Effect of Moisture Content of Made Tea on the Growth of Yeast and Mould
No Thumbnail Available
Date
2013
Journal Title
Journal ISSN
Volume Title
Publisher
Uva Wellassa University of Sri Lanka
Abstract
Moisture content is an important factor which determines the quality of made tea. During tea
processing even though the moisture content of tea is reduced to around 3% in the drying step,
further gain of moisture occurs during transportation, storage and blending operations due to the
hygroscopic nature of tea. The achievable level of moisture at the point of destination lies in the
range of 10% to 12%. The impact of moisture on the quality of tea affect in two ways. Moisture
brings about moisture related chemical changes in tea over period of time and high moisture
leads to microbial growth (Dougan et al., 1978). Yeast and mould are the major microorganisms
found in tea which affect the quality deterioration rather than bacteria, because yeast and mould
can be grown in low moisture foods comparing to bacteria. This study is to identify the effect of
moisture content on yeast and mould growth of black tea and to determine the critical limit of
moisture content.
Methodology
The current study was carried out at Microbiology Laboratory, Ceylon Tea Services PLC. Three
black tea grades were selected for the experiment based on their particle size. Tea grades were
Dust, BOP and OPA. Experiment I was conducted to determine the maximum absorbance of
moisture content by black tea and carried out at 70% RH and 27 C. Initial moisture contents of
each samples were analyzed. Study was continued for five weeks and moisture content analyzed
in weekly interval. Moisture content of tea was determined according to the ISO 1573.
Experiment II was conducted to determine the effect of moisture content and particle size of
black tea on yeast and mould growth. Aspergillus niger (ATCC 8739) and Saccharomyces spp
were used. Experiment was carried out at 55% RH and 25 C. Initially black tea samples were
oven dried to bring moisture content down to around 1% and to minimize microbial growth.
Then a moisture series were prepared from 6% to 14% for each 200 g of tea grade by adding
sterilized water and kept for stabilizing. Known amount of microbial inoculums were inoculated
to the pre prepared three tea samples and thoroughly mixed. These samples were kept for 24
hours to stabilize. Known quantity of contaminated tea samples were inoculated into each
prepared samples of all three grades and mixed thoroughly. Incubation was done at room
temperature. Initial moisture content and the yeast and mould counts were analyzed in the same
day. Yeast and mould counts were taken in weekly for one month duration by using the method
described in Sri Lanka Standard Institution (SLS 516 part 2). The data obtained in present study
was statistically analyzed with analysis of variance (ANOVA) using Minitab 16 statistical
package. Pair wise comparisons were done by turkey at 5% level of significance level.
Description
Keywords
Agriculture, Export Agriculture, Tea Industrials, Tea Technology, Crop Production