Hydrolysis of fish waste using fruit wastes of Ananas comosus and Carica papaya for the formulation of liquid fertilizers

PurposeFish waste is a protein-rich source that can be used as a value-added product in the formulation of organic liquid fertilizers. This study carried out to investigate the utilizing potential of fruit wastes of Ananas comosus and Carica papaya that contain bromelain and papain as major proteases in order to hydrolyze fish waste proteins to fulfill plant nitrogen requirements.  MethodProteases were extracted from A. comosus (leaves, crown, unripe fruit pulp, ripe fruit peels and pulp) and C. papaya (leaves, ripe fruit peels and unripe fruit peels). The optimum temperature and pH for the enzymatic activities were determined. Four liquid organic fertilizers were produced with hydrolyzed fish waste that enriched by adding Gliricidia sepium, Chromolaena odorata, Tithonia diversifolia, Mikania scandens and coconut husk-ash. Fertilizers were tested on the growth of Basella alba comparing with a standard fertilizer.  Results Ananas comosus ripe fruit peels and the mixture of (A. comosus + C. papaya) showed the highest enzyme activities (0.33±0.02 and 0.36±0.01 U mL-1 enzyme respectively) at 55 oC and 70 oC. The optimum pH for all the studied extracts was 7.5 at 37 oC. The highest plant fresh and dry weights were recorded in the foliar-applied fertilizer produced by hydrolyzing the fish waste using A. comosus and C. papaya, showing no significant differences to the standard fertilizer.  Conclusion Hydrolysis of fish waste using the fruit wastes ofA. comosus and C. papaya could be effectively used as an organic fertilizer for the growth of B. alba that leads towards sustainable waste management.