Cereal Processing By-Products Within the Biorefinery Concept

Cereal grains comprise the principal component of human diet for thousands of years and therefore their processing represents a big asset of the food production chain. Wheat, rice, oat, barley and corn processing via dry and wet milling, pearling and malting includes complex procedures that generate an important amount of by-products that differ in their physical state and chemical composition.

Cereal processing by-products represent abundant and low-cost resources of phytochemicals (e.g. carbohydrates, proteins, dietary fibre, lipids, vitamins, polyphenols, inorganic and trace elements) with potential nutraceutical and pharmaceutical applications. To this line, their re-utilization and upgrade to high added-value applications is a great challenge towards the sustainable development of the agro-food sector for the years to come.

Oat processing and the alternative optionsThe target compounds and substrates are plenty and have been covered adequately through the whole book. Oat, its processing by-products and healthy components is a typical example of the available valorization and upgraded choices. Oats possess high amounts of water soluble fibers and particularly β-glucan (e.g. 2.2-7.8 g/100 g) as well as proteins (11-20 g/100 g). Their nutritional advantages in spite of diabetes and the control of blood cholesterol level have been attributed to the contained β-glucan.

To this line, the attribution of cereal β-glucan as functional ingredient has increased the interest concerning their incorporation in food formulations. Oat grains have been subjected to amylase hydrolysis (converting starch, carbohydrates and dietary fibers to maltose and β-glucan) in order to develop nondairy products. This process is monitored via enzyme kinetics modeling that optimizes the viscoelastic behavior of hydrolysates and simulates biodegradation processes of multienzymatic system based on cultures, e.g. hydrolysis of starch wastes.

Carbohydrate hydrolysis generates a drink that is consumed alternatively to milk products due to the lactose intolerance and cholesterol content issues of human populations, and a by-product (oat mill waste), which is usually dried and utilized as animal feed. The latest is rich in proteins and β-glucan that could be recovered using extraction and membrane technologies and utilized further in different applications, e.g. to replace fat of yoghurt and cheese.

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The Trend of Polyphenols

In the past 10 years, the growing interest of consumers has arised to a number of “superfoods”, which has been motivated by their high content of “polyphenols”. These compounds constitute a heterogeneous group of molecules which differentiate according to their chemical structure.

Polyphenols is a collective term for several sub-groups of compounds, but the use of this term has been somewhat confusing and its implied chemical structures are often vague even to researchers. Even today the scientific community is not consistent with a universal use of the term denoting plant polyphenols, since some call them plant phenols while some others use the term polyphenols.

The first definition of plant polyphenols in the scientific literature pertains to this initial utilization of polyphenolic plant extracts. As these compounds were highly required in the leather industry, considerable efforts were devoted from the beginning of the 20th century onwards to the study of the chemistry of tanning plant extracts in an attempt to tackle the structural characterization of their polyphenolic constituents.

Research on plant polyphenols shifted gears after 1945, as the discovery of paper chromatography and more and more other advanced analytical techniques made it possible to separate in numerous individual constituents.

In 1957 an industrial chemist Theodore White, pointed out that the term “tannin” should strictly refer to plant polyphenolic materials having molecular masses between 500 and 3000 Da and a sufficiently large number of phenolic groups to be capable of forming hydrogen-bonded cross-linked structures with collagen molecules (the act of tanning).

Today, the main reason for the interest of scientists and consumers for polyphenols is the recognition of their antioxidant properties, their great abundance in our diet, and their probable role in the prevention of various diseases associated with oxidative stress, such as cancer and cardiovascular and neurodegenerative diseases. Due to the considerable diversity of their structures, polyphenols are considered even more efficient than other antioxidants.

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