Selected metals and polyphenol content in Sri Lankan branded and loose black teas and their compliance with Sri Lankan standards and ISO standards

Abstract

Tea is a widely consumed beverage around the world and recent findings on health benefits have contributed to increased consumption. Due to the long history and reputation for producing high-quality tea, Ceylon tea is well-established in the world tea market. It is also an important part of the Sri Lankan economy. The current study aimed to evaluate some selected metals and total polyphenol levels in black teas available in the local market, to find the adherence to national and international standards. Branded and loose tea samples were randomly selected from the Sri Lankan market. Ten branded samples were used for the analysis of twenty-five metals using microwave digestion and Inductively Coupled Plasma– Mass Spectrometry (ICP-MS) (2 replicates from each brand). For polyphenol content, 15 branded and 15 loose tea samples were evaluated based on ISO 14502-1:2005- Determination of characteristics of green and black tea (2 replicates from each brand). The results of metal analysis were statistically analyzed with basic descriptive analysis. One–way analysis of variance (ANOVA) test at p = 0.05 followed by Tukey’s pairwise comparison was done for total polyphenol analysis. Both were carried out using the Minitab 22 software package. Results revealed that Ag, As, Be, Cd, Cs, Ga, Li, Se, Tl, U, and V were present within 0.01-1.00 mg/kg, while Cr, Co, Ni, Pb, and Sr ranged from 1.00 to 10.00 mg/kg. Cu, Zn, Rb, and Ba were found in the 10.0–100.0 mg/kg range. Mn and Fe were detected below 1000.0 mg/kg, and Mg, K, and Al exceeded 1000.0 mg/kg. Total polyphenol content varied from 14.20% to 27.67%. The findings revealed that the concentration of Cr in all samples was above the maximum limits (1.00 mg/kg) set by the Sri Lanka Tea Board whereas, as (samples 2, 6, and 10 only) and Pb (samples 1 and 4 only) were above the maximum limit in some samples (As max limit - 0.05 mg/kg and Pb max limit - 2 mg/kg). Additionally, all samples exceeded the recommended minimum polyphenol content. These findings emphasize the general compliance with safety standards for metals but highlight the need for stricter monitoring, particularly for Cr levels since it reached 15.02 mg/kg mean value, significantly exceeding the recommended maximum of 1 mg/kg. Further studies with a larger sample size are recommended to validate these results and guarantee continued adherence of Ceylon tea to quality standards.