Abstract: The aim of this study was to evaluate the volatile flavor compounds of grapefruit juice fermented with two isolates, Lactobacillus plantarum L1 and L. fermentum L2, which were previously isolated in our laboratory. The volatile flavor compounds were measured by static-headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and analyzed by principal component analysis (PCA). The aroma compounds were detected by electronic nose. Results indicated that a total of 79 volatile flavor compounds were identified, including 20 alcohols, 15 olefins, 12 alkanes, 10 ketones, 5 aldehydes, 2 esters and 15 other compounds, 59, 36 and 35 of which were present in fermented grapefruit juices with L1, L2 and both, respectively. Fermented grapefruit juice with probiotics contained more volatile compounds than fruit grapefruit juice; some esters were detected only in the former. In addition, aldehydes accounted for a much lower percentage of the total volatiles, while alcohols, ketones and alkanes accounted for a significantly higher percentage after fermentation as compared with fresh grapefruit juice. All four samples were clearly discriminated by PCA on the basis of their characteristic flavor components. The results of electronic nose revealed fermented grapefruit juices with different Lactobacillus species to be significantly different in flavor. In conclusion, these results provide insight into the flavor characteristics of fermented grapefruit juice and also provide a basis for product quality evaluation.

Key words: Lactobacillus plantarum, Lactobacillus fermentum, volatile flavor compounds, electronic nose