Effect of Frozen Periods on Volatile Flavor Compounds of Coconut Water Based on GC-IMS and Chemometrics Analysis

In this paper, gas chromatography-ion mobility spectroscopy (GC-IMS) and chemometrics were used to investigate the changes of volatile substances in mature coconut water after freezing at −18 ℃ for 0, 1, 2 and 3 months (CW0, CW1, CW2 and CW3). Results showed that GC-IMS could identify 29 volatile substances from four kinds of coconut water, including 13 alcohols, 6 esters, 6 aldehydes, 2 ketones and 2 acids. And the total amount (peak volume) of volatile substances decreased significantly with the extension of freezing periods. As the extension of freezing periods, the peak volume of acid compounds gradually increased and reached a maximum value in the coconut water freezing for two month (CW2) and then decreases. The peak volume of alcohols, esters, and aldehydes gradually increased and reached a maximum value in the coconut water freezing for three month (CW3), while the peak volume of ketones gradually decreased and reached a minimum value in the freezing coconut water for two month (CW2). Both principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) could distinguish four kinds of coconut water without over-fitting. Furthermore, 9 key markers were selected from the identified volatile substances based on the variable importance projection (VIP) value>1, which could achieve the respective clustering and effective differentiation of four coconut water in the cluster heat map analysis. Among them, ethyl acetate (D, M), isobutyral, acetaldehyde, ethyl caproate, 2-butanone, acetic acid (M) were the characteristic volatile substance of coconut water of different freezing periods. These results would provide support for the rapid identification of coconut water by GC-IMS at different freezing periodss