Abstract
Fermentation via lactic acid bacteria (LAB) is a viable option for producing natural flavour volatile organic compounds (VOCs). To better understand the relationship between the composition of the substrate used and the VOCs produced during fermentation, a defined medium (DM) is required. As a first step, the current study developed a DM consisting of glucose, peptone, sodium acetate, vitamins, and minerals. The growth of Levilactobacillus brevis WLP672 (LB672) and Pediococcus damnosus (PD5733) in the DM, was evaluated at different sodium acetate concentrations (0.1, 0.5, and 1.2%) after 0, 3, 5, 7, 9, 11, and 14 days of fermentation at 35 oC, by measuring the medium pH, OD600, and estimating the cell numbers by plating dilutions onto MRS agar plates. A 0.1% sodium acetate concentration was chosen to achieve the optimum growth for LB672 in DM. The DM was subsequently supplemented with either L-leucine (Leu), L-phenylalanine (Phe), or L-methionine (Met) to determine the impact of each amino acid on the VOCs produced by growing in LB672 in DM at 35 oC. To study the impact of glutamic acid on LB672 metabolism and VOC production, the first amino acid trial was carried in DM with and without glutamic acid (Glu) supplementation. Subsequently, to confirm some of the initial findings, a second amino acid trial was carried out using DM without Glu. In both amino acid trials, VOCs were measured using headspace-solid phase microextraction (HS-SPME) gas chromatography-mass spectrometry (GC-MS) after 3 and 9 days of LB672 fermentation. VOCs associated with the specific amino acids added included: benzaldehyde, phenylethyl alcohol, benzyl alcohol, and benzeneacetaldehyde with Phe; methional, methionol, dimethyl disulphide, and dimethyl trisulphide with Met; 3-methyl butanol, and 3-methyl butanal with Leu. Importantly, the relative abundance of VOCs was higher after 9 days of fermentation compared to 3 days of fermentation by LB672 in DM. This study reaffirms the importance of understanding the substrate composition when targeting the production of specific VOCs by LAB fermentation.