Use of a Milk Assay to Evaluate the Effects of Potassium on Commercial Yeast Lactases

ABSTRACT A reliable enzyme assay was developed that could routinely be used to accurately reflect lactase activity. The assay was performed with a nonfat dry milk substrate at 37°C. This procedure was then utilized to evaluate the effects of potassium ions as a stabilizer and activator on four yeast lactase enzymes. Low levels of potassium ions (K+), incorporated as potassium chloride (KCl), increased enzyme units by 20% and 30% in two liquid lactases derived from Saccharomyces lactis. Levels as high as 9.4% KCl increased the activity of one liquid lactase as much as 160%. The K+ activated and stabilized a powdered form of lactase isolated from Kluyveromyces fragilis. The activity of the fourth lactase tested, also derived from S. Zactis, was slightly enhanced.