Flesh temperature during impact injury and subsequent storage conditions affect the severity of colour change caused by red drupelet reversion in blackberries

Abstract

Red drupelet reversion (RDR) is a physiological occurrence in blackberries where drupelets revert from black at harvest to red postharvest. The objectives of this trial were to assess the effects of temperature during mechanical injury and temperature changes following injury of blackberries on the subsequent development of RDR. Individual fruit were subjected to mechanical injury from a steel ball dropped from a height of 25 cm at initial temperatures of 15, 25, and 35°C. Following injury, fruit were cooled to 2°C rapidly in a -24°C cooler or slowly in a 2°C cooler. Colour of the impact site and of undamaged control fruit were measured 24 h and 7 days after the initial impact injury using a colourimeter. Impact injury caused a significant colour difference (∆E) compared to control in 95% of fruit. There were significant interactions between initial temperatures and cooling rates on the colour of the impact site 24 h and 7 days after treatment. Higher fruit temperatures at the time of mechanical injury and a faster cooling rate post-injury were associated with increased lightness and chroma. The results confirm that mechanical injury to blackberry fruit leads to RDR, and that temperature of fruit at the time of injury and subsequently can influence the severity of RDR.