review session deck Flashcards
Describe beer fermentation
Beer consists of malting, milling, mashing, addition of hops, followed by cooling and storage.
1) Malting is the process of letting the grains, usually barley, to sprout/germinate. The barley is soaked, dried, and soaked again followed by air drying to allow dispersion of CO2, which promotes germination. 2) Milling is the process of crushing up the germinated/already sprouted grains to make nutrients more available. 3) Mashing is the process of taking the milled barley, adding brewing water, and mixing the two to allow a fermentable extract to be produced. Extracting these sugars from the germinated spores allows yeast to utilize these carbohydrates and convert them into ethanol. The fermentable extract also promotes growth of yeast. The end product of mashing is the wort. 4) Addition of hops: hops are added to promote a desired level of bitterness, or a particular fruity or citrusy flavor. There are 3 varieties of hops: alpha (flavor), aroma, and dual purpose hops. The hops are boiled with the wort an hour before the beer is cooled down. 5) Cooling: cooling of the finished beer product is done to prevent formation of fusel alcohols which gives off-flavors
Describe wine fermentation
Wine making consists of sampling, harvesting, crushing/pressing, fermentation (of the grapes), blending, stabilizing, aging, filtration, bottling/labelling, and then consumption.
○ Depending on whether or not red grapes or white grapes are being used, there could either be a pre-fermentation step where the skin of the grapes are removed (for white wine), or a post-fermentation step after inoculation.
- sulfur dioxide is added once the grapes are crushed to get rid of wild yeast
○ In the initial process of wine fermentation, there is a lag phase for the first few hours followed by a short growth phase that lasts 24-36 hours
○ Sugar is converted into ethanol (by yeast) which most of occurs during the stationary phase of wine making (after the short growth phase). During the stationary phase, is where most of the yeast activity is occurring, but also the yeast population begins to decrease. Sugars degrade and produce ethanol and Carbon Dioxide.
○ Yeast activity is 90% viable until all the sugar is depleted
○ Ethanol and carbon dioxide are the two products produced by yeast, which provide metabolites and aroma compounds
○ In the case of chardonnay making, a particular type of wine, malolactic fermentation occurs which is the conversion of L-malic acid to L-lactic acid and Carbon Dioxide.
○ During the rapid exhaustion of sugars, it is important that anaerobic conditions are maintained to prevent AAB contamination, as well as sulfiting to promote anti-oxidative and antipeptide activity.
Describe cider fermentation
• Cider
○ First step of cider making is to squeeze the juice out from the apples
○ Send the juice into a settling tank, where at cool temperatures, the juice will begin to undergo fermentation
○ During this fermentation, naturally occurring yeast in the apple juice will convert the sugars into ethanol
○ Yeast is then filtered out
describe chocolate/cocoa bean fermentation
• Chocolate
○ The pulp layer containing a high amount of rich carbohydrates and pectin, with a low pH of 3.0-4.0, provides an anaerobic environment allowing yeast to convert these carbohydrates into ethanol. In addition, pectinolytic enzymes are also present at this initial stage of fermentation because they are produced by the yeast. They function to break down pectin in the pulp layer, allowing more air to come in which then allows LAB to grow and convert available sugars into lactate, carbon dioxide, and acetic acid. As ethanol production increases via anaerobic alcoholic fermentation of the yeast, acetic acid bacteria then start to grow after LAB, producing more acetic acid. At some point, so much acetic acid is produced, that it causes the death of the embryo, concluding the fermentation.
Cocoa bean death is critical because it prevents germination, which would use valuable components of the cocoa bean, i.e., cocoa butter. It also allows for the necessary biochemical reactions to occur to produce the wanted flavor to develop. Lastly, death of the cocoa bean also allows cellular membrane components to leak out and permit enzymes and substrates to react to form flavor precursor compounds.
Describe coffee bean fermentation
• Coffee
○ Coffee fermentation can occur via dry processing, wet processing, or honey processing. Dry processing yields natural coffee and wet processing yields washed coffee. In dry processing, the coffee beans are dried in the sun where the pulp and mucilage layer is broken down by yeasts and pectinolytic molds. Pectinolytic molds include: Fusarium, penicillium, Aspergillus, and Bacillus. LAB then start to grow and contribute to the degradation of the pulp layer via homolactic fermentation and heterolactic fermentation. During the drying stage, the sugars and flavors are absorbed by the bean.
