The polygalacturo:rase (E.C. 3.2.1.15) @'Case) activity in papayas increased with fru: t ripeness. PGase activity was highest in the placenta with the aclivity decreasing outwardly from the placenta to the exocarp. Exte:tded hot water treatments (46°C for 65 and 90 mm) caused delay:d softening of the fruit tissue which was correlated to a decrease in PGase activity. The decrease in PGase activity after the heat treatments was more severe in the riper fruits (quarter and half ripe) than the less ripe fruits (colorbreak stage).

Heat inactivation studies were conducted on the ethylene-forming enzyme system (EFE) in papayas. Heat inactivation of the papaya EFE was biphasic and both phases followed first order kinetics. The activation energies E, for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFEs were 68.3 and 51.2 Kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both EFEs were; enthalapy, 5 1.2 kcal/mole for HS and 66.7 kcal/mole for HR; free energy, 22.5 kcal/mole for HS and 23.3 kcal/mole for HR; entropy, 87.2 cal/deg-mole for HS and 137.8 calI deg-mole for HR. The heat resistant EFE appeared to compromise about 25% of the total EFE activity. Commercial heat treatments used for quarantine treatments affected mainly the heat susceptible portion which comprised the remaining 75% of the total EFE activity.

The effects of drying temperature (74", 84" and 94"C), storage time (1, 2 and 3 months), storage temperature (-18") 24" and 38"(Z), and sulfur dioxide on the quality of papaya leather were investigated. Drying rate was decreased when high SO, levels were used. The color of the leather depended on drying and storage temperature and the presence of SO,, which protected against darkening at high drying and high storage temperatures. However, residual SO, levels declined at high storage temperature, thus decreasing protection. Sensory data for color, flavor and off-flavor correlated significantly with the alcohol-soluble color index.

Effects of storage temperature and time on the quality of aseptically processed, "bag-m-box" packaged guava and papaya puree were investigated. During aseptic processing of guava puree there was virtually no loss of ascorbic acid (AA) and flavor but significant losses in color. After 6 months ambient storage the AA loss was about 30% and further color changes and flavor losses occurred. Samples stored at 38°C for 3 months showed an-AA loss of about 47% and losses in color and flavor. For papaya puree AA losses of about 6% and 56% occurred during aseptic processing and after 6 months ambient storage, respectively. Color changes during aseptic processing and the first month of storage was characterized by a hypsochromic shift of the carotenoids' absorption spectra. After the first month of storage further color changes were attributed to the products of nonenzymatic browning. Papaya flavor was stable during both aseptic processing and 6 months ambient storage. Flavor of papaya puree stored at 38°C for 3 months changed significantly and AA retention was 39%.

An invertase in papaya was extracted, partially purified and character-I ized. Substrate specificity studies showed the enzyme to be a p-fructofuranosidase. The enzyme has a pH optimum of 4.6 and a temperature optimum of 40°C. The Km of the enzyme, with sucrose as a substrate, was 7.7 mM. Heat inactivation of papaya invertase was biphasic, and the kinetics of both phases were first order. The activation energies for the thermal inactivation of the two phases were 33.5 kcal and 53.6 kcal. The enzyme's apparent molecular weight as determined by gel filtration was 275,000.