food spoilage

Submitted to: - Compiled by:-
Dr. Pooja Tandon Ramandeep Kaur
Lovely School Of Technology MSc Microbiology
And Sciences Roll no.:R291A02
Regd no.:10800274




ACKNOWLEGEMENT

It was a golden opportunity for me to associate myself with this highly professional organization.
I am indebted to Mr.Ashok Mittal vice chancellor and my class incharge Miss Sonia Chawla
I wish to acknowledge my deep sense of gratitude to Miss.Pooja Tandon who provided me full co-operation and knowledge whenever I needed.
I am also very happy to include the names of my friends, well wishers for their valuable help and friendly advice during my term paper.










Ramandeep Kaur










INDEX

CONTENTS PAGE

 Introduction 4 - 7

 Methodology 8

 Result and Discussion 8 - 10

 Conclusion 10

 References 10
























INTRODUCTION
Food spoilage means the original nutritional value, texture, flavor of the food are damaged, the food becomes harmful to people and unsuitable to eat It can deteriorate as a result of 2 things: the growth of microorganisms or the action of enzymes. As it is presumed that spoilage of foods dates from around 6000 B.C. and A. Kircher was the first person who introduced the role of microorganisms in spoiling food in 1658. In 1837 Louis Pasteur showed that souring of milk was caused by microorganisms and in 1860 he used heat to destroy undesirable organisms in wine and beer. The common microbes which causes food spoilage are Pseudomonas ,Lactobaccilus, Erwinia ,Leuconostoc , Acetobacter. Spoilage in foods is characterized by their appearance , odour , taste and some chemical tests. Food preservation could be done to avoid food spoilage. In 1810 preservation of food by canning was patented by Appert in France. In 1813 use of SO2 as a preservative is originated.
Spoilage may be caused due to growth or activity of microorganisms, by insects , by action of enzymes and by physical changes which is caused by freezing , burning , drying. But the discussion to follow will be devoted mainly to spoilage caused by microorganisms. There are following types of microorganisms that cause food spoilage -- yeasts, moulds and bacteria. Moulds are multicellular , filamentous fungi and they grow from cells called spores present in the air. They settle and multiply on suitable foods. At this stage, moulds grow in filaments forming a tough mass and its growth on foods is recognized by its fuzzy or cottony appearance . Then food is said to have gone mouldy. Moulds grow most readily in most conditions, at temperatures between 20ºC and 40ºC. They grow on a variety of foods, particularly meat, cheese, fruit and bread, especially if the food is stored in damp conditions.Usually the main symptoms from eating mouldy food will be nausea or vomiting from the bad taste and smell of the mouldy food. Moulds may remain active at the low temperatures of a refrigerator but they are destroyed by heat above 70ºC. They also like a slightly acid medium. Yeasts may be spherical to ovoid, lemon shaped, pear shaped or elongated, which are found in the air and soil, and on the surface of fruit. Some are able to tolerate fairly high acidic, salt and sugar concentrations and can grow without the presence of oxygen. 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. Yeast cells reproduce by budding They need oxygen, warmth, food and moisture in order to grow successfully. Yeast grow best at temperatures between 25ºC and 30ºC. They are destroyed at temperatures above 60ºC. Both yeasts and moulds can thrive in high acid foods like fruit, tomatoes, jams, jellies and pickles. Both are easily destroyed by heat.

Fungal Spoilage


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.


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: spore-forming and non spore-forming. Bacteria generally prefer low acid foods like vegetables and meat. Many types of bacteria present are harmless but some do cause illness. The bacteria that cause infections in humans are known as pathogens. It is important to avoid conditions which favour their growth in order to prevent infection. They are active over a wide range of temperatures. Some like warm conditions and are active at 75ºC. Others like cold conditions and grow at temperatures as low as 5ºC. This may cause problems in storage of foods. Eating spoiled food can cause food poisoning.
Bacterial Spoilage

Soft rot in tomato caused by Erwinia carotovora.
Moreover food spoilage can also caused through the action of enzymes present in the food. The enzymes are mainly composed of protein, they are sensitive to heat .When the enzymes are activated ,it causes the decay by breaking down the tissues and components of the food in the various ways such as oxidation, browning and ripening. When oxidation occurs the enzymes cause the destruction of certain nutrients e.g. Vitamin C and thiamine . Enzymes can also cause browning in foods as we cut the food such as apple, the exposed surface will turn into brownish colour due to activity of enzymes. Enzymes also play role in ripening process in certain foods as in banana due to enzymes skin colour changes from green to yellow and when its colour changes to dark brown then it is no longer fit to be consumed . The activity of these enzymes stops when they are heated above 70 oC. Heat treatment by blanching (i.e. a mild heat treatment designed to inactivate enzymes that may cause deterioration during storage) is recommended .
SPOILAGE OF MEAT :Raw meat is subject to change by its own enzymes and by microbial action and its fat may be oxidized chemically.Autolytic changes include some proteolytic action on muscle and connective tissues and slight hydrolysis of fats. This preliminary hydrolysis of proteins by the meat enzymes helps microorganisms start growing in the meat by furnishing the simpler nitrogen compounds needed by many microorganisms that cannot attack complete native proteins.
Meat is an ideal culture medium for many microorganisms because it is high in moisture , rich in nitrogenous foods and supplied with minerals and accessory growth factors. The factors that influence growth of microorganisms are : Intrinsic and Extrinsic factors. Intrinsic factors includes food composition which is a critical factor that influences microbial growth. As meat contains large amounts of proteins or fats so spoilage can produce foul odors. This proteolysis and anaerobic breakdown of proteins that yields foul smelling amine compounds which is called as putrefaction. And pH of food is also another intrinsic factor. In meats at neutral and alkaline pH bacteria are more dominant than yeasts and moulds to cause spoilage and putrefaction. Water availability also affects the ability of microorganisms on food. In general, lower water activity inhibits microbial growth. Water activity lowered by drying and addition of salt or sugar. As meat is rich in moisture so growth of microorganisms occurs on it to cause spoilage. Also the oxidation-reduction potential of a food influences spoilage. When meat products are cooked, they have low oxidation –reduction potentials. These products with their available amino acids, peptides and growth factors are ideal media for growth of anaerobes. Another type is Extrinsic factors which includes Temperature which is an important factor to determine whether a food will spoil. Lower temperatures retard microbial growth. Also relative humidity is a critical factor as higher levels of humidity promote microbial growth.
Upon the death of animal, invasion of tissues by contaminating microorganisms takes place. The greater the load in the gut, the greater invasion of tissues occurs. If the animal is fatigued, bacteria are more likely to enter the tissues. But rapid cooling will reduce the rate of invasion of the tissues by microorganisms. Microorganisms are spread in the meat through the blood and lymph vessels and connective tissue interspaces. (Refrence: www.wikipedia.com, www.wikieducator.org& home.pacific.net.hk)

