Lingonberry pomace as a clean label processing aid when producing food protein ingredients from fish co-products

Abstract: The pH-shift process is a promising tool to recover functional proteins from fish filleting co-products. However, when levels of heme-proteins are high, lipid oxidation can be a problem that negatively affects the protein ingredient quality. We recently reported on a clean label and sustainable cross-processing concept in which 30% (per dry weight) lingonberry pomace (LP) added at the start of the pH-shift-process stabilized herring co-product-derived protein ingredients from lipid oxidation. However, the phenolics and organic acids of the LP mitigated protein solubilization and increased the consumption of acid and base. To counteract these problems, and rather use the LP both as an antioxidant and precipitation agent, LP (2.5-30%) was here added in the precipitation step of the pH-shift process instead of at the start. Protein yield as well as lipid-oxidative stability, composition, visual appearance, and sensorial attributes of the protein ingredients were then studied.

Results revealed that 5-30% LP reduced HCl consumption by 13-61% and 19-79% when precipitating proteins at pH 5.5 and pH 6.5, respectively. Higher LP% indeed decreased protein content and lightness of protein ingredients but raised lipid content. No lipid oxidation-derived volatiles developed during 21 days of ice storage of protein isolates precipitated with 10% and 30% LP. This stabilization was even more profound than adding LP at the start of the process. Further, the sweetness and fruity flavor of ingredients were enhanced when adding LP during the precipitation step compared to at the process start. In summary, LP was identified as a promising dual-functioning processing aid when subjecting herring co-products to alkaline pH-shift processing. The concept creates a basis for new types of industrial symbiosis where side streams from different food industries act synergistically in the creation of new products.