Explain the beer making process:
- to make beer you start with malt
- malt is made from grinding semi-germinated barley
- the malt is mashed by heating with water for a few hours to extract the fermentable sugars
- hops are then added, before boiling for 1 hour to flavor beer
- the wort is then cooled before being passed to the fermenter where yeast is added
- this starts the fermentation phase that lasts for 5 days to produce green beer
Brewing is:
the combined process of preparing beverages from the infusion of grains that have undergone sprouting, and subsequent fermentation of the sugary solution produced, by yeast - where a proportion of the carbohydrate is converted to ethanol and carbon dioxide
Why Wine yeast it resistant to sulfite?
- In wine yeast but in no other yeast there is a reciprocal translocation between chromosome 8 and 16
- This translocation results in a dominant allele for the sulfite pump SSU1-R1 which is expressed at much higher levels than SSU1 and confers a very high level of sulfite resistance
Malt vinegar
- made from malting barley which results in the conversion of starch to maltose
- the maltose is converted to ale, and then turned into vinegar, which is then aged
- light-brown in color
Cider vinegar
- made with apple juice through a double fermentation with alcohol and acetic acid fermentation in the same barrel by naturally occurring yeasts and acetic acid bacteria
Explain Acid Coagulation
- Acid coagulation occurs when LAB ferment lactose to lactic acid while growing in milk
- As pH is decreased, the isoelectric point of casein is reached (pH 4.6), H atoms accumulate and neutralize the polar surfaces of casein micelles, forcing them into chains of micelles
- The chains of casein micelles entraps all the water and solid component and form a fragile coagulum
Explain Acid-Heat Coagulation
- Caseins micelles in fresh milk are highly heat stable and remain soluble up to 140C
- However if milk is moderately acidified (6.2 to 5.4), it becomes susceptible to heat-induced coagulation at relatively lower temperatures (85C)
- Coagulations occurs because whey proteins unfold and loose their ability to interact with water
- The denatured whey proteins attach onto the micellar surfaces and the micelles aggregate into clusters that entrap fat globules.
Explain Rennet Coagulation
- Rennet is a group of proteinases that cleave casein at the surface of micelles when added to milk
- Rennet preferentially cleaves K-casein at the surface of micelles and initiates coagulation (aggregation in a net-like matrix)
- Rennet enzymes can be derived from a number of animal, plant, and microbial sources
- Rennet coagulation may occur at high pH 6.6-6.3 before any extensive acidification by starter LAB
Relationship between L.bulgaricus and S.thermophilus in yogurt
- S.thermophilus produces purines, purimidines, CO2, formic acid, oxaloacetic acid and fumaric acid
- Formic acid + CO2 are growth factors for L.bulgaricus
- After inoculation S.thermophilus grows the fastest until it accounts for approx 90% of the total bacterial cells
- Then the release of lactic acid, CO2 and formic acid synergistically stimulates L.bulgaricus to grow faster
- L.bulgaricus grows better than S.thermophilus at low pH
- The growth of L.bulgaricus in turn produces peptides + AA that stimulates the growth of thermophilus
Explain acidification of yogurt
1) During acidification, at pH 5.0, the calcium phosphate is completely released from the casein micelle, and the integrity of the micelle is reduced
2) The denatured whey proteins also interact with k-casein increasing hydrophobicity, consequently, when the micelles become unstable aggregation starts which leads to gelation
Explain the formation of metmyoglobin and reduction to myoglobin
1) The increased oxygen consumption (by growing facultative aerobes) reduces the oxygen tension on the meat surface
2) Bacteria can then form a physical barrier that limits oxygen form diffusing to the meat underneath
3) Metmyoglobin forms (brown)
4) As the microbes continue to consume oxygen, metmyoglobin gets reduced to myoglobin derivatives (bright red)
What are the steps in semidry sausage manufacture?
- reduce the particle size of the high-quality meat
- incorporate salt, nitrate or nitrite, glucose, spices, seasoning and specific starter culture
- uniformly blend all ingredients
- vacuum stuff the meat into a semipermeable casing to reduce the presence of oxygen
- incubate at or neat the starter culture optimum temperature until a specific pH point is reached
- heat (not always required) can be used to inactivate the starter culture and for pathogen destruction
- dry (aging) to the required MPR
How do you make fish sauce?
- fish is layered with salt in concrete vats at 3:1 ratio to allow supernatant to develop
- 0-25d salt penetrates fish tissue by osmosis, proteases increase the soluble protein content but this eventually stops due to AA buildup.
