Rice Grains from Slightly Saline Field Exhibited Unchanged Starch Physicochemical Properties but Enhanced Nutritional Values

Abstract

This study aims to investigate grain quality and nutritional values of rice (Pokkali, a salt-tolerant cultivar; RD73, a new cultivar improved from KDML105 introgressed with Saltol QTL from Pokkali, and KDML105, a moderately salt-susceptible cultivar) grown under non-saline (0.04–0.87 dS/m) and slightly saline (1.08–4.83 dS/m) field conditions. The results revealed that salinity caused significant reduction in grain size but significant increments in reducing sugar and total protein contents in the grains. Nevertheless, the amounts of starch in the grains of KDML105 and Pokkali rice genotypes were unaffected by the stress. The starch granule size distribution was also unaffected by salinity. Interestingly, only starch from Pokkali was significantly diminished in amylose content, from 19.18% to 16.99%. Accordingly, parameters relating to starch gelatinization, retrogradation, and pasting properties of KDML105 and RD73 were unaffected by salinity; only Pokkali showed a significant increase in percentage of retrogradation along with a significant reduction in gelatinization enthalpy. In the saline field, total phenolic content and antioxidant capacity in the grains of all rice cultivars tended to increase, particularly in Pokkali. On average, essential element contents in grains from the saline-treated plants showed a 33%, 32%, 32%, 22%, 20%, 11%, and 10% increase in total P, N, K, Mg, Zn, Fe, and Ca content, respectively. Interestingly, total Fe content exhibited the greatest percentage of increments in KDML105 (187%). Taken together, cultivation of rice in the slightly saline field did not alter its eating and cooking qualities, while enhanced some nutritional properties such as proteins, minerals, and secondary metabolites like phenolic compounds.