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BIOL 345 Set 4 Preservation 1.pdf

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University of Waterloo
BIOL 345
Barbara Butler

Preservation of Food (MMK 3rd ed, chpts 25- PR1 28) • major consumer trends have an impact on future food preservation techniques consumers want products that are: • convenient • easy to store; satisfactory shelf life • of high quality • less severely processed • less intensely heated; minimally freeze-damaged • less heavily preserved • free from ‘artificial additives’ • fresher • more natural • nutritionally healthier, with • lower salt, lower fat, less saturated fats, more unsaturated fats, lower sugar, fewer calories • safer (Gould) PR2 Controlling microorganisms in foocontrol growth of spoilage and pathogenic microorganisms by modifying: • intrinsic characteristics of food products • extrinsic characteristics of storage environment • implicit factors (e.g., add a harmless competitor) strategies to achieve control: • prevention of initial microbial contamination, or mechanical removal of microbes from food • inhibit, slow, or prevent growth of microorganisms present in or on food • destruction (irreversible inactivation) of microorganisms present but you cannot destroy the food’s quality! PR3 Food preservation strategies: 1. control access (sanitation, cleaning) 2. control by physical removal 3. preservation with chemicals (organic acids, nitrite, etc.) 4. preservation by lowering aw (drying; sugar, salt addition) 5. low-temperature food preservation (refrigeration, freezing) 6. modification of atmospheric conditions (MAP) 7. use of high temperature (incl canning) Loading... 8. use of radiation in preservation 9. other methods (e.g., high pressure processing; biologically-based methods) control of PR4 access: • proper sanitation in processing aids reduction of initial microbial load • easier to produce food that meets microbial standards (e.g., pasteurized milk) • extends shelf life (a) good agricultural practices • on-farm food safety programs • best management practices (BMPs) • What is a "best management practice?" a practical, affordable approach to conserving a farm's soil and water resources without sacrificing productivity (OMAF’s website) PR4a (ii) food processing considerations (a) plant design (b) good manufacturing practices (GMPs) (c) quality of water, ice (d) proper training of food handlers (e) cleaning of processing facilities (f) sanitization of food processing equipment OMAFRA’s Advantage programs for food processors: Level 1: Advantage Good Manufacturing Practices (GMP) GMPs control hazards related Loading...and the processing environment. These practices are the basis of any effective food safety program. The Advantage GMP program covers the hazards associated with: personnel practices shipping, receiving, handling and storage, sanitation equipment pest control recall water safety processing environment g.htm)// PR4b • hair nets, lab coats • record lot numbers of the ingredients going into every batch • elimination of dough-tasting step; introduction of a formal taste-testing step for final product • retention of units of finished product over shelf life duration • detailed tracking records employees of Le Bon Croissant (OMAFRA‘s site; PR5 examples of physical procedures to control microbial load: centrifugation - liquids, e.g., raw milk, fruit juice, syrups • leucocytes, dust, clumps of microbes pelleted to bottom • levels in liquid reduced filtration - liquids, e.g., soft drinks, fruit juices, beer, wine • 2-step process: coarse, then fine filter (0.45-0.7 µm) • air filtration – e.g., spray drying of nonfat dry milk trimming - of damaged vegetables, meats • remove outer leaves from cabbage destined for sauerkraut • visible mold growth from hard cheeses washing - fruits, vegetables, poultry, meat • automated machine washing at high pressure • use of steam, ozonated/chlorinated water for carcass washing • addition of organic acids (acetic, propionic, lactic), tripolyphosphates to wash water PR6 Biofilms • :form on almost any surface • major problem for sanitation; difficult to access and destroy interior cells • equipment surfaces: physical + chemical means of removal where possible biofilm in a water supply pipe PR7 Chemical preservatives: • additives may be antimicrobial; also antioxidants, neutralizers, stabilizers the “ideal” antimicrobial chemical preservative: • wide range of antimicrobial activity • nontoxic to humans, animals • cheap • no effect on flavour, aroma • not inactivated by food or any substance in food • does not encourage development of resistant strains • kills (-cidal) rather than inhibits (-static) microorganisms groupings: (a) antimicrobial preservatives historically used; not legally “additives” (b) “generally recognized as safe” (GRAS) for addition to foods • legally additives, some have restrictions (iii) other chemicals considered to be food additives • legally cannot be used unless proven safe and approved by appropriate authority organic acids (and derivatives): PR8 (i) Na benzoate: 1st chemical preservative permitted by USFDA (1908) COO- COOH Na+ benzoic acid • antimicrobial activity is pH-related • undissociated (protonated) acid is effective agent (i.e., benzoic acid) → active at lower pH; used in “high acid” foods COOCH COO(CH2)2CH 3 3 methyl propyl paraben paraben (methyl p-hydroxy- increasing chain length benzoic acid) → decreasing H2O solubility OH OH parabens: benzoate derivatives that possess esterified carboxyl group (a) undissociated form retained over wider pH range → effective at higher pHs • affect microbial membrane; specific mechanism of action unclear benzoates cont. PR9 • maximum tolerance ~0.1% (may impart “peppery” taste) • primarily affect molds, yeasts (fungistats) • jams, jellies, carbonated beverages • parabens – as above & baked goods, syrups, wine, salad dressings (ii) sorbates: CH3CH=CHCH=CHCOOH (sorbic acid) • Ca, Na, K salts; maximum level of ~0.3% • work best below pH 6.0, ineffective above pH 6.5 • more effective than Na benzoate between pH 4.0-6.0 • used against fungi, some bacteria (not lactic acid bacteria) • cheeses, bakery products, fruit juices, salad dressings, wine • cakes: can use at higher levels than propionates without imparting flavour Loading... (iii) propionates: CH3CH2COOH (propionic acid) • Na, Ca salts; used at 0.3% & above • upper limit of use ~pH 5 to 6 • primarily fungistat (molds); affects rope-forming bacteria in bread • breads, cakes, wrappings for cheese, butter • benzoic, sorbic, propionic acids are lipophilic, weak acids → all have similar mechanism of antimicrobial activity mechanism of action : (see MMK 3rd ed Fig 25.1; 2nd ed, Fig PR10 23.1) organic acid, e.g., benzoic, propionic, sorbic RCOO- + H+ exterior pH = 4.0 H + membrane ATPase RCOOH ATP ADP + Pi RCOOH RCOO- + H+ intracellular pH = proton motive force (PMF) 7.0 {∆Ψ + ∆pH}
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