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37 Cards in this Set
- Front
- Back
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Main starter cultures in dairy
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Lactococcus lactis
Propionic freudenreichii/P. jensenii, P. acidopropionici (Swiss cheese) Streptococcus thermophilus (cheese sometimes, yogurt main) Lactobacillus bulgaricus (excessive acid- important in yogurt) Lb. casei (sometimes yogurt/cheese adjunct) Brevibacterium linens (surface ripened cheese) Staphylococcus/Enterococcus: opportunistic pathogens Molds: penicillum roqueforti, P. camemberti |
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Common pathogenic bacteria in dairy
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E. coli- enteroinvasive and enterotoxigenic
Listeria monocytogenes- brie, mexican-style, Mont d'Or; able to grow at fridge temperatures, especially in low heat treated samples Salmonella typhimurium- cheddar (1984) Salmonella javiana- mozzarella (1989) Staphylococcus & enterococcus- opportunistic pathogens, naturally present |
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Sugar utilization in dairy
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Utilize lactose (glucose and galactose)- glucose used faster than galactose by Lactococci species.
Homofermentation via glycolysis- lactic acid only end product Heterofermentation via pentose phosphate pathway, mixed end products involving CO2, lactic acid and other C2 compounds (ethanol, acetic acid etc..) Citrate- fermented to diacetyl via permease Proponic acid- limited to swiss-cheese and propionic bacteria, ferment lactic acid to propionic |
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Sugar transport in LAB
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Utilize PEP-dependent PTS
Lactose is phosphorylated by plasma and cytoplasm enzymes and carried into the cell Enz II and Enz III are sugar/lactose specific |
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Proteolytic system in dairy
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Utilize nitrogen source from milk- peptides provided from casein and whey (mainly casein)
Supports rapid growth of LAB |
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Synergistic relationship in yogurt
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L. bulgaricus and S. thermophilus- L. bulgaricus provides the amino acids necessary for the weakly proteolytic S. thermophilus, S. thermophilus generates CO2 and formic acid necessary for L. bulgaricus growth
L. bulgaricus provides most of the lactic acid in yogurt (4%), S. thermophilus only 0.6-1.1% |
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Vegetable fermentation principles
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Triggered by natural fermentation with a definitive LAB sequence requirement- under appropriate conditions most vegetables with undergo a spontaneous lactic acid fermentation.
No heat process to inactivate flora. LAB minor population but dominant in successful product |
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Sauerkraut microbial succession
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Starts with coliforms (like Klebsiella and Enterobacter sp.)
Then heterofermentation via Leuconstoc mesenteroides- reduces the pH and creates anaerobic environment via CO2 production Then combination of hetero LAB- Lb. brevis, and homo Lb. plantarum and Pediococcus cerevisiae |
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Spoilage of sauerkraut
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G-coliform and pseudomonas types undetectable for a few days, molds/yeast responsible for "spoilage" and over-softening.
Common defects- discoloration (autochemical oxidation), loss of acidity, off-flavors and odors (moldy, yeasty, rancid), slimy, softened and pink-color (due to aerobic growth of molds and/or yeasts) |
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Pickle Manufacturing principles
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Rely on salt, oxygen exlusion, anaerobic environment for the growth of less diverse microflora
Brine instead of dry salt- salt concentration higher than in sauerkraut- brine inhibitory to coliforms/other non-LAB and L. mesenteroides Fermentation initiated by Lb. plantarum and Pediococcus sp. De-salted after fermentation |
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Defects in pickles
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Bloaters and floaters- excessive gas pressure, internal cavity formation, LAB (heterolactic, malolactic fermentation), coliforms, yeasts.. L. mesenteroides unwanted.
Controlled: removed dissolved CO2 by flushing or purging with nitrogen gas Destruction and softening- slippery, loses crispness and crunch, cannot be used, from pectinolytic enzymes from M/Os FUNGI- penicillum, etc. Controlled via increased acidity |
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Fermented Olives- overview
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Spanish-style:
Treated with lye-reduced initial microflora but first 2-4 days are coliforms, pseudomonas, bacillus, clostridium can still grow (stage one) Stage 2- L. mesenteroides and Pediococcus sp.: pH drops below 5 and inhibits non-LAB Stage 3: (2-3 weeks later) Lb plantarum, Lb brevis, Lb fermentum.. plantarum dominant Final- facultative yeast possible (produce ethanol) Greek-style: Not lye-bitter treated. Fermentation of natural flora- mixed end products, less acidic Black or green style: Not fermented, lye-treated- go through oxidation to produce color |
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Alcoholic fermentation cultures
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Saccharomyces cerevisiae- wine and ales. In ales, faster, warmer top-down fermentation
Saccharomyces pastorianus- lagers, slower, cooler, bottom-up fermentation Kloeckera apiculata- natural flora on grape skins (wine) |
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Alcoholic fermentation process
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Basic: sugars (from malted grains or grapes) converted to ethanol
In red wine- warmer (20-30C) In white wine- cooler (7-20C) Wine also has malolactic fermentation via Oenococcus oeni- malic acid to lactic acid- necessary for acid control |
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Spoilage in beer/wines
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Beer: "skunking" oxidation of hops from sunlight, contamination from unwanted LAB, non-LAB, yeasts, etc (gives yeasty flavor or worse), DMS formation from in proper wort boiling
Wine: off-flavors from unwanted LAB or yeast strains |
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Vinegar fermentation- raw materials/process
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Can start from any fruit, grain, mash (alcohol-containing), beer or wine.
