Non-spectrophotometric methods for the determination of Vitamin C

Fruit Quality Analysis and Flavor Comprehensive Evaluation of Cherry Tomatoes of Different Colors

Cherry tomatoes are popular vegetables worldwide owing to their variety of colors and nutrients. However, an integrated evaluation of color and flavor has rarely been reported. This study examined the differences among red, brown, yellow, and green cherry tomatoes grown in the Jiuquan area. A comprehensive analysis of the flavor quality of these tomatoes, including sensory evaluation, electronic nose analysis, nutritional and flavor quality measurements, targeted metabolomics, and chemometrics, was conducted. Red tomatoes had the highest lycopene content, and green tomatoes had the highest soluble protein and vitamin C content. In cherry tomatoes, K is the most abundant macro element and Fe and Zn are the most abundant trace elements. Brown cherry tomatoes had significantly higher K, P, Mg, Cu and Fe contents than other colored tomatoes, and red tomatoes had significantly higher Zn content than other cherry tomatoes (218.8-724.3%). Yellow cherry tomatoes had the highest soluble sugar content, followed by red, brown and green tomatoes. A total of 20 amino acids of tomatoes were simultaneously determined by LC-MS. Yellow cherry tomatoes have the highest content of essential amino acids, aromatic amino acids and sweetness amino acids. Red tomatoes have the highest levels of non-essential and sourness amino acid contents. An analysis of 30 flavor indicators revealed that yellow tomatoes had the best flavor, followed by red, brown, and green tomatoes. Our work lays the foundation for future research on color and flavor formation in cherry tomatoes.

Comparative study of the quality indices, antioxidant substances, and mineral elements in different forms of cabbage

BACKGROUND

As the second largest leafy vegetable, cabbage (Brassica oleracea L. var. capitata) is grown globally, and the characteristics of the different varieties, forms, and colors of cabbage may differ. In this study, five analysis methods-variance analysis, correlation analysis, cluster analysis, principal component analysis, and comprehensive ranking-were used to evaluate the quality indices (soluble protein, soluble sugar, and nitrate), antioxidant content (vitamin C, polyphenols, and flavonoids), and mineral (K, Ca, Mg, Cu, Fe, Mn, and Zn) content of 159 varieties of four forms (green spherical, green oblate, purple spherical, and green cow heart) of cabbage.

RESULTS

The results showed that there are significant differences among different forms and varieties of cabbage. Compared to the other three forms, the purple spherical cabbage had the highest flavonoid, K, Mg, Cu, Mn, and Zn content. A scatter plot of the principal component analysis showed that the purple spherical and green cow heart cabbage varieties were distributed to the same quadrant, indicating that their quality indices and mineral contents were highly consistent, while those of the green spherical and oblate varieties were irregularly distributed. Overall, the green spherical cabbage ranked first, followed by the green cow heart, green oblate, and purple spherical varieties.

CONCLUSIONS

Our results provide a theoretical basis for the cultivation and high-quality breeding of cabbage.

Electrochemical determination of ascorbic acid using palladium supported on N-doped graphene quantum dot modified electrode

To precise screening concentration of ascorbic acid (AA), a novel electrochemical sensor was prepared using palladium nanoparticles decorated on nitrogen-doped graphene quantum dot modified glassy carbon electrode (PdNPs@N-GQD/GCE). For this purpose, nitrogen doped GQD nanoparticles (N-GQD) were synthesized from a citric acid condensation reaction in the presence of ethylenediamine and subsequently modified by palladium nanoparticles (PdNPs). The electrochemical behavior of AA was investigated, in which the oxidation peak appeared at 0 V related to the AA oxidation. Considering the synergistic effect of Pd nanoparticles as an active electrocatalyst, and N-GQD as an electron transfer accelerator and electrocatalytic activity improving agent, PdNPs@N-GQD hybrid materials showed excellent activity in the direct oxidation of AA. In the optimal conditions, the voltammetric response was linear in the range from 30 to 700 nM and the detection limit was calculated to be 23 nM. The validity and the efficiency of the proposed sensor were successfully tested and confirmed by measuring AA in real samples of chewing tablets, and fruit juice.

Dual-spot ratiometric microfluidic paper-based analytical device for accuracy and precision improvement

Instrumental and environmental fluctuations are common sources of error in smartphone-based optical detection, significantly affecting the accuracy of analytical measurements. In this regard, spotting the sample and reference simultaneously and in close proximity compensates for the fluctuations. This "dual-spot" design is similar to the double-beam technique used in spectrophotometry, which reduces fluctuations in the results. The underlying hypothesis is that any instrumental and/or environmental factors influencing the color intensity in the detection zones will similarly impact the color intensity in the control zone under the same conditions. To test our design, a ratiometric microfluidic paper-based analytical device (μPAD), functionalized with a mixture of green-emissive carbon dots (CDs) and red-emissive ethidium bromide, was developed for the selective detection of ascorbic acid (AA). The green emission of the CDs is quenched by both AA and Fe3+; NaF was thus loaded onto the 3D connector as a masking agent to remove the interference effect of the Fe3+ ions. The color variations were monitored under a UV lamp, using a smartphone to capture the images, and the RGB intensities were processed using the Color Grab application. The proposed double-spot method greatly enhanced the analytical precision and accuracy of the device. A linear working range from 0 to 125 μM was obtained, and the limit of detection was 2.71 μM. The μPAD was successfully used for the detection of AA in human serum, with recoveries from 87.27 to 98.52 %.

Improvements in the Appearance and Nutritional Quality of Tomato Fruits Resulting from Foliar Spraying with Silicon

Research on silicon (Si), an element considered beneficial for plant growth, has focused on abiotic and biotic stress mitigation. However, the effect of Si on tomato fruit quality under normal growth conditions remains unclear. This study investigated the effects of applying different levels of Si (0 mmol·L-1 [CK], 0.6 mmol·L-1 [T1], 1.2 mmol·L-1 [T2], and 1.8 mmol·L-1 [T3]) in foliar sprays on tomato fruit quality cultivated in substrates, and the most beneficial Si level was found. Compared to CK, exogenous Si treatments had a positive influence on the appearance and nutritional quality of tomato fruits at the mature green, breaker, and red ripening stages. Of these, T2 treatment significantly increased peel firmness and single-fruit weight in tomato fruits. The contents of soluble sugars, soluble solids, soluble proteins, and vitamin C were significantly higher, and the nitrate content was significantly lower in the T2 treatment than in the CK treatment. Cluster analysis showed that T2 produced results that were significantly different from those of the CK, T1, and T3 treatments. During the red ripening stage, the a* values of fruits in the T2 treatment tomato were significantly higher than those in the other three treatments. Moreover, the lycopene and lutein contents of the T2 treatment increased by 12.90% and 17.14%, respectively, compared to CK. T2 treatment significantly upregulated the relative gene expression levels of the phytoene desaturase gene (PDS), the lycopene ε-cyclase gene (LCY-E), and the zeaxanthin cyclooxygenase gene (ZEP) in the carotenoid key genes. The total amino acid content in tomato fruits in the T2 treatment was also significantly higher than that of CK. In summary, foliar spraying of 1.2 mmol·L-1 exogenous Si was effective in improving the appearance and nutritional quality of tomato fruits under normal growth conditions. This study provides new approaches to further elucidate the application of exogenous silicon to improve tomato fruit quality under normal conditions.

Synergistic effects of earthworms and cow manure under reduced chemical fertilization modified microbial community structure to mitigate continuous cropping effects on Chinese flowering cabbage

The substitution of chemical fertilizers with organic fertilizers is a viable strategy to enhance crop yield and soil quality. In this study, the aim was to investigate the changes in soil microorganisms, soil chemical properties, and growth of Chinese flowering cabbage under different fertilization treatments involving earthworms and cow manure. Compared with the control (100% chemical fertilizer), CE (30% reduction in chemical fertilizer + earthworms) and CFE (30% reduction in chemical fertilizer + cow dung + earthworms) treatments at soil pH 8.14 and 8.07, respectively, and CFC (30% reduction in chemical fertilizer + cow manure) and CFE treatments increased soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), and available potassium (AK) contents. Earthworms and cow manure promoted the abundance of Bacillus and reduced that of the pathogens Plectosphaerella and Gibberella. The mantle test revealed that pH was not correlated with the microbial community. Random forest analysis verified that AN, SOM, and TN were important factors that jointly influenced bacterial and fungal diversity. Overall, the synergistic effect of earthworms and cow manure increased soil fertility and microbial diversity, thereby promoting the growth and development of Chinese flowering cabbage. This study enhanced the understanding of how bioregulation affects the growth and soil quality of Chinese flowering cabbage, and thus provided a guidance for the optimization of fertilization strategies to maximize the yield and quality of Chinese flowering cabbage while reducing environmental risks.

A High-Performance Liquid Chromatography with Electrochemical Detection Method Developed for the Sensitive Determination of Ascorbic Acid: Validation, Application, and Comparison with Titration, Spectrophotometric, and High-Performance Liquid Chromatography with Diode-Array Detection Methods

L-ascorbic acid (vitamin C, VC), an essential nutrient obtained from the diet to maintain various vital signs for the human body, is a crucial indicator of food quality and nutritional value. Herein, high-performance liquid chromatography with electrochemical detection (HPLC-ECD) was developed and validated with the advantages of higher sensitivity, simpler operation processes, and more rapid detection in measuring VC levels in honey samples when compared with the common methods (titration, spectrophotometric, and HPLC-DAD methods). The results of the HPLC-ECD methodological validation showed that the limit of detection (LOD) was 0.0043 µg mL-1; the relative standard deviations (RSDs) of the intra- and inter-day values were between 2.51% and 5.15%, and the regression coefficient was >0.999 in the linear range of 0.1 to 20 µg mL-1. The validated HPLC-ECD method was also successfully utilized to evaluate the VC levels in different varieties of honey samples with various storage durations as well as in fruit and biological samples. This study provided a perspective for the further accurate determination of VC content in food and biological samples.

A Comprehensive Evaluation of Tomato Fruit Quality and Identification of Volatile Compounds

Tomatoes (Lycopersicon esculentum) are the most valuable vegetable crop in the world. This study identified the morphological characteristics, vitamin content, etc., from 15 tomato varieties in total, that included five each from the three experimental types, during the commercial ripening period. The results showed that the hardness with peel and the moisture content of tasty tomatoes were 157.81% and 54.50%, and 3.16% and 1.90% lower than those of regular tomatoes and cherry tomatoes, respectively, while the soluble solids were 60.25% and 20.79% higher than those of the latter two types. In addition, the contents of vitamin C, lycopene, fructose, glucose, and total organic acids of tasty tomatoes were higher than those of regular tomatoes and cherry tomatoes. A total of 110 volatile compounds were detected in the 15 tomato varieties. The average volatile compound content of tasty tomatoes was 57.94% higher than that of regular tomatoes and 15.24% higher than that of cherry tomatoes. Twenty of the 34 characteristic tomato aroma components were identified in tasty tomatoes, with fruity and green being the main odor types. Ten characteristic aroma components in regular tomatoes were similar to those of tasty tomatoes; ten types of cherry tomatoes had floral and woody aromas as the main odor types. The flavor sensory score was significantly positively correlated with the content of soluble solids, fructose, glucose, citric acid, fumaric acid, and β-ionone (p < 0.01), and significantly negatively correlated with water content and firmness without peel. Regular, tasty, and cherry tomatoes were separated using principal component analysis, and the quality of tasty tomatoes was found to be better than cherry tomatoes, followed by regular tomatoes. These results provide valuable information for a comprehensive evaluation of fruit quality among tomato varieties to develop consumer guidelines.

