Food micro

• Food spoilage


  Any changes in the visual, smell and texture of food that makes it unacceptable for consumption

  
• Food spoilage


  The process in which food deteriorates to the points it is not edible to humans or its quality of edibility becomes reduced
• Causes of food spoilage

  • Insect damage
  • Physical injury
  • Enzymatic degradation
  • Microbial activity

  
• Types of food spoilage

  • Physical spoilage (moisture loss or gain)
  • Chemical spoilage (oxidation of fat, browning of fruits and vegetables)
  • Microbial spoilage (growth of microorganisms, enzyme production)

  
• Microbial spoilage


  When bacteria breaks down the food, acids and other waste products are created in the process
• Yeast


  Can be responsible for the decomposition of food with a high sugar content
• The same effect of yeast decomposing food is useful in the production of various types of food and beverages, such as bread, yogurt and alcoholic beverages
• Some spoiled foods are harmless to eat, and may simply be diminished in quality
• Foods exhibiting certain types of spoilage may be harmful to consume. Uncooked or under-cooked animal flesh that spoils is typically quite toxic, and consumption can result in serious illness or death
• The toxic effects from consuming spoiled food are known as "food poisoning", and more properly as"foodborne illness"
• How microbial spoilage manifests itself

  • Visible growth
  • Gas production
  • Slime
  • Off-flavours
• Sequence of events in food spoilage

  1. Microorganisms have to get into the food from a source or more

  2. Food environment should favour the growth of microbes

  3. Food need to be stored under the growth condition for a sufficient length of time
• Chemical changes caused by micro organisms

  • Degradation of carbohydrates
  • Degradation of N- compounds
  • Degradation of lipids
  • Pectin hydrolysis
• Common Causes of Food Spoilage

  • Inadequate storage temperatures
  • Prolonged storage times
  • Improper ventilation
  • Cross contamination
  • Excessive delays between receiving and storing

  
• Spoilage Signs


  • Odor (breakdown of proteins, "rotten egg" smell)
  • Sliminess (surface accumulation of microbial cells, tissue degradation)
  • Discoloration (mold on bread, blue and green mold on citrus fruit and cheese)
  • Souring (production of acid, sour milk from production of lactic acid)
  • Gas formation (meat becomes spongy, swollen or bubbling packages and cans)
• Classification of food by ease of spoilage

  • Stable or non perishable foods (e.g. sugar, flour and dry beans)
  • Semi perishable foods (e.g. potatoes, apples and nuts)
  • Perishable foods (e.g. meats, fish, milk, vegetables, eggs)

  
• Sources of meat contamination

  • Cutting board contamination
  • Conveyor belts
  • Temperature
  • Delay between storage and distribution
  • Fecal contamination from intestines

  
• Storage temperature is the single most important control factor for meat spoilage
• Several genera of molds grow on the surface of meat and can cause spoilage like Penicillium, Mucor, Cladosporium, Alternaria, but cannot grow on meat stored below 5oC

  
• Meat spoilage is characterized by the appearance of off odors and slime, which are manifest when surface loads exceed 107 CFU/cm2

  
• The slime is due to the accumulation of bacterial cells
• Meat spoilage (including poultry and fish) occurs without any significant breakdown of the primary protein structure

  
• Instead, spoilage bacteria utilize glucose, free amino acids or other simple nitrogenous compounds to attain population of about 108 CFU/cm2, at which point the organoleptic quality of the meat will clearly reveal it is spoiled
• Chemical composition of fresh meats

  • 75% water
  • 18% protein
  • 3% fat
  • 1% ash
  • Traces of carbohydrates, vitamins, etc.

  
• Microflora of fresh whole meats

  • Gram negative aerobic rods (Pseudomonas spp., Acinetobacter, Psychrobacter immobilis)
  • Bacillus and clostridia (e.g. C. perfringens)
• Although subsurface portions of meat are generally sterile, some parts such as lymph nodes may be heavily contaminated

  
• Mechanical disruption of the tissue during processing can distribute microorganisms from the meat surface throughout the product

  
• Ground meats


  Have higher microbial loads than whole meats due to greater surface area, trapping of air, and additional contamination from handling and processing
• Vacuum-packed meats


  Not all oxygen is removed, resulting in increased CO2 levels and a longer shelf life. The microflora shifts from predominantly gram-negative aerobes to gram-positive anaerobes and microaerophilic lactic acid bacteria
• Spoilage signs in vacuum-packed meats

  • Slime development
  • Greening (from microbial production of H2O2 or H2S)
  • Off odors (from release of short chain fatty acids, production of volatile compounds)
• The type of spoilage bacteria that will dominate is influenced by whether the meat is raw or cooked, and the nitrite concentration
• Spoilage in processed meats

  • Slimy spoilage (buildup of cells of yeasts, lactobacilli, enterococci or Brochothrix thermosphacta)
  • Sour spoilage (growth of lactic acid bacteria, fermentation of lactose and other carbohydrates)
  • Greening (from H2O2 or H2S production)
• During the initial stages of poultry spoilage, the skin supports bacterial growth better than the tissue, so the skin can sometimes be removed to salvage the food
• Eggs


  Have several intrinsic parameters which help protect the nutrient-rich yolk from microbial attack, including the shell, membranes, lysozyme, and high pH in the white
• Freshly laid eggs are generally sterile, but soon become contaminated with numerous genera of bacteria that can eventually penetrate the eggshell and cause spoilage
• Fish have high nitrogen content but no carbohydrate, and the microbial quality is heavily influenced by the quality of the water from which they were harvested
• Unsanitized processing steps are principal culprits in fish products with high microbial loads, and frozen fish products generally have lower counts than fresh products
• Egg protection from microbial attack


  • Shell and associated membranes
  • Lysozyme
  • High pH (>9.0) in the white
• Freshly laid eggs are generally sterile, but soon become contaminated with numerous genera of bacteria
• Bacteria penetrate the eggshell


  Spoilage will occur