Abstract
The valorisation of agro-industrial by-products and the search for alternative sources of protein to produce peptides are of great importance. This work proposes the development of a process enabling the production of fractions rich in bioactive peptides from the by-product from brewing called “spent brewer’s yeast”. The motivation of this subject of research is based on the increasing demand to reuse agro-industrial by-products such as spent yeasts and on the production bioactive peptides using clean and efficient technologies. Spent brewer’s yeast slurry was collected after maturation and was submitted to cell wall disruption methods. Autolysis, glass bead milling and enzymatic hydrolysis using Brauzyn® were compared, and enzymatic hydrolysis presented a higher protein recovery and improved antioxidant activity. A simultaneous cell wall disruption and peptide production was proposed using a mixture design employing Brauzyn®, Protamex™ and Alcalase™ (pH 7.0, 50 °C, 2000 U g-1 for 2 h), being able to reduce steps during the processing of spent brewer’s yeast. Protein hydrolysates characteristics varied with the proportion of enzymes used, changing the extent of the release of hydrophobic residues, the degree of hydrolysis, antioxidant properties, browning extent and yield of solids and peptides. Membrane separation of the complex protein hydrolysate was studied firstly using polymeric membranes of regenerated cellulose and polyethersulfone and then in ceramic ones. A smaller susceptibility to fouling was observed for more hydrophilic surfaces, and at higher feed pH values. Results confirmed that the main foulants during ultrafiltration of spent brewer’s yeast protein hydrolysate are peptides that adsorb easily onto the membrane surface. Fractionation using ceramic membranes of 50-1 kg mol-1 of molecular weight cut-off was able to separate multi-active peptides from total sugars and ribonucleic acids. Spent brewer’s yeast peptides presented antioxidant activity by different mechanisms, in vitro anti-diabetic activity (inhibition of α-glucosidase and α-amylase) and anti-Alzheimer activity (inhibition of acetylcholinesterase). Sequential processing of spent brewer’s yeast using enzymatic and membrane separation technologies was able to recover peptides with multiple bioactivities from an underused by-product from brewing. Fractions produced represent an alternative as peptide-rich ingredients in the food and pharmaceutical industries.