Recommended storage temperature for green tea based on sensory quality

Uncovering characteristic and enantiomeric distribution of volatile components in Huangshan Maofeng and Zhejiang baked green teas

Huangshan Maofeng (HSMF) is a famous baked green tea from the Anhui Province of China, known for its "clean and fresh" flavor. Zhejiang, another major tea-producing province, focuses on the production of green teas. This study aimed to analyze the characteristic aroma components and specific enantiomeric distribution of significant chiral volatile compounds in HSMF and Zhejiang baked green tea (ZJ-BGT) with respect to their origins, cultivars and grades using stir bar sorptive extraction combined with non-targeted gas chromatography-mass spectrometry (GC-MS) and enantiomeric GC-MS approaches. Unique enantiomeric distributions were identified for 2-methylbutanal, γ-nonanolactone, jasmine lactone, α-pinene, cis-linalool oxide (furanoid), and linalool in HSMF and ZJ-BGT. Furthermore, the concentrations of hexanal, cis-3-hexenyl butyrate, geraniol, and the enantiomeric ratio of R-α-terpineol demonstrated a positive correlation with the HSMF grade. Additionally, S-jasmine lactone and R-γ-nonanolactone present in HSMF, along with S-linalool found in ZJ-BGT, significantly contribute to the flavor quality of their respective teas.

Impact of utilization of oxygen scavenger on aroma quality of Longjing tea during storage at elevated temperature

The fresh aroma of Longjing tea is vulnerable to unfavorable storage conditions. However, limited research has addressed effective solutions apart from low-temperature storage. This study aimed to investigate the impact of oxygen scavenger on aroma quality of packaged Longjing tea samples at elevated storage temperatures. As a result, the utilization of oxygen scavenger could effectively mitigate aroma deterioration of Longjing tea caused by elevated temperature during storage, resulting in a decrease in the stale odor scores by more than 3.0. The utilization of oxygen scavenger achieved aroma-preserving effect by inhibiting the accumulation of key stale odor compounds and maintaining the levels of volatiles related to freshness aroma. The key volatile contributors to stale odor are primarily ketones and alcohols resulting from thermal carotenoids degradation/lipid oxidation, which exhibit woody or fatty odors. These findings provide essential theoretical principles for improving Longjing tea preservation technology.

Development of sensory tools for green rooibos (Aspalathus linearis (Burm.f.) R.Dahlgren) and changes in quality attributes during shelf-life storage

BACKGROUND

Green rooibos (Aspalathus linearis (Burm.f.) R.Dahlgren) herbal tea is popular due to its health-promoting properties. Information on its characteristic sensory profile is scarce and sensory tools to define product variation are needed. The storage conditions and time during its shelf-life are hypothesized to affect the product quality.

RESULTS

Production batches from two producers spanning 5 years (n = 57) were analyzed using descriptive sensory analysis. Primary attributes (>30 median intensity; 100% occurrence frequency) included 'hay/dried grass', 'cooked oats', 'tobacco', 'honey' and 'caramel' aromas, and astringent mouthfeel. 'Cooked vegetables', 'green grass', 'stewed fruit', 'rooibos-woody', 'marmalade' and 'cardboard' aromas, sweet taste and bitter taste were secondary attributes (10-20 median intensity; 100% occurrence frequency). The same flavor attributes were present, except for sweet-associated and fruity notes. A sensory lexicon and sensory wheels for aroma and palate attributes were constructed from the data. The shelf-life stability of green rooibos was evaluated in moisture-impermeable (pouches) and moisture-permeable (sachets) packaging at 25 and 40 °C at 60% relative humidity over 24 weeks. Green rooibos samples stored in pouches at 4 °C were also evaluated. Storage in sachets led to moisture uptake (~10 g (100 g)-1 dry basis) and an increase in water activity (>0.6), causing degradation of chlorophyll and dihydrochalcones. Changes in color and sensory profile (decreased vegetal, cereal and cardboard aromas and increased sweet-associated and fruity aromas) were evident and more pronounced at the higher storage temperature.