- The bacteria population is mostly facultative anaerobes
- 80-120d protein rich liquid develops through autolysis
- 140-200d fish tissue is converted to a nitrogen containing liquid
How do you make fish paste ?
- mix fish with salt (3:1)
- place in vats to ferment
- proteolytic enzymes from visceral tissue and to some extent from bacteria break down fish tissue into a pasty consistency
- pickle is the liquid that is released from the fermentation due to osmostic differential
- when no more pickle is released it means that the fermentation is over and the fish paste is ready
Explain the process of vegetable fermentation?
- Fruits and vegetables already harbor a variety of microorganisms including aerobic spoilage microbiota as well as yeasts and molds
- Brining vegetables results in the production of organic acids and a variety of antimicrobial compounds by LAB
- Organic acids diffuse into the brine and this results in the pH drop that influences microbial growth
- As vegetable cells die, sugars diffuse into the brine resulting in rapid growth of LAB
- In the absence of brine spoilage microbiota are able to grow and deteriorate vegetable tissue
Why vegetables must be fermented in the presence of brine?
Without brine, spoilage microbiota are able to grow. They will deteriorate the vegetable material due to elaborate destructive enzymes (proteases, lipases)
What are Leuconostocs mesenteroides, why are they important in vegetable fermentation?
1) They initiate the fermentation of several vegetables
2) They grow more rapidly than other LAB over temperature ranges and brine concentration
3) Carry out heterolactic fermentation until an acidity level of 1.5-2.0%
4) Above 22 C they will not grow
Why bacteriophages are not a problem in vegetable fermentations?
- Vegetable fermentations don’t typically use a starter culture (contrast to dairy where if it infects starter culture, the fermentation fails)
- If phages are present and inhibit 1 strain of LAB another resistant strain will grow instead
What happens to L.mesenteroides and other LAB when acidity reaches greater than 2%
- growth is inhibited
- growth of homofermentative microbes is favorized
- Lb.plantarum can survive elevating acid levels and produce exclusively lactic acids from the remaining sugars (outcompetes other LAB)
What happens at the end of the log phase of Lb.plantarum?
- little sugar left
- vegetable ferment is at an acceptable quality level to be served or canned
- lactobacillus brevis will then take over and continue fermenting until acidity 2.5-3.0% is reached and no sugar is left
How do you make kimchi?
- cut cabbage in 1/2
- soak cabbage in 5-10% brine to wilt the cabbage
- cabbage is drained
- paste of red pepper is added
- ingredients are packed into jars and held in kimchi refrigerators at temp 18C for a few days
- Cold refrigeration 1-2C
Treatment of green table olives
- strong NaOH treatment (1-3%)
- strong base reduces bitterness and reduces natural antimicrobial activities of the phenolic compounds
- makes skin of olives + permeable to allow sugars to diffuse out during the fermentation
- olives are washed in 10% NaCl
Natural black olives fermentation
- picked at a ripened state and have a softer texture than green table olives
- fermentation is much slower due to the lack of NaOH treatment
- antimicrobial phenolic compounds diffuse into the brine slowing the fermentation
- diffusion of sugars out of the olives is slower than black olives
- takes months to complete fermentation
Explain how you go from ethanol to acetic acid
- Alcohol dehydrogenase (ADH) takes electrons from the ethanol and transfers them to terminal oxidase via ubiquinone
- The oxidized alcohol becomes acetaldehyde
- Aldehyde dehydrogenase (ALDH) transfers electrons via ubiquinone to oxygen as a final electron acceptor and acetaldehyde becomes acetic acid
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Microbial Spoilage Part 133
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Microbial Spoilage Part 220
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Physical methods to preserve food48
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Acetic Acid Bacteria39
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Lactic Acid Bacteria37
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Yeasts and molds (Saccharomyces Cerevisiae)66
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Beer, wine & cider51
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Antibiotics In the Food Supply24
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Fermented Dairy Products32
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Fermented Cocoa, Tea & Coffee products52
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Fermented Meat Products20
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Fermented vegetable products53
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Probiotics22
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Chemical preservatives and Natural Antimicrobial compounds43
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Biological methods for Food Preservation37
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Foodborne Viral Infections24
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Foodborne Bacterial Infections38
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Biosecurity, Food adulteration and Food supply Protection18
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Hazard Analysis and Critical Control Points15
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Extra28
