Disruption treatments on two strains of Streptococcus thermophilus: Levels of lysis/permeabilisation of the cultures, and influence of treated cultures on the ripening profiles of Cremoso cheese

Abstract

The influence of several disruption treatments on the viability and the release of intracellular enzymes of two strains of Streptococcus thermophilus (St1 and St2) was studied. In addition, the impact of the incorporation of disrupted cultures of St2 in Cremoso cheese was investigated. Enzymatic (mutanolysin) and mechanical treatments (bead mill and ultrasound) were the most effective for lysis, while chemical methods (ethanol and SDS) were effective as permeabilising agents. Physical methods (freeze and heat shock) were not suitable for disruption. The application of disrupted cultures of St2 in Cremoso cheese led to slight changes on the ripening profiles: decrease in lactose level, and increase in total free amino acids and acetic acid. This work demonstrated that certain types of disrupted St2 cultures could be suitable as source of key enzymes for the production of food with improved properties, such as lactose-hydrolysed dairy products or cheeses with higher proteolysis.