- Cereals and cereal products are globally significant sources of human and animal nutrition.
- The surfaces of harvested grains retain a portion of the natural flora they had while growing, in addition to contamination from dirt, insects, and other sources.
- Freshly harvested grains are loaded with between a few thousand and one million bacteria /gm and mould spores.
- Molds can grow in cereals, grains, flours, and other cereal-based foods that have excessive moisture, but yeasts and bacteria can thrive in foods with even more moisture.
- Pseudomonas, Micrococci, Lactobacilli, and Bacillus are the most prevalent spoilage bacteria.
- The scouring and washing of grains eliminates some bacteria.
- During milling, the majority of microorganisms are eliminated along with the exterior regions of the grain.
- The milling processes, particularly bleaching, diminish the number of organisms.
- Recontamination may occur during the mixing and conditioning processes.
- Bacillus spores, coliform bacteria, and a few species of the genera Achromobacter, Flavobacterium, Sarcina, Micrococcus, Alcaligenes, and Serratia are found in wheat flour.
- In addition to aspergilli and penicillia, Alternaria, Cladosporium, and other genera also produce mould spores.
- Aspergillus flavus and A. parasiticus are responsible for the production of aflatoxin.
- There are several hundred to several thousand bacteria and mould per gramme in corn meal and flour. Fusarium and penicillum species are the most prevalent moulds.
- Malts contain a high number of microorganisms, typically in the millions per gramme, due to their incubation in wet circumstances.
- The surface of freshly baked bread is devoid of living microorganisms, however it is susceptible to contamination by airborne mould spores during cooling and prior to packaging. Similarly, cakes are susceptible to contamination.
- Bacteria spores that can induce ropiness in bread will survive the baking process.
- Due to the existence of mycotoxin, contamination of cereal grain products with mould has become a significant concern.
What is spoilage?
- Spoilage is the process by which food degrades to the point where it is no longer edible or its quality of edibility is diminished. Any alteration that renders a product unfit for human consumption.
- Spoilage is a complex process in which a mix of microbiological and metabolic processes can lead to the formation of aberrant end products. One of the primary reasons for preservation.
- Growth of microorganisms in diet depends on
- The attributes of a product.
- Method of processing.
- Method of storage.
- Methods of preservation and treatment Growth-affecting factors
- Fundamental parameters.
- Extrinsic parameters.
Contamination of Cereals and Cereal Products
- The surfaces of harvested grains retain part of the microbes they had while they were growing, in addition to contamination from soil, insects, and other sources.
- Few thousand to millions of microorganisms per gramme and zero to several hundred thousand mould spores are present in freshly harvested grains.
- The majority of bacteria belong to the Pseudomonadaceae, Micrococcaceae, Lactobacillaceae, and Bacillaceae families.
- Scouring and washing the grains remove some bacteria, but milling removes the vast majority along with the exterior areas of the grain.
- The milling processes, particularly bleaching, lower the number of organisms, but there is a risk of contamination during subsequent operations, such as mixing and conditioning.
- Bacillus spores, coliform bacteria, and a few species of the genera Achromobacter *, Flavobacterium, Sarcina, Micrococcus, Alcaligenes, and Serratia are found in wheat flour.
- In addition to aspergilli and penicillia, Alternaria, Cladosporium, and other genera also produce mould spores. The number of microorganisms per gramme ranges from a few hundred to millions.
- Most retail samples of white wheat flour contain several hundred to several thousand bacteria per gramme, twenty to thirty bacillus spores per gramme, and fifty to one hundred mould spores per gramme.
- Patent flours often yield lower counts than straight or clear flours, and the counts drop with storage. On average, 8,000 to 12,000 per gramme are found in graham and wholewheat flours, which contain the exterior portions of the wheat kernel and have not been bleached.
- The table depicts the typical microflora found on several cereal grains and cereal products. There are several hundred to several thousand bacteria and moulds per gramme in cornmeal and flour.
- Fusarium and Pencillium species are the predominant moulds. Due to their incubation in a damp environment, malts typically include millions of bacteria per gramme.
- The surface of freshly baked bread is nearly devoid of living microorganisms, however it is susceptible to contamination by airborne mould spores during cooling and prior to wrapping.
- During slicing, contamination from germs in the air, on the knives, or on the packaging is possible.
