Introduction:
Aquaculture is expected to be the fastest growing food sector this century. Small pelagic fish such as herring, Clupea harengus, are currently used in fishmeal, a feed constituent that is used as the main marine source of protein in aqua feeds (FAO 2012). In Sweden, work is being done to establish a knowledge base for the development of sustainable marine aquaculture, focusing on two species: Spotted wolffish, Anarhichas minor and European lobster, Hommarus gammarus. One of the aims is to develop new feeds for the two species during larval and juvenile on-growth stages. Although both wolffish and lobster larvae can be given formulated feeds at early weaning, previous studies have shown that live feeds are still superior regarding larval survival, growth and development. Currently, formulated feeds are highly dependent on raw materials from wild fisheries and are costly to produce. The development of diets composed from sustainable materials with suitable texture that increases survival and quality is an important challenge. In this study, pH-shift processing was used to isolate protein concentrates from herring by-products, in order to investigate the potential incorporation of these concerntrates as an alternative protein source in aqua feeds.
Material and methods:
Herring by-products were sorted into back bones, heads and guts which thereafter, in different combinations, were subjected to pH-shift processing. For each raw material combination, the acidic version of the pH-shift process was compared with the alkaline process version to identify protein yield as well as potential functional and chemical differences in protein isolates, and how these could affect the potential of isolates as a feed ingrediant. Among studied factors were mineral content (e.g. calcium), fatty acid pattern, floatability and palatability.
Results and discussion:
Initial results show that the highest protein yields were given with heads and spines, and, also that the alkaline version of the pH-shift process generally gave higher yields than the acid version. Functional and chemical differences were found in isolates from different treatments and this will have consequences on future feed incorporation. For example, the acid process version generated higher calcium levels in the protein isolates than the alkaline version, something which is particularly important in lobster feeds. Also, preliminary feeding trials indicate satisfactory floatability and palatability of some isolates for both lobster and wolffish.