Effect of Different Harvesting Dates on Tea Quality of Five Mulberry Varieties in Turpan City

This study aimed to investigate the influence of different harvest dates on the chemical composition of Morus nigra leaf tea in Turpan City, Xinjiang Province. Morus (mulberry) varieties belong to the order Rosales, family Moraceae and genus Morus, and are widely cultivated around the world. Mulberry leaf tea is made from the processing of mulberry leaves and is a primary way of high-value utilization of mulberry tree resources. Leaves of five mulberry varieties,‘Yao Sang’ (M. nigra L.), ‘Bai Sang’ (M. alba L.), ‘Hei Sang’(M. alba L. var. Tatarica), Nong Sang Number 14 (M. multicaulis Perr.), and‘Danbai Sang’(M. alba), were collected on seven different dates in 2024 and tea was made from each sample following a replicated standardized process. The main chemical components, including free amino acids, flavonoid glycosides, total phenols, total polysaccharides, alkaloids, γ-aminobutyric acid (GABA), and 1-Deoxynojirimycin (DNJ) were analyzed and sensory evaluations were conducted. Two-way ANOVA was conducted, and pairwise comparisons were performed between groups in which the interaction was statistically significant. The optimal harvest date was determined using principal component analysis to comprehensively evaluate tea quality and identify the optimal date for harvesting. Based on the results of the two-way ANOVA, a correlation was found between the repeated measurement data (p ≤ 0.05) and Tukey’s post-hoc test was used to make pairwise comparisons. Among the five species groups, there were significant differences in the mean values for most varieties. At the same time, there were significant differences between the mean values at most of the seven time points. The index values of the mulberry leaves at different harvest dates were used to calculate the primary component score function. The overall quality ranking was determined based on the comprehensive score: Yao Sang and Nong Sang 14 achieved their highest scores on May 27th, Danbai Sang peaked on June 24th, Bai Sang reached its maximum on July 8th, and Hei Sang attained its highest score on April 29th. This analysis method integrated the contents of several main bioactive substances and sensory scores of mulberry leaf tea to objectively and comprehensively determine the optimal harvest date for the five mulberry leaf varieties in Turpan City. These findings provide a theoretical reference for the preparation and utilization of mulberry leaf tea.