OHMIC HEATING TREATMENT IN HIGH-PROTEIN VANILLA FLAVORED MILK: ENGINEERING FACTORS AND PHYSICAL ASPECTS

The use of ohmic heating (OH) as an alternative method for pasteurizing dairy foods deserves attention from the scientific community. However, the use of OH in high-protein liquid dairy product processing has not been reported so far. This study assessed the impact of OH at different electric field strengths on the physical parameters of high-protein vanilla-flavored milk; in addition, the performance of the system was also evaluated. Six formulations were prepared: raw product (CONTROL, no conventional heat treatment or OH), conventional pasteurization (72-75 ºC/15 s; PAST), ohmic heating at 5.22 V/cm (OH6), ohmic heating at 6.96 V/cm (OH8), ohmic heating at 8.70 V/cm (OH10), and ohmic heating at 10.43 V/cm (OH12). All the samples had the same temperature-time profile. Energy consumption and processing parameters were calculated as well as optical (L, a, b, whiteness index, WI and yellowness, YI) and rheology (flow curve) parameters. OH12 and PAST took shorter times (4.16 and 4.58 min, respectively) to achieve the processing temperature than OH6, OH8, and OH10 (20, 12, and 6 min, respectively). In addition, the increase in the electric fields (OH12: 10.43 V/cm and OH10: 8.70 V/cm) resulted in shorter processing times, in the same proportion that heat generation increased (10.8 mV, OH12; and 5.3 mV, OH10). These results suggest that OH may be an alternative to conventional pasteurization, but reduced processing times may be achieved if high electric field strengths are used. The energy consumption in all OH treatments was lower than in conventional heating, being the energy expenditure of samples submitted to OH ranging from 121.3 KJ (OH10) to 166.9 KJ (OH8), suggesting that the greater the electric field intensity, the lower the energy expenditure due to the shorter processing time. On another side, PAST was the sample with the highest energy consumption (503.5 KJ), emphasizing the advantage of using OH, regardless of the electric field strength. Rheological data showed an excellent adjustment to the Power-law model (0.9781<R²<0.9940), and the PAST sample (PAST) exhibited the highest shear stress and viscosity profiles, numerically expressed by the highest consistency index (0.9985 Pa.sn), implying a well-structured protein network with low mobility. On the other hand, ohmic-heated samples (OH) have lower consistency indexes (0.0144-0.4585 Pa.sn, p < 0.05), suggesting a more fluid sample, which is interesting for consumers. Regards the optical parameters, PAST and OH resulted in changes, with an increase in luminosity (L*), red color (a*), and WI, and decreases in yellow color (b*), C*, h*, and YI. Therefore, the exposure of milk to increasing temperature may affect the concentration of lutein and beta-carotenoids, resulting in changes in milk color. The decrease in OH processing times can be linked to these findings. