IMPACT OF HIGH HYDROSTATIC PRESSURE (HP) ON THE BAI INDEX OF SALTED COD (BACCALÀ) DURING REFRIGERATED STORAGE

Fish freshness is traditionally judged by sensory methods, although several chemical indexes have also been proposed, such as BAI index (Veciana-Nogués et al., 1997), calculated considering the quantities of some biogenic amines in the product. Biogenic amines (BA) are useful in estimating freshness or spoilage degree of fish, as their presence is often associated with bacterial activity. Moreover, BA and particularly histamine could also determine a risk for consumers’ health (EFSA, 2011). High pressure (HP) processing has been proposed as a non-thermal technique to improve food safety and shelf-life (Knorr, 1993), without affecting its nutritional characteristics. Thus, the aim of the work was to study the effect of high hydrostatic pressure on some quality characteristics of salted cod, and particularly on BAI index. Gadus macrocephalus salted fillets were prepared as follows: one batch (sample T) was HP treated (6000 atm for 8 minutes), one batch (sample IT) was inoculated (about 5 Log ufc/g) with one strain of Shewanella baltica ST10 previously isolated from tuna fish, then exposed to the same HP treatment. As controls two batches were also taken: no-inoculated and untreated samples (B); inoculated with S. baltica and untreated samples (I).All samples were vacuum packed and stored for 28 days at 8°C, to simulate domestic storage; analysis (biogenic amines content, psychrophilic microorganisms, mesophilic Gram negative bacteria and pH) were carried out on weekly basis.Results highlighted that blank samples reached the end of shelf-life at day 14 of storage, both for sensory characteristics and quality parameters, while HP treated samples showed acceptable quality properties at day 28. As regards BA, their content was below detection limit at time 0, in agreement with a high hygienic quality of fish. At day 14, only putrescine and cadaverine were detected for batches B and I, while no amines were found for the other samples. Histamine was detected only for samples I, starting from day 21, with quantities ranging from 10.2 and 11.1 mg/Kg. BAI index was calculated according both to Karmas (1981) and to Veciana-Nogues et al. (1997). The value of 10, proposed by Karmas as the limit of fish acceptability was exceeded in samples B and I at day 14 of storage, even reaching values of 196.7 and 202, in samples I at day 28 of storage. On the other end, HP treated batches showed a BA content below detection limit until the end of refrigerated storage. This result is particularly important, since all samples were vacuum packed, and microbial production of BA is stimulated in absence of oxygen. Results regarding HP treated samples were supported also by microbiological data, as psychrophilic and Gram negative bacteria had load levels respectively below 5.0 and 4.0 Log ufc/g until the end of storage. Values of pH were higher in HP treated samples (around 6.90) just after treatment, with respect to blank batches (6.7), likely due to the denaturation of some protein fractions (Angsupanich and Ledward, 1998), and did not change during storage.In conclusion, HP treatment of salted cod had a positive effect on some quality parameters, and particularly on BAs content and therefore on BAI index, due to the process inactivation of microorganisms able to grow during refrigerated storage under vacuum packaging conditions. [...