Visual detection of vitamin C in fruits and vegetables using UiO-66 loaded Ce-MnO2 mimetic oxidase

A nanocomposite (UiO-66/Ce-MnO₂) was fabricated by combining UiO-66 with cerium-doped manganese dioxide (Ce-MnO₂) for colorimetric detecting vitamin C (Vc). Compared with traditional artificial enzymes, the as-synthesized UiO-66/Ce-MnO₂ were simple to prepare and did not require the participation of other active substances. The doping of cerium increased the oxygen vacancies and the UiO-66 as a carrier improved the dispersibility. The formation of superoxide anion (O₂^-) and the inside Ce⁴⁺/Ce³⁺ and Mn⁴⁺/Mn³⁺ redox couples of UiO-66/Ce-MnO₂ endowed UiO-66/Ce-MnO₂ with a high catalytic capability, which could catalytically oxidize 3, 3', 5, 5'-tetramethylbenzidine (TMB) into oxidation state TMB (oxTMB) without H₂O₂, accompanying with color change and a prominent peak at 652 nm in UV-vis spectra. Based on the inhibitory effects of Vc on catalytic oxidation of TMB, detection of Vc can be achieved, exhibiting a linear relationship in the concentration of 1.13-17.01 μmol L^-1 with a low detection limit of 65.82 nmol L^-1. This system can also be detected by smartphone, the linear detection range is 12.47-22.67 μmol L^-1. Vc contents in fruits and vegetables detected by the sensor were in good agreement with the 2, 4-Dinitrophenylhydrazine colorimetry method (P > 0.05), indicating a reliable sensor for Vc detection.

A New Method for the Determination of Total Content of Vitamin C, Ascorbic and Dehydroascorbic Acid, in Food Products with the Voltammetric Technique with the Use of Tris(2-carboxyethyl)phosphine as a Reducing Reagent

The objective of the study was to develop a new method for the determination of the total content of vitamin C and dehydroascorbic acid in food, based on the technique of differential pulse voltammetry with the use of a boron-doped diamond electrode modified with mercury film. A comparison was made between the results obtained with the developed method and a proposed reference method based on high-performance liquid chromatography with spectrophotometric detection. The reduction of dehydroascorbic acid was performed with the use of tris(2-carboxyethyl)phosphine. The interference caused by the presence of tris(2-carboxyethyl)phosphine during the voltammetric determination of ascorbic acid was effectively eliminated through a reaction with N-ethylmaleimide. The conducted validation of the voltammetric method indicated that correct results of analysis of the total content of vitamin C and ascorbic acid were obtained. Analysis of the content of dehydroascorbic acid was imprecise due to the application of the differential method. The results of the analyses and the determined validation parameters of the developed method are characterised by a high degree of conformance with the results obtained with the chromatographic reference method, which indicates the equivalence of the two methods.

Comprehensive fruit quality assessment and identification of aroma-active compounds in green pepper (Capsicum annuum L.)

The wrinkled pepper (Capsicum annuum L.) is a type of chili pepper domesticated in northwestern China, with a characteristic flavor. Fifteen wrinkled and four smooth-skinned pepper varieties were evaluated for morphology, texture, color, nutrients, capsaicinoids, and volatile compounds at the mature fruit stage. The sensory evaluation showed wrinkled pepper was superior to smooth pepper in texture, and it has a highly significant correlation (p < 0.01) with cuticle thickness, maximum penetrating force, lignin content, and moisture content. Citric acid was the major organic acid in peppers, accounting for 39.10-63.55% of the total organic acids, followed by quininic acid. The average oxalic acid content of smooth peppers was 26.19% higher than that of wrinkled peppers. The pungency of wrinkled pepper fruits ranged from 1748.9 to 25529.4 SHU, which can be considered slightly to very spicy, while the four smooth varieties ranged between 866.63 and 8533.70 SHU, at slightly to moderately spicy. A total of 199 volatile compounds were detected in the 19 pepper varieties. The average volatile content of wrinkled pepper was 39.79% higher than that of smooth pepper. Twenty-nine volatile compounds, including 14 aldehydes, four alcohols, three esters, three ketones, two furans, one pyrazine, one acid, and one phenol, contributed to the fragrance of peppers and could be regarded as aroma-active compounds, with 2-isobutyl-3-methoxypyrazine being the major contributor among the 19 pepper varieties. Wrinkled pepper can be confidently distinguished from smooth pepper and is of superior quality. The current findings outlined the major texture-related characteristics of pepper as well as the main aroma-active compounds, providing valuable information for pepper quality breeding and consumer guidelines.

Moderate Salinity of Nutrient Solution Improved the Nutritional Quality and Flavor of Hydroponic Chinese Chives (Allium tuberosum Rottler)

Sodium chloride (NaCl), as a eustressor, can trigger relevant pathways to cause plants to produce a series of metabolites, thus improving the quality of crops to a certain extent. However, there are few reports on the improvement of nutrient quality and flavor of hydroponic Chinese chives (Allium tuberosum Rottler) by sodium chloride. In this study, five NaCl concentrations were used to investigate the dose-dependent effects on growth, nutritional quality and flavor in Chinese chives. The results show that 10 mM NaCl had no significant effect on the growth of Chinese chives, but significantly decreased the nitrate content by 40% compared with 0 mM NaCl treatment, and the content of soluble protein and vitamin C was increased by 3.6% and 2.1%, respectively. In addition, a total of 75 volatile compounds were identified among five treatments using headspace solid-phase microextraction gas chromatography/mass spectrometry (HS-SPME/GC-MS). Compared with the 0 mM NaCl treatment, 10 mM NaCl had the greatest effect on the quantity and content of volatile compounds, with the total content increased by 27.8%. Furthermore, according to the odor activity values (OAVs) and odor description, there were 14 major aroma-active compounds (OAVs > 1) in Chinese chives. The “garlic and onion” odor was the strongest among the eight categories of aromas, and its highest value was observed in the 10 mM NaCl treatment (OAVs = 794).Taken together, adding 10 mM NaCl to the nutrient solution could improve the nutritional quality and flavor of Chinese chives without affecting their normal growth.

A facile fluorescence platform for chromium and ascorbic acid detection based on "on-off-on" strategy

In this paper, a facile and rapid fluorescence "on-off-on" strategy for the detection of chromium (Cr(VI)) and ascorbic acid (AA) was developed, which was based on the water-soluble carbon dots (CDs). The CDs was synthesized by a microwave-assisted treatment of L-tartaric acid, citric acid, and urea. The CDs have many advantages, such as high fluorescence quantum yield (20.5%) and good fluorescence stability. Based on inner filter effect (IFE) and static quenching, the fluorescence of the CDs can be quenched by Cr(VI) quickly; while the reduction of IFE and reducing action can make the fluorescence of the CDs recover by AA efficiently. Moreover, under the optimal experimental conditions, the CDs had a good detection performance for Cr(VI) in the range of 0.8 ∼ 189 µM with the limit of detection (LOD) of 0.16 µM. The linear detection for AA was ranged from 0.43 to 25.7 µM with a LOD of 0.1 µM. More importantly, the as-constructed fluorescence detecting platform was successfully applied for Cr(VI) and AA detection in the environmental samples and fruit samples, respectively. In addition, the application potential of the CDs in fluorescent films and anti-counterfeiting materials was further discussed in detail. This work will provide a novel idea for designing a portable sensor based on the CDs to quickly and sensitively detect Cr(VI) and AA.

