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level: 17 - Indicators of Food Microbial Quality and Safety

Questions and Answers List

level questions: 17 - Indicators of Food Microbial Quality and Safety

QuestionAnswer
Indicator organismsuse: assess microbial quality of food related to... - shelf-life: how long will the food maintain good quality? - food sanitation: were GMPs and SSOPs applied in food production? - safety from food borne pathogens: were pathogens eliminated from the food?
Food microbial quality or shelf-life indicatorsspoilage organisms: increasing numbers result in loss of productivity - "total" viable count (aerobic plate count) microbial metabolic products: used to assess and predict microbial quality of some foods - diamines (cadaverine and putrescinie) - histamine, trimethylamine (TMA) - diacetyl, ethanol, lactic acid
Microbial food safety indicatorsmicroorganisms used to assess food safety and sanitation no single bacterial group or species meet all the criteria of an ideal indicator! indicator organisms (eg. coliforms) - surrogates/substitutes for pathogens - not harmful to humans - indicate potential health risk
Criteria for an ideal food safety indicator organism- easily and rapidly detectable - easily distinguishable from other organisms - history of constant association with the target pathogen - always present when pathogen is present - indicator numbers correlate with those of pathogen - growth requirement and rate equal to those of the pathogen - death rate similar to that of pathogen - absent from foods when the target pathogen is absent
Additional criteria for fecal indicator organsims- occur only in the intestinal tract - high numbers in feces so that they could be detected in high dilutions - resistant to the extra-enteral environment (eg. the food product that is being tested) - easy and reliable detection even in low numbers
Coliforms- g-, non-sporeforming, fac. anaerobic ford - ferment lactose @ 35C to produce acid and gas within 48h in lactose broth - grow in the presence of bile salts (selective agent in VRB agar) - no growth in foods at pH 4 or aw < 0.92 - destroyed by pasteurization (presence of coliforms indicate under-processing or post-processing contamination)
Coliforms: common generafour genera from the Enterobacteriaceae family - Citrobacter - Escherichia - Enterobacter - Klebsiella
Coliforms: occurrence and significance in food- present on raw foods of plant and animal origin - very high numbers in some plant foods due to contamination with soil - some Enterobacter spp and Klebsiella spp are found in soil where they can multiply and reach high population levels - some found in water/plants - can reach high numbers in food during storage - specificity as an indicator of fecal contamination in raw foods reduced due to non fecal origin of some coliforms and their ability to grow in many foods - coliform presence in heat-processed foods can represent under processing or post-processing contamination
Escherichia coli & IMViC formulamost representative of fecal contamination than the other three genera IMViC formula: classical method to differentiate E. coli from the other coliforms I: inodole productino from tryptophan + M: methyl red test (acid from glucose) + Vi: Voges Prosakeur test (acetoin from glucose) - C: citrate utilization -
Fecal coliforms- g-, non-spore forming, fac anaerobic rods - ferment lactose to produce acid and gas in EC broth between 44-45 C - a fecal coliform tests is a test SPECIFICALLY for E. coli along with some Klebsiella spp and Enterobacter spp - specificity as fecal contaminants is much higher than coliforms - non-fecal coliforms eliminated due to the use of high temperature in selective broth containing lactose - lactose fermentation with gas production is a presumptive test
Enterococci- g+, non-spore forming cocci - aerotolerant anaerobes - grow between 10-45C, some at 50C - some survive pasteurization temps - more resistant than coliforms to refrigeration temp, freezing, drying, low pH, and salt - found in intestinal tract of humans and warm-blooded animals, birds, and insects - can survive longer than coliforms - ex. Enterococcus spp: Enterococcus faecalis, Enterococcus fecium
Enterococci: occurence and significance in foods- can contaminate foods via feces, soil, water, vegetation, food processing equipment, processing environment - ability of some strains to survive pasteurization reduces their value as an indicator presence in high numbers in heat-processed foods indicates: - contaminated raw materials - improper sanitation during processing