Ultrasensitive Electrochemiluminescence Sensor Utilizing Aggregation-Induced Emission Active Probe for Accurate Arsenite Quantification in Rice Grains

Arsenic (As) constitutes a substantial threat to global ecosystems and public health. An accurate quantification of inorganic arsenite (As(III)) in rice grains is crucial for ensuring food safety and human well-being. Herein, we constructed an electrochemiluminescence (ECL) biosensor utilizing aggregation-induced emission (AIE) active Pdots for the sensitive detection of As(III) in rice. We synthesized tetraphenylethylene-based AIE-active Pdots, exhibiting stable and highly efficient ECL emission in their aggregated states. Owing to the overlap of spectra, we employed an electrochemiluminescence resonance energy transfer (ECL-RET) system, with the Pdots as the donor and black hole quencher (BHQ) as the acceptor. Upon the introduction of As(III), the conformational changes of As(III)-specific aptamer could trigger the detachment of BHQ-labeled DNA aptamer from the electrode surface, leading to the recovery of the ECL signal. The target-induced "signal-on" bioassay enabled the sensitive and specific detection of As(III) with a linear range of 10 pM to 500 nM, with an ultralow limit of detection (LOD) of 5.8 pM/0.4 ppt. These values significantly surpass those of existing sensors designed for As(III) quantification in rice. Furthermore, by employing amylase hydrolysis for efficient extraction, we successfully applied our sensor to measure As(III) in actual rice samples sourced from diverse regions of China. The results obtained using our sensor were in close agreement with those derived from the reference method of HPLC-ICP-MS. This study not only presents a sensitive and reliable method for detecting arsenite but also underscores its potential applications in enhancing food safety, agriculture practices, and environmental monitoring.

Mercury Accumulation in Commercial Varieties of Oryza sativa L. Cultivated in Soils of La Mojana Region, Colombia

The Hg accumulation in different commercial varieties of Oryzasativa L. was evaluated in the region of La Mojana, Colombia, where rice cultivation has become the staple food of the population living in this area. The varieties studied were Fedearroz-473 (FA473), Fedearroz-2000 (FA2000), and Fedearroz-Mocari (FAM). Soil spiked at different Hg levels was evaluated, (130, 800, and 1500 µg kg-1) using a 32 factorial design that consisted of 3 (rice varieties) × 3 (Hg contents). The biomass, 1000-grain weight, and the accumulation of Hg in the roots, grains, and husks were determined. The highest biomass was found in the FA473 (308.76 ± 108.26 g), and the lowest was found in FAM (144.04 ± 26.45 g) in the 1500 µg kg-1 Hg soil in both cases. The weight per 1000-grains decreased significantly in the soil containing 800 µg of Hg kg-1. Hg accumulation in the organs of the evaluated varieties was higher in the roots, followed by in the husks and grains. The Hg in the rice grains of the evaluated varieties presented levels close to the permissible limit of the Chinese standard (20 μg Hg kg-1) in the evaluated soils and were only exceeded by FA473. Although in natural soil concentrations, the non-cancer health risk (HQ) from rice consumption was lower for FA473 and FAM; Hg enrichment in the soil of La Mojana region may endanger the health of future populations due to their high consumption of rice.

Early identification of Aspergillus spp. contamination in milled rice by E-nose combined with chemometrics

BACKGROUND

Rice grains can be contaminated easily by certain fungi during storage and in the market chain, thus generating a risk for humans. Most classical methods for identifying and rectifying this problem are complex and time-consuming for manufacturers and consumers. However, E-nose technology provides analytical information in a non-destructive and environmentally friendly manner. Two-feature fusion data combined with chemometrics were employed for the determination of Aspergillus spp. contamination in milled rice.

RESULTS

Linear discriminant analysis (LDA) indicated that the efficiency of fusion signals ('80^th s values' and 'area values') outperformed that of independent E-nose signals. Linear discriminant analysis showed clear discrimination of fungal species in stored milled rice for four groups on day 2, and the discrimination accuracy reached 92.86% by using an extreme learning machine (ELM). Gas chromatography-mass spectrometry (GC-MS) analysis showed that the volatile compounds had close relationships with fungal species in rice. The quantification results of colony counts in milled rice showed that the monitoring models based on ELM and the genetic algorithm optimized support vector machine (GA-SVM) (R²  = 0.924-0.983) achieved better performances than those based on partial least squares regression (PLSR) (R²  = 0.877-0.913). The ability of the E-nose to monitor fungal infection at an early stage would help to prevent contaminated rice grains from entering the food chains.

CONCLUSIONS

The results indicated that an E-nose coupled with ELM or GA-SVM algorithm could be a useful tool for the rapid detection of fungal infection in milled rice, to prevent contaminated rice from entering the food chain. © 2021 Society of Chemical Industry.