A Comprehensive Evaluation of Effects on Water-Level Deficits on Tomato Polyphenol Composition, Nutritional Quality and Antioxidant Capacity

Tomatoes have high nutritional value and abundant bioactive compounds. Moderate water deficit irrigation alters metabolic levels of fruits, improving composition and quality. We investigated the effects of water deficit (T1, T2, T3, and T4) treatments and adequate irrigation (CK) on tomato polyphenol composition, antioxidant capacity, and nutritional quality. Compared with CK, the total flavonoid content increased by 33.66% and 44.73% in T1 and T2, and total phenols increased by 57.64%, 72.22%, and 55.78% in T1, T2, and T3, respectively. The T2 treatment significantly enhanced antioxidant’ capacities (ABTS, HSRA, FRAP, and DPPH). There were multiple groups of significant or extremely significant positive correlations between polyphenol components and antioxidant activity. For polyphenols and antioxidant capacity, the classification models divided the treatments: CK and T4 and T1−T3. The contents of soluble solids, soluble protein, vitamin C, and soluble sugar of the treatment groups were higher than those of CK. The soluble sugar positively correlated with sugar−acid ratios. In the PCA-based model, T3 in the first quadrant indicated the best treatment in terms of nutritional quality. Overall, comprehensive rankings using principal component analysis (PCA) revealed T2 > T1 > T3 > T4 > CK. Therefore, the T2 treatment is a suitable for improving quality and antioxidant capacity. This study provides novel insights into improving water-use efficiency and quality in the context of water scarcity worldwide.

Combined Straw and Plastic Film Mulching Can Increase the Yield and Quality of Open Field Loose-Curd Cauliflower

To evaluate the impact of straw mulching on the production of open field loose-curd cauliflower, this study analyzed the “Feicui No.9” cauliflower variety, grown in field trials in Northwest China, in 2019 and 2020. Plots in an open field were prepared without mulch (CK1) and with plastic film mulch (CK2), as experimental controls, along with three experimental mulching methods, including dual straw and plastic film mulch (T1), inter-row straw mulch (T2), and full straw mulch (T3). The effects of the different ground cover alternatives on loose-curd cauliflower's dry matter accumulation, yield, quality, and volatile compounds, were explored. The results showed that, compared with CK2 treatment, T1 treatment promoted the accumulation of dry matter, and increased the economic and biological yield, by 12.98 and 6.51%, respectively. The soluble sugar and vitamin C content in loose-curd cauliflower heads, subjected to T1 treatment, increased by 18.46 and 8.12%, respectively, and the nitrate content decreased by 25.57%. Moreover, the T1, T2, and T3 treatments significantly increased the levels of macro-, meso-, and microelements. Headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to determine the volatile substances in loose-curd cauliflower heads from the 2020 harvesting period. Detected compounds included 17 aldehydes, 15 ketones, 10 alcohols, 15 esters, 29 hydrocarbons, 12 nitrogen-containing compounds, and 17 other substances. T1, T2, and T3 treatments increased the volatile substance content, whereas T1 treatment increased the quantity of volatile substances. In summary, dual mulching with straw and plastic film could promote dry matter accumulation, significantly increase the yield and quality, and effectively improve the flavor of loose-curd cauliflower. This mulching technique can be applied to open field vegetable and corn production areas, providing technical and theoretical support for the realization of high-yield, high-quality production models and a new straw recycling method.

Non-destructive assessment of vitamin C in foods: a review of the main findings and limitations of vibrational spectroscopic techniques

The constant increase in the demand for safe and high-quality food has generated the need to develop efficient methods to evaluate food composition, vitamin C being one of the main quality indicators. However, its heterogeneity and susceptibility to degradation makes the analysis of vitamin C difficult by conventional techniques, but as a result of technological advances, vibrational spectroscopy techniques have been developed that are more efficient, economical, fast, and non-destructive. This review focuses on main findings on the evaluation of vitamin C in foods by using vibrational spectroscopic techniques. First, the fundamentals of ultraviolet–visible, infrared and Raman spectroscopy are detailed. Also, chemometric methods, whose use is essential for a correct processing and evaluation of the spectral information, are described. The use and importance of vibrational spectroscopy in the evaluation of vitamin C through qualitative characterization and quantitative analysis is reported. Finally, some limitations of the techniques and potential solutions are described, as well as future trends related to the utilization of vibrational spectroscopic techniques.

Reduced Chemical Fertilizer Combined With Bio-Organic Fertilizer Affects the Soil Microbial Community and Yield and Quality of Lettuce

Reducing chemical fertilizers in combination with bio-organic fertilizers can limit the use of chemical fertilizers while maintaining soil fertility. However, the effects of combined fertilization on soil chemical properties, microbial community structure, and crop yield and quality are unknown. Using high-throughput sequencing, we conducted field experiments using lettuce plants subjected to five fertilization treatments: chemical fertilizer with conventional fertilization rate (CK), chemical fertilizer reduction by 30% + 6,000 kg ha–1 bio-organic fertilizer (T1), chemical fertilizer reduction by 30% + 9,000 kg ha–1 bio-organic fertilizer (T2), chemical fertilizer reduction by 40% + 6,000 kg ha–1 bio-organic fertilizer (T3), and chemical fertilizer reduction by 40% + 9,000 kg ha–1 bio-organic fertilizer (T4). Compared with CK, the T1–T4 had significantly higher soil pH and soil organic matter (SOM) and showed increased richness and diversity of the bacterial community, and decreased richness and diversity of the fungal community. Principal coordinate analysis evidenced that the bacterial and fungal communities of CK and T1–T4 were distinctly separated. The Kruskal-Wallis H-test demonstrated that the fungal community was more sensitive than the bacterial community to chemical fertilizer reduction combined with bio-organic fertilizer. Among the soil chemical parameters measured, only TN (total nitrogen) was significantly correlated with bacterial and fungal community composition. The T1 and T2 increased lettuce yield. Moreover, T1–T4 characterized reduced nitrate content and increased levels of soluble sugars and vitamin C in lettuce. Overall, the combined application of reduced chemical fertilizer and bio-organic fertilizer effectively improved soil fertility, microbial community structure, and lettuce yield and quality. These findings have valuable implications for vegetable safety and long-term environmental sustainability.

