Table 2.

The significance probability (p-value, t-ratio) of regression coefficients in final reduced second-order polynomial models.

Variables	Significance	Main effects			Quadratic effects			Interaction effects
		x1	x2	x3	x11	x22	x33	x1 x2	x1 x3	x2 x3
PA%, Y1 (HIT1)	p-value	0.694	0.178	–	0.317	0.530	–	0.034*	–	–
	t-ratio	−0.402	1.419	–	1.037	0.643	–	−2.249	–	–
PA%, Y1 (HIT2)	p-value	0.535	0.899	0.921	0.329	0.872	0.117	0.420	0.287	0.405
	t-ratio	−0.642	−0.130	−0.102	1.026	−0.166	1.718	0.840	−1.125	−0.870
MI%, Y2 (HIT1)	p-value	–	0.112	0.125	–	0.927	0.668	–	–	0.003*
	t-ratio	–	−1.697	−1.633	–	−0.093	−0.439	–	–	3.514
MI%, Y2 (HIT2)	p-value	–	0.016*	0.216	–	0.000*	0.049*	–	–	0.058*(∼)
	t-ratio	–	−2.747	−1.296	–	4.890	2.157	–	–	−2.066
GA%, Y3 (HIT1)	p-value	0.554	0.100	0.013*	0.010*	0.089	0.341	0.001*	0.013*	–
	t-ratio	−0.611	1.794	2.959	3.110	1.866	−0.994	−4.331	−2.963	–
GA%, Y3 (HIT2)	p-value	0.072	0.271	–	0.067	0.306	–	0.027*	–	–
	t-ratio	−2.013	−1.166	–	2.054	1.079	–	2.584	–	–
TA%, Y4 (HIT1)	p-value	0.286	0.120	–	0.063	0.522	–	0.017*	–	–
	t-ratio	1.109	−1.657	–	−2.024	−0.657	–	2.700	–	–
TA%, Y4 (HIT2)	p-value	0.092	0.043*	0.868	0.172	0.013*	0.039*	0.024*	0.329	0.017*
	t-ratio	1.864	2.322	0.171	−1.473	−3.043	−2.379	−2.666	1.026	2.849

Abbreviation:HIT1, heat irradiation treatment; HIT2, heat ionization treatment; x₁, x₂, and x₃ are temperature (°C), time (min), and mass (g) for HIT1, respectively; x₁, x₂, and x₃ are temperature (°C), time (hrs), and pH for HIT2, respectively. *Significant at p < 0.05.