Micro 4070 - notes Feb 15 through Feb 19
Micro 4070 - notes Feb 15 through Feb 19 Micr 407
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This 6 page Class Notes was uploaded by Molly Gersbach on Tuesday February 23, 2016. The Class Notes belongs to Micr 407 at Clemson University taught by Xiuping Jiang in Spring 2016. Since its upload, it has received 21 views. For similar materials see Food and Dairy Microbiology in Microbiology at Clemson University.
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Date Created: 02/23/16
2.15.16 – 2.19.16 Preservation by Temperature & Drying Cont. I. Calculating heat processes for foods a. Modify preservation for different types of foods b.Time at new temp= F /00 (new temperature – 121)/Z c. Come-up & cool-down time II. Timp/Temperature in a can during sterilization graph a. Know that any temperature over 70*C (room temp) will contribute to killing of microbes b. Need to use prev. equation to graph III. Decimal Reduction Times (D-values) for various bacteria a. Longer time, more resistant b. Only target organism in food if it is a human pathogen (if safety is jeopardized) IV. Pasteurization o a. Low heat processing <100 C: finished products not sterile but with less population i. Some enzymes of foods: destroyed ii. Food quality: preserved 1. Vitamins are denatured slower than enzymes iii. Thermoduric cells of spoilage organisms and spores: survived 1. mild heat treatment iv. Heat stable enzymes & toxins: survived b. Combined with other control methods: refrigeration, modified atmosphere packaging, addition of preservatives, reduction of a w c. NOT sterile – room temperature will decrease shelf-life considerably; usually needs to be refrigerated or frozen d. Generally a reduction of 2-5 log e. Milk Pasteurization i. Low temperature/long time (LTLT): at 62.8*C for 30 min ii. High-temp/short time (HTST): at 71.7*C for 15 sec – better products, nutrition, and flavor 1. Much better products than LTLT iii. Ultra high temp/short time (UHT): at 135-140*C for 1- 2 seconds 1. UHT milk has a shelf-life of 6-9 months 2. Energy-saving for industry – profitable f. Add salt into egg – causes an increase V. Canning a. Foods packed into sealed “airtight” containers b. Heated under steam pressure at temps of 240-250*F (116- 121*C) c. Amount of time needed for processing varies from food to food d. Shelf-stable i. Essentially “commercially sterile” e. Spoilage of canned foods i. Inadequate heat processing ii. Leakage of cans iii. Abusie storage conditions f. Microbes of concern i. C. botulinum 1. Anaerobic, spore-former ii. Spore-forming spoilage microorganisms 1. B. stearothermophilus VI. Drying Preservation a. Objectives i. Reduce or prevent growth of vegetative cells ii. Prevent germination/out growth of spores iii. Prevent microbial toxin production b. Method for reducing a of woods i. Dehydration ii. Crystallization iii. Addition of solutes c. Drying Methods i. Natural drying – sun drying 1. Fish & other meats ii. Mechanical drying – controlled – plants, fruits, veggies 1. Spray drying - liquid food sprayed as small droplets into hot air, causing rapid drying 2. Freeze drying (lyophilization)- food rapidly frozen, and then exposed to a high vacumm. The frozen water is removed by sublimation. a. Basically water goes from solid vapor (skips liquid phase) b. Adding water back recovers product freshness 3. Smoking -food products are exposed to low heat and smoke which contains some antimicrobial components. d. Effect of drying on microorganisms: i. The process of drying is not lethal per se to m/o: bacteria endospores survive, as do yeasts, molds, and many gram-negative and positive bacteria. 1. Osmophilic (probably Yeasts that are highly resistant to osmotic pressure), halotolerant (salt tolerant), xerotolerant ii. Most troublesome group of m/o in dried foods are the molds such as Aspergillus glaucus group iii. Difference in dry resistance due to osmoregulatory capacities (to maintain homeostasis with respect to water content) 1. Can grow at lower water activities e. Mechanism of drying preservation i. Temperature effect ii. Reducing a welow growth limit of m/o iii. Extended lag time and reduced growth rate 1. Longer shelf life f. low-moisture foods (LMF): i. less than 25% moisture, and water activity (a ) w between 0.00 and 0.60 g. Intermediate-moisture foods (IMF): i. 15 to 50% moisture, and an a between 0.60 and 0.85 ii. jelly/jams h. fully preserved dried foods i. Dried milk powders (a 0.w): o 1. evaporation: 140-150 C o 2. spray drying: inlet air temp. 190-250 C 3. jet or nozzle dryer 4. rotary atomizer dryer, Modified Atmosphere Packaging I. “The enclosure of food products in gas-barrier materials, in which the gaseous environment has been changed to slow respiration rates, reduce microbiological growth and retard enzymatic spoilage, with the intent of extending shelf life” a. Extends shelf life but does not improve the