Preservation of fish by embedment in Sphagnum moss, peat or holocellulose: experimental proof of the oxopolysaccharidic nature of the preservative substance and of its antimicrobial and tanning action

• Published in: Innovative food science & emerging technologies 2001-03, Vol.2 (1), p.63-74
• Main Authors: Børsheim, K.Y, Christensen, B.E, Painter, T.J
• Format: Article
• Language: English
• Subjects: Non-cytotoxic antimicrobials; Oxopolysaccharidic preservatives; Sphagnum moss and peat; Storage life of fish; Tanning
• ISSN: 1466-8564; 1878-5522
• DOI: 10.1016/S1466-8564(00)00029-1

Strips of salmon ( Salmo salar) skin or whole zebra fish ( Brachydanio rerio) were preserved for many weeks by embedment in untreated Sphagnum palustre moss (A), peat derived mainly from Sphagnum mosses (B), acetone-extracted moss (C), or the chlorite holocellulose of the moss (D). Preservation occurred in the presence of oxygen at 20–23°C, and between pH 3.4 and 5.1. Product D, which was a pure, insoluble, white polysaccharide, performed as well or better than the other materials. It contained ∼0.5 mmol g −1 of highly reactive carbonyl groups, and when these were removed by borohydride reduction or condensation with ammonia, the preservative property was lost. Preservation was invariably accompanied by a browning of the dermis and a yellowing of the scales, and was attributed to a Maillard reaction, since neither occurred when the carbonyl groups were removed. A water-soluble fragment (‘sphagnan’) of D, containing 1.0 mmol g −1 of carbonyl groups, had an astringent taste in aqueous solution and produced effects similar to those brought about by embedment in A, B, C or D, albeit more rapidly. Films of mackerel ( Scomber scombrus) skin became brown and completely bio-resistant after repeated immersion in aqueous (3% w/v) sphagnan with intermittent drying, whereas similar treatment with borohydride-reduced sphagnan had no effect. Differential thermal analysis (DSC) of the sphagnan-treated skin gave results consistent with tanning by covalent cross-linking. Hence, the chemical and visible color changes associated with embedment in the moss products or immersion in aqueous sphagnan resembled those brought about by exposure to wood smoke. Filleted fish muscle cannot, however, be preserved in these ways because soluble protein diffuses out from the muscle too quickly, and neutralizes the carbonyl groups selectively.