Liquid-core alginate hydrogel beads loaded with functional compounds of radish by-products by reverse spherification: Optimization by response surface methodology

Liquid-core hydrogel beads (LHB) were formulated through reverse spherification, by sodium alginate and using calcium lactate (CL) to replace the common calcium source, calcium chloride. The effect of four independent variables: first gelation time (X1), CL concentration in first gelation (X2), secondary gelation time (X3), and CL concentration in secondary gelation (X4), on seven physical properties of LHB: diameter, hardness (Y1), loading efficiency (LE, Y2), release amount of total phenolic compounds (TP) in simulated gastric (Y3) and small intestinal (Y4) fluid, swelling capacity (Y5), and sphericity (Y6), were evaluated. Furthermore, a central composite design with response surface methodology was used for the optimization of LHB properties Y1-Y6, and the importance of the four independent variables to physical properties was analyzed. The diameter of LHB was in the range of 4.17-5.84 mm. The optimal conditions of LHB formulation were first gelation time of 23.99 min, 0.13 M CL in the first gelation, secondary gelation time of 6.04 min, and 0.058 M CL in secondary gelation. The optimized formulation of LHB demonstrated 25.5 N of hardness, 85.67% of LE and 27.38% of TP release in simulated gastric fluid with the small error-values (−2.47 to 2.21%).