Studies on indigenous preparation practices, effects of ingredients, fermentation time and pasteurization on quality and shelf stability of tella

Abstract

Tella is one of the Ethiopian traditional fermented beverages prepared from different malted and unmalted grains. It is brewed from local hops (Rhamnus prinioid), malts of barley, maize, wheat, sorghum, finger millet and even from teff in some parts of the country. Tella being the most consumed indigenous beverage in Ethiopia it’s the least investigated in terms of effects of ingredients and shelf stability. Therefore it is important to study effect of different ingredient compositions on physicochemical properties and pasteurization on the shelf stability of tella in order to improve its keeping quality. This study aimed at assessing the traditional processing of tella and improving its shelf life stability. The study was carried out in three phases. During phase one, a survey was conducted in five purposively selected kebele’s of Jimma town: Bosa addis, Bosa kito, Merkato menahariya, Merkato mentina and Becho bore to assess the indigenous knowledge regarding its processing. A semi structured questionnaire was used to gather relevant information and SPSS (version 20) was used to analyze the survey data. Phase two evaluated the effect of malt combination, adjunct combination and fermentation duration on physicochemical properties of tella. It was a three factorial having each factors with three levels in three replication laid out in RCBD design. During phase three, a time-temperature study was carried out and two pasteurization temperatures, 15.86 PU at 60°C and 7.79 PU at 65°C were selected. The effect of pasteurization on the physicochemical properties, microbial and sensory qualities of tella were studied. SAS (version 9.2) was used to analyze data from phase 2 and 3. The survey result showed that 100% of the respondents were women who were in the age group of 31-40 (30%) and the majority (51.5%) had been in tella selling business for more than 10 years. Physicochemical properties of tella were significantly (P<0.05) affected by malt, adjunct combination and fermentation time. The changes in pH, TSS, TA, alcohol content of pasteurized tella samples were much slower during the storage period. Result of the sensory evaluation showed that there was no significant difference between unpasteurized and pasteurized samples at 60°C in terms flavor, aroma, mouth feel and overall acceptability. Samples pasteurized at 65°C scored the lowest mean for flavor, taste, color, mouth feel and over all acceptability. Pasteurization had a significant effect on microbial load (P<0.05). Unpasteurized samples had the highest microbial growth during the storage period. While pasteurized at 60°C and 65°C had no microbial growth on day one and maintained a very low microbial growth during the storage period. The microbial load of pasteurized sample was initially zero which later showed a small change during storage. Control samples had higher microbial count compared to pasteurized samples. Pasteurization extended shelf stability of tella for 45 days without a significant change in terms of physicochemical and microbial changes. Effect of pasteurization at higher temperature needs further studies.