Sustainable strategies to obtain protein from brewery wastes and evaluation of film forming properties

Abstract

Sustainability studies and waste management have gained worldwide attention due to the decrement of resources. Factors such as environmental pollution, and increase in world population lead to the development of more efficient production methods. Thus, recycling of waste and by-products and producing high value-added products from these wastes become a must. Beer is a widely produced and consumed alcoholic beverage. Waste management in beer production is an important step for the industry since the amounts of waste generated are enormous. Considering the composition of the waste generated, most brewery waste products can be suitable for reuse in the food industry as a source of valuable food components, bioactives or food additives due to their low cost and nutritive value. This study aimed to utilize brewery wastes, malt sprout and malt dust, as value-added products. For this purpose, alkali extraction, enzyme pre-treatment and ultrasound-assisted extraction techniques were applied in order to obtain malt protein. Enzyme pre-treated extraction had the highest yield (0.55%) for both of the samples and among the other methods. However, protein contents of the enzyme pre-treated extracts were the lowest (32.40% and 43.03%). Moreover, the moisture contents were the highest among the other samples (15.69% and 13.62%). After malt protein extraction, biodegradable films composed of malt protein and agar (15:85, w:w) were obtained. Film forming solutions were compared in terms of their colour, pH, dry matter content, and transparency. Film forming solutions having enzyme-pretreated extracts had the lowest dry matter content (1.20% and 1.90%) while having the highest pH value (7.41 and 7.33). Biodegradable films were obtained after evaporation at 60°C for 24 hours. Enzyme-pretreated extracts showed a limited capability of film forming. Film properties of all extracts were investigated. Differential scanning calorimetry (DSC), water vapour transmission rate (WVTR) and water vapour permeability (WVP), colour, thickness, transmittance and opacity analysis were performed for the determination of physical properties. Moreover, moisture content and swelling behaviour analysis of biodegradable films were also conducted. Antimicrobial activities of the prepared films having alkali and ultrasound-assisted extracts were determined against gram negative bacteria Escherichia coli, gram negative bacteria and human pathogen Pseudomonas aeruginosa, gram-positive Staphylococcus aureus and yeast Candida albicans. Disc diffusion method was conducted for the antimicrobial analysis. There were no antifungal effect observed against C.albicans; whereas, no bacterial growth of E. coli and P. aeruginosa was observed under discs. Ultrasound-assisted extracts showed antibacterial activity against S. aureus. Inhibitory zone diameters were determined as 6 mm, including the discs. Total phenolic contents of the biodegradable films were determined according to Folin-Ciocalteu assay. There were no statistical significance observed between the film samples (p>0.05). In conclusion, this study proves that malt protein extracted from malt sprout and malt dust, with the addition of agar, can form functional biodegradable films successfully. Moreover, brewery wastes can be used as high value added products in the food industry.