Abstract
The cheese-derived strains Streptococcus thermophilus 84C isolated from Nostrano cheese, and Lactobacillus brevis DSM 32386 isolated from Traditional Mountain Malga cheese have been previously reported as γ-aminobutyric acid (GABA)-producers in vitro. In the present study, the ability of these strains to produce GABA was studied in experimental raw milk cheeses, with the aim to investigate the effect of the culture and the ripening time on the GABA concentration. The cultures used consisted on S. thermophilus 84C alone (84C) or in combination with L. brevis DSM 32386 (84C-DSM). The control culture was a commercial S. thermophilus strain, which was tested alone (CTRL) or in combination with the L. brevis DSM 32386 (CTRL-DSM). The pH evolution, microbiological counts, MiSeq Illumina and UHPLC-HQOMS analysis on milk and cheese samples were performed after 2, 9, and 20 days ripening. During the whole ripening, the pH was always under 5.5 in all batches. The concentration of GABA increased during ripening, with the highest content in 84C after 9 days ripening (84 ± 37 mg/kg), in 84C-DSM and CTRL-DSM after 20 days ripening (91 ± 28 and 88 ± 24 mg/kg, respectively). The data obtained support the hypothesis that S. thermophilus 84C and L. brevis DSM 32386 could be exploited as functional cultures, improving the in situ bio-synthesis of GABA during cheese ripening.
Highlights
Milk and dairy products are a good food source of high-quality proteins, minerals and vitamins
Several authors reported the ability of selected lactic acid bacteria (LAB) and bifidobacteria to produce this GABA in vitro from the precursor L-glutamic acid (Siragusa et al, 2007; Li and Cao, 2010; Carafa et al, 2015; Franciosi et al, 2015), and investigated the GABA-producing ability of LAB belonging to S. thermophilus, L. plantarum, L. paracasei, L. delbrueckii subsp. bulgaricus, and Lactococcus lactis in fermented cows’ milk and yogurt
The GABA concentration detected in the latter studies ranged between 15 and 5000 mg/kg, even though L-glutamate was added to milk before starting the fermentation process (Siragusa et al, 2007; Lacroix et al, 2013; Nejati et al, 2013; Linares et al, 2016). i.e., we reported the ability of Lactobacillus brevis BT66 and Streptococcus thermophilus 84C isolated from traditional alpine cheeses, to produce high concentration of GABA (Carafa et al, 2015; Franciosi et al, 2015)
Summary
Milk and dairy products are a good food source of high-quality proteins, minerals and vitamins. The GABA concentration detected in the latter studies ranged between 15 and 5000 mg/kg, even though L-glutamate was added to milk before starting the fermentation process (Siragusa et al, 2007; Lacroix et al, 2013; Nejati et al, 2013; Linares et al, 2016). I.e., we reported the ability of Lactobacillus brevis BT66 (hereafter DSM 32386) and Streptococcus thermophilus 84C isolated from traditional alpine cheeses, to produce high concentration of GABA (Carafa et al, 2015; Franciosi et al, 2015). The hypothesis that both strains (S. thermophilus 84C as starter and L. brevis DSM 32386 as non-starter) are able to produce GABA in cheese and to increase the concentration of GABA over ripening (2, 9, and 20 days) was tested. The use of raw milk was chosen for enhancing the natural production of free amino acids (including L-glutamate) by the proteolytic activity of milk resident bacteria on the peptides released by the hydrolytic action of the calf rennet on caseins (McSweeney, 2004)
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