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Received: July 29, 2015
Accepted: December 9, 2016
Summary
This study evaluated the use of three solid brewery wastes: brewer's spent grain, hot trub and residual brewer's yeast, as alternative media for the cultivation of lactic acid bacteria to evaluate their potential for proteolytic enzyme production. Initially, a mixture experimental design was used to evaluate the effect of each residue, as well as different mixtures (with the protein content set at 4 %) in the enzyme production. At predetermined intervals, the solid and liquid fractions were separated and the extracellular proteolytic activity was determined. After selecting the best experimental conditions, a second experiment, factorial experimental design, was developed in order to evaluate the protein content in the media (1 to 7 %) and the addition of fermentable sugar (glucose, 1 to 7 %). Among the wastes, residual yeast showed the highest potential for the production of extracellular enzymes, generating a proteolytic extract with 2.6 U/mL in 3 h. However, due to the low content of the fermentable sugars in the medium, the addition of glucose also had a positive effect, increasing the proteolytic activity to 4.9 U/mL. The best experimental conditions of each experimental design were reproduced for comparison, and the enzyme content was separated by ethanol precipitation. The best medium produced a precipitated protein with proteolytic activity of 145.5 U/g.
Key words: brewery waste, waste reuse, lactic fermentation, proteolytic enzymes
(ProQuest: ... denotes formulae omitted.)
Introduction
Beer is the most consumed alcoholic beverage in the world. During the beer production, four solid wastes are generated: the brewer's spent grain (derived from the grain processing), hot trub (protein coagulation that occurs during the boiling of the wort), residual brewer's yeast (microbial fermentative activity) and the diatomaceous earth (result of the beer clarification process) (1).
The world beer market is characterised by the production on large scale, resulting in the generation of significant amounts of these wastes. It is estimated that for every 100 litres of beer produced, 14 to 20 kg of brewer's spent grain (2), 0.2-0.4 kg of hot trub (3), and 1.5-3 kg of residual brewer's yeast are generated (1). Considering only the three largest producers (China, USA and Brazil), the world production of beer reaches almost 84 billion litres per year,...