Ratiometric fluorescent test strips based on CB-Ni2+@CDs probes for visual detection of histamine.

Histamine is a biogenic amine with various physiological functions. However, excessive consumption of histamine can lead to various symptoms, and pose a threat to human lives. A ratiometric fluorescent test strip for visual detection of histamine was developed based on CB-Ni2+@CDs probes. As the concentration of histamine increases, the test strips exhibit a transition in fluorescence signal from yellow-green to blue. The RGB values were extracted from the images, and used for quantitative analysis of histamine. The method had a linear range of 0-1.0 mM, with a detection limit of 0.086 mM. The test strips were employed for the detection of histamine, and the recovery rate was found to be in the range of 88.3% to 104.69%, indicating a high level of accuracy. The uniqueness of the test strips lies in their ability to be produced simply by mixing CB, Ni2+ on a suitable polyvinyl alcohol/wood cellulose fiber substrate.

Fe-MOF/AuNP-based ratiometric electrochemical immunosensor for the detection of deoxynivalenol in grain products.

A ratiometric assay was designed to improve the sensitivity and reliability of electrochemical immunosensors for deoxynivalenol (DON) detection. The indicator signal caused by the Fe-based metal-organic framework nanocomposites loaded with gold nanoparticles and the internal reference signal from the [Fe(CN)6]3-/4- in the electrolyte came together at the immunosensor. When immunoreactivity occurred, the indicator signals decreased as the concentration of DON increased, while the internal reference signals increased slightly. The ratio of the indicator signal to the internal reference signal was available for reproducible and sensitive monitoring of DON. The prepared immunosensor showed excellent performance in the range from 0.5 to 5000 pg mL-1, and the detection limit was 0.0166 pg mL-1. The immunosensor achieved satisfactory detection toward DON in spiked and actual samples and has a promising application in the control of DON in grain products.

Quality changes in Chinese high-quality indica rice under different storage temperatures with varying initial moisture contents.

The planting area of high-quality indica rice varieties has been growing rapidly in China. However, the storage characteristics of these varieties remains unclear. In this research, different moisture contents (13.5, 14.5, and 15.5%) of high-quality rice (variety Xiadao No.1) were stored at different temperatures (15, 20, 25, and 30°C) for 360 d, and then evaluated for lipid metabolism, redox enzyme activities, fatty acid composition, and sensory attributes. With the prolongation of storage, rice displayed an upward trend in fatty acid value, malondialdehyde content, and cooked rice hardness and a downward trend in contents of total fat and non-starch lipid, peroxidase and catalase activities, and sensory score of cooked rice. The change trends of these quality parameters were aggravated by elevating storage temperature and moisture content. Linoleic acid content of rice generally decreased with prolonged storage. After 300 d of storage, rice with initial moisture content of 13.5% at 30°C showed a fatty acid value of higher than 30 mg KOH/100 g, while rice of other two initial moisture contents reached similar level at 25°C. After the whole storage period, only rice with initial moisture contents of 13.5 and 14.5% stored at 15°C had a sensory score of higher than 60. These results suggested that the aging process of high-quality rice can be inhibited by decreasing the storage temperature and initial moisture content. These results can provide reference for grain storage enterprises to select proper storage condition to store high-quality rice.

Amine vapor-responsive ratiometric sensing tag based on HPTS/TPB-PVA fluorescent film for visual determination of fish freshness.

In this study, amine vapor-sensitive films with ratiometric fluorescence attributes were developed. The pH-sensitive fluorescein 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and its tetraphenylethylene derivative (TPB) were selected as ratiometric indicators and incorporated into a polyvinyl alcohol (PVA) matrix to produce HPTS/TPB-PVA films. The films responded well to amine vapors, and the interference of aromatic vapors did not substantially affect the fluorescence signals of the films. Under UV light at a wavelength of 365 nm, the fluorescence of the films changed from dark pink to light pink and finally to yellow when the freshness of the fish was visually checked during storage. In addition, the color difference values of the films showed a positive correlation with the total volatile basic nitrogen (TVB-N), ranging from 12.7 to 24.8 mg/100 g at 25 °C and 8.4 to 25.6 mg/100 g at 4 °C, respectively. This indicates that fluorescent films have good potential for quantifying fish freshness in the near future when connected to an automatic data processing system based on color differences.

Lateral Flow Immunoassay Based on Quantum-Dot Nanobeads for Detection of Chloramphenicol in Aquatic Products.

Quantum dot nanobeads (QBs) were used as signal source to develop competitive lateral flow immunoassay (LFIA) for the detection of chloramphenicol (CAP). The quantitative detection of CAP was achieved by calculating the total color difference (∆E) values of the test line (T line) using the images of test strips. QB-based LFIA (QBs-LFIA) allowed the effective dynamic linear detection of CAP in the range of 0.1-1.5 ng/mL. The limit of detection (LOD) was 3.0 ng/mL, which was 50 and 667 times lower than those achieved for two different brands of colloidal gold kits. The recoveries of CAP during real-sample detection were 82.82-104.91% at spiked levels of 0.1, 0.7, and 1.5 ng/mL. These results indicate that the developed QBs-LFIA facilitates the sensitive detection of CAP.

The component of the Chamaecyparis obtusa essential oil and insecticidal activity against Tribolium castaneum (Herbst).

Tribolium castaneum (Herbst) is a worldwide grain storage pest controlled by chemical control methods of phosphine fumigation, which results in many hazards, damages human health, makes pests resistant to pesticides, and pollutes the environment. In recent years, the popularity of botanical insecticides has continued to rise, and plant essential oils (EO) are considered potential alternatives for developing insecticides. In the current study, we selected the Chamaecyparis obtusa EO to determine its insecticidal effects and component analysis on T. castaneum. Through gas chromatography-ion mobility spectrometry (GC-IMS) technology, cedrol was the most obvious compound in the signal peak of the volatile components detected in the C. obtusa EO. The results of the bioassay showed that the C. obtusa EO had certain contact activity against T. castaneum, and the LD50 was 52.54 µg/adult. At three concentrations (0.41,1.62, 2.83 uL/cm2), the repellent rates of C. obtusa EO against T. castaneum were all above 80% at 15, 30, 60, and 120 min, respectively, indicating that the repellent effect was strong. Meanwhile, the C. obtusa EO exhibited fumigant toxicity against T. castaneum with LC50 values of 7.09 µg/L air. In addition, C. obtusa EO significantly increased the activity of AChE, CarE, POD, CAT, T-SOD, and chitinase in T. castaneum. Finally, the mechanism of C. obtusa EO on T. castaneum adults was explored based on transcriptome sequencing. We found that the DEGs focused on the chitin metabolic process and some aging genes in T. castaneum. Therefore, C. obtusa EO could be used as potential eco-friendly candidates for stored grain pest management.

Zeolitic Imidazolate Framework-8 Composite-Based Enzyme-Linked Aptamer Assay for the Sensitive Detection of Deoxynivalenol.

The mycotoxin deoxynivalenol (DON) is a prevalent contaminant in cereals that threatens the health of both humans and animals and causes economic losses due to crop contamination. The rapid and sensitive detection of DON is essential for food safety. Herein, a colorimetric biosensor based on horseradish peroxidase- and gold nanoparticle-encapsulated zeolitic imidazolate framework-8 (HRP&Au@ZIF-8) was developed for the sensitive screening of DON. The synthesized HRP&Au@ZIF-8 probes not only held great potential for signal amplification but also exhibited stable catalytic activity even under extreme conditions, which endowed the biosensor with both good sensitivity and stability. Under the optimized conditions, qualitative measurement of DON can be achieved through visual inspection, and quantitative evaluation can be performed via absorbance measurements at a characteristic wavelength of 450 nm. The proposed method has demonstrated high sensitivity with a linear detection range of 1-200 ng/mL and a detection limit of 0.5068 ng/mL. It also presented good selectivity and reliability. Furthermore, DON in spiked cereal samples has been quantified successfully using this method. This novel approach demonstrates significant potential for the facile and expeditious detection of DON in cereal products and brings us one step closer to enhancing food safety.

NH2-MIL-125(Ti)/Reduced Graphene Oxide Enhanced Electrochemical Detection of Fenitrothion in Agricultural Products.

The abuse of organophosphate pesticides causes serious threats to human health, which threatens approximately 3 million people and leads to more than 2000 deaths each year. Therefore, it is necessary to determine the residue of fenitrothion (FT) in environmental and food samples. Herein, we developed a non-enzymatic electrochemical sensor with differential pulse voltammetry signal output to determine FT in model solutions and spiked samples. Delicately, the sensor was designed based on the fabrication of hydrothermally synthesized titanium-based metal-organic frameworks (MOFs) material (NH2-MIL-125(Ti))/reduced graphene oxide (RGO) (NH2-MIL-125(Ti)/RGO) nanocomposites for better target enrichment and electron transfer. The peak response of differential pulse voltammetry for FT under optimized conditions was linear in the range of 0.072-18 µM with the logarithm of concentrations, and the detection limit was 0.0338 µM. The fabricated sensor also demonstrated high stability and reproducibility. Moreover, it exhibited excellent sensing performances for FT in spiked agricultural products. The convenient fabrication method of NH2-MIL-125(Ti)/RGO opens up a new approach for the rational design of non-enzymatic detection methods for pesticides.