○ Wet processing is when the pulp layer of the bean is mechanically removed, allowing for fermentation of the bean. The mucilage layer is converted into water-soluble products by yeast, pectinolytic enzymes, and LAB. The resulting water-soluble products are then washed off, prior to final drying.
describe cheese fermentation
• Cheese
○ Raw milk is taken and pasteurized, followed by inoculation of LAB. The milk is heated and then coagulation occurs, either by acid coagulation, acid/heat coagulation, or rennet coagulation. If by acid coagulation, curd contraction occurs via LAB growth resulting in a higher acidic environment. As the acidity increases, casein micelles are cleaved which allows for H-atoms to bind to the outer structure of the casein protein. As more H-atoms bind to casein, the hydrophilicity of casein decreases which causes the expulsion of whey proteins. Due to the loss of hydrophilicity, the casein matrices separate from the rest of the milk’s constituents, promoting curd contraction. Acid coagulation usually results in cheeses like cottage cheese that have a very short shelf-life.
○ Acid/heat coagulation occurs by applying heat to moderately acidified milk (pH: 6.2-5.4) which causes the denaturation of whey proteins. Due to whey proteins denaturing, they lose their ability to interact with water. Hydrophobicity rises and increases curd formulation.
○ Rennet coagulation occurs via adding an enzyme known as, rennet. Rennet is a group of proteinases that cleave casein micelles at the surface, when added to milk. K-casein is what is specifically cleaved, which causes more hydrophobicity and initiation of coagulation. Rennet can be derived from a plant, animal, or microbial source.
Cutting, cooking, dripping & draining, knitting, pressing, aging
describe sauerkraut fermentation
• Sauerkraut
○ Sauerkraut fermentation begins when chopped up cabbage is placed in a closed container (anaerobic environment) with a brine solution. To start, cabbage is chopped up and massaged with non-ionized salt. When put into a container with a tightly sealed lid, the brine works to expel organic acids and sugars from the cabbage leaves. This process of brining favors growth of LAB which can then convert these sugars into lactic acid. In the beginning of the sauerkraut fermentation, during the first 24-48 hours of fermentation, heterolactic fermentation occurs via the presence of Leuconostoc mesenteroides. L. mesenteroides initiates the fermentation and serves as a viable species of LAB because they are resistant to acidity, and can grow in a wide range of temperatures (5-35C). However, as the acidity increases during sauerkraut fermentation, the reaction switches from homofermentative to heterofermentative. The two critical heterofermentative species in sauerkraut fermentation are Lactobacillus plantarum and Lactobacillus brevis. These two species of LAB can survive even higher acidic concentrations than L. mesenteroides. By the end, fructose and glucose are depleted and conditions are very acidic.
describe kombucha fermentation
• Kombucha
○ Kombucha fermentation is begun by back-slopping, by taking a previously made SCOBY and putting it in a solution of tea and water. SCOBY is a thin cellulose pellicle that floats on the surface of the product, preventing contamination and providing nutrients for the bacteria involved in kombucha fermentation. It contains a mixture of several species of yeast, AAB, and LAB.
○ After making SCOBY, fermentation first begins with alcoholic fermentation and then acetic acid fermentation. Alcoholic fermentation of kombucha is mainly carried out by Saccharomyces cerevisiae due to its efficiency. Saccharomyces cerevisiae convert sugars from the SCOBY into ethanol which can then be utilized by acetic acid bacteria for oxidation to create acetic acid. The acetic acid fermentation lowers the alcohol content, which is why although there is alcoholic fermentation in part of kombucha making, the product contains a very low amount of alcohol.
describe kefir fermentation
• Kefir
○ Fermentation begins by first inoculating the milk with kefir grains
○ Kefir grains consist of water-insoluble kefiran that is an extracellular polysaccharide produced by LAB. The kefir grains are used to start a culture via back slopping
○ Addition of yeast is done to enhance the performance of lactobacillus kefiranofaciens which produce kefiran. This a symbiotic relationship that is beneficial for the process of kefir fermentation.
○ LAB in kefir generally include Lactobacillus, Lactococcus, Streptococcus, and Leuconostoc
○ Yeasts include saccharomyces, Kazachstania, and Torulaspora.
What is scombroid food poisoning?
• A foodborne intoxication that results from eating spoiled fish
• Results in similar symptoms to an allergic reaction due to too much histamine from the spoiled fish being ingested
• Results from improper storage of the fish, causing microbial growth, resulting in the production of biogenic amines, i.e., histamine
Anti-histamines can be taken to alleviate symptoms of scombroid food poisoning
what is ethylene?
- Compounds that promotes aging of fruit tissue
- Ethylene is secreted out from the fruit and therefore has the ability to age tissues in other fruit
- This is a non-reversible reaction
what is appressorium?
A formation at the end of the spoilage fungi’s germ tube. This structure is used to attach to and penetrate plant surfaces by mechanical pressure, initiating fungal spoilage
What is phytoalexin?
• Small molecules produced by plants in response to PAMPs on bacteria
Explain the biochemistry of the brewing process?
- Lag phase: glucose, fructose, and sucrose are starting to be utilized by yeast
- Logarithmic phase: high consumption of these sugars by yeast, ethanol is increasing, and the pH has dropped somewhere between 3.7 and 4.2
- Retardation phase: most of the sugars have been consumed. pH is at a constant level now between 3.7 and 4.2 and is not continuing to decrease. Maltose has been utilized by yeast for conversion to ethanol. Temperature has peaked to 37C.