- Similarly, cakes are susceptible to contamination. Bacteria spores that can induce ropiness in bread will survive the baking process.
- Due to the potential presence of mycotoxins, the mould contamination of grains and cereal products has become a significant public health concern.
- Aspergillus flavus and Aspergillus parasiticus, which can create aflatoxin, are frequently isolated, highlighting the need to decrease mould contamination and avoid conditions conducive to their growth.
- Other commonly isolated moulds, such as fusaria and penicillia, can also produce mycotoxins.
Contamination source of cereal products
- Air and dust
- environmental conditions (such as drought, rainfall, temperature, and sunlight).
- harvesting and processing machinery
- Unsanitary equipment and handling practises.
- Condition and temperature of storage.
- Transport containers
Spoilage Preservation of Cereals And Cereal Products
There is minimal problem in avoiding the growth of germs on the vast majority of cereals and cereal products as long as they are kept dry. These materials are stored in bulk or in containers to deter vermin, resist fire, and prevent abrupt fluctuations in temperature and, consequently, the accumulation of moisture. Dry items should be kept at a temperature between 4.4 and 7.2 degrees Celsius. Numerous bakery products, such as breads, rolls, cakes, pastries, pies, and canned mixes, contain sufficient moisture to be susceptible to deterioration absent particular preservation techniques or rapid turnover.
1. Asepsis Technique
- Similar to other food sectors, proper cleaning and sanitization of equipment is crucial for both sanitation and preservation purposes.
- Inadequately sterilised equipment may be a source of rope bacteria and acid-forming bacteria responsible for sour doughs.
- Bread, cakes, and other baked foods susceptible to deterioration by moulds should be safeguarded from mould spore contamination.
- Protection of bread is very crucial. The bread should be quickly cooled in an atmosphere devoid of mould spores, sliced with spore-free utensils, and wrapped without delay once it is removed from the oven.
2. Use of Heat
- Unbaked, partially-baked, or fully-baked bakery products may be sold. It has been reported that mould spores on proofer cloths in bakeries can develop sufficient heat tolerance to survive baking.
- Unbaked or partially baked products are typically stored on a retailer’s shelf for a brief length of time or are refrigerated for prolonged storage.
- Some specialty loaves, such Boston brown bread and nut bread, have been canned successfully.
3. Use of Low Temperatures
- Homemakers may use normal room temperatures for short-term storage of baked goods; however, keeping times could be extended and the risk of food poisoning reduced if extremely warm temperatures, such as those of hot kitchens or summer weather, were avoided and the foods were stored in a cool place or even the refrigerator.
- The frozen storage of bread products is growing. Products that are unbaked or only half baked, waffles, cheesecake, ice cream pie, and fish, poultry, and meat pies are typically frozen.
- Bread and rolls can be effectively frozen and preserved for months.
4. Use of Chemical Preservatives
- Due to insufficient drying facilities or wet weather, grain may be stored with a relatively high moisture content.
- For instance, corn held at moisture levels above 20 percent is susceptible to mould growth and probable mycotoxin generation.
- In addition to insecticides and fumigants, the efficiency of ammonia and propionic acid in reducing mould growth and mycotoxin generation has been investigated.
- Two percent ammonia and one percent propionic acid inhibit mould growth in damp corn.
- More preservatives, notably mould inhibitors, have been added to bread, rolls, cakes, and other bakery products.
- Extensive use is made of sodium and calcium propionate, sodium diacetate, and sorbates. To combat rope, dough acidification with acetic acid has been utilised.
5. Use of Irradiation
- In bakeries, UV radiation have been used to eliminate or reduce the amount of mould spores in dough and proofing rooms, on the blades of slicing machines, in the bread packaging room, and on the surface of bread, cakes, and other bakery items.
- It has been stated that the application of radio-frequency radiations to loaves of bread reduces the chance of mould growth, and that ionising radiations, gamma and cathode rays, have been used experimentally to preserve baked foods.
- Low-level irradiation can also be utilised to eliminate insects from stored grains.
Spoilage of Cereals and Cereal Products
Because their moisture content is too low to support even the growth of moulds, cereal grains and the meals and flours formed from them should not be susceptible to microbial spoiling provided they are properly prepared and kept. Nonetheless, microbial growth will occur if the moisture content of these goods exceeds the minimum required for their growth.
