R. Sugahara

The effects of an all- E -isomer-rich astaxanthin diet (E-AST-D) and Z -isomer-rich astaxanthin diet (Z-AST-D) supplementation on astaxanthin accumulation and isomer composition in the edible orthopterans, migratory locust ( Locusta migratoria ) and two-spotted cricket ( Gryllus bimaculatus ), were investigated. Z -Isomer-rich astaxanthin was prepared from the all- E -isomer via thermal treatment in corn oil at 160 °C for 30 min, increasing the total Z -isomer ratio from 1.3 to 57.7%. Supplementation with E-AST-D and Z-AST-D to L. migratoria had little effects on astaxanthin concentration and isomer composition in the body. In contrast, astaxanthin supplementation to G. bimaculatus significantly improved the astaxanthin concentration, and when Z-AST-D was fed, the astaxanthin concentration was approximately eight times higher than that of supplementation with E-AST-D. This suggests that L. migratoria exhibits very low astaxanthin isomer bioavailability, whereas G. bimaculatus can absorb astaxanthin isomers from its diet. L. migratoria may synthesise astaxanthin endogenously regardless of dietary astaxanthin content. The Z -isomers were more bioavailable than the all- E -isomer in G. bimaculatus . Furthermore, astaxanthin isomer ratios in the faeces of both species were different from the dietary sources, suggesting that these ratios were modulated during digestion. These findings are important for increasing the added value of insect foods and for elucidating the mechanism of astaxanthin isomerisation in insects.