Researcher Chalmers University of Technology Goeteborg, Sweden
Abstract: The pH-shift technique is an effective tool for extracting functional proteins from fish filleting co-products; however, challenges, such as lipid oxidation influenced by the presence of polyunsaturated fatty acids (PUFA) and hemoglobin (Hb) under critical pH conditions, have been noted. This oxidation impacts the quality of proteins by inducing off-flavors, color changes, and nutrient loss.
Our research introduces lingonberry pomace (LP), rich in antioxidants, as a novel solution to counter these challenges. Initial trials with a 30% (dw/dw) LP blend in herring co-products showed a marked reduction in lipid oxidation during protein extraction and ice storage but also led to decreased protein yields, increased base solution usage, and darkened protein isolates. Then, the additional level of LP was gradually reduced to 2.5%, hypothesizing that it would improve the extraction process and the quality of protein isolates. Our findings were positive: even with a 2.5% LP level, lipid oxidation was negligible in freshly produced isolates, and a dose-response relationship was observed during the entire 16 days of ice storage. The key antioxidant compounds in this process were investigated using an Hb-fortified washed fish muscle model. Cyanidin 3-O-galactoside (Cy3Gal, also known as 'ideain') and procyanidin A1 were determined as the key antioxidants. The lipid oxidation in the fish protein isolates correlated with the total phenolic, Cy3Gal, and procyanidin A1 contents. Most notably, the reduced LP amount mitigated the drawbacks seen in earlier experiments, resulting in lighter-colored isolates without affecting protein yield. Further optimization led us to identify a 10% LP additional level as ideal, striking a balance between antioxidative benefits, processing efficiency, and product quality.
Our study promotes a sustainable method in the food industry, using marine and agricultural by-products together. This new process enhances protein isolates' stability and quality and exemplifies industrial symbiosis, revolutionizing the use of food co-products.