Microstructure of Fat Globules in Whole Milk after Thermosonication Treatment

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Abstract
ABSTRACT:  The structure of fat globules in whole milk was studied after heat and thermosonication treatments to observe what happens during these processes at the microscopic level using scanning electron microscopy. Raw whole milk was thermosonicated in an ultrasonic processor—Hielscher® UP400S (400 W, 24 kHz, 120 μm amplitude), using a 22‐mm probe at 63 °C for 30 min. Heat treatment involved heating the milk at 63 °C for 30 min. Color and fat content were measured to correlate the images with analytical measurements. The results showed that the surface of the fat globule was completely roughened after thermosonication. Ultrasound waves were responsible for disintegrating the milk fat globule membrane (MFGM) by releasing the triacylglycerols. Furthermore, the overall structure of milk after sonication showed smaller fat globules (smaller than 1 μm) and a granular surface. This was due to the interaction between the disrupted MFGM and some casein micelles. Minor changes in the aspect of the globules between thermal and raw milks were detected. Color measurements showed higher L * values for sonicated samples. Sonicated milk was whiter (92.37 ± 0.20) and generally showed a better degree of luminosity and homogenization compared to thermal treated milk (88.25 ± 0.67) and raw milk (87.82 ± 0.18). Fat content analysis yielded a higher value after sonication (4.24%) compared to untreated raw milk (4.04%) because fat extraction is more efficient after sonication. The advantages of thermosonicated milk are that it can be pasteurized and homogenized in just 1 step, it can be produced with important cost savings, and it has better characteristics, making thermosonication a potential processing method for milk and most other dairy products.

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