Microorganisms in food spoilage
Chemical reactions that produce sensual changes that are offensive in food are controlled by a wide range of microbes that utilize food as a source of carbon and energy source. The organisms that cause these changes comprise prokaryotes (bacteria) as well as single-celled organisms that lack defined nuclei and organelles, as well as eukaryotes unicellulated (yeasts) as well as multicellular (molds) organisms that possess organelles and nuclei.
There are a few microbes that are found in all kinds of spoilt foods, while others are more selective about the food they consume. several species are typically found in one spoiled food item, however there may be a single kind of species (a particular spoilage organism SSO) that is responsible for the the creation of the chemicals that produce off-odors and flavors. When food spoils it is common to see an array of diverse populations that fluctuate in size and frequency as various nutrients become accessible or exhausted. Certain microbes, like molds and lactic acid bacteria release compounds that hinder the competition.
Spoilage microbes can be found as residents of water, soil or the intestinal tracts of animals . They are dispersed through air and the water, and also through the actions that small mammals, specifically insects. It is worth noting that due to the advancement of novel molecular typing methods the scientific names of the spoilage organisms, specifically the bacteria that are present, have changed over the last few times and some names are no longer used. Small mammals and insects can also contribute to the degradation of food, however these are not considered in this article.
1. Food spoilage bacteria
Foods are usually affected by bacteria since it is able to grow in a myriad of conditions , but bacteria can be used to make beneficial fermentations of pickles, dairy products, and even some fermented vegetables. Bacteria don’t thrive when the water activity level is less than 0.91 and need a pH of neutral (6.5-7) in order to lead to food spoilage (e.g. milk, meat, green vegetables, fruits, etc.)
Certain bacteria are capable of creating spores. They are very resistant to heat and can produce toxic substances that are heat resistant. Consumption of spoilt food can cause food-borne illnesses. The most prevalent bacteria responsible for food spoilage are:
Spore-forming bacteria
Spore-forming bacteria are typically found in food products that have been heated because their spores can withstand temperatures of high processing. Gram-positive bacteria can be facultative anaerobes, or strict anaerobes (capable of growing in oxygen or without). Certain spore-forming bacteria are thermophilic, that prefer to thrive at temperatures higher than (as as high up to 55oC).
Some anaerobic thermophiles produce hydrogen sulfide (Desulfotomaculum) and others produce hydrogen and carbon dioxide (Thermoanaerobacterium) during growth on canned/hermetically sealed foods kept at high temperatures, for example, soups sold in vending machines. Thermophiles of other kinds (Bacillus as well as Geobacillus spp.) result in a flat sour deterioration of low or high pH canned foods that have little to no production of gas and one species can cause the bread to become ropy when it is kept at temperatures that are high (126). Mesophilic anaerobes that grow in ambient temperature, trigger different types of spoilage of fruits and vegetables (Bacillus spp. ) and putrefaction in canned goods and the early blowing out of cheeses and the production of butyric acid in cans of fruits and vegetables (Clostridium spp. ) as well as “medicinal” flavours found in low-acid canned food items (Alicyclobacillus) (29). The sporeformers of psychrotolerant produce gas and unpleasant odors in brine-cured and chilled meats as well as Hams (Clostridium species.) in addition to releasing off-odors and gas when vacuum packed chilled foods, chilled beverages and milk (Bacillus spp. ).
Lactic acid bacteria (LAB)
The Lactic Acid bacteria (LAB) comprise a family of Gram-positive bacterial species, which includes species like Lactobacillus, Pediococcus, Leuconostoc and Oenococcus and others. Some are beneficial in making fermented foods like pickles and yogurt. However, in low oxygen as well as low temperature or acidic circumstances, they are the most prevalent spoilage organisms on various foods. Undesirable effects due to LAB include the greening of meat, gas production on cheeses (blowing) and pickingles (bloater damage) and canned or packaged meats and vegetables. Off-flavors such as mousy malty, cheesy or liver-like can be found in meats, wine and milk or juices spoilt by the bacteria. LAB could also produce large amounts of an exopolysaccharide , which creates slime on meats as well as spoilage of some drinks.
