The influence of aging time at 4C has been studied for three ice cream mix emulsions containing 10% weight fraction of milk fat samples differing by their composition. Milk fat composition was varied by partially replacing anhydrous milk fat (AMF) either by a high melting temperature, stearin (AMF/S), or a low melting temperature, oleain (AMF/O) fraction. Among the three ice cream mix emulsions, the AMF/O emulsion containing the lowest proportion of saturated triglycerides had slightly lower proportion of high‐size fat droplets regardless of the storage time periods, but it presented a higher shear sensitive behavior with aging time. In addition, the structural recovery following a shearing test (100/s for 1 min) observed in fresh emulsions was in the following order: AMF/S > AMF > AMF/O. However, structural recovery decreased faster with aging time for AMF/S than AMF, while it remained unchanged for AMF/O emulsion, where development of crystalline fat was most delayed. Based on these results, it is suggested that different shear stability and structure recovery after shearing can be related to the rate of development of fat crystals in the milk fat droplets which affects the interaction properties between the weak network of biopolymers in the aqueous phase and the fat droplets in the emulsions, depending on milk fat composition.
PRACTICAL APPLICATION
Our studies indicated an important role of unsaturated milk fat on the functional properties of ice cream mix emulsions, through modifying their rheological behavior as a result of changes in the crystallization properties of the fat in the emulsion droplets. We showed that higher amount of crystallized fat may prevent structure enhancement in the emulsions, and the resultant structure is more sensitive against shearing. This phenomenon will have effects on the aging time of the emulsions at 4C before whipping and, finally, on their overrun and the microstructure of incorporated air bubbles, which have been discussed elsewhere (Bazmi et al. 2007).
An understanding of the effects of processing parameters can be applied to formulate emulsions with higher unsaturated fatty acid content. Emulsions using the typical ice cream formulation were produced by anhydrous milk fat alone or in a mixture with either olein or stearin at a 2:1 weight ratio. Effects of both pasteurization holding time (40 or 120 s at 80 degrees C) and aging time (ranging from 2 to 24 h) on the structural and whipping properties of the emulsions were studied. Effects of these processing conditions on emulsion structural characteristics were determined using laser light-scattering measurements, rheological properties, microscopic observations, and image analyses of the whipped emulsions. Furthermore, foaming properties of these emulsions were compared and discussed with regard to effects of both processing and composition on properties of the emulsions, such as thixotropy and sensitivity to shearing. We observed changes in fat globules when different pasteurization holding times were applied, but no changes in either apparent viscosity values or sensitivity to shearing were traceable. However, enrichment of milk fat with the olein fraction increased the whipping ability of the emulsions, as evaluated in terms of overrun and the homogeneity of air bubbles, whatever the aging time. The lowest monodispersity of air bubbles was observed in the formulation rich in stearin. After 24 h of aging, this formulation showed the same overrun as the emulsion made with anhydrous milk fat. Increasing the aging time decreased the overrun by approximately 30%, and increasing the pasteurization holding times decreased it by approximately 20%. In general, in our conditions, increasing the aging time and unsaturated fatty acid content reduced changes in the dynamic rheological and structural properties observed just after production of the emulsions, whatever the pasteurization holding time or fat composition applied.
Cheese is a highly appreciated dairy product of most people all over the world. Traditional cheeses which are normally produced from raw milk are very popular due to their intense and unique taste and aroma, as well as high nutritional value. However, several diseases related to the consumption of raw milk cheese have reported in the United States and other parts of the world. For example, many cases of death have been reported in raw milk cheeses contaminated with E. coli in the United States, Canada, and Europe. Therefore, raw milk cheese is one of the risky products (Yoon et al., 2016). Various foodborne bacteria including
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