Food Spoilage & Preservation

FOOD TECHNOLOGY, HYGIENE & SAFETY (DEMT 2333)

DIPLOMA IN ENVIRONMENTAL HEALTHVICTORIA INTERNATIONAL COLLEGE

BY: MR KHAIRUL NIZAM MOHD ISADEPARTMENT OF ENVIRONMENTAL HEALTH

OBJECTIVES

• Understand the condition that trigger bacteria to cause spoilage to the food

• Identity the spoilage bacteria

• Study the food preservation methods

FOOD SPOILAGE

• Fruits, vegetables, animals – when harvested or slaughtered decompose by bacteria, moulds, yeast and enzymes.

• Rate of decomposition – type of food and handling• Spoilage may also caused by insects, vermin, parasites,

chemical contamination, physical damage e.g. freezer burn and oxidation.

• Most common due to microorganisms.

• Multiplication of spoilage organisms depends on:▫ type of organism▫competition▫ initial numbers▫composition of food▫Aw (water activity)▫PH▫Temperature▫Oxygen tension▫Presence of inhibitory substances

• Most susceptible to microbial spoilage – perishables e.g.1. meat2. poultry3. fish4. dairy products5. fruits6. vegetables

• Non-perishables or stable foods e.g.▫ sugar▫ flour▫ dried fruit

• stable unless badly handled e.g. store in damp condition

• Spoilage bacteria multiply more rapidly than moulds and used up surface oxygen e.g. meat store in fridge of high humidity – spoiled by aerobic bacteria e.g. pseudomonas causing off odours, slime.

• If low humidity – spoiled by moulds e.g. Cl. Adosporium (Blackspot)

• Mould cause musty odour, off flavour which is harmless but may have mycotoxins.

FRUITS AND VEGETABLES

• Acidity – spoilage by moulds and yeasts thus able to multiply at lower pH than bacteria. e.g. Rhizopus, penicillium

• Vegetable store in vinegar – may be attack by yeast – rusty brown color, pinky white precipitate at base of jar (due to fermentation of yeast). Yeast spoilage detected by alcoholic taste and smell & presence of bubbles in liquid.

COMMON SPOILAGE BACTERIA

FOOD SPOILAGE BACTERIACOMMONLY ISOLATED

TYPICAL SIGNS OF SPOILAGE

Fresh Meat & poultry

ClostridiumPseudomonasAchromobacterAcinobacterMicrococcusFlavobacterium

Slime, greenish discoloration,White spots (bacterial colonies)Souring, putrefaction, off-odours and flavours

Processed meats

AchromobacterPseudomonasLactobacillusStreptococcusClostridiumMicrococcus

Souring, gas production, discoloration, surface slime

FOOD SPOILAGE BACTERIACOMMONLY ISOLATED

TYPICAL SIGNS OF SPOILAGE

Bacon * * if faulty seam – mould spoilage

Streptococcus #MicrococcusLactobacillus

Slime formation, white spots, discoloration, off-odours, souring of vacuum packs (which may blow)

Fish PseudomonasAcinobacter

Off-odours, discoloration

Vegetables PseudomonasErwina/leuconostocCorynebacteriaBacillus/Clostridium

Soft rot, foul odour, discoloration, black spots

Raw milk Streptococcus #MicrococcusLactobacillusBacillusPseudomonas

Tainting, off-flavours and odours, souring (above 15 C), rancidity

# Strep. Fecalis quite salt tolerant** Thermoduric strains resist temp of pasteurization e.g. Strep. fecalis

FOOD SPOILAGE BACTERIACOMMONLY ISOLATED

TYPICAL SIGNS OF SPOILAGE

Pasteurized milk

B. cereusStreptococcus **Lactobacillus **

Bitty cream (sweet curdling), off-odours and flavours

** Thermoduric strains resist temp of pasteurization e.g. Strep. fecalis

BAKED PRODUCTS

• Examples: bread, pies - moulds spores destroy by cooking temperature but post-process contamination from air borne spores.

