Impact of postharvest drying conditions on in vitro starch digestibility and estimated glycemic index of cooked non-waxy long-grain rice (Oryza sativa L.)

J Sci Food Agric. 2017 Feb;97(3):896-901. doi: 10.1002/jsfa.7812. Epub 2016 Jun 21.

Abstract

Background: Wet paddy needs to be dried to reduce its moisture content after harvesting. In this study, effects of postharvest drying condition on in vitro starch digestibility and estimated glycemic index of cooked rice (Oryza sativa L.) were investigated. Varying drying conditions, i.e. hot-air drying at 40, 65, 90 and 115 °C, and sun drying were applied to raw paddy. After husking and polishing, polished grains were cooked using an electric rice cooker. Cooked samples were analyzed for their moisture content and amount of resistant and total starch. Five samples in both intact grain and slurry were digested under simulated in vitro gastrointestinal digestion process. The in vitro starch digestion rate was measured and the hydrolysis index (HI) and estimated glycemic index (eGI) were calculated.

Results: Cooked rice obtained from hot-air drying showed relatively lower HI and eGI than that obtained from sun-drying. Among samples from hot-air drying treatment, eGI of cooked rice decreased with increasing drying temperature, except for the drying temperature of 115 °C. As a result, cooked rice from the hot-air drying at 90 °C showed lowest eGI.

Conclusion: The results indicated that cooked rice digestibility was affected by postharvest drying conditions. © 2016 Society of Chemical Industry.

Keywords: cooked rice; glycemic index; postharvest drying; starch; temperature.

Publication types

  • Comparative Study

MeSH terms

  • Cooking
  • Crops, Agricultural / chemistry
  • Crops, Agricultural / metabolism
  • Dietary Carbohydrates / analysis
  • Dietary Carbohydrates / metabolism
  • Digestion*
  • Food Handling*
  • Food Quality
  • Food, Preserved / analysis
  • Glycemic Index*
  • Hot Temperature / adverse effects
  • Humans
  • Hydrolysis
  • Japan
  • Kinetics
  • Microscopy, Fluorescence
  • Models, Biological*
  • Oryza / chemistry*
  • Oryza / metabolism
  • Seeds / chemistry*
  • Seeds / metabolism
  • Starch / analysis
  • Starch / metabolism*
  • Water / analysis

Substances

  • Dietary Carbohydrates
  • Water
  • Starch