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Y2S1_FST2110 - Microbiology and fermentation > Lect 4 : Food Spoilage Pt 2 > Flashcards

Lect 4 : Food Spoilage Pt 2 Flashcards

1
Q

What is food spoilage often associated with?

A

it is often associated with organoleptic defects

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2
Q

What kinds of organoleptic (sensorial) defects can arise from food spoilage? [6]

A

TASTE
1. Acidity
2. Changes in taste

SMELL
3. off odours

SIGHT
4. swelling packaging due to gas formation
5. Slime formation
6. Discolouration

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3
Q

RECALL : What are the 4 different spoilage indicators?

A
  1. Total colony count (aerobic / anaerobic)
    - NOTE : cant have total count of BOTH aerobic and aerobic bacteria bc the envt (in packaging or storage) either have or dont have oxygen to inhibit growth of certain MO
  2. Total aerobic/anaerobic count of SPORE-FORMING BACTERIA AND/OR SPORES
  3. LAB
  4. Yeast
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4
Q

Food spoilage show correlation with sensorial defects. As total colony count increases, what sensorial defects are observed?

A

Off odours are smelt first –> when grow to even higher levels, observe slime formation

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5
Q

How does initial level of contamination affect rate of food spoilage?

A

The higher the inital level contamination from MAINLY PSYCHOTROPHIC bacteria, the faster the rate of spoilage

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6
Q

MEAT AND POULTRY

What are th intrinsic factors of meat which causes microbial growth?

A

◡̈ High wter activity
◡̈ High in protein
◡̈ High in vit and minerals
◡̈ netural pH of 5.5-7.0

limiting factor for bacteria
ᴖ̈ Low in carbs (and therefore glucose)

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7
Q

MEAT AND POULTRY
The spoilage process of FRESH meat stored in AIR occurs in 2 steps. What are they?

A
  1. Depletion of glucose (rate of depletion determines the rate of spoilage)
  2. Degradation of amino acids (since MO need to digest amino acids to be able to utilise them) –> leading to metabolites such as amines and H2S.
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8
Q

MEAT AND POULTRY

There are 2 main sensorial defects in fresh meat stored in air. At how many CFU can these sensorial defects be observed?

A
  1. Off-odours at 10^7 CFU
  2. Slime formation at 10^8 CFU AND water activity of ±0.99
  3. Discoloration
    - green slime forms due to H2S ad myoglobin reacting

(myoglobin : oxygen and iron binding protein which stores O2)

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9
Q

MEAT AND POULTRY
There is a possibility that fresh meat turns brown in air. Is this a sign of discoloration (i.e. a sign of spoilage)? Explain

A

No, fresh meat turning brown is not considered discoloration and not considered spoilage.

Brown meat is due to :
1. less O2 in meat
2. oxidation of Fe2+ in oxymyoglobin to Fe3+ metmyoglobin

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10
Q

MEAT AND POULTRY

What temperatures can meat spoil at and what kind of MO causes the spoilage at those specific temps? [2]

A
  1. < 7°C : caused by psychrotrophic bacteria [SPA]
    - Shewanella
    - Pseudomonas
    - Acinetobacter-Moroxella
  2. Spoilage at 10°C [LE]
    - LAB
    - Enterobacteriaceae
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11
Q

MEAT AND POULTRY

What is the name of meat that is associated with :

  1. low pH (lower than normal meat)
  2. high pH (higher than normal meat)
A
  1. PSE meats (pink, soft, extrusive)
  2. DFD meats (dark, firm, dry)
    pH > 6.2
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12
Q

MEAT AND POULTRY

How does the pH in PSE and DFD meat correlate with levels of glycogen in pigs before slaughter?

A

PSE has lower pH –> more H+ –> there is more glycogen before slaughter –> after slaughter, muscles undergo postmortem and still respire mainly anaerobically –> more glycogen reduced into glucose which is further reduced into lactic acid by LAB

  • pigs were stressed before slaughter –> causing glycogen to increase

DFD meats : glycogen levels were low before slaughter
- due to long-term exhaustion of pigs, causing glycogen to be converted into energy

  • less glycogen = less glucose = less lactic acid = less H+ = lower pH
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13
Q

MEAT AND POULTRY

How can fresh meat be preserved? What is the idea behind it?

