ASHS 2015 Annual Conference

In order to minimize postharvest chilling injury (CI) in ‘Marsh’ grapefruit, freshly harvested fruit were 1) untreated, 2) coated with a shellac-based coating, 3) treated with 8.69 mM proline solution, or 4) dipped in the proline solution, allowed to dry, and then coated. The fruit were harvested in December (mid season) and late March (late season), stored at 4.5 C, and sampled every other week for 10 weeks. All treatments significantly reduced CI symptoms (peel pitting) compared to the control, but shellac coating was more effective than proline treatment. The combination of coating and proline was similar to coating alone in reducing CI symptoms. Proline-treated fruit had higher proline concentration in the peel (flavedo), indicating uptake, while coating had no effect on peel proline.  Free amino acids and reducing sugars in the peel were not affected by coating or proline treatments, but total sugars were higher in the peel of coated fruit. The proline treatment had lower non-reducing sugar content than the other treatments, while reducing sugar levels were lower in the control and combination treatments. Fluctuations in peel sugar levels observed within the individual treatments suggest a rather complex situation possibly involving simultaneous consumption of simple sugars along with degradation of polysaccharides and possibly movement of sugars between different tissues. Ascorbic acid content in the juice was maintained at higher concentration in proline-treated fruit than in coated fruit. When the two harvest dates were compared, it was evident that CI symptoms in fruit from the late harvest were minimal and appeared much later in storage compared to the mid season harvest (6 weeks versus 2 weeks). Higher contents of free amino acids, proline, and reducing sugars were found in the peel of fruit from second harvest compared to the first. It was concluded that all these constituents played an important role in alleviating CI symptoms. It is evident that proline plays an active role in reducing CI. However, the mechanism of coating and that of proline in reducing CI symptoms appear to be different with the possibility that reduction of water loss by coating physically impedes the cell collapse required for pitting to occur.