In situ assessment of quality-related compounds in fruits by using fluorescence sensors

Fruit quality compounds, such as antioxidant phenolics and chlorophyll, were assessed in situ by using a fluorescence method applied by a portable sensor. Indices of anthocyanins (ANTH) and flavonols (FLAV) localized on the fruit surface were obtained based on their screening of chlorophyll fluorescence excitation. The chlorophyll content was estimated by the far red to red chlorophyll fluorescence ratio (CHL index), due to the partial reabsorption of red fluorescence by chlorophyll itself. In kiwifruits, the CHL index was found to be well linearly correlated to the chlorophyll content determined by wet chemistry on the same fruit samples. Full sunlight exposed kiwifruits possessed a higher content of chlorophyll than shaded kiwifruits. This is an important parameter to know for assessing fruit quality and storability. Based on the estimation of the red-pigmented anthocyanins, we defined a new rapid method to determine the maturity level of olives after harvest, giving the proportion of red and green olives, important for the quality of the olive oil produced. In plums, ANTH and FLAV were found to be linearly correlated to the actual content of compounds measured by HPLC analysis of skin extracts. These indices can be, therefore, used to predict the phenolic antioxidant potential of plums and to define their maturity stage.