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Bacterial fermentation is considered to be a cost-effective means of generating desired flavour compounds from plant-based substrates. However, the wide range of substrates present in plants makes it challenging to understand how individual components impact on flavour volatile organic compound (VOC) production. To simplify this, a defined medium can be used to better understand VOCs production with regard to individual compounds. In the current study, the VOCs produced by the lactic acid bacterium, Levilactobacillus brevis WLP672, growing in a defined medium containing different carbon sources (either glucose (DM), fructose (DMFr) or citrate (DMCi)) under a range of fermentation conditions (time: 0, 7, and 14 days; and temperature: 25 and 35 °C) were assessed using proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). Among the detected mass peaks (m/z), after 7 days of fermentation, the concentrations of m/z 45.033 (t.i. acetaldehyde), m/z 49.011 (t.i. methanethiol), and m/z 89.060 (t.i. ethyl acetate) were significantly (p < 0.05) higher in DM at 35 °C than all other treatments at either temperature. The knowledge obtained will help to produce desirable LAB fermentation flavour VOCs or VOC mixtures that could be used in developing plant-based analogues with acceptable sensory properties. [ABSTRACT FROM AUTHOR]

Lactic acid bacteria (LAB) fermentation is a viable approach for producing plant-based flavour compounds; however, little is understood about the impact of different LAB strains and medium compositions on the production of volatile organic compounds (VOCs). This study investigated the impact of the addition of individual amino acids (AAs) (L-leucine, L-isoleucine, L-phenylalanine, L-glutamic acid, L-aspartic acid, L-threonine, or L-methionine) to a defined medium (DM) on the generation of VOCs (after 0, 7, and 14 days) by one of three LAB strains (Levilactobacillus brevis WLP672 (LB672), Lactiplantibacillus plantarum LP100 (LP100), and Pediococcus pentosaceus PP100 (PP100)), using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS). The concentration of m/z 45.031 (t.i. acetaldehyde) was significantly (p < 0.05) higher after 7 days of fermentation by LP100 in the DM supplemented with threonine compared to all other media fermented by all three strains. The concentrations of m/z 49.012 (t.i. methanethiol) and m/z 95.000 (t.i. dimethyl disulfide) were significantly (p < 0.05) higher after 7 days of fermentation by either LP100, PP100, or LB672 in the DM supplemented with methionine compared to all other media. Information on the role of individual AAs on VOCs generation by different LAB strains will help to guide flavour development from the fermentation of plant-based substrates. [ABSTRACT FROM AUTHOR]

The varieties of vines tolerant to the main fungal diseases are the object of growing interest because they require fewer treatments for the production of quality grapes. These varieties are considered qualitatively unsuitable especially for some characteristics such as the foxy aroma, the level of anthocyanin diglucosides and the level of methyl alcohol in wines. In the three-year period 2016-2018, from a population of 74 medium resistant varieties placed in a single collection, in Marlengo (BZ), young leaves were taken for DNA analysis; annually 2 surveys of the OIV 452 453, 455 and 456 descriptors were carried out, and, at 18° Brix, sombunches were collected for the analysis of different metabolites. Nano-vinifications were carried out for 32 genotypes. Genotypes with different levels of stacked loci associated with resistance to downy and powdery mildew were detected, with different resistance behaviors over the years. Only some genotypes have aromas of foxy and only 20% of the genotypes analyzed have levels of anthocyanin diglucosides higher than the levels required by current legislation. Some vinifications showed methanol levels higher than the legal limit set. High percentages of genotypes respected the legal levels of metabolites required by current regulations and only genotypes with the presence of V. labrusca showed the aroma of foxy.