Production of gelatin from Bigeye tuna (Thunnus obesus) skin and characterisation of gelatin properties: An alternative to minimise fish waste in tuna fish processing industries in Sri Lanka

Abstract

Fish skin that can be used to produce fish gelatin is a major by-product of fishery and aquaculture industries. Gelatin is most commonly used ingredient in food processing industry especially in dairy products. Objective of this study was adding value to the fish skin by developing a suitable processing method for extracting gelatin. Bigeye tuna (Thunnus obesus) was selected for production of gelatin due to its high commercial value and availability in the local market. Six treatments of Bigeye tuna skin samples were subjected to concentration series of alkaline pretreatments ((0.1% for 24 h (T1), 0.2% for 24 h (T2), 0.3% for 24 h (T3), 0.1% for 36 h (T4), 0.2% for 36 h (T5), 0.3% for 36 h (T6) followed by different acid extractions (0.1% for 24 h (T1), 0.2% for 24 h (T2), 0.3% for 24 h (T3), 0.1% for 36 h (T4), 0.2% for 36 h (T5), 0.3% for 36 h (T6)) under various soaking periods. Final products were analysed for different physico-chemical parameters such as yield, gel strength, melting point, color, odour, pH and proximate composition to assess the best sample. The highest gelatin extraction efficiency was recorded in the T1 sample (19.67 ±0.42) while the lowest gel yield was recorded in T6 sample (16.03±0.33). Gel strength of T1 fish gelatin sample (260 Bloom) was within the standard range; while protein (82.1%) and lipid (0.97%) contents of T1 gelatin product were within satisfactory nutritional level. The lowest melting points were recorded for all the treated samples compared to the commercial Bovine gelatin product. Lower melting point of the products signifies faster dissolution, which is a highly beneficial character in food processing industry. Bigeye tuna fish skin treated with 0.1% NaOH and H2SO4 and a soaking time of 48 h at 60 °C hot water extraction for 5 h was selected as the most suitable method for gelatin production, based on the physico-chemical properties of the final products. Bigeye tuna fish skin marks a novel approach in value addition sector of by-products in Sri Lanka.