ARS | Publication request: PROPERTIES OF STICKWATER FROM FISH PROCESSING BYPRODUCTS

Submitted to: Journal of Aquatic Food Product Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 12, 2004
Publication Date: September 1, 2005
Citation: Bechtel, P.J. 2005. Properties of stickwater from fish processing byproducts. Journal of Aquatic Food Product Technology. Vol. 14(2):25-38.

Interpretive Summary: Fishmeal is made by first grinding whole fish or fish processing byproducts and then heating to approximately 95 °C and then separating the solids using a screw press or decanter centrifuge. The press cake is dried for fish meal and the liquid phase (after removal of the oil) is referred to as stickwater. The stickwater fraction is usually 50-70% of the initial weight of the raw material, and often contains approximately 5-10% solids. Stickwater protein from pollock/cod and salmon byproducts was characterized. The protein was very soluble and contained large amounts soluble connective tissue protein. Stickwater had protein was very digestible but the estimated protein efficiency ratio was low at 1.6 to1.8. It is possible to make an ingredient out of stickwater protein from fish processing byproducts, which has a number of interesting chemical and functional properties.

Technical Abstract: The objective of this study was to determine selected chemical and nutritional properties of stickwater protein obtained from the processing of fish byproducts. Raw materials for three stickwater samples were pollock and cod fish processing byproducts and one was salmon processing byproducts. Stickwater samples were approximately 6% protein, and after freeze dying samples contained 70.5 to 86.2% protein. The pH of the stickwater samples ranged from 6.5 to 7.0. Samples had high levels of proline and hydroxyproline and the calculated connective tissue protein as a percent of total protein was 22.8 to 25.7. Percent soluble protein ranged from 54 to 70% at 30 'C. Major proteins bands observed using SDS gel electrophoresis had molecular weights of 198,000, 120,000 and 39,000. All samples had protein digestibility in excess of 95% and calculated rat protein efficiency ratios from amino acid analysis data ranged from 1.6 to1.8.