Table 1. List of proteases used in this study

	Enzyme	Type	Activity (U/mg)	Optimal condition
1	Alcalase 2.4 L FG	Endo	0.54±0.05	pH 6.5-8.5, 55-70°C
2	Flavourzyme 1,000 L	Exo	0.76±0.09	pH 6, 55-60°C
3	Neutrase 0.8 L	Endo	2.10±0.06	pH 8.0, 50°C
4	Protamex	Endo	3.02±0.31	pH 5.5-7.5, 35-65°C
5	Papain T100 MG	Endo	0.24±0.01	pH 5-8, 65°C
6	Bromelain BR 1200	Endo²exo	0.30±0.10	pH 7.0, 50°C
7	Prozyme 2000P	Exo	3.60±0.10	pH 5-5.5, 55-60°C
8	Foodpro alkaline protease	Endo	1.09±0.06	pH 6.5-9, 55-60°C
9	Protease (Asp. saitoi)	-	0.09±0.04	pH 3.5-5.5, 45°C
10	Ficin (fig tree latex)	Endo	0.20±0.05	pH 6.5, 60°C
11	Sumizyme LP	Endo	0.69±0.03	pH 6.0, 50°C

Protease activity was assayed using casein sodium salt as the substrate, according to the He et al. (2004) and Joung et al. (2018) with some modfication. The reaction mixture (2 mL) containing each 1 mL of diluted enzyme, 2% casein and 0.9 mL of 50 mM Tris-HCl (pH 7.0) was incubated at 40°C for 20 min. The reaction was terminated by adding 2 mL of 0.4 M trichloroacetic acid. After centrifugation, 1 mL of supernatant was mixed with 5 mL of 0.4 M sodium carbonate and 1 mL of 1 N Folin-Ciocalteu reagent, and incubated at 40°C for 20 min. The absorption value of the mixture was measured at 660 nm. One unit of protease activity was defined as the amount of the enzyme required to release 1 μM of tyrosine from casein per minute under the above conditions.