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

Abstract

BackgroundDrinking 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.ResultsThis 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.ConclusionsResults obtained demonstrated the need to develop targeted regulations for the safety of herbal teas.

Risk assessment of ochratoxin A in food

“…Transfer rates for green and black teas were reported by Carraturo et al. (), with values in the range from 33% to 55%.…”

Studying the contamination of tea and herbal infu-sions with myсotoxins (Message 2)

“…Однако результаты исследований чая из разных регионов мира подтверждают возможность накопления опасных МТ -FB, OTA, AFL, T-2, ZEA на высоких детектируемых уровнях [11]. Например, в образцах черного и зеленого чая из розничных магазинов в Италии ОТА обнаруживался в 82 %, а в 50 % случаев в количестве 7-21 мкг/кг (на фоне доминирования A. niger и A. tubingensis), что превышало уровень, установленный для других пищевых продуктов, объемы потребления которых сравнимы с чаем, в частности для кофе -5 мкг/кг [33]. Исследования в Швейцарии показали, что черные аспергиллы были одной из наиболее распространенной групп плесеней в 22 образцах травяных чаев, а выделенные штаммы A. niger и A. awamori в условиях in vitro продуцировали фумонизины [34].…”

Studying the contamination of tea and herbal infusions with mold fungi as potential mykotoxin producers: The first step to risk assessment (Message 1)

“…Research on microbe contamination that can be found in foreign literature primarily focuses on teas that underwent deep fermentation, for example, Pu'er teas; but such teas have rather insignificant share on the market, and as for mass consumption teas, there is very little research on them or such research is fragmentary [22][23][24]. The report on the results of the 23rd session held by the FAO Intergovernmental Group (IGG) on Tea in Hangzhou, China, on May 17-20, 2018 which was presented to the FAO Committee on Commodity Problems highlighted there was a necessity to promote scientific research in the sphere of natural contaminants and to reveal relationships that caused their occurrence in tea [25].…”