Rice Ageing Effect of Changes in Protein on Starch Behaviour
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_3_4_03_162_169.doc |
| Abstract: | Summaries. Pasting properties of starch were affected by storage at 37 °C; the most significant changes were seen in peak viscosity and breakdown. In contrast, storage at 4 °C retarded the changes. The composition of the leachate from the RVA pastes was significantly affected by storage temperature (P< 0.01) with a lesser proportion of amylose in samples stored at 37 °C. Thus, ageing was associated with decreased leaching of starch and particularly amylose. Protease treatment increased the ratio of amylose to amylopectin in the hot-water soluble fraction significantly (P < 0.05) for samples following storage at 37 °C while the ratio did not change for samples stored at 4 °C. Of greater significance was that the ratio was the same for samples stored at both temperatures following protease treatment. Similarly, after protease treatment the peak temperatures of the gelatinisation endotherm (Tp) of samples stored at 37 °C were identical to those of the samples stored at 4 °C. Protein was considered an important factor in the ageing process and the changes in proteins associated with storage were investigated. Higher storage temperature caused a reduction in the amount of prolamin and glutelin in the propanol-extractable fractions. Conclusion. Rice storage produced changes in the associated viscograms and DSC endotherms. Following storage, the most significant changes in the pasting curves were the decrease in breakdown over time and the gradual disappearance of a clearly defined peak and in thermal curves were the shift to higher peak temperature and a broader peak width. However, protease treatment of stored rice produced an obvious peak and trough as normally seen in fresh rice in pasting curves and a shift of the gelatinization endotherm to lower temperature in thermal curves. A plausible explanation for these phenomena is that changes in protein molecules during storage enhance the rigidity or strength of starch granules whilst proteolysis made the rice grain less structured allowing the gelatinized granules to swell to a greater extent than previously possible. |
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| ISSN: | ISSN 0038-9056 |
