Quantitative and qualitative changes in added phosphates in cod (Gadus morhua) during salting, storage and rehydration

Phosphate blend can be used in salted cod processing to improve yields, water holding capacity and appearance of the final product. However, added phosphates are gradually degraded during processing and storage, leading to changes in functional properties of phosphates. The objective of the study was to monitor the quantitative and qualitative changes in added phosphates in cod during salting, storage and rehydration using ion chromatography (IC) and spectrophotometric analysis. The phosphates diffused into the fish muscle during brining but the phosphate content (mg P2O5/g sample) decreased again as liquid drained away from the muscle in the following dry salting step. Changes during six months storage of the dry salted products were minor. Further losses were observed during rehydration where the phosphates were washed out to levels lower than in the raw material. The advantage of the IC method was the ability to separate and determine different soluble phosphate species in the fish muscle. The IC results showed that pyrophosphate (P2O7) and triphosphate (P3O10) were partly degraded into orthophosphate (PO4) during the storage period. Lower values were obtained for the total phosphate content by IC than with the spectrophotometric method, which explained by difference is sample preparation. ► Phosphates diffuse in during brining and diffuse out during dry salting. ► Most added and natural phosphates are washed out during rehydration. ► Pyro- and triphosphate are partly degraded into orthophosphate during storage. ► Ion chromatograph is capable to separate and determine different phosphate species. ► Total phosphate content is only obtained by spectrophotometric method.