EFFECT OF HIGH-PRESSURE PROCESSING ON NUCLEOTIDE DEGRADATION IN REFRIGERATED SARDINES

The preservation of fresh sardines remains challenging due to their rapid postmortem deterioration. Despite their global economic importance, the application of emerging preservation technologies to this species remains poorly explored. Therefore, this study investigated the effects of high-pressure processing (HPP) at 100–400 MPa, applied either as a single pulse (0 min) or with a 15 min holding time, on the nucleotide profile of vacuum-packed sardines stored at 5 ± 2 °C for 21 days. Nucleotide concentrations were determined by HPLC using a waters® e2695 system equipped with a photodiode array detector and a c18 column). ATP, ADP, and AMP were detected at low concentrations from day 1, indicating substantial postmortem degradation before processing. IMP was the predominant nucleotide up to day 7, and its degradation was markedly delayed by HPP. While the control exhibited approximately 44% IMP loss by day 7, all pressurized samples maintained IMP concentrations comparable to or higher than those of the control. Initial HXR and HX concentrations were low (≈1 μmol g⁻¹), confirming the high freshness of the raw material, and their accumulation during storage was reduced by HPP. These effects were reflected in the k-value, which increased more slowly in pressurized samples, demonstrating a pressure-dependent inhibition of postmortem nucleotide degradation. Sardines showed high initial freshness (k-value on day 1 = 16.7–18.5%), whereas the onset of advanced deterioration (k = 70%) occurred shortly after day 7 in the control and was delayed to approximately day 14 under the 300 MPa/15 min treatment. The observed effects may be attributed to HPP-induced inhibition of nucleotide-degrading enzymes, including acid phosphatase, Ca²⁺- and Mg²⁺-atpases, and dephosphorylases. By slowing postmortem nucleotide degradation, HPP attenuated the increase in k-value during refrigerated storage, thereby extending freshness retention and delaying quality deterioration. Finally, although some studies assess nucleotide degradation using the k′ (or k1) index, which excludes ATP, ADP, and AMP from the calculation, k and k′ showed an almost perfect correlation in the present study (r = 0.999, p ≤ 0.01). These results indicate that k′ can reliably replace k for freshness assessment, reducing analytical time, reagent consumption, and research costs.