It is important to clarify the effects of starch fine structure and protein components on the eating quality of indica rice. In this study, seven indica rice varieties with similar apparent amylose content (AAC) and protein content (PC) but different sensory taste values were selected and compared systematically. It was found that except for AAC and PC, these varieties showed significant differences in starch molecular structure and protein components. Compared with rice varieties with a low sensory taste value, varieties with a higher sensory taste value showed significantly lower amylose and higher amylopectin short chains (degree of polymerization 6–12) content; the protein component showed that the varieties with good taste value had higher albumin and lower globulin and glutelin content (p < 0.05). Rice varieties with lower AC, globulin, and glutelin content, as well as a higher content of albumin and amylopectin short chains, resulted in a higher swelling factor, peak viscosity, breakdown value, and ratio of hardness to stickiness, in which condition cooked rice showed a higher sensory taste value. Moreover, this study indicated that rice varieties with a higher content of albumin and amylopectin short chains were conducive to the good appearance of cooked rice. This study lays the foundation for the taste evaluation of good-tasting indica rice.

Apparent amylose content (AAC) is one of the most important parameters in rice quality evaluation. In this study, four rice reference materials used to test rice AAC were developed. The AAC of rice reference materials were measured by a spectrophotometric method with a defatting procedure, calibrated from potato amylose and waxy rice amylopectin at the absorption wavelengths of 620 and 720 nm. Homogeneity test (n = 20) was judged by F-test based on the mean squares of among and within bottles, and short- and long-term stability monitoring was performed by T-test to check if there was significant degradation at the delivery temperature of under 40 °C (14 days) and at 0–4 °C storage condition (18 months), respectively. After joint evaluation by ten laboratories, Dixion and Cochran statistical analyses were presented. The expanded uncertainties were calculated based on the uncertainty of homogeneity, short- and long-term stability, and inter-laboratory validation containing factor k = 2. It found that the four reference materials were homogenous and stable, and had the AAC (g/100 g, k = 2) of 2.96 ± 1.01, 10.68 ± 0.66, 17.18 ± 1.04, and 16.09 ± 1.29, respectively, at 620 nm, and 1.46 ± 0.49, 10.44 ± 0.56, 16.82 ± 0.75, and 24.33 ± 0.52, respectively, at 720 nm. It was indicated that 720 nm was more suitable for the determination of rice AAC with lower uncertainties. The determinations of the AAC of 11 rice varieties were carried out by two methods, the method without defatting and with calibration from the four rice reference materials and the method with a defatting procedure and calibrating from potato amylose and waxy rice amylopectin. It confirmed that the undefatted rice reference materials could achieve satisfactory results to test the rice samples with the AAC ranging from 1 to 25 g/100 g. It would greatly reduce the time cost and improve testing efficiency and applicability, and provide technical support for the high-quality development of the rice industry.

Understanding the effects of genotype, environment and their interactions on rice quality is of great importance for rice breeding and cultivation. In this study, six rice varieties with two indica, two japonica and two indica–japonica types of rice were selected and planted at ten locations in Zhejiang Province to investigate the genotype (G) × environment (E) on physicochemical and sensory properties and the differences of volatile organic compounds (VOCs) among the three types of rice. Analysis of variances showed that apparent amylose content (AC), total protein content (PC), alkali spreading value (ASV), RVA profiles, and appearance (ACR), palatability (PCR), and sensory evaluation value (SEV) of cooked rice and texture of cooled cooked rice (TCCR) were mainly affected by genotypic variation, whereas the smell of cooked rice (SCR) was mainly affected by environment (p < 0.05). The G × E effect was significant for most parameters. The weather in the middle and late periods of filling had important effects on the formation of rice quality, especially on setback (SB) and pasting temperature (PT) (p < 0.01). They were negatively correlated with the texture of cooked rice (TCR) and SEV (p < 0.05). Peak viscosity (PV) and breakdown (BD) were positively related to the sensory evaluation parameters (p < 0.01) and could be used to predict cooked rice quality. A total of 59 VOCs were detected, and indica, japonica and indica–japonica had 9, 6 and 19 characteristic compounds, respectively. The principal component analysis showed that the physicochemical and sensory properties and VOCs of indica–japonica rice were more stable than those of indica and japonica rice at ten locations in Zhejiang Province. It is helpful for rice breeders to understand how the environment affects the physicochemical, sensory properties and VOCs of the three rice types, and it is also important for food enterprises to provide rice products with stable quality.

Rice eating quality is a core determinant of consumer preference and commercial value. Although it is chemically determined by the accumulation and distribution of the substances in rice seeds, the comprehensive physicochemical basis underlying this trait in japonica rice remains insufficiently clarified. To identify the key physicochemical indicators that predict and regulate japonica rice eating quality, the taste value of 59 japonica rice varieties was evaluated, and the protein content (PC), apparent amylose content (AAC), starch pasting properties, gelatinization characteristics, and textural attributes were systematically measured. The results indicated that japonica rice has an average taste value of 72.0 with a range between 54.0 and 87.8. The taste value was significantly negatively correlated with PC, onset (To), peak (Tp) and conclusion (Tc) gelatinization temperatures, but was significantly positively correlated with appearance score, mouthfeel score, hot paste viscosity (HPV), and cool paste viscosity (CPV). PCA further indicated that AAC, HPV, CPV, peak viscosity (PV), and setback value (SB) were the major contributors to the first principal component, explaining 38.5% of the total variation. Stepwise regression analysis showed that the best regression equation for predicting taste value was: Taste value = 142.526 − 5.226 PC − 0.425 To (R² = 0.455; p < 0.001), confirming PC and To as the core parameters accounting for 45.5% of the taste value variation. Path analysis further indicated that PC and To affected japonica rice eating quality through direct and indirect pathways. These findings suggest that low PC, low gelatinization temperature, high HPV, and high CPV can serve as good physicochemical indicators for the breeding of high-eating-quality japonica rice.

To characterize intraspecific variation in phenolic acid composition and in vitro antioxidant capacity, color parameters, total phenolic contents (TPC), hydrolyzable phenolic acid profiles, and DPPH and ABTS radical scavenging capacities were systematically determined in the flesh of 33 Cucurbita pepo accessions. All accessions exhibited bright yellow flesh, with significant variation in red-green value (a). TPC and antioxidant capacity differed markedly among accessions and generally followed right-skewed distributions, indicating that a limited number of accessions accumulated high levels of phenolics and antioxidant activity. Eight phenolic acids were quantified by high-performance liquid chromatography (HPLC), with p-hydroxybenzoic acid (8.97–341.98 μg/g), p-coumaric acid (2.42–761.88 μg/g), and ferulic acid identified as the major compounds. Ferulic acid and caffeic acid showed strong positive associations with both DPPH and ABTS scavenging capacities. Hierarchical clustering separated the accessions into two major groups, with Group 2 exhibiting higher TPC (208.89–657.69 µg GAE/g), total phenolic acid content (109.92–890.85 µg/g), and ABTS antioxidant capacity than Group 1. The high-antioxidant accessions may serve as promising candidates for antioxidant-enriched C. pepo products and quality-oriented breeding.