Pasta is a popular carbohydrate-based food with a low glycemic response. A continuous protein matrix which entraps starch granules and/or limits/retards starch hydrolysis by α-amylase is thought to be an important factor in explaining the slow digestion of starch in pasta. The characteristics of the protein matrix may also play an important role in determining the rate of starch digestion in pasta and therefore its glycemic response. In this study, the structural and physicochemical characteristics of the protein matrix of pasta were modified by varying the number of passes through sheeting rollers to investigate their effect on in vitro starch digestibility. The results show that the proteins dissociated from the starch granules with increasing sheeting passes thereby allowing an increased degree of digestion of starch.

The effect of a number of laboratory‐scale pretreatments on the proportions of rapidly digested (RDS), slowly digested (SDS) and resistant starch (RS) in raw and cooked potato has been examined using an in vitro digestion procedure. Potatoes of the variety Frisia were prepared in three states: raw, cooked, and cooked followed by a cold treatment (4°C, two days). Each preparation was then subjected in triplicate to freeze‐drying, coarsely mincing, pasting, freezing, dry‐milling after freeze‐drying, in 22 different combinations, before digesting. In raw potato, very little RDS and SDS (<5% total starch (TS)) were present, and the mechanical treatments of the potato did not affect the amounts of RDS and SDS. Cooking resulted in an almost complete conversion to RDS (>95% TS) in freshly‐cooked potato, but after post‐cooking cold treatment much of the RDS transformed to SDS, which reached a maximum of about 45% TS. SDS formation was independent of the degree of tissue disruption after cooking, and was generally associated with formation of RS, however, freezing after cooking allowed SDS formation without prolonged cold treatment and with very little associated RS (SDS 35% and RS 4% of TS). Freeze‐drying caused an increase in RS in most treatments of the cooked potatoes. The observed effects provided guidance for sample handling in potato research, but also suggested several approaches to the enrichment of SDS and/or RS, with a concurrent reduction in RDS, that could be used to improve the nutritional profile of potato products by decreasing RDS (lowered glycaemic impact), and increasing SDS (more sustained energy availability) and RS (prebiotic benefits).

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Glycaemic responses to foods reflect the balance between glucose loading into, and its clearance from, the blood. Current in vitro methods for glycaemic analysis do not take into account the key role of glucose disposal. The present study aimed to develop a food intake-sensitive method for measuring the glycaemic impact of food quantities usually consumed, as the difference between release of glucose equivalents (GGE) from food during in vitro digestion and a corresponding estimate of clearance of them from the blood. Five foods -white bread, fruit bread, muesli bar, mashed potato and chickpeas -were consumed on three occasions by twenty volunteers to provide blood glucose response (BGR) curves. GGE release during in vitro digestion of the foods was also plotted. Glucose disposal rates estimated from downward slopes of the BGR curves allowed GGE dose-dependent cumulative glucose disposal to be calculated. By subtracting cumulative glucose disposal from cumulative in vitro GGE release, accuracy in predicting the in vivo glycaemic effect from in vitro GGE values was greatly improved.). Furthermore, the difference between the curves of cumulative GGE release and disposal closely mimicked in vivo incremental BGR curves. We conclude that valid measurement of the glycaemic impact of foods may be obtained in vitro, and expressed as grams of glucose equivalents per food quantity, by taking account not only of GGE release from food during in vitro digestion, but also of blood glucose clearance in response to the food quantity. Carbohydrate: Glycaemic impact: Glucose disposal: In vitro digestionFor practical consumer and dietetic use in glycaemia management, food values are required which will '. . . communicate glycaemic response in grams per serving of food' (1) , and which should be measured using '. . . validated in vitro methodology that accurately mimics in vivo behaviour' (2) . Current in vitro digestion methods for predicting relative glycaemic responses to foods measure carbohydrate that is rapidly available (for example, Englyst et al. ), or the area under the glucose release curve relative to a reference (5) . However, they cannot provide accurate or robust predictions of relative responses to whole foods varying in quantity, or accurately mimic the in vivo glycaemic response, because they do not allow for the effects of homeostasis. They do not take into account the fact that glycaemic responses to foods are a net effect of the balance between blood glucose loading and blood glucose disposal (GD), which depends dynamically on the rates of both. Not allowing for blood GD, and its dependence on the amount and rate of blood glucose loading, may lead to large inaccuracies when using glycaemic impact values from experimental portions to gauge the effect of the very different and varying food quantities that are consumed in a community setting. For instance, customarily consumed food portions often have a much lower glycaemic impact than would be expected from a glycaemic load value calculated from the glycaemic in...

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