Pseudomonas
Pseudomonas and the related genera are Gram-negative, aerobic soil bacteria, a few of which are capable of degrading an array of bizarre substances. They typically require high level of water activity to grow (0.95 or greater) as well as being inhibited when pH lower than 5.4. Certain species thrive at refrigerant temperatures (psychrophilic) while others are more suited to growth at ambient temperatures that are warmer. There are four species in Pseudomonas (P. fluorescens P. Fragi, P. the lundensis as well as P. viridiflava), Shewanella putrefaciens, and Xanthomonas campestris are the primary food spoilage organisms that belong to this group. Soft rots from plant-based food sources occur when the pectins that keep plants together are destroyed by pectic lyase enzymes released from X. campestris, P. fluorescens, and P. viridiflava.
The two types of Pseudomonas can comprise as much as 40% of naturally occurring bacteria found on the surfaces of vegetables and fruits. They contribute to about half of post-harvest rot in fresh produce that is stored in cold temperatures. P. fluorescens P. Fragi P. thelundensis as well as S. putrefaciens are responsible for the spoilage of animal-derived food items (meat fish, milk, and meat) by producing lipases and proteases that result in the formation of sulfides and trimethylamine (off-odors) and also by creating biofilms (slime) on the surfaces (55;73). Certain strains are specially adapted to the cold temperature and can spoil food items when stored in refrigerators.
Enterobacteriaceae
Enterobacteriaceae is a Gram-negative and facultatively aerobic bacteria which comprise a range that are human disease-causing organisms (Salmonella, E. coli, Shigella, Yersinia) and also a vast number of organisms that spoil food. These bacteria are found in the natural world in soil and on surfaces of plants as well as in the digestive tracts of animals, and consequently are present in many food items. Erwinia carotovora is among the most prominent bacteria that cause soft rot on vegetables in the field, or when stored at temperatures that are ambient. Biogenic amines are made in fish and meat by various members of this category while other species produce off-odors and colors within beer (Obesumbacterium) Bacon, beer and other preserved products like meats (Proteus, Serratia), cheeses (several genera) and cole slaw (Klebsiella) as well as eggshells (Proteus, Enterobacter, Serratia). The salt concentration, temperature, and pH constitute the primary elements that determine which, if any of these microbes can cause food spoilage.
A variety of Gram-negative bacteria, like enterobacteriaceae and pseudomonads, release Aryl homoserine lactones (AHLs) to control the expression of specific genes, including the virulence factors depending on cell density. These AHL signals that sense quorum can regulate proteolytic enzyme production and iron chelation in the process of the spoilage of certain foods (134) but the significance for these signaling molecules in different spoilage mechanisms isn’t clear (20;97).
Other bacteria
Other bacteria are involved in the spoilage of chilled, high protein food items like fish, meat or dairy foods. They might not be the most common spoilage organisms but can contribute to destruction of the food ingredients and could cause off-odors. The majority of species are aerobic however some are able to grow in low oxygen levels and can withstand vacuum packaging. Another (Brochothrix) is an anaerobe facultative. Some examples include:
- Acinetobacter and Psychrobacter are the predominant bacteria found on carcasses of poultry at the point of processing, they have also been identified from various spoilt fish and meat. Acinetobacter is found to thrive at pH of as lower to 3.3 as well as has been found in soft drinks that have been spoiled. Both genera don’t produce extracellular lipases, hydrogen Sulfide or trimethylamine (fishy smell) which is why they are thought to be low-risk for risk of spoilage.
- Alcaligenes is a possible contamination of dairy products as well as meat. It has been identified from rancid butter and milk that has an off-odor. The bacteria are naturally present in the digestive tracts of certain animals, and in water and soil.