An electrochemical immunosensor based on prussian blue@zeolitic imidazolate framework-8 nanocomposites probe for the detection of deoxynivalenol in grain products.

The presence of deoxynivalenol (DON) in grains poses a threat to human health, which is critical for sensitive detection of DON. In this electrochemical immunosensor, zeolitic imidazolate framework-8 (ZIF-8) loaded with Prussian blue (PB) nanoparticles was coated by polydopamine (PDA) as a redox probe. The high porosity of ZIF-8, the unique electrochemical activity of PB and the outstanding electrical conductivity of PDA improved the sensitivity of the immunosensor. Under the optimized conditions, the peak current in differential pulse voltammetry displayed a good linear relationship over DON concentrations in a range of 0.1-5000 pg mL-1 with a detection limit of 0.0186 pg mL-1. In addition, the immunosensor also had good selectivity and stability. Good recoveries of 85.67 to 118.00 % have been achieved for the detection of DON in spiked grain products. This new strategy exhibits great potential for simple and rapid detection of DON in grain and feed products.

Quality attributes of paddy rice during storage as affected by accumulated temperature.

In actual storage processes of rice, environment temperatures fluctuate rather than remain constant. Accumulated temperature is the sum of temperature during the storage period. In this research, six different temperature-varied conditions with two accumulated temperatures (low intensity: 7200°C⸱d; high intensity: 9000°C⸱d) were designed to store rice for 12 months and the stored rice samples were compared in quality. Three low-accumulated temperature conditions were set as follows: No. 4-15°C for 6 months followed by 25°C; No. 5-25°C for 6 months followed by 15°C; No. 8-alternating between 15°C and 25°C every 2 months. Similarly, three high-intensity conditions, No. 6, No. 7, and No. 9, were set with a temperature change from 25°C to 35°C. Three constant temperature conditions, No. 1, No. 2, and No. 3, with storage temperature of 15, 25, and 35°C, respectively, were used as controls. Under temperature-varied conditions, rice demonstrated a decline in germination rate (GR), catalase (CAT) and peroxidase (POD) activities, and an increase in fatty acid value (FAV) as storage time increased. After storage, rice exhibited higher water absorption rate (WAR) and volume expansion rate (VER), but reduced stickiness and sensory scores for appearance, taste and overall quality. Generally, three batches at high-accumulated temperature conditions had lower GR and sensory scores, and higher FAV, WAR, and VER compared to those under low-intensity conditions. Furthermore, variations in the sequence of temperature also affected quality parameters, even at the same accumulated temperature. These findings indicate that under temperature-varied conditions, increased accumulated temperature exacerbates rice deterioration, and different temperature sequences can influence quality at a given accumulated temperature.

Ozone reduces lifespan and alters gene expression profiles in Rhyzopertha dominica (Fabricius).

Rhyzopertha dominica is one of the most important stored grain pests that seriously damage rice and wheat. At present, the method of controlling stored grain pests mainly relies on insecticide fumigation. However, the excessive use of pesticides not only leaves pesticide residues, with harmful effects on human health and the environment, but also induces insect resistance. Ozone is a strong oxidant with the characteristics of easy decomposition and without residue. Although ozone has been widely used in the food industry in recent years, research on the control of stored grain pests is limited. In this research, we used ozone treatment to control R. dominica adults and explore the molecular mechanisms that affect them. Here, we found that ozone treatment on R. dominica adults could decrease life span and increase malondialdehyde (MDA) content, as well as reduce activity of total superoxide dismutase (SOD) and catalase (CAT). Using RNA-seq technology, we identified 641 genes that were differentially expressed between ozone-treated and control R. dominica adults [fold-change of ≥ 2 (q-value < 5%)]. When comparing ozone treatment with control R. dominica adults, 330 genes were significantly upregulated and 311 were downregulated. RT-qPCR confirmed that 11 genes were differentially expressed in ozone-treated and control R. dominica adults. These genes were involved in insect cuticle protein and antioxidant system. This research showed that ozone treatment could reduce the lifespan of R. dominica through antioxidant system. It is an environmentally benign method for the control of stored grain pests and has great development potential.

Physicochemical and Digestible Properties of Parboiled Black Rice With Different Amylose Contents.