A small amount of moisture will only let the formation of moulds, however a greater amount of moisture will permit the growth of yeasts and bacteria. Although the microbial load of cereal grains, meals, and flours may not pose a spoiling issue on their own, the numbers and types of microbes in these goods are cause for concern because they are employed in the formulation of numerous other foods. The microbiological contribution of cereal grains and flours to convenience foods is significant from a public health standpoint and as a potential source of spoiling agents.
Cereal Grains and Meals
- Since cereal grains and meals are not typically processed to significantly reduce their natural flora of microorganisms, they are likely to include moulds, yeasts, and bacteria that are ready to multiply if sufficient moisture is introduced.
- In addition to starch, which is inaccessible to many organisms, these grains contain sugar, available nitrogen compounds, minerals, and accessory growth substances; and if the grains are moistened, the amylases will release more sugar and the proteinases will produce more available nitrogenous foods.
- A small amount of additional moisture will result in the growth of mould near the surface, where air is present. A wet mash of the grains or a mash of the meals will undergo acid fermentation, primarily attributable to the lactic acid and coliform bacteria that are typically found on plant surfaces.
- After the acidity has grown to a point where yeasts can thrive, an alcoholic fermentation may occur.
- Lastly, moulds (and maybe film yeasts) will form on the surface, although acetic acid bacteria, if present, may oxidise the alcohol to acetic acid and hinder mould growth.
- Mold contamination of stored grain is mostly caused by microbial content, moisture levels exceeding 12 to 13 percent, physical damage, and temperature.
- Molds of the genera Aspergillus, Penicillium, Mucor, Rhizopus, and Fusarium are the most prevalent culprits.
- As stated above, a number of these moulds can create mycotoxins. Moldy grains pose a potential risk to animal or human health and a substantial economic loss.
- Dry cleaning and washing grains, as well as milling and sifting flour, reduce the microbe concentration; nonetheless, the major types are still present in wholegrain flours, such as whole wheat or buckwheat, and the spoiling would be comparable to that stated for cereal grains and meals.
- However, white wheat flour is typically bleached with an oxidising agent, such as nitrogen oxide, chlorine, nitrosyl chloride, or benzoyl peroxide, in order to minimise microbial numbers and types.
- It has been claimed that a moisture content of less than 13 percent in flour prevents the growth of all bacteria. According to other workers, 15 percent permits strong mould development and over 17 percent both mould and bacteria growth.
- Therefore, mould growth occurs when white flour is slightly moistened. Due to changes in the microbial load of different batches of flour, it is difficult to anticipate the type of deterioration in a flour paste.
- If acid-forming bacteria are present, an acid fermentation commences, followed by an alcoholic fermentation if yeasts are present and finally the formation of acetic acid by Acetobacter species.
- This sequence of alterations would be more likely to occur in freshly milled flour than in flour that has been held for an extended length of time, resulting in a decrease in the types and quantities of microorganisms.
- In the absence of lactics and coliforms, micrococci acidify the paste, and in their absence, Bacillus species proliferate and produce lactic acid, gas, alcohol, acetoin, and trace amounts of esters and other aromatic chemicals.
- It is typical for flour pastes to develop a smell of acetic acid and esters.
- The fermentations occurring in the doughs for different types of bread, where it will be observed that some modifications generated by microorganisms are beneficial and even necessary for the production of particular types of bread.
- Normal acid fermentation by lactics and coliform bacteria in flour pastes and doughs may become excessive if given too long time, causing the dough and bread created from it to be overly “sour.”
- Excessive growth of proteolytic bacteria during this time may ruin a portion of the dough’s vital gas-holding capacity and result in a sticky dough.
- However, sticky doughs are typically the result of excessive mixing or gluten breakdown by reducing agents, such as glutathione. There is also the risk of microbes producing unwanted flavours other than sourness.
- Historically, the most common types of microbiological decomposition of baked bread have been moldiness and ropiness, commonly referred to as “mould” and “rope,” respectively.
- Molds are the most prevalent and hence most significant cause of bread and other bakery product deterioration. Typically, the temperatures reached during the baking process are high enough to destroy all mould spores within and on the bread; therefore, moulds must reach the surface or penetrate after baking.
- They can originate from the air during cooling or after, from handling, or from packaging, and typically begin to form in the bread’s crease and between the slices.
