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The in-vitro availability of starch in Heudebert breads and Lu biscuits was assessed.Starch digestibility increased in the order semi-sweet biscuits, muesli, wholemeal breads, white breads, French toast, extruded crispbread. The results confirm that manufacturing conditions play a determinant role in starch availability in vitro.The samples were ground to pass through a 0.5-mm screen; products with more than 7 % fat were defatted first. Reducing sugars, sucrose, starch and rate of hydrolysis of starch in vitro were determined by the method of Wong et a1 (1985).The results are given in Table 1. The reducing sugars content of biscuits varies between 6 and 119 g kg-'. The sucrose content of the analysed products varies between 0 (bread) and 254 g kg-' for the semi-sweet biscuit n.4.The proportion of the starch hydrolysed in 30 min is 4 % in the uncooked soluble starch (Merck No 1252), 2&44% in biscuits, 4&72% in the breads, crackers and French toast, and 86 % in the extruded crispbread. Wootton and Chaudhry (1980) also showed that the in-vitro availability of starch increased in the order of shortbread biscuits, sweet cookies, crackers and bread; the extent of starch gelatinisation is correlated with the availability of starch in vitro. Ross et a1 1987 showed that the rate of starch hydrolysis in vitro was similar in a water biscuit and wholemeal bread (74 and 76%, respectively), whereas in a shortbread biscuit starch was significantly less available, 58 % ( P < 0.001).Jenkins et a1 (1982a) observed a relatively low blood glucose response to biscuits, the glycaemic index of four kinds of sweet biscuit varying between 54 and 63 %; the authors attributed the low glycaemic index to the poor response to sucrose. It may also be due to the limited degree of gelatinisation of starch in biscuits and to the slowing down of gastric emptying by the fat. 499 J Sci Food Agric 0022-5142/89/$03.50

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