A

Vacuum packaging

  • Idea is to remove most of the oxygen, with ~21% of oxygen left and more CO2 –> prevent aerobic bacteria from growing (Psuedomonas, Acinetobacter-Moraxella)
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14
Q

MEAT AND POULTRY

If vaccum packaged meat is stored after some time, what will be the composition of O2 / CO2 in it?

A
  • Residual O2 will be used up to <1% due to tissue respiration in meat (still possible! but v little)
  • CO2 : 10-40% (increase as it is a product of tissue respiration)
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15
Q

MEAT AND POULTRY : FROZEN MEAT

What kind of spoilage is possible at -5°C to -10°C, -18°C and -24°C for frozen meats?

A

-5°C to -10°C : mould growth, black spots

-18°C
- no microbial spoilage
- enzymatic spoilage

-24°C
- no enzymatic and microbial spoilage possible

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16
Q

MEAT AND POULTRY : RAW CURED MEAT

What 2 strategies are used to cure raw meat? What is the rationale behind it?

A

salting + drying

Rationale : reduce water activity to inhibit microbial growth

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17
Q

MEAT AND POULTRY : RAW CURED MEAT

What 3 kinds of MO can still survive on raw cured meat?

A
  1. LAB – highly competitive!!
  2. Salt tolerant micrococci
  3. Moulds – can grow at low water activity

[LSM]

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18
Q

MEAT AND POULTRY

What is the benefit of raw cured meat? [in terms of sensory property]

A

it has a better taste

  • the action of microbes on raw cured meat is more lipolytic (break down lipid) rather than proteolytic==> fatty acid to provide flavour
  • recall : break down of protein eventually results in degradation of amino acid into H2S –> may cause off flavour
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19
Q

MEAT AND POULTRY
What are the 3 sensorial defects that tells us the raw cured meat is spoilt?

A
  1. off odour
  2. slime formation
  3. off flavour
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20
Q

FISH, SHELLFISH AND MOLLUSCs

What are the intrinsic factors that make seafood vulnerable to microbial spoilage?

A

◡̈ high in vit and minerals
◡̈ high water activity
◡̈ neutral pH
◡̈ RICH IN N-COMPOUNDS!
- Protein
- Protein free N fraction : TMAO (Trimethylamine oxide) , urea, peptides, a.acids, nucleic acids)

CARBOHYDRATES
◡̈ for molluscs : high
ᴖ̈ for shellfish and fish : low

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21
Q

FISH, SHELLFISH AND MOLLUSCs

Why is a non-protein N fraction beneficial for MO survival?

A

It is smaller than proteins, making them easier to digest

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22
Q

FISH, SHELLFISH AND MOLLUSCs

What is the main type of MO that causes spoilage in seafood? (bacteria/yeast/mould)

What 4 species of MO cause spoilage?

A
  1. Bacteria (95% of spoilage is bacterial, 5% autolytic aka enzymes found in seafood)

[PASE]
Pseudomonas
Acinetobacter-Moraxella
Schewanella
Enterobacteriaceae

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23
Q

FISH, SHELLFISH AND MOLLUSCs

What are the 2 phases of spoilage in seafood, specifically fish and shellfish?

A
  1. Breakdown of TMAO (regulates osmotic pressure in seafood) into TMA (1 O atom removed)
  2. Break down of amino acids
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24
Q

FISH, SHELLFISH AND MOLLUSCs

What is the important spoilage inidcator in seafoods, and how to calculate?

What are its units

A

Total volatile bases (TVB) = TMA + DMA (dimethyl amine) + amines + ammonia

units : milligrams (mg) of N / 100g of meat

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25
Q

FISH, SHELLFISH AND MOLLUSCs

Do shellfish spoil faster or slower than fish? Why?

A

faster

they contain more non-protein N –> spoil faster as it is more easily digested compared to if there was more protein

  • but provides fresh, less fishy, umami flavour
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26
Q

FISH, SHELLFISH AND MOLLUSCs

Molluscs contain no TMAO. True or False?

