1. Vcf
1.1. - Most M.O. grow best between 6.6 and 7.5 pH. - Pathogenic m.o. are less acid tolerant than mould and yeast and there are no bacteria grow if pH below 3.5.
1.1.1. ■Some foods have biological structures that prevent microbial entry. ■For example, meat has fascia, skin and other membranes that prevent microbial entry. ■Eggs have shell and inner membranes that prevent yolk and egg white from infection.
1.1.1.1. ■Microorganisms require proteins, carbohydrates, lipids, water, energy, nitrogen, sulphur, phosphorus, vitamins, and minerals for growth. ■Various foods have specific nutrients that help in microbial growth. ■Foods such as milk, meat and eggs contain a number of nutrients that are required by microorganisms. ■These foods are hence susceptible to microbial spoilage.
2. biological structures
3. Stationary phase
3.1. No of cells produced is equal to the no. of cells dying
4. Decline phase
4.1. The growth rate decrease due to shortage of growth factors such as vit. and minerals
5. Log phase
5.1. The cell multiply for few hr. or even days
6. Lag phase
7. There is no multiplication about 30 min. where the cells metabolizing rapidly leading to slight increase in cell size
8. The bacterial lif cycle divided into :
9. Under optimum condition most bacteria reproduce by binary division once every 20 min. - So every single cell of bacteria produce 2x106 every 7 hr.
10. antimicrobial substances ad
10.1. ■Antimicrobial substances in food inhibit microbial growth. ■Various foods have inherent antimicrobial substances that prevent (inhibit) microbial attack. ■Such inhibitors are like lactinin and anti-coliform factors in milk and lysozyme in eggs.
11. moisture content
11.1. ■The effect of moisture is in terms of water activity: -the amount of free water in a food medium. ■The amount of free water is important for growth of microorganisms. ■ If there is lack of this free water microorganisms will not grow. ■Water activity is defined as the vapour pressure of a food substance to that of water at the same temperature. (Aw = VPFood/VPWater)
11.1.1. ■The water activity is therefore equal to 1.0. ■Food products have a water activity of less than 1.0. ■A saturated salt solution has a water activity of 0.75. ■Salting and drying reduces the water activity of a food product.