- Principal bread-spoiling fungi include the so-called bread mould, Rhizopus stolonifer (syn., R. nigricans), with its white cottony mycelium and black dots of sporangia; the green-spored Penicillium expansum or P. stoloniferum; Aspergillus niger with its greenish- or purple-brown to black conidial heads and yellow pigment diffusing into the
- Molds of the genera Mucor, Geotrichum, or any of a vast number of other genera may form.
- Mold spoilage is favoured by (1) heavy contamination after baking, as a result of, for example, air heavily laden with mould spores, a long cooling time, substantial air circulation, or a contaminated slicing machine, (2) slicing, in that more air is introduced into the loaf, (3) wrapping, particularly if the bread is warm when wrapped, and (4) storage in a warm, humid location.
- Below 90 percent relative humidity, there is minimal commercially significant development on the bread crust.
- Bread containing 6 percent milk solids holds moisture marginally better than bread containing no milk solids; as a result, there is less moisture between loaf and wrapper and, consequently, less mould growth; however, this benefit is insufficient to be of practical significance.
- Mold typically occurs within a loaf of sliced bread, where there is more moisture than on the top, particularly in the crease.
Methods are employed to prevent moldiness of bread
- Mold spore contamination of bread is avoided as much as possible. By removing potential mold-breeding sites, such as returned bread, walls, and equipment, the air around the bread is maintained free of mould spores. Bread’s increased moldiness has been attributed to spore-laden flour dust from other areas of the bakery. Filtration and cleansing the air in a space, as well as irradiating the room and especially the air with UV rays, reduce contamination.
- Prompt and proper cooling of the product prior to wrapping to prevent moisture condensation beneath the wrapper.
- Ultraviolet irradiation of the loaf’s exterior and the blades of the slicing knives.
- The destruction of surface moulds using electrical heating.
- Keeping the bread cool to delay mould growth or freezing and storing it in a frozen state to completely avoid growth.
- Incorporation of a mycostatic chemical into bread dough. Sodium or calcium propionate at a rate between 0.1% and 0.3% of the flour’s weight, which is also effective against rope, is currently the most popular treatment for flour fungus. Sorbic acid concentrations of up to 0.1% and sodium diacetate concentrations of up to 0.32 % are also employed. The addition of vinegar or acetate to the dough, or the treatment of the loaf’s exterior with vinegar, was an ancient therapy.
- Ropiness of bread is quite prevalent in home-baked bread, especially during hot weather, although it is uncommon in commercially-baked bread due to the adoption of preventative measures.
- A mucoid variation of Bacillus subtillis or B. licheniformis, formerly known as B. mesentericus*, B. panis*, and other species names, causes ropiness.
- The spores of these species can survive the bread’s baking temperature, which does not exceed 100 degrees Celsius, and can germinate and thrive in the loaf under favourable conditions.
- The ropy condition appears to be the result of bacillus encapsulation, as well as the breakdown of the flour proteins (gluten) by the organism’s proteinases and starch by amylase to produce sugars that promote rope formation.
- The area of ropiness ranges in hue from yellow to brown and is soft and tacky to the touch. When the bread is torn apart, the slimy material can be extracted into long threads in a single step.
- The stench is difficult to describe, but has been compared to that of rotting or overripe melons. The odour appears first, followed by discoloration, softening of the crumb, and lastly stickiness and stringiness.
- This book’s second edition has a thorough explanation of the factors that promote rope formation and the means of preventing it.
- Red, or “bloody,” bread is uncommon but stunning in appearance. The red colour is a result of the proliferation of pigmented bacteria, typically Serratia marcescens, an organism that is typically brilliantly red and thrives on starchy foods.
- In ancient times, the mysterious appearance of blood-like drips was regarded as magical. Accidental infection of the bread with the red organisms and abnormally wet conditions conducive to their growth are necessary for the phenomena.
- Molds, such as the previously described Monilia (Neurospora) sitophila, can give bread a pink to crimson hue. Geotrichum aurantiacum is responsible for the reddish hue of black bread’s crumb (syn. Oidium aurantiacum).
- Chalky bread, which is also uncommon, gets its name from its white, chalklike markings.
- The growth of yeastlike fungus, Endomycopsis fibuligera and Trichosporon variable, has been attributed to the deficiency.
Cakes and Bakery Products
- Molds are the leading cause of microbial deterioration in cakes and other baked goods, as the baking process eliminates a significant portion of the original microflora. Prevention methods are comparable to those previously stated for bread.
