Discrimination of internal browning in pineapple during storage based on changes in volatile compounds

Internal browning (IB) is a physiological disorder without external symptoms of postharvest pineapples, but whether and how IB influences pineapple volatiles remain unknown. We examined eigenvalues of volatiles in 'Comte de Paris' pineapples with or without IB using electronic nose (E-nose) and gas chromatography-mass spectrometry (GC-MS). Correlation coefficients between the responses of E-nose sensors S7 and S9 and IB were 0.836 and 0.804, respectively. The multilayer perceptron neural network and radial basis function neural network models classified IB degree with accuracy of 94.77% and 91.67%. GC-MS analysis revealed 30 volatile substances upregulated in pineapple with IB compared to those without, of which 15 were esters. IB regulated volatile compound synthesis through the lipoxygenase pathway which involved lipoxygenase, pyruvate decarboxylase 1, alcohol dehydrogenases, acyl-CoA oxidase 1, and alcohol acyltransferase genes and their related enzymes. These results suggested that volatiles regulated by IB could be used to discriminate IB severity in pineapples.