2.1.2. Proteolytic Activity. The proteolytic activity of the isolates during fermentation of milk was measured by assessing
the free amino groups using the o-phthaldialdehyde (OPA) method. Briefly, 3 mL aliquots of the samples were mixed with 3 mL of 1% (w/v) TCA (trichloroacetic acid) and filtered using a filter paper (Dublin, CA, USA). The filtrate was collected and approximately 150