Detection of Thioarsenates in Rice Grains and Rice Products

Inorganic and methylated thioarsenates have recently been reported to contribute substantially to arsenic (As) speciation in paddy-soil pore waters. Here, we show that thioarsenates can also accumulate in rice grains and rice products. For their detection, a method was developed using a pepsin-pancreatin enzymatic extraction followed by chromatographic separation at pH 13. From 54 analyzed commercial samples, including white, parboiled and husked rice, puffed rice cakes, and rice flakes, 50 contained dimethylmonothioarsenate (DMMTA) (maximum 25.6 μg kg^-1), 18 monothioarsenate (MTA) (maximum 5.6 μg kg^-1), 14 dimethyldithioarsenate (DMDTA) (maximum 2.8 μg kg^-1), and 5 dithioarsenate (DTA) (maximum 2.3 μg kg^-1). Additionally, we show that the commonly used nitric acid extraction transforms MTA to arsenite and DMMTA and DMDTA to dimethylarsenate (DMA). Current food guidelines do not require an analysis of thioarsenates in rice and only limit the contents of inorganic oxyarsenic species (including acid-extraction-transformed MTA), but not DMA (including acid-extraction-transformed DMMTA and DMDTA).

Optimization of the autoclave preparation process for improving resistant starch content in rice grains

The autoclave preparation process to increase the content of resistant starch (RS) in rice grains was optimized, and the results showed that the optimal preparation process was obtained with a water content of 41.63%, a pH of 5.95, an autoclave time of 60.96 min, and a refrigeration time of 17.11 hr. Under these conditions, the theoretical value of RS content in rice grains reached 17.57%. After autoclaving, the estimated glycemic index (EGI) in rice grains was reduced from 78.35 to 66.08 measured after cooking, suggesting that autoclaving was capable of increasing the RS content in rice grains and reducing its EGI value. These results may help spark new concepts and methods for the development of specialized foods for specific populations, such as people with diabetes.

Momilactones A, B, and Tricin in Rice Grain and By-Products are Potential Skin Aging Inhibitors

We previously reported the inhibitory potentials of momilactones A (MA) and B (MB) against key enzymes related to type 2 diabetes and obesity. In this study, antioxidant and anti-skin-aging activities of MA and MB were investigated and compared with tricin, a well-known antioxidant and antiaging flavonoid in rice. MA, MB, and tricin were purified from rice husk by column chromatography and their biological activities were subsequently assayed by in vitro trials. The contents of MA, MB, and tricin of different commercial rice cultivars in Japan were quantified and confirmed by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry (UPLC-ESI-MS) and high-performance liquid chromatography (HPLC) analyses. The antioxidant assays revealed a synergistic activity of the mixture MA and MB (MAB, 1:1, v/v). In addition, in 2,2'-azino-bis (ABTS) assay, IC₅₀ values of MAB (0.3 mg/mL) and tricin (0.3 mg/mL) was 4-fold and 9-fold greater than that of individual MB (1.3 mg/mL) or MA (2.8 mg/mL), respectively. The in vitro enzymatic assays on pancreatic elastase and tyrosinase indicated that MA and MB were potential to relief skin wrinkles and freckles. In detail, MA exerted higher inhibition on both enzymatic activities (30.9 and 37.6% for elastase and tyrosinase inhibition, respectively) than MB (18.5 and 12.6%) and MAB (32.0 and 19.7%) at a concentration of 2.0 mg/mL. Notably, MA and the mixture MAB exhibited stronger inhibitions on elastase and tyrosinase in comparison with tricin and vanillin. MA, MB, and tricin in rice are potential to develop cosmetics as well as supplements for skin aging treatments.

Towards Managing and Controlling Aflatoxin Producers Within Aspergillus Species in Infested Rice Grains Collected from Local Markets in Kenya

Rice grains can be attacked by a range of pathogens, including Aspergillus species, which can cause the accumulation of aflatoxins and represent a serious threat to the consumers. Aflatoxins are secondary metabolites synthesized by Aspergillus species and naturally occur in various foodstuffs. In this study, we sought to analyze the prevalence of aflatoxin-producing Aspergillus spp. in rice grains currently sold in Kenyan local markets. We analyzed a total of 98 samples randomly collected and primarily analyzed to observe moisture content and fungal growth. We then isolated Aspergillus species, characterized them morphologically and using the Internal transcribed spacer (ITS) primers. Finally, we screened them for aflatoxin-producing isolates targeting Norsolorinic Acid (nor-1) and Versicolorin (ver-1) specific genes involved in aflatoxin biosynthesis. We observed that all tested samples were contaminated. The highest prevalence of Aspergillus species and aflatoxigenic fungal species, had values of 66% and 36.4% for nor-1 and ver-1, respectively. In total, 66% of all isolates were confirmed to be aflatoxin producers. The occurrence of high contamination levels of Aspergillus species points to the possibility of production of aflatoxins in rice grains. This work provides a baseline for future studies on the occurrence of mycotoxigenic fungal species in rice grains being sold in local markets and strategies to control these aflatoxigenic strains at pre- and post-harvest levels.

