3.3. Optimization of Extraction Parameters

One-factor-at-a-time experiments were conducted to evaluate the effects of ultrasound frequency (from 20 KHz to 60 KHz), ultrasound power (from 60 W to 240 W), extraction temperature (from 30 °C to 70 °C), extraction time (from 10 min to 50 min), number of extractions (from 1 to 4 times) and liquid/solid ratio (from 10:1 to 50:1) on the polysaccharide yields of V. volvacea fruiting bodies.

Response surface methodology (RSM) was used to investigate the influence of ultrasound power (X₁), extraction temperature (X₂), extraction time (X₃) and liquid/solid ratio (X₄) on the polysaccharide yields of V. volvacea fruiting bodies. A Box-Behnken design with four factors and three levels was used for fitting a second order response surface [46].

Table 1 gave the factors, their values, and the experimental design, respectively. A mathematical model, describing the relationships between the response (the polysaccharide yield) and the process parameters in second order equation, was developed as follows:

where Y is the predicted response variable; A₀, A_i, A_ii, A_ij are constant regression coefficients of the model, and X_i, X_j (i = 1, 4; j = 1, 4, i ≠ j) represent the independent variables (extraction parameters) in the form of coded values. The accuracy and general ability of the above polynomial model could be evaluated by the coefficient of determination R².