Susceptibility to postharvest peel pitting in Citrus fruits as related to albedo thickness, water loss and phospholipase activity

To study the influence of albedo thickness and phospholipase activity on the incidence of postharvest peel pitting (PP) in citrus fruit the tangor Ortanique, mandarin, with a thin albedo and tolerant to peel pitting were compared to that of the sensitive Navelate Navel orange with a thick albedo. Fruit from both cultivars was subjected to identical postharvest practices consisting of washing and/or waxing on a commercial packline and thereafter the fruit was stored for 3 weeks at 30% or 90% relative humidity (RH). For comparison, other fruit lots were washed manually and stored as above. Periodically, water loss, water, osmotic and turgor potentials were monitored and peel pitting incidence was evaluated. For both cultivars fruit weight loss was higher in packline than in manually processed, however, only 'Navelate Navel' orange fruit developed peel pitting with higher incidence in the packline treatments compared with manually processed fruit. In addition, wax coating exacerbated this effect leading to higher pitting of 'Navelate Navel' orange. Accordingly, water potential variations were more pronounced in wax coated fruit from 'Navelate Navel' orange as compared to 'Ortanique' mandarin. Furthermore, Phospholipase D and A(2) (PLD and PLA(2)) activities were higher in the peel from the pitting susceptible cultivar, suggesting their activation by sharper changes in peel water potential. Collectively, results suggest that water movement through cell layers in a thick albedo is related to postharvest peel pitting and support the notion that inability to properly adjust water status in peel tissue after prolonged water stress results in cell collapse and tissue damage. Moreover, enhanced phospholipase activity appears to be also a response of peel tissues to conditions causing peel pitting. (C) 2016 Elsevier B. V. All rights reserved.