Impact of harvest season on bioactive compounds, amino acids and in vitro antioxidant capacity of white tea through multivariate statistical analysis

The effect of maturity of tea leaves and processing methods on the formation of milky flavor in white tea - A metabolomic study

Targeted metabolomics combined with chemometrics were applied to investigate the flavor profiles of 4 white tea samples, which were produced from different maturity fresh tea leaves with different withering methods. Mature leaves that underwent novel withering process at higher temperature (28-30℃) and humidity (75 ± 3 %) (MN) were characterized by intense milky flavor. The content of free amino acids, catechins, and soluble sugars in MN were significantly lower than that in the other 3 tea samples, resulting in a sweet and mellow taste with low bitterness. Meanwhile, MN possessed the highest intensity of milky aroma, which could be mainly attributed to the existence of dihydro-5-pentyl-2(3H)-furanone and 2-pentyl-furan as the key volatile substances with coconut and creamy fragrance. These findings provide insight into the substance foundations of milky flavor, and identified leaf maturity and processing method as the determining factors of the milk-flavored white tea (MFWT).

The Effects of Nitrogen Fertilizer on the Aroma of Fresh Tea Leaves from Camellia sinensis cv. Jin Xuan in Summer and Autumn

Nitrogen fertilization level and harvesting season significantly impact tea aroma quality. In this study, we analyzed the volatile organic compounds of fresh Jin Xuan (JX) tea leaves under different nitrogen application levels (N0, N150, N300, N450) during summer and autumn. A total of 49 volatile components were identified by gas chromatography-mass spectrometry (GC-MS). Notably, (E)-2-hexenal, linalool, and geraniol were the main contributors to the aroma of fresh JX leaves. The no-nitrogen treatment (N0) presented the greatest quantity and variety of volatiles in both seasons. A greater difference in volatile compounds was observed between nitrogen treatments in summer vs. autumn. The N0 treatment had a greater total volatile concentration in summer, while the opposite was observed in the nitrogen application treatments (N150, N300, N450). Summer treatments appeared best suited to black tea production. The concentration of herbaceous aroma-type volatiles was higher in summer, while the concentration of floral volatiles was higher in autumn. Volatile concentrations were highest in the N0 and N450 treatments in autumn and appeared suitable for making black tea and oolong tea. Overall, this research provides valuable insights into how variations in N application rates across different harvesting seasons impact the aroma characteristics of tea leaves.

Effect of edible coatings and films enriched with plant extracts and essential oils on the preservation of animal-derived foods

Edible coatings and films for food preservation are becoming more popular thanks to their environmentally friendly properties and active ingredient-carrying ability. Their application can be effective in contrasting quality decay by limiting oxidation and deterioration of foods. Many reviews analyze the different compounds with which films and coatings can be created, their characteristics, and the effect when applied to food. However, the possibility of adding plant extracts and essential oils in edible coatings and films to preserve processed animal-derived products has been not exhaustively explored. The aim of this review is to summarize how edible coatings and films enriched with plant extracts (EXs) and essential oils (EOs) influence the physico-chemical and sensory features as well as the shelf-life of cheese, and processed meat and fish. Different studies showed that various EXs and EOs limited both oxidation and microbial growth after processing and during food preservation. Moreover, encapsulation has been found to be a valid technology to improve the solubility and stability of EOs and EXs, limiting strong flavor, controlling the release of bioactive compounds, and maintaining their stability during storage. Overall, the incorporation of EXs and EOs in edible coating and film to preserve processed foods can offer benefits for improving the shelf-life, limiting food losses, and creating a food sustainable chain.

Identification of the chemical composition of distiller's grain polyphenols and their effects on the fecal microbial community structure

Distiller grains are the main by-products of Baijiu production and are usually discarded, ignoring their abundant functional phytochemicals. The free and bound polyphenols from distiller grains were extracted and their potential effect on modulating fecal microbiota was investigated using in vitro fecal fermentation. The results showed that 34 polyphenols were quantified from distiller grains. The antioxidant activity was positively correlated with quercetin, myricetin, epicatechin, and naringenin. The abundance of Bifidobacterium, Ruminobacterium, Lactobacillus, Akkermansia, and butyrate-producing bacteria was enhanced by distiller's grain polyphenols by approximately 10.66-, 6.39-, 7.83-, 2.59-, and 7.74-fold, respectively. Moreover, the production of short-chain fatty acids (SCFAs), especially acetic, butyric, and propionic acid, was promoted (increased 1.99-, 1.71-, and 1.34-fold, respectively). Correlated analysis revealed quercetin, daidzein, and kaempferol as the key polyphenols by analyzing the effects on gut microbiota and SCFAs. This study could provide a reference for converting distiller grains into high-nutrient functional food ingredients and feeds.

Impact of the Season on Total Polyphenol and Antioxidant Properties of Tea Cultivars of Industrial Importance in Northeast India

Tocklai vegetative (TV) cultivars are extensively planted in the tea-growing regions of Northeast India. The present investigation explores the impact of season on the total polyphenol (TP) content and the antioxidant activity of thirty-one TV cultivars (TV1-TV31) and four other commercially popular cultivars, namely, Betjan, Kharijan, S.3A/3, and T.3E/3. The TP content of the cultivars was observed to be highest in the monsoon season, with values ranging from 230.57 to 283.53 mg g-1. In the pre-monsoon season and autumn, the TP content ranged from 197.87 to 256.77 mg g-1 and from 169.97 to 223.50 mg g-1, respectively. Antioxidant activity was measured through DPPH, ABTS, FRAP, and lipid peroxidation inhibition assays. The cultivars showed the highest antioxidant activity in the monsoon in tandem with TP content. A bivariate correlation indicated a highly significant (p ≤ 0.01) positive correlation of antioxidant activity with TP content (R2 = 0.83-0.96).

