Comparative assessment of the quality of commercial black and green tea using microbiology analyses

Drinking tea constitutes a tradition which is deeply rooted in the culture of several countries. Moreover, in recent years, tea consumption is growing all over the world. Improper herbal tea storage (long periods, humid environments) represents a relevant health hazard for consumers because of the growth of bacteria and molds.

This study analyzed 32 samples of commercially available black and green teas - purchased from southern Italy markets and online-shops - and the monitoring of microbiological quality of the tea bag content was performed. Evaluations were conducted with the aim of characterizing pathogens indicated by the European and American guidelines (total bacterial count, fungi and Escherichia coli) and on the research of Pseudomonas spp. and Clostridium perfringens. The presence of ochratoxin A in tea matrix-leaves and infusions was further assessed, using a validated and accredited HPLC-FLD method. Microbial loads, for over 80% samples, ranged from 1.0 × 10² to 2.8 × 10⁵ CFU/g tea: most of identified microorganisms were classified as Bacillaceae. The utilization of rapid detection and identification methods (PCR and sequencing), allowed the characterization of strains of Pseudomonas psychrotolerans, Staphylococcus warneri, Pantoea gaviniae and the isolation of one strain of Clostridium perfringens, whose ability to produce toxins can result in harmful outcomes for consumers. Fungi were isolated from 70% samples: the most prevalent molds were Aspergillus niger strains, followed by Aspergillus tubingensis. Ochratoxin A was detected in 22 of 32 tea solid samples investigated: concentrations resulted over the indicated limits for food products for 50% samples.

Results obtained demonstrated the need to develop targeted regulations for the safety of herbal teas.