BB-rel+ner@ldeleger:BB-rel+ner-F-17953562-001 JSONTXT

The E. faecalis strains were characterized by a relevant reduction power. In fact, this species showed the lowest Ehmin (−221 ± 13·4 mV), the largest Δmax (326 ± 93·1 mV), and was the fastest to reach Δmax (t*: 1·1 ± 0·3 h) (Table 2). The behaviour of the 10 strains was the same except for VS368, which was the most rapid E. faecalis strain (t*: 0·5 h) and, at the same time, the one showing the highest Ehmin (−189 mV). At 37°C, the mean curves for E. faecium, E. durans and L. lactis ssp. lactis had similar Eh evolution (sharp decrease around the second hour of culture), but the minimum values were different. The strains of L. lactis ssp. lactis were more reducing than the strains of the other two species: Ehmin: −162 ± 32·9 mV vs−138 ± 31·3 and −120 ± 29·0, respectively (Fig. 2). The 10 strains of E. faecium had similar reduction power, although after 24 h of incubation three strains, FK5, FK6 and FK7, isolated from Scimudin cheese, showed higher reducing activity than the other seven. The slowest and least reducing strain, 174, was isolated from Caciocavallo Ragusano cheese. The E. durans strains showed similar Eh evolution over 24 h, except for VS263 isolated from Formagèla Valseriana cheese. VS263 was the fastest to achieve Ehmin and Δmax (tmin: 2·0 h; t*: 1·0 h) and had higher reduction power (Ehmin: −171 mV) than the others. The L. lactis ssp. lactis strains had the highest reduction activity after the E. faecalis strains. Their Ehmin values were: −162 ± 32·9 mV, and they were characterized by a rapid decrease in tmin 3·8 ± 0·8 h and t* 2·2 ± 0·3 h. Once again ‘atypical’ behaviour was detected in the strains isolated from Formagèla Valseriana, namely VS179 and VS180, these being revealed to have lower reduction power compared with the other lactococci belonging to the same species. Streptococcus thermophilus, the major species used as the starter culture in cheese manufacture, was the slowest of the tested LAB species. Its reduction activity increased constantly, and it consequently had a smaller Δmax; all the strains reached Ehmin at the end of the 24-h incubation period, the exception being O2A isolated from Fontina, found to be the most reducing and reaching Ehmin after 14 h. Instead, strain LOD11 was the slowest S. thermophilus strain (t*: 4·5 h), however it also had the highest Ehmin (−45 mV). Among the lactobacilli, the highest reducing species was L. paracasei ssp. paracasei: their strains showed the lowest Ehmin (−169 ± 13·8 mV), and were the fastest to achieve Δmax (4·2 ± 1·3 h). The B1B strain showed similar behaviour to the enterococci (Ehmin: −186; t*: 3 h) (Table 3). On the contrary, the BB3 strain isolated from Formai de Mut cheese was very slow: it took 12 h to reach Ehmin. The redox curve of L. paracasei ssp. paracasei, comparable with that of E. faecalis and reaching similar final values, shows a more gradual slope (lower Δmax) reached over longer times. With regard to the strains of L. plantarum, the redox potential course is characterized by an initial stabilizing period followed by a rapid and consistent decrease corresponding to the major Δmax (229 ± 88·6 mV) found among the tested lactobacilli. This species showed good reduction power and was as fast in reaching Δmax as L. paracasei ssp. paracasei. The lowest reducing lactobacilli were found to be L. delbrueckii ssp. bulgaricus and L. helveticus (Ehmin: −54 ± 20·4 mV and −54 ± 23·8 mV). Furthermore, for both the thermophilic lactobacilli species, Eh decreased slowly (L. delbrueckii ssp. bulgaricus: t*: 6·0 ± 1·7 h and L. helveticus t*: 6·4 ± 1·6 h), the mean curves showing similar evolution over the 24-h period. All the strains of P. pentosaceus had poor reduction activity. In fact, they showed the highest Ehmin (−59 ± 23·5 mV), the smallest Δmax (24 ± 8·9 mV) and were the slowest to achieve Δmax (5 ± 2·2 h). Most of the selected isolates for this investigation came from cheeses produced in the mountains, and it is interesting to note that the majority of the strains from Scimudin cheese (77·7%) were the fastest to achieve Ehmin, while the strains isolated from Formai de Mut took more time to reach the minimum Eh value. Isolated from Formagèla Valseriana were the strains L. lactis ssp. lactis and E. durans; these strains, except for VS263, showed lower reduction power than the other strains of the same species, but, nevertheless, took less time.