Rice is generally considered a high-glycemic index (GI) food, but numerous studies show that parboiling reduces the GI. There are no studies on GI of Indica and Japonica subspecies parboiled rice grown in Italy. The aim of this study was (1) to evaluate GI in different varieties of parboiled rice (ribe, white and brown long B, basmati, black, red, roma, and arborio); (2) to evaluate GI of same variety of rice subjected to different rice parboiling processes (parboiled ribe and parboiled long B with two different methods: flora and conventional method); (3) to evaluate GI of two by-products of parboiled rice: white and brown rice cake. Participants were 10 healthy individuals (20-30 years old, body mass index 18.5-25 kg/m2). Proximate composition and GI were determined by using standard methods. All parboiled rice assessed is low-GI (brown long B 48.1 ± 6.4 by flora method, ribe 52.0 ± 1.8 GI by flora method, black rice 52.3 ± 7.6 by flora method, long B 52.4 ± 3.9 by flora method, long B 53.4 ± 5.1 by conventional method, ribe 54.4 ± 4.3 GI by conventional method, Roma 54.4 ± 7.9 GI by flora method, and arborio 54.4 ± 7.9 GI by flora method), except red rice that is of medium-GI (56.1 ± 7.0 GI), and both classic and brown cakes that are high-GI (respectively, 83.3 ± 8.9 GI and 102.2 ± 5.5 GI). Parboiled rice is low-GI and so is favorable for the dietary management of metabolic disorders and celiac disease. Clinicaltrials.gov (NCT05333081).
Keywords: Indica; glycemic index; parboiled rice; rice.