Zhiwei Zhu

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.

Phenolic acids and phytosterols, the main functional compounds in cereals, could promote wellbeing and reduce the risks of diet‐related diseases. This study aimed to demonstrate phenolic acid and phytosterol profiles in rice grains and wheat flours, and estimate their intakes in five geographical regions and among different age groups. Phenolic acids and phytosterols mainly existed in bound form, and the whole rice grain had high amount of 161.39 to 368.74 µg/g and 37.50 to 93.31 mg/ 100 g, respectively. In total, nine phenolic acids and six phytosterols were detected with ferulic and p ‐coumaric acid, and β‐ sitosterol the most abundant. The dietary intakes of phenolic acids and phytosterols were calculated combined with the dietary foods intake data of Chinese people. The intakes of total phenolic acids and phytosterols from rice grains and wheat flours varied across different regions with Beijing the highest among the five regions. At the age of 2 to 70 years, the average intakes of phenolic acids and phytosterols from rice and wheat flours were 7.74 to 17.52 and 58.02 to 135.61 mg/sp/day, respectively. If 3‐ounce of polished rice was replaced by black rice grain, the predicted intakes of total phenolic acids and phytosterols from rice grains and wheat flours would increase by at least 196% and 68%, respectively, especially for free phenolic acids and phytosterols. Practical Application: This study would help the consumers know how much phenolic acids and phytosterols they would get from 3 ounces of black rice in a reasonable intake of staple food but shift away other kinds of foods. It could also provide inspirations for food industries to explore the functional cereal foods that are rich in phenolic acids and phytosterols for different regions and different age groups.

Plant glutathione S-transferases (GSTs, EC 2.5.1.18) are multifunctional enzymes involved in heavy metal cellular detoxification by conjugating the tripeptide (g-Glu-Cys-Gly) glutathione to heavy metals. Previous studies demonstrated that individual rice GSTs were differentially induced by heavy metal exposure at the mRNA transcript level. However, little information is available concerning changes in protein concentration of rice GSTs under heavy metal stress. Because the correlation between changes in protein concentration and gene expression under abiotic stress is poor, direct determination of rice GSTs protein concentrations during cadmium (Cd) exposure is a more effective and reliable approach to explore possible mechanisms of rice Cd translocation and accumulation. This study established an optimized and advanced liquid chromatography–tandem mass spectrometry (LC–MS/MS)-based targeted proteomics assay for quantification of OsGSTF14 and OsGSTU6 proteins in Cd-stressed rice roots. The tryptic signature peptides were chosen as surrogate analytes and winged peptides containing the isotope-labeled signature peptides were used as the internal standards. The signature peptides exhibited good linearity in the range of 0.6–60 and 0.3–30 nM, respectively. The limit of detection and limit of quantification were 4.5 and 14.5 µg/g for OsGSTF14, respectively, and 2.1 and 7.0 µg/g for OsGSTU6. The spiking recoveries rates at low, medium and high levels were in the range of 72.5–93.4%, with intra- and inter-day precisions of 5.5–9.1 and 4.2–10.2%, respectively. The assay successfully quantified the temporal and dose responses of OsGSTF14 and OsGSTU6 proteins in Cd-stressed rice roots, with good accuracy, precision and high-throughput. This assay will have significant application in developing quantification methods of other proteins in Cd-stressed rice, which may provide more insight into the mechanisms of Cd translocation and accumulation in rice.

Determination of apparent amylose content in rice is a key function for rice research and the rice industry. In this paper, a novel approach with paper-based microfluidic chip is reported to determine apparent amylose content in rice. The conventional color reaction between amylose and iodine was employed. Blue color of amylose–iodine complex generated on-chip was converted to gray and measured with Photoshop after the colored chip was scanned. The method for preparation of the paper chip is described. In situ generation of iodine for on-chip color reaction was designed, and factors influencing color reaction were investigated in detail. Elimination of yellow color interference of excess iodine by exploiting color removal function of Photoshop was presented. Under the optimized conditions, apparent amylose content in rice ranging from 1.5 to 26.4% can be determined, and precision was 6.3%. The analytical results obtained with the developed approach were in good agreement with those with the continuous flow analyzer method.