- When these items are decorated with frostings or fruits or filled with custard, imitation creams, or sauces, their microbiology becomes more complicated.
- Typically, toppings and fillings are more susceptible to microbial deterioration than the baked component itself.
- It is not uncommon for the fillings of many pastries to encourage microbial growth.
- Frostings are quite stable due to their high sugar content, however they can be ruined by moulds or yeast during storage.
- Staling refers to the degradation of breads, cakes, pies, and other bakery products caused primarily to physical changes during storage and not microbes.
Pasta, Macaroni, and Tapioca
- Pasta refers to egg-based pastas that typically contain flour, water, and eggs.
- Pasta is supplied and stored dry; hence, there are few instances of these products spoiling.
- Typically, macaroni merely contains flour, water, and other nutrients. Gas generation by bacteria like Enterobacter colacae is purportedly responsible for the expansion of damp macaroni.
- During the drying of macaroni on paper, a mould of the species Monilia was discovered to be the cause of purple streaks at paper contact places.
- Despite the lengthy and gradual drying process of macaroni, the occurrence of these faults is infrequent.
- Tapioca, which is made from the root starch of cassava, will deteriorate if hydrated. It has been documented how an orange-colored, starch-hydrolyzing bacterium causes spoilage.
Breakfast Cereals and Other Cereal Snacks
- According to Hobbs and Green (1984), there are three fundamental manufacturing steps for breakfast cereal: These items are flakes, puffs, or extrusions.
- There is the potential for microbial development due to the high quantities of moisture present during the earliest stages of production.
- However, in their final form, they typically represent low-quantity products.
- A significant portion of retail products are fundamentally prepared, refrigerated, or frozen bread product doughs.
- These convenience foods may include inoculums of yeast or lactic acid bacteria.
- The quantity of contamination and the resulting microbiological quality would be a direct outcome of the quality of the ingredients and the sanitary manufacturing procedures applied.
- Until the product receives its final “heat treatment” at the consumer level, the quantity of microorganisms may increase during refrigeration.
Decontamination of Mycotoxins
Mycotoxins are extremely stable at high temperatures, with minimal or no degradation occurring during standard cooking or processing. The treatments are limited since the treated items must be safe for human health in regards to the chemicals employed, the formation of new compounds, and the loss of nutritional content. For the removal of some mycotoxins from food, the following approaches may be suggested.
- Mold- or mycotoxin-contaminated seeds can be removed manually or with photoelectric detectors.
- The approach would need time and labour, making it costly.
- Organic solvents (such as chloroform, acetone, hexane, and methanol) can be used to extract aflatoxins from agricultural products, however they are primarily accessible during the refining of vegetable oil.
Heating and Cooking Under Pressure
- At high temperatures and pressures, most of the aflatoxin in rice can be eliminated. Dry and oil-roasting can diminish aflatoxin levels.
- Peanut aflatoxin can be diminished by heating up to 100 °C.
- However, prolonged cooking and excessive heat would destroy vital vitamins and amino acids in treated foods, as aflatoxin is resistant to temperatures up to 260 degrees Celsius.
- Irradiation with gamma rays (5–10 Mrad) can reduce aflatoxin levels, but cannot eliminate the toxin entirely.
- For further aflatoxin decontamination, gamma irradiation and ammonization can be considered.
- Mycotoxins in contaminated foods can be eliminated through chemical treatment. The detoxification mechanism should be able to transform toxins into harmless derivatives without altering the original substance.
- Numerous common compounds are capable of detoxifying aflatoxin. These include acetic acid, ammonia gas, ammonium salts (3% to 5%), calcium hydroxide, formaldehyde, hydrogen peroxide, methylamine, ozone gas, phosphoric acid, phosphine gas (very poisonous), sodium bicarbonate, sodium bisulfite, and sodium hypochlorite.
- For detoxification of mycotoxins, various variables (such as moisture content, heat, ultraviolet, gamma irradiation, sunshine, and pressure) and treatment durations can be used.
- To eliminate aflatoxins from contaminated food products, ammonization is an effective chemical approach.
Prevention of Mold and Mycotoxin Contamination
Molds and their mycotoxins can contaminate agricultural and other food products on three levels: (i) primary prevention, (ii) secondary prevention, and (iii) tertiary prevention.
