Lactic acid and propionic acid fermentations of fish hydrolyzates

Abstract

Fish waste or gurry comprises up to 60% of the original weight of fish after fillets are removed. The entrails of certain fish species such as haddock, cod and flounder are usually removed and discarded at sea so that the gurry comprises of heads, tails and skeletons. Species of flat fish, which are landed intact, often yield gurry composed, in part, of about 20% entrails. At present, processors in North America have more fish waste than can be utilized by traditional means such as conversion to fishmeal for animal feeds. Disposal at sea along US coastal zones is presently restricted (Clean Water Act, 1991) which has resulted in a disposal problem for the fish processing industry. In addition, fish farms that also perform processing have recently developed an interest in converting gurry to a product of nutritional value for incorporation into fish feeds to reduce feed costs and to eliminate the problem of waste disposal. One of the more expedient methods for the conversion of gurry to a microbially stable product consists first of grinding, followed by proteolytic hydrolysis and removal of the bone chips by screening. Preservation of the resulting hydrolysates is most readily achieved by acidification. If a mineral acid such as sulfuric or phosphoric is used alone the pH must be reduced to 2.0 to achieve long-term preservation (Wignall and Tatterson, 1976). Reduction of the pH to 2.0 with sulfuric acid involves some level of hazard and usually requires neutralization for subsequent use as a feed or fertilizer.