Analysis of Indonesian salted-dried catfish (Arius thalassinusRuppell

No abstract

Whole mackerel (Scomber scornbrus) were frozen using a horizontal plate freezer, wrapped in plastic bags and frozen stored at -20°C. At suitable intervals (11, 22 and 33 weeks) the fish were removed from the cold store and subsequently hot smoked (in gutted from) using an AFOS-Torry Mini Kiln. All smoked mackerel samples, despite their different previous histories, were assessed by the panellists as moderately acceptable products in terms of their texture and flavour, even after 33 weeks frozen storage prior to smoking. Protein denaturation, as related to salt-soluble protein, was influenced by the frozen storage history (24% drop after 33 weeks frozen storage) and seemed to be affected by the free amino acids formed during frozen storage. After smoking the denaturation was extensive (above SOY0) in all mackerel samples. Lipid oxidation was quite extensive (PV 108 meq kg-') in the 22 and 33 weeks frozen stored mackerel samples. However, no rancid flavour in the latter smoked mackerel samples was detected by taste panellists. A 58% increase in free amino acids during frozen storage was observed. Extensive losses of 74% in available lysine were observed in the 22 and 33 weeks frozen stored mackerel samples after smoking which could be due to aminocarbonyl reactions with the products of lipid oxidation. A 40% loss of thiamine was observed in the 33 weeks frozen stored samples after smoking. The histamine contents did not exceed 94 mg kg-' and would not be expected to cause symptoms of scombrotoxin poisoning.

A B S T R A C TThe lipid of traditional salted, sun-driedfish is highly susceptible to oxidation during processing and storage at tropical ambient temperatures

Abstract:In relation to studies of lipid oxidation during the processing and storage of salted sun-dried fish, the measurement of the initial rate of oxygen uptake has been studied on a model system consisting of a highly polyunsaturated fish oil. This parameter has been used for assessing the effects of temperature and light conditions on the model system and has been compared to changes in the peroxide value and the polyene index. Assessment of oxygen uptake using a Gilson respirometer was found to give a clearer indication than other methods of assessment of the effect of different conditions on fish oil oxidation. At 30°C the initial rate of oxygen uptake increased from 0.103 p10, g-' min-' to 0.1 58 p 1 0 , g-' min-l with a change in light conditions from dark to photosynthesis light. At 40"C, the rate of oxygen uptake was faster than at 30 "C, and the effect of light was more pronounced, giving values of 0.188p10, g-lmin-' and 0.483 p l 0 , g-' min-', for dark and photosynthesis light, respectively. The observed results for the measurement of the initial rate of oxygen uptake suggest its use as a sensitive and reliable method for the investigation of the contribution of the many components in salted sun-dried fish towards the rate of oxidation and subsequent rancidity.