Starch multiscale structure and physicochemical property alterations in high-quality indica rice quality and cooked rice texture under different nitrogen panicle fertilizer applications

Long-term straw return improves cooked indica rice texture by altering starch structural, physicochemical properties in South China

Straw return can improve rice eating quality by modifying starch formation from long-term field trials, whereas the relevant mechanisms are still unknown. A long-term field experiment, including straw removal (CK), straw burning return (SBR), and straw return (SR) was conducted to investigate the starch structure, physicochemical properties, and cooked rice textures of indica early- and late-rice. Compared with CK, SBR and SR enhanced relative crystallinity, amylopectin long chains in both rice seasons, and gelatinization temperatures in late rice. Compared to SBR, SR decreased protein content and amylopectin short chains but increased starch branching degree, breakdown, and stickiness, ultimately contributing to improved starch thermal and pasting properties. Meanwhile, SR decreased hardness, cohesiveness, and chewiness, resulting in cooked texture meliorated, which was mainly attributed to amylopectin chain length and starch granule size. The results suggest that SR increased cooked texture of indica rice by altering starch structural and physicochemical properties.

Effects of postponing nitrogen topdressing on starch structural properties of superior and inferior grains in hybrid indica rice cultivars with different taste values

Introduction

Nitrogen (N) fertilizer management, especially postponing N topdressing can affect rice eating quality by regulating starch quality of superior and inferior grains, but the details are unclear. This study aimed to evaluate the effects of N topdressing on starch structure and properties of superior and inferior grains in hybrid indica rice with different tastes and to clarify the relationship between starch structure, properties, and taste quality.

Methods

Two hybrid indica rice varieties, namely the low-taste Fyou 498 and high-taste Shuangyou 573, were used as experimental materials. Based on 150 kg·N hm-2, three N fertilizer treatments were established: zero N (N0), local farmer practice (basal fertilizer: tillering fertilizer: panicle fertilizer=7:3:0) (N1), postponing N topdressing (basal fertilizer: tillering fertilizer: panicle fertilizer=3:1:6) (N2).

Results

The starch granules of superior grains were more complete, and the decrease in small granules content and the stability of starch crystals were a certain extent less than those of inferior grains. Compared with N1, under N2, low-taste and high-taste varieties large starch granules content were significantly reduced by 6.89%, 0.74% in superior grains and 4.26%, 2.71% in inferior grains, the (B2 + B3) chains was significantly reduced by 1.61%, 0.98% in superior grains, and 1.18%, 0.97% in inferior grains, both reduced the relative crystallinity and 1045/1022 cm-1, thereby decreasing the stability of the starch crystalline region and the orderliness of starch granules. N2 treatment reduced the ΔHgel of two varieties. These changes ultimately contributed to the enhancement of the taste values in superior and inferior grains in both varieties, especially the inferior grains. Correlation analysis showed that the average starch volume diameter (D[4,3]) and relative crystallinity were significantly positively correlated with the taste value of superior and inferior sgrains, suggesting their potential use as an evaluation index for the simultaneous enhancement of the taste value of rice with superior and inferior grains.

Discussion

Based on 150 kg·N hm-2, postponing N topdressing (basal fertilizer: tillering fertilizer: panicle fertilizer=3:1:6) promotes the enhancement of the overall taste value and provides theoretical information for the production of rice with high quality.