Inhibitory effects of apple polyphenol extract (AP) and procyanidin contained in AP on in vitro pancreatic lipase activity and in vivo triglyceride absorption in mice and humans were examined. AP and procyanidin considerably inhibited in vitro pancreatic lipase activity. However, polyphenols, except for procyanidin, in AP (i.e., catechins, chalcones, and phenol carboxylic acids) showed weak inhibitory activities on pancreatic lipase. Procyanidins separated by normal-phase chromatography according to the degree of polymerization were also examined. Inhibitory effects of procyanidins increased according to the degree of polymerization from dimer to pentamer. On the other hand, pentamer or greater procyanidins showed maximal inhibitory effects on pancreatic lipase. These results suggested that with respect to in vitro pancreatic lipase inhibition, the degree of polymerization was an important factor and oligomeric procyanidin mainly contributed. Next, we performed a triglyceride tolerance test in mice and humans. Simultaneous ingestion of AP and triglyceride significantly inhibited an increase of plasma triglyceride levels in both models. These results suggested that the oligomeric procyanidins contained in AP inhibited triglyceride absorption by inhibiting pancreatic lipase activity in mice and humans.

Oligomeric Procyanidins in Apple Polyphenol Are Main Active Components for Inhibition of Pancreatic Lipase and Triglyceride Absorption [Erratum: 2007 July 11, v. 55, no. 14, p. 5906.]

Molecular mechanisms underlying health benefits of tea compounds

The bitter and astringent taste of tea and tea extract is still not favored by many consumers, which limits its applications to bakery foods and functional foods. Many bitter and astringent compounds in tea leaves are susceptible, which transform during tea processing or can be modified by food production technologies. Besides, the accumulations of the major bitter and astringent compounds in fresh tea leaves, such as alkaloids and flavonoids, can be regulated by agronomic practices. Many attempts have been made to reduce the bitter and astringent compounds, in order to improve the sensory quality of tea and tea products. The aim of this review is to describe the characteristics of major bitter and astringent compounds in different types of teas as well as the bitterness and astringency reducing strategies from the aspects of preharvest, processing and post-processing. Alkaloids, catechins, anthocyanins, phenolic acids, flavonol glycosides, and theaflavins importantly contribute to the bitter and astringent taste of tea infusion, the contents of which can be modulated during preharvest, processing, and post-processing. Shade treatment is a conventional agronomic practice to reduce the bitterness and astringency of tea. Processing methods like oxidation, roasting/baking and microbial fermentation effectively reduce the bitter and astringent intensities of teas, but have restricted applications to special types of tea. There is a need of new compounds or strategies to decrease the bitterness and astringency of tea and tea products. Employment of these bitterness and astringency reducing strategies should consider the appearance or application requirements of final products. 

Bitterness and astringency of tea leaves and products: Formation mechanism and reducing strategies

In the present study, volatile compounds from 15 yellow tea samples were extracted and examined using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS), and the key odorants were identified by gas chromatography-olfactometry (GC-O) analysis. Results revealed 74 volatile compounds in these yellow teas, geraniol (3.89 μg/g) being the most abundant aroma compound. Alcohols and esters were the dominant volatiles, accounting for approximately 52.44% of the total volatiles in content. Moreover, 25 key odorants were identified by GC-O method, and were considered to be responsible for the unique aroma quality of yellow tea. Major key odorants included (E, E)-3,5-octadien-2-one, (Z)-linalool oxide (furanoid), (E)-2-heptenal, naphthalene, geraniol, (E)-linalool oxide (furanoid), styrene, linalool, α-ionone, 1-octen-3-ol, trans-β-ionone, and (E, Z)-3,5-octadien-2-one. In addition, huge differences were observed among the content levels of key odorants in three types of yellow tea samples, namely MengDingHuangYa (MDHY), WeiShanHuangCha (WSHC), and PingYangHuangTang (PYHT). This is an important study describing the characterization of aroma and key odorants in yellow tea. The results obtained from this study advance our understanding of the aroma quality of yellow tea, thereby providing a theoretical basis for the processing and quality control of yellow tea aroma quality.

Volatile components and key odorants of Chinese yellow tea (Camellia sinensis)

Yellowing is the key process used to produce the unique yellow tea, but the effect of the yellowing process on tea quality and chemical composition remains unclear. Here, electronic eye and tongue and metabolomics were applied to investigate dynamic changes in tea leaves during the yellowing process for the first time. During the first 18 h of yellowing, the colour of tea leaves was observed becoming yellowish. Compounds related to umami and sweetness (amino acids, catechins, sucrose, phenolic acids, etc.) are at high levels. However, after 24 h of yellowing, the colour of tea becomes darker, with richness of tea infusion decreasing significantly. The levels of most catechins, amino acids, phenolic acids, and glycosidically bound volatiles (GBVs) decreased significantly, whereas betaine, piperidine, theasinensin B, and lysophosphatidylcholines (LPCs) increased significantly. Meanwhile, according to partial least-squares (PLS) analysis, most amino acids and sucrose were positively correlated with umami and sweetness; most catechins and phenolic acids had positively correlated with bitterness and astringency; phaeophorbides were positively correlated with red value (+a*) of tea leaves’ colour. This work provides a comprehensive, novel knowledge on the quality and chemical changes of yellow tea during the yellowing process.

