Volatile Compound Analysis of ‘Monthong’ Durian Harvested at Different Maturity Stages using Flash Gas Chromatography Electronic Nose

Abstract

This research investigated the effects of maturity stage on the development of volatile compounds during ripening of ‘Monthong’ durian. Eighty-six raw durians were obtained from orchards, then stored at 30°C and 70% relative humidity to allow the fruits to ripen. Dry matter (DM) content of each ripe durian was determined using an oven method and then the DM content was used to classify each fruit into one of the four groups, with group 1 to group 4 having DM contents of <26.00%, 26.00-29.99%, 30.00-33.99% and >34.00%, respectively. The DM contents of durians in group 1 to group 4 corresponded to 60, 70, 80 and 90% maturation levels, respectively. Volatile compounds of ripe durian flesh from each fruit were identified and quantified using a flash gas chromatography electronic nose equipped with MXT-5 and MX-1701 columns and AroChembase software. Results showed that, based on DM contents, 22, 17, 23 and 24 durian samples were categorized into group 1 to group 4, respectively and that 14 volatile compounds (5 alkanes, 2 ketones, 3 alcohols, 3 esters, and 1 alkanethiol) were detected in all durian groups at varying concentrations. These compounds mainly described fruity, sweet and sulfurous characteristics of the samples. The highest concentration was detected for decane, followed by 2-(5H)-furanone and 1-hydroxy-2-(methylthio)-ethane, respectively. Durian samples in group 1 tended to have lower volatile compound concentrations than those in group 2, although the differences were not significant (p>0.05). Contrarily, differences were evident between durians in group 2 and 3, with the former having lower (p<0.05) concentrations of methyl cyclohexanecarboxylate, butanoic acid, octadecane, decane, benzyl alcohol, eicosane and ethyl tetradecanoate than the latter. When comparing between the samples in group 3 and 4, concentrations of all volatile compounds were not significantly different (p>0.05). Results suggest that maturity stage at harvest is a critical factor that determines eating quality of durian and that the fruit should be harvested after reaching at least 80% maturation level (group 3) so that volatile compounds can be fully developed during ripening. Sensory evaluation should be further performed to substantiate the results of the present study.