In this article we will discuss about:- 1. Spoilage of Vegetables and Fruits 2. Spoilage of Meat and Meat Products – Fresh and Processed Meat 3. Spoilage of Poultry 4. Spoilage of Seafood- Fish and Other Seafoods 5. Spoilage of Dairy Products and Miscellaneous Foods 6. Spoilage of Miscellaneous Foods. Also learn about their causes.
- Spoilage of Vegetables and Fruits
- Spoilage of Meat and Meat Products – Fresh and Processed Meat
- Spoilage of Poultry
- Spoilage of Seafood- Fish and Other Seafoods
- Spoilage of Dairy Products and Miscellaneous Foods
- Spoilage of Miscellaneous Foods. Also learn about their causes
1. Spoilage of Vegetables and Fruits:
The average water content of vegetables is about 88%, with an average content of 8.6% carbohydrates, 1.9% proteins, 0.3% fat and 0.84% ash. The total percentage composition of vitamins, nucleic acids and other plant constituents is generally less than 1%. So the nutrient content, vegetables are capable of supporting the growth of moulds, yeasts and bacteria and being spoiled by any or all of these organisms.
The higher water content of vegetables favors the growth of spoilage bacteria and the relatively low Carbohydrate and fat contents suggest that much of this water is in available form. The pH range of most vegetables is within the growth range of a large number of bacteria, so these are common agents of vegetable spoilage.
The relatively high oxidation- reduction (O/R) potential of vegetables suggests that the aerobic and facultative anaerobic types are the more important organisms. The common spoilage patterns displayed by microorganisms are referred to as soft rot.
They are two types:
Soft rots occur in plants of a number of species and those of carrots are well known. There are different types of bacterial soft roots.
The most common are explained below:
A “soft” root refers to the mushy consistency of the plant or vegetable in contrast to some other spoilage conditions where the product remains firm. The bacteria most commonly associated with the soft rotting of carrots are Erwinia spp., especially E. carotovora. For fruits and vegetables like tomatoes and potatoes, E. Carotovora causes soft rot by entering surface wounds. The cementing substance of the vegetable body induces the formation of pectinases by different microorganisms, which hydrolyzing pectin and producing the mushy consistency.
It is caused by Xanthomonas citrii. The canker consists of external scabs and cork-like lesions that occur on oranges, limes, grapefruits and other citrus fruits.
The largest number of market fruit and vegetable spoilage conditions occur after harvesting and the fungi most often invade bruised and damaged products, some enter specific areas.
The different types of fungal soft roots are:
Gray mold rot is caused by Botrytis cinerea, which produces a gray mycelium. This type of spoilage is favored by high humidity and warm temperature. Among the vegetables affected are – asparagus, onions, garlic, beans (green, lima and wax), carrots, parsnips, celery, tomatoes, endives, lettuce, cabbage, brussels sprouts, cauliflower, broccoli, radish, turnips, cucumbers, pumpkin, squash, peppers and sweet potatoes.
(ii) Sour Rots (Watery Soft Rot):
Sour rots of vegetables are caused by Geotrichum candidum. Among the vegetables affected are asparagus, onions, garlic, beans (green, lima and wax), carrots, parsnips, parsley, endives, globe artichokes, lettuce, cabbage, brussels sprouts, cauliflower, broccoli, radishes, rutabagas, turnips and tomatoes.
The causal fungus is widely distributed in soils and on decaying fruits and vegetables. Drosophila melanogaster (fruit fly) carries spores and mycelial fragments on its body from decaying fruits and vegetables to growth cracks and wounds in healthy fruits and vegetables.
This condition is caused by Rhizopus stolonifer and other species that make vegetables soft and mushy. Cottony growth of the mould with small black dots of sporangia often covers the vegetables. Among those affected are beans (green, lima and wax), carrots, sweet potatoes, potatoes, cabbage, brussels sprouts, cauliflower, broccoli, radish, rutabagas, turnips, cucumbers, cantaloupes, pumpkins, squash, watermelons and tomatoes.
This disease is caused by Phytophthora spp., especially P. infestans. Among the vegetables affected are asparagus, onions, garlic, cantaloupes, watermelons, tomatoes, eggplants, and peppers.
This plant disease is characterized by spotting of leaves, fruit, or seed pods. It is caused by Colletotrichum coccodes and other species.
(vi) Blue Mold Rot:
It is a post-harvest disease of apples and pears that is caused by Penicillium expansum.
The Primary Sources and Routes of Microorganisms to Fresh Meat and Meat Products:
(i) The stick knife.
(ii) Animal hide.
(iii) Gastrointestinal tract.
(iv) Hands of handlers.
(vi) Handling and storage environment.
(vii) Lymph nodes.
The fresh meat like beef, pork and lamb contaminated with various types of microorganisms including anaerobic pathogens. Processed meats are those meat products that are cured, smoked, or cooked. These are also contaminated with some heat resistance anaerobic bacteria such as Clostridium perfringens and CI. bolulinum. Different fungal species are also causing the spoilage to meat products including Thamnidium, Mucor, Rhizopus, etc.