The profile of dynamic changes in yellow tea quality and chemical composition during yellowing process

Qingzhuan tea (QZT), a post-fermented tea, has been reported to have anti-obesity and anti-hyperglycemic effects, perhaps due to bioactive compounds that inhibit lipase and α-amylase. It is unknown what chemical constituents' changes and what bioactive compounds occur during the manufacture of QZT. The aim of this study was to determine the secondary metabolites changes that occur during post-fermentation and how these changes affect the ability of QZT to inhibit the activities of lipase and α-amylase. During the processing steps, metabolites levels and their inhibitory effects on lipase and α-amylase were assessed. Changes in content and activities suggested that the first turn over or the second turn over was critical for the formation and conversion of bioactive compounds responsible for the anti-obesity and hypoglycemic effects. The relationship between constituents and activities was further evaluated by correlation analysis, which showed that amino acids and flavonoids might be responsible for the anti-obesity and anti-hyperglycemic effects of QZT. This study clarified that compounds were altered during pile fermentation of QZT and tentatively identified the bioactive compounds formed during QZT manufacture.

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Chemical profile changes during pile fermentation of Qingzhuan tea affect inhibition of α-amylase and lipase.

In this study, the aroma components of bead-shaped green teas were compared through headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry/olfactometry (GC–MS/O) coupled with chemometrics A total of 62 volatile compounds were identified in 16 green tea samples Notably, comparison of GC–MS/O and odour activity values (OAV) results revealed that nonanal, decanal, (E)-2-nonenal, β-ionone, and 1-octen-3-one were the most powerful aroma-active compounds that contributed to the aroma profile of the bead-shaped green teas Furthermore, multivariate statistical techniques (such as principal component analysis, partial least squares-discriminant analysis, and hierarchical cluster analysis) were used to characterise the bead-shaped green teas according to their geographical origin and the flavour characteristics of their volatile compounds Additionally, the variable importance in the projection method was used to identify 20 volatile markers that could successfully distinguish bead-shaped green teas on the basis of three flavour characteristics The results of the analysis revealed that HS-SPME and GC–MS/O coupled with chemometrics can provide an effective method for characterising and classifying bead-shaped green teas

Comparing characteristic aroma components of bead-shaped green teas from different regions using headspace solid-phase microextraction and gas chromatography–mass spectrometry/olfactometry combined with chemometrics

The invention provides a method for predicting the water content of spread green leaves of green tea based on the near infrared spectrum technology. A near infrared spectroscopy is applied, and an integrating sphere is used as an optical platform for conducting scanning. The method comprises the following steps that the spread fresh leaves are selected, the water content of the spread fresh leaf sample is measured, the spread fresh leaf sample is subjected to near infrared spectrum scanning, a spread fresh leave sample near infrared spectrum predicting model is established, a water content predicting model is established by converting all fresh leaf sample near infrared spectra into paired data points and utilizing a partial least squares method in a union section, and the water content of the spread green leaves of the green tea is quickly predicated through model stability checking; thus, a quick, accurate and lossless quantitative predicting method is provided for prediction of the water content of the spread green leaves of the green tea.

Method for predicting water content of spread green leaves of green tea based on near infrared spectrum technology

This study aimed to compare the effect of hot roller (HR) drying and hot air (HA) drying on the sensory evaluation, chemical quality, antioxidant activity, and metabolic profile of Yihong Congou black tea processed from E’cha NO1. The Yihong Congou black tea dried with HA obtained higher sensory scores and better chemical qualities such as the hue of tea brew color (a and b), content of theaflavins, thearubigins, water extract, free amino acids, tea polyphenol, and the ratio of polyphenol to amino acids as well as higher antioxidant capacities compared to that dried with HR. The HA drying tea increased the contents of volatile compounds that had positive correlation with sweet and flowery flavor, while the HR drying tea increased the contents of volatile compounds related to fruity flavor. Moreover, non-targeted metabolomics data indicated that the levels of most free amino acids significantly increased, while the levels of most soluble sugars reduced in the HA drying method compared to the HR drying method. The metabolic analysis was also consistent with the above results and revealed that D-ribose and gallic acid were the main characteristic metabolites of HA drying. Our results could provide a technical reference and theoretical guide to processing a high quality of Yihong Congou black tea.

Metabolomics Provides A Novel Interpretation of the Changes in Main Compounds during Black Tea Processing through Different Drying Methods.

A single node and side shoot cutting seedling raising method adopting a plug tray and applied to tea trees comprises the following steps: greenhouse preparation, substrate preparation, loading of the substrate to the plug tray, cutting selection, shoot cutting, processing of cutting shoots with rooting powder, cutting and seedling management. Moisture of the substrate and moisture of the cutting shoots are kept in an intermittent spraying manner, the survival rate of the cutting shoots is increased, and the callus forming time and rooting time are shortened; seedlings develop fast after rooting of the cutting shoots provided with the side shoots, and the seedling raising period is shortened; seedling raising through the light substrate and the plug tray is adopted, the root systems of the tea tree seedlings are in a net shape and cluster with the substrate, so that the seedlings are not prone to damage during pulling up, transportation and transplanting, the transplanting survival rate is increased, and the problems of long seedling raising period of single node cutting in an open field by adopting a double-layer film, difficult moisture management of single node and side shoot cutting and the like are solved.

Zheng Lin

Papers

Chemical profile changes during pile fermentation of Qingzhuan tea affect inhibition of α-amylase and lipase.

Comparing characteristic aroma components of bead-shaped green teas from different regions using headspace solid-phase microextraction and gas chromatography–mass spectrometry/olfactometry combined with chemometrics

Method for predicting water content of spread green leaves of green tea based on near infrared spectrum technology

Metabolomics Provides A Novel Interpretation of the Changes in Main Compounds during Black Tea Processing through Different Drying Methods.

Single node and side shoot cutting seedling raising method adopting plug tray and applied to tea trees