Semidried Isada krill (Euphausia pacifica) was treated with boiling water and subcritical water at 100-240C for 10 min with a semidried krill to a water ratio of 8/52 w/v to produce seasoning. The protein concentration, lipid content and odor concentration of the extract increased after increasing the treatment temperature. The highest protein content of the extract (0.047-0.049 kg/kg-extract) was obtained by subcritical water treatment at 180 or 200C. Compounds with lower molecular mass were detected in the extracts derived from subcritical water treatment at temperatures higher than 160C. The extract prepared by subcritical water treatment at 160 and 180C received the high score in the flavor preference test by a group of panelists. Treatment at temperatures lower and higher than 160-180C, respectively, conferred undesirable fishy and smoky or burnt odors to the extracts and residues. PRACTICAL APPLICATIONAlthough Isada krill is abundant in the Sanriku coast, Japan, its usage is limited to low-value-added products such as animal and aquaculture feeds. However, we found that subcritical water treatment of the krill produces an extract solution and a solid residue, both of which possess good flavor and proffer a great prospective for use as seasoning. Establishment of a method for using the krill as a raw material for seasoning with shrimp-like flavor would increase the value of the krill as a food resource for human consumption.

Pacific krill () contains high amounts of astaxanthin, a carotenoid pigment with strong antioxidative activities. In this study, the effects of subcritical water temperatures (100-180 °C) and times (0-10 min) on color changes (*, *, and*) and astaxanthin degradation in Pacific krill were investigated. In addition, an aqueous solution of pure astaxanthin and that of crude astaxanthin from Pacific krill, both at a concentration of 5 mg/L, were subjected to treatment under subcritical water conditions using a flow-type reactor to compare the degradation of free astaxanthin and astaxanthin fatty acid esters. To compare the results of the different treatment conditions on the properties of astaxanthin, the severity factor (log ) was calculated, which ranged from 0.38 to 3.52. The extractability of astaxanthin enhanced when the subcritical water treatment was carried out at log values of 2.00-2.44. In contrast, astaxanthin underwent 50% degradation at log > 2.44. The changes in the * values correlated well with the astaxanthin content in the treated krill, while the* and * values might relate to the browning components forming owing to Maillard reaction. The results show that free astaxanthin was less stable than crude astaxanthin under subcritical water treatment.

Comparative analysis of subcritical water (SCW) treatment and ambient pressure boiling one of raw Isada krill was performed for the nutritive, flavour and antiradical properties of krill extracts and residues as well as the molecular mass and odour intensity of the extract. SCW treatment was performed for 10 min in a batch-type vessel in the temperature range of 100-240°C, using a 1:1 weight ratio of raw krill to water. Higher protein and lipid contents were obtained by SCW treatment relative to boiling. The lipid content of the SCW extracts increased with increasing treatment temperature. Protein was the main component in these extracts, and the highest protein content was achieved by SCW treatment at 200°C. High-molecular-mass species decomposed under SCW treatment at high temperatures with consequent generation of smaller molecules. The antiradical activity of the SCW extract, determined by DPPH and ABTS assays, increased with increasing treatment temperature. The krill extracts and residues exhibited shrimp-like flavour, and the most desirable flavour was obtained by SCW treatment at 140°C or 160°C for 10 min. The treatment would be applicable for the production of seasonings from Isada krill.

The aim of this study was to optimize the conditions for subcritical water treatment of krill, as expressed with a single parameter: the severity factor (log R). Raw krill was treated under subcritical water conditions at various log R values (1.54-3.75) by varying the treatment temperatures (120-180 °C) and times (0-10 min) in two different sizes of batch-type vessel (10 and 117 mL). The log R value could efficiently describe changes in various properties of the obtained liquid extracts and solid residues. The most desirable shrimp-like flavor intensity and highest sensory preference were obtained for log R values of 2.75-3.01. The results also proved that severity factor can be used as a single parameter to control subcritical water treatment conditions in differently sized batch-type vessels to produce shrimp-like flavor extract and residue from krill.

SummaryCharacterization, sensory evaluation, and astaxanthin stability of isada krill under various subcritical water conditions were investigated to optimize the quality of krill extract and residue for producing food seasoning. Raw krill (82 % wet basis moisture content) without additional water was treated in a pressure-resistant vessel for 10 min at a temperature range of 100-240 °C. The yield of water-soluble protein was maximized by treatment at 200 °C and decreased with treatment at higher temperatures. The degradation of large molecules and the concomitant production of small molecules depended on the treatment temperature. Astaxanthin in the krill was unstable at temperatures higher than 140 °C. The odour intensities of krill extract and residue increased with higher treatment temperature; however, the highest intensity of pleasant shrimp-like fl avour was obtained by treatment at 140 °C. Subjective preference scores were the highest for extract and residue obtained at 140 °C. Thus, treatment at 140 °C is the most promising method for production of seasoning with shrimp-like fl avour from isada krill.