Profiling of the glycaemic index of the underutilised vegetables

Glycaemic Index is a term used to describe the effect on blood glucose of consuming a carbohydrate rich meal. It is a measure of the rise in blood glucose following consumption of a test food relative to a reference food. Various associations have been found between dietary GI and a number of chronic diseases. Whilst there has been considerable research into the GI values of commonly consumed foods, very little is known about the GI values of plants that fall into the category of underutilised species. These include numerous fruit, vegetables, legumes, herbs, spices and nuts that are generally grown and consumed by subsistence and small-scale farmers and their communities. Anecdotal evidence suggests that some of these underutilised plants have particular medicinal properties, in particular can be used to control diabetes mellitus. The total starch and reducing sugar content of white rice plus four selected underutilised species (ginger, turmeric, bitter gourd and fenugreek) were analysed using the DNS method to determine the levels of reducing sugars after acid hydrolysis. The effects of cooking method (raw, boiled or fried) on the rate of starch digestibility were also investigated using in vitro and in vivo digestibility studies. White rice had the highest starch content (78.47g/100g DM) and lowest (0g) level of reducing sugars present. Out of the underutilised plants, both ginger and turmeric had high levels of starch (57.54-68.11 g/100g DM) and reducing sugars (2.71-3.12 g/100g DM). The total starch and reducing sugars in bitter gourd were very low (3.52-4.16g/100g DM and 0.86-1.2 g/100g DM respectively) across all three treatments. Mean values for starch and reducing sugars in turmeric and fenugreek respectively were 64.78 g/100g DM and 51.94g/100g DM: and 2.7g/100gDM and 0.7 g/100g DM respectively. The glucose response of a single meal (individual species) and a mixed meal (rice plus one of the test species) was estimated using an in vitro model of digestion. The samples underwent digestion with α amylase followed by protease and pancreatic amylase. Aliquots of the digesta were removed at 30 minute intervals over a 3 hour period and tested for reducing sugars (using the DNS method) to evaluate the rate of digestion. This was used to estimate the GI response. There was a significant effect of cooking process (raw, boiled or fried) on the rate of glucose release from all four test samples (p