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20 Cards in this Set
- Front
- Back
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Food spoilage definition |
Spoilage is the process by which the quality of a food deteriorates to the point where it is considered unacceptable for human consumption (issue of quality rather than safety). |
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Spoilage can occur as a result of... |
1. insect damage 2. physical injury (bruising, freezing, drying) 3. Indigenous enzyme activity 4. Indigenous chemical changes 5. Microbial growth and metabolism |
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Intrinsic factors affecting food spoilage |
a) pH b) Moisture content c) Oxidation/reduction potential (Eh) d) Nutrient composition e) Antimicrobial composition f) Biological structures |
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Extrinsic factors affecting food spoilage |
a) Temp of storage b) r. humidity of environment c) Gaseous atmosphere d) Presence of other microorganisms |
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a) pH - how does this affect food spoilage? |
- Most bact. prefer pH~7 but can grow in range of pH. Changes in pH can effect functioning of microbial enzymes and uptake of nutrients - Moulds and yeast: tolerate broader pH, can grow at pH <4 (e.h. fruit) - Spoilage organisms tolerate broader pH than path. organisms - Well rested/non-stressed animal: glycogen->lactic acid -> decrease pH -> inhibit bact growth. Glycogen depletion in stressed animal -> higher final pH of meat. |
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b) How does moisture content affect food spoilage? |
- moisture required by microbe - moisture content of food as it relates to microbial growth referred to as water activity (aw) (0-1.00) - fresh foods: aw = 0.99 - yeast and mould tolerate wider aw range than bact. Minimum aw of most moulds = 8.00 - Exception: Staph A minimum aw = 0.86 - addition of sugar/salt reduces aw - as temperature decreases, aw increases |
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c) How does oxidation-reduction potential (Eh) affect food spoilage? |
= ease with which a substance loses/gains electrons (expressed in millivolts (Eh value) - Microbes have varying Eh requirement for growth. - Aerobic organisms require positive Eh value for growth - Anaerobic animals require -ve Eh value for growth. - Atmosphere at storage also influences Eh |
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d) How does nutrient composition effect food spoilage? |
- Sugars, alcohols, and AA used as energy source by most microbes; some microbes can use complex CHO e.g. starches after breakdown of simple sugars. Few use fats as E source. - AA = N source, after these depleted -> complex proteins may be used - B vits = most important micro-nutrient.. G+ bact have poor capacity to manufacture => require ready source |
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e) How do antimicrobial constituents affect food spoilage? |
- Some naturally occurring - Lactoferrin, and lactoperoxidase system important in cows' milk - Antimicrobials in eggs: lysozyme, conalbumin and ovotransferrin |
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f) How do biological structures affect food spoilage? |
- Natural coverings - Egg membranes and shell - Animal skin |
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a) How does temp of storage affect food spoilage? - yeast and mould |
- Moulds tolerate broader temp range. - Yeasts: generally psychotrophes or mesophiles but not thermophiles |
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a) How does temp of storage affect food spoilage? - psychotroph |
- Psychotrophic organisms grow <7degrees C, optimum temp = 20-30 degrees. e.g. Pseudomonas sp., will grow at refridgeration temps
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a) How does temp of storage affect food spoilage? - thermophile |
- Thermophilic bact. grow at T >45 degrees. T(optimum) = 55-65 degrees. e.g. Clostridium and Bacillus sp., important e.g. in canned foods where high temps used in processing.
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a) How does temp of storage affect food spoilage? - mesophile |
- Mesophilic bact. grow between 10-40 degrees, optimum temp = 30-40 degrees. Coliform bact are mesophiles, can spoil food stored incorrectly or at temp >5 degrees. |
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b) How does r. humidity of environment affect food spoilage\? |
- Influences aw |
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c) How does gaseous atmosphere affect food spoilage? |
- Obligate aerobes: e.g. Pseudomonas, growth inhibited by vac-pac/ modifies atmosphere packing - Obligate anaerobes: e.g. Clostridium spp., spoilage of deep tissues/ packaged foods - Facultative anaerobes - grow in presence/absence of oxygen e.g. Enteric bact, potential to spoil food in any packaging |
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d) How does presence of other microorganisms affect food spoilage? |
Production of antimicrobial substances, competition.. |
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What is the most common food spoilage microorganism? |
PSEUDOMONAS SPP. |
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Pseudomonas spp. |
- G- bacillo - most common food spoilage organism - esp. food w/ high water availability, near-neutral pH, stored in aerobic atmosphere, e.g. red meat, fish, dairy - widespread in environment - psychotrophic (can multiply at fridge temps) (min growth temp = 0 degrees) - obligate aerobe (not in vac-pac/mod. atm packing) - in meat: use glucose -> fruity odour. May see slime and pigmentation of meat. |
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Other non-enteric, G- bact |
e.g. Aeromonas spp., Acinetobacter spp., Alcaligenes spp., Flavobacterium spp. - Psychotrophic - Red meat, poultry, fish, dairy - Susceptible to heat |
