# Pasteurization of Foods with Ultrasound: The Present and the Future
## 6 Quality  
Ultrasound is one of the newest technologies that offer the possibility to have novel ingredients for product development. Some changes in quality parameters have been reported in some products and can be used for product development. In the case of milk, ultrasound can affect some quality characteristics of the product. For example, the color parameters \(L^{\star}\), \(a^{\star}\), and \(b^{\star}\) can differ from raw milk if the product contains fat. The main effect of cavitation in milk is perfect homogenization. During this process, the fat globules suffer a reduction in size and combine with other molecules present in the milk. The luminosity of milk, \(L^{\star}\) is increased as a result [58; 59]. This fact can be used for dairy product development for those products that require a white color and perfect homogenization (i.e., yogurt). However, in skim milk, where there are no fat globules, cavitation acts between the lactose and the milk proteins, likely promoting a Maillard reaction and decreasing the luminosity (\(L^{\star}\)) [63]. The \(b^{\star}\) parameter tends to move to the yellowish region when whole milk is processed with ultrasound, likely because of the presence of \(\beta\)-carotene in the fat. On the contrary, plant-based milk decreased the \(L^{\star}\) parameter after sonication. The main reason is the increase in the cloudiness of these products. Some of the particles suspended in these plant-based milk are breakdown because of the cavitation, increasing the turbidity of the product and decreasing the luminosity. Examples of almond and hazelnut milk are shown in Table 4. In fruit and vegetable juices, color parameters such as \(L^{\star}\) remained unchanged or slightly higher. In this case, the cavitation breaks down the vegetable tissue and increases the product's luminosity. The Browning Index (BI) is slightly increased in sonicated products, as shown in Table 4. Amora juice, hog plum juice, and almond milk showed a higher value of BI. These minor changes in BI can be attributed to the Maillard reaction triggered by ultrasound. However, this chemical reaction does not occur when the processing temperature is below 50 \({}^{\circ}\)C [46]. Two of the three products with higher BI listed in Table 4 were thermo-sonicated at 60 \({}^{\circ}\)C. Additional variations were observed in other color parameters such as chroma, hue, and yellow index for the products listed in Table 4. The most significant change was observed for the blueberry juice, where the chroma was from 4.86 to 0.98, the hue was from 22.88 to \(-\)28.61, and the yellow index changed from \(-\)12.26 to \(-\)2.61. The authors of this research discussed these changes in the color parameters of sonicated blueberry juice based on the production of free radicals. During this process, hydroxylation of the aromatic ring of phenols occurs as previously described. This chemical change affects the juice's color, increasing the product's red component and changing chroma and hue values [89]. Regarding the pH of the sonicated products, most values remained close to the raw product. Minor variations were observed in those products that exhibited a longer processing time. The only significant change in pH presented in Table 4 was for the liquid whole egg. [PERSON] et al. [53] explain this fact based on the decomposition of carbonic acid in the egg white during sonication. Because of the release of CO\({}_{2}\) into the medium, there is an increase in the pH of the product. Some rheological properties have also been reported for sonicated products. For almond milk, the viscosity was increased after sonication, as shown in Table 4. For butter, the firmness and the work of shear were also increased for the sonicated product. Chocolate milk beverage showed an increase in the apparent viscosity and flow behavior index after treatment but decreased in the consistency index. These changes in rheological properties can be explained based on the emulsifying effect of the ultrasound.