Food Deterioration & Control
*Enzyme activity can cause flavor deterioration
(LIPASE) flavor deterioration (POLYPHENOLOXIDASE) color deterioration (PECTINASE) texture deterioaration
Optimum conditions
*MOs reproduce and in the process synthesize by-products
CHEMICAL (enzymatic)
*Naturally occurring, also microbial produced *substrates for enzymes: proteins, fats, carbohydrates
TIME NOT ON OUR SIDE
*deterioration will occur over time *quality decreases with time (most cases) *Goal: capture and maintain freshness *cannot extend shelf life indefinitely (chem will happen)
BIOLOGICAL - Macroorganisms
*rodent, insects in cereal products, up to 50% of stored grain *may not consume entire food, cause damage *introduce pathogens
Proteolytic Enzymes: Protease
-All enzymes that hydrolyze peptide bonds *polypeptides *amino acids -Off odors and flavors, bitter cheese products -Meat tenderizing, cheese manufacturing, textural modification
Pectic Enzymes: *Pectinase *Pectin *Pectin Methyl Esterase
-Catalyze the degradation of pectin in plant cell walls -associated with fruit ripening -can result in cloud loss in citrus juices -used to clarify apple and grape juice
Lipolytic Enzymes: *Lipases *Lipoxygenase
-Pancreatic, gastric, and intestinal lipases, found in milk, plant tissues (produced by microorganisms) -Off flavors: rancid, unclean, bitter, soapy, cowy, butyric
Polyphenoloxidase
-reacts with molecules associate with COLOR -found in plant tissue -causes browning (bruises, cuts, other mechanical damage allow o2 in and cause rapid browning) ^^Brown color is unacceptable (peaches, apples, grapes, bananas, lettuce) ^^Brown Color is desirable (coffee, tea, cocoa, prunes, raisins)
CHEMICAL
1. Food component can react among: *Themselves * Environment * packaging material 2. Mallard Browning: protein and sugar react with temperature to produce brown color 3. Oxidative Rancidity: oxygen in the environment interacts with unsaturated lipids 4. Hydrogen swell in canned acid foods: iron interacts with the acid and cause internal corrosion and hydrogen gas release ^^ Swell in canned goods: can also be caused by microbial activity due to under processing or post process contamination
PHYSICAL
1. Moisture Migration: water vapor migrates from a region of high humidity to a region of lower humidity (water gain or loss in food typically undesirable) 2. Lack of Temperature Control (avocados 7Degrees internal browning, tomatoes (ripe) 10Degrees, nullifies flavor and turns the flesh mealy) 3. Mechanical Damage (Packaging, vibration, stacking, dropping, etc) 4. Freeze-thaw cycles can damage frozen foods (vegetables and ice cream)
Deterioration Classification:
1. Physical 2. Chemical (enzymatic) 3. Biological (microorganisms, macroorganisms)
Factors For Food Deterioration
1. growth & activity of microorganisms 2. activities of food enzymes 3. Infestation by insects, parasites, rodents 4. inappropriate storage temp 5. Gain or loss of moisture 6. reaction with oxygen 7. light 8.physical stress/ abuse 9. time
More Food Enzymes
AMYlolytic Enzymes: Starch-degrading (used in starch sweetener industry) high-maltose syrup. (found in saliva) CelluLOLytic Enzymes: Celluslose, conversion of waste material, straw husks, sawdust to fuel-grad alcohol Xylose Isomerase: glucose to fructose, high-fructose corn syrup
Types of Microorganism
Bacteria, Yeast, Mold
Deterioration Factors...
DONT operate in isolation
CHEMICAL (enzymatic) [foods were once living: depend on enzymes for metabolism and subsequent growth]
Enzymes: *large protein molecules *act as catalysts *Only need SMALL amounts to be effective *temporarily combine with substrate
Food Bourne Illness:
Food infection and intoxications
Frozen Strawberries Video
Ice crystals from when it freezes. Ice crystals damage product (why??)
Infection:
MO present in food at time of consumption. grows in host (e coli, listeria, salmonella)
Intoxication:
MO produces toxins in the food prior to consumption (Staphylococcus aureus, clostridium botulinum, aspergillus flavus)
NOTE**
Pathogens may not alter the foods organoleptic properties
What affects microbial activity??
Temp: psychrophiles, mesophiles, thermophiles (??) measure of free moisture
cont. affects of microbial activity (pH)
acid and low acid foods (21 CFR) acid foods - foods that have a pH of 4.6 or below (naturally acid, acidified) low acid foods: foods with a finished equilibrium pH greater than 4.6 and a water activity greater than .85
cont. affects of microbial activity (oxygen)
aerobic and anaerobic (no oxy?)
Bacteria, yeast, and mold...
ferment sugar, hydrolyze starches, hydrolyze fats, digest proteins, form acid, produce gas, produce toxins
BIOLOGICAL - Microorganisms
main cause of food deterioration because: *ubiquitous (??) *reproduce rapidly *can cause food-borne illness Passed on through: soil, air, skin, intestines, processing environment, food handling personnel **Not normal found in healthy living tissue
cont. affects of microbial activity (Aw)
measure of free moisture
Food Deterioration
organoleptic desirability, nutritional value, safety, aesthetic appeal, color, texture, flavor
