Biochemistry of Guava (Psidium guajava L.) fruit ripening: Changes in respiration rate, ethylene production and enzyme activity

Guava fruit respiration followed a typical climacteric rise and maximum ethylene production preceded climacteric peak during ripening. Cellulase and ß-galactosidase activity declined during ripening while that of PE and PG declined from green-to-peel colour-turning and or yellow hard stage and increased in ripe fruits. Amylase and phosphorylase activity showed marginal changes, while acid phosphatase activity decreased during ripening. Sucrose phosphate synthase, sucrose synthase and acid invertase activity decreased in general with ripening and had no definite relation with sucrose content. Glycolytic enzymes, hexokinase, PFK, PK activities remained high until green mature stage and declined in later ripening stages. Gluconeogenic enzymes, G6Pase, FBFase and PEPCK as well as ME and PEPC activity increased until peel colour turning and or yellow hard stage and declined in ripe fruit. Catalase and peroxidase activity declined during ripening. The PPO activity increased until yellow hard stage and decreased in ripe fruits. Chlorophyllase, GDH and MDH activity increased until peel colour turning and or yellow hard stage and decreased in ripe fruit. The high level of EFE activity observed at peel colour turning stage coincided with pre-climacteric rise in respiration.