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Unripe banana, edible canna and taro flours, which have been reported to contain significant amounts of fibre, were investigated for their physicochemical properties, resistant starch (RS) content and in vitro starch digestibility, and compared with commercial high-fibre-modified starches from corn and tapioca. Differential scanning calorimetry showed a single endothermic peak located around 70-83°C for the samples except the modified starches, which exhibited no transition enthalpy. The samples showed different pasting behaviours in the Rapid Visco-Analyser (RVA) ranging from full to restricted swelling. The RS content varied from 1-26 g per 100 g dry sample, and the estimated glycaemic indices (GIs) of the samples were from 67% to 99%. Generally, samples with high RS were low in GI values. The starches produced acceptable rice noodles but with reduced rate of starch digestion and GI. The effects of the unripe banana, edible canna and taro flours on starch digestibility were either comparable or better than the commercial modified starches. These flours can substitute commercial modified starches to lower GIs of noodles and identical foods.

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Physicochemical properties and starch digestibility of modified tapioca starch using various citric acid concentrations (10, 30, and 50 g/100 g dry starch) and heating temperatures (100, 120, and 140 °C for 5 h) are investigated. It is found that the degree of esterification increases with increasing dose of citric acid and heating temperature. Differential scanning calorimetry shows that citrate starch samples exposed to high acid dose (30 g/100 g citric acid) and temperature (120 °C) are resistant to gelatinization. In addition, transitional enthalpy also decreases with increasing concentration and temperature. The microstructure of esterified starch is observed to have agglomerated granules, with corrosions/fissures and small overlapping layers on the surfaces, which are observed in all modified samples. Citric acid esterification of tapioca starch provided advantages in terms of the increase resistant starch content and slow digestion rate when compared to native starch.

In vitro starch digestibility of 10 Thai brown rice samples was investigated for foundational in-depth understandings of treated/processed and untreated/non-processed rice. The samples were uncooked pigmented, non-pigmented and differed in amylose contents and chemical and functional properties. The starch digestograms were modelled using innovative techniques involving objective logarithm of slope (Sopade Objective Procedure) and one-term and two-term exponential and non-exponential models. The samples significantly (P ≤ 0.05) revealed monophasic and biphasic starch digestograms, and the digestion parameters were sample-dependent. Using the Sopade Objective Procedure, which better predicted the digestograms, the biphasic samples exhibited rapid-slow and slow-rapid in vitro starch digestion phenomena. The estimated glycaemic index (eGI) of the samples ranged from 41 to 95 g/100 g, and the sample with the slow-rapid digestion pattern exhibited the lowest eGI. The results are discussed as baselines for follow-up treatments that typify rice as a notable global food commodity.

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