Saran's Learn Microbiology

FOOD AS A SUBSTRATE FOR MICROORGANISMS Factor Description Effect on Microbial Growth Examples / Notes 1) pH (Hydrogen-ion concentration) Each microbe has minimum, optimum, maximum pH Low pH inhibits bacteria; yeasts & molds more tolerant Fruits, pickles, soft drinks resist bacteria Foods with low pH (<4.5) Natural or fermentation acidity Prevent bacterial spoilage Spoilage mainly by yeasts & molds Buffering capacity Some foods resist change in pH Strong buffers allow longer microbial growth Milk (high buffer), fruit juice (low buffer)   Microbe Type Preferred pH Outcome Bacteria Near neutral (6–7) Grow widely in many foods Yeasts Slightly acidic (4–5) Fruit juices, fermented foods ...

  FOOD CONTAMINATION AND FOOD SPOILAGE FOOD CONTAMINATION Source of Contamination How Contamination Occurs Common Microorganisms Green Plants & Fruits Naturally on surface, damaged tissues, during harvesting & transport Molds (Penicillium, Aspergillus), Yeasts, Lactic acid bacteria, Bacillus Animals Skin, hair, intestines, hides, slaughter, milking, egg laying Salmonella, Staphylococcus, Streptococcus, E. coli Soil Contact with soil, unwashed vegetables, root crops, eggs, meat Clostridium, Bacillus, Mucor, Rhizopus, Actinomycetes Water Washing, cleaning, processing, contaminated ice E. coli, Shigella, Salmonella, Vibrio Sewage Leakage, irrigation of crops, water contamination Pathogens – E. coli, Salmonella, Viruses, Parasites Air Dust particles, ...