- Stationary phase: yeast activity is still prevalent, overall temperature has decreased to around 16C. Specific gravity has reached its level at around 3.6. Fusel alcohols have been produced.
in terms of acetic acid, what happens in the diauxic growth curve?
- Ethanol is being oxidized exponentially during the log phase, producing an acetic acid content at around 1.4%.
- The acetic acid content increases a little more during the transition phase and overoxidation phase to a level of 1.5%
- A diauxic growth curve is present when the initial ethanol concentration is below 1%
- Is the starting ethanol concentration is above 3%, overoxidation does NOT happen, since the products of the fermentation (acetic acid) is too high and kills the cells.
important species of AAB?
acetobacter, gluconobacter, gluconoacetobacter, komagateibacter
explain the relationships between the D value, Z value, and F value
• Z value:
○ Change in temperature required to change the D-value of a microorganism by an order of magnitude (10-fold)
• D value:
○ Represents the time it takes for a 10-fold reduction to occur in the number of survivors at a given temperature.
• F value:
The time it takes, in minutes, at a specified temperature, required to achieve a targeted reduction in a homogenous population having a specific z value
What value is the most important to the commercial canning industry?
The F-value: 2.52 minutes
Compare and contrast aseptic processing with canning?
• Aseptic processing is used industrially where foods and cans are sterilized separately and then foods are packaged under aseptic conditions
what is humectant?
A substrate used to lower the water activity, in efforts to restrict microbial growth
Define Reappertization? Radicidation? Radurization?
• These three methods are all ways to preserve different foods at different levels, by using three different dosing methods.
○ Redappertization: using a high dose, used in commercial sterility, 10-75 kGy
○ Radicidation: using a medium dose to produce an equivalent effect to thermal pasteurization - effective against vegetative bacteria but not against spores (1-10kGy(
○ Radurization: involves low dose irradiation to control the presence of insects in grains or to stop the sprouting of potatoes, or delay fruit ripening (0.05-1kGy)
What does HPP stand for?
○ HPP stands for High Pressure Processing
○ (involves treating food with pressures in the range of 100-600 Mpa, which will inactivate most bacteria, yeasts, molds, and viruses
Define bio preservation
Bio preservation is the use of microorganisms, and/or their metabolic products, to preserve foods. (excludes fermentation)!!
Involves the use of bacteriocins, bacteriophages, and controlled acidification where acid is produced by LAB in temperature-abused foods
What is controlled acidification?
where acid is produced by LAB in temperature-abused foods
What is the Wisconsin Process?
The use of less nitrites, 0.7% sucrose, and LAB in bacon, instead of using a high amount of nitrites which would turn into carcinogenic nitrosamines. LAB ferment the sucrose, producing lactic acid which is what preserves the meat.
Define bacteriocin
○ Antimicrobial peptides of bacterial origin
○ Inhibit pathogens of serious concern by drastically increasing the permeability of the targeted cell, causing membrane degradation and cell death
○ Categorized into 4 classes
Define colicin
Proteins produced by, and are toxic for, some strains of E. Coli
Come from a colicinogenic plasmid that bears the genetic determinants for:
-Colicin synthesis
-Immunity
-Release
Can be divided into two groups: enzymatic colicins or pore-forming colicins`
Legally, how is food adulteration defined?
Intentional or unintentional addition of food
When a food product fails to meet legal standards
Is spoiled food safe to eat?
- Can or cant be- depends on socioeconomic factors
- There are situations where it is actually dangerous - C. botulinum
Which genus of bacteria is considered to be the best at attaching to meat?
Pseudomonas
What are some signs of microbial spoilage?
Greening, off-flavor, slime
What are some characteristics of the ideal spoilage indicator?
Off-flavors, off-odors, off-texture, off-discoloration, and slime
What happens, in terms of meat spoilage, if the animal is exercised before slaughter?
○ Microbial spoilage will occur faster due to depleted levels of glucose. Glucose will be utilized much quicker leading to a faster time until amino acids are broken down which leads to spoilage indicators quickly after the slaughtering process.
What is scombroid food poisoning?
Scombroid food poisoning is the result of eating spoiled fish, leading to a high ingestion of histamine which causes similar symptoms to an allergic reaction
How does the lactoperoxidase system work?
Inhibits microbial growth in cow’s milk by catalyzing the oxidation of thiocyanate in the presence of hydrogen peroxide, yielding hypothiocyanite, which is a highly reactive oxidant, and is antimicrobial.
Why is it important to refrigerate milk prior to pasteurization? Why or why not?
Prevents production of heat-stable toxins, which are able to survive pasteurization.
Also prevents the overall growth of Psychrotropic bacteria (usually aerobic Gram-negative rods)
