The total carotenoid content of the shrimp shell homogenate recovered with and without barbel trypsin treatment was noted to reach a maximum at 60 min. Thereafter, and up to 300 min of hydrolytic time, the total carotenoid content tended to show a sharp decrease (Fig. 5b). The decrease in the total carotenoid content with the increase of the hydrolytic time could presumably be attributed to the decrease in the stability of carotenoids. The excessive hydrolysis of proteins associated with the carotenoprotein complex might have led to insolubility in the aqueous extraction solution or to instability of the carotenoid content, as a result of the disruption of the protective environment provided by the association with protein (Klaui & Bauernfeind, 1981). Cano-Lopez et al. (1987) reported that carotenoprotein is more stable than the carotenoid pigment alone.