Table 1. Face-centered central composite design with independent (temperature and time) and response variables (extraction yield and gel strength) for gelatin extraction from Korean native black goat skin

Experiment number	Factors		Response variables
	X1	X2	Extraction yield (%, w/w)	Gel strength (g)
1	60	3	12.1	260.4
2	60	3	12.6	262.9
3	60	3	12.5	263.9
4	70	4	13.3	251.8
5	70	3	13.2	255.6
6	50	3	10.7	271.6
7	60	2	12.0	264.3
8	60	3	12.6	262.2
9	60	4	13.4	252.5
10	60	3	13.0	266.4
11	70	2	12.7	256.1
12	50	2	10.2	263.2
13	50	4	11.2	265.2

X₁, extraction temperature (°C); X₂, extraction time (h).