Storage Stability of Nutritional Qualities, Enzyme Activities, and Volatile Compounds of "Hangjiao No. 2" Chili Pepper Treated With Different Concentrations of 1-Methyl Cyclopropene

This study aimed to determine the effects of different concentrations of 1-methyl cyclopropene (1-MCP) on the nutritional quality, antioxidant enzyme activities, and volatile compounds of "Hangjiao No.2" chili pepper during 12 days of storage at ambient temperature. The chili fruit were randomly selected and divided into four groups corresponding to the four treatments, thus, 0.5, 1.0, and 1.5 μl L^-1 1-MCP and a control. The analysis of the nutritional value, enzyme activities, and volatile compounds were determined at 3 days interval. The results showed that the malondialdehyde (MDA) content was lower in the fruit treated with 1-MCP compared to the control. The treatment with 1.5 μl L^-1 and the control showed the lowest superoxide dismutase (SOD) activity compared to the other treatments. Peroxidase (POD) and Catalase (CAT) were highest in the fruit treated with 0.5 μl L^-1 compared to the control and treatment with 1.0 μl L^-1. The 1.5 μl L^-1 treatment delayed the decline in vitamin C and protein content compared to the control. Nitrate levels increased 1.34-fold at 0.5 μl L^-1 and 2.01-fold in the control. Chlorophyll content degradation was delayed at 1.0 μl L^-1 compared to the control. A total of 88 volatile compounds, including terpenes, aldehydes, alkanes, esters, alcohols, acids, phenolic derivatives, ketones, and other aromatic compounds, were detected in "Hangjiao No.2" pepper during the 12-day storage period and treatment concentrations. The production of volatile terpenes was higher in the control than in the 1-MCP treatments, while the 0.5 μl L^-1 1-MCP treatment generally suppressed the production of volatile compounds during storage. Overall, the production of volatile compounds after treatment was higher in the "Hangjiao No.2" chili fruit treated with 1.0 μl L^-1 1-MCP than in the other treatments throughout the storage period. The results indicate that 1-MCP treatment was more effective in maintaining fruit quality, enhancing the activities of SOD, POD, and CAT, retarding the accumulation of MDA and restoring volatile aromas, with 1.0 μl L^-1 having the best preservative effect on "Hangjiao No.2" chili fruit during storage, which could be useful for future marketing and processing.

Gamma radiation crosslinking of PVA/myrrh resin thin film for improving the post-harvest time of lemon fruits

Preparation of a thin film of polyvinyl alcohol (PVA)/myrrh natural resin using a low gamma irradiation dose (1 kGy) was investigated towards increasing the post-harvest time of lemon fruit. Different analytical techniques, such as Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and mapping techniques were used to characterize the prepared thin film. This investigation was carried out to evaluate the effect of different concentrations of myrrh as an edible coating in prolonging shelf life and preserving the quality of lemon fruits (Citrus aurantifolia). Lemons were immersed directly in PVA solution containing 1%, 2%, and 3% concentrations of myrrh and then stored at ambient (25 ± 1 °C) and low (4 ± 1 °C) temperatures. The disease severity, acidity, total soluble solids (TSS), and ascorbic acid contents were tested after the coating with the PVA/myrrh thin film at different temperatures (4 °C and 25 °C) for different storage times (7 and 14 days). The application of different concentrations of the synthesized PVA/myrrh thin film (1%, 2%, and 3%) significantly reduced green mold disease symptoms and disease severity in the lemon fruits. The acidity value (pH value) was the lowest for the 2% myrrh treatment after 7 °C days at 25 °C, followed by the 1% myrrh treatment under the same conditions. The highest TSS was observed after the treatment for 7 days at 25 °C, with a value of 8.1 g dL-1. A high ascorbic acid concentration (33.5 mg dL-1) was noted after coating the lemons with the 1% PVA/myrrh thin film for 7 days at 25 °C. The results show that the application of a PVA/myrrh thin film extends the shelf-life and maintains the quality of lemon fruits by decreasing the levels of evaporation from the fruits and loss of weight due to the delay of the complete ripening stage of the lemon fruits.

Effects of Preharvest Methyl Jasmonate and Salicylic Acid Treatments on Growth, Quality, Volatile Components, and Antioxidant Systems of Chinese Chives

Methyl jasmonate (MeJA) and salicylic acid (SA) regulate the production of biologically active compounds in plants and stimulate the accumulation of plant aromatic substances. However, the underlying mechanisms of how MeJA and SA influence characteristic flavor compounds and the antioxidant activity of vegetables are poorly understood. Five MeJA and SA concentrations were used to investigate the dose-dependent effects of these phytohormones on the dry and fresh weight; chlorophyll abundance; the contents of vitamin C, soluble protein, and sugar, nitrate, total phenols, flavonoids, volatile components, and enzymatically produced pyruvic acid; and antioxidant activity in Chinese chive. We found that MeJA and SA at concentrations of 500 and 150 μM, respectively, significantly increased the levels of total chlorophyll, phenols and flavonoids, vitamin C, and volatile components and significantly reduced the accumulation of nitrate. In addition, compared with the control, 500 μM of MeJA significantly increased the soluble sugar and protein content, and 150 μM SA significantly increased the dry and fresh weight of Chinese chive. Furthermore, these concentrations of MeJA and SA significantly increased the enzymatic pyruvate content and the amount of sulfide and aromatic volatile compounds and improved the characteristic flavor compounds. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity, Trolox-equivalent antioxidant capacity, and ferric-reducing antioxidant capacity were significantly improved after a preharvest treatment with 500 μM MeJA and 150 μM SA, which could improve the antioxidant activity, thus improving the postharvest quality and preservation characteristics of Chinese chives. Taken together, a preharvest treatment with 500 μM MeJA and 150 μM SA is optimal to improve the growth, quality, antioxidant activity, and flavor of Chinese chive, thereby enhancing its commercial value.

