EFFECT OF PROCESSING ON IN-VITRO STARCH DIGESTIBILITY AND GLYCEMIC INDEX OF SELECTED RICE VARIETIES OF ASSAM
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Date
2019-07
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AAU, Jorhat
Abstract
Rice is one of the most widely consumed staple foods, especially in Asia. It
accounts for 20 per cent of the world’s dietary energy supply. As a major component of
rice, starch plays an important role in human nutrition, and consequently its
characterisation in rice variants is of high nutritional importance. To this, the present
study estimated the in-vitro starch digestibility (resistant starch (RS), non-resistant starch
(NRS) and total starch (TS)), available starch (AS), hydrolysis index (HI) and in-vitro
glycemic index (GI) of different processing techniques. Ten red kernel rice varieties of
Assam were analyzed for the effect of both raw rice flour and freshly cooked rice in
dehusked rice and 6 per cent degree of polishing. Dehusked and polished rice yield were
68.33±0.38 to 75.23±0.19 per cent and 64.14±0.13 to 73.67±0.29 per cent, respectively.
Head rice yield (HRY) and broken rice yield (BRY) of the dehusked rice varieties were
54.03±0.34 to 74.34±0.05 per cent and 0.68±0.06 to 14.55±0.32 per cent, respectively.
Polishing of rice grains decreased HRY (41.76±0.40 to 68.39±0.09%) but increased
BRY (2.05± 0.11 to 22.52±0.41%). The dehusked samples had 17.64±0.11 to 19.17±0.04
g/100 g of RS, 61.19±0.07 to 66.28±0.19 g/100g of NRS and 80.01±0.11 to 85.02±0.20
g/100g of TS. Resistant starch decreased significantly (p≤0.05) on polishing as well as
cooking, while NRS and TS increased significantly (p≤0.05) in polishing. However, TS
decreased on cooking. Available starch, hydrolysis index and glycemic index of the
dehusked rice samples were in the range of 51.80±0.14 to 89.57±0.51 per cent,
3.37±0.02 to 14.67±0.03 per cent and 41.91±0.03 to 50.99±0.11 per cent, respectively.
Polishing of the rice samples showed no significant (p≥0.05) change in AS, HI and GI.
Cooking significantly reduced AS, whereas HI and GI content increased significantly
(p≤0.05) upon cooking. Therefore, polishing and cooking of rice grains had significant
effect on the in-vitro starch digestibility and GI. In addition, varieties of Jul and Kaoi
Jamfri had comparatively higher RS and lower GI, and thus can be recommended for
popularization. Also, further research can be extended for analyzing the effect of degree
of polishing and different cooking methods on starch digestibility and GI. Such
nutritionally distinguished rice varieties could be used to develop rice based products and
supplementary food mixes which have therapeutic values.