Characterization of Bacterial and Fungal Contaminants Of Black Cut, Tear & Curl and Green Teas (Camellia Sinensis) From Selected Factories in Kenya.

Abstract

Tea (Camellia sinensis) is considered a low risk food in terms of microbial contamination because of the way it is processed, packaged and consumed. It is the most popular and widely consumed beverage worldwide, only after water. Its popularity is mainly due to its refreshing taste, attractive aroma, and potential health benefits such as antioxidant activity, ability to improve oral health, antibacterial, antifungal, and antiviral properties. However, there are possibilities of microbial contamination along the value chain and for this reason care should be taken to eliminate them. The primary objective was to develop comprehensive microbial quality control strategies aimed at minimizing cross-contamination risks during and after tea processing. By identifying and quantifying microbial populations at each processing stage, this study aimed to contribute valuable insights that could inform the implementation of effective hygiene protocols and ensure the production of microbiologically safe teas for consumers. This study focused on both cut, tear, and curl (CTC) and green orthodox tea processing steps. Key objectives included profiling microbes along the steps, evaluating microbial quality in black CTC teas per KS EAS 65:2018, identifying heat-resistant microbes post-brewing and assessing aflatoxin levels. Microbial assays encompassed total plate counts for yeast and moulds, Escherichia coli, Salmonella spp. and Staphylococcus aureus, detection of heat-resistant microbes and aflatoxin-producing fungi. Made tea samples consisting of primary and secondary tea grades from the drier mouth and bins of 14 pre-selected Kenya Tea Development Agency (KTDA) tea factories from the East and West of Rift Valley tea growing areas were collected. In-process teas from a private factory and a multinational company were also assayed up to the finished product stage. The microbial quality status of teas were assayed as stipulated in Kenyan Black Tea Standard and ISO protocols and checked for conformance. Heat-resistant microorganisms in tea which survived brewing in hot or boiling water of 90-100 °C were assayed. Bacteria and fungi were isolated using Nutrient Agar (NA) and Potato Dextrose Agar (PDA). Aflatoxin levels were quantified using High Performance Liquid Chromatography (HPLC) following Thin Layer Chromatography (TLC) screening. The key findings of this research study included the isolation of Escherichia coli and Staphylococcus spp. from tea samples, while Salmonella spp. was absent in the made tea samples. This research study also revealed the existence of heat-resistant bacteria in the black CTC tea and this causes great concern as they may pose a health risk. Among them were some heat-resistant E. coli and heat-resistant staphylococcus aureus. Stored black teas showed acceptable levels of yeast and moulds, although contamination was observed. This research study addressed the gap in existing research regarding the microbial status of teas across various stages of processing in Kenyan tea factories, encompassing leaf reception, withering, maceration, oxidation, drying, sorting and grading, packaging and storage. Prior to this investigation, no documented research had systematically examined microbial contamination throughout these critical processing stages. Some teas did not meet microbial quality standards, highlighting the need for improved handling practices in certain factories. Importantly, teas from selected KTDA factories were generally free from aflatoxins, underscoring satisfactory control measures in place for mycotoxin management. This study also identified critical control points in tea processing to enhance microbial safety and recommended operational procedures for processing, sorting, packaging, storage and brewing. The findings confirm the microbial safety of processed tea for human consumption, providing insights into the diversity and quantity of microbes identified.