Rice starch is a useful hydrocolloid for the food industry, not least because it is bland in taste, white, and as a gel has a smooth texture.
However the researchers from Mahidol University in Bangkok point out that in common with other cereal starches, it also has some negative aspects like gel retrogradation and the tendency to produce “weak bodied, cohesive, rubbery pastes or gels” under cooking.
Some research has already been done on blending native rice starch with other hydrocolloids to overcome these problems. Little work has been done, however, on the effects of oat, barley, curdlan and spent brewers’ yeast beta-glucans.
Furthermore, no comparative work has been done on the effects on these different beta-glucans on gelatinisation and retrogradation of rice starch.
For the new study accepted for publication in the journal Food Chemistry, researchers Rawiwan Banchathanakij and Manop Suphantharika undertook chemical analyses for rice starch and each beta-glucan preparation, including amylose, nitrogen, fat, moisture and ash contents, carbohydrates and insoluble dietary fibre.
They also determined the pasting properties, took differential scanning calorimetry and rheological measurements, and conducted textural analysis.
All of beta-glucan preparations were seen to “significantly increase” the paste viscosities of the rice starch suspensions during pasting; pasting temperatures were decreased with oat and curdlan beta-glucans but were unaffected by the barley and yeast beta-glucans.
All the beta-glucans were seen to slow the retrogradation of the rice starch gels when they were kept in refrigerated storage – but the soluble oat and barley beta-glucans were seen to do this more effectively than the insoluble curdlan and yeast beta-glucans.
However gelatination behaviour did not seem to be affected by the addition of any of the beta-glucans.
“These results do not appear to be related solely to the beta-glucan contents, but may also be [related] to their molecular weight and structures, as well as impurities present in the various beta-glucan preparations,” concluded the researchers.
As well as providing practical information on improving hydrocolloids properties of the rice starch, the new study also supports the usefulness of beta-glucan – a natural polysaccharide that is attractive to the food industry not only because of its thickening and gelling properties, but also for its researched benefits for health.
For instance, it has been researched for its role in immune stimulation, anti-inflammatory, antimicrobial, antitumoural, heptoprotective and cholesterol-lowering properties.
Food Chemistry (published online ahead of print)DOI: 10.1016/j.foodchem.2008.09/016“Effect of different beta-glucans on the gelatinisation and retrogradation of rice starch”.Authors: Rawiwan Banchathanakij and Manop Suphantharika