Food Deterioration
Bacteria can form spores
-Dormant form -Resistant coat for protection -Can withstand high temp -Can't grow in high/low water activity conditions
Three types of water in food products
1) Free H2O: concern for microbial growth 2) Bound H2O: not available for microbes (0.69) 3) Absorb H2O: in cell walls and not available for microbes (0.3) Ex: making jam: adding dugar and convrting free H2O into bound
Three types of food deterioration
1) Physical: bruising on apple--> apple falls and bruises 2) Chemical: oxidation 3) Biologial: microbes. (mold, etc., spoiled milk)
Thermophilic Optimum temperature
131-152 F
Psychrophilic
68-77 F
Mesophilic Optimum temperature
95-98 F
Aw of most foods
Above 0.99 -Lowering Aw can control microbial growth -Drying can help preserve the food from microbial spoilage by lowering the Aw
Intrinsic parameters pH values
Around 7.0 (neutral) except more fruits have a lower pH
Types of microorganisms in food
Bacteria, yeast, molds -Live in liquid, even on the suface
Yeast reproduce by
Budding Fission Spore Formation -Some produce spores some do not
Aerobes
Can only grow and survive in presence of oxygen
Humecants
Can turn food products into IMF (intermediate moisted foods) which lower H2O activity level and give a longer shelf life -Absorb water and lower the Aw (glycerol, sorbitol, other sugars) -Found in cakes/pastry products
The biological kingdom
Contamineated with microorganisms Feed on food and reproduce Function through enzymes they produce Changes by the chemical actions of these enzymes (by products of the enzymatic reactions-->make changes in our foods)
Methods for preserving food
Drying Salting Adding sugar Using additives or ingredients as humecants
Fatigued animal vs. a rested animal
Fatigued: spoils faster than meat from a rested animal -Rested animals convert the usual 1% glycogen to lactic acid which drops the pH of the meat from 7.4 to 5.6 Hunted animals= more prone to bacterial growth
Miroorganisms can greatly influence
Food production Food processing Food distribution Food consumption
Intermediate Moisture Foods
Foods that are intermediate moisture range but have a prolonged shel life -They contain humecants
Moisture Content: Water found in 2 forms
Free Water: microbes grow in Bound Water
What spoils fruit vs. vegetables
Fruits: molds (lower pH) Vegetables: bacteria (higher pH)
Factors that control growth of micro organisms
Intrinsic parameters: inherent part of the plant or animal tissue (inside the food) Extrinsic parameters
Yeast
Larger than bacteria, reproduction is different -Single cells, chain of cells, spherical, cylindrical
High acid vs. low acid ph
Lower than pH 4.6 = high acid 4.6 = borderline
Microaerophiles
MO can grow and survive in low concentration of oxygen (little O2)
Strict Anaerobe
MO will grow only in the absence of oxygen
Bacteria
Microscopic organisms, 1 um in size -Single cell -Reproduce by binary fission (Cell division) -Rapid rate of reproduction, dividing once every 20 minutes
Intrinsic parameters
Moisture content Oxidation/Reduction Potential Nutrient Conents
Molds are strict aerobes
Need O2 for growth
Molds
Not heat resistant (can kill with heat) Resistant to high acidic environment: can grow on acidic berries Resistant to low Aw conditions
Deterioration changes
Organoleptic quality Nutritional Value Food safety Color Texture Flavor Aesthetic
Oxidation Reduction Potential
Oxidation: yields electrons Reduction: captures electrons -More oxidization= more positive -More reduction= more negative
Extrinsic parameters
Properties of storage environment which affect both the food and the microorganisms present -Thermophilic -Mesophilic -Psychrophilic
Aerobic microorganism
Requires oxygen to suvive -Most micro organisms need oxygen and are aerobic
Common yeasts in foods
Saccharomyces: wine making, tomato sauce, salad dressing, mayonnaise Kloekera: damages wine Candida: beers, ales, fruit juices
Aw means
Shelf life for each product (0-1) Closer to 0 = longer shelf life (less free H2O)
How molds reproduce
Sporulation (sexual or asexual) -Molds sporulate to reproduce, unlike bacteria that sporulate to survive adherse environmental conditions
Initial contamination
This number is important because if there is too many at initial contamination then there is no time to recover food (will deteriorate faster)
Anaerobes
Want enviroment with no oxygen -Like reduced environemnts (canned foods)
Optimum temperatures for microbial growth
Want the humidity of the room to stay constant -Relative humididty = Aw x 100 -Mainly oxygen and carbon dioxide present
Nutrient content micro organisms need in order to grow and survive
Water energy source (sugars, alcohols, amino acids) Nitrogen source Vitamins/ related growth factors Minerals -Food= best place for microbes to grow
Aw
Water activity -Water requirments of mo's is expressed as water acitvity in the environment
Facultative Anaerobe
Will grow with or without oxygen -The worst
Time and temperature relationship on yeast
at 250 F/ 121 C = Kills spores
Causes of food deterioration
loight cold, heat radiation industrial conatmination oxygen dryness enzymes time micro organisms
Examples of intrinsic parameters
pH Moisture content Oxidation reduction potential Nutrient content Antimicrobial constituents Biological structures
Main task of food preservation
prevent frowth of microorganisms
