Title: Evaluation of suitable chemical methods for seafood products in Mozambique

Evaluation of suitable chemical methods for seafood products were investigated with respect to their accuracy and suitability for determination of additive in seafood products, freshness, nutritional value and scombroid poisoning in fish in Mozambique. Methods were tested using different fish species and deep shrimp at various freshness stages. The samples were from Iceland and were kept in insulated plastic boxes and in the most aseptic manner, some of them for subsequent microbiological, sensorial and chemical analyses. The methods selected were simple, rapid and inexpensive. Volhard titration and Mohr methods were used for salt determination and enzymatic method for sulphite determination. The enzymatic method for sulphite determination was based on the oxidation of sulphite ion to sulphate by oxygen in the presence of sulphite oxidise. Quantitative total volatile basic nitrogen (TVBN) and trimethylamine (TMA) methods were performed. For the TMA the procedure included a deproteinisation of primary and secondary amine using formaldehyde at alkaline pH and finally steam distillation of TMA. TVB and TMA were also performed using Flow Injection Gas Diffusion (FIGD) methodology. Due to unsteady baseline on the chart recorder the TMA procedure needed more time than TVB. The TVB could however be determined successfully. Good correlation was found between following methods: MgO, TCA-extract steam distillation with FIGD for TVB determination and FIGD with Picric acid for TMA determination. Kjeldahl and fluorometric methods were used for protein and histamine determination respectively. The assay of histamine consisted of histamine extraction with methanol, purified by cation-exchange resin and determination by photoflurometer. All analyses were performed with standardised solutions and reagents of purified grade. For each determination different chemical methods were used and the results were compared. It was concluded that the Volhard, Mohr, enzymatic, TCA-extract steam distillation, FIGD and MgO methods were suitable for and applicable to present Mozambican conditions.