A

True

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27
Q

FISH, SHELLFISH AND MOLLUSCs

Since molluscs have no TMAO, which 2 substances are broken down to cause spoilage?

A
  1. 3% glycogen (q high) –> broken down and produces acid –> causing pH to fall
  2. amino acids –> amines + NH3
28
Q

MILK AND DAIRY PRODUCTS : RAW MILK

Raw milk is mainly spoilt by which category/categories of MOs?

A. Psychrophiles
B. Mesophiles
C. Thermophiles
D. Psychrotrophs

A

A and D

29
Q

MILK AND DAIRY PRODUCTS : RAW MILK

What are the various spoilage MOs in raw milk and how do they affect the sensorial properties in milk, if any?

A
  1. Coliforms ; LAB ; Enterococci, Micrococci –> lower pH of milk
  2. Alicaligenes viscolactis : increases pH of milk. Increases milk viscosity resulting in ropiness
  3. Pseudomonas florescens : produces enzymes such as proteases and lipases which are heat resistant, show stability at 140°C
    - with proteases, sulfur-containing protein is broken down to form H2S, generating off odour and flavour
30
Q

MILK AND DAIRY PRODUCTS : RAW MILK

How can raw milk be preserved in its own form, without additional processing such as pasteurisation?

A

Refrigerating (but cant last long)

31
Q

MILK AND DAIRY PRODUCTS : PASTEURISED MILK

Which type of MO can grow in pasteurised milk? List some names [5].

A

Thermal resistant bacteria

MEAAL

  1. Micrococci
  2. Entereococci
  3. Aerobic sporeformers
  4. Anaerobic sporeformers
  5. LAB

recall that most spores / bacteria that produce spores (spore-formers) are heat resistant!!!

32
Q

MILK AND DAIRY PRODUCTS : CHEESE

There are different types of cheese, which are mainly classified based on their ______ ______

A

moisture (water) content

33
Q

MILK AND DAIRY PRODUCTS : CHEESE

The spoilage and shelf life of different kinds on cheese depends on which 2 factors?

A
  1. Moisture content
  2. Salt content

(Factors that affect water activity)

33
Q

DRINKS : Natural Mineral Water

Why do autochronous bacteria increase in population specifically during FILLING of bottles?

A
  • Organic compounds adhere to bottle wall and permeates into water
  • During filling, plastic bottles have increased permeability of O2 into the bottle –> since autochronics bacteria are AEROBES, start to multiply in presence of O2

(FYI : maybe cuz during bottle filling, there is high temp. This results in plastic expanding and thus more oxygen can permeate into plastic)

34
Q

MILK AND DAIRY PRODUCTS : CHEESE

Which spoilage MOs are usually found in cheese?

A

yeasts and moulds

35
Q

MILK AND DAIRY PRODUCTS : CHEESE

How to prevent spoilage in cheese?

A
  1. Addition of potassium sorbate : inhibit growth of yeast and mold
  2. Anaerobic packaging to inhibit mould growth (reccall that moulds are strict aerobes!!!)
36
Q

MILK AND DAIRY PRODUCTS : BUTTER

How is butter made ?

How is butter usually processed?

A
  1. Butter is made through pasteurisation of cream
  2. (Pasteurization— heat treatment ) + Lightly salted (solute to lower water activity)
37
Q

MILK AND DAIRY PRODUCTS : BUTTER

Salted butter has a low water content. What is the maximum salt content in salted butter?

A

16%

38
Q

MILK AND DAIRY PRODUCTS : BUTTER

Butter has a lot of microbial growth on it. True or False?

A

False, there is no / limited microbial growth in butter

39
Q

MILK AND DAIRY PRODUCTS : BUTTER

What spoilage MOs can be found on butter?

A

Moulds on lightly salted butter

*Thus dont need much strategiees to prevent MO growth in butter, just store in fridge so it wont melt

40
Q

MILK AND DAIRY PRODUCTS : YOGHURT (fermented milk)

LAB is a spoilage MO in yoghurt. True or False?

A

False. LAB is a beneficial MO in yoghurt

41
Q

MILK AND DAIRY PRODUCTS : YOGHURT (fermented milk)

What are common spoilage organisms in yoghurt, and what sensorial defects do they cause, if any?

