The effect of guar galactomannan and water availability during hydrothermal processing on the hydrolysis of starch catalysed by pancreatic α-amylase
The effect of guar galactomannan and water availability during hydrothermal processing on the hydrolysis of starch catalysed by pancreatic α-amylase
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DOI：
10.1016/s0304-4165(02)00209-x
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发表时间：
2002-05-10
影响因子：
3
通讯作者：
Butterworth, PJ
中科院分区：
文献类型：
--
作者：
Slaughter, SL;Ellis, PR;Butterworth, PJ
水溶性非淀粉多糖(SNSP)对人体代谢的影响被认为是有益的，因为它们可以降低摄入富含淀粉的食物后的餐后血糖和胰岛素血症。SNSP抑制餐后血糖升高的机制尚不清楚，但它们的存在会增加胃肠内容物的粘度，从而影响胃排空和蠕动等生理功能。在淀粉水热处理过程中，粘度的增加和水分活度的降低会影响α-淀粉酶的作用。以瓜尔豆半乳甘露聚糖为代表，我们发现半乳甘露聚糖对α-淀粉酶具有直接的非竞争性抑制作用，其K-I值约为0.5%(3.3um)。这种抑制不是时间依赖的，研究表明该酶直接与半乳甘露聚糖结合；由此产生的半乳甘露聚糖-淀粉酶复合体是不活跃的。低水位下的淀粉加工对α-淀粉酶的催化效率有很大影响。与在过量水中糊化的淀粉相比，在有限水中处理的淀粉的K-m值升高，而k(CAT)降低。由于半乳甘露聚糖对α-淀粉酶的K-m没有影响，我们得出结论，聚合物的抑制作用不是次要的，因为有效水的减少。它似乎也不是酶、底物和产物扩散受损的结果，因为介质的粘度增加。因此，SNSP降低餐后血糖的作用不仅包括改善肠道生理功能，还包括直接抑制淀粉的第一阶段生化降解。(C)2002 Elsevier Science B.V.保留所有权利。
The effects of water-soluble nonstarch polysaccharides (sNSP) on human metabolism are considered to be beneficial because they decrease postprandial glycaemia and insulinaemia following ingestion of starch-rich foods. The mechanisms by which sNSP attenuate the postprandial rise in blood glucose are not well understood but their presence increases the viscosity of gastrointestinal contents, which affects physiological functions, e.g. gastric emptying and peristalsis. Increased viscosity and decreased water activity during hydrothermal treatment of starch could influence alpha-amylase action. Using guar galactomannan as a representative of sNSP, we found that galactomannan has a direct noncompetitive inhibitory effect on alpha-amylase with a K-i value of approximately 0.5% (3.3 muM). The inhibition is not time dependent and studies suggest direct binding of the enzyme to galactomannan; the resulting galactomannan-amylase complex being inactive. Processing of starch at low water levels greatly affects the catalytic efficiency of a-amylase. The K-m value for starch heat treated in limited water is raised and k(cat) is lowered relative to starch gelatinised in excess water. Since galactomannan has no effect on the K-m of alpha-amylase, we conclude that the inhibitory action of the polymer is not secondary to a decrease in available water. Neither does it seem to be a consequence of impaired diffusion of enzyme, substrate and products because of an increase in viscosity of the medium. Thus, the effects of sNSP in lowering postprandial glycaemia not only involve modifications of gut physiology, but also include direct inhibition of the first stage in the biochemical degradation of starch. (C) 2002 Elsevier Science B.V. All rights reserved.