In this article we will discuss about the microorganisms that are present in various food products.
Microorganisms of Plant Food Products:
1. Fruits and Vegetables:
Fruits and vegetables are generally contaminated by bacteria including species of Bacillus, Enterobacter, Lactobacillus, Leuconostoc, Pseudomonas, Sarcina, Staphylococcus, Streptococcus etc.
Various moulds and yeasts also inhabit the fruits and vegetables. Fruits and vegetables get rotten as a result of the microbial degradation of pectin, the substance responsible for maintaining the firmness and texture of fruits and vegetables.
Microbes produce pectin esterases and a polygalacturonases enzymes that hydrolyse pectins resulting in the formation of soft rots in fruits and vegetables. 20% of the harvested crops of fruits and vegetables are lost to spoilage mainly because of the activities of bacteria and micro-fungi.
(i) Contamination through infection:
Fruits and vegetables are normally susceptible to bacterial, fungal and viral infections. These infections invade the fruit and vegetable tissue during various stages of their development and result in the subsequent spoilage.
(ii) Contamination through post-harvest handling:
Usually, mechanical handling of fruits and vegetables during post-harvest period produce “breaks” in them which invite microbial invasion. Since the pH of the fruits is relatively acidic (i.e., high in sugar), they are more susceptible to fungi in contrast to vegetables which are more susceptible to bacteria because of their pH being slightly higher (5.0 to 7.0; less in sugar).
2. Cereals:
Cereals and cereal products contain microorganisms from insects, soil and other sources. Bacillus, Lactobacillus, Micrococcus, Pseudomonas, etc. are the bacteria which are generally found on freshly harvested grains.
Wheat flours are contaminated mostly by bacteria such as species of Bacillus, Micrococcus, Sarcina, Serratia, coliforms, etc. Moulds like Aspergillus, Penicillium, Rhizopus, Neurospora, Endomyces are also very common.
Microorganisms of Animal Food Products:
1. Meats:
The interior portions of meat are usually free of microbial contaminations if healthy animal is properly slaughtered. The fresh cut meat gets immediately contaminated with microorganisms derived from globes, hands, implements used to cut the meats, hides, hairs, intestines of animals, and the air of the slaughter house.
Each new surface of meat, resulting from a new cut, adds more microorganisms to the exposed tissue. The more common microorganisms occurring on fresh meats include both bacteria and moulds. Bacteria such as species of Bacillus, Clostridium.
Escherichia, Pseudomonas, Lactobacillus, Micrococcus. Streptococcus, Sarcina. Salmonella occur most commonly. Moulds that contaminate fresh meat include Cladosporium, Geotrichum, Mucor, Penicillium, Sporotrichum, etc. Yeasts are less common in occurrence.
2. Eggs:
Clean eggs with un-cracked shell normally do not contain microorganisms within. Poor sanitary and storage conditions under which it is held determine its subsequent microbial content.
Bacteria and moulds may enter the egg through cracks in the shell. The microbial flora recovered from the egg shells generally include the species of bacteria Micrococcus, Pseudomonas, Streptococcus, Staphylococcus, Sarcina, and the moulds.
3. Poultry:
The surface of freshly dressed eviscerated poultry has microbial flora which is derived from the live birds or from the manipulations during killings, defeathering and evisceration. Species of Bacillus, Enterobacter, Escherichia, Proteus, Pseudomonas, Salmonella, and Staphylococcus constitute the major microbial flora on the skin of freshly dressed eviscerated poultry.
4. Fish:
The microbial flora of freshly caught fish usually reflects the microbial conditions of water from where they are harvested. Fish micro-flora includes bacteria like Alcaligenes, Micrococcus, Pseudomonas, Serratia, Vibrio, etc.
When the fish are cleaned and cut on shipboard under poor handling conditions, they invite more microorganisms to grow on it. These microorganisms can be examplified by the species of Achromonobacter, Bacillus, Micrococcus, Pseudomonas, etc.
Microorganisms of Processed Food Products:
The quality and quantity microorganisms associated with processed food including baked and fermented ones depends upon the ingredients used and processing methods. Microorganisms present in flour, sugar, fat, milk, egg, water, colours, manhandling, instruments, etc. may contaminate the baked food products.
Spore forming bacteria may escape destruction and become responsible for ropiness in baked bread during baking process. The ropiness of the bread is caused by Bacillus subtilis or Bacillus licheniformis. Further, the baked products are subject to contamination by moulds such as Mucor, Rhizopus, Aspergillus, etc.
The fermented foods like pickles get contaminated by microorganisms through air, man, and equipment’s. Most of these organisms do not multiply as the reduction of the medium is considerably acid. Some yeasts and yeast-like forms such as Torula, Oidium, etc. which are acid-tolerant, establish in these foods on exposure.