Differences in 1-Methylcyclopropene Sorption Processes in Fresh-cut Apple, Tomato, and Avocado Fruits

Our earlier studies demonstrated that fresh-cut apple slices consumed 1-methylcyclopropene (1-MCP) rapidly when incubated in static system with 20 µL·L^-1 1-MCP. Sorption/consumption was strongly suppressed in slices exposed to ascorbate (360 mol·m^-3) prior to 1-MCP exposure. In the present study, fresh-cut tomato, avocado and apple fruits were examined to determine whether sorption patterns noted for fresh-cut apple reflected characteristics of other fruits. Slices of fruit tissue (total 25 to 30 g) were placed in 495 mL jars and 1-MCP injected at 20 µL·L^-1.  Fresh-cut apple (‘Delicious’) consumed headspace 1-MCP at high rates, approximately 64.0 ng·kg^-1·s^-1, and depleted headspace 1-MCP in 1.5 hours. Apple slices pretreated with ascorbate showed 80% reduction in sorption rate (12.84 ng·kg^-1·s^-1), depleting 60% of system 1-MCP in 6 hours.   Fresh-cut avocado (‘Hass’) tissue showed moderately high sorption at 35.2 ng·kg^-1 s^-1  that was unaffected in tissue pretreated with ascorbate (35.0 ng kg^-1·s^-1). Avocado slices depleted about 95% of system 1-MCP over 6 hours.  By sharp contrast with apple and avocado fruits, fresh-cut tomato (‘Tasti-Lee’) showed very low sorption of 1-MCP, with control and ascorbate-treated tissue consuming 1-MCP at around 1.3 to 1.9 ng·kg^-1·s^-1 and depleting only about 6% of headspace 1-MCP (relative to controls—empty jars) over 6 hours. In experiments with apple and avocado fruits, fresh-cut slices were heated to 90 °C, returned to room temperature, and monitored for 1-MCP sorption. Non-heated apple tissue consumed headspace 1-MCP at 61.4 ng·kg^-1·s^-1 . Heated apple slices exhibited an 80% reduction in 1-MCP sorption (12.3 ng·kg^-1·s^-1). The non-heated and heated apple tissue consumed around 100% and 50% of headspace 1-MCP in 1 h and 6 h, respectively.  Avocado tissue was far less affected by heating. Non-heated avocado consumed 1-MCP at 54.9 ng·kg^-1·s^-1 compared with 44.0 ng·kg^-1·s^-1 in heated tissue, a reduction of 19.8%.  It is evident that  fresh-cut fruit tissues exhibit significant differences in 1-MCP sorption/consumption capacity, and in their responses to heat and antioxidants. These differences likely represent proportional differences in thermo-tolerant, physical binding processes versus oxidative metabolism.  The extent to which the processes contributing to sorption of 1-MCP in fresh-cut fruit tissue are operative in intact fruits is unknown.