Impact of two starter cultures on proteolysis in Kashkaval cheese

Summary Kashkaval cheese is produced with a traditional yogurt starter culture S. thermophilus 13a + Lb. delbrueckii ssp. bulgaricus 2–11. The present paper has investigated the contribution of a selected starter culture (Lactococcus lactis ssp. lactis C11 + Streptococcus thermophilus P23 + Lactobacillus casei ssp. casei RP5) for proteolysis of Kashkaval (A) in comparison with a traditional yogurt culture (B) and soluble nitrogen (at pH 4.6 and in 12% TCA) and free amino acids as indicators of Kashkaval ripeness. After the microflora was isolated and differentiated, the largest count of mesophilic cocci (69%) and lower counts of thermophilic cocci (19.8%) and mesophilic lactobacilli (11.2%) were found in cheddared curd A, whereas in cheddared curd B thermophilic cocci (69%) prevailed over thermophilic lactobacilli (30%). Hot-brining of curd at 72 °C for 2 min destroyed 91 and 84.5%, respectively, of the starter microflora A and B and two batches of Kashkaval started ripening with 3.9 × 10⁸ c.f.u. g⁻¹ and 3.4 × 10⁸ c.f.u. g⁻¹. The ripening of Kashkaval cheese occurred mainly under the influence of the starter microflora. Ripening of Kashkaval A occurred with dominating presence of Lactobacillus casei ssp. casei RP5 from 64% at day 30 to 95.2% at day 90. In Kashkaval B the participation of Lactobacillus delbrueckii ssp. bulgaricus 2–11 increased from 36.3 to 39.9%, however it always remained relatively smaller (1.5–2.3-fold) than that of thermophilic cocci. Great activity of transformation of pH 4.6-soluble nitrogen into TCA-soluble nitrogen in Kashkaval A was registered. The high proteolytic activity of starter culture A shortened the ripening process by 30 days (30-day-old Kashkaval A had 17.3% level of proteolysis, 29.9% depth of proteolysis). Kashkaval B reached satisfactory ripeness properties when it was 60 days old (20.2% level of proteolysis, 24.9% depth of proteolysis). The high activity of amino acid release mainly by Lactobacillus casei ssp. casei RP5 and to a lesser extent by the cocci caused accumulation of a considerable amount of free amino acids in ripe Kashkaval A (421.9 mg (100 g)⁻¹ for 30-day-old Kashkaval). In ripe 30-day-old Kashkaval A the concentration of free amino acids was three times higher than in Kashkaval B, with domination of lysine, leucine, phenylalanine, valine and threonine.