Micr 4070: Week of Feb 22 - Feb 26
Micr 4070: Week of Feb 22 - Feb 26 Micr 407
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This 5 page Class Notes was uploaded by Molly Gersbach on Tuesday March 1, 2016. The Class Notes belongs to Micr 407 at Clemson University taught by Xiuping Jiang in Spring 2016. Since its upload, it has received 36 views. For similar materials see Food and Dairy Microbiology in Microbiology at Clemson University.
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Date Created: 03/01/16
1 2.22.16 – 2.26.16 1. Other types of MAP a. Satchet generator i. Oxygen absorbents: additional means of lowering residual O2 content. These products scavenge O2 to less than 100 ppm. ii. Most employ finely divided iron powder… 1. Fe Fe2+ + 2e 2. ½ O2 + H2O + 2e 2OH 3. Fe 2+ 2OH Fe(OH)2 4. Fe(OH)2 + 1/2O2 + ½ H2O Fe(OH)3 iii. Relies on oxidationreduction potential! b. Ethanol gas generators i. When food is packaged the water vapor penetrate the sachet containing food grade ethanol (50%, w/w) absorbed into silicon dioxide powder, water releases ethanol from its encapsulation and permeates the head space. Effective against mold and some bacteria. Primary use is on high moisture bakery products. c. Radiation Preservation of food i. A lot of pressure to start using this more today ii. Cold process: no increase in temperature, no denaturing of proteins 1. Preserve quality of food products iii. History: patent issued in 1929 iv. Ionizing radiation: 1. Electromagnetic radiation: causes ejection of electrons & formation of ion pairs a. H2O + = H2O+ + e 2. Types: a. Alpha i. Paper b. β Beta i. Electron beams/accelerated electrons (cathode rays) ii. Less penetration depth c. ϒ Gamma i. Co (halflife: 5.27 year) ii. 13Cs (halflife: 30 years) iii. You need a facility that can hold radioisotopes – keep in huge water tank that shields radiation 3. Units: a. Source strength i. Curie (Ci) = 3.7 x 10 disintegrations/sec b. Delivered dose i. Roentgen (r) = radiation delivered in 1 hr from 1 g radium at 1 yard distance c. Absorbed dose – focus on this for food preservation, but don’t need to memorize numbers i. 1 Rad = 100 ergs/g substrate 2 ii. 1 Gray (international/universal unit) = 100 Rads iii. 1 kGy (kilogray) = 1000 Grays 4. Dose Measurement a. NBS calorimeter i. 2.4 x 10 cal/g/Rad b. Operating dosimeter i. Cobalt glass: color change ii. Fricke: Fe Fe proportional to dose 1. When exposed to oxygen, it will be reduced +++ 2. (15.45 Fe /100 eV) Organisms Dose (kGy) Higher animals 0.0050.1 Insects 0.011 Nonsporeforming bacteria 0.510 Bacterial spores 1050 Viruses 10200 5. Effects a. Inhibit sprouting b. Decrease of afterripening c. Milling and sterilizing insects d. Prevention of growth & reproduction of parasites transmitted by food e. Reduction of microbial population 6. Types of treatments – TARGET SPORES D = 3.75 kGy a. Radappertization: commercial sterilization i. 4550 kGy b. Radurization: pasteurization for reducing spoilage m/o i. 0.510 kGy ii. many target spoilage m/o iii. extends shelf life for many products c. Radicidation: pasteurization for eliminating nonsporeforming and nonviral pathogen i. 310 kGy 7. All irradiated foods require a special green symbol label 8. Effects, contd. a. Direct effects: i. DNA breaks ii. Larger the target, more sensitive to radiation b. Indirect effects i. Formation of free radicals/ion pairs such as –H, OH, and eaq 9. Inactivation of m/o a. Similar to thermal inactivation i. Dvalue: number of kGy to reduce m/o population by 1 log or by 90% 3 b. Radiation sensitivity among m/o i. G > G+ > fecal streptococci > spores > Micrococcus radiodurans ii. Micrococcus radiodurans – doesn’t effect the safety of the food as much, no spoilage causing, not a pathogen. Just resistant to radiation. iii. Give a range for each m/o because depends on type of food and strain 10. Molds/Yeasts a. Radiation resistance of molds = radiation resistance of vegetative