Colour changes in thawed Tuna tretated with vegetable extracts vacuum packaged and stored at refrigeration temperature

Tuna fish is one of the largest selling fishery products. Naturally fresh tuna has a red pigmentation but over time pigmentation turns brown depending to oxidation process. Nitrates and nitrites are used in foods as antimicrobials but also because their property to enhance color [1]. Use of these additives is not authorised in unprocessed fishery products; however food operators use vegetable extracts containing nitrates and nitrites to enhance tuna’s colour. This treatment is not allowed because masks the real freshness of the fish; so public health issues have to be considered regarding potential high level of histamine and formation of carcinogenic nitrosamines during cooking. Aim of the work was to evaluate the colour changes in thawed tuna fillets treated with a commercial blend containing vegetable extracts. For the trial were used no. 4 fillets of thawed tuna (Thunnus albacares) each of 2.5 kg belonging from the same lot, originated from tuna caught 2 months earlier, prepared on board and quickly frozen. The commercial mixture was prepared according to the manufacturer's specifications and injected by the means of a multi-needle automatic machine in n. 3 fillets. No. 1 fillet was used as control. After treatment, each fillets was packed in nylon- polyethylene pouches with a Multivac model A 300 vacuum packaging machine (Bury, Lancs., UK) and stored at refrigeration temperature. Before treatment (T0) and after 7 days (T1) a slice (200 g) of each fillets was subjected to colorimetric assessment (Konica Minolta CR300, Minolta, Osaka, Japan), histamine [2], nitrates [2], TVB-N [3] and TBA [4] analysis. After 7 days treated fillets showed a bright red colour with no significant differences with respect to colorimeter values of T0. Differently control samples colour turns brown and significant differences were highlighted compared to colorimeter values of T0. Nitrates were found only in treated samples, reflecting that commercial blend contains these compounds. Histamine at T0 was <5 ppm. After 7 days storage levels detected in treated samples were 580±110 ppm, higher than those set by the Reg. EC 2073/05. The average values of TVB-N at T0 were 9.35 mg/100g. At the end of trial concentrations of 17.33 mg/100g were detected, indicating a good tuna quality. Malonaldehyde values were lower than those reported in literature for lipid oxidation. Reg. EU 1129/2011 in unprocessed fishery products allows only ascorbates, citrates, erythorbates and polyphosphates. If in the next future UE legislation will allow the use of vegetable extracts, in our opinion is mandatory analysis on histamine residues on fillets treated. In fact histamine levels detected in our study confirm that this treatment should mask potential high level of histamine.