Table 4. Response surface model for making condition

Responses	Quadratic polynomial model	R2	p-value
Y1	Y1=85.6667+3.5792X1–0.7542X2+6.8292X3+0.3542X4+0.4313X1X2–0.4062X1X3–0.4937X1X4–1.4313X2X3–0.8938X2X4+0.2687X3X4–1.0823X12–1.2823X22–5.0948X32+0.3302X42	0.791	0.000
Y2	Y2=5.14667+0.06167X1–0.02000X2–0.44417X3–0.06583X4+0.0000X1X2+0.01875X1X3+0.01250X1X4+0.12250X2X3+0.06125X2X4–0.01500X3X4–0.01896X12–0.07521X22+0.08979X32–0.00646X42	0.905	0.000

X₁, skim milk conc. (%); X₂, temperature (°C); X₃, incubation time (h); X₄, starter conc. (%); Y₁, ACE inhibitory activity (%); Y₂, pH; ACE, angiotensin converting enzyme.