Role of lipids and phytate in oxidative stability of cereal beta-glucan
Wang, Yujie
University of Helsinki, Faculty of Agriculture and Forestry, Department of Food and Nutrition
Doctoral dissertation (article-based)

Abstract:
β-Glucan (β-(1→3),(1→4)-D-glucan) is the major non-starch polysaccharide in oats and barley, and it is well-known due to its physiological and technological benefits, which are related to the ability to increase the luminal or solution viscosity.
However, cereal β-glucan is susceptible to degradation during processing and storage, which may deteriorate the product stability and/or β-glucan functionality. Oxidative degradation of β-glucan has been shown in aqueous systems. In multi-phased food
systems containing lipids, the oxidative stability of β-glucan has not yet been studied. In these systems, lipid oxidation is a major source of radicals which can cause co-oxidation of other components. The aim of the study was to understand the
oxidative stability of cereal β-glucan during lipid oxidation, and the simultaneous role of β-glucan in retarding lipid oxidation. Furthermore, the study investigated the contribution of the residual phytate in β-glucan to the oxidative stability of β
-glucan.

Results showed that lipid oxidation induced significant degradation of β-glucan in an oil-in-water emulsion model, as evidenced by a decrease in viscosity and decrease in molecular weight of β-glucan. The increase in the degree of oil oxidation, the
concentration of transition metal or the storage temperature caused a greater extent of β-glucan degradation. Simultaneously, a retardation of lipid oxidation was observed in the emulsions containing β-glucan. The mechanism was further investigated by
using purified oat and barley β-glucans with different molecular weights. Initially, it seemed that retardation of lipid oxidation was determined by the β-glucan source and the molecular weight. However, the retardation was found to correlate with the
content of residual phytate in the β-glucan samples. When the phytate was removed, the retardation of lipid oxidation by β-glucan disappeared regardless of the β-glucan source and molecular weight. Therefore, the residual phytate in the β-glucan
samples, instead of β-glucan structural features, played a major role in the retardation of lipid oxidation. The study further proved that the residual phytate protected the β-glucan from oxidative degradation. Under oxidative conditions, oat β-glucan
containing a high amount of phytate was more stable than barley β-glucan containing less phytate. The oat β-glucan became as vulnerable as barley β-glucan to the oxidative degradation when the residual phytate was removed.

The addition of phytic acid also retarded the degradation of β-glucan, which was affected by the ratio of phytic acid to iron (Fe) and the presence of competitors such as ascorbic acid. The studies indicate that oxidized lipids and co-passengers of β-
glucan can influence the oxidative stability of β-glucan, and consequently influence its technological and physiological functionality.

http://urn.fi/URN:ISBN:978-951-51-4269-6

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