Evaluation of browning ratio in an image analysis of apple slices at different stages of instant controlled pressure drop‐assisted hot‐air drying (AD‐DIC)

Abstract BACKGROUND Computer vision‐based image analysis systems are widely used in food processing to evaluate quality changes. They are able to objectively measure the surface colour of various products since, providing some obvious advantages with their objectivity and quantitative capabilities. In this study, a computer vision‐based image analysis system was used to investigate the colour changes of apple slices dried by instant controlled pressure drop‐assisted hot air drying ( AD‐DIC ). RESULTS The CIE L* value and polyphenol oxidase activity in apple slices decreased during the entire drying process, whereas other colour indexes, including CIE a* , b* , Δ E and C* values, increased. The browning ratio calculated by image analysis increased during the drying process, and a sharp increment was observed for the DIC process. The change in 5‐hydroxymethylfurfural (5‐ HMF ) and fluorescent compounds ( FIC ) showed the same trend with browning ratio due to Maillard reaction. Moreover, the concentrations of 5‐ HMF and FIC both had a good quadratic correlation ( R 2 > 0.998) with the browning ratio. CONCLUSION Browning ratio was a reliable indicator of 5‐HMF and FIC changes in apple slices during drying. The image analysis system could be used to monitor colour changes, 5‐HMF and FIC in dehydrated apple slices during the AD‐DIC process. © 2016 Society of Chemical Industry