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Table 4 Levels of independent variables established according to the central composite design (CCD)

From: Influence of astaxanthin, emulsifier and organic phase concentration on physicochemical properties of astaxanthin nanodispersions

Variable Independent variable levels
Independent variables Low - α Center - α High
 Concentration of astaxanthin (wt %, x1) 0.02 0.1 0.2 0.3 0.38
 Concentration of emulsifier(wt %, x2) 0.2 1 2 3 3.8
 Concentration of astaxanthin (wt %,x3) 2 10 20 30 38