Influence of soil amendment of different concentrations of amino acid water-soluble fertilizer on physiological characteristics, yield and quality of "Hangjiao No.2" Chili Pepper

Amino acids are well known as natural stimulators of plant growth and are widely used to promote crop yield and quality. Several studies have been conducted to investigate the effects of amino acid (s) as a foliar spray on a variety of plant species. However, the effects of soil amendment of different concentrations of amino acid water-soluble fertilizer on the physiological characteristics, yield, and quality of pepper remain unclear. Following this, three experimental sets of amino acid water-soluble fertilizer in the ratio 1.8: 2.7: 3.6 kg including control (CK) were conducted in Lintao county, Gansu province. The treatments were applied through furrow method at 6 weeks after planting. The results showed that physiological characteristics of the pepper plants, such as chlorophyll a (1.35 mg g⁻¹), and b (0.67 mg g⁻¹), total chlorophyll (2.02 mg g⁻¹), carotenoid (0.63 mg g⁻¹), ETR (26.25 µmol m⁻²s⁻¹), Fv/Fm (0.75), Qp (0.92) contents of the leaves were increased by the 1.8 kg treatment while NPQ (71.37%) and root activity (2185.52 µg g⁻¹ h⁻¹) were improved by the 3.6 kg treatment compared to the control. Fertilization with 2.7 kg of amino acid water-soluble fertilizer also had a significant influence on fruit length (25.50 cm), and yield of pepper (37.92 t ha⁻¹) while fruit diameter (24.51 mm), firmness (5.30 kg cm⁻²), fresh (48.10 g) and dry (4.71 g) weights were higher in the 1.8 kg treatment compared to the control. The lowest rate of fertilizer (1.8 kg) applied again resulted in a significant increase in soluble protein (79.79%), capsaicin (5.80 mg g⁻¹), dihydrocapsaicin (1.08 mg g⁻¹), vitamin C (72.33%) and the essential and non-essential amino acid contents of the pepper which ranged from (235.15 to 11.16 µg g⁻¹) and (1,605.10 to 16.63 µg g⁻¹) respectively, while soluble sugar (9.02%) was enhanced by 3.6 kg treatment compared to the control. The findings suggest that soil amendment with low concentration of amino acid water-soluble fertilizer (1.8 kg) could be successfully used to improve the physiological characteristics and fruit quality of peppers in vegetable production.

Application of a New Dehydroascorbic Acid Reducing Agent in the Analysis of Vitamin C Content in Food

The analysis of total vitamin C content in food is most frequently performed by reducing dehydroascorbic acid to ascorbic acid, which is then assayed with the technique of high-performance liquid chromatography combined with spectrophotometric detection. Tris(2-carboxyethyl)phosphine is currently the only agent in use that efficiently reduces dehydroascorbic acid at pH < 2. Therefore, there is a continued need to search for new reducing agents that will display a high reactivity and stability in acidic solutions. The objective of the study was to verify the applicability of unithiol and tris(hydroxypropyl)phosphine for a reducing dehydroascorbic acid in an extraction medium with pH < 2. The conducted validation of the newly developed method of determining the total content of vitamin C using tris(hydroxypropyl)phosphine indicates its applicability for food analysis. The method allows obtaining equivalent results compared to the method based on the use of tris(2-carboxyethyl)phosphine. The low efficiency of dehydroascorbic acid reduction with the use of unithiol does not allow its application as a new reducing agent in vitamin C analysis.

Effects of foliar spray of agricultural grade mineral oil in springtime, in combination with potassium and calcium sulfates on the phenological and biophysical indices of clusters, and foliar nutritional levels in grapevine (Vitis vinifera L.) cv. Sultana (Id. Thompson seedless, Sultanina)

Background

Improving the nutritional condition of grapevine in spring to regulate bloom, fruit set, and yield is among the management goals of vineyards.

Methods

In the present study, the early season spray of calcium sulfate (C; 0.00 and 2.00%), potassium sulfate (K; 0.00 and 3.00%), and agricultural grade mineral oil (V; 0.00 and 1.00%) on flower and fruit phenology, nutrient concentration, and cluster biophysical indices and yield of Sultana grapevine (Vitis vinifera L.) were investigated for two consecutive years.

Results

Based on the results, the spray of this nutrient combined with mineral oil significantly affected all the treatments except cluster length, berry length, and phosphorus concentration. The highest concentrations of potassium, calcium, and magnesium were obtained in the vines treated with V₀K₁C₁, and the highest concentrations of zinc and iron were obtained only in the vines treated with mineral oil. In treatments containing mineral oil, especially in combination with the second level of calcium and potassium (V₁K₁C₁), bloom time, berries pea-sized time, and harvest time were delayed by 3, 3, and 6 days compared with control vines. While in vines treated with a combination of the second level of potassium and calcium (V₀K₁C₁), bloom time, berries pea-sized time, and harvest time were advanced by 5, 4, and 1.50 days, respectively, compared with control vines. Regarding the biophysical indices of the cluster, it was found that the vines treated with V₁K₁C₁ had higher cluster weight, berry weight, fruit, and raisins yield than other treatments. Also, the highest berry quality, including total soluble solids, titratable acidity, and total phenol content, were obtained in the vines treated with V₀K₁C₁. However, the lowest berry quality was observed in the vines treated with mineral oil.

Conclusions

Therefore, the combination of nutrients with mineral oil can alleviate the adverse effect of mineral oil solely on some phenological indices and berry quality-related traits in vineyards.

