Cereal moisture content
The water content of these products should not be the necessary to allow the development mainly of molds. If during the post -harvest of cereal grains the moisture of the grain increases, this will allow the development mainly of molds, but if this is abundant not only molds will be developed but also bacteria and yeasts. Usually the microorganisms that pollute cereals, are found on the outside of the grains that have been harvested; These microorganisms belong to the natural flora in which the grain was located or these are also contaminated by extrinsic factors such as contaminants of the soil, air, water, animals, among others.
Grains and flour are not the most favorable means for the development of pathogenic bacteria such as Salmonella, Clostridium, Staphylococcus. The most important microflora, as far as grain conservation is concerned, are fungi. The contamination of the grains depends on some factors such as cleaning, washing and in the products in the process of the operations to which the grain is subjected such as grinding, whitish, etc. The main contaminating bacteria of the grains are: the genres Bacillus, Flavobacterium, Achomobacter, Micrococcus, Sarcina, Serratia and Alkaline. The mold spores that can contaminate the grains are of the genre: Aspergillus, Penicillium, would alternate, mucor, cladosporium, rhizopus and fusarium.
Alteration of grains
The importance of contamination of grains and seeds by molds and other fungi is because the seeds are an important source of primary inoculum in the transmission and dissemination of diseases in plants, cause the death of the embryo and the consequent drastic decrease From the germination of the seeds, the grains are totally or partially stained, which in some items is an important quality factor, alter the nutritional value by decreasing the contents of oil, proteins and carbohydrates, contaminate the grains with mycotoxins that have serious implications in the health of animals and humans. Fungi thrown with relative moistures of the air filed much lower than those necessary for another microflora (Callejo, 2002).
The damages that these microorganisms cause in the grains are:
- GERMINATIVE POWER REDUCTION
- Embryo and also grain
- Heating
- Weightloss.
Fungi in cereals
The fungi that infect the grains, in general, can be divided n two ecological groups, according to the moment of pollution: the so -called field fungi and storage fungi.
Field fungi
Species that significantly contaminate the grains in the field, before the harvest, only grow in the field when the AW = 0.95-1.0 and belong to the following genera: Alternaria, Cadadosporium, Cercospora, Curvularia, Drechelera, Sclerotiun, Verticillium, Heinthosporium and Fusarium. All these do not have real importance in grain losses.
The molds can invade the grains in the field because they have a higher humidity (22 to 25% and AW of 0.95 to 1.0), when the mature grain, the water content descends and the growth of the mold ceases , so they must be molds that can grow at very low AW values and are the so -called warehouse molds. The molds cause the main problems in cereal production and storage.
Storage fungi
Present in small quantity during harvest, they can mostly colonize the grain during inappropriate storage. More abundant in the corners of silos and deposits, these species, in addition, very sporulants, are often the origin of secondary contamination during the manipulation and transformation of grains. They are the only ones capable of developing on grains with a 15-16% water content and can synthesize extremely toxic molecules for men and animals, called mycotoxins.
Storage fungi are represented, by species of Aspergillus and Penicillium, fundamentally. The latter invade the grains whose moisture contents are in balance with a relative humidity of 70%. They also need moisture values of about 16%. Warehouse fungi is the one that causes most of the losses. The deterioration of stored grains results from the interaction between physical, chemical and biological variables. In this ecological system, the main living organism is grain. Both the grain and the mass of grains have physical and biological attributes, some of which depend mainly on the surrounding environment. The abiotic means of grain mass includes physical variables such as temperature, inorganic chemical variables, oxygen and carbonic gas, and physicochemical variables such as humidity and a set of organic compounds, which are the byproduct of biological activity.
Microflora of stored grains
The microflora of the stored grains is constituted by a wide variety of microorganisms, the fungi being the main. Water availability and temperature are the main factors that influence the growth of microorganisms in stored grains. Undoubtedly, the fundamental agents of deterioration of stored grains are fungi.
Flour alterations
The cleaning and washing of the grains eliminates part of the microorganisms, but most leave with the external portions of the grain during grinding. The different processes that are carried out during grinding, especially bleached, reduces the number of microorganisms, but there is also the risk of pollution during some of these processes, such as mixing and conditioning.
Invasion of mold to the grain produces a mohoso smell (moisture) decreases the quality of the flour and decreases the germination of the malt, increases the concentration of fatty acids by lipolitic activity of the fungus.
Genericly, flours are products of the grinding of cereals and seeds or fruits of other plants. In the course of grinding, flora from cereals, seeds and fruits are distributed throughout the product. Similarly, due to the various manipulations to which the flour is subjected to obtain, there are recontaminations by the air and through the mainly used machinery.
The flour flora is essentially constituted by spores of Bacillus and Coliforms, representatives of the Achromobacter, flavobacterium, sarcina, micrococcus, alkaligen, serratia, pseudomonas, and numerous mold spores (penicillium, aspergillus, fusarium, alternarium, cladosporium, mucor, and Rhizopus).
Flour is a stable product due to its shortage in water, its alterations evolve in parallel to the increase in moisture, with the presence of molds on the surface and yeasts and in -depth bacillus that originate fermentations (alcoholic, acetic) and gas.
The origin of microorganisms can be grain and grinding machinery
- 12% moisture there is no microbial growth
- 15% moisture can grow fungi
- 17% moisture can grow fungi, yeasts and bacteria.
Microbiological origin alterations
The flours with very high microbiological loads (by spores, mainly), compromise the stability of the products to which they are incorporated, being able to cause problems in the elaboration of bread, pasta and other products. The total microflora of the flours ranges between 2×104/g and 5×106/g. It would be desirable that, to avoid alterations, the microbial rate does not exceed 1×104/g.
Biochemical and technological alterations
The loss of germinative capacity of the grains and the increase in fatty acidity during storage are directly related to the development of fungi on grains. Fungal lipases produced by field fungi or during pre storage, by the genus Penicillium are capable of producing a lens acidification of grains and flours.
Organoleptic modifications and the presence of undesirable molds can also occur in the flours that will persist, even in the products made with already cooked flour.
Toxicological modifications
The main effect, from the health point of view, of the development and activity of filamentous fungi in cereals, is the increased risk of mycotoxin production.
Mycotoxins that present problems in the field of food are those that resist oxidation phenomena and cooking processes. Therefore, they are thermostable and have a period of life in contaminated food much broader than the synthesizer fungus. The chemical nature of mycotoxins is very varied, which makes it difficult to define mycotoxin, if it is nothing more than its fungal origin and toxicity.
In the case of flours, when they have a high aw, it can favor the development of bacteria of the Bacillus genre and the development of molds such as Rhizopus, which are the two main microorganisms causing flour alterations. In the mills the type of alteration that can occur in the product is hardly predictable because the microbial content varies in each of the lots. Alterations caused by the presence of acid -producing bacteria have been found, producing acid fermentation;This fermentation as mentioned is followed by an alcoholic fermentation caused by clear yeasts if they are present, reaching a acetic fermentation, by the action of acetobacter, which produce acetic acids.
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