These organisms producing certain visible changes produce whiskers over meat surfaces. (Cladosporium causes black spot, Spirotrichum and Chrysosporium produces some green patches). The most common organism contaminating the ground beef is fungal yeast, Candida lipolytica.
The important bacteria are responsible for the meat spoilages are – Bacillus, Clostridium, Acinetobacter, Pseudomonas, Alcaligenes, Micrococcus, Serratia and Staphylococcus. Meat and meat products will have high nutritional value and the presence of easily metabolized carbohydrates, fats and proteins provide ideal environment for microbial spoilage. Proteolysis and putrefaction are typical results of microbial spoilage of such high protein materials.
The enterobateriaceae members capable of producing the decarboxylase enzyme which decarboxylate the lysine present in the meat to produce cadaverine. Similarly Pseudomonas can produce the same enzyme and can decarboxylate arginine or ornithine present in the meat and produces putrescine. This will leads to the formation of some undesirable properties and offensive odours. This is called putrefaction.
The important poultry items susceptible for microbial spoilage are the skin, the lining of the body cavity, any cut surfaces and other decomposition products. The primary organisms responsible for poultry spoilages are belong to the genus Pseudomonas. This organism produces fluorescent pigment pyroverdine on the surface of poultry products in presence of iron and magnesium.
The other organisms involved in the spoilage are Acinetobacter, Flavobacterium, Corynebacterium, enterobacteriaceae and yeasts such as Torulopsis, Candida, Rhodotorula, Debaryomyces, etc. The essential feature of poultry spoilage is sliminess at the outer surfaces of the carcass or cuts. The visceral cavity often displays sour called visceral taint.
The breast muscle of chicken spoil differently than leg muscles because the latter have a higher pH. The organisms isolated from such parts are Pseudomonas, Acinetobacter, Moraxella and S. putrefaciens. These organisms produces sulfide like odors produces H2S, methyl mercaptan and dimethyl sulfide.
The primary reason of poultry spoilage is mainly restricted to the surfaces than other region. The inner portions of poultry tissue are generally sterile, or contain relatively few organisms, which generally do not grow at low temperatures. So the spoilage organisms are restricted to the surfaces and hide where it is deposited from water, processing and handling.
The surfaces of fresh poultry stored in an environment of high humidity are susceptible to the growth of aerobic bacteria such as Pseudomonas. These organisms grow well on the surfaces, where they form minute colonies produce the sliminess characteristic of spoiled poultry.
The term seafood covers fish, shellfish and mollusks from all waters-fresh, marine, warm or cold. The most important factors influences the spoilage of fish are the kind of fish, the condition of fish, the type and nature of contamination of the fish flesh with bacteria, temperature and use of antibiotics, ice or dip.
In fish, the microbial biota is found generally in three places: the outer slime, gills and the intestines of feeding fish. Fresh or warm-water fish composed of more mesophilic gram-positive bacteria than cold- water fish, which tends to be largely gram-negative (the indigenous bacterial biota of marine water is gram-negative).
Fresh iced fish are spoiled by bacteria, whereas salted and dried fish are more likely to undergo fungal spoilage. The bacteria which are spoiling fish are found to consist of gramnegative rods of the Psendomonas Acinetobacter and Moraxella types. Many fish-spoilage bacteria are capable of good growth between 0°C and 1°C. A large number of Psendomonas spp. are capable of causing fish spoilage at 3°C. The most susceptible part of fish is the gill region, including the gills.
The earliest signs of organoleptic spoilage may be noted by examining the gills for the presence of off-odors. Like meat, fish and other sea foods may be spoiled by autolysis, oxidation or bacterial activity or combinations of these. Fish are more fleshy than meat so rapid autolysis and microbial growth will take place.
The important types of fish spoilage organism are Pseudomonas, Flavobacterium, Proteus, Serratia, E. coli, Clostridium, etc. The other sea foods such as crustaceans, mollusks, etc. are spoiled by many gram-positive and gram-negative bacteria.
Milk is an excellent culture medium for many kinds of microorganisms because of its high nutritional content, moisture, nearly neutral pH and other properties. Dairy products provide high content of milk sugar (lactose), butterfat, citrate and nitrogenous compounds such as proteins, amino acids, ammonia, urea and accessory foods and minerals required by microorganisms. In raw milk at lower temperature, below 37°C, the organism such as Streptococcus lactis, Coliforms, Enterococcus, Lactobacillus and Micrococcus may grow and causes the souring.
At higher temperature, below 50°C Streptococcus thermophilus, Streptococcus faecalis and Lactobacillus bulgaricus produce acids and proteolyses the milk proteins. Similarly, coliform bacteria produce lactic acids and high amount of volatile products such as hydrogen, carbon dioxide, acetic acid, formic acid alcohols, etc. Clostridium spp. and its spores ferment butyric acid with the production of hydrogen and carbon dioxide gas. Like acid production microorganism produces gas also constitutes the spoilage of dairy products. The most important gas producers are coliforms, Clostridium spp, Bacillus spp and some yeast.