Total Vitamin C, Ascorbic Acid, Dehydroascorbic Acid, Antioxidant Properties, and Iron Content of Underutilized and Commonly Consumed Fruits in Sri Lanka

Sri Lanka is rich in a wide diversity of fruits, but many are underutilized by the people in Sri Lanka despite their nutritional value. This is mainly due to little awareness of the palatability of many fruits and hence low popularity in the market. The present study aimed at providing comparative data on the main biochemical and nutritional parameters of thirty-seven (37) species of fruits grown in Sri Lanka, including 22 underutilized fruits and 15 commonly consumed fruits. The main parameters of the comparison were the contents of ascorbic acid (AA), total vitamin C (TVC), total phenolic content (TPC), total flavonoid content (TFC), total iron (Fe), and antioxidant capacities (ACs). The mean AA, TVC, TPC, TFC, and Fe contents in 100 g of fresh edible portions of fruits ranged from 2.0 to 185.0 mg, 8.1 to 529.6 mg, 12.9 to 2701.7 mg gallic acid equivalent, 0.2 to 117.5 mg quercetin equivalents, and 0.1 to 1.1 mg, respectively. The IC₅₀ values in a DPPH assay varied between 0.8 to 1856.7 mg/mL and FRAP values in a FRAP assay ranged from 4.2 to 2070 μmol FeSO₄/g in the studied fruits. Fruits were ranked based on the levels of the abovementioned biochemical properties. Using this ranking, 12 of the top 15 fruits were underutilized. Phyllanthus emblica (Indian gooseberry) is at the top of these underutilized fruits, and Psidium guajava (guava) is the best among commonly consumed fruits. These results indicate that underutilized fruits in Sri Lanka can be recommended as high quality and low-cost alternatives for securing nutritional requirements. Hence, underutilized fruits can be promoted as healthy additional fruits in Sri Lanka.

Direct analysis of ascorbic acid in food beverage samples by flow injection analysis using reduced graphene oxide sensor

In this paper, a simple, sensitive and precise electroanalytical method was developed using flow injection analysis (FIA) with amperometric detection and reduced graphene oxide sensor for ascorbic acid determination in samples of multivitamin beverages, milk, fermented milk, and milk chocolate. The advantages of this sensor include a potential displacement of 450 mV and a 2-fold peak current increase for electrochemical oxidation of ascorbic acid, which resulted in a highly sensitive method. No interference of sample matrix was observed, avoiding solvent extraction procedures (samples were only diluted). The FIA allowed a high analytical frequency, approximately 96 injections per hour, together with adequate detection limit of 4.7 μmol L^-1. Good precision (RSD < 7%) and accuracy (recoveries between 91 and 108%) evidenced the robustness of the method. The method was compared with ultra-fast liquid chromatography (UFLC) obtaining statistically similar results (95% confidence level). The ascorbic acid content in samples varied from 0.065 to 2.53 mmol L^-1.

Appropriate Ammonium-Nitrate Ratio Improves Nutrient Accumulation and Fruit Quality in Pepper (Capsicum annuum L.)

Ammonium (NH4+) and nitrate (NO3−) are the two forms of inorganic nitrogen essential for physiological and biochemical processes in higher plants, but little is known about how the NH4+:NO3− ratio may affect nitrogen metabolism. This study determined the effect of NH4+:NO3− ratios on plant growth, accumulation, and distribution of nutrient elements, fruit quality, enzyme activity, and relative expression of genes involved in nitrogen (N) metabolism in pepper (Capsicum annuum L.). In a pod experiment, the NH4+:NO3− ratios of 0:100, 12.5:87.5, 25:75, 37.5:62.5, and 50:50 were arranged in a complete randomized design with three replicates. The application of NH4+:NO3− at 25:75 resulted in highest dry matter and N, phosphorus (P), and potassium (K) accumulation. Pepper treated with 25:75 ratio increased root length, surface areas, and root volume and tips. The contents of vitamin C, soluble sugar, soluble protein, total phenols, flavonoids, and capsaicinoids in the fruits were significantly higher with the NH4+:NO3− ratio of 25:75 compared with 0:100 treatment, while lowering nitrate content was found in NH4+:NO3− ratios of 25:75, 37.5:62.5, and 50:50 treatments. Activity of glutamine synthetase (GS), glutamate synthases (GOGAT) enzyme and the levels of relative expression of genes coding these enzymes were superior when the NH4+:NO3− ratio of 25:75 were applied. Therefore, an appropriate ratio of NH4+:NO3− (25:75) in nitrogen application can stimulate root development, promote enzyme activities, and enhance the productivity and fruit quality in pepper.

Organosilane-functionalized carbon quantum dots and their applications to "on-off-on" fluorometric determination of chromate and ascorbic acid, and in white light-emitting devices

Organosilane-functionalized carbon quantum dots (Si-CQDs) were synthesized by reacting glucosamine and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane in acetone. The surface morphology, crystal structure, functional groups, elemental composition, and optical properties of the Si-CQDs were characterized using TEM (HRTEM), XRD, FT-IR, XPS, UV-vis absorption and fluorescence spectroscopy. They show that N-containing groups including C=N and C-N, and Si-containing groups including Si-O-C and Si-O-Si have been formed on the surface of Si-CQDs. The element doping and surface functionalization of Si-CQDs endow their novel chemical, physical and optical properties. The Si-CQDs dispersed in acetone are almost monodisperse with an average particle diameter of 3.6 nm. The Si-CQDs dispersed in acetone display blue fluorescence (excitation/emission maxima of 380/460 nm). In contrast, the solid-state Si-CQDs exhibited yellow fluorescence (with excitation/emission maxima of 470/595 nm). The fluorescence emission spectra of acetone-suspended Si-CQDs are concentration-dependent, and the emission peak becomes red-shifted as the concentration is increased. The Si-CQDs are sensitive and selective fluorescent "on off on" nanoprobes for chromate [Cr(VI)] and ascorbic acid (AA). Fluorescence is quenched by Cr(VI) via an inner filter effect from the absorption of Si-CQDs excitation at 380 nm by Cr(VI). Upon addition of AA, fluorescence is restored because of reduction of Cr(VI) by AA. Under optimal conditions (excitation/emission wavelength of 380/460 nm), the response is linear in the 0.4-160 μM Cr(VI) concentration range, and the detection limit is 34 nM. The respective data for AA are 1-80 μM and 84.6 nM. The practical use of the nanoprobe for Cr(VI) determination in real river water samples is also demonstrated successfully. Their concentration-dependent fluorescence, good thermal stability and self-crosslinking behavior also make the Si-CQDs a candidate material for white light-emitting diodes that displays color conversion and can act as an encapsulation layer in a blue light-emitting diode (LED) chip. Graphical abstract One-pot solvothermal synthesis of organosilane-functionalized carbon quantum dots (Si-CQDs) with blue fluorescence in solution, yellow fluorescence in solid state and concentration-dependent fluorescence property, and their applications for chromate (Cr(VI)) and ascorbic acid dual determinations and white light-emitting device. Graphical Abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have changed the poor quality graphical abstract into the jpg and pdf.

