Table 2.

The regression models for the process variables and the product properties when using the independent variables of feed moistures (x₁) and 4th barrel zone temperatures (x₂) of the pigmented rice extrudates

Response	BRE regression modelsa	R2	RRE regression modelsb	R2
SME (KW/kg)c	50.53 − 9.42x1 − 2.81x2 + 2.09x21 + 4.43x22	0.9947	57.68 − 8.50x1 + 2.82x22	0.8199
WSI (%)d	2.75 − 0.70x1 + 0.09x2 + 0.43x21 − 0.22x1x2	0.9834	7.37 − 2.75x1 + 0.44x2 − 0.53x21 − 0.43x22	0.9643
WAI (g/g)e	6.30 + 0.21x1 − 0.10x2 − 0.12x21 + 0.36x1x2	0.9428	ns	ns
Cold viscosity (cP)	51.25 − 13.23x1 + 3.63x2 + 4.43x21	0.9652	164.46 − 56.68x1 + 18.06x2 + 10.16x21 − 12.73x22	0.9762
Expansion Index	2.35 − 0.34x1 + 0.10x2 + 0.05x21 − 0.12x1x2	0.9656	2.77 − 0.40x1 + 0.03x2 − 0.12x22 − 0.05x1x2	0.9918
Specific volume (mL/g)	2.73 − 1.00x1 + 0.38x21	0.8854	2.77 − 1.18x1 + 0.46x21 − 1.04x1x2	0.9077
Compression force (N)	67.95 + 36.57x1 + 4.63x21 − 8.54x22 + 4.94x1x2	0.9814	29.13 + 25.82x1 − 4.76x2 + 14.06x21	0.9525
L* (lightness)	21.45 − 2.57x1 + 0.50x21 + 0.31x22	0.9785	36.13 − 3.23x1 − 0.32x2 − 0.34x21 − 0.70x22	0.9858
C* (chroma)	2.24 − 0.08x1 + 0.09x2 − 0.05x21 + 0.04x22	0.8702	ns	ns
h* (hue angle)	77.94 − 5.41x1 − 1.54x22 + 2.31x1x2	0.9474	40.86 + 0.87x1 + 0.38x21 + 0.39x1x2	0.9173

R², regression coefficient; ns, the mathematical models were not statistically significant (P ≤ 0.10)

^aBRE black rice extrudate

^bRRE red rice extrudate

^cSME specific mechanical energy

^dWSI Water Solubility Index

^eWAI Water Absorption Index