Texture and unsaccharified residual starch content in steamed roots of sweet potato cultivars with varying levels of beta-amylase activity
2017
Nakamura, Y. (Institute of Crop Science, NARO, Tsukuba, Ibaraki (Japan)) | Masuda, R. | Kuranouchi, T. | Katayama, K.
Texture and unsaccharified residual starch contents in steamed storage roots of 6 sweet potato cultivars with different levels (high, moderate and extremely low) of beta-amylase activity were investigated. In the cultivars with high activity ('Beniharuka' and 'Himeayaka'), the residual starch content in steamed roots was about 47 % of that in their fresh roots. Comparatively, these values were 62 % in the cultivars with moderate activity ('Tamayutaka' and 'Kokei 14') and 93 % in the cultivars with extremely low beta-amylase activity ('Okikogane' and 'Satsumahikari'). The decrease in starch content during steam-cooking was nearly equal to the amount of starch degradation estimated from the maltose concentration of steamed roots, and the rate of starch degradation was highly correlated with the beta-amylase activity of fresh roots (r=0.77 sup(***), n=34). The texture of steamed sweet potato roots showed a higher correlation with the concentration of unsaccharified residual starch after degradation by beta-amylase than with the starch concentration in their fresh roots. In the cultivars with extremely low beta-amylase activity, the starch concentration of storage roots hardly changed after steaming because of the extremely low starch digestion by beta-amylase, resulting in a mealy texture of the steamed roots.
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