Nitrogen-doped fluorescent graphene nanosheets as visible-light-driven photocatalysts for dye degradation and selective sensing of ascorbic acid

Facile synthesis of water soluble fluorescent N-doped graphene nanosheets for multifunctional applications in photocatalysis and sensing.

A flower-structured MoS2-decorated f-MWCNTs/ZnO hybrid nanocomposite-modified sensor for the selective electrochemical detection of vitamin C

We synthesized an MoS₂/f-MWCNTs/ZnO composite and successfully used it to prepare an electrochemical sensor for the selective detection of AA in blood serum samples.

N,S co-doped carbon dots based fluorescent "on-off-on" sensor for determination of ascorbic acid in common fruits

A switchable sensor based on N and S co-doped carbon dots (N,S-CDs) was developed to determine ascorbic acid (AA) content in common fruits via fluorescence quenching of N,S-CDs by Fe³⁺ (off) and recovery by AA (on). TEM showed that the particle size was 2.35-7.95 nm with an average diameter of 5.12 nm. XPS and FTIR confirmed the presence of -OH, -COOH and -NH₂ on N,S-CDs surface. UV-vis and FTIR revealed that the coordination of -COOH and -NH₂ on N,S-CDs surface with Fe³⁺ accounted for FL quenching, and the release of -NH₂ from coordination complexes due to the reduction of Fe³⁺ by AA led to partly FL recovery. The sensor allowed detecting AA in the linear range of 10-200 μmol/L with a LOD of 4.69 μmol/L. AA contents in common fruits detected by the sensor were in good agreement with the reference method (P > 0.05), indicating a practical fluorescent sensor for AA detection in common fruits.

An "on-off-on" fluorescent nanoprobe for recognition of chromium(VI) and ascorbic acid based on phosphorus/nitrogen dual-doped carbon quantum dot

Chromium (VI) [Cr(VI)] is a harsh environmental contaminates and has been proved to be highly toxic, carcinogenic and mutagenic. Therefore, developing an inexpensive, good selective and highly sensitive nanoprobe for the detection of Cr(VI) is in urgent demand. Recently, the highly fluorescent carbon quantum dots (CQDs) have been successfully utilized as efficient fluorescent nanoprobes for the detection of ions, pH and molecular substances. In this work, an "on-off" fluorescence phosphorus/nitrogen dual-doped CQDs (PNCQDs) probe was developed for the determination of Cr(VI) based on inner filter effect (IFE). The proposed PNCQDs nanoprobe shows its distinct merits of simplicity, convenience, fast implementation, good selectivity and high sensitivity towards Cr(VI), allowing its potential application in the determination of Cr(VI) in environment and biosystem. In addition, the chelation effect of the functional groups in reductant and Cr(VI), and the easy-conversion of Cr(VI) to reduced states (i.e. Cr(III) and Cr(0)) by reductants makes the minimization of IFE with a concomitant recovery of PNCQDs fluorescence possible. Hence, the PNCQDs/Cr(VI) hybrid was used as an "off-on" fluorescence probe for sensing ascorbic acid (AA), which is a model reductant. For the detection of Cr(VI), the linear range and the limit of detection achieved were 1.5-30 μmol/L and 23 nmol/L, respectively. For the detection of AA, the linear range and the limit of detection obtained were 5.0-200 μmol/L and 1.35 μmol/L, respectively. The as-constructed "on-off-on" PNCQDs fluorescent nanoprobe was successfully applied for detecting Cr(VI) and AA in biosystem. Furthermore, the as-constructed fluorescent sensing system was successfully applied to the analyses of AA in fresh fruits and in commercial fruit juices with satisfactory results.

A New Indirect Spectrofluorimetric Method for Determination of Ascorbic Acid with 2,4,6-Tripyridyl-S-Triazine in Pharmaceutical Samples

Ascorbic acid (AA) is a water-soluble vitamin which shows no fluorescence. However, in reaction with iron(III), AA is oxidised to dehydroascorbic acid and iron(III) is reduced to iron(II) which forms a complex with 2,4,6-tripyridyl-S-triazine (TPTZ) in buffered medium. The relative fluorescence intensity of the resulting Fe(TPTZ)₂²⁺ complex can be measured at excitation and emission wavelengths of 393 and 790 nm, respectively. Based on this data, a new indirect spectrofluorimetric method for the determination of AA in pharmaceutical samples was proposed. Influence of the reaction conditions, such as acidity of acetic buffer, concentration of TPTZ and iron(III), reaction time and instrumental parameters were investigated in detail. The linear range was from 5.4 × 10⁻⁴ to 5.4 × 10⁻⁶ mol·L⁻¹ (R = 0.9971). The LOD was 7.7 × 10⁻⁷ mol·L⁻¹ and LOQ was 2.3 × 10⁻⁴ mol·L⁻¹. Fourteen pharmaceutical samples containing various amounts of AA were analysed. Influences of potential interfering substances were also examined. Analysis of commercial pharmaceutical formulations showed good correlation with the nominal values given by the manufacturers and with the results obtained by a titration method. The proposed method can be applied in routine quality control in the pharmaceutical industry due to its sensitivity, simplicity, selectivity and low cost.

"Switch-On" Fluorescent Sensing of Ascorbic Acid in Food Samples Based on Carbon Quantum Dots-MnO2 Probe

This work describes a "switch-on" fluorescence approach for sensing of ascorbic acid (AA) in food samples. In the present method, the fluorescence intensity (FL) of carbon quantum dots (CQDs) was first quenched by addition of MnO2 nanosheets through an inner filter effect to form a CQDs-MnO2 probe. When reductive AA was introduced into the quenched CQDs solution, the added MnO2 was destroyed due to the redox reaction between AA and MnO2 nanosheets, and the FL of the system was recovered. Under the optimal conditions, the limit of detection for AA was 42 nM, with a wide concentration linear range of 0.18-90 μM. Furthermore, the as-fabricated fluorescent sensing system was successfully applied to the analysis of AA in fresh fruits, vegetables, and commercial fruit juices samples with satisfactory results.