Meyve Suyu Endüstrisi Atıklarından Alternatif Protein Üretimi

Abstract

As the global population continues to expand, plant-based and animal protein sources are unable to adequately meet the growing demand for food due to their significant energy, water, and land requirements and their unsustainable production methods. Therefore, there is a need for alternative protein sources to address the potential future protein shortages. To prevent future protein shortages, products with low raw material costs and sustainable production principles should be developed. Microbial proteins are proteins produced by purifying and drying the biomass obtained by incubating of pure or mixed cultures of various microorganisms such as bacteria, algae, and fungi in a specific medium which is prepared by using raw materials or industrial wastes. The use of food industry wastes as substrates for microbial protein production enables the transformation of low-value raw materials into high-value end products, thus ending the dependence of economic growth on resource consumption.

In this context, the aim of this study was to produce microbial protein from fruit juice industry waste using Saccharomyces cerevisiae yeast. In the first stage of the study, 18 strains of S. cerevisiae from the culture collection of the FoodOmics Laboratory of Hacettepe University Food Engineering Department (HUF) were revived, their purities were checked and their identifications were confirmed. Subsequently, a fundamental cell growth profile was established by working with S. cerevisiae ATCC 9763, which is selected as the control strain, in YPD Broth medium to monitor and interpret cell growth during fermentations to be carried out within the scope of the study. The growth profiles of cells, protein concentrations, and biomass yields of local strains which have been previously characterized for their technological properties and commercial S. cerevisiae strains were determined in white grape juice medium. Based on the results obtained, local strains coded HUF16M2K10004 and HUF16M3G11088, as well as the control strain coded 9763, were selected for further study.

Within the scope of the study model media formulations were developed for microbial protein production using fruit pomace. To achieve this, two different nutrient media, Basal I and Basal II, were developed by modifying the composition of the Basal medium commonly used to support S. cerevisiae growth and microbial protein production. Fermentations were carried out with the control strain S. cerevisiae ATCC 9763 in these media to monitor physicochemical (pH and protein content) and biological parameters (cell concentration and biomass yield). Based on the results obtained, the composition of Basal I medium was selected as the basic formulation supportive of S. cerevisiae growth and microbial protein production. Subsequently, compositional analyses of fruit pomaces (moisture, ash, crude fiber, reducing sugars, and protein) were performed to evaluate their suitability for microbial protein production in the bioprocess. It was observed that pomegranate seeds, pomegranate peel, apricot, apple, pear, and peach fruit pomaces were outstanding this regard. Based on the sugar profiles and harvest times of the pomaces, four different nutrient medium formulations were created as apple-pear (%50-50 w/w), apricot-strawberry (%70-30 w/w), peach (%100 w/w), and pomegranate peel-pomegranate seed (%50-50 w/w) fruit pomaces.

Fermentations were carried out at 28°C for 72 hours with local strains coded HUF16M2K10004 and HUF16M3G11088, as well as the control strain coded 9763, in four different nutrient media formulated using fruit pomaces. During fermentation, physicochemical (pH and protein content) and biological parameters (cell concentration and biomass yield) were monitored. According to the results obtained, the pomegranate peel-pomegranate seed (%50-50 w/w) nutrient medium stood out as a substrate for microbial protein production due to its high biomass yield (25,51-33,14 mg/mL) and protein content (19,20-23,51 %w/w). Furthermore, the local strain HUF16M3G11088 exhibited high biomass yield and protein production capacity in this nutrient medium.

In the final stage of the study, advanced analyses were performed on lyophilized dry powder form of microbial protein produced with pomegranate peel-pomegranate seed nutrient medium and the local strain HUF16M3G11088, which showed the highest protein and biomass production in this medium. These analyses included dry matter and moisture content analysis, primary metabolite analysis, nucleic acid analysis and life cycle assessment (LCA). The results indicated that the produced microbial protein contained metabolites with positive effects on metabolism and physiology in the human body, had nucleic acid concentrations within acceptable limits for human consumption, and the production process had a lower carbon footprint compared to traditional methods of managing fruit juice industry waste.