Effect of 1-Methylcyclopropene on Shelf-Life and Postharvest Qualities of Four Annona ( Annona spp.) Species in Sri Lanka

Annona ( Annona spp.) is a tropical underutilized fruit with growing demand in both local and export markets for their distinct tastes and promising health benefits. However, vulnerability to postharvest damages with the short postharvest life of this commodity has significantly affected their market potential. The present study attempts to extend postharvest life while maintaining postharvest qualities in Atemoya ( Annona atemoya ), Bullock’s heart ( Annona reticulata ), Soursop ( Annona muricata ) and Sugar apple ( Annona squamosa ). The experiment was conducted according to the Complete Randomized Design (CRD) using four treatments. Fruits were treated with 0, 0.3, 0.6 and 0.9 µL L -1 1-Methylcyclopropene (1-MCP) for 15 hours and stored under ambient temperature (27±1 ˚C). Fresh weight loss, ______________________________________ firmness, total soluble solids, titratable acidity and peel colour changes were evaluated in two-day intervals. Fruit weight loss, firmness loss and concentration of titratable acidity showed strong positive correlation with time. Among the treatments, Annona fruits treated with 0.6 µL L -1 1-MCP reduced the chlorophyll degradation, fresh weight loss, total soluble solids and firmness loss. Peel colour indices L* and b* could be used to detect ripening of Annona. This study provides different 1-MCP concentrations that are effective to increase the postharvest life and postharvest qualities of four selected Annona species in Sri Lanka.


INTRODUCTION
Postharvest management is the main quality dependent factor of any horticultural commodity. It includes all kinds of postharvest treatments. Freshly harvested fruits and other horticultural commodities undergo different postharvest management practices to increase their postharvest life, minimize losses and add value to the product (Ramady et al., 2015). Worldwide fruit production is over about 850 million metric tons (FAO statistics, 2018) per year. But worldwide postharvest fruit losses are as high as 30 to 40 % and even much higher in some developing countries due to inappropriate post-harvest management (Ekanayake and Bandara, 2002). Average postharvest losses of fruits in the South Asian region are in the range of 20-50% (Khalid et al., 2011;Gautam and Bhattarai, 2012;Wasala et al., 2014).
Annona which is considered an underutilized crop in Sri Lanka, is a tropical fruit in the family Annonaceae (Ratnayake et al., 2020). Annona contains a remarkable amount of carbohydrates, proteins, fat, fibre, vitamins and minerals. Annona has a growing demand in the local and export market due to distinct taste and promising health benefits. Atemoya (Annona atemoya), Bullock's heart (Annona reticulata), Soursop (Annona muricata) and Sugar apple (Annona squamosa) are major Annona species grown in Sri Lanka (Heenkenda et al., 2009;Dilrukshi et al., 2020). All four species have huge market demand, for both processed and fresh fruits.
Family Annonaceae is classified as climacteric: with significant ethylene (C2H4) production and high respiration rate during fruit ripening as well as with short postharvest life (Prasanna et al., 2000). Thus, Annona shows high postharvest losses resulting in short postharvest life and poor marketable quality.
Ethylene is well documented as being the ripening hormone of climacteric fruits (Burg and Burg, 1967;Bruinsma and Paull, 1984). At a certain maturation stage, ethylene links to its binding-site in the cell and promotes several alterations which culminate in the ripening and senescence of fruits (Lelievre et al., 1997). Such Ethylene actions can be blocked by some compounds such as 1- acts as an antagonist (Sisler and Serek, 1997

Experimental Site and Plant Materials
The  Figure 1).

Treatment Application
The treatment solution was prepared by dissolving powder form 1-MCP (4%) in NaHCO3 (10%) solvent. Then, it was diluted to the concentrations of 0.3, 0.6 and 0.9 µL L -1 to be used as treatments.
In each treatment, randomly selected fruits were exposed to the

Determination of Physical Parameters
During the storage period, fruit fresh weight loss % (g kg -1 ) was estimated as follows,

Determination of Chemical Parameters
The  days only at 0.6 and 0.9 µL L -1 1-MCP concentrations. In contrast, Bullock's heart fruits were not viable beyond 6 days even after treatments. Therefore, Soursop and Sugar apple were shown a better response to 1-MCP treatments at 0.6 and 0.9 µL L -1 concentrations.

Fresh Weight Loss of Annona
Annona is marketed as a fresh product based on its weight. Therefore, postharvest weight loss directly affects the farmer's income. The highest rate of fresh weight loss during the postharvest period was recorded in Atemoya (30.5 g kg -1 day -1 ) and that was lowest in Bullock's heart (18.5 g kg -1 day -1 ) ( Figure 2).
In all Annona species, the application of 1-MCP significantly reduces the rate of weight loss. It could be observed as the slope difference between two regression lines (5.8 g kg -1 day -1 ) as indicated in Figure 3. This could be due to irreversibly binding of 1-MCP to the ethylene receptors and blocking the actions of the ethylene (Hofman et al., 2001). Moreover, less respiration and lower ethylene evolution rate delayed fruit ripening (rigid tissues) and thereby reduce the transpiration losses (Hofman et al., 2001).
The rate of fresh weight loss after harvesting at different treatment levels is given in Table 1

The Firmness of Annona (N)
Regardless of cultivars, fruit firmness shows a strong negative correlation with time (Days after harvesting) ( Table   2). Even though 1-MCP 0.6 and 0.9 µL L -1 treatments were able to retard the firmness loss in comparison to control treatment (0.0 µL L -1 ), 0.3 µL L -1 concentration showed some inadequacy.

Species Treatment Regression coefficient
Correlation coefficient   According to present study, there was no significant effect of 1-MCP on Soursop peel colour.

Total Soluble Solids (% TSS) of Annona
Strong positive correlation between TSS and time (days after harvesting) was observed in Atemoya (Table 3)      Means of physical and chemical parameters (Weight loss, firmness, peel colour L*, a* and b*, total soluble solids and titratable acidity) at initial (2 days after treatments) and end of the postharvest periods (6-8 days after treatment) were given in Table 5.