bacteria b. Yeasts are distinctly more resistant than the molds are and as resistant as the more resistant bacteria need Wednesday’s notes Physical methods… 2. Pulsed electric fields a. PEF processing: application of short pulses (microseconds) of high electric fields to foods between electrodes i. Very effective; comparable to radiation ii. Non thermal process iii. High voltage: 2080 kv/cm iv. Processing time: less than seconds – food must be removed very quickly v. Air bubbles = cause fire 1. So liquid food must be pressurized before going through the chamber b. Gen. properties of PEF i. G more sensitive ii. Vegetative cells more sensitive iii. m/o physiological stage iv. disruption of cell membrane or electroporation v. antimicrobial effects due to these factors: 1. electric field strength (pulse intensity, pulse width, and pulse repetition rate) a. high voltage, increase rate 2. treatment time 3. treatment temperature 3. Microwave heat treatment a. Microwave energy (500 MHz to 10 GHz) b. Internal heat generation caused by intermolecular friction c. Low cost but thermal nonuniformity 4. Ohmic heating a. Also called direct electrical heating b. Thermal effect on m/o c. Stove/oven d. Heat converted from electricity to heat 4 Preservation by Chemicals Understand mechanism of organic acids as antimicrobes Understand how other natural synthetic preservatives work and foods theyre used in Link chemicals preservatives to their abilities to prevent food spoilage 1. Chemical preservatives – GRAS Standards (“generally regarded as safe”) a. Food antimicrobial agents are chemical compounds added or already present in foods i. Ex. In yogurt, lactic acid is already present ii. Ex. Add ascorbic acid or salt to foods b. Mostly bacteriostatic or fungistatic and not –cidal c. Cellular target include the cell wall, cell membrane, metabolic enzymes, protein synthesis, and genetic systems d. Top 4 preservatives: all shortchain fatty acids (carbon from 2 to 6) i. Sorbates ii. Propionates iii. Benzoates iv. Lactates e. Major Short Chain Fatty Acids i. Benzoic Acid and benzoates (salt form of acid) 1. pKa = 4.19, optimum pH 2.5 to 4.5 a. pka is dissociation constant; when the H dissociates 2. Antifungal agent primarily – yeast/mold 3. Antibacterial agent for L. monocytogenes 4. Foods: up to 0.1% in beverages, syrups, cider, margarine, olives, pickles, soy sauce, pie a. Naturally present in cranberries, cinnamon, cloves, berries, etc b. 0.1% is EPA limit: 1,000 microgram/mL ii. Parabens 1. Esterification of the carboxyl group of benzoic acid: methyl, propyl, and heptylparabens 2. Effective range of pH: 3.0 – 8.0 3. Antimicrobial activity proportional to the chain length of alkyl compounds a. Longer the side chain, the more antimicrobial activity b. Want them to dissolve and have strong activity so use a combination of short and longer chain parabens 4. More active against molds and yeast than bacteria 5. Used in foods: baked goods, beverage, fruit products, jams/jellies, fermented foods iii. Propionic Acid and propionates 1. pKa = 4.87 2. Produced by Priopionibacterium freudenreichii subsp. Shermanii 3. Antimolds (primarily) 4. Antibacterial agent 0.15% E. coli, S. aureus, Salmonella, L. plantarum, L. monocytogenes, proteus vulgaris 5. Foods: generally <0.4%, baked goods and cheeses iv. Sorbic acid and sorbates 5 1. pKa = 4.75, optimum pH <6.0 2. antifungal agent: mold/yeast 3. Antibacterial agent: catalaspositive bactria (aerobic m/o) and some FDBRN pathogens v. Acetic acid/acetates 1. pKa 4.75 2. oldest antimicrobial agent – more effective against yeasts and bacteria than molds 3. Antibacterial agent: L monocytogenes, E. coli, salmonella, pseudomonas, Yersinia 4. Foods: baked goods, cheese, fats, oils, gravies, and sauces, and meats vi. Lactic acid/lactates 1. 3.79 PKA, produced naturally by LAB 2. pH control agents and flavoring a. sanitize meat vii.
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