Evaluation of Chongqing Tuo Tea at Different Grades: An Integrated Approach by Artificial and Intelligent Sensory, Non-Volatile, and Volatile Compounds Analysis.

This study aims to investigate the relationship between the grades of Tuo tea and the quality of compounds. A combination of artificial sensory evaluation, intelligent sensory technologies (electronic nose and electronic tongue), gas chromatography-mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), chemical-physical analysis, and multivariate statistical analysis were employed to examine the differences among three grades of Tuo tea (SG, 1G, and 2G). The results of artificial sensory evaluation, electronic tongue, and electronic nose revealed that the aroma and taste of different grades of Tuo tea varied greatly. A total of 112 volatile compounds and 44 non-volatile compounds were identified. In order to elucidate the key components that cause differences in the quality of Tuo tea, 2 partial least squares discriminant analysis (PLS-DA) models with excellent parameters (volatile, R2Y = 0.999 and Q2 = 0.996; non-volatile, R2Y = 0.992 and Q2 = 0.972) were established. A total of 80 key differential volatile compounds were identified with the double selection criterion of variable importance in projection (VIP) greater than 1 and p < 0.05. Among these, 43 compounds with OAV > 1 were further identified as the odor-active compounds in all three grades of Tuo. Moreover, 22 key non-volatile compounds that contribute to the quality differences have been screened out. This investigation implied that the volatile and non-volatile compounds of Tuo tea could serve as indicators of its quality. The results provided a new approach to distinguish the grades of Tuo tea.

Sensory-directed isolation and identification of an intense salicin-like bitter compound in infected teas with bird's eye spot disease.

Teas infected with bird's eye spot disease generally exhibited a lingering and long-lasting, salicin-like bitter taste, which was unpalatable to consumers. Sensory-directed isolation processes have been performed in this study to investigate the salicin-like bitter compounds in infected teas. Results showed that infected teas were extracted using a 70% methanol aqueous solution to produce methanol extract, which was then further separated by sequential solvent extraction (SSE) to obtain dichloromethane extract, which contained the salicin-like bitter compounds. The dichloromethane extract was then isolated by flash chromatography to produce two salicin-like bitter fractions, eluted using 60% and 65% methanol aqueous solution. Finally, these two salicin-like bitter fractions were analyzed by RP-HPLC using 60-68% and 70-75% methanol aqueous solution, respectively, affording the location of the salicin-like bitter compounds in RP-HPLC chromatograms. Moreover, a new ursane-type triterpenoid, camellisin A methyl ester, was identified from infected teas. This study has provided preliminary isolation methods of salicin-like bitter compounds from the infected teas, which were essential to designing targeted debittering strategies for infected teas and improving the quality of the finished tea and the effective utilization of fresh tea leaves.

Characterization of triterpenoids as possible bitter-tasting compounds in teas infected with bird's eye spot disease.

Tea infected with bird's eye spot disease generally imparts a long-lasting bitter taste, which is unacceptable to most consumers. This study has comprehensively evaluated the taste profiles of infected and healthy teas and investigated their known bitter compounds previously reported in tea. Quantification analyses and calculation of dose-over-threshold (DoT) factors revealed that no obvious difference was visualized in catechins, caffeine, bitter amino acids, and flavonols and their glycosides between infected and healthy tea samples, which was also verified by principal component analysis (PCA) and hierarchical cluster analysis (HCA). Therefore, these known bitter compounds have been ruled out as critical contributors to the long-lasting bitterness of infected teas. Furthermore, Gel permeation chromatography, sensory analysis, and UPLC-Q-TOF-MS were employed and identified 13 substances from the target bitter fractions, including caffeine, ten triterpenoids, and two oxylipins. The higher triterpenoid levels were supposed to be the reason causing the long-lasting bitterness. This study has provided a research direction for the molecular basis of the long-lasting bitterness of infected tea leaves with bird's eye spot disease.

Effects of Hot Air Drying on Drying Kinetics and Anthocyanin Degradation of Blood-Flesh Peach.

The purpose of this study was to explore the drying kinetics, effective moisture diffusivity, activation energy, color variation, and the thermal degradation properties of anthocyanins of blood-flesh peach under hot air drying for the first time. The results showed that the hot air-drying process of blood-flesh peach belongs to reduced-speed drying. The Page model could accurately predict the change of moisture ratio of blood-flesh peach. The effective moisture diffusivity during hot air drying of blood-flesh peach was in the range between 1.62 × 10-10 and 2.84 × 10-10 m2/s, and the activation energy was 25.90 kJ/mol. Fresh samples had the highest content (44.61 ± 4.76 mg/100 g) of total monomeric anthocyanins, and it decreased with the increase of drying temperature. Cyanidin-3-O-glucoside and delphinidin-3-O-galactoside were the main anthocyanins of blood-flesh peach as identified and quantified by UPLC-QqQ-MS. Interestingly, during the drying process, the content of cyanidin-3-O-glucoside increased at the beginning, and then decreased. However, the content of delphinidin-3-O-galactoside kept decreasing during the whole drying process. Considering the drying efficiency, fruit color and quality, 70 °C would be a suitable temperature for drying blood-flesh peach. This research will provide beneficial information for understanding the anthocyanin degradation of blood-flesh peach during drying, and guide the production of high-quality dried products.

Effects of air-impingement jet drying on drying kinetics and quality retention of tomato slices.

The purpose was to explore the drying kinetics, the moisture effective diffusivities, color, total polyphenols, lycopene and antioxidant activities of dried tomato slices by air-impingement jet drying (AIJD). The results showed that high temperature increased the drying rate, and Modified Page model accurately predicted the AIJD characteristics of tomato slices. AIJD is better than hot air drying in shortening drying time, enhancing drying rate and decreasing the loss of total polyphenols, lycopene and antioxidant capacity of tomato slices. Tomato slices dried by AIJD also showed higher lightness and redness. Lycopene content and antioxidant activity of tomato slices dried by AIJD were increased by higher drying temperature. Based on experimental data, AIJD at 80 °C can be used in tomato drying process due to the advantages in drying efficiency and content of bioactive compounds. This study will provide helpful information for the production of high quality of dried tomato products.

Lycopene, polyphenols and antioxidant activities of three characteristic tomato cultivars subjected to two drying methods.

The aim of this study was to evaluate the effects of freeze drying and oven drying on appearance, chemical components and antioxidant activities of three cultivars of tomatoes. This study showed cultivar 18,131 would provide the highest phenolic contents and ABTS radical scavenging activity, and cultivar 1862 provide the highest lycopene content after oven drying. On the basis of appearance and contents of polyphenols, freeze drying showed better results. However, oven drying was found superior in decreasing degradation of lycopene. The effects of drying on the polyphenol contents varied depending on the cultivars. In addition, there is no significant difference of antioxidant activities between freeze dried and oven dried tomatoes. These results also demonstrated that freeze drying is superior in maintaining physical structure and phenolic contents of tomato slices. However, oven drying is a viable option for drying tomatoes considering both costing and contents of lycopene.