Has to result from "acetous" fermentation of ethanol Contains at least 4g of acetic acid per 100mL Step one: alcoholic fermentation (Alcohol-> acetaldehyde-> acetic acid *via alcohol dehydrogenases*), oxidative fermentation of ethanol oxidized with air to acetic acid and water If sugar is the starting point should use yeasts (s. cerevisiae) Step 2: acidification Acetic acid bacteria (acetobacter, gluconbacter, gluconoacetobacter, acidomonas). |
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Vinegar fermentation- requirements and troubleshooting
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Requirements: usually doesn't need addition nutrients, ammonium phosphate sometimes added to apple cider vinegar, water free from chlorine, and if its distilled additional nutrients added in.
Troubleshooting: Lack of oxygen- significant cell damage (10-100%) time dependent Lack of ethanol- causes severe damage to cells Changes in temperature- too quickly can cause cell damage. Over-oxidation- undesirable oxidation to CO2 (automation) **all affect growth rate |
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Sausage fermentation starters
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Pediococcus- most common LAB, homofermentative with short lag phase.
Lb. plantarum- best for dry sausage (ferments better between 60-90F) Micrococci- not as common, reduces nitrates and nitrites to nitric oxide, reduces H2O2 and prevents fat and color oxidation Non-pathogenic staphylcoccus- lipolytic and proteolytic- reduces nitrates and nitrites. Not as common for obvious reasons. |
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Sausage fermentation- microbial ecology and considerations
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Use of natural flora- no pre-processing because of naturally rich starting substrate (lots of amino acids available)
Addition of dextrose as fermentable sugar Want to lower pH below 5.0 in end-product! |
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Use of chemical acidulants in sausage
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Shorter process time
Glucono delta lactone (GDL): reduces pH, cold fermentation, produces gluconic acid in contact with moisture- mild flavor. Encapsulated citric acid: Gives citrus flavor, reduces pH- doesn't contribute to moisture loss, never grind or add water to mix Encapsulated lactic acid: Gives lactic acid flavor, reduces pH, doesn't contribute to moisture loss, never grind or add water to mix |
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New cultures used in sausage and protective cultures
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Molds: to establish the traditional white bloom on the surface of genoa salami, pencillum chrysogenum and penicillum nalgiovensis used.
Protective cultures: bacteriocins from lb and pediococcus- inhibit L. monotocytogenes *Nisin and pedocin most common- added to the inside of casings and packing films |
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Bread fermentation- starter cultures
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Yeast cultures used- S. cerevisiae or bakers' yeast
--gas producing, flavor development, stable to drying (want viable), stable during storage, easy to dispense, can handle ethanol present, cryotolerant. *Available as a cream (highest viable), cake, or dry active yeast (most common in home bread making) * ~5% contaminating LAB If lab added deliberately, lower pH to below 4 and cause distinctive sour but appealing flavors/better preservation Lb. sanfranciscensis and Lb. brevis- Sour dough specific |
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Bread fermentation- spoilage
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Molds and yeast forming spores?
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Bread fermentation- ingredients/nutrient sources
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Sugar/Carbohydrates- comes from wheat (most common), other cereal grains..
75% of total weight- largely starches (amylose and amylopectin) Amino acids- from wheat flour protein. High protein flours work best in breads, low protein flours work best in cakes, cookies and pastries. Proteins: gliadin and glutenin ~85%- when hydrated and mixed form gluten. Water- solvent to hydrate flour Salt- toughens the gluten Other ingredients added as functional properties- i.e. emulsifiers, biological preservation, vitamins |
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Bread fermentation-fermentation, sugar metabolism, end-products etc.
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Lag phase usual- Bakers' yeast is facultative metabolism, aerobic (via TCA) or anaerobic glycolytic fermentation- becomes anaerobic due to evolved CO2, ethanol-forming, reduction rxn generates NAD, necessary to maintain glycolysis.
Transport and utilization: Sequential use-regulation: glucose represses enzymes involves in maltose transportation, maltose represses invertase expression, mutants available. Sugar transport- invertase: convert sucrose to fructose and glucose GLYCOLYSIS- end products: CO2, various acids and organic compounds by the yeast/LAB- flavor and texture properties |
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Koji and tane
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Essential for many Asian fermented foods- koji is a moldy mass of grain (usually rice) (mixed culture starter). Tane koji is a dried koji that has been allowed to spore.
