Influence of autochthonous lactic acid bacteria on cheese microflora and free amino acids of sweet Pecorino Sardo PDO

Abstract

Pecorino Sardo Protected Denomination of Origin (PDO) is a half-cooked paste cheese produced only with full cream ewes’ milk that can be thermised if necessary. Pecorino Sardo PDO is a cylindrical-shaped cheese with flat faces and a straight or slightly convex rim. Two typologies of Pecorino Sardo PDO are currently produced: "sweet" when the ripening time is short (20-60 days), and "ripened" when the ripening is longer than 2 months. In this study we evaluated the influence of autochthonous lactic acid bacteria (LAB) on the microbiological and nutritional characteristics of the “sweet” type of Pecorino Sardo PDO. For this aim two cheese-making trials (experimental and control) were carried out on an industrial scale. Experimental Pecorino Sardo cheese was manufactured with the addition of an autochthonous starter culture prepared with Streptococcus thermophilus + Lactobacillus plantarum + Lactococcus lactis subsp. lactis + Lactobacillus casei subsp. casei while control cheese was manufactured with the addition of a commercial starter including Streptococcus thermophilus + Lactococcus lactis subsp. lactis + Lactococcus lactis subsp. cremoris. The evolution of free amino acids (FAAs) and cheese microflora were then monitored in both cheeses at different ripening times. The addition of the selected autochthonous starter resulted in a substantial increase of the mesophilic lactic microflora, lactobacilli in particular, in the experimental curd and cheeses. The presence of spoilage microorganisms in the experimental cheeses, such as total and fecal coliforms, was significantly reduced compared to the control indicating a suitable activity of the starter during the fermentation phase. Moreover, the use of the selected autochthonous LAB allowed the production of experimental cheeses with a significantly higher amount of FAAs compared to Pecorino Sardo control cheeses. It is concluded that the selected starter used in the experimental trials is suitable for the production on a industrial scale of the “sweet” type of Pecorino Sardo PDO