• Cleansable surfaces, ventilation stop condensation thus prevent mould growth.▫Rhizopus & Mucor spp – white growth with black spots▫Penicillium spp – green▫Monilia sitophilia – red/pink

ROPE

• Caused by Bacillus subtilis , spores present in flour.• Not destroyed by baking temperature• Slow cooking, warm, humid storage – multiplication• e.g. Bread – develops a fruity smell, soft, sticky texture,

discolor (yellow, brown).• Staleness of bread usually develops with prolonged holding

due to physical changes in carbohydrate • Staling does not occur during frozen storage at –18C• Prevented by the use of proprionates.

• Lemau

RANCIDITY

• Fats in dairy products – broken down of fat by microorganisms or natural enzymes, lipase to free fatty acids, produce off-odours, off-flavours.

• Process called hydrolytic rancidity• Heating destroy lipase-producing bacteria but not lipase

already formed.• Oxidative rancidity may also occur in dairy products – due to

presence of copper or iron contamination. Off-odour, flavour due to formation and decomposition of peroxides.

• Prolong storage of fatty fish, meat – rancid unless vacuum packed.

SPOILAGE OF POULTRY

• Rate depend on:▫ storage temperature, ▫number of organism & ▫ type of organism

• Spoilage is evident at around 108 organism per cm 2

• Smell due to Hydrogen sulphide by spoilage bacteria – diffuse into muscle + haem pigments of blood and muscle + air form green pigment under skin (sulphaemoglobin)

Temperature(C) 100 organism/cm2 (days) 10,000 organism/cm2 (days)051015

11.56.23.91.8

7.64.12.61.2

FOOD PRESERVATION

• Preservation – treatment of food to prevent or delay spoilage & inhibit growth of pathogenic organism which render food unfit. May involve:1. Use of low temperature/high temperature2. Dehydration (moisture control)3. Chemicals4. Controlled atmospheres & reduced oxygen5. Physical methods (smoking, irradiation)

1. USE OF LOW TEMPERATURE/HIGH TEMPERATURE• based on metabolic reaction of microorganism, speed of

enzyme depend on temperature▫above freezing (refrigerator)▫at freezing▫below freezing (freezer)

• Temp. above freezing , 1 to 4 °C, perishables, short storage.• Most pathogens slow multiplication below 6°C except:

▫Yersinia, Aeromonas, Listeria monocytogenes.▫Psychrophilic bacteria – Pseudomonas, Acinobacter,

Flavobacterium▫Mould – Penicillium, Mucor.

• Temperature below freezing – inhibition of enzyme reactions, also reducing available moisture.

• Aw (water activity) at 0 °C = 1.0 -15°C = 0.85(is defined as the ratio of the vapor pressure of water in a material (p)

to the vapor pressure of pure water (po) at the same temperature)

• freezing destroys some bacteria thus reduce number of organism especially at –2°C and – 5°C but enzymes active at this temperature

• Spores and toxins not affected by freezing.• Some parasites destroyed.

▫ Trichinella cyst = -18°C for 21 days▫ Cysticercus bovis = -10°C for 14 days▫ Fish nematode = -20°C within 24 hrs

• Lowest recorded temperature for bacteria growth is = -20°C Yeast = -34 °C

• In practice very few organism grow below -8°C, even at 0°C takes one day to increase ten-fold in number.

 • Thawing – rapid growth especially at 20 – 30°C• Vegetables – Blanched before frozen (immersed in hot water

for short period approxmately one minute)• Blanching destroy enzymes e.g. peroxidases (which produce

off-odours, flavours), reduce bacterial load, fix color, remove trapped air, induce wilting to aid packing.

 • Over blanching – loss of vitamin C by leaching.

• Careful handling of frozen food – to avoid Staphylococcus contamination.

 • Most foods will keep for prolonged periods in freezer,

although a recommended shelf-life is given because of loss of texture, flavor, tenderness, color, nutritional quality.

 • Packaging/wrapping to avoid loss of moisture from surface

i.e. freezer burn. Oxidation of food slower at –18°C.