CONCLUSIONS

Storage at ≤25 °C in moisture-impermeable packaging material is recommended for green rooibos herbal tea. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Rapid Color Quality Evaluation of Needle-Shaped Green Tea Using Computer Vision System and Machine Learning Models

Color characteristics are a crucial indicator of green tea quality, particularly in needle-shaped green tea, and are predominantly evaluated through subjective sensory analysis. Thus, the necessity arises for an objective, precise, and efficient assessment methodology. In this study, 885 images from 157 samples, obtained through computer vision technology, were used to predict sensory evaluation results based on the color features of the images. Three machine learning methods, Random Forest (RF), Support Vector Machine (SVM) and Decision Tree-based AdaBoost (DT-AdaBoost), were carried out to construct the color quality evaluation model. Notably, the DT-Adaboost model shows significant potential for application in evaluating tea quality, with a correct discrimination rate (CDR) of 98.50% and a relative percent deviation (RPD) of 14.827 in the 266 samples used to verify the accuracy of the model. This result indicates that the integration of computer vision with machine learning models presents an effective approach for assessing the color quality of needle-shaped green tea.

The manufacturing process provides green teas with differentiated nonvolatile profiles and influences the deterioration of flavor during storage at room temperature

Hundreds of green tea products are available on the tea market and exhibit different characteristics. In the present study, seven types of green tea were processed, and their nonvolatile profiles were analyzed by liquid chromatography-mass spectrometry. Non-spreading green tea contained higher concentrations of catechins and flavonoid glycosides, but lower concentrations of amino acids, caffeine, and theaflavins. Non-rolling green teas with a straight appearance contained higher concentrations of flavonoid glycosides and theaflavins. In contrast, leaf-rolling green teas contained much lower concentrations of flavonoid glycosides and catechins. These seven green tea qualities all decreased following prolonged storage, concurrent with increasing concentrations of proanthocyanidins, catechins dimers, theaflavins, and organic acids. The leaf-rolling green teas exhibited reduced levels of deterioration during storage in terms of their nonvolatile profile and sensory quality. Findings show that moderate destruction on tea leaves during green tea processing is beneficial to both tea flavor and quality maintenance during storage.

Predicting the storage time of green tea by myricetin based on surface-enhanced Raman spectroscopy

The quality of green tea changes rapidly due to the oxidation and degradation of polyphenols during storage. Herein, a simple and fast Surface-enhanced Raman spectroscopy (SERS) strategy was established to predict changes in green tea during storage. Raman spectra of green tea with different storage times (2020-2015) were acquired by SERS with silver nanoparticles. The PCA-SVM model was established based on SERS to quickly predict the storage time of green tea, and the accuracy of the prediction set was 97.22%. The Raman peak at 730 cm^-1 caused by myricetin was identified as a characteristic peak, which increased with prolonged storage time and exhibited a linear positive correlation with myricetin concentration. Therefore, SERS provides a convenient method for identifying the concentration of myricetin in green tea, and myricetin can function as an indicator to predict the storage time of green tea.

Mycotoxins along the tea supply chain: A dark side of an ancient and high valued aromatic beverage

ABSTRACTSTea (Camellia sinensis L.) is a high valued beverage worldwide since ancient times; more than three billion cups of tea are consumed each day. Leaf extracts of the plant are used for food preservation, cosmetics, and medicinal purposes. Nevertheless, tea contaminated with mycotoxins poses a serious health threat to humans. Mycotoxin production by tea fungi is induced by a variety of factors, including poor processing methods and environmental factors such as high temperature and humidity. This review summarizes the studies published to date on mycotoxin prevalence, toxicity, the effects of climate change on mycotoxin production, and the methods used to detect and decontaminate tea mycotoxins. While many investigations in this domain have been carried out on the prevalence of aflatoxins and ochratoxins in black, green, pu-erh, and herbal teas, much less information is available on zearalenone, fumonisins, and Alternaria toxins. Mycotoxins in teas were detected using several methods; the most commonly used being the High-Performance Liquid Chromatography (HPLC) with fluorescence detection, followed by HPLC with tandem mass spectrometry, gas chromatography and enzyme-linked immunosorbent assay. Further, mycotoxins decontamination methods for teas included physical, chemical, and biological methods, with physical methods being most prevalent. Finally, research gaps and future directions have also been discussed.

