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Food Spoilage
Prepared by
القزاز عدنان محمد
Supervisor
المناعمة الرؤوف عبد
Food spoilage :means the original nutritional value, texture, flavor of the food are damaged, the food become harmful to people and unsuitable to eat.
:Food poisoning (or food borne illness ) is an illness that you
may get after eating food contaminated by , , , certain bacteria parasites viruses or
chemicals.
Conditions for Spoilage :
•Water
•pH
•Physical structure
•Temperature
Intrinsic Factors: Composition
pH
presence and availability of water
physical structure
presence of antimicrobial substances
Composition and pH
pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food
Water availabilityin general, lower water activity inhibits microbial growth
water activity lowered by:DryingAddition of salt or sugar
osmophilic microorganismsprefer high osmotic pressure
xerophilic microorganismsprefer low water activity
Physical structure
grinding and mixing increase surface area and distribute microbes promotes microbial growth
outer skin of vegetables and fruits slows microbial growth
Antimicrobial substancescoumarins – fruits and
vegetables
lysozyme – cow’s milk and eggs
aldehydic and phenolic compounds – herbs and spices
allicin – garlic
polyphenols – green and black teas
Extrinsic FactorsTemperature :
lower temperatures retard microbial Growth
relative humidity :higher levels promote microbial growth
Atmosphere :oxygen promotes growthmodified atmosphere packaging (MAP)
use of shrink wrap and vacuum technologies to package food in controlled atmospheres
Microbial Growth and Food Spoilage
food spoilageresults from growth of microbes
in food alters food visibly and in other ways, rendering it unsuitable for consumption
different foods undergo different types of spoilage processes
toxins are sometimes produced algal toxins may contaminate shellfish and finfish
Microbial spoilage :
There are three types of microorganisms that cause food spoilage -- yeasts, moulds and bacteria.
•Yeasts growth causes fermentation which is the result of yeast metabolism. There are two types of yeasts true yeast and false yeast.
True yeast metabolizes sugar producing alcohol and carbon dioxide gas. This is known as fermentation.
False yeast grows as a dry film on a food surface, such as on pickle brine. False yeast occurs in foods that have a high sugar or high acid environment.
•Moulds •grow in filaments forming a tough mass which is visible as `mould growth'. Moulds form spores which, when dry, float through the air to find suitable conditions where they can start the growth cycle again.
•Mould can cause illness, especially if the person is allergic to molds. Usually though, the main symptoms from eating mouldy food will be nausea or vomiting from the bad taste and smell of the mouldy food.
•Both yeasts and moulds can thrive in high acid foods like fruit, tomatoes, jams, jellies and pickles. Both are easily destroyed by heat. Processing high acid foods at a temperature of 100°C (212°F) in a boiling water canner for the appropriate length of time destroys yeasts and moulds.
Fungal SpoilageStorage rot in grapes caused
by Botrytis cinerea.
Storage rot in strawberry caused by Botrytis cinerea.
Blue mould rot in tomato caused by Penicilliumi spp. (also
by Fusarium spp.)
Black mummy rot of grapes caused by Guignardia bidwellii
Watery soft rot in apple caused by Sclerotinia sclerotiorum.
Blue mould on oranges caused by Penicillium digitatum.
•Bacteria are round, rod or spiral shaped microorganisms. Bacteria may grow under a wide variety of conditions. There are many types of bacteria that cause spoilage. They can be divided into: sporeforming and nonspore-forming. Bacteria generally prefer low acid foods like vegetables and meat. In order to destroy bacteria spores in a relatively short period of time, low acid foods must be processed for the appropriate length of time at 116°C (240°F) in a pressure canner. Temperatures higher than 100°C [212°F] can be obtained only by pressure canning
•Eatting spoiled food caused by bacteria can cause food poisoning.
Soft rot in tomato caused by Erwinia
carotovora
Microorganisms involved in food spoilage(Other than Canned Foods) with some examples of causative organisms
Food Type of Spoilage Microorganisms involved
BreadMouldy
Rhizopus nigricans Penicillium
Aspergillus niger
Ropy Bacillus subtilis
Maple sap and syrup
Ropy Enterobacter aerogenes
YeastySaccharomyces
Zygosaccharomyces
Pink Micrococcus roseus
MouldyAspergillus Penicillium
Fresh fruits and vegetables
Soft rotRhizopus Erwinia
Gray mold rot Botrytis
Black mold rot A. niger
Pickles, sauerkraut Film yeasts, pink yeasts Rhodotorula
Fresh meat Putrefaction
Alcaligenes Clostridium
Proteus vulgaris Pseudomonas fluorescens
Cured meat
MouldyAspergillus Rhizopus Penicillium
SouringPseudomonas Micrococcus
Greening, slimeLactobacillus Leuconostoc
Fish
Discoloration Pseudomonas
PutrefactionAlcaligenes
Flavobacterium
Eggs
Green rot P. fluorescens
Colorless rotsPseudomonas
Alcaligenes
Black rots Proteus
Concentrated orange juice "Off" flavorLactobacillus Leuconostoc Acetobacter
Poultry Slime, odorPseudomonas
Alcaligenes
Diseases of spoiled food
two primary typesfood-borne infectionsfood intoxications
Food-Borne Intoxications
ingestion of toxins in foods in which microbes have grown
include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning
Toxins ergotism
toxic condition caused by growth of a fungus in grains aflatoxins
carcinogens produced in fungus-infected grains and nut products
fumonisins carcinogens produced in fungus-infected corn
•EnzymesEnzymes are proteins found in all plants and animals. If uncooked foods are not used while fresh, enzymes cause undesirable changes in colour, texture and flavour. Enzymes are destroyed easily by heat processing.
•Oxidation by airAtmospheric oxygen can react with some food components which may cause rancidity or color changes.
Other factors
Infestations (invasions) by insects and rodents, which account for huge losses in food stocks.
Low temperature injury - the internal structures of the food are damaged by very low temperature.
Controlling Food Spoilage
Removal of Microorganisms
usually achieved by filtration
commonly used for water, beer, wine, juices, soft drinks, and other liquids
Low Temperature
refrigeration at 5°C retards but does not stop microbial growth psychrophiles and psychrotrophs
can still cause spoilage growth at temperatures below -10°C
has been observed
High Temperature
Canning
Pasteurization
Canning
food heated in special containers (retorts) to 115 °C for 25 to 100 minutes
kills spoilage microbes, but not necessarily all microbes in food
Pasteurization
kills pathogens and substantially reduces number of spoilage organisms
different pasteurization procedures heat for different lengths of time shorter heating times result in
improved flavor
Radiation
ultraviolet (UV) radiation used for surfaces of food-handling
equipment does not penetrate foods
Gamma radiation use of ionizing radiation (gamma
radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables
Detection of Food-Borne Pathogens
must be rapid and sensitive methods include:
culture techniques – may be too slow
immunological techniques - very sensitive
molecular techniques probes used to detect specific DNA
or RNA sensitive and specific
T ANKH S