Swelling Characteristics of Native and Chemically Modified Wheat Starches as a Function of Heating Temperature and Time
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| Online Access: | http://www.viks.sk/chk/star_5_04_181_189.doc |
| Abstract: | Summaries. The effects of hydroxypropylation (molar substitution, MS 0.05, 0.12, and 0.18) and cross-linking (0.03%, 0.1 %, and 0.2%) on swelling properties of wheat starch granules at several temperatures and heating times were investigated by laser diffraction particle size analysis. Starch samples were dispersed in water at temperatures ranging from 30 to 90°C, for 1 to 360 min. All starch granules exhibited distinct bimodal size distributions: small B-granules with mean diameter of 2.3 m and large A-granules with mean diameter of 20.4 (im. As temperature increased, the B-granules swelled more than A-granules. Swelling of A-granules sharply increased at 60°C. Swelling was more pronounced with increasing molar substitution of hydroxypropyl groups, while increased swelling was not observed in cross-linked starches. The dependence of swelling capacity on heating time was different at 60 and 80°C as well as amongst modified starches. As heating time was prolonged, mean granule sizes for native, control, and hydroxypropylated starches at 80°C decreased after reaching maximum size due to loss of granule integrity, while those at 60°C showed no significant change. Conclusions. Native, control, hydroxypropylated, and cross-linked wheat starches have DSC gelatinization temperature ranges of 53 to 63°C. The granular mean diameter and size distribution showed temperature and heating time dependency. The changes in granule size in response to temperature and/or time reflect the swelling properties of wheat starch granules. As temperature increased, sharp increases in granular swelling of all starch samples occurred below the DSC gelatinization temperature. This indicates that initial swelling precedes gelatinization and facilitates the transition. The temperatures at which sharp swelling occurred were decreased by hydroxypropylation. At higher temperatures, the mean granule size increased. The increased mean diameter of starch granule was in the order of HP (MS = 0.18) > HP (MS = 0.12) > HP (MS = 0.05) > native = control > CL (0.03%) > CL (0.1 %) > CL (0.2%). As heating time increased, no significant changes in granule size were observed at 60°C, which is below the onset gelatinization temperature for native, control, and cross-linked starches. However, at 80°C, the mean diameter of granules increased more rapidly to the maximum size, and disrupted or disintegrated as heating time prolonged. The study confirms literature data that hydroxypropylated starches showed the most sensitivity to temperature and heating time, while cross-linked starches had the highest resistance. |
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| ISSN: | ISSN 0038-9056 |