• Vacuum packing reduce oxidative rancidity.

• Laminate packaging – RTE (ready-to-eat) foods, Boil-in-bag e.g. Berahims

• Others :- Films of low density polyethylene, polyesters, aluminum foils, polypropylene

• Fish fillets – thin coat of ice to avoid dehydration during storage

• Slow freezing causes damage and loss of quality.

FREEZING SYSTEMS

1. Fluidized-bed freezing – particulate vegetable e.g. peas -move along tray very cold air blast approximately 3-8 minutes (quick frozen so products does not weld together).

2. Air-blast freezing – commonest – static tunnel, trolleys of boxed products e.g. beef, cakes, pizzas, fish fillets are pushed through continuous belt, air temp –30 to –40°C approximately 2-3 hrs.

3. Plate freezing – food pack in cartons on narrow metal shelves e.g. boil-in-bag. Takes 2-3 hrs.

4. Cryogenic freezing – spray or dip into refrigerant e.g. liquid Nitrogen e.g. raspberry, prawns

5. Pellofreeze system – freeze liquids and semi-solids in pellet form e.g. spinach, cream, orange juice, egg, soup.

HIGH TEMPERATURE PRESERVATION

• destroy spoilage and pathogens except heat resistant organism : toxins, spores

• Number of organism survived depend on initial number and strain of organism time and temperature, pH, presence of protective substances e.g. fat and protein e.g. boiling chicken at internal temp of 95°C reduce viable organism e.g. Salmonella by 99%.

1.Pasteurization ▫heat at low temperature, short time e.g. 72°C for 15 sec.

(depend on type of food)▫Able to destroy vegetative pathogens. Toxin and spore

generally survive.▫minimal effect on flavor, nutritional value e.g. milk, ice-

cream, liquid egg, canned fruit.

HIGH TEMPERATURE PRESERVATION

2. Sterilization▫destruction of all microorganisms (commercially sterile)

e.g. low acid canned food▫ - temp > 100 deg C (steam under pressure)

• Factors affecting :-1.humidity (lower moisture more resistant the organism)2.fat, sugar, protein (increase heat resistance)3.pH (neutral preferred –acid/alkaline increase heat sensitivity

e.g. fruits)4.chemicals e.g. nitrites reduce heat resistance5.Aw – reduce water activity will increase heat resistance of

Salmonella, • Disadvantages : reduce nutritional value, flavor, texture.

HIGH TEMPERATURE PRESERVATION3. Ultra heat treatment (UHT)

▫ extended shelf-life without organoleptic changes▫Milk is heated 132°C for one sec before filling into aseptic

containers.▫UHT milk will keep for several month without refrigeration.

4. Cooking ▫Form of preservation, make food palatable and safe for immediate

consumption. Reduce vegetative organism.▫ Internal temperature 75°C, beef 63°C, poultry 71°C

5. Ohmic heating▫Heat food by passing high-voltage electric current through liquid

and solid type of food – cooled and packed aseptically.

DEHYDRATION

• Reduce water, dried foods contain < 25% moisture, Aw <0.6• Most bacteria require Aw 0.95 except spore forming

organism e.g. Bacillus cereus• Gram –ve most sensitive to drying• Gram +ve most resistant to drying (can grow at Aw 0.85)• Yeast and moulds grow at lower levels of Aw than bacteria.• Role of dehydration:

▫more important with packet convenience foods.▫Prevent mould and enzyme spoilage if in air tight packs.

• e.g. sun drying – raisins, figs• artificial drying

DEHYDRATIO

• Methods:1. Hot air e.g. tunnel drying, fluidized-bed, roller drying,

spray drying, denatures protein.2. Spray drying – solution, paste or slurry dispersed into

stream of hot air. Pasteurization required prior to spraying3. Roller drying – paste made – feed on heated drum e.g.

dried cake4. Tunnel dryer – fruits and vegetable 10-15 m long with

trays passed along, hot air blown across trays.5. Accelerated freeze drying – food frozen quickly – mild

heat treatment under vacuum – ice in food change directly to water vapour (sublimation) – removed.

