secondary; have additional function (appearance or dietetic  

purposes)

3. Propionibacterium, Brevibacterium, Bifidobacterium,  

Enterococcus

4. Bifidobacterium

a. Predominant in the stools of breast-fed infants

b. G+, nonsporeforming, nonmotile, & catalase negative

c. Strict anaerobes

d. Optimum growth temp: 37-41*C

e. Principle probiotic bacteria

f. Optimum pH is neutral range

5. Molds

6. Yeasts

III. Types of Dairy Fermentation – just know the different end products; don’t have to  memorize pathways in the powerpoints.

a. Homofermentative LAB:

i. Produce lactic acid as major product of glucose fermentation

ii. >60%

b. Heterofermentative LAB:  

i. Producing equal molar amounts of lactate, CO2, and ethanol from  hexose fermentation

IV. Microbiology of selected fermented foods

a. Butter milk

i. Fermented skim milk

1. MESOTHERMIC fermentation

ii. Solids removed

iii. Pasterurization at 95*C for 5 min

1. This is very severe heat treatment

iv. Starter cultures: Lactococcus lactis subsp. lactis or cremoris  

(homofermentative), Leuconostoc mesenteroides subsp. cremoris  (heterofermentative)

v. The fermentation end products are composed of: lactic acid,  acetic acid, diacetyl and CO2

b. Yogurt production

i. Skim, low or full fat homogenized milk

ii. Pasteurized at 85*C (30 min) or 90-95*C (5-10 min)

iii. Starter cultures: Lb. delbrueckii subsp. bulgaricus and S. thermophiles iv. THERMOPHILIC fermentation

v. Fermentation at 43*C for 6 hr (pH 4.8, ~0.9% acidity)

1. pH must be very controlled; added m/o will not be viable if not  

controlled

vi. Cool to 15-20*C

V. Inhibtors of starter cultures

a. Susceptible to infection by host-sepcific bacteriophages

b. Changes in the activity of starter cultures due to routine subculturing c. Presence of antibiotics or other inhibitory substance

VI. Synergistic interactions of starter cultures

a. Lb. delbrueckii subsp. bulgaricus: proteolytic activity on casein

b. S. thermophiles: peptidase to liberate amino acids from peptides c. The growth of Lb. bulgaricus is stimulated by CO2 & formic acid produced by  S. thermophiles

VII. Kefir

a. Alcoholic milk beverages

b. Starter cultures are not well-defined

c. Yeast-lactic fermentation

d. End products: lactic acid, CO2, alcohol, free fatty acids, diacetyl

VIII. Koumiss

a. Traditional drink of fermented mare’s milk

IX. Therapeutical milk products

a. Fermented milk products containing beneficial/probiotic cultures such as  lactobacilli and bifidobacteria

b. Term “probiotics” – live m/o which when administerd in adequate amounts  confer a health benefit on the host

i. Digestion, immunity, etc

c. Usually these genera: Lactobacilli, Bifidobacteria, Enterococci

i. Health effects attributed to consumption of probiotics:

1. Alleviation of lactose intolerance

a. Beta-galactidose can break lactose apart and digest

2. Prevention/treatment of infection

a. Act against pathogens  

3. Reduction of serum cholesterol

4. Chemopreventative effects

5. Modulation of immune system

ii. Probiotic dairy products

1. “Yakult” containing Lb. casei Shirota

2. Nestle’s LC1, containing Lb acidophilus strain La 1

iii. Probiotic survival in food systems

1. Post-acidification in yogurt or fermented milk

2. Oxygen toxicity

a. Start cultures that use oxygen very well

3. Processing parameters

a. Glass jar rather than polymer-containing ones