Effect of natural antioxidants on protein and lipid oxidation in fish (Siganus sutor) processed in a locally fabricated hybrid windmill-solar tunnel dryer.

Abstract

The aim was to evaluate the drying characteristics, quality, safety, carbon footprint and physico-chemical properties of fresh and antioxidant-treated dried Siganus sutor fish fillets. An innovative hybrid windmill-solar tunnel dryer was designed and fabricated in Kenya to harness solar and wind energy, day and night and in damp weather conditions. The moisture content for both salted and unsalted Siganid fish reduced exponentially to 19.9 % over a 3-day drying period. The quality and yield of Siganid fish fillets after delayed icing for 0, 2 and 4 h that was determined using the Quality Index Method, was linearly related to storage time. Biochemical evaluation of solar dried fish, stored for up to 75 days, showed lowest levels of Peroxide Value (PV), Thiobarbituric Acid Reactive Substances (TBARS), Volatile -Total Basic Nitrogen (TVB-N), trimethylamine, pH and moisture in vacuum packaging, followed by polythene packs and highest levels in samples with no packaging. Microbial plate counts were significantly reduced after solar tunnel drying of the Siganids. Fish fillets were treated with synthetic antioxidant BHA (control) and extracts from water hyacinth, seaweeds and turmeric as sources of natural antioxidants. The efficacy of antioxidants to reduce lipid oxidation products PV and TBARS was in the order BHA>tumeric>seaweed>water hyacinth and significant (p<0.05). Small deformation rheology of stored (up to 90 days) solar dried fish fillets treated with natural antioxidants had lower G’ values compared to the control, reflecting desirable texture qualities. The thermodynamic properties (denaturation temperature (Tm) and heat enthalpy change (∆H) altered significantly only after 60 days storage. The carbon footprint was low because of low labour input, non-motorized fishing vessels and renewable energy-wind and solar used for drying. A descriptive generic Hazard Analysis Critical Control Point tool for solar dried fish was obtained for the first time. The above findings can enhance the processing and preservation of fish and influence fish quality and fisheries policies.