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

Abstract

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 ( degrees C), and dasher speed (rpm)] on the principal constituent parameters of ice cream [rate of fat destabilization (%), mean air cell diameter (mum), and mean ice crystal diameter (mum)]. 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 (R(2)) were greater than 0.9 for all 3 responses, but Q(2), 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 R(2), Q(2), and ANOVA. The effects of freezer conditions were expressed quantitatively in terms of the 3 responses. The drawing temperature ( degrees C) was found to have a greater effect on ice cream characteristics than any of the other factors.

Mechanisms of Ice Crystallization in Ice Cream Production

“…Dasher speed is known to have an effect on the final ice crystal size; however, literature sources are not in agreement as to this effect. Increasing dasher speed has been found to increase (Russell and others 1999), slightly increase (Drewett and Hartel 2007), not to affect (Koxholt and others 2000), and to have mixed effects (Inoue and others 2008) on ice crystal size. Crystal size could increase with dasher speed because of the extra mechanical energy and frictional heat being put into the system via the rotation of the dasher, which accelerates recrystallization (Russell and others 1999).…”

“…Although no new ice crystals nucleate after the freezer (heat transfer is not fast enough), the existing ice crystals continue to grow as the product cools from the draw temperature to −18 °C. Typically during hardening, ice crystals grow by about 30% to 40% (Marshall and others 2003) to an average size of about 25 to 45 μm (Berger and others 1972; Caldwell and others 1992; Donhowe and Hartel 1996a; Hagiwara and Hartel 1996; Koxholt and others 2000; Sofjan and Hartel 2004; Inoue and others 2008; Kusumaatmaja 2009). Because higher temperatures accelerate recrystallization, quick hardening limits the growth of the ice crystals (Hartel 1996; Marshall and others 2003).…”

“…The dispersion and emulsion consist primarily of a freeze‐concentrated aqueous serum phase containing sugar and the dry matter contents surrounding dispersed ice crystals and fat globules (Marshall and others 2003). Ice crystals range in size from about 1 to over 150 μm in diameter, with an average size of about 35 μm (Berger and others 1972; Caldwell and others 1992; Donhowe and Hartel 1996a; Hagiwara and Hartel 1996; Hartel 1996; Koxholt and others 2000; Marshall and others 2003; Sofjan and Hartel 2004; Inoue and others 2008; Kusumaatmaja 2009). Fat globules are 2 μm or less in diameter (Marshall and others 2003).…”

Effects of Manufacturing Process Conditions on Sensory Attributes and Microstructure of Ice Cream

“…In a previous study focusing on freezing, which is the principal process in the manufacture of ice cream, we demonstrated that the condition settings can cause a significant variation in the fat destabilization rate, air bubble diameter, and ice crystal diameter in the microstructure. (11) We also identified a correlation between these air bubbles, ice crystals, and fat destabilization, as well as the hardness and melt-inmouth qualities of the ice cream. (12,13) The finding that a food matrix structure plays an important role in controlling flavor release (14) suggests that variations in the structure of ice cream, owing to process conditions, also affect changes in sensory attributes such as aroma and flavor.…”

“…Cluster analysis (by Ward's method) of the sensory evaluation scores for samples, in terms of the PC1 and PC2 PCA scores for the sensory evaluations of each sample, yielded the following three cluster groups: Group 1 that had a positive correlation with PC1 (3, 6, 9, 10, 12, 15); Group 2 that had a low correlation (1, 2, 5, 13); and Group 3 that had a negative correlation (4,7,8,11,14). The fact that samples 1, 2, and 13, which are central to the experiment, belonged to Group 2 (located close to the origin) also lends credence to the theory that the process conditions altered sensory perceptions of the ice cream samples.…”