Ultrasonic monitoring of lard crystallization during storage

This work addresses the use of ultrasonics as a non-destructive technique with which to monitor lard crystallization during cooling and storage. The ultrasonic velocity was measured during both the isothermal crystallization of lard (at 0, 3, 5, 7, 10 and 20 °C) and during the non-isothermal crystallization. In addition, lard crystallization was also studied through Differential Scanning Calorimetry (DSC) and instrumental texture analysis (penetration tests). The measurement of the ultrasonic velocity allowed the bulk crystallization to be detected. The evolution of the ultrasonic velocity and the textural measurements during isothermal crystallization showed two steep increases, which may be explained by the two fractions of triglycerides found in DSC thermograms. At 7, 10 and 20 °C the second fraction did not crystallize within the first 11 days of storage. A two-step crystallization model based on the Avrami model was used to properly describe (% var > 99.9 and RMSE < 1.99 m s− 1) the relationship between the ultrasonic velocity and the isothermal crystallization time. In addition, a model was developed to estimate the percentage of solid fat content during isothermal crystallization. Therefore, it may be pointed out that ultrasonic techniques could be useful to monitor the crystallization pattern of complex fats during long periods of storage.