When purchasing Lysozyme, the most critical factor is Enzymatic Activity, usually measured in Units per milligram (U/mg). For food preservation, an activity level of 20,000 U/mg is common, whereas pharmaceutical grades may require >40,000 U/mg. You must also verify the Purity level (typically >95%) and the Source (most commercial lysozyme is derived from Egg White/Hen Egg White Lysozyme - HEWL). Ensure the pH stability range (usually 3.0 to 7.0) aligns with your specific application to prevent denaturation.