Optimisation and utilisation of resistant starch for value addition in rice products

Abstract

The present study was undertaken to standardise processing treatments for optimising resistant starch (RS) formation in rice starch and to evaluate the changes in rice starch properties. The study also aimed to standardise rice flour supplemented with RS, to evaluate its quality attributes during storage and the effect of RS supplemented food products on postprandial glycaemic response. Starch was isolated from the raw and parboiled rice of variety Uma. Raw rice had lower starch content and higher RS, compared to parboiled rice. The effect of processing conditions on the RS content of rice starch was studied in 48 treatments by autoclaving at 121°C and 141°C for 20, 40 and 60 minutes without moisture and with 10, 20 and 40 percentage moisture levels. After autoclaving, the samples were cooled at room temperature and at -20°C. The yield of RS was found to be maximum in samples autoclaved at 141°C for 40 minutes with 10 per cent moisture and cooled at -20°C. Increasing the duration of autoclaving up to 60 minutes at a lower temperature of 121°C was also found to be effective in improving the RS content of rice starch. RS formation not only depends on a single factor but also on multiple factors like time and temperature of autoclaving, moisture as well as cooling conditions. To study the effect of repeated autoclaving and cooling, five treatments yielding maximum RS content were selected. The RS content increased with increase in the number of autoclaving and cooling cycles irrespective of the temperature and time of autoclaving, moisture content and cooling conditions. Repeated autoclaving and cooling lowered the content of rapidly and slowly digestible starch. The moisture and protein content of repeatedly autoclaved and cooled samples were significantly lower than the native starch. The total carbohydrate and amylose content increased during processing and found to be maximum in samples autoclaved at 141°C for 40 minutes and cooled at -20°C. The standardisation of resistant starch supplemented rice flour (RSRF) was carried out by incorporating 10, 15 and 20g of RS to 100g of puttu and idiappam flour. For this, two treatments with maximum RS content were selected. Physical qualities of the flour, in vitro starch digestibility and organoleptic qualities of the products were evaluated. Incorporation of RS decreased the bulk density (BD) and water absorption index (WAI) of flour whereas water solubility index (WSI) increased. In vitro starch digestibility was found to be inversely proportional to the RS content of rice flour. The puttu and idiappam prepared with RS supplemented rice flour were found to be organoleptically acceptable. The storage studies of RSRF were carried out by selecting RS incorporated puttu and idiappam flour having better organoleptic acceptance of their products. The flour was stored for six months under ambient condition after packing in polythene bags. The physical qualities like BD, WAI and WSI of puttu and idiappam flour decreased during six months of storage. A decrease in protein and total carbohydrate content was noticed with an increase in the moisture level. The RS content of flour improved during storage. The count of bacteria, yeast and fungi increased towards the end of storage in both the flour. Insect infestation was not observed throughout the storage period. The organoleptic qualities of the puttu and idiappam decreased slightly, when they were prepared from stored flour. Postprandial glycaemic responses of puttu and idiappam supplemented with RS was assessed among diabetic and non-diabetic individuals in comparison with non-supplemented products. The increase in blood glucose level was relatively at a lower rate when RS supplemented puttu and idiappam were given to diabetic as well as non diabetic subjects. Better response was observed among diabetic subjects.