Astaxanthin stability and color change of krill during subcritical water treatment.

Pacific krill (Euphausia pacifica) 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 (L*, a*, and b*) 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 R0) 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 R0 values of 2.00-2.44. In contrast, astaxanthin underwent 50% degradation at log R0 > 2.44. The changes in the a* values correlated well with the astaxanthin content in the treated krill, while the b* and L* 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.

Direct Treatment of Isada Krill under Subcritical Water Conditions to Produce Seasoning with Shrimp-Like Flavour.

Characterization, 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 flavour 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 flavour from isada krill.

Using severity factor as a parameter to optimize krill treatment under subcritical water conditions.

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 R0). Raw krill was treated under subcritical water conditions at various log R0 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 R0 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 R0 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.