Comparative proteomics analysis reveals the effect of germination and selenium enrichment on the quality of brown rice during storage

Effect of illite pretreatment on germinated Brown rice with Special Reference to amino acids, antioxidants, texture, and mineral elements

The pretreatment process of various foods has been reported to improve their nutritional properties. The soaking of brown rice improves the texture and nutrients, which are crucial for cooking and maintaining its high functional value. Illite, a clay mineral, has recently been discovered to improve the nutritional value of seeds. Based on these findings, we soaked brown rice with different concentrations of illite solution for different durations and allowed the germination to perform analyses. Soaking the brown rice for 6 h with a germination period of 48 h was determined to be the optimal condition because of its higher sprout length. In addition, this optimal condition had improved textural characteristics such as reduced hardness, gumminess, chewiness, and cohesiveness, and it also had increased adhesiveness and stabilized resilience and springiness. The treatment solutions were free from heavy metal contaminants, whereas the mineral contents such as K, Ca, Fe, Mg, and Na were significantly increased with the increase in illite concentration. Moreover, our results showed that illite treatment could preserve the color appearance and seed germination. The ratio of essential amino acids to non-essential amino acids and antioxidants (phenolic contentγ-oryzanol, and flavonoid) of germinated brown rice was considerably increased with illite treatment. In germinated brown rice, an increase in DPPH and superoxide dismutase levels, a slight decrease in flavonoids, and no difference in polyphenol content were observed. These findings suggest that pre-soaking brown rice seeds with the appropriate concentration of illite could enhance their nutritional properties, which might attract consumers' interest to include this in their daily diet.

Controlled atmosphere storage drive proteomic change in Chinese Daohuaxiang

Although the use of a controlled atmosphere is one of the most successful storage techniques, the mechanism thereof in rice storage remains unclear. We stored aromatic rice cultivar Daohuaxiang in a package filled with 98 % N2 and 35 % CO2 for 3 months. We investigated 2-acetyl-1-pyrroline loss, enzyme activities, and proteomics changes of rice during storage. The results showed that the content of 2-acetyl-1-pyrroline was reduced by 37.40 %, 25.65 %, and 43.89 % during storage using 98 % N2, 35 % CO2 controlled atmosphere storage, and conventional storage. Controlled atmosphere storage slowed down the increase of malondialdehyde content in Daohuaxiang. The results showed that 26S proteasome regulatory particle triple-A ATPase subunit 6, superoxide dismutase, glutathione transferase, and other key proteins were upregulated during 35 % CO2 regulation. This study provided a meaningful basis for exploring the regulation strategy of aromatic rice quality and strengthening the quality control of aromatic rice industry.

Lipid and Protein Oxidation of Brown Rice and Selenium-Rich Brown Rice during Storage

Selenium-rich rice has become one of the effective ways to increase people's selenium intake. Selenium-containing proteins have higher antioxidant properties, which may lead to selenium-rich brown rice (Se-BR) having better storage stability than ordinary brown rice (BR). By measuring the peroxidation value, fatty acid value, carbonyl value and protein secondary structure, it was found that Se-BR had higher oxidation resistance stability than BR. The biological function of the differential proteins (DEPs) between ordinary brown rice stored for 0 days (BR-0) and 180 days (BR-6) as well as Se-rich brown rice stored for 0 days (Se-0) and 180 days (Se-6) was investigated by using iTRAQ. A total of 237, 235, 113 and 213 DEPs were identified from group A (BR-0/BR-6), group B (Se-0/Se-6), group C (BR-0/Se-0) and group D (BR-6/Se-6), respectively. Kyoto Encyclopedia of Genes and Genomes analysis showed that the DEPs were mainly enriched in glucose metabolism, tricarboxylic acid cycle, fatty acid biosynthesis and degradation, glutathione metabolism, sulfur metabolism, peroxisome and other metabolic pathways. This study provides theoretical support for the study of protein oxidation kinetics and storage quality control of brown rice during storage.

Comparison of high-pressure, freeze-thaw cycles and germination-parboiling treatments on lipids digestibility and rancidity of brown rice

Brown rice (BR) contains more lipids, as compared with white rice, but its indigestibility and rancidity limit the consumer acceptability. Therefore, the objective of this study was to compare the effect of high-pressure (HP), freeze–thaw cycles (FTC) and germination-parboiling (GP) treatments on lipid in vitro digestibility and rancidity of BR. GP treated BR released the most fatty acids (especially palmitic acid and stearic acid) after in vitro digestion, followed by FTC treated BR. FTC treated BR kept the highest value of fat acidity during storage, while opposite results were observed in GP treated BR. Although HP treatment increased fat acidity value immediately, it slowed down the increase of fat acidity with storage. The results of conjugated dienes and malonaldehydes content in BR stored under accelerated conditions indicated better lipid oxidation stability after HP and GP treatment, and that it’s necessary for FTC treated BR products to be stored under anaerobic conditions.