CHEMICAL METHODS OF PRESERVATION

• Additives – prevent spoilage, chemical deterioration and mould growth. Controlled by Food Regulations 1985

1. Salt • Due to osmosis water passes out of the cells (add to 100g

water + 1.7g NaCl decrease Aw by 0.01)• effectiveness depend on concentration, water content,

contamination level, pH, temp, protein content. • Staphylococci grow in high salt concentration (halophiles)

associated with food poisoning from semi-preserved salted meats.

• curing – use salt as preservative• Brining – use for flavour or coloring

2. Nitrates and Nitrites• Curing meat to stabilize red pigment, reduce spoilage• Salt and nitrate solution injected into meat – immersed in

brine solution. In presence of bacteria nitrate converted to nitrite which + amines will produce nitrosamine (carcinogen).

3. Sugar• Act like salt but need higher concentration (6x higher) e.g.

jams, candy, condensed milk, cake.

4. Benzoic acid/Sodium benzoate• inhibit mould and yeast in high-acid foods e.g. fruit juice,

pickles, dressing. Inhibit cellular uptake of amino acids

5. Sulphur dioxide/sulphite• antioxidant, inhibit bacteria and moulds. Use in wine, fruit

juice, sausage.

6. Sorbic acid/potassium sorbate• like benzoate, only active in acid food. Destroy mould, yeast,

Salmonella, Strep, Staph use in bread, jam, syrup, cakes

7. Acetic and lactic acid• lowers pH• Vegetable in brine decrease growth of Gram –ve. Yeast/mould

grow below pH3.0• PH 4.5 (Cl. Perfringen), Cl. Botulinum, Staph.

8. Sodium and calcium propionate• active in low acid food. Prohibit mould. Use in bread, cakes,

cheese, grain, jellies

9. Antibiotics• nisin use in cheese, canned foods. It is heat resistant but

destroyed in stomach by trypsin thus no problem of pathogen drug resistance.

PHYSICAL METHODS OF PRESERVATION

▫Controlled atmospheres• Modified atmosphere packaging (MAP). The air around a

product is modified to contain a different proportion of the gases normally present. Example: lower level of O2, higher level of N2 and CO2 slow down the growth of many spoilage organism.

• Must combine with correct chill temperature• 10% Carbon dioxide for beef last for up to 70 days

▫Restriction of oxygen• Prevented by vacuum packing.• However removal of O2 allows the growth of anaerobes such

as Clostridium perfingens.

▫Smoking• Use in meat, fish after brining or pickling by suspending over

fire – to enhance flavour. Dehydrating effect – non-sporing bacteria destroyed but mould, Clostridium botulinum may survive therefore needs refrigeration < 3°C.

▫ Food irradiation• Ionizing radiation by using gamma rays from Cobalt 60 (x-rays with

energies up to 5 MeV)• Destroys parasite, insects, microorganism except spores, toxins e.g.

chicken, fish, onions, potatoes, spice, strawberries.• Also refer as “cold pasteurization process”• Must be never be considered as a substitute for good hygienic practices• Dose in kiloGray or Grays, 5 Gy is lethal to man• Vitamin destroyed, enzymes not deactivated.

• Disadvantage – increases oxidative rancidity in fatty foods – free radicals and softening of some fruit.

• Dose varies according to product, thickness, orientation, packaging• Max dose = 10 kGy.• Inhibit sprouts e.g. onions, potatoes, delay ripening of fruit.

• Acceptability of food irradiation process▫ Production of toxic agents▫ Some chemical reactions but no toxigenic compounds demonstrated▫ Possible Carcinogenicity▫ No real proof▫ Induced radioactivity▫ Only at very high doses food become radioactive. No danger at

levels used in food processing.▫ Nutritional quality▫ Depend on type of food, radiation dose, processing temp. Generally

vitamin A and E most susceptible.▫ Microbiological interactions▫ At lower dose levels some microorganisms survive. Could cause

radiation-resistant organism

Thank You