Manufacture of koji- many types, correspond to specific products or raw materials. Function- source of enzymes converting non-fermentable substances into simple products (starch, proteins, lipids, cellulose, pectin..) |
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Sake/Alcoholic rice beverages
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Manufacture process is close to beer brewing- start with starch conversion to simple sugar,(rice= mold gives amylase).
Starch--(mold)->simple sugar--(yeast)-> alcohol+ spent grain |
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Sake Manufacturing
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Raw materials prepared:
Soybeans soaked, cooked (steam)- denatured soy protein are hydrolyzed by fungal proteinases. May contain roasted wheat kernels (more starch) M/Os: Pure culture containing spores of Aspergillus oryzae and/or A. sojae- or inculated with tane koji (rice koji with starter spores). Mix & incubate: OXYGEN! and moisture circulation- temperature control is important for proteolytic and amylase enzymes. Process takes days. |
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Soy Sauce Manufacturing
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Soybean (or defatted soybean meal or flakes)- moistened, cooked, mixed with roasted and crushed wheat (increase CHOs).
Inoculate with starter (tane koji, chung chu) 0.1-0.2%- A. oryzae, A. soyae. Incubate in shallow wooden box (oxygen=^mold growth) at 30C for 24 hours followed by high temp (up to 40C) for 72hours. Molded mixture- shoyu koji, dark green, please aroma, high activity of proteases and amylases. BRINE fermentation! Mashing- process when koji enzymes hydrolyze proteins, polysaccharides etc- start from high salt brine:solid materials, high salt restrict growth of most microbes (except halo/osmotolerant) Mash known as moromi- ferments in large tank for up to one year |
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Soy Sauce- Moromi enzymology
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A. oryzae and A. sojae produce lots of enzymes/lower temperature gives greater activity (20-35C)-
Proteinases, peptidases, cellulases, amylases. Funal proteinases and peptidases: wide pH range, salt tolerant- release glutamic acid (flavor), nearly complete hydrolysis of soy proteins- for subsequent LAB and yeast fermentation, color and flavor development. Amylolytic enzymes- same concept as beer, substrate for fermentation Other enzymes- tissue degrading, enhance substrate extraction, increase yield and nutrient availability, formation of pentose and browning sugars |
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Soy Sauce- Fermentation
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Mash contains Aspergillus strains and yeasts and bacteria- addition of salt brine, fungi salt sensitive (die)
Micrococcus and Bacillus start high, LAB and yeast start low- salt sensitive (micrococcus, wild yeasts and bacillus) die. Lb delbrueckiim, tetragenococcus halophilus- high after 6-8 weeks Yeasts: zygosaccharomyces rouxii, candida versitalis dominant when pH <5 FERMENTATION generates: complex flavors/end products- LA, ethanol, CO2, other alcohols, esters, furanones, flavor volatiles etc. Pasteurization inactivates enzymes and enhances color and concentrates flavors. |
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Soy Sauce Spoilage and Defects
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Hard to spoil true soy sauce, but non-fermented soy sauce-
add benzoate, ethanol: inhibit fungi Excessive browning during mashing or aging Formation of undesirable compounds: isobutyric acid and isovaleric acid during prolonged storage |
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Miso starting materials
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Fermenting cereals, soybeans and salt with molds, yeasts, and bacteria. Rice miso, barley miso, soybean miso
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Tempeh basics/starting cultures
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Mold-fermented soy beans- contain B12, uses bacillus from fungi to bind the beans together. Endogenous flora- acid produced by LAB select for acid resistance- controls pathogens, low pH also achieved by adding organic acids.
Inoculate with spores of Rhizopus oligosporus!! Wild culture may also contain: R. oryzae, R. stolonifer, R.microsporus.. |
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Tempeh fermentation/biochemistry
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R. oligosporus responsible for biochem changes.
Lipids and proteins serves as substrate- fungi excretes lipases and proteinases. 1/3 lipids, 1/4proteins degraded. **pH increases to above 7 (example of when pH increase is beneficial) |
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Tempeh nutritrion/safety
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Concentration of major macronutrients decreases due to enzymatic hydrolysis (more digestible, but not protein efficient).
Decrease in undesirable soy oligosaccharides Increase in vitamins (B12, B2, B6/biotin, pantothenic acid, folic acid increased by non-starter) B1 decreased. Decrease in anti-nutritional factors by soaking and enzymatic degradation (examples: tripsin inhibitors, tannind, phytic acid, goitrogens). No mycotoxins! |
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Tempeh spoilage and defects
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Okay if eaten within a day or two= "fresh product"
Otherwise- high pH means other bacteria can grow Shelf-life short at room temperature (freezing preferred) |
