Elucidating the effects of Lactobacillus plantarum fermentation on the aroma profiles of pasteurized litchi juice using multi-scale molecular sensory science

Abstract

Three Lactobacillus Plantarum (LP), namely LP28, LP226 and LPC2W, were employed to investigate the effect on the aroma profiles of pasteurized litchi juice using E-nose, GC-IMS, GC-MS, and sensory evaluation. The E-nose results showed that pasteurization weakened the flavor profile of litchi juice, while LP fermentation effectively promoted flavor formation. The GC-MS analysis demonstrated that pasteurization significantly reduced the content of alcohols (28.51%), especially geraniol and citronellol, which give litchi juices a fruity and floral aroma. Different LP fermentation enhances the characteristic aroma and produces some new compounds that give it a strong fruity and citrus-like aroma. Moreover, 37 aroma-active compounds (OAV>1) indicated that the linalool (OAV 7504) was the highest, followed by (Z)-rose oxide (OAV 4265), 1-octen-3-ol (OAV 1055) and geraniol (OAV 764), which jointly form the main characteristic flavor. More esters were identified by GC-IMS, indicating the advantage of the combined approach for a better understanding of the impact of pasteurization and fermentation on the litchi juice. The sensory evaluation confirmed that the aroma attributes of fruity, citrus-like, floral, sweet and litchi-like were stronger for the samples fermented by LP28 than those for the other samples. The combination strategy used in this study would facilitate the awareness of litchi juice aroma and broaden our insight into the deep processing of litchi.

Keywords: Fermentation; Gas chromatography-ion mobility spectrometry; Gas chromatography-mass spectrometry; Lactic acid bacteria; Litchi juice; Odor activity value.

Graphical abstract

Fig. 1

(A) Radar chart of the electronic nose (E-nose) response data; (B) PCA sample distribution diagram and component distribution plot of E-nose of litchi juices, pasteurized litchi juices and LAB fermented litchi juices. (F: original litchi juices, F–P: pasteurized litchi juices, F–C2W: F–P fermented by Lactobacillus plantarum C2W, F-226: F–P fermented by Lactobacillus plantarum 226, F-28: F–P fermented by Lactobacillus plantarum 28).

Fig. 2

The result of original litchi juice, pasteurized litchi juice and LAB fermented litchi juices via GC-IMS. (A) 3D chromatogram; (B) 2D chromatogram; (C) discrepancy image. (F: original litchi juices, F–P: pasteurized litchi juices, F–C2W: F–P fermented by Lactobacillus plantarum C2W, F-226: F–P fermented by Lactobacillus plantarum 226, F-28: F–P fermented by Lactobacillus plantarum 28).

Fig. 3

The result of original, pasteurized and LAB fermented litchi juices via GC-IMS. (A) fingerprints. Each row represents all the signals selected in a sample. Each column represents the signals of the same volatile aroma compounds. M and D denote monomer and dimer, respectively; (B) principal component analysis results; (C) nearest neighbor analysis. (F: original litchi juices, F–P: pasteurized litchi juices, F–C2W: F–P fermented by Lactobacillus plantarum C2W, F-226: F–P fermented by Lactobacillus plantarum 226, F-28: F–P fermented by Lactobacillus plantarum 28).

Fig. 4

Comparison of volatile compounds in the original, pasteurized and LAB fermented litchi juices by HS-SPME-GC-MS. (A) Numbers of volatile compounds types in the litchi juices. (B) PLS-DA score plot of volatile compounds. (C) VIP scores in PLS-DA. (D) Heat map clustering of volatile compounds. (F: original litchi juices, F–P: pasteurized litchi juices, F–C2W: F–P fermented by Lactobacillus plantarum C2W, F-226: F–P fermented by Lactobacillus plantarum 226, F-28: F–P fermented by Lactobacillus plantarum 28).

Fig. 5

The Venn diagram and the common aroma-active compounds with >1.0 OAVs in the litchi juices and fermented litchi juices. (A): The Venn diagram of aroma-active compounds in the original litchi juice and pasteurized litchi juice; (B): The Venn diagram of aroma-active compounds in the pasteurized litchi juice and fermented litchi juices; (C): The common aroma-active compounds with >1.0 OAVs in all litchi juice samples. Note: Compound name, scent description, and OAVs were listed in detail. (F: original litchi juices, F–P: pasteurized litchi juices, F–C2W: F–P fermented by Lactobacillus plantarum C2W, F-226: F–P fermented by Lactobacillus plantarum 226, F-28: F–P fermented by Lactobacillus plantarum 28).

Fig. 6

The radar profile of sensory evaluation of the samples. (F: original litchi juices, F–P: pasteurized litchi juices, F–C2W: F–P fermented by Lactobacillus plantarum C2W, F-226: F–P fermented by Lactobacillus plantarum 226, F-28: F–P fermented by Lactobacillus plantarum 28).