Foodtecb 1 Food technologies to control the development of microbiological hazards Module 02 - Lecture 04b

Foodtecb 2 Technologies  temperature control  control of water activity  control of pH  control of redox potential  antimicrobial agents Technologies based on:

Foodtecb 3 Temperature HotCold C (Minimum) B (Optimum) A (Maximum) How temperature affects growth rate of a bacterial population

Foodtecb 4 Temperature range for growth of pathogens Temperature°C Min.Opt.Max. Salmonella Campylobacter E. coli S. aureus C. botulinum (proteolytic)1050 C. botulinum (non - proteolytic) B. cereus

Foodtecb 5 Temperature °C Min. Opt. Max. Penicillium verrucosum02031 Aspergillus ochraceus82837 Aspergillus flavus Fusarium moniliforme Temperature range for growth of toxigenic moulds

Foodtecb 6 0° 10° 36.5° 60° 72° 100° Boiling point Pasteurising temperature Freezer Fridge Body temperature Temperature zones SAFETY DANGER DANGER

Foodtecb 7  Water is required for the growth and metabolism of microorganisms  All the water in foods is not available for microorganisms  The degree of availability of water is measured by water activity (a w )  Chemical and enzymatic reactions are also affected by availability of water Water activity

Foodtecb 8 a w is the ratio of water vapour pressure of food (p) to that of pure water (p o ) at the same temperature. a w = p/ p o 0 < a w < 1 Water activity (definition)

Foodtecb 9 Water activity (3) AwAw Reaction rate Growth of: Moulds Yeasts Bacteria

Foodtecb 10 Minimum levels of a W permitting growth ( at near optimum temperatures ) MouldsAspergillus chevalieri 0.71 Aspergillus ochraceus 0.78 Aspergillus flavus 0.80 Penicillium verrucosum0.79 Fusarium moniliforme 0.87 YeastsSaccharomyces rouxii0.62 Saccharomyces cerevisiae 0.90 BacteriaBacillus cereus 0.92 Clostridium botulinum (proteolytic) 0.93 Clostridium botulinum (non-proteolytic) 0.97 Escherichia coli 0.93 Salmonella0.95 Staphylococcus aureus 0.83

Foodtecb 11 Range of a W in foods and their microbial flora a w rangeFoodsMicrobial flora > 0.98 Fresh meats Fresh fish Fresh fruits Fresh vegetables Canned vegetables in brine Canned fruit in light syrup (<3.5 % salt, 26% sugar) (C. perfringens, Salmonella) (Pseudomonas) Fermented sausages Processed cheese Bread Evaporated milk Tomato paste (10% salt, 50% sugar) (B. cereus, C. botulinum, Salmonella) lactobacilli, bacilli and micrococci

Foodtecb 12 Range of a W in foods and their microbial flora a w rangeFoodsMicrobial flora S. aureus Mycotoxin producing moulds Spoilage yeasts and moulds Dry fermented sausages Raw ham (17% salt, saturated sucrose) Xerophilic fungi Halophiles Osmophilic yeasts Dried fruit Flour Cereals Salted fish Nuts < 0.6 No growth but may remain viable Confectionery Honey Noodles Dried egg, milk

Foodtecb 13 a w can be reduced by :  Removing water (drying)  Decreasing availability of water by crystalization (freezing)  Decreasing availability by binding water with water binding agents e.g. salt, sugar Water activity (4)

Foodtecb 14 a w Concentration of NaCl and glucose at various a w values (at 25°C) % w / w glucose % w / w NaCl

Foodtecb 15 Drying methods  sun drying  air drying  spray drying  freeze drying Examples of drying methods are :

Foodtecb 16 Drying rate (1) Drying rate depends on :  air velocity  surface area  air temperature  humidity of the air

Foodtecb 17 pH values limiting the growth of pathogens pH MinMax. Escherichia coli Salmonella typhi Bacillus cereus Clostridium botulinum Staphylococcus aureus 49.8 Saccharomyces cerevisiae Aspergillus flavus Fusarium moniliforme Penicillium verrucosum

Foodtecb 18 pH Acidification  addition of vinegar Fermentation  organic acid  competitive exclusion  antimicrobial agents

Foodtecb 19 pH of different foods Approximate pH ranges of some common food commodities pH Fermented shark Egg white fish meat Citrus fruits milk Soft drinks flour vegetables beer

Foodtecb 20 Redox (E h ) low / negative: reducing medium high / positive: oxidizing medium E h = E o + RT / nF. (oxidant). H+ / (reductant) E h (mv)

Foodtecb 21 Redox (1) E h depends on :  availability of oxygen  ratio of oxidant and reductant  pH  poising capacity  microbial activity

Foodtecb 22 Redox and bacterial growth Obligate or strict aerobes: positive E h Obligate anaerobes: negative or low E h

Foodtecb 23 E h & pH values of foods E h & pH values of foods pH E (mV) to to Raw meat Raw minced meat Cooked sausages and canned meats Wheat (whole grain) Barley (ground grain) Potatoe tuber Spinach Pear

Foodtecb 24 Control of E h  Vacuum packaging  Modified atmosphere packaging by gas flushing: CO 2, N 2

Foodtecb 25 Antimicrobial agents  Curing salts e.g nitrites  Bacteriocins e.g. nisin  Gas: e.g CO 2  Organic acids / salts e.g benzoic, sorbic and propionic acid

Foodtecb 26 Antimicrobial activity Depends on :  pH  lipid  microorganism

Foodtecb 27 Smoking Combination of several factors :  heat treatment  drying  antimicrobial agent in the smoke

Foodtecb 28 Combinations of food technologies Combined technologies  Milk pasteurization and aseptic packaging  Hurdle technologies  fermentation, smoking  Refrigerated processed food of extended durability (REPFED)