Spoilage of Fresh and Processed Food.pptx

Spoilage of Fresh and Processed Food

1. Spoilage of fresh and processed food

2. Spoilage: • Spoilage is the process in which food deteriorates to the point in which it is not edible to humans or its quality of edibility becomes reduced. It involves any change which renders food unacceptable for human consumption.
• Spoilage of food can occur through: 1. Insect damage
2. Physical injury due to freezing or moisture loss
3. Activity of indigenous enzymes in plant and animal tissues
4. Chemical changes involving oxygen (oxidation) and light e.g. oxidative rancidity of fats and oils, the discoloration of cured meats,
5. Growth and activity of microorganisms: bacteria, yeasts and moulds . 6. Temperature fluctuation

3. Classification of food on the basis of Stability: Highly perishable foods; If no preservation is applied, the quali retention time is about 1-3 days. It incudes meat, poultry, fish, raw milk, eggs, many fruits and vegetables and all cooked foods except the dry and very acid ones. Semi perishable foods; Lightly processed Such as pasteurized milk and egg products and refrigerated food. The quality retention time is about 1-3 weeks. Other examples frozen foods, baked goods, hard cheeses and fruits. Semi shelfstable foods; Two or more preservation process can be used (the hurdle concept) such as vacuum packaging the cooked meat products, the quality retention time is about 1-4 months.

4. 4. Shelf stable foods (nonperishable foods) Highly processed (such as heat processed, sterilizes and hermetically sealed)such as vegetable, dried milk products with a quality retention up to 1 year or more. Other examples are sugar, flour, dry foods, etc. Potentially Hazardous Food is a term used by food safety organizations to classify foods that require time-temperature control to keep them safe for human consumption. A PHF is a food that:

Contains moisture – usually regarded as a water activity greater than 0.85
Contains protein
Is neutral to slightly acidic – typically having a pH between 4.6 and 7.5 Potentially Hazardous food:-

5. Basic type of food spoilage: Appearance: Spoilage of foods due to microbial growth may include mycelia or colonies visible on surface and development of cloudiness in liquids
Changes in food color due to heme or chlorophyll breakdown
Slime formation due primarily to surface accumulation of microbial cells
Tissue softening due to enzymatic degradation Changes in taste and odor due to development of nitrogenous compounds (ammonia, amines, etc.), sulfides, organic acids .

6. Types of Agents causing food spoilage: 1. Growth activity of m.o’s 2.Insects, rodents and animals
3.Action of enzymes
4. Purely chemical reactions in the food such as oxidation and browning
5. Physical changes caused by freezing, burning, drying, pressure, etc.
6. Presence of foreing material in the food such as heavy metals, toxins, non food materials and etc.
7.Presence of parasites or their eggs.

7. Microbial food spoilage: Microbial spoilage occurs as a result of microbial contamination with foods and activities of microorganisms under suitable conditions
Factors Effecting Food Spoilage
a) Kinds and numbers of m.o’s in food
b) Food residues
c) Moisture content
d)Time
e) Temperature
f)Physical state and structure of Food
g)Significance of microbia types

8. Metabolism of food nutrients and chemical changes: Metabolism of nitrogenous compounds The nitrogen in foods is present in the form of proteins . Microbial extracellular proteinases hydrolyze proteins to polypeptide , simpler peptides and amino acids. Peptide give a bitter taste. Catalysis the hydrolysis of polypeptides to simpler peptides and amino acids. They can give desirable or undesirable flavor.
Decomposition of proteins or amino acids may result in the production of odors and is called putrefaction results in foul-smelling, sulfur-containing products. These are hydrogen, methyl and ethyl sulfides, mercaptan , ammonia, amines, indole and others.

9. B) Metabolism of non-nitrogenous compound mo’s use carbohydates to obtain energy. Organic acids, aldehydes, ketones, alcolhols , glycosides, cyclic compounds and lipids are also used as carbon and energy sources.
• Carbohydrates: polysaccharides are hydrolyzed by extracellular enzymes and simple sugars are used. Glucose can be decomposed in 6 main fermentation.1) alcoholic form 2)Simple lactic form. 3)a mixed lactic form ( heteroform .) 4)coliform type form. 5)the propionic form 6)butyric-isopropyl form. Organic acids; m.o ’ oxidase organic acids to carbohydrates and medium become more alkaline. Some mo’s can oxidase organic acids to CO2 and water such as yeast(film on pickle).

10. Lipids; Fats hydrolyzed to glycerol and fatty acids. Phospholipids can degraded to phosphate, glycerol, fatty acids, nitrogenous base. Lipoproteins can be hydrolyzed to proteins, cholesterol ester and phospholipids. Other compounds; alcohols are oxidized to organic acids acetaldeydes may be oxidized to acetic acid or ethanol. Carbohydrates Protein Fat

11. Non microbial Food Spoilage 1.Enzymatic spoilage: The enzymes on banana cause maturation and color changes Ripening and softening fruits Bacteria also produce enzymes Enzymes in vegetable can be inactivated by blanching or their activities can be decreased at cold temperatures below 4 °C. Extracellular enzymes causing spoilage in thermally treated foods are proteinases, lipases,amylase,cellulase and phospholipases of psychrotrophic bacteria and amylases.

12. 2.Chemical spoilage -The Maillard reaction occurs between a carbonyl compound like a reducing sugar, and an amine, like an amino acid, peptide, or protein.
-lipid oxidation
Examples: repetitive usage of frying oils in restaurants, odor becomes heavy.
Discoloration of surface of red meat is caused by non enzymatic reactions, oxidation of myoglobin to metmygoglobin .

13. Food preservation: Different methods of food preservation are:- Freezing Food kept in a refrigerator remains fresh for some days. Germs do not grow easily in cool places. We preserve food items, like milk fruit, vegetables and cooked food by keeping them in a refrigerator. 2. Boiling By this method, we can preserve food for a short period of time. Germs in milk are killed by pasteurization. It is done by boiling milk for sometimes and then cooling it quickly.

14. 3. Salting We can add salt to preserve pickles and fish. 4. Sweetening
Excess sugar in food also acts as a preservative. We store food for a long time in the form of jams, jellies, and murabbas by adding sugar. 5. Dehydration
In this method, the food items are dried in sun to stop the growth of bacteria in them. Certain foods, like raw mangoes, fishes, potato chips and papads are preserved by this method. 6. Canning
In this method, air is removed from food and put in airtight cans so that germs do not grow on them. Food items like vegetables, seafood, dairy products etc. Are preserved through this method.