Protein structural properties and proteomic analysis of rice during storage at different temperatures

Rice quality changes during storage, but there have been few studies of how rice proteins changes during aging. The present study characterized the structural properties of protein in stored rice and identified the mechanism of quality deterioration using proteomics. Compared with protein from newly harvested rice, the free sulfhydryl content of protein from stored rice was significantly reduced and the disulfide bond content and surface hydrophobicity was higher. Storage resulted in a loss of α-helix and β-sheet structures and increase in β-turn and random coil structures. High-molecular-weight protein subunits decomposed to produce low-molecular-weight subunits at 30 °C, while protein aggregation occurred at 70 °C. At 30 ℃ 157 differential proteins were found and 70 ℃ 395 such proteins occurred. Redox homeostasis, response to oxidative stress, glutathione metabolism, tricarboxylic acid cycle, glycolysis/gluconeogenesis, starch and sucrose metabolism, and fatty acid biosynthesis and degradation led to the different quality of stored rice.

Effect of storage on metabolites of brown rice

BACKGROUND

Storage is an essential part of brown rice circulation. During the storage process, the metabolic activity of brown rice is still ongoing, and long-term storage leads to the deterioration of brown rice. Metabolomics analysis was performed using gas chromatography-mass spectrometry to investigate the changes in metabolites of brown rice after storage at 18 °C for 12 months.

RESULTS

In terms of quantity, sugar, fatty acids, and other metabolites in brown rice decreased after storage, and alcohols, aldehydes, phenols, and amines increased. A total of 34 differential metabolites were screened. In terms of contents, carbohydrates, amino acids, and fatty acids of brown rice decreased after storage, while those of sugar alcohol, amines, and aldehydes increased after storage. Cluster analysis of the samples at zero storage time revealed that the metabolites expressed least became highly expressed after storage and those expressed highly became low after storage. Metabolic pathway analysis showed that storage significantly influenced the lipid metabolism in brown rice. Palmitoleic acid, cholesterol, linoleic acid, and lauric acid are four key metabolites in lipid metabolism during storage of brown rice.

CONCLUSION

Significant changes occurred in quantity and type of brown rice metabolites after storage. Storage has the greatest effect on lipids. Storage caused a 'reverse change' in the metabolites content of brown rice. The results obtained may help in understanding the changes in metabolites profile and delaying of the quality deterioration of brown rice during storage.

Determination of Selenium in Common and Selenium-Rich Rice from Different Areas in China and Assessment of Their Dietary Intake

In this study, 41 common rice varieties and 211 selenium-rich rice varieties from ten representative areas in China were collected in 2017–2019. The selenium contents of rice were analyzed with optimized inductively coupled plasma mass spectrometry (ICP-MS). Selenium concentrations of common rice and selenium-rich rice ranges were 0.81–7.26 and 0.76–180.73 µg/100 g, respectively. The selenium contents in selenium-rich rice from different areas were significantly different (p < 0.001) while those in common rice from different areas were not. The selenium-rich rice in Harbin and Keshan showed the lowest selenium level and those from selenium-rich areas (Enshi and Ankang) were highest. Based on the estimation of the risk assessment software @risk7.0 (Palisade Corporation, New York, NY, USA), the consumption of selenium-rich rice can effectively increase dietary selenium intake for the population. However, the risk index of P95 (Percentile 95) selenium exposure at the tolerable upper intake level for children at 2–14 years old exceeded 100%, with potential risk currently. Therefore, the consumption of selenium-rich rice should be properly monitored for young children and adolescents.

Analysis of tartary buckwheat (Fagopyrum tataricum) seed proteome using offline two-dimensional liquid chromatography and tandem mass spectrometry

The whole seed of tartary buckwheat (Fagopyrum tataricum) is considered as a healthy and functional food, which is rich in kinds of flavonoids and with potential antioxidant effect. An in-depth analysis of tartary buckwheat seed (TBS) proteome was performed using a shotgun proteomics strategy. Total protein of TBS was extracted and digested, then the peptides were separated by offline two-dimensional liquid chromatography and identified by tandem mass spectrometry. Total of 3,363 high-confidence proteins were identified from 13,730 matched peptides, in which, 2,499 proteins were annotated by the Gene Ontology (GO) analysis with 1,720 involved in "biological process," 2,241 in "molecular function," and 693 in "cellular components." Based on the GO functional enrichment and Kyoto Encyclopedia of Genes and Genomes pathway enrichment results, buckwheat seed proteins were mostly enriched in metabolism of nucleic acid, respiration and energy metabolism, as well as synthesis and metabolism of protein. PRACTICAL APPLICATIONS: This study characterized the tartary buckwheat seed proteome on a scale of 3,000+ proteins and provide important information and clues for future research, especially in the mechanism of seed germination, nutrient composition changes, and metabolite production seed germination and material metabolism.