| Indicator organisms | use: 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 indicators | spoilage 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 indicators | microorganisms 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 genera | four 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 formula | most 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 |