A
  1. Yeasts – results in CO2 (gas) formation and fruit odour (undesirable, smells rancid)
  2. Moulds

** since yoghurt has low pH 0f 4.5-4.7 <–> yeasts and moulds thrive**

42
Q

VEGETABLES AND FRUITS : RAW VEGETABLES

What are the intrinsic factors that make raw vegetables vulnerable to microbial spoilage? [5]

A
  1. Higher water activity
  2. High in carbohydrates (cellulose, pectin in cell walls, starch for starchy veg etcetc)
  3. Vitamins and minerals
  4. Weak acid to NEUTRAL pH
  5. High redox potential (Eh) – thus can undergo reduction and provide O2 for MO
43
Q

VEGETABLES AND FRUITS : RAW VEGETABLES

What is the main group of MO that causes spoilage in vegetables, and what are the sensorial defects?

A

Pectinolytic micro-organisms (which digest pectin in cell walls)

  • It causes “soft rot” –> causing vege tissue to soften –> very soft and soggy and mushy
44
Q

VEGETABLES AND FRUITS : RAW VEGETABLES

MOs which digest pectin in cell walls of veges make invasion of other MOs possible as nutrients are released. Name these other MOs

A

MY PE\

  1. Mould
  2. Yeast
  3. Pesudomonas
  4. Erwinia
45
Q

VEGETABLES AND FRUITS : RAW VEGETABLES

Are fresh, whole vegetables or cut vegetables susceptible to microbial spoilage ? Explain.

A

Cut vegetables.

When vegetables are cut, their cells are damagedd, causing the release of nutrients.

This causes MOs to invade more easily since there are more butrients available

46
Q

VEGETABLES AND FRUITS : RAW VEGETABLES

How can we prevent microbial spoilage in shredded vegetables? [2]

A

MAP, high in nitrogen
- prevent aerobic bacteria

+
refrigeration
- slow down metabolic process of bacteria and thus slow down the multiplication of bacteria, though bacteria may still grow

47
Q

VEGETABLES AND FRUITS : RAW FRUITS

What are the intrinsic factors that can cause microbial growth on raw fruits?

A

◡̈ high water activity
◡̈ high in carbs (sugars)
◡̈ high in vitamins, minerals

ᴖ̈ / ◡̈ low pH, weakly acidic to acidic – not too ideal for bacteria, but good for yeasts and moulds

48
Q

VEGETABLES AND FRUITS : RAW FRUITS

What part of raw fruits serve as a natural protection against microbial growth?

A

Fruits which have peels

49
Q

VEGETABLES AND FRUITS : RAW FRUITS

What kind of spoilage MO can be found on raw fruits with peels and what sensorial defects are there?

A

Moulds
Spoilage can be seen by green stuff growing on fruit peels

50
Q

VEGETABLES AND FRUITS : RAW FRUITS

What kind of spoilage MO can be found on raw fruits which are peeled (no more peel left) ?

A

Yeasts, and eventually LAB

51
Q

DRINKS : Natural Mineral Water

What is the name of the group of MO that is innately present in natural mineral water, and can still survive even after bottling ?

A

Autochtonous bacteria

specific names : F&N, M C (dont need to memorise, FYI)
- Flavobacterium
- Nocardia
- Micrococus
- Cytophaga

52
Q

DRINKS : Natural Mineral Water

Since water is low in nutrients, how do these bacteria grow?

A

The bacteria obtain energy from organic compounds that may be in the plastic bottle / organic compounds which may diffuse through the permeable plastic packaging (esp in gasoline stations, where organic compounds diffuse easily –> dont drink mineral water there!!)

  • “Chemo-organotroph”
53
Q

DRINKS : Natural Mineral Water

Why does autochronous bacteria population fluctuate (alternate increase and decrease) in mineral water?

What is the total count they can grow up to per ml?

A
  • at first, there are resources (organic compounds) to support growth of bacteria, population increases
  • as population increases, resources become limited and some bacteria start to die, population decrease
  • When bacteria die, their cells decompose and release organic material for remaining bacteria and the cycle repeats
  • TOTAL COUNT THEY CAN GROW UP TO : 10^4 to 10^5
54
Q

DRINKS : Natural Mineral Water

Why do autochronous bacteria increase in population specifically during FILLING of bottles?

