Properties and characteristics of aflatoxins

Aflatoxins are fungal metabolites found in feeds and foods. Aflatoxins (a type of Mycotoxins) are a group of approximately 20 related fungal metabolites produced in cereals, maize grains, peanuts and animal feeds mainly by the fungi Aspergillus flavus and Aspergillus parasitica.

Although it is well known that a hot and humid climate promotes diffusion of aflatoxin-producing moulds, representing a greater hazard in tropical areas of the world, the contamination is commonly due to the combination of meteorological conditions, environmental factors and improper agricultural practices, like incorrect harvesting and storage of crops.

Aflatoxins are colorless to pale yellow crystals, exhibiting fluorescence under UV light. They are slightly soluble in water (10-20μg/ml) and freely soluble in moderately polar solvents such as chloroform, menthol and dimethyl sulfoxide.

Ten-odd isomers of aflatoxin have been discovered. However, most of those detected in feed contaminated with molds are B1, B2, G1 and G2. M1 is a substance that is detected in the milk of cows which have taken feed contaminated with B1.

As for physicochemical properties, aflatoxin is a highly fluorescent substance, and B1, B2, M1 and M2 emit blue fluorescence, while G1 and G2 emit green fluorescence.

Among these toxins, Aflatoxin B1 (AFB1) is considered the most recurrent and also the most harmful. Its carcinogenicity and immunosuppression capacity have been extensively reported in all kind of animals, including poultry, trout, cattle and rats with different incidence across species, gender and age.

Aflatoxins were first identified in 1961 in United Kingdom in animal feed responsible for the deaths of 100 000 turkeys.

Properties and characteristics of aflatoxins 

Gluten in wheat flour: Composition and properties

The grain proteins determine the viscoelastic properties of dough, in particular, the storage proteins that form a network in the dough called gluten. Gluten are capable of having extensibility and elasticity required for bakery products and pasta. Gluten was associated with the water absorption, mixing time, and strength index of dough.

Gluten is a complex mixture of hundreds of related but distinct proteins, mainly gliadin and glutenin (more than 80%). Similar storage proteins exist as secalin in rye, hordein in barley, and avenins in oats and are collectively referred to as “gluten.” The gliadins (ω-, αand γ type) are relatively small molecules that are soluble in alcohols, which may act as a plasticizer in dough systems.

Gluten has four important properties: it absorbs twice its weight in water, it is sticky, it is extensible; this means it will stretch when pulled and it is elastic; when stretched it will return to near its original size.

Gluten is shown to be polymers with molecular weights (MW) in the millions, formed from smaller proteins.

Wheat flour quality is directly related to the wheat gluten formed by mixing the flour with water and with the use of appropriate application of mechanical work to form a viscoelastic network, whose structure is the basis for bakery products and pasta.

The wheat gluten proteins correspond to the major storage proteins that are deposited in the starchy endosperm cells of the developing grain. These form a continuous proteinaceous matrix in the cells of the mature dry grain and are brought together to form a continuous viscoelastic network when flour is mixed with water to form dough.

Gluten may be defined as the ‘cohesive, visco-elastic proteinaceous material prepared as a by-product obtained by isolation of starch from wheat flour. A biological definition might include the origins of the gluten–protein complex as being derived from the ‘storage proteins of the wheat grain’.
Gluten in wheat flour: Composition and properties