The application of starter cultures in the fermentation of pito towards industrial production

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February, 2018
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Pito is a popular traditional sour sorghum beer widely consumed in Ghana and Nigeria. It is brewed mostly by women at an artisanal level but has huge economic potential for industrial production and commercialization. The brewing methods are not standardized and vary according to the ethnic group of the processor or the tribal area where it is brewed. The brewing processes are tedious and uncontrolled resulting in inconsistent product quality. There are two fermentation steps involved in the pito brewing process; an initial spontaneous lactic acid fermentation (souring) by lactic acid bacteria which come with the sorghum grains from the field and from the brewing environment followed by an inoculated alcoholic fermentation. The product is drunk while still fermenting and has a limited shelf life of 2 to 3 days. In this study, the fermentation performance of two commercial lactic acid bacteria, L. delbrueckii and L. amylolyticus and two commercial brewers’ yeast strains of S. cerevisiae, Anchor Brewers’ yeast and Munich Wheat Beer yeast as single strain starter cultures in pito wort were investigated using the Response Surface Methodology. The optimum fermentation conditions for their application in industrial production of pito were determined to be 12 h at 45°C for L. delbrueckii, 19 h at 45°C for L. amylolyticus, 71.6 h at 22.6°C for Munich Wheat Beer Yeast and 71.5 h for Anchor Brewer’s Yeast at 24°C. Both lactic acid bacteria and and yeasts were found capable of achieving the desired end product characteristics of pito. L. delbrueckii and Anchor Sorghum Beer yeast were however selected preferentially on account of the economic advantages of their use over the other two for industrial production. The fermentation profiles of the experimental pito brew fermented with pure single strain starter cultures of L. delbrueckii and Anchor Brewers’ yeast using the derived optimal fermentation conditions was evaluated alongside those of a pito brew fermented using the traditional process. Lactic acid formation, pH change and extract utilization with time were monitored. Both brews followed the general lactic acid and alcoholic fermentation profiles but differences were observed which were on account of the intrinsic specific characteristics and capabilities of the microorganism to utilize the wort substrates and convert them into the fermentation products. Similar levels of sourness as indicated by pH and lactic acid content were achieved in both brews. The starter culture brew had a lower apparent degree of fermentation and lower alcohol level than the traditionally fermented brew. The product quality from the two optimized fermentation processes was also evaluated based on physicochemical analysis, shelf life, volatile fermentation by-products and consumer acceptance sensory evaluation. The pito brewed with the starter cultures compared favourably with pito brewed with the traditional process. Both had physicochemical analytical values within the range established for traditional pito. There was an improvement of shelf life of 2 days in pito brewed with pure single strain starter cultures of L. delbrueckii and Anchor Brewer’s Yeast over traditionally brewed pito. The total level of volatile aroma compounds formed in the pito brewed with the starter cultures was higher (353.13 mg/l) than in the pito brewed with the traditional process (229.04 mg/l). The traditionally brewed pito was characterized by higher levels of ethyl acetate and iso-amylalcohol while the pure single strain culture brew was characterized by higher levels of n-propanol, i-butanol and acetaldehyde. In the consumer acceptance sensory evaluation, there was no significant difference between the two pito products for overall liking and taste liking. There was however a statistical significant difference between them for aroma liking. The fermentation process became predictable and controlled through the application of starter cultures and provided a basis for standardization of the fermentation process towards consistency in product quality and industrial production.  
A thesis submitted to the Department of Food Science and Technology, College of Science in partial fulfilment of the requirements for the degree of Doctor of Philosophy.