Journal of Food, Agriculture and Environment

The effect of thermal processing on soluble dietary fibre fraction in wheat

Author(s):

Adrian Caprita, Rodica Caprita ^*

Recieved Date: 2011-06-27, Accepted Date: 2011-10-16

Abstract:

Dietary fibre (DF) includes all non-starch polysaccharides resistant to digestion in the small intestine and fermentable in the large intestine, and consists of a mixture of components with a varying degree of solubility. Wheat contains substantial amounts of both soluble (SDF) and insoluble (IDF) dietary fibre. The predominant water SDF in wheat is arabinoxylan (6-8%). The main polysaccharide constituents of wheat endosperm cell walls are arabinoxylans, whereas arabinoxylans and ß-glucans predominate in wheat aleurone layers, arabinoxylan and cellulose predominate in cell walls of pericarp/testa. Soluble polysaccharides give viscous aqueous solutions. The viscous properties depend on molecular weight and molecule size (linear or branched), ionically charged groups, surrounding structures, and concentration of DF. In aqueous solutions, water molecules penetrate the amorphous regions of soluble DF. The increase in viscosity is explained by formation of Ca²⁺ bridges and hydrogen bonds, resulting in a loose network that can hold considerable amounts of water. Most food processing methods are essentially based on heating. Thermal processing of plant tissues alters the physical and chemical properties of plant cell wall and modifies fibre solubilization, which modifies the water extract viscosity (WEV). The study had in view the effect of thermal processing on WEV of wheat flour. Wheat samples were heated for 5, 10 and 15 min at 150 and 180ºC in a forced air oven, or by exposing for 30, 60, 90 and 120 seconds to microwave radiations. The water-soluble fraction was obtained using a single extraction at 1:2 flour: water ratio, for 60 min at 40ºC. The experimental data revealed that thermal processing has a marked effect on the viscosity of water extracts. Heat treatment at 150ºC increased WEV demonstrating an increase in the proportion of SDF in the total DF content of the cooked flour with cooking time. These observations suggest a redistribution of the total DF content from insoluble to soluble components. WEV increased up to 3.09 cP (20% increasing) when heating at 150ºC for 15 min. Thermal processing at 180ºC did not induce a significant increase in WEV. WEV increased slightly with heating in microwave, up to 8% after 90 s. Further heating decreased WEV to 2.17 cP.

Keywords:

Dietary fibre, non-starch polysaccharides, wheat, arabinoxylans, water extract viscosity, thermal processing

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Journal: Journal of Food, Agriculture and Environment
Year: 2011
Volume: 9
Issue: 3&4
Category: Food and Health
Pages: 14-15

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