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Food Fermentation Technology > UAS End of Chapter Questions > Flashcards

UAS End of Chapter Questions Flashcards

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1
Q

[13] Why some fermented food cause food poisoning

A
  • lack of hygiene
  • improper/incomplete fermentation process
  • not all fermenting microbes produce antimicrobial agents
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2
Q

[13] How to make sure fermented foods are safe

A
  • applying good hygiene practices
  • use safe and high quality raw materials
  • control environment and other critical factors in natural fermentation
  • add sufficient starter
  • prevent contamination when preparing starter
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3
Q

[13] tempe bongkrek and why its poisonous

A

Tempe made by soybeans and coconut pulp

Contaminated with Pseudomonas (Burkholderia) cocovenenansthat produces bongkrek acid, very toxic

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4
Q

[13] controlling aflatoxin during fermentation

A

??? make sure fermentation is long enough?

add LAB to inhibit

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5
Q

[13] why LAB most responsible

A

Produce antimicrobial agents:
- organic acids
- CO2
- diacetyl (2,3-butanedione)
- H2O2
- Reuterin
- Reutericyclin

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6
Q

[13] acidity inhibition

A

denature proteins, disrupt cell membrane permeability (destabilize outer membrane)

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7
Q

[13] do all LAB produce bacteriocin + mechanism of action

A

Not all;

Inhibition of cell wall synthesis and pore formation in the cell wall, depleting transmembrane potential and/or pH gradient, resulting in leakage of cellular materials

activity increased at low pH, high temp, presence of detergent, during log phase

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8
Q

[13] bacteriocin to inhibit G(-) bacteria

A

Has to damage their lipopolysaccharide by physical and chemical stresses (e.g. addition of EDTA)

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9
Q

[8] benefit of using microorganisms to produce EPS

A
  • produce consistent quality
  • independence of plant resources
  • independence of external factors
  • possibility of invention of new gum with unique properties (rgeological properties for food additives)
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10
Q

[8] how microbes synthesize polysaccharides/gum

A
  • secreted or synthesized directly by cell wall anchored enzymes
  • polymerized and secreted by membrane spanning multiprotein complex
  • nucleoside diphosphate sugars, acids and derivatives are direct precursors for EPS synthesis
  • ^ eg ADP glucose is formed from glucose-1-phosphate + ADP
  • glucose donated to end of growing glycogen and starch
  • polymer specific biosynthesis enzymes required
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11
Q

[8] nutrients and conditions needed to synthesize EPS

A
  • High C/N ratio
  • pH 6-7.5, NOT LOW
  • some require mineral, some inhibited by mineral
    *incubation time adjusting with when N is low, at end of log phase
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12
Q

[8] uses of SCP

A

Microbial cells grown and harvested for animal or human food ingredient, raw material or food product

  • yeast: bakers yeast
  • mold: quorn (synthetic meat made with mycoprotein)
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13
Q

[8] limitation of SCP for human consumption and how to deal

A

High nucleic acid content, which may increase uric acid levels – TREATMENT WITH RNAses

Sensitivity/allergic reaction

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14
Q

[8] choosing microbes for producing SCP

A

Use yeast or bacteria?

advantage of yeast
- better public acceptance
- lower NA content
- easier harvesting
- growth in low pH

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15
Q

[8] optimum condition for bakers yeast production

A
  • aerobic
  • 30C
  • pH 4-5
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16
Q

[8] can we use byproduct of brewing/alcoholic bev to produce SCP and how

A
  1. spent grain obtained from brewing (of grain husk and protein rick materials)
  2. drying and milling to reduce moisture and avoid spoilage
  3. enzymatic hydrolysis: to break down complex carbohydrates in spent grain to simple sugars
  4. fermentation: with yeast or filamentous fungi to convert available sugars to biomass, primarily SCP
  5. harvesting and drying of biomass (eg w centrifugation)
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17
Q

[8] example of microbes producing coloring agents

A

ANGKAK
- red pigment or yellow???
- Monascus spp.
(also monascorubamin and rubropunctatin)

ANTHRAQUINONE
- red pigment
- P. ocalicum

LYCOPENE
- red pigment
- Fusarium sporotrichoides

CANTHAXANTHIN
- orange/pink
- Monascus aureus

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18
Q

[9] principles of alcohol and acetic acid fermentation

A

sugar > ethanol + CO2
ethanol > acetaldehyde > acetaldehyde hydrate > acetic acid

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19
Q

[9] differences in fermentation of rice wine and beer

A

Rice wine
Rice > simple sugar (koji)
Simple sugar > alcohol (kobo)

Beer
Barley > maltose (malting)
Maltose > alcohol (yeast)