METHADOLOGY
The methods to determine meat spoilage should be based on cause and mechanism of spoilage. Firstly organoleptic characteristics are determined to check spoilage of meat such as colour, odour, touch and taste .Colour is changed into brown, gray or green and surface sliminess or sticky surface occurs. Souring and putrefaction also occurs as a indicative of spoilage. Also the production of ammonia, indoles and amines occurs from spoiled meat. The metabolic byproducts such as diamines cadaverine and putrescine have been considered as spoilage indicators of meat. Analysis of these compounds in meat spoilage occurs by using a chemiluminescence -flow injection system with a photomultiplier detector. There are also some chemical methods to determine meat spoilage such as - Determination of volatile reducing substances, Determination of amino acids and indoles. Physical methods – Measurement of pH changes, Determination of surface tension. Physicochemical methods- Determination of meat swelling capacity, Determination of extract release volume. ( Refrence: An Introduction to Microbiology)

RESULTS AND DISCUSSION
MICROORGANISMS ISOLATED FROM MEATS:
Bacteria :Pseudomonas , Aeromonas ,Micrococcus ,Lactobacillus, Staphylococcus, Streptococcus.
Molds: Sporotrichum, Mucor , Aspergillus , Penicillium , Rhizopus , Cladosporium
Yeasts :Candida , Torulopsis, Torula , Rhodotorula.
Under aerobic conditions 1. Surface slime occurs which is caused by Pseudomonas, Streptococcus, Leuconostoc and Micrococcus. 2. Changes in colour occurs which is caused by bacteria Lactobacillus , Leuconostoc and black spots is caused by mould Cladosporium. 3. Rancidity of fats is caused by Pseudomonas. 4. Phosphorescence is caused by phosphorescent or luminous bacteria such as Photobacterium. And under anaerobic conditions souring is caused by Clostridium and putrefaction is caused by Pseudomonas and Alcaligenes.
There are following measures that could be taken to avoid food spoilage. The preservation of meats as of most perishable foods is accompanied by variety of methods. It is important to reduce or eliminate the disease causing microorganisms and to maintain the quality of a food with proper storage and packaging.
Asepsis: It begins with the avoidance of contamination from the exterior of animals. To remove the dust water spraying of animals should be done before slaughter and knives used to bleed animals should be clean.
Use of low temperature : It is the most commonly used method to preserve the meat. Chilling – For chilling storage temperature vary from -1.4 to 2.2ºC. The relative humidity is lowered with an increase in storage temperature. Increasing amounts of carbon dioxide in the atmosphere inhibit microorganisms but also increase the formation of metmyoglobin which causes loss of natural colour. But there are some microorganisms that give trouble in chilling storage of meats such as Pseudomonas , Micrococcus, Lactobacillus , Leuconostoc and Alcaligenes. Freezing- The preservation of frozen meats is effective as the storage temperature drops from -12.2 toward -28.9 ºC. The freezing process kills or decrease the number of bacteria slowly during storage. But the bacteria that grow on meat during chilling can resume growth during thawing of meat.
Use of irradiation : It is mainly employed on large, hung pieces of meat and the ultra violet rays are used to reduce the numbers of microorganisms in the air and it has been used in conjunction with chilling storage to increase the keeping time.
Preservation by drying: Salt is used as a drying agent and once the moisture is removed from the meat, it will spoil at a much slower rate.
Use of preservatives: Curing – In older days curing of meats was for the purpose of preserving by salting without refrigeration but now refrigeration must done. The curing agents are sodium chloride, sugar, sodium nitrite and vinegar. Sodium chloride is used as a preservative and flavoring agent. Its primary purpose is to lower the water activity. Sugar adds flavor and also serves as an energy source for nitrate –reducing bacteria in curing solution or pickle. Most commonly sucrose is used for this. Sodium nitrite is the source of nitric oxide which is the real colour fixative and has some bacteriostatic effect. (Refrence: Food Microbiology By William & Dennis and www.answers.com)
CONCLUSION
Based upon the results the best method to preserve the meat would be by chilling. More meat is preserved by the use of chilling storage. But there are also some microorganisms that give problem in the chilling storage of meats—Psychotrophic bacteria such as Pseudomonas, Streptococcus, Leuconostoc , Micrococcus and Alcaligens.
REFRENCES
www.wikieducator.org www.wikipedia.com home.pacific.net.hk www.answers.com Food Microbiology By William C. Frazier & Dennis C. Westhoff An Introduction to Microbiology By P. Tauro & K.K Kapoor.