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Thermal processing:Controlled processes using heat 3 types:a. Blanching b. Pasteurizationc. Commercial sterilization37. Irradiation:Using ionization energy to inactivate microorganisms.Method How Principle Blanching, usually combine with other preservation methods Mild intensity heat process by exposing food to boiling water or steam for a short period of time 1. Inactivate endogenous enzymes 2. Drive off O2 and other gases to minimize pressure buildup so that containers are not deformed Pasteurization Moderate intensity heat process: 30-40 mins @ 60C=LTLT 15 sec @ 72C=HTST eg. refrigerated juice need to have durable life date 1. Low acid food: To destroy pathogenic bacteria & viruses and to inactivate enzymes 2. Acid food: To extend shelf life by destroying spoilage-causing MOs but not all of them & enzymes Need to combined with other forms of preservation. Food usually will be consumed within short period of time. Canning (Commercial Sterilization) High intensity 121C for 15 mins CS is done once the food is packaged. Containers must withstand high temp. and pressures and hermetically sealed so impermeable to gases, liquids and MOs. 1. Destroys spoilage-causing & disease-causing MOs 2. free from viable forms of MOs 3. Ensures spores of Clostridium botulinum is destroyed = “botulinum cook” BOTULISM: present in soil, water, air, strict anaerobe, grows well in low acid foods, produces a potent toxin (neurotoxin) that affects central nervous system and death from respiratory collapse. Shelf life > 2yrs UHT processing and Aseptic packaging - CS UHT: Injection of hot steam under 140-150C for 4-6 sec, followed by immediate cooling. Aseptic: UHT food is aseptically placed & sealed into pre-sterilized containers and aseptic environment eg. shelf stable milk juice Some UHT food does NOT have commercially sterile package, has longer shelf life at refrigeration temps. 38. Thermal Death Curve:a. Thermal death rate curves (TDRC) D-value:Time at a particular temp. required to kill 90% of a microbial population. It is NOT affected by # of microbials; will be LOWERED when temp. is decreased because rate of microbial death increases. Thermal Death time curve TDTC:Time required for destruction of a microbe under specific conditions at different temps. Z-value(°C):Resistance of an MO to temp. variation. The temp. change that changed 1 log cycle in D-value. F-value(min): Time required to kill MOs at 121°C, lethality of heat treatment 39. Margin of Safety: used to minimize possibility of viable survivors of C. botulinum. 1. Low acid food – use 12D thermal process 2. Acid food use 5D b/c C. botulinum doesn’t grow in acidic conditions. Use Clostridium sporogenes to determine if botulinum has been killed. 40. Milk Pasteurization: 1. Receiving: Raw milk is delivered to the plant, tested for quality, pumped into storage silos 2. Clarification: Centrifuge spins pre-heated milk to obtain butter fat content 3. Homogenization: Milk is forced into nozzles at high pressure to keep fat globules in suspension. 4. Pasteurization: 77C for 16 sec, cooled in heat exchanger, kills pathogen, NOT spoilage-formers. 5.