BY- ABHISHEKA G.(MSIWM013)
Food spoilage is defined as the process in which the destruction of food occurs then it becomes non edible to humans and it’s quality of edibility is decreased. It is also referred to be the changes in the visual, smell, and texture of the food that makes it unacceptable for consumption. The growth of microbes in food results in food spoilage. Spoilage of food occurs due to the action of microbial enzymes in the absence of viable cells. The microbial spoilage of food results in changes such as color, odor, texture, the formation of slime, accumulation of gas, and release of liquids.
The microbes like Bacteria, yeasts, and molds causes of food spoilage in high amount. These microbes synthesis different enzymes to decompose the various food items. Molds are the major causes of spoilage of foods with reduced water activity like dry cereals and cereal products. Bacteria spoil foods with relatively high water activity such as Milk and its products.
RELATION BETWEEN WATER ACTIVITY AND FOOD SPOILAGE MICROBES:
1.Water activity has an important role in food preservation. Each microbe has a critical water activity, below this critical water activity, the growth of the microbes do not occur.
2.For example, pathogenic microbes cannot grow at water activity below 0.86, Yeasts and molds are tolerant to water activity and they grow at or below water activity 0.62. Hence water activity is important in foods and it is a major factor in food spoilage and food safety.
3. Decrease in water activity retards the growth of microorganisms by slowing down enzyme-catalyzed reactions and retards nonenzymatic browning.
WATER ACTIVITY OF SOME OF THE FOODS:
Fruits and Vegetables – 0.97 to 1.
Cheese – 0.68 – 1.00
Jams and Jellies- 0.75 – 0.94
Honey – 0.54 – 0.75
Noodles – 0.50
Dried Milk – 0.20
MINIMUM WATER ACTIVITY REQUIRED FOR THE GROWTH OF MICROBES IN FOOD
Clostridium botulinum – 0.95
Bacillus cereus – 0.95
Pseudomonas aeruginosa- 0.95
Salmonella species – 0.95
Staphylococcus aureus- 0.90
Candida species- 0.90
Saccharomyces cerevisiae- 0.90
Staphylococcus aureus – 0.86
Penicillium species – 0.82
Most spoilage yeast – 0.88
Most spoilage molds – 0.80
SOURCES OF MICROBES IN FOOD:
- Soil and water
- Plant and plant products
- Food utensils
- The Intestinal tract of Humans and Animals
- Air and dust
- Food handlers.
PROCESS OF FOOD SPOILAGE BY MICROBES: Microbes like bacteria, molds attack the food items. Then preserved food items undergo degradation. As a result of degradation, food items result in changes such as physical changes like the texture of food, visual, smell, and quality of the food and loss of taste, etc. Later the microbes which attacked the food items releases the necessary enzymes required for the degradation of spoiled food items. Then enzymatic action brings about the degradation process.
FOODS AFFECTED BY VARIOUS GROUPS OF MICROBES:
- Anaerobic or facultatively anaerobic: These groups of microbes are most likely to grow in canned foods.
- Microaerophilic bacteria: These are most likely to grow in vaccum packed foods since they have low oxygen tension.
- Aerobic bacteria: They grow on the surface of the raw meat.
- Aerobic molds: Grow on insufficiently dried or salted products.
FACTORS AFFECTING THE GROWTH OF MICROBES IN FOOD:
- pH: Most of the bacteria grow best at neutral or slightly alkaline nature of foods, the pH ranging from 6.8 to 7.5. Bacteria like Salmonella grow at a pH range of 4.5 to 9.0. Molds grow between 1.5 to 11.0, whereas yeasts grow between 1.5 to 8.5.
- Moisture content: The effect of moisture is measured in terms of water activity. The water activity of a food is defined as the amount of free water present in the food medium. If there is a lack of water the microorganisms do not grow in the food medium.
- Nutrient contents in the food: Microbes require proteins, carbohydrates, lipids, water, energy, nitrogen, Sulphur, phosphorous, vitamins, and minerals for their growth. Various foods have specific nutrients which support the growth of microbes in the food. Foods like meat, milk, and eggs contain a large number of nutrients required for the growth of microbes. Hence these foods are more susceptible to microbial spoilage.
- Anti-microbial substances: The antimicrobial substances like lactenin, anti-coliform factors in milk, and lysozyme in eggs prevents the growth of microbes.
- Temperature: Microbes require optimum temperature for their growth. Psychrophilic bacteria causes spoilage of food at low temperature conditions. Mesophilic bacteria can grow between 5*c to 40*c. Thermophilic bacteria grow above 45*C temperaturze.