Effects of withering on the main physical properties of withered tea leaves and the sensory quality of congou black tea

Abstract

To explore the relationship between the moisture content of withered tea leaves and their physical properties (i.e., elasticity, plasticity, flexibility, and texture) during withering, texture analyzer was employed to test the elasticity and flexibility of withered tea leaves with different moisture contents. The texture was evaluated by computer vision technology. The withered tea leaves with different moisture contents were used to process congou black tea, which was then subjected to sensory evaluation.Results showed that good elasticity, optimal flexibility, and plasticity were achieved when the moisture content of the withered tea leaves of Fudingdabai comprising two leaves and one bud varied arranging from 65.51 to 61.48%. The sensory evaluation of congou black tea revealed that moderate withering was better than long-term withering and that both moderate and long-term withering were better than no withering during processing. The moisture content was significantly correlated with the flexibility and plasticity of the withered tea leaves. Fresh tea leaves undergoing moderate withering with moisture content of 65.51-61.48% to process congou black tea, good tea shape and liquor color were achieved. This study provided new evidence that the moisture content of withered tea leaves significantly affected the quality of black tea. K E Y W O R D Scongou black tea, machine vision, sensory evaluation, texture analysis, withering

Quantitative Measurement Reveals Dynamic Volatile Changes and Potential Biochemical Mechanisms during Green Tea Spreading Treatment

“…Phenylalanine is the precursor of benzyl alcohol and 2-phenylethanol synthesis (Figure a). Its content was highly increased during tea withering through up-regulation of chorismite mutase, prephenate dehydratase, and tryptophan synthase. , This would provide abundant intermediates for indole, methyl SA, and phenylpropanoid synthesis at the late stage of tea withering. These data suggest that shikimic acid-derived aroma synthesis during green tea spreading could be regulated at the transcriptional level and by substrate availability.…”

“…However, the volatile changes during tea spreading were not temporally resolved in that study, which limits the mechanistic interpretation. The length of withering time has significant effects on metabolite degradation and transformation. ,, …”

“…The length of withering time has significant effects on metabolite degradation and transformation. 13,23,24 For green tea making, spreading is regarded as "mildwithering" 19 and is essential to develop the mellow umami taste and delicate fragrance of green tea. 25 To date, about 270 volatile compounds have been identified in green tea.…”

Improving black tea quality through optimization of withering conditions using artificial neural network and genetic algorithm

“…The physical and chemical changes during withering are influenced by duration of withering and environmental conditions like air temperature, relative humidity, air flow rate etc. In recent days studies have been reported to correlate degree of withering with textural properties, color of leaves, or machine vision-based image analysis (Liang et al, 2018;Ye et al, 2019;Yu et al, 2019). and aroma of black tea.…”

Emerging techniques for determining the quality and safety of tea products: A review

“…Ultraviolet–visible spectroscopy (UV‐vis) (Diniz, Barbosa, De Melo Milanez, Pistonesi, & De Araújo, 2016; Yu & He, 2018), near‐infrared spectroscopy (Chen, Zhao, Zhang, & Wang, 2006, 2007; Zhao, Chen, Huang, & Fang, 2006), Fourier transform infrared (FT‐IR) spectroscopy (Li, Sun, Luo, & He, 2015, 2016), Raman spectroscopy (Li et al., 2015; Zhang et al., 2020), laser‐induced breakdown spectroscopy (LIBS) (Yu, Peng, Liu, & He, 2017), and terahertz (Chen, Cao, & Liu, 2011) in spectroscopic techniques, electric nose (E‐nose) (Chen, Liu, Zhao, & Ouyang, 2013; Dutta, Hines, Gardner, Kashwan, & Bhuyan, 2003), electric tongue (E‐tongue) (Zhi, Zhao, & Zhang, 2017), electric eye (E‐eye) (Xu, Wang, & Zhu, 2019), adsorptive stripping voltammetry (ASV) (Guo, Zheng, Mo, & Ye, 2009), cyclic voltammetry (CV) (Kilmartin & Hsu, 2003; Liu et al., 2014), square‐wave voltammetry (SWV) (Novak, Šeruga, & Komorsky‐Lovrić, 2010), and capillary zone electrophoresis (Horie, Mukai, & Kohata, 1997) in electrochemical methods, nanozymes (Wang, Liu, Qin, Chen, & Shen, 2016; Zhang & Huang, 2015), computer vision (Wang et al., 2015; Xu, Wang, & Gu, 2019; Ye et al., 2019), and modified chromatographic techniques are the five main emerging techniques for quality and safety evaluation of tea products, determining parameters qualitatively and quantitatively, with their distinct advantages and disadvantages, as well as suitable but different detection target. To the best of our knowledge, no study has reviewed the applications of these emerging techniques for the evaluation of different parameters in tea products.…”