The varieties of black rice with different amylose contents (waxy; medium-amylose: 16.03%; high-amylose: 27.14%) were parboiled and then evaluated for physicochemical and digestible properties. The color, crystalline structure, and swelling property of parboiled rice were analyzed, and the water molecular mobility, texture, and starch digestibility of cooked parboiled rice were determined. The color of black rice was only slightly changed after the parboiling treatment. The crystalline structures of waxy and medium-amylose rice were severely damaged by the parboiling treatment, while the highly crystalline structure was retained in parboiled high-amylose rice. During heating in water, parboiled high-amylose rice had a lower water absorption ratio (WAR) and volume expansion ratio (VER) than the other two varieties. After cooking, parboiled high-amylose rice had higher water molecular mobility and harder texture compared with the other two varieties. Cooked parboiled high-amylose rice contained higher content of resistant starch than cooked parboiled waxy and medium-amylose rice.

Colorimetric ELISA based on urease catalysis curcumin as a ratiometric indicator for the sensitive determination of aflatoxin B1 in grain products.

There is an urgent need to measure aflatoxin B1 (AFB1) in food to prevent contaminated food consumption. In this work, a novel colorimetric enzyme-linked immunosorbent assay (ELISA) was developed for the detection of AFB1 using curcumin as a colorimetric indicator. An indirect competitive enzyme-label immunoassay was developed using urease and rabbit anti-mouse immunoglobulin G labeled with gold nanoparticles as the signal-transduction tag. Urease catalyzed the hydrolysis of urea to produce ammonia, which increased the pH of the solution. The phenolic hydroxyl group of curcumin ionized into phenolic oxygen anions under alkaline conditions, which strengthened the synergistic effect of electron supply and absorption in curcumin. As a result, the color of curcumin changed from yellow to reddish-brown, producing a visible color change. Under optimal conditions, AFB1 could be qualitatively determined with the naked eye, and quantitatively assessed by measuring the ratio of absorbance at wavelengths of 550 and 428 nm. The change in the ratio of absorbance Δ550/Δ428 decreased linearly in a range of 0.01-5 ng mL-1, and the limit of detection was 67 pg mL-1. Therefore, the selectivity and reliability of this proposed method were well validated. This method was also successfully used for the quantitation of AFB1 in spiked rice flour and wheat flour samples. This approach may broaden the application field of colorimetric ELISA for aflatoxin, providing a promising platform for the rapid screening of aflatoxin in food.

Structure and Properties of Octenyl Succinic Anhydride-Modified High-Amylose Japonica Rice Starches.

Starches rich in amylose are promising functional ingredients for calory-reduced foods. In this research, a high-amylose Japonica rice starch (amylose content 33.3%) was esterified with octenyl succinic anhydride (OSA) to improve the functional properties. The OSA-modified derivatives were evaluated for structure and functional properties, with OSA-modified normal Japonica rice starch (amylose content 18.8%) used as control. Fourier transform infrared spectra confirmed the introduction of OSA groups to starch. OSA modification made little change to morphology and particle size of high-amylose starch, but decreased the relative crystallinity and pasting temperature and increased the pasting viscosity, swelling power, emulsifying stability, and resistant starch (RS) content. The changes of properties were related to the degree of substitution (DS). Typically, OSA-modified high-amylose starch at DS of 0.0285 shows polyhedral-shape granules, with a volume-average particle diameter of 8.87 µm, peak viscosity of 5730 cp, and RS content of 35.45%. OSA-modified high-amylose starch had greater peak viscosity and RS content and lower swelling power than OSA-modified normal starch of similar DS, but the two kinds of derivatives did not have a significant difference in emulsifying stability. The OSA-modified high-amylose Japonica rice starch could be used as an emulsifier, thickener, and fat replacer in food systems.

Properties of flour from pearled wheat kernels as affected by ozone treatment.

Two different pearling degrees of wheat kernels (lightly-pearled: 14.4% and heavily-pearled: 38.9%) and un-pearled kernels were treated with ozone and evaluated for flour compositions and properties. Ozonation did not change main compositions and damaged starch content of three kernels' flours. Flour brightness of all three kernels was improved after ozone treatment. Ozonation enhanced the dough strength of the flours from un-pearled and pearled kernels and the effect elevated with increasing pearling degree. Ozone treatment increased the peak viscosity of flour and the level of increase in heavily-pearled kernels was greater than un-pearled and lightly-pearled. Ozonation resulted in an increase in the insoluble protein polymer content of heavily-pearled kernels' flour, but only had a slight effect on un-pearled lightly-pearled kernels. After ozone treatment, un-pearled and lightly-pearled kernels exhibited increases in molecular weight of starch, but heavily-pearled resulted in the opposite trend.