What does the microorganism need to grow Factors

What does the microorganism need to grow?

Factors affecting microbial growth in food 1. 2. 3. 4. 5. 6. 7. ………….

Factors affecting microbial growth in food Temperature Water (water activity Aw) Oxygen availability O Presence of nutrition p. H - acidity Presence of antimicrobial substances Physical structure 2

Temperature The most important factor affecting microbial growth Sterilisation Pasteurisation Optimum: 37°C lower temperatures retard microbial growth !!! Higher temperatures eliminate microbes ◦ refrigeration at 5°C retards but does not stop microbial growth ◦ microorganisms can still cause spoilage with extended spoilage ◦ growth at temperatures below -10°C has been observed Cooling Freezing Frozen food

Temperature (2) To prevent growth To eliminate

Water activity Water Activity – Aw: Amount of Water available for chemical reactions and microbial growth 0 No water 1 Pure water Most Fresh Foods - Aw > 0. 99 !

Water activity (2) 0 No water 1 Pure water Ø Foods with lower water activity: ……………… Ø Foods with higher water activity: ……………… Water activity lowered by: Ø drying Ø addition of salt or sugar Ø freezing

Water activity (3) Moulds< Yeasts < Bacteria < Spoilage Bacteria Spoilage Yeasts Spoilage Moulds < 0. 91 0. 88 0. 80

Quiz The best source of bacteria in your kitchen? a) fridge c) sink b) sponge d) dustbin

Oxygen Aerobic– must have oxygen Pseudomonas aeruginosa Anaerobic - no oxygen Clostridium botulinum Micro-aerophiles- small amounts of oxygen Helicobacter pylori Facultative anaerobes – both aerobic and anaerobic Escherichia coli, Listeria, Staphylococcus

Oxygen (2) Preservation: Changes with packaging – canning, MAP, vacuum packaging

p. H - acidity Moulds>Yeasts>Bacteria Optimal: 6. 6 -7. 5 Meat, corn, vegetable, eggs p. H 6 -7 p. H: most pathogens not grow below p. H 4. 5 (except Lactic acid bacteria), Clostridium botulinum: p. H 4. 5 Yeast and Moulds can grow at lower p. H. Acidic Foods-fruits, soft drinks, vinegar, wines, Citrus fruits, pickles, kiwi, condiments (mayo) p. H<3, 5 Fermentation and acidification to reduce p. H

Presence of nutrition Bacteria need protein, fats, vitamins, minerals Structure ◦ Grinding and mixing increase surface area and distribute microbes - promotes microbial growth ◦ Outer skin of vegetables and fruits slows microbial growth are natural microbiological barriers - Whole lemons last longer than slices ◦ Shells on nuts and eggs

Antimicrobial Factors Antimicrobial Factors: ◦ Organic acids (fruits), some enzymes (milk and egg), essential oils (spices), pesticides, antibiotics, food preservatives, chlorine. ◦ Naturally occurring factors ◦ coumarins – fruits and vegetables ◦ lysozyme – cow’s milk and eggs ◦ aldehydic and phenolic compounds – herbs and spices ◦ allicin – garlic ◦ polyphenols – green and black teas ◦ Preservatives: E 200 – E 285

Bacteria are single-celled microorganisms found in nearly all natural environments. Size: ◦ 10 µm length, 0, 5 -2, 5 µm diameter Morphology: Morphological types are grouped into the general categories of: spherical (the cocci), cylindrical (the rods) and spiral.

Fungi - Yeasts Unicellular microorganisms 2 -6 µm width and 10 -30 µm Important role both in ◦ production and ◦ spoilage of food p. H > 4. 5

Fungi - Moulds Multicellular microorganisms 1. 6 – 9. 3 µm Ability to produce toxins (peanut, maize) Aspergillus Food spoilage Food production Rhisopus, Penicillum Roquefort cheese

Fungi - Moulds Toxin in the farm! Mycotoxins can appear in the food chain as a result of fungal infection of crops cooking and freezing, do not destroy mycotoxins Aflatoxin Ochratoxin Fusarium toxins Patulin Cancer, kidney’s damage, damage of immune and nervous systems, death.

Viruses Alive or not? They require living cells of plants, animals, or bacteria for growth. Extremely small (0. 2 – 0. 012 µm) Only visible with electronic microscope Sources: ◦ Water, foods Pathogen

Food spoilage Results from growth of microbes in food Sometimes harmful Bacteria tend to spoil moist foods; fungi dry or acidic foods Spoilage organisms cost the food industry millions of dollars each year.

„GOOD”- Why do we need them?

Good microbes - Why do we need them in a food industry? Bread involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions Dairy Products Yoghurt: Milk is fermented by a mixture of Streptococcus salivarius ssp thermophilus and Lactobacillus bulgaricus Cheese: milk is treated with lactic acid bacteria Other Fermented Foods ◦ ◦ ◦ ◦ sausages hams bologna salami izushi – fish, rice, and vegetables katsuobushi – tuna sauerkraut

Why do we love them? „Beer is dear” Produced by the fermentation of malted grain “Liqueur is quicker” Produced by the fermentation of grain mash followed by distillation to increase the alcohol content „Wine is fine” Produced from the fermentation of fruit juice, usually from grapes

Why do we hate some of them? - Food born diseases

Physical and chemical hazards

What is the hazard? � Hazard – a biological, chemical or physical agent, or condition of food with the potential to cause an adverse health effect � In addition to biological agents (bacteria, viruses, parasites), there are further contamination risk in foods: � Chemical � Physical � Condition of food