Food Deterioration

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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


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