The microbiology of instant tea

Abstract

The microbial ecology of an instant tea line was studied using samples from different points of the line. Only lactic acid bacteria were found at certain manufacturing stages. The main contaminant was identified as Lactobacillus plantarum. As no other bacteria were found in this line, lactic acid bacteria may be considered as quality ‘indicators’ and their determination might be a means to monitor Good Manufacturing Practices (GMP). In addition, the total tea solids (TS) concentration that inhibits the growth of certain isolated L. plantarum strains was determined on the instant tea line. A TS concentration of 60% inhibited these organisms during 48 h. The same TS concentration did not inhibit the growth of a non-identified cluster of Lactobacilli isolated from the same line. The bacteriostatic effects of pure theophylline and pure theobromine on the growth of L. plantarum were also examined. No bacteriostatic effect in the presence of either compound was observed at normal concentration or at concentrations higher than those calculated to be normally present in tea lines. The standard aroma profile of an instant tea solution was modified as a result of inoculation with a wild strain of L. plantarum. This implies that heavy contamination and fermentation by such organisms might result in products with altered aroma profiles that are unacceptable to the consumer. It should be noted that altered tea aroma might eventually be used as an indicator of microbial build-up by analysing certain of the altered aroma components. Further work is needed to investigate this possibility. Challenge tests with known pathogens and spoilage organisms revealed that, although pathogens were unable to multiply in instant tea solutions, spoilage organisms could grow or survive and thus might pose problems.