Antarctic Krill: Extraction and Storage

By: Dr C N Ravishankar
Antarctic krill is found in huge swarms in the waters of the Southern Ocean. The krill despite being a promising source of protein is still largely unfit for human consumption due to its high fluoride content, blackening and unpleasant flavour.
Wildlife

Antarctic krill, Euphausia superba, a promising sources of protein, demands sustainable utilisation at a time when most conventional resources are reaching or exceeding optimal limits. The primary problem in utilising krill lies in its intense postmortem proteolytic activity. Also its high fluoride content, excessive loss of exudates during storage at non freezing temperature, blackening and development of unpleasant flavour need to be contended with during krill processing.

The present investigation pertains to the study of various aspects of krill processing and product development, besides assessing its biochemical and other changes during storage.

The krill samples were collected from the Southern Ocean between 57° 53’- 61° 13’S and 31° 40’ – 36° 31’E, on board Fishery and Oceanographic Research Vessel (FORV) Sagar Sampada. Only non feeding and slightly feeding krill, which were pinkish red in colour, with an average length of 35 mm and above were taken in for processing. Feeding krill (green in colour) were removed before further processing activity. The duration of trawling was reduced in order to reduce the quantity of catch and thus minimise physical damage.

Freshly caught krill had to be processed immediately, as krill became unfit for processing after four hours of harvest. So as soon as the krill taken aboard, cleaned, weighed and packed in cartons lined with polyethylene sheets, it was frozen at -35°C and stored at -30°C for further studies. Apart from this, the fresh whole krill was processed to mince, tail meat, coagulate and boiled krill, which were frozen and stored as above. Krill body comprises of cephalothorax and abdomen. The cephalothorax forms about 32-36 per cent of body weight. Abdomen and carapace accounted for 26-28 per cent and 25-27 per cent of body weight. The balance of 10-18 per cent was lost on separation.

 

Chemical analysis: The moisture and fat content of krill was found to be high with low crude protein. An increase of up to 44 per cent of fluoride content in the tail meat was observed during the frozen storage at -30°C for 3 months. The changes in fluoride content of other products from krill on storage were marginal. Because of the migration of fluoride from the shell to the meat, it is recommended that the whole catch may be converted to intermediate products like tail meat, mince, coagulate etc. which can be used as food.

There are concentration of various trace metals in whole krill and head – concentrations of copper, iron, zinc, chromium were above 10 ppm while those of lead, cadmium, nickel and manganese were less than 1 ppm. Marine crustaceans in Antarctic Ocean have been reported to accumulate as much as 13 mg/kg (d.w) of cadmium. The concentrations of pesticides in krill were all below detectable limits and no traces of any organochlorine pesticides were found in any of the samples.

 

Fatty acid analysis: Krill lipids were extracted from samples with chloroform-methanol mixture and cholesterol in the unsaponifiable fraction was estimated. Eighty per cent of krill lipids are reported to be phospholipids – the proportion of unsaponifiable fraction of lipids was 7.26 per cent.

 

Amino acid analysis: Nutritional studies of the krill meat were also carried out. Protein of the krill tail meat appeared to be quite balanced and all the essential amino acids were present in adequate amounts. Whole krill had a slightly lower concentration of sculpture containing amino acids. Krill meat was evidently a good dietary source of protein. There were no ill effects seen in the test animals after four weeks of feeding.

 

Product development: Various products were developed from krill to find out the suitable methods to utilise the krill meat. The whole krill was dried to find out the acceptability. The samples were then stored at ambient temperature for shelf life studies. The dried samples were analysed for total nitrogen, non­ protein nitrogen, moisture, fat, ash, salt and total volatile basic nitrogen. Another attempt was made to prepare surimi from krill by mixing it with C. catla mince. The surimi was prepared with the mince from krill mixed with C. catla mince at 10, 20, 30 and 40 per cent (w /w) proportions and chemical, physical and organoleptic properties of the mixtures were studied.

Value added fish products such as fish burger, fish cutlets and fish wafers were also prepared by incorporating cooked krill mince at 10, 20, 30 and 40 per cent with cooked Nemipterus japonicus meat.

The krill cooked at 5 per cent brine showed the highest acceptability while samples cooked in water showed the least. The dried product prepared by cooking in water became powdery after two months of storage while the product cooked in salt solution did not show any change in their shape and physical characteristics. The dried products prepared after cooking in 1 and 2 per cent salt solution had a pinkish dark appearance while that cooked in 5 per cent brine showed a pinkish white appearance.

The chemical, physical and sensory quality changes of C. catla mince incorporation of krill meat changed to unpleasant upon increasing the concentration of krill meat. Also the acceptability of the other products reduced with the increase in krill meat concentration in the product.

 

Conclusions: Based on the results it is suggested that the whole catch may be immediately converted into intermediate products like head less, tail meat, mince, coagulate etc. to reduce the migration of fluoride from the shell to the meat. Various value added products can be prepared by incorporating small quantities of
krill mince.

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