3. Results and discussion
3.1. Lactococci counts
No significant differences in lactococci counts from commercial starter were found among all cheeses at day 1, remaining nearly constant until day 30 and decreasing after 60 d (Table 1). However, a higher survival of starter lactococci was observed at the end of ripening in cheeses inoculated with C. tyrobutyricum CECT 4011 and INIA 68 than in control cheese and cheeses contaminated with other Clostridium species. This fact points out a positive effect of the metabolism of C. tyrobutyricum strains in cheese, creating a propitious environment for lactococci endurance. G omez-Torres et al. (2014) also reported higher levels of lactococci in bovine milk cheese made with commercial starter MA 16 and C. tyrobutyricum CECT 4011 spores than in cheese made only with commercial starter. Carbohydrate starvation and energy depletion prompt lactococci to shift their metabolism from glycolysis to amino acid catabolism and the additional source of energy increases the survival of L. lactis (Stuart, Chou, & Weimer, 1999). In a previous work in our laboratory C. tyrobutyricum strains showed proteolytic activity in milk (S. Garde, unpublished results) and could have supplied the amino acids that lactococci needed for amino acid metabolism.