计算机代考 Food Microbiology & Safety

Food Microbiology & Safety
Helen Billman-Jacobe

Sources of microorganisms in food_Fish

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Ray and Bhunia Chapter 3

Intended learning outcomes
Differentiate between normal flora in plant and animal derived foods, contaminants, spoilage organisms, pathogens and functional organisms
Relate the intrinsic and extrinsic factors of food substances to how microorganism can grow and survive

Intrinsic factors
•may be up to 25% lipid
•Low amount of connective tissue •15 – 20% protein
•<1% carbohydrate •The intrinsic factors on species and rearing environment Microbes in fish Muscle essentially sterile Skin, gills and gut carry large numbers of microbes Fish are cold blooded and the microbes that live on them reflect the normal body temperature of the fish • Temperate waters -2 – 12°C Bacteria associated with marine fish are likely to be salt tolerant .~ 2-3% salt Skin ~102 – 107 cfu/ml Alimentary canal 103 – 109 cfu/ml Gills 103 – 109 cfu/ml Farmed vs wild The flesh of molluscs differs from vertebrate fish and crustaceans •It may contain up to 3% carbohydrate in the form of glycogen •Molluscs are filter-feeders •The filter small particles from large volumes of water •They can concentrate microbes including viruses Oyster farming FSANZ Microbiological limits n=number of samples, m=acceptable microbiological limit Non-microbial spoilage: Fatty fish containing large amounts of polyunsaturated fats may go rancid Most spoilage is of microbial origin Very little carbohydrate in fish has 2 consequences • there is little chance of acidification of the muscle ~pH6.5 • Bacteria on the fish have to use nitrogenous compounds as an energy source → off odors Trimethylamine oxide is an osmoregulator in fish TMAO can be used by some bacteria i.e Shewanella putrifaciens under microaerophiic and anaerobic conditions Shewanella putrifaciens TMAO Trimethylamine TMAO has a high redox potential Off odors and flavours •Products of protein decomposition •hydrogen sulphide •Methyl mercaptan •Dimethyl sulphide •Skatole (from tryptophan) TMAO and near neutral pH means that MAP does not improve keeping quality Gaseous atmosphere Moderate pH6.5 Extrinsic factors temperature Catch, gut then chill asap Intrinsic factors Water activity pH and buffering High due to TMAO Redox potential Antimicrobial factors Nutrient content Fish protein rich Shellfish carbohydrate rich 程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com