Membrane studies in Japanese plums (Prunus salicina Lindl.)

[摘要] ENGLISH ABSTRACT:The export of Japanese plums from South Africa is challenging, since most cultivars are prone todevelop chilling injury (CI) when stored at low temperatures. This injury manifests as gelbreakdown or internal browning in the mesocarp tissue of the fruit on removal from low storagetemperature conditions, i.e. in the consumer's fruit basket, who subsequently does not buy plumsagain.Loss of cell membrane integrity and oxidative stress are, respectively, the primary and secondaryphysiological responses to CI. The main aim of this study was to investigate changes in cellmembrane composition and levels of antioxidants in plums throughout fruit development andmaturation, during forced air cooling (FAC) and storage under different temperature regimes.'Sapphire' (a chilling susceptible cultivar) accumulated high levels of glutathione andpolyunsaturated fatty acids (PUFAs) during fruit development. Therefore, the cultivar is protectedagainst lipid peroxidation while developing on the tree, but the high levels of PUFAs, which areeasily oxidised, may cause this cultivar to be chilling susceptible when stored at low temperatures.It is suggested that the high levels of monounsaturated fatty acids (MUFAs), which are not easilyoxidised, and ascorbic acid that accumulated in 'Angeleno' (a chilling resistant cultivar) during fruitdevelopment, render this cultivar CI resistant during long-term cold-storage.When stored at -0.5 °C, CI development increased at a higher rate, ethylene evolution rates werehigher and water soluble antioxidant activity (HAA), ascorbic acid and glutathione levels, and theMUFA:PUFA ratio were lower in H2 (more mature) 'Sapphire' plums than H1 fruit (less mature).Therefore, concurrent with H2 fruit having lower levels of antioxidants to quench free radicalscaused by chilling stress, their cell membranes were more vulnerable to oxidation due to theirphospholipid fatty acid composition. H2 fruit also had higher levels of saturated fatty acids, andhence less fluid cell membranes than H1 fruit when stored at -0.5 °C.An intermittent warming (IW) regime delayed symptom appearance and reduced CI severity inplums significantly compared to storage at -0.5 °C. Fruit stored under the IW regime had a more optimal phospholipid fatty acid composition and lower membrane sterol levels under shelf-lifeconditions to keep the membranes fluid. It also had higher levels of HAA and lipid solubleantioxidant activity, ascorbic acid and glutathione, which rendered fruit better protected againstoxidation.Elevated storage temperatures (2.5 °C to 7.5 °C) caused higher levels of lipid peroxidation or lowascorbic acid levels and poor fruit quality compared to the IW regime in 'Sapphire' plums. 'Laetitia'plums stored at 5 °C and 7.5 °C had significantly less CI than under the IW regime, but softenedquicker due to higher ethylene evolution rates.'Sapphire' tolerated both long and short FAC durations, but a slower initial FAC rate prevented CImanifestation and caused a higher HAA after cold-storage in this fruit. 'Laetitia' cooled with aslower initial FAC rate and for a longer duration resulted in the best fruit quality and had higherHAA, total phenolic, phospholipid and saturated phospholipid fatty acid concentrations duringstorage.

[发布机构] Stellenbosch University