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20
Q

[9] producing acetic acid from rice

A

Rice as raw material

  1. cooking rice to break starch granules and disperse it and increase availability of fermentable sugars + sterilize
  2. inoculate with starter (e.g. S. cerevisiae) for alcoholic fermentation to convert sugars to ethanol. Ensure alcoholic fermentation complete before next step (concentration 10-13%)
  3. Inoculate with AAB (e.g. Acetobacter or Gluconacetobacter) for acetic acid fermentation to occur (alcohol to acetic acid)
  4. Ensure parameters: acidic environment, oxygen, temp 30C
  5. Let ferment undisturbed at 25-30C for weeks to months
  6. Harvest
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21
Q

[9] characteristic of yeast for alcohol and bread fermentation

A
  • gassing power
  • flavor development
  • stable to drying
  • stable duirng storage
  • easy to disperse
  • ethanol tolerant
  • cryotolerant
22
Q

[9] what is scoby and explain biochemical rxn

A

Symbiotic culture of bacteria and yeast
(acetobacter and various yeasts)

  • Yeast in SCOBY ferments sugars in sweet tea, mainly sucrose, concerting it to ethanol and CO2
  • Bacteria in SCOBY convert ethanol produced by yeast to acetic acid by oxidation
  • organic acids such as gluconic and lactic acid also produced
  • carbonation due to CO2 produced
23
Q

[9] diff between fermentation in western vs tropical countries

A

Western
* especially alcoholic beverages (wine, beer)
* raw material: grape and barley
* starters well characterized

Tropical
* food and alcoholic beverages
* main raw materials: starchy foods
* some are use coconut sap
* involve mold, yeast, bacteria (starters not well characterized)

24
Q

[9] control vinegar fermentation to obtain desirable concentration of acetic acid

A
  • maintain parameters (temp at 29-35C)
  • maintain adequate aeration
  • ensure alcoholic fermentation complete before proceeding (10-13%)
25
Q

[9] why alcoholic fermentation yeast done anaerobically

A

if done aerobically, yeast will utilize oxygen for respiration, forming CO2 and H2O

26
Q

[10] symbiotic growth in yogurt fermentation

A
  • Initially, streptococcus grows rapidly and forms formic acid and CO2
  • anaerobic conditions, formic acid, CO2 stimulate growth of lactobacillus (good proteinase and peptidaset systems), producing peptides and amino acids necessary for streptococcus
  • at pH 5.5 growth of streptococcus slows down
27
Q

[10] how to control undesirable microbes and promote desirable microbes in spontaneous LAB fermentation

A

Usage of salt to as a barrier to non-halophilic microbes, creating anaerobic condition to avoid growth of mold

28
Q

[10] Roles of LAB in cheese fermentation

A
  • ability to produce lactic acid in curd
  • ability to break down protein
  • ability to produce CO2 when applicable
29
Q

[10] differences between yogurt and cultured buttermilk

A

Raw material
- yogurt: homogenized milk 12%TS
- buttermilk: skim milk >9% SNF

Aeration
- yogurt: no
- buttermilk: agitated to aerate after starter culture added

Product
- yogurt: glucose, galactose (from lactose), peptides and amino acids (from proteinase and peptidase, supply necessary amino acid for Str)
- buttermilk: glucose, galactose (from lactose), CO2, diacetyl, acetaldehyde (from citrate)

30
Q

[10] roles of each microbe group in kefir fermentation

A

Mesophilic, thermophilic LAB
- acidification: convert lactose to lactic acid

Yeast
- ethanol and CO2 production by ethanol fermentation

Acetic acid bacteria
- conversion of ethanol to acetic acid

31
Q

[10] what are kefir granules/grains

A

Combination of live bacteria and yeast culture forming a symbiotic matrix of polysaccharides, proteins lipids.
Composed of:
- Mesophilic LAB
- thermophilic LAB
- Yeast
- Acetic acid bacteria

32
Q

[10] characteristics of bacterial ripened cheeses

A
  • texture ranges from semi-soft to hard
  • flavors range from mild and buttery to sharp and tangy depending on the bacteria used
  • longer ripening period compared to mold ripened cheeses
33
Q

[12] Difference between fermentation of fish sauce and soy sauce

A

Raw material
- fish sauce: low grade fish (salted, spontaneous)
- soy sauce: soybeans, cracked wheat, wheat bran

Microbes
- fish sauce:
- soy sauce: three stages (mold with koji, yeast and LAB during moromi)

Method
- fish sauce: proteolytic and LAB
- soy sauce: mold (formation of proteinases, amylases, and other enzymes; development of LAB and yeast) then brine fermentation (proteinases, amylases and other enzymes continue to work)

