The decrease in the total carotenoid content with increasing hydrolysis time was presumably because of the decrease in stability of carotenoids. As a consequence, free carotenoids associated with protein could be more released and were prone to oxidation. Carotenoproteins from shrimp heads were recovered by autolysis at 50 °C and pH 8.0. Highest carotenoid content in carotenoprotein was reported when autolysis was conducted for 4 h ( Sowmya et al., 2011). For carotenoprotein extracted from brown shrimp shell, trypsin showed higher recovery of carotenoid than pepsin and papain, when the same hydrolysis time was implemented ( Chakrabarti, 2002). Cano-Lopez et al. (1987) reported that proteolytic enzymes were used to disrupt the protein–carotenoid bond, thus increasing carotenoid recovery. Therefore, the optimum conditions for carotenoprotein extraction by crude protease were 20 units/g shrimp shells with hydrolysis time of 120 min at 60 °C.