Insights into Recent Updates on Factors and Technologies That Modulate the Glycemic Index of Rice and Its Products

Endosperm structure and Glycemic Index of Japonica Italian rice varieties

Introduction

Given that rice serves as a crucial staple food for a significant portion of the global population and with the increasing number of individuals being diagnosed with diabetes, a primary objective in genetic improvement is to identify and cultivate low Glycemic Index (GI) varieties. This must be done while ensuring the preservation of grain quality.

Methods

25 Italian rice genotypes were characterized calculating their GI "in vivo" and, together with other 29 Italian and non-Italian genotypes they were studied to evaluate the grain inner structure through Field Emission Scanning Electron Microscopy (FESEM) technique. Using an ad-hoc developed algorithm, morphological features were extracted from the FESEM images, to be then inspected by means of multivariate data analysis methods.

Results and Discussion

Large variability was observed in GI values (49 to 92 with respect to glucose), as well as in endosperm morphological features. According to the percentage of porosity is possible to distinguish approximately among rice varieties having a crystalline grain (< 1.7%), those intended for the preparation of risotto (> 5%), and a third group having intermediate characteristics. Waxy rice varieties were not united by a certain porosity level, but they shared a low starch granules eccentricity. With reference to morphological features, rice varieties with low GI (<55) seem to be characterized by large starch granules and low porosity values. Our data testify the wide variability of Italian rice cultivation giving interesting information for future breeding programs, finding that the structure of the endosperm can be regarded as a specific characteristic of each variety.

Ultrasound-Assisted Extraction of Antioxidant Compounds from "Cẩm" Purple Rice Bran for Modulation of Starch Digestion

Purple rice, locally known as "Cẩm" rice, is cultivated in the southern region of Vietnam. The bran of "Cẩm" rice is often disregarded and underutilized; nevertheless, it harbours substantial nutritive value, particularly in terms of antioxidant compounds. Additionally, sonication, an emerging and "green" technological approach, has been employed to augment the extraction efficiency of these antioxidants. This research is aimed at optimizing and maximizing the antioxidant recovery capacity including phenolic and total flavonoid compounds, along with their antioxidant activities, through the assistance of ultrasound waves. The effect of the extract on the starch digestion process was also investigated. The study employed the Box-Behnken experimental design, encompassing three variables: extraction time (20-40 minutes), temperature (60-80°C), and solvent-to-material ratio (8 : 1 to 12 : 1). Analysis was conducted on total phenolic compounds, total flavonoid content, and antioxidant activities. Results demonstrated that the peak yield of antioxidant compounds and their corresponding activities were attained at an extraction duration of 29.38 minutes, a temperature of 69°C, and a solvent-to-material ratio of 9.92. Under these optimal conditions, the yields were as follows: total phenolic compounds at 60.821 mg GAE/g, total flavonoid compounds at 3.2696 mg QE/g, percentage inhibition of DPPH at 74.778%, and FRAP value at 54.112 μmol Fe (II)/g. The established models were validated and exhibited a strong alignment between predicted and actual values, with disparities of less than 3% under optimal conditions. Furthermore, the extract was codigested with cooked corn starch, revealing a dose-dependent effect on starch digestibility. The sluggishness of digestion rate was observed when 20 mg of the extract was supplemented to 200 mg of cooked corn starch. This suggests that rice bran extract holds promise as an effective ingredient for mitigating starch digestion, particularly beneficial for individuals dealing with diabetes.