quality b. Reduced O2 content, increased CO2, increased nitrogen II. History a. 1882 - Discovered CO2 can help meat b. 1889 - Antibacterial activity of CO 2stablished c. 1895 - 100% CO in2ibited germination of mold spores d. 1928 - First use of MA for apples in Europe (1940 in U.S.) e. 1938 - Beef from Australia (60%) and New Zealand (26%) shipped under CO 2 f. 1977 - 41% retail meat in U.S. vacuum packaged III. Types of MAP a. Controlled atmosphere packaging (CAP): replacement of air with a gas (mixture) and maintaining continuous control of the atmosphere i. Requires sturdy packaging ii. 2-3 combinations of a gas iii. Sealed b. Modified atmosphere packaging (MAP): changing the atmosphere of a package by evacuating and back-flushing with gas or purging with a gas mixture during packaging and sealing i. 2-3 gasses ii. sealed iii. Normally have to do 2-3 times to get desired gas mixture c. Vacuum packaging (VP): removal of air from package and hermetically sealing to maintain a vacuum i. Reduce air significantly IV. Types of Gases Used a. You must gas design a suitable gas composition for your foods i. Normal O2 content in air is 20-25% ii. 78% Nitrogen iii. .03% CO2 iv. 1% Argon b. Most commonly used: i. CO2: Both bacteriostatic and fungistatic, inhibition of product respiration ii. N2: normally a filler gas, doesn’t react with other food products; chemical control 1. Bag of chips to prevent cracking/crumbling iii. O2: color control, control of anaerobic pathogens 1. Keeps meat products bright red 2. Possible anaerobic m/o – Clostridium botulinium iv. CO: antioxidant and decay inhibiting 1. Debate: food industry is being pushed to use this more bc of its effectiveness, however it is technically poisonous to humans – so its safety is being questioned V. Packaging a. Polymers: 4 used (don’t need to memorize which four) but know: i. Polyethylene (PE): used very frequently b. Factors to consider when selecting: i. Barrier properties: permeability to various gases and water vapor ii. Machine capability: resistance to tear, possible to be heat-formed 1. “Heat formed” – make sure the material of packaging can be sealed without being damaged iii. Sealing reliability: ability to seal itself and to the container iv. Anti-fog properties: good product visibility VI. MAP food products a. Red meats: color stability, oxidation control i. Bacon, or high fat meats/foods b. Fresh produce: delay fruit ripening, reduce respiration, retard softening (2~5% O , 2~10% CO ) 2 c. Poultry: precooked products d. Seafood: little use e. Prepared foods: increasing use on fresh pasta, salad, sandwiches, sous vide f. Bakery products: retard the mold growth VII. Changes in meat, fish, and poultry produced by MAP storage a. Enzymatic aging process is unaffected b. Microbial spoilage: bacteriostatic activity of CO2 c. Fat oxidation: reduced O2 levels reduce the oxidation of fats, although oxidation can still occur at low oxygen tensions d. Oxidation of myoglobin: increased CO2 promotes metmyoglobin formation and color darkening i. Myoglobin makes red meat VIII. Changes in fresh produce by MAP storage a. Anaerobiosis created by respiration b. Subsequent anaerobic respiration IX. Effects of MAP on m/o a. Following bacteria have relative sensitivity of m/o to MAP storage at refrigerated temps: i. Pseudomonas (most sensitive), Aeromonas, Bacillus, molds, Enterobacteriaceae, Lactobacillus, Clostridium (most resistant) b. Inhibitory effects of carbon dioxide i. Mechanism unknown: disrupting membrane function, enzyme inactivation, reduction of intracellular pH ii. Extended lag phase and generation time iii. Reduction of total bacterial population c. Effect of MAP on meat spoilage flora i. Shift from G- to G+ 1. b/c Aerobic spoilage m/o ii. Prevents mold growth d. Effect of MAP on foodborne pathogens i. Growth inhibition: 1. S. aureus, Salmonella, Yersinia ii. Possible growth: 1. L. monocytogenes, Clostridia, major concern in MAP packed seafood X. Advantages a. Slower moisture loss and increased shelf life b. Increased market area c. Lower production and storage cost i. No need for so many preservatives ($$) d. High quality products with no or less preservatives e. Improved presentation: fresh appearance, clear view of product XI. Disadvantages a. Initially high cost of packaging equipment, films b. Temperature control required c. Discoloration of meat pigments d. Leakage costs i. Accidental holes in packaging e. Fermentation and swelling f. Potential growth of organisms of public health significance XII. Summary of safety issues of MAP products a. Extended shelf life but pathogens will have time to grow b. Reduced oxygen favors the growth of anaerobic or micraerophilic pathogens c. Organoleptic warning is retarded d. Temperature abuse will allow growth of m/o inhibited by low temp. or CO 2 e. Pathogens of concern: L. monocytogenes, C. botulinum f.
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