Primary Prevention Level
- Before mould and mycotoxin infection, this preventative measure should be implemented.
- This level requires a physical, chemical, and biological plan for decreasing or avoiding mould contamination, development, and mycotoxin generation.
- Developing mold-resistant plants, applying agricultural practises before and after harvesting, drying cereals and seeds after harvesting, preventing moisture increase during storage, storing foods and ingredients at unfavourable conditions to control mould growth, using fungicides against mould, and controlling insect infestation in stored grains and seeds can be recommended to maintain unfavourable conditions for moulds and mycotoxin contamination.
Secondary Prevention Level
- If mould contamination begins during harvesting, existing toxigenic moulds must be eradicated or their growth must be halted using physical, chemical, and biological means to prevent further degradation and mycotoxin formation.
- For this purpose, the following steps are suggested: inhibition of contaminated moulds by control methods (such as drying the products), removal of mould from contaminated feeds, detoxification of mycotoxins, and protection of stores where mould development is permitted.
Tertiary Prevention Level
- Once products are substantially polluted with hazardous moulds, tertiary preventive actions would no longer be possible.
- Since it will be fairly late to entirely halt the growth of toxigenic moulds and prevent their mycotoxin contamination, any intervention would be less successful than in the first and second levels.
- By destroying all mycotoxins from contaminated items, mycotoxin contamination can be eliminated or reduced to a minimum level.
Control of Mold Growth
Physical, chemical, and biological variables can be used to suppress mould growth.
- After crops have been harvested, it is crucial to prevent mould formation by drying, storing, and transporting them properly.
- Several variables contribute to mould growth and mycotoxin generation, including high levels of moisture, warm temperatures (25–40 °C), insect infestation, and pest damage.
- Seeds and agricultural products are dried to safe levels of moisture (such as 9% for peanut kernel and 13% for corn).
- Molds cannot grow as swiftly in properly dried foods as they may in fresh produce. Keeping foods below aw = 0.7 is an excellent approach for preventing mould growth and mycotoxin formation.
- The meticulous drying of grain followed by storing in a moisture-resistant plastic sheet can limit the growth of moisture in foods.
- The changed environment prevents the growth of mould and the formation of mycotoxins. Packaging can keep insects and other pests at bay.
- Mold development can be inhibited through the use of synthetic fungicides (such as organic acids, NaCl, benzoic acid derivatives, potassium sulfite, and potassium fluoride), fumigants (such as ammonia and phosphine), and natural plant extracts.
- Butylated hydroxyanisole and a phenolic antioxidant can suppress the development of toxigenic Aspergillus, Fusarium, and Penicillium species.
- Low quantities of NaCl accelerate the synthesis of aflatoxin, while high concentrations prevent mould growth and aflatoxin production.
- High NaCl concentrations may impair the water activity necessary for growth and toxin generation. Alternatively, sodium ions may inhibit ion transport in moulds.
- Plant extracts have the ability to inhibit the growth of toxigenic moulds and the synthesis of toxins. Cinnamon, peppermint, basil, oregano, clove, and thyme essential oils prevent the growth of A. flavus and A. parasiticus.
- Antifungal enzymes, chitinase and B-1,3-glucanase, in a plant seed may serve as a defence against pathogenic moulds, since chitin and glucan are the primary polymeric components of the cell walls of many moulds.
- These polysaccharides in mould cell wall can be degraded enzymatically into smaller compounds, resulting in the destruction or death of mould mycelia. Most likely, seeds rich in such antifungal enzymes are resistant to mould invasion.
- Antifungal enzymes can be utilised at both the primary and secondary levels of prophylaxis. Multiple microorganisms influence aflatoxin synthesis in a competitive context.
- A combination of Lactobacillus species can suppress mould growth and aflatoxin generation. In tempeh, Rhizopus oligosporus suppresses the growth of Aspergillus flavus and Aspergillus parasiticus, as well as aflatoxin synthesis.
- A. flavus and Fusarium moniliforme’s growth is inhibited by Trichoderma’s antagonism resulting from antibiotics, enzyme production, and parasitism.
- Spoilage of Cereals and Cereal Products. (2016). Food Microbiology: Principles into Practice, 364–375. doi:10.1002/9781119237860.ch21
- Cook, Frederick & Johnson, Billie. (2009). Microbiological Spoilage of Cereal Products. 10.1007/978-1-4419-0826-1_8.