Poly (Octadecyl Methacrylate-Co-Trimethylolpropane Trimethacrylate) Monolithic Column for Hydrophobic in-Tube Solid-Phase Microextraction of Chlorophenoxy Acid Herbicides

Chlorophenoxy acid herbicides (CAHs), which are widely used on cereal crops, have become an important pollution source in grains. In this work, a highly hydrophobic poly (octadecyl methacrylate-co-trimethylolpropane trimethacrylate) [poly (OMA-co-TRIM)] monolithic column has been specially prepared for hydrophobic in-tube solid-phase microextraction (SPME) of CAHs in rice grains. Due to the hydrophobicity of CAHs in acid conditions, trace CAHs could be efficiently extracted by the prepared monolith with strong hydrophobic interaction. Several factors for online hydrophobic in-tube SPME, including the length of the monolithic column, ACN and trifluoroacetic acid percentage in the sampling solution, elution volume, and elution flow rate, were investigated with respect to the extraction efficiencies of CAHs. Under the optimized conditions, the limits of detection of the four CAHs fell in the range of 0.9–2.1 μg/kg. The calibration curves provided a wide linear range of 5–600 μg/kg and showed good linearity. The recoveries of this method ranged from 87.3% to 111.6%, with relative standard deviations less than 7.3%. Using this novel, highly hydrophobic poly (OMA-co-TRIM) monolith as sorbent, a simple and sensitive online in-tube SPME-HPLC method was proposed for analysis of CAHs residue in practical samples of rice grains.

Fast Determination of Phenolic Compounds in Rice Grains by Ultraperformance Liquid Chromatography Coupled to Photodiode Array Detection: Method Development and Validation

There are several phenolic compounds in rice grains providing benefits for human health. The concentration of phenolic compounds in rice is strongly affected by the polishing steps during rice production. A new sensitive ultraperformance liquid chromatography-ultraviolet-visible spectroscopy method with a photodiode array detection protocol has been developed and validated for the quantitation of phenolic compounds in rice grains. Several working variables and two different columns were evaluated. Finally, a less than 3 min analysis time was developed to achieve enough resolution for the simultaneous determination of the 20 most common phenolic compounds in rice. The analytical properties for the separation method produced an adequate sensitivity for all phenolic compounds in the regular range for phenolics in rice, 0.5-100 mg L^-1 ( R² > 0.997), with high precisions for both repeatability and intermediate precisions (coefficients of variation less than 0.4 and 2.5% for the retention time and area of the peaks, respectively).

Determination of Melatonin in Rice (Oryza sativa) Grains by Pressurized Liquid Extraction

Melatonin provides a number of benefits for human health. The study reported here concerns the optimization, validation, and application of analytical pressurized liquid extraction and high-performance liquid chromatography coupled to a fluorescence detector for the determination of melatonin in rice grains. The factors that are most likely to affect the extraction efficiency were optimized with a 2_IV^7-2 fractional factorial design. The optimum extraction conditions were achieved by applying 70% EtOAc in MeOH at 200 °C and 200 atm for a static time of 5 min in two cycles with 50% flushing and a 60 s purge to extract a 2.5 g rice sample. The method validation ensured excellent linearity, limit of detection, limit of quantification, precision, and recovery. Furthermore, the method was applied to various rice products composed of polished, whole grain, aromatic, black, black glutinous, red, and parboiled rice. All kinds of pigmented rice grains showed high levels of melatonin (>100 μg kg ^-1), and the highest levels were found in red rice.

Elevated tropospheric ozone increased grain protein and amino acid content of a hybrid rice without manipulation by planting density

BACKGROUND

Rising tropospheric ozone affects crop yield and quality. Rice protein concentration, which is closely associated with eating/cooking quality, is of critical importance to nutritional quality. The ozone effect on amino acids of rice grains was little known, especially grown under different cultivation conditions. A hybrid rice cultivar Shanyou 63 was grown in 2010 and 2011 to investigate the interactive effect of ozone exposure and planting density on rice protein quality in a free-air ozone enrichment system.

RESULTS

The content of protein, total amino acids (TAA), total essential (TEAA) and non-essential amino acids (TNEAA) in rice grain was increased by 12-14% with elevated ozone. A similar significant response to ozone was observed for concentrations of the seven essential and eight non-essential amino acids. In contrast, elevated ozone caused a small but significant decrease in percentage of TEAA to TAA. The year effect was significant for all measured traits; however, interactions of ozone with year or planting density were not detected.

CONCLUSION

The study suggested that season-long elevation of ozone concentration to projected 2050 levels will increase protein and amino acids of Shanyou 63, and crop management such as changing planting density might not alter the impact.