Daily freshness decay of minimally processed apples using Vis/NIR Multispectral imaging : preliminary tests

In recent years, a substantial increase in the consumption of fresh-cut, or minimally processed, fruit and vegetables has been occurred. Changes in human life styles in fact often lead the consumers towards ease of use and healthy products. Monitoring the quality decay of fresh-cut products is necessary to control the freshness level during the entire production chain. Hence fresh-cut fruit and vegetable sector could be greatly helped by new analytical methods that are no-destructive and could be integrated into the production chain. The objective of this preliminary study was to test vis/NIR multispectral imaging to qualitatively assess the freshness decay throughout the day (12 h) of fresh-cut apple slices. Three Cripps Pink apples were bought at a large retail supermarket. Three samples were obtained by cutting a slice from an apple, transversally with respect to the stem-calyx axis. Only half slice portion was treated to simulate a ready-To-eat product, by dipping it for 5 min into an aqueous solution of 2 % (w/v) L-Ascorbic acid, while the other half was left unprocessed as a control portion. The apples were monitored every sixty minutes for twelve consecutive hours through the use of an 18-channel imaging system (430-970 nm, VideometerLab, by Videometer A/S, Denmark). A colour correction was performed on each acquisition through a normalization with respect to a multicolour reference acquired together with each sample, in order to take into account the stability of measuring conditions. Each image was segmented by using the k-means algorithm on the RGB picture and the apple flesh, i.e.The only part of interest, was separated from the background, the peel and the fruit core. After these pretreatments, all the acquisitions of the day for each slice were put together in a single dataset, unfolded in a two dimensional matrix, and the Principal Component Analysis (PCA) was applied. False color scores images were finally recomposed in order to highlight significant differences developed in a single apple slice. The results are encouraging. For all the samples the analysis distinguished between the treated portion of the slice and the unprocessed one, in particular with PC2 scores surface. Furthermore a clear time evolution along hours is shown by the apple slices for both the processed and unprocessed portions. This preliminary study demonstrated the applicability of multispectral imaging as a rapid and non-destructive approach for monitoring the freshness decay throughout the hours of minimally processed apple slices.