Integration of lipidomics and metabolomics approaches for the discrimination of harvest time of green tea in spring season by using UPLC-Triple-TOF/MS coupled with chemometrics

The production season is one of the judgment standards of the green tea quality and spring tea is generally considered of higher quality. Moreover, early spring tea is usually more precious and sells for a higher price. Therefore, a multifaceted strategy that integrates lipidomics and metabolomics, based on UPLC-Triple-TOF/MS coupled with chemometrics, was developed to discriminate early spring green tea (ET) and late spring green tea (LT). Twenty-six lipids and forty-five metabolites were identified as characteristic components. As for characteristic lipids, most of glycerophospholipids and acylglycerolipids have higher contents in ET. By contrast, glycoglycerolipids, sphingolipids and hydroxypheophytin a were shown higher levels in LT samples. Most of the differential metabolites identified were more abundant in ET samples. LT samples have much higher catechin, procyanidin B2, and 3',8-dimethoxyapigenin 7-glucoside contents. Based on the integration of differential lipids and metabolites, the reconstructed orthogonal partial least squares discriminant analysis (OPLS-DA) model displayed 100% correct classification rates for harvest time discrimination of green tea samples. These results demonstrated that the integration of lipidomics and metabolomics approaches is a promising method for the discrimination of tea quality.

Discrimination of the harvesting season of green tea by alcohol/salt-based aqueous two-phase systems combined with chemometric analysis

The flavor and aroma quality of green tea are closely related to the harvest season. The aim of this study was to identify the harvesting season of green tea by alcohol/salt-based aqueous two-phase system (ATPS) combined with chemometric analysis. In this paper, the single factor experiments (SFM) and response surface methodology (RSM) optimization were designed to investigate and select the optimal ATPS. A total of 180 green tea samples were studied in this work, including 86 spring tea and 94 autumn tea. After the active components in green tea samples were extracted by the optimal ethanol/(NH₄)₂SO₄ ATPS, the qualitative and quantitative analysis was realized based on HPLC-DAD combined with alternating trilinear decomposition-assisted multivariate curve resolution (ATLD-MCR) algorithm, with satisfactory spiked recoveries (86.00 %-112.45 %). The quantitative results obtained from ATLD-MCR model were subjected to chemometric pattern recognition analysis. The constructed partial least squares-discriminant analysis (PLS-DA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) models showed better results than the principal component analysis (PCA) model, and the R²X_cum values (>0.835) and R²Y_cum (>0.937) were close to 1, the Q²_cum values were greater than 0.75 (>0.933), and the differences between R²Y_cum and Q²_cum were not larger than 0.2, indicating excellent cross-validation prediction performance of the models. Furthermore, the classification results based on the hierarchical clustering analysis (HCA) were consistent with the PCA, PLS-DA and OPLS-DA results, establishing a good correlation between tea active components and the harvesting seasons of green tea. Overall, the combination of ATPS and chemometric methods is accurate, sensitive, fast and reliable for the qualitative and quantitative determination of tea active components, providing guidance for the quality control of green tea.

Identification and Field Evaluation of Sex Pheromone Components and Its Antagonist Produced by a Major Tea Pest, Archips strojny (Lepidoptera: Tortricidae)

Pesticide application is the only known control method for the tea tortrix Archips strojny (Lepidoptera: Tortricidae), which is a major pest of spring tea in China. To develop sex pheromone-based, environmentally safe control strategies, here we identified the sex pheromone components of this species. The male moths' antennae responded electrophysiologically to two compounds in female pheromone gland extracts. Gas chromatography-mass spectrometry analysis indicated that the two bioactive compounds were (Z)-11-tetradecenyl acetate (Z11-14:Ac) and (Z)-11-tetradecenyl alcohol (Z11-14:OH). Field trapping assays showed that lures baited with only the major component Z11-14:Ac were the most attractive to male moths, and the attractiveness decreased significantly when the lure was impregnated with increased relative ratios of the minor component Z11-14:OH. Our study demonstrated that Z11-14:Ac was the major attractant in the A. strojny sex pheromone, and the minor component Z11-14:OH seemed to serve as an antagonist. The results indicate that lures baited with 1 mg of Z11-14:Ac could be used as a monitoring or mass trapping tool for A. strojny management in Chinese tea plantations. Furthermore, Z11-14:Ac was identified as a common sex pheromone attractant of nine Archips species; these results lay the foundation for developing mating disruption techniques that target multiple leafroller pests.

Distinguishing Different Varieties of Oolong Tea by Fluorescence Hyperspectral Technology Combined with Chemometrics

Oolong tea is a semi-fermented tea that is popular among people. This study aims to establish a classification method for oolong tea based on fluorescence hyperspectral technology(FHSI) combined with chemometrics. First, the spectral data of Tieguanyin, Benshan, Maoxie and Huangjingui were obtained. Then, standard normal variation (SNV) and multiple scatter correction (MSC) were used for preprocessing. Principal component analysis (PCA) was used for data visualization, and with tolerance ellipses that were drawn according to Hotelling, outliers in the spectra were removed. Variable importance for the projection (VIP) > 1 in partial least squares discriminant analysis (PLS−DA) was used for feature selection. Finally, the processed spectral data was entered into the support vector machine (SVM) and PLS−DA. MSC_VIP_PLS−DA was the best model for the classification of oolong tea. The results showed that the use of FHSI could accurately distinguish these four types of oolong tea and was able to identify the key wavelengths affecting the tea classification, which were 650.11, 660.29, 665.39, 675.6, 701.17, 706.31, 742.34 and 747.5 nm. In these wavelengths, different kinds of tea have significant differences (p < 0.05). This study could provide a non-destructive and rapid method for future tea identification.