Evaluating Freshness Loss of Green Tea with Q10 Method and Weibull Hazard Analysis under Accelerated Shelf Life Testing

The important quality of green tea is freshness, but high temperature, light, oxygen, and humidity during storage may reduce the freshness of green tea. Thus, this study investigated the freshness loss of green tea (FLGT) under an accelerated shelf-life testing (ASLT) by sensory evaluation and acceptability test. The FLGTs of the samples stored at 20°C, 30°C, and 40°C, were determined as 67 days, 55 days, and 45 days, respectively by the Q10 method. In addition, they were further determined as 67 days, 57 days, and 42 days, respectively, by the Weibull Hazard Analysis (WHA). The sensory evaluation and acceptability test confirmed the correctness of the above results by 2-alternative choice analysis and chemical analysis. The Q10 method was applied to predict the FLGTs stored at 4°C and −20°C which were 93 days and 150 days, which was further verified by 2-alternative choice analysis and chemical analysis. The results show that it is possible to predict the suitable drinking period of green tea during storage by the Q10 method.

Metabolomics Analysis Reveals Four Novel N-Ethyl-2-pyrrolidinone-Substituted Theaflavins as Storage-Related Marker Compounds in Black Tea

Tea market is currently oversupplied, and unsold tea often needs to be properly stored for a period of time. However, the chemical changes occurring in black tea during storage are limitedly understood. In this study, a comprehensive nontargeted and targeted metabolomics approach was used to investigate the dynamic changes in compounds in time-series (0-19 months)-stored black teas. The contents of flavanols, theaflavins (TFs), theasinensins, procyanidins, most phenolic acids, amino acids, quercetin-O-glycosides, and myricetin-O-glycosides decreased during storage, while the contents of N-ethyl-2-pyrrolidinone-substituted flavanols, flavone-C-glycosides, and most kaempferol-O-glycosides increased. More importantly, four novel compounds strongly positively correlated with storage duration (r = 0.922-0.969) were structurally assigned as N-ethyl-2-pyrrolidinone-substituted TFs and validated with synthetic reactions of TFs and theanine standards. The content of N-ethyl-2-pyrrolidinone-substituted TFs was 51.54 μg/g in black tea stored for 19 months. To the best of our knowledge, N-ethyl-2-pyrrolidinone-substituted TFs were discovered in tea for the first time.

N-Ethyl-2-Pyrrolidinone-Substituted Flavan-3-Ols with Anti-inflammatory Activity in Lipopolysaccharide-Stimulated Macrophages Are Storage-Related Marker Compounds for Green Tea

Fresh green tea (GT) is commonly considered to have better sensory flavor and higher commercial value than long-term-stored GT; however, the chemical variations during storage are unclear. In this study, the chemical profiles of stored GT were surveyed among time-series samples from 0 to 19 months using a nontargeted metabolomics method. Seven N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) increased from 0.022 ± 0.019 to 3.212 ± 0.057 mg/g within 19 months (correlation coefficients with storage duration ranging from 0.936 to 0.965), and they were the most significantly increased compounds among the 127 identified compounds. Two representative EPSFs (R-EGCG-cThea and S-EGCG-cThea) possess potential anti-inflammatory properties by suppressing the expression, phosphorylation, and nuclear translocation of nuclear factor kappa-B (NF-κB) p65 in lipopolysaccharide-stimulated macrophages based on western blotting and immunofluorescence results. In conclusion, EPSFs were found to be marker compounds for stored GT and showed potential anti-inflammatory activity by regulating the NF-κB signaling pathway.

Quality characteristics of infusion and health consequences: a comparative study between orthodox and CTC green teas

The present study compares the effects of two green tea processing techniques, viz. orthodox and CTC (curl, tear and crush) on the quality parameters and sensory profiles under the geographical and climatic conditions of Assam, India. The results showed that CTC green tea infusions had 13.3, 7.5, 7.1, 9.8, 5.4, 17.3, 17.1 and 18.6% more total polyphenol, total catechin, (-)-epigallocatechin-3-gallate (EGCG), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC), (-)-epicatechin (EC), water extract and theanine level, respectively than the infusions prepared from orthodox green tea. The sensory evaluation preferred the orthodox over CTC processing mode. Risk assessment with daily consumption of five cups (10 g) of green tea reveals that the EGCG level is free from the risk of hepatotoxicity and caffeine will not inflict any health hazard.