Milkfish collected from brackish water culture ponds were wet and dry salted for 24 h and the dry-salted fish were sun dried for 48 h. Biochemical changes, ie changes in α-amino nitrogen, non-protein nitrogen, salt-soluble nitrogen, total free amino acids, essential amino acids and sulfhydryl groups, during salting and sun drying were studied. The reduction in these parameters was slightly higher in wet-salted fish compared with dry-salted fish. Further reduction in these parameters was noticed on sun drying of dry-salted fish. Electrophoretic studies showed a decrease in the number of bands during wet and dry salting at a slow rate up to 9 h, after which high-molecular-weight proteins decreased faster than medium-molecular-weight proteins in both the 24 h wet-and dry-salted samples. Further reduction in the number of bands and their intensity was observed on sun drying for 48 h. The medium-molecular-weight protein seems to be more stable. INTRODUCTIONSalting, drying and smoking are the traditional methods of fish preservation, with 8.2% of the world's fish catch being preserved by these methods. 1 Considerable quantities of cured fish are consumed in developing countries; for example, 32% of the fish consumed in India is reported to be in cured form. 2 The importance of such products is not likely to decline appreciably in the near future despite attempts to introduce modern preservation methods to these areas. Various methods of salting fish are in use, and the one selected depends upon the climatic conditions, the characteristics of the industry and the organisation of the salted fish trade specific to each country. 3 Salting and drying result in the loss of significant quantities of proteins, peptides and amino acids, and these losses are greater during wet salting than during dry salting. 2,4 -6 In split-open salted and dried fish the lipids on the cut surface interact with oxygen, leading to oxidative rancidity and browning. 7,8 Although an enormous literature is available on various aspects of the biochemical changes taking place in cured products, much work remains to be done to perfect our knowledge on changes during curing. This study was undertaken to investigate the changes in proteins and related constituents during curing of the brackish water fish Chanos chanos.

The antioxidative effect of herring (Clupea harengus) light muscle press juice (PJ) against hemoglobin-(Hb-) mediated oxidation of washed cod mince during ice storage was tested. The PJ was fractionated into low-molecular-weight (LMW; <1 [corrected] kDa) and high-molecular-weight (HMW; >1, >3.5, and > 50 kDa) fractions; it was preheated (10 min, 100 degrees C) and tested with or without removing heat coagulated proteins. Its antioxidative effect was compared with that given by endogenous levels of two tentative antioxidant candidates: ascorbic acid and uric acid. Oxidation was followed by determining rancid odor, peroxide value, and redness. Whole herring PJ and the LMW-PJ fraction significantly (p < 0.001) extended the oxidation lag phase of controls, from 2 up to 8 and 7 days, respectively. The HWM-PJ fractions were significantly (p < 0.05) less efficient than the whole and LMW-PJ samples, giving only 3.5-4.5 days of lag phase. Heat-treated PJ, with and without the heat-coagulated proteins, gave 7 and 5 days of oxidation lag phase, respectively. Heating different batches of the LMW-PJ fraction grouped the results into two categories: one where heating almost fully destroyed the antioxidative activity (fractions prepared from spring-caught herring) and another where heating had no or a minor effect (fractions prepared from fall-caught herring). The spring LMW-PJ had low ascorbic acid levels (18-42.6 microM), and 50-100% were destroyed by the heating. In fall LMW-PJ, the levels were 76.2-137.6 microM, and only 43-51% were destroyed. Ascorbic acid fortification of heated spring LMW-PJ to reach the levels found in the corresponding unheated spring LMW-PJ sample and the heated fall LMW-PJ gave back most of the antioxidative activity, which proved an important role of ascorbic acid for the antioxidative activity of LMW-herring PJ. This conclusion is drawn despite the fact that pure solutions with endogenous levels of ascorbic acid (giving 8.4-19.6 microM in final model) only very slightly delayed Hb-mediated oxidation of the washed cod mince.

Reactive oxygen species (ROS) can cause oxidative stress, which has been linked to various diseases. It has been suggested that antioxidant-rich foods can reduce such oxidative stress. However, the lack of suitable model systems to screen for in vivo effects of food-derived antioxidants has prevented a clear consensus in this area. In this study, the aim was to use a single-cell model system (human monocyte) to evaluate whether certain pure antioxidants and complex muscle extracts (herring light muscle press juice, PJ) could prevent ROS formation under in vivo like conditions. ROS were excreted from the monocytes upon stimulation with phorbol myristate acetate and were then detected as isoluminol-enhanced chemiluminescence (CL). Adding 2000 units of catalase and 50 units of superoxide dismutase to the monocytes model lowered the CL response by 35 and 86%, respectively. Ascorbate (14.1 mM) lowered the response by 99%, alpha-tocoperhol (188 microM) by 37%, and Trolox (50 microM) by almost 100%. Crude herring PJ gave a dose-dependent reduction in the CL response. At 10, 100, and 1000 times dilution, the PJ reduced the CL signal by 93, 60.5, and 10.6%. PJ fractionated into low molecular weight (LMW) (<1000 Da) and high molecular weight (>3500 Da) fractions decreased the CL response by 52.9 and 71.4%, respectively, at a 100-fold dilution. Evaluation of the PJ samples in the oxygen radical absorbance capacity test indicated that proteins may be the primary radical scavenging compounds of PJ, whereas the ROS-preventing effect obtained from the LMW fraction may also be attributed to other mechanisms. Thus, this study proved that the monocyte assay can be a useful tool for studying whether food-derived antioxidants can limit ROS production under physiologically relevant conditions. It also showed that herring contains numerous aqueous compounds demonstrating antioxidative effects in the monocyte model system.

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