Another way of spoilage of dairy products is accomplished by proteolysis. The hydrolysis of milk protein by microbial enzymes leads to the formation of shorter peptides causes bitter flavor to variety of milk products. Proteolysis is favored by storage at a low temperature, by the destruction of lactic and other acid formers by heat and destruction of the acid already produced by mould or neutralization of acids by products of other microorganisms. The most important non spore forming proteolytic bacteria are Micrococcus, Alcaligenes, Pseudomonas, Proteus, Flavobacterium, Serratia and spore formers are Clostridium and Bacillus.
Ropiness is a condition sometimes seen in raw milk that is caused by Alcaligenes viscolactis. Its growth is favored by low- temperature maintenance of raw milk for several days. The “rope” consists of a slime-layer material produced by the bacterial cells and it gives the product a stringy consistency.
The other organisms causes the ropiness include Enterobacter aerogenes, Enterobacter cloacae, Klebsiella oxytoca and E. coli. Ropiness caused by Enterobacter usually is worse near to the top of the milk. Certain strains of lactic acid bacteria, Streptococcus lactis var hollandicus causes ropiness in milk, similarly Lactobacillus bulgaricus, Lactobacillus casei and Lactobacillus plantarum are also produces ropiness.
There are reports revealing that variety of bacteria can grow and produce various colors over milk products. The color may be due to the surface growth of pigmented bacteria or moulds in the form of a scum or ring or may be present throughout the milk. Pseudomonas syncyancea produces a bluish to brownish color in milk called blue milk.
Pseudomonas synxantha and Flavobacterium may cause yellow color in the cream layer milk results lipolysis and proteolysis is termed as yellow milk. Brevibacterium erythrogenes and Serratia marcescens are responsible for red milk, a red layer at the top of the milk due to their pigmentation. A brown color may result from Pseudomonas putrefaciens termed as brown milk. Butter is mainly spoiled by the combined activities of lactic acid bacteria, gas formers and mould such as Geotrichum candidum.
The spoilage of egg may exhibit crack, leak, loss of bloom, stained or dirty spots on the exterior. Due to spoilage, the egg white will become thinner and more watery; the yolk membrane becomes weaker. More spoilage of egg is caused by bacteria than moulds. The bacterial spoilage of egg is called rots.
Different types of bacterial rots are:
(i) Green rot-Pseudomonas fluorescens
(ii) Colorless rot-Alcaligenes, Acenitobacter, etc.
(iii) Black rot-Pseudomonas
(iv) Pink rot-Pseudomonas
(v) Red rot-Serratia marscescens
Some moulds are also causing spoilage of egg are called fungal rotting (Penicillium, Cladosporium, Mucor, Alternaria, etc).
ii. Spoilage of Cereals, Flour and Dough Products:
The microorganism of wheat, rye, corn and related products may be expected to be that of soil, storage environments and those picked up during the processing of these food items. Although these products have high proteins and carbohydrates, their low aw is restricting the growth of all microorganisms.
The microbial flora of flour is relatively low, as some of the bleaching agents present in it. When aw generate at proper level Bacillus and moulds are usually developed. Many aerobic spore formers are capable of producing amylase, which enables them to utilize flour and related products as sources of energy.
If the moisture content is too low mould growth occurs and may be seen as typical mycelial growth and spore formation. Members of the genus Rhizopus and Aspergillus are common and may be recognized by their characteristic spores. The spoilage of fresh dough products, including buttermilk biscuits, dinner and sweet rolls and pizza dough, is caused mainly by lactic acid bacteria, Lactobacillus spp., Strptococcus spp. and Leuconostoc spp.
Fermented bread generally lacks sufficient amounts of moisture to allow for the growth of any organisms except moulds. The most common organisms are bread mould, Rhizopus stolonifer and “red bread mould,” Neurospora sitophila contaminating bread and spoiled the item.
Storage of bread under low humidity restricts mould growth. Homemade breads may undergo a type of spoilage known as ropiness, which is caused by the growth and amylase production of certain strains of Bacillus subtilis, B. pumilus and B. licheniformis. The ropiness maybe seen as stringiness by breaking a batch of dough into two parts.
The source of the organisms is flour and their growth is favored by holding the dough for sufficient time at suitable temperatures. Cakes of all types rarely undergo bacterial spoilage due to their unusually high concentrations of sugars, which restrict the availability of water. Moulds are the common organisms spoiled such kind of food.
Moulds may enter baked cakes from handling and from the air. Growth of moulds on the surface of cakes is favored by conditions of high humidity. On some fruitcakes, growth often originates underneath nuts and fruits if they are placed on the surface of such products after baking. Continued growth of moulds on breads and cakes results in a hardening of the products.