34
Q

[12] Role of salts in fermentation

A

Provide a barrier for non-halophilic bacteria, kill pathogenic bacteria

35
Q

[12] microbes that survive in high salts

A

halophiles

36
Q

[12] difference between high salt fermentation and lower salt fermentation

A

high salt: halophilic archaea (halobacterium, halococcus)
lower salt: tetragenococcus, halobacillus, lentibacillus, halomonas

37
Q

[12] How flavor develop during high salt fermentation

A
  • proteolysis by halophilic bacteria affects texture and flavor of fermented products by inducing formation of low Mr compounds (peptides, amino acids, aldehydes, organic acids, amines)
  • lipolysis causes the release for free fatty acids for aroma development
  • oxidation products (aldehydes and ketones) contribute to development of typical taste and flavor of product
38
Q

[11] can you make tempe witohut soaking overnight? whats the purpose?

A

No, soaking hydrates and softens soybeans, activating the enzymes naturally present in it which play roles in breaking down fats and proteins during fermentation, as well as provides an even moisture distribution for the mold to grow. it also prevents development of undesirable bacteria as acidification occurs here

39
Q

[11] microbes present in tempe during fermentation and their effect

A

molds for fermenttaion: Rhizopus spp., Mucor rouxii and javanicus, A. niger, Fusarium, Trichosporon pullulans

LAB: L. fermentum, delbrueckii, mucosae causing acidification

Acetobacter

Klebsiella pneumonia: produces vit B12

40
Q

[11] requirements of packaging used for tempe

A
  • permit sufficient O2 for growth of mold but not enough for sporulation
  • control temperature
  • retain moisture during fermentation
  • avoid free contact of free water from the bean
41
Q

[11] role of mold in cheese fermentation

A

proteolysis, lipolysis, rind formation, gas formation in certain cheeses, flavor development

42
Q

[11] what happens during cheese ripening

A

PRIMARY
- lipolysis (cat. by endogenous lipase from milk and cheese microflora)
- proteolysis (cat. by residual rennet, plasmin from milk, proteinases and peptidases from LAB and mold)
- metabolism of residual lactose, lactate, citrate

SECONDARY (development of volatile compounds)
- metabolism of fatty acids
- metabolism of amino acids

43
Q

[11] how microbes synthesize citric acid

A
  1. mutation
    mutant organisms that only use part of a metabolic pathway, or regulatory mutants who lack enzyme of a cycle
  2. inhibition of free flow of cycle through altering environmental conditions
    - medium composition: elimination of ions and cofactors
    - temp, pH
    - limited conc of Fe, Mn, Mg, Zn, Ph
    - treatment with ferro-cyanide
    - mechanical agitation, bubbled, anti foam
44
Q

[11] critical factors for citric acid fermentation

A
  • pH never higher than 3.5
  • Cu used up to 500 ppm as antagonist of aconitase
  • aeration for o2 but not too much
  • fermentor made of acid resistant materials
45
Q

[14] can you expect to get probiotic effects if you buy yogurt using common yogurt bacteria? howe to make traditional yogurt to probiotic yogurt?

A

No because the bacteria are not resistant to bile in the small intestine whereas to be considered a probiotic it has to resist upper GI tract to adhere to and colonize intestinal cells

  • add probiotic with starter culture or used as starter culture but fermentation will be longer
46
Q

[14] what is probiotic? benefits? how to get probiotic microbes?

A

live microbes that when administered in adequate amounts confer health benefits to host

prevent diarrhea, alleviate lactose intolerance, modulation of immune system, prevent IBS, obesity, allergic reaction, regulate blood tension

obtained by isolation from humans or LAB isolated from fermented foods

47
Q

[14] why probiotics have to resist upper GI tract?

A

the microbes have to adhere to and colonize human intestinal tract such that the bacteria can produce antimicrobial substances, antagonize carcinogenic/pathogenic organisms and provide other phisiological health benefits

48
Q

[14] example of health benefits of fermented milk and corresponding bioactive compounds

A
  • probiotics: enhance digestion, alleviate GI disorders
  • lactic acid: inhibit growth of harmful bacteria in gut
  • bioactive peptides: antioxidant, antimicrobial, blood pressure regulating
49
Q

[14] why health benefits of tempe > soybeans

A
  • decrease if antinutritional factors (trypsin inhibitor)
  • enzymes break high Mw substants to low (improve digestion)
  • bioactive compounds (ergosterol)
  • more bioactive peptides
50
Q

[14] example of other fermented products with health benefits

A

kimchi, kombucha

Food Fermentation Technology (4 decks)

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