Analysis of Biochemical Composition and Heavy Metal Elements Contents of Processing By-Products from Different Tea Categories in Guangxi

Objective To achieve the high-value comprehensive utilization of processing by-products from different tea categories in Guangxi.

Methods Broken tea and tea stems from green tea, black tea, modern-processed Liupao tea and traditionally processed Liupao tea were investigated, with corresponding first-grade finished teas as controls. Major biochemical components and heavy metal elements were measured, and multivariate statistical analysis was used to evaluate their biochemical quality.

Results For the same tea category, significant differences were generally observed in the contents of biochemical components and limit-regulated heavy metal elements among different processing by-products (P＜0.05). The processing by-products of traditionally processed Liupao tea and green tea had higher contents of free amino acids, tea polyphenols, total flavonoids, total catechins, EGCG and ECG. Specifically, the contents of free amino acids (4.83%) and tea polyphenols (13.91%) in broken tea of traditionally processed Liupao tea, as well as total flavonoids (14.84%), ECG (30.42 mg·g⁻¹) and total catechins (149.73 mg·g⁻¹) in green tea broken, were higher than those in their corresponding tea twigs and first-grade finished tea. Processing by-products of black tea and modern-processed Liupao tea contained higher levels of soluble protein, theabrownin, theaflavin; the contents of soluble protein in modern-processed Liupao tea broken, and theabrownin and theaflavin in black tea broken exceeded those in tea stem and finished tea. The highest contents of thearubigins and tea polysaccharides were detected in broken tea of traditionally processed Liupao tea (5.69%) and modern-processed Liupao tea (3.91%), respectively. The contents of heavy metal elements do not exceed the permitted limits. Principal component analysis based on core biochemical components showed that the comprehensive scores of processing by-products of all tea varieties followed the order of broken tea ＞ tea stem, with broken tea of black tea scoring higher than first-grade finished black tea.

Conclusion The study clarified the biochemical components and heavy metal elements in processing by-products of different tea categories from Guangxi. These findings provide a scientific basis for further research, high-value comprehensive utilization, and safety assessment of tea processing by-products in Guangxi.