PRINCIPLES OF FOOD SPOILAGE

Transcription

1 PRINCIPLES OF FOOD SPOILAGE

2 SPOILAGE Microbial growth- microbial food spoilage Changes in color, odor, and texture Formation of slime Accumulation of gas Release of liquid

3 SPOILAGE MICROFLORA Food types Food environment Temp, aw, ph etc. Microbial types

4 CLASIFICATION OF FOODS DEPENDING ON STABILITY 1. Highly perishable foods 1. No preservation process 1. Heating, food additives, freezing 2. Shelf-life-1-10 days 3. Meat, poultry, fish, raw milk, eggs, fruit and vegetables

5 2. SEMIPERISHABLE FOODS Lightly processing pasterization of milk Refrigeration Shelf-life- 1-3 weeks Frozen foods, hard cheese and fuits

6 3.SEMISHELF-STABLE FOODS Two or more preservation process can be used Vacuum packaging the cooked products 1-4 months

7 4. SHELF-STABLE FOODS Highly processed Heat prpcessed-strelized and hermeticaly sealed Suga, flours, dry foods, vegetable cans

8 MICROBIAL SPOILAGE a)kinds and numbers of M.O. Main sources of M.O.: People, raw materials, ingredients, equipment, air, dust and pests. Initial numbers of M:O. Can be kept low by Good personal hygiene Santizing equipment Controlling temperature Using clorinated water Sanitary conditions during handlng the food

9 NUMBER OF M.O Washing the fresh foods can reduce numbers of M.O. Food with 100 M.O. Shelf life-12 days Food with 5000 M.O shelf life-7 days

10 Contamination Growth Type of organisms Utilize nutrient Competion Bacteria hgrow faster than yeast and molds İntial number Environmental condition ph, aw, oxygen, inhibitory substance Pretreatments Remove or destroy M.O. Heat stable enzymes-no cell left by heating Thermoduric M.O.

11 B)Food residiues On the equipment or wall, floor Must be clean troughly C)Moisture content Food with high water activity- must be refrigerated D) Time-generation time Bacteria with shorter generation time dominate in growth environment Pseudomonas-shortest generation time

12 E) Temperature The most important factor- opt. growth temp. The shelf life of a food is doubled for every 10C decrease in storage temp. F) Significance of microbial type Bacterial spoilage yeast spoilage - mold spoilage

13 PRODUCTS OF SPOILAGES Odor- production of volatile compound Ammonuim, H 2 S, indole Color- pigment production, Serratia mercescens produce red pigment Oxidation of natural color compounds Myoglobin Texture-break down of pectin or protein Vegetable softening meat softening Gas- CO 2, H 2, H 2 S Slime- production of dextran (Leuconostoc mesenteroides) too many bacterial cells Loss of liquied (meat)-low water holding capacity Taste- Souring-organic acid production Bitterness-peptid, amino acids, fatty acids

14 METABOLISM OF CARBOHYDRATES Glucose anaerobicaly decomposed in six main taypes of fermentation: 1. An alcoholic fermentation 1. Sacharomycess cerevisiae 1. Ethanol +CO2

15 METABOLISM OF CARBOHYDRATES Simple lactic acid fermentation Homofermentative-lactic acid main products Mixed lactic acid fermentation Heterofermentative Lactic acid, acetic acid, ethanol, CO2 Colfiform type fermentation Lactic, acetic, ethanol, hydrogen, acetone, butandiol, CO2 Propionic fermentation Propionibacterium-propionic, acetic, succinic acid, CO2 Butyric-isopropyl fermentation Anerobic m.o.- clostridium, butyric, acetic acid, hydrogen, acetone, butylene, butanol, proponal

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18 METABOLISM OF FOOD NUTRıENTS Metabolism of Nitrogenous compounds Proteins peptides amino acids Peptidases catalyze the hydrolysis Peptides gives bitter taste

19 Some of the amino acids can give undesirable taste

20 Decomposition of proteins or amino acids may results in the production of odors Called putrefaction Sulfur containing products, H 2 S Hydrogen Amines histamine, tyramine, piperdine, putrecine and cadavarine ammonia, metyl, ethyl sulfides, indole

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22 ORGANIC ACIDS Can present in foods as salts Lactate, citrate M.O. Oxidise organic acids to carbohydrates Causing more alkaline ph Film yeasts anarerobicaly oxidise organic acids to CO 2 and water

23 LIPIDS Fats are hydrolysed by microbial lipase to glycerol and fatty acids Some M.O. degrate phospholipids to their phosphate, glycerol, fatty acids and nitrogenous base

24 LIPIDS M.O. hydrolyse lipoproteins to proteins, cholesterol esters and phospholipids

25 PECTIC SUBSTANCES Protopectin is converted to pectin, a water soluble polymer of galactrnic acid It gels with sugar and acid

26 PECTIC SUBSTANCES Pectine esterases hydrolyse the methyl ester linkage of pectin to yield pectic acid and methanol

27 Polygalacturanase: break the linkage between galactronic acid units of pectin or pectic acid to yield short chains and D-galactronic acid

28 OTHER COMPOUNDS Alcohols usually are oxidized to the organic acids Athanol acetic acid Acetaldehyde acetic acid (oxidised) or ethanol (reduced) Glycerol dissimilate to glucose

29 PREFERENCES FOR METABOLISM M.o. Use carbohydrates first nonprotein nitrogenous (NPN) Proteinaceous compounds Lipids Small molecules are prefered tp large ones For example: monosaccharides are prefered to polysaccahrides Example: Pseudomonas grow aerobically in fresh meat Metabolise first glucose Then free amino acids and other NPN Then they will produce extracellular proteinases to break down proteins They will produce lipase also

30 PREFERENCES FOR METABOLIS In milk: Lactose is the main carbohydrate Only lactose utilizing m.o. can produce acid and gas Non lactose-utilising m.o. use NPN and proteinaceous compounds to produce amines, NH3, inole