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Effects of gelatinization and gel storage conditions on the formation of canna resistant starch

Abstract
The effects of gelatinization and gel storage conditions on the formation of canna resistant starch (RS) were investigated. Starch slurries (10%, dwb) were autoclaved at 121 °C for 30, 60, and 120 min. The gels obtained were subsequently stored at different temperatures (4 °C, 30 °C, and 100 °C) and times (0, 1, 3, 5, and 7 days). Analyses of the RS content in gelatinized starch samples in comparison with that in granular starch showed that the RS fraction in granular starch was very high (97.3% w/w); however, nearly all of the RS was thermally unstable, as indicated by a great reduction in RS content (to 1.9% w/w) after cooking at 100 °C for 20 min. The RS contents in gelatinized starch samples were 12.0–15.9% w/w, which were reduced to 7.9–10.8% w/w after cooking. Storage of gels resulted in a significant increase in the amount of the thermally stable RS fraction, e.g., a thermally stable RS content of 16.8% w/w was found in the gel sample gelatinized for 120 min and stored at 4 °C for 3 days. This indicated that the ordered structures of the RS portion were tightened under the storage conditions. The gelatinization temperature of canna starch was 72.2 °C, whereas the RS products exhibited two melting temperature ranges, 51.1–76.3 °C and 163.1–165.1 °C, indicating that the newly formed crystals were very strong.

Keywords
Resistant starch; Canna starch; Gelatinization; Retrogradation; Storage

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