A
  • Organic compounds adhere to bottle wall and permeates into water
  • During filling, plastic bottles have increased permeability of O2 into the bottle –> since autochronics bacteria are AEROBES, start to multiply in presence of O2

(FYI : maybe cuz during bottle filling, there is high temp. This results in plastic expanding and thus more oxygen can permeate into plastic)

56
Q

DRINKS :BEER

What are the intrinsic charactersitics of beer? [2]

(hint : 1 factor got to do with gas in beer)

A
  1. Low pH of 4-5
  2. CO2 production due to fermentation by LAB
57
Q

DRINKS : BEER

What sensorial defects can exist in beer?

(if possible, name the specific MO that causes the defects – but dont need to memorise)

A
  1. Ropiness : causes increased viscocity and acidification
  • caused by PAL –> Pediococcis, Acetobacter, Lactobacillus
  1. Acidification (ethanol into ethanoic acid)
    - caused by Acetobacter
  2. Turbidity : cloudy, opaque, or thick with suspended matter. [beer, like water, is suppoed to be clear!!]
    - caused by Saccharomyces spp.
58
Q

DRINKS : BEER

Beer can cause Sarcina disease. What kind of odour does this kind of spoilt beer have?

A

Honey odour

59
Q

DRINKS : WINE

Which 2 groups of MO can spoil wine?

(If can, give specific names of the species of MO that cause the spoilage)

A
  1. Spoilage by yeasts
    - Candida Mycoderma : causes film formation
  2. Spoilage by bacteria
    - Lactic acid bacteria (LAB) –> acids, off-odour
    - Acetobacter (converts ethanol –> ethanoic acid)
60
Q

CANNED FOODS
Which type(s) of canned food are at high risk of microbial spoilage?

A. Acid canned foods (3.7 < pH < 4.5)
B. Strong acid (pH < 3.7)
C. Weak acid canned foods (pH > 5.3)
D. Semi-acid canned foods (4.5 < pH <5.3)

A

C, D

** weak acid and semi acid canned foods have more neutral pH, which is more desirable for microbial growth

61
Q

CANNED FOODS

Canned foods are usually sterilised under heat. However, weak acid and semi acid foods are highly susceptible to microbial growth.

What specific group of bacteria causes spoilage of weak/semi acid canned foods?

A

Thermophilic spore forming bacteria

62
Q

CANNED FOODS

Desribe what is “flat sour spoilage” (what kind of foods, phenomenon) and which 2 bacteria causes “flat sour spoilage”?

A

Flat sour spoilage occurs in weak acid canned foods, and is characterised by the formation of acid without gas.

  • Caused by Bacillus coagulans, Bacillus sterarothermophilus (Bacillus famil)
63
Q

CANNED FOODS

_____ acid canned foods can be caused by spoilage of thermophilic anaerobes that DO NOT FORM H2S.

What phenomena is observed, when these foods are spoilt by thermophilic anaerobes that do not form H2S?

A
  • Weak and semi
  • Cans swell due to the formation of CO2 and H2 gas
64
Q

CANNED FOODS

What is the name of the specific kind of thermophilic anaerobes that do not form H2S, which causes spoilage in canned foods?

A

Clostridium Thermosaccharolyticum

65
Q

CANNED FOODS

_____ acid canned foods can be caused by spoilage of thermophilic anaerobes that FORM H2S.

A
  • weak
66
Q

CANNED FOODS

thermophilic anaerobes that FORM H2S, which causes spoilage in canned foods, are less heat resistant compared to other thermophiles that cause spoilage in canned foods.

What do the presence of thermophilic anaerobes that FORM H2S indicate about processing conditions?

A

Suggests that there is insufficient heating or leakage of cans

less heat resistant = die in heat more easily –> so if it dont die, means temp wasnt high enough, not enuf heat

67
Q

What is the specific name of thermophilic anaerobes that FORM H2S, which causes spoilage in canned foods?

A

Clostridium Nigrificans

Y2S1_FST2110 - Microbiology and fermentation (12 decks)

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