Identification of annonaceous acetogenins in the ripe fruit of the North American pawpaw ( Asimina triloba ).

The North American pawpaw [ Asimina triloba (L.) Dunal] is a tree fruit in the early stages of commercial production in the United States. This plant contains annonaceous acetogenins in the twigs, unripe fruit, seeds, roots, and bark tissues, which display antitumor, pesticidal, antimalarial, anthelmintic, piscicidal, antiviral, and antimicrobial effects, suggesting many potentially useful applications. However, commercial development of these compounds, based on twig extracts, has been problematic due to limited availability of biomass for extraction. Additionally, acetogenin compounds contained in fruit of pawpaw relatives (soursop or Annona muricata ) and tea made from the leaves of these plants may lead to an increased risk of atypical Parkinsonism later in life with overconsumption of these compounds. Therefore, the objectives of this study were (1) to determine if extracts of ripe pawpaw fruit pulp displayed acetogenin activity, (2) to identify potential acetogenin compounds in the fruit tissue, and (3) to determine if the acetogenin activity varied in diverse pawpaw genotypes and closely related Annona species. Extracts of ripe fruit had total extract weights and bioactivity using the brine shrimp bioassay similar to those from 'NC-1' pawpaw twig tissue. Pulp from soursop, cherimoya, and several additional pawpaw cultivars ('Mitchell', 'Overleese', 'NC-1','Zimmerman', 'Wells', and 'Sunflower') also displayed bioactivity, but peach or banana pulp did not. Ripe pawpaw pulp extract subjected to HPLC-MS analysis identified three prominent acetogenins: asimicin, bullatacin, and bullatalicin. This study points to pawpaw fruit pulp serving as a new biomass source for the extraction of acetogenin compounds for product development. An assessment of the potential human health risk of overconsumption of fruit and acetogenin bioavailability and degradation studies should be pursued.

Loss of ripening capacity of pawpaw fruit with extended cold storage.

The fruit ripening traits of pawpaw [ Asimina triloba (L.) Dunal] were examined after harvest and after cold storage at -2, 2, 4, and 6 degrees C for up to 12 weeks. Generally, fruits stored at 2-4 degrees C for 4 weeks ripened normally, but those stored at -2 degrees C did not ripen normally, those stored at 6 degrees C were overripe, and by 6-8 weeks those stored at 2-4 degrees C had a lower respiration rate and ethylene production, lower firmness, and lower pH than fruit cold-stored for 4 weeks or less. These changes, and the occasional development of brown discoloration in the pulp once the fruits were moved back to room temperature, were evidence of chilling injury by 6 weeks. After harvest and through 4 weeks of cold storage, the main volatile compounds produced by fruit were methyl and ethyl octanoates and hexanoates. Volatile production significantly increased >5-fold in fruit ripened for 72 h after harvest or after removal from up to 4 weeks of cold storage. Fruit cold-stored for 6 weeks or more produced fewer total volatiles and esters but increased levels of such off-flavor compounds as ethyl acetate, ethyl propionate, and hexanoic and decanoic acids. Alcohol acyltransferase (AAT) activity declined in cold-stored fruit but was not correlated with either total volatile production or total ester production. Alcohol dehydrogenase activity did not change during ripening after harvest or cold storage. Lipoxygenase activity was highest just after harvest or after 2 weeks of cold storage, but was low by 4 weeks. Thus, ripening of pawpaw fruit seems to be limited to 4 weeks at 2-4 degrees C with loss of ability to continue ripening and chilling injury symptoms evident at colder temperatures and after longer periods of cold storage.