- Flavobacterium is abundantly found in the natural environment as well as in chilled food items, including the dairy industry, seafood and even meat. It makes use of lipases as well as proteases to cause unpleasant smells in margarine, butter cheese, cream, and other dairy-based products. ingredients.
- Moraxella along with Photobacterium are essential components of the microflora found on the surface of the fish. Photobacterium is able to grow and create trimethylamine in ice-stored vacuum-packed fish.
- Brochothrix is isolated from fish, meat dairy products, along with frozen veggies. When it spoils, it releases an odor that is described as sour sweaty and musty.
2. Fungi in food spoilage
Fungi is the largest microorganisms in the world that play an crucial roles in the spoilage of food. Fungi are osmotrophic and obtain their nutrients through absorption. Fungi are classified into yeast and mold.
Molds
The fungi known as filamentous are not able to produce large fruiting bodies as mushrooms do. Molds are essential to recycle dead animal and plant remains, but also attack a variety of food items and other substances beneficial to human. They’re well-suited for development on and in solid substrates. They generally produce airborne spores and require oxygen to carry out metabolism. The majority of molds thrive in an alkaline pH between 3 and 8, but certain species can thrive at extremely low levels of water activity (0.7-0.8) on dried food items. Spores can withstand extreme conditions in the environment, but they are intolerant to the heat treatment.
The exception is Byssochlammys the spores of which have the D time of between 1 and 12 minutes, at 90oC. Different species of mold have different ideal temperatures for growth that allow some species to thrive in refrigerators. They possess a variety of secondary metabolism, producing a range of carcinogenic and toxic mycotoxins. Certain spoilage molds are toxic and others aren’t. Spoilage molds can be classified into four categories:
Zygomycetes
Zygomycetes have been described as primitive fungi, but they are widely distributed in nature. They grow rapidly using carbon sources that are simple in soil and plant debris and their spores can be found in the air inside. They generally require high-water activities to grow and are known for causing rots on various vegetables and fruits, including sweet potatoes and strawberries. A few common bread molds are Zygomycetes. Certain zygomycetes are used to produce fermented soy products, enzymes and organic chemical. The most commonly used species that spoilage is Mucor as well as Rhizopus. Zygomycetes aren’t well-known for their mycotoxins, but there have been reports of toxic substances produced by certain species.
Penicillium
Penicillium and its related genera can be found in soils and plant waste from in tropical and Antarctic conditions. However, they tend to dominate spoilage in temperate areas. The species are identified by the reproductive structures , which produce conidia chains. They can be beneficial to humans by creating antibiotics and blue cheese some species are also important spoilage organisms. Some produce mycotoxins that are potent (patulin citreoviridin, ochratoxin and penitrem).
Penicillium spp. cause visible decay on pear, citrus as well as apple fruits. They result in massive losses to these crop varieties. They also deteriorate other vegetables and fruits, such as cereals. Some species may be a threat to refrigerated and processed food items like jams and margarine. A similar Genus, Byssochlamys, is the most significant organism responsible for the spoilage of pasteurized drinks because due to the strong heat resistance to its spores.
Aspergillus
Aspergillus and its related molds typically develop quickly and have a greater resistance to extreme temperatures and low activity than Penicillium Spp. and generally dominate the spoilage of warmer environments. Mycotoxins are produced by many aspergilli: aflatoxins, ochratoxinand Territrems, cyclopiazonic acids. Aspergilli can cause a variety of spoilage of non-food and food products (paper leather, paper, etc.) However, they are most likely best known for their rotting of grains, dried beans as well as trees, peanuts and a few spices.
Other molds
Other molds, that belong to a variety of species, are identified from food that has been spoiled. They are generally not the main reasons for spoilage, but they can be a concern for some food items. Fusarium spp. cause plant diseases and generate many important mycotoxins but aren’t significant spoilage organisms. Their mycotoxins can be found in the harvested grains and can pose a health risk.
Yeasts
The yeasts are part of a larger species of organisms known as fungi which includes mushrooms and molds. They are mainly single-celled organisms which are designed to live in specific, typically fluid, environments. They unlike other mushrooms and molds, do not produce harmful secondary metabolites. They can develop in a vacuum the presence of oxygen or not (facultative) they are recognized for their beneficial fermentations that create bread and alcohol-based drinks. They typically colonize food items with an excessive salt or sugar content, which can lead to the loss of pickles, maple syrup sauerkraut, and pickles. Fruits and juices that have low pH are another option, and there are yeasts that develop on the surfaces of food items such as meat as well as cheese (84;129;150). There are four major groups of spoilage yeasts:
Zygosaccharomyces
Zygosaccharomyces and its related genera can tolerate the high levels of sugar and salt levels and are the typical spoilage organisms found in food items like honey, dried fruits jams, along with soy sauce. They typically slow-growing, producing off-odors and flavors , and carbon dioxide, which can trigger food storage containers to expand and then explode. Debaryomyces Hansenii can thrive at concentrations of salt that are as high as 24%, which accounts for its frequent exclusion from brines of salt used to make cheeses, cured meats, and olives. It also contains the most significant spoilage organisms that are found in salad dressings.
Saccharomyces spp.
Saccharomyces spp. are known for their part in the making of wine and bread, however certain strains can also ruin wines and other alcohol-based beverages by causing gassiness, turbidity , and off-flavors caused by hydrogen sulfide and Acetic acid. Certain species thrive on fruit, such as yogurt that contains fruit and some are intolerant to heating.
Candida and related genera
Candida, and the related genera form an eclectic collection of yeasts, a few are also responsible for human infections. They can cause food spoilage, some vegetables , and dairy products.
Dekkera/Brettanomyces are principally involved in spoilage of fermented foods, including alcoholic beverages and some dairy products. They may create volatile phenolic compounds that are that cause off-flavors.
3. Protozoa in food spoilage
Protozoa are single-celled microorganisms with an impermeable cell wall. the form that transmits the organisms is known as cysts. Protozoan parasites are often connected with waterborne and food-borne outbreaks of illness. Food and water act as a conduit for transfer of protozoan parasites one host to the next. The most prevalent foodborne parasites include Giardia lamblia Entamoeba histolytica Cyclospora cayetanensis, Toxoplasma gondii as well as Trichinella spiralis.
4. Algae in food spoilage
Algae are the main producers and provide a variety of nutrients. They are also a component in aquatic habitats. They can contaminate water sources with their toxin . This causes the accumulation of toxic substances in marine life and fish. The toxin may or may not cause harm to marine life. When these fish and other marine creatures are eaten by human beings, this can lead to food-borne illnesses. The algal species that cause poisoning include Gonyaulax catenella Gonyaulax tamarensis Gambierdiscus toxicus Ptychodiscus Brevis Microcystis aeruginosa, Blue-green algae.
5. Viruses in food spoilage
Viral parasites are intracellular parasites which cause a range of ailments that affect animals, plants and human beings. The virus requires specific living cells to reproduce which is why they are not able to reproduce in water or food. Food and water act as carriers for the transmission of viruses between hosts. Foodborne viruses are very solid outside of their host, and they are resistant to acid. A few of the foodborne viruses are Norovirus Hepatitis A virus (HAV), Hepatitis E virus (HEV), Astrovirus (AstV), Rotavirus (RV), Coronavirus, Sapovirus (SaV).
6. Prions in food spoilage
Prions are agents that cause infectious diseases which are the normal proteins in the brain that is misfolded, and is unable to carry a genome, which results in a pathological infective form. When misfolded, it may cause other proteins normally folded to be misfolded. Prion diseases can be a problem for animals and humans. It is also transmitted in humans from animals via the consumption of affected meat and other meat products. Examples of prion disease include Bovine spongiform Encephalopathies’ (BSE), Scrapie Chronic wasting disorder (CWD) as well as Creutzfeldt Jacob Disease (CJD).
