Food Preservation (Chapter 4) PDF

Death of Microorganisms Food Preservation (Chapter # 4) Natural causes of microbial death Depletion of nutrients Change in pH Build up of toxic substances Lack of O2 Combination of the above  Induced microbial killing 1. Heat treatment 2. Chemical agents 3. Acidul...

Death of Microorganisms Food Preservation (Chapter # 4) Natural causes of microbial death Depletion of nutrients Change in pH Build up of toxic substances Lack of O2 Combination of the above  Induced microbial killing 1. Heat treatment 2. Chemical agents 3. Acidulants 4. Radiation 5. Lowering water activity 6. Lowering Temp. 7. Hydrostatic Pressure ( very high pressure applied) 8. Pulse electric field 9. Hurdle effect (combining several approaches (freezing, heating, low aw, irradiation…), each of which is insufficient on its own, to control or even eliminate pathogens in food products. Thermal processing: Logarithmic order of death !!!? Time of heating No. Survivors Log No. (min) survivor 0 106 6 5 105 5 10 104 4 15 103 3 20 102 2 25 101 1 30 100 0 Inactivation Kinetics D-value:  Time at a given temperature necessary to achieve a 1 log reduction in viable cells/spores Z-value:  Change in heating temperature required to change D-value by 1 log Z-Value Factors Affecting Heat Resistance of Microbial Cells  Type of M.O  Stage of microbial growth  pH  water activity D-value at 70 C S. tyhimurium-milk = 0.0008 min -Chocolate = 72-78 min  presence of fatty and protein  salt concentration  Why to calculate D and Z-values Develop pasteurization Processes Develop sterilization processes Pasteurization is based on inactivating the vegetative cells of Mycobacterium paratuberculosis (7 D process). Sterilization is based on destroying the spores of C. botulinum in process low acid canned foods (12 D process).  Types of thermal processes Blanching Pasteurization: Heat treatment to inactivate vegetative pathogen in food.  Low Temp Long Time (LTLT) High Temp Short Time (HTST) Commercial sterilization: A thermal process of low acid canned foods, especially applied to destroy spores of C. botulinum. The temp should reach 121 C at the cold spot. Ultra High Temp treatment  Effect of Radiations on M.O Microwaves o Should have water to heat food o Make oscillation motion (dipole motion) that generates heat o Applications 1- Cooking 2- Defrosting 3- Reheating of food 4- Drying o Advantages: 1- Heating inside package 2- Rapid Heating o Disadvantage: Un-uniform heat treatment  Ultraviolet light (UV light) Cause damage to bacterial genetic material Applications 1- Disinfection of water 2- Disinfection of packaging material used in the UHT milk 3- Control of mold spores in baked products Viruses > mold spores > bacterial spores >yeast and mold > G(+) bacteria > G(-) bacteria