The total resistant starch (RS) content and glycaemic index (GI) of freshly cooked polished rice grains were predicted using an in vitro incubation system which models the buccal, gastric, and pancreatic phases of food digestion as occurs in the human upper gastrointestinal tract. The methods have been extensively validated to have a high correlation with in vivo RS levels and GI values (AR Bird, S Usher, B Klingner, DL Topping, and MK Morell, unpublished data). Rice samples were prepared using the absorption method using a ratio of water to rice depending on amylose content (Supplementary Table S2 at JXB online). A total of 50 mg and 500 mg of available carbohydrates were used to predict GI and RS, respectively. For GI prediction, aliquots of supernatant were sampled at the designated time points for up to 5 h and the glucose concentration determined using an automated electrochemical procedure.
The total starch content of freshly cooked rice was determined based on a previously published protocol (McCleary et al., 1994 ) after freeze drying and milling into a fine powder. The predicted GI of the sample was calculated as the percentage of available carbohydrate converted to glucose and released during the time course of the incubation. For RS, the incubation period was extended to 16 h and the amount of starch remaining in the sample at that time was determined using conventional enzymatic and spectrophotometric techniques. The predicted RS content of the sample was calculated as the amount of starch remaining in the digest as a percentage of sample weight.
Neutral non-starch polysaccharides (NNSPs) were measured by a gas chromatographic technique using a slightly modified version of Theander et al. (1995) (link) (AOAC 994.13). The insoluble and soluble NNSPs were separated by selective precipitation. The insoluble NNSPs were hydrolysed with 1 M sulphuric acid, while the soluble NNSPs were hydrolysed with 2 M trifluoroacetic acid.
The total starch content of freshly cooked rice was determined based on a previously published protocol (McCleary et al., 1994 ) after freeze drying and milling into a fine powder. The predicted GI of the sample was calculated as the percentage of available carbohydrate converted to glucose and released during the time course of the incubation. For RS, the incubation period was extended to 16 h and the amount of starch remaining in the sample at that time was determined using conventional enzymatic and spectrophotometric techniques. The predicted RS content of the sample was calculated as the amount of starch remaining in the digest as a percentage of sample weight.
Neutral non-starch polysaccharides (NNSPs) were measured by a gas chromatographic technique using a slightly modified version of Theander et al. (1995) (link) (AOAC 994.13). The insoluble and soluble NNSPs were separated by selective precipitation. The insoluble NNSPs were hydrolysed with 1 M sulphuric acid, while the soluble NNSPs were hydrolysed with 2 M trifluoroacetic acid.
