Objective instrumental method for blueberry (Vaccinium spp.) juiciness determination compared to sensory evaluation

The sensory appreciation of blueberry depends, amongst other factors, on its juiciness. Blueberry juiciness levels differ between varieties and even within the same variety across different batches. The aim of this research was to develop an objective method for juiciness quantification as a screening tool to facilitate future research on the various factors affecting blueberry juiciness. The method is based on the measurement of the juice spot area (Ajuice) on a filter paper after mechanical compression of blueberry using a texture analyzer. This was achieved through image processing of the scanned images of wetted filter papers as an alternative to weighing. The measured juice spot area proved to be reliable given its high correlation to the actual mass of absorbed juice on the filter paper (Mjuice) (r = 0.990) and to a sensory juiciness evaluation response (Sjuice) (r = 0.776) established by a consumer panel. No clear correlations were observed between any of the measured fruit mechanical properties and juice release. Most likely, this was due to the inseparable contribution of the skin as a consequence of analyzing intact blueberries. In contrast, a stepwise linear regression model revealed that sensorially perceived juiciness was not only related to juice spot area but also to the inflection point of the force deformation curve and drop slope as measured during fruit compression. This study has established the practical use of Ajuice for juiciness screening of blueberry varieties and its potential for tracking juiciness changes over time such as during fruit ripening and storage.