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Modeling of the Effect of Freezer Conditions on the Principal Constituent Parameters of Ice Cream by Using Response Surface Methodology

K. Inoue^*,1, H. Ochi, M. Taketsuka^*, H. Saito, K. Sakurai^*, N. Ichihashi^*, K. Iwatsuki and S. Kokubo

^* Food Research & Development Institute,
Food Science & Technology Institute, and
Research & Development, Morinaga Milk Industry Co., Ltd., 1-83, 5-Chome Higashihara, Zama, Kanagawa 228-8583, Japan

¹ Corresponding author: ke-inoue{at}morinagamilk.co.jp

A systematic analysis was carried out by using response surface methodology to create a quantitative model of the synergistic effects of conditions in a continuous freezer [mix flow rate (L/h), overrun (%), cylinder pressure (kPa), drawing temperature (°C), and dasher speed (rpm)] on the principal constituent parameters of ice cream [rate of fat destabilization (%), mean air cell diameter (µm), and mean ice crystal diameter (µm)]. A central composite face-centered design was used for this study. Thirty-one combinations of the 5 above-mentioned freezer conditions were designed (including replicates at the center point), and ice cream samples were manufactured and examined in a continuous freezer under the selected conditions. The responses were the 3 variables given above. A quadratic model was constructed, with the freezer conditions as the independent variables and the ice cream characteristics as the dependent variables. The coefficients of determination (R²) were greater than 0.9 for all 3 responses, but Q², the index used here for the capability of the model for predicting future observed values of the responses, was negative for both the mean ice crystal diameter and the mean air cell diameter. Therefore, pruned models were constructed by removing terms that had contributed little to the prediction in the original model and by refitting the regression model. It was demonstrated that these pruned models provided good fits to the data in terms of R², Q², and ANOVA. The effects of freezer conditions were expressed quantitatively in terms of the 3 responses. The drawing temperature (°C) was found to have a greater effect on ice cream characteristics than any of the other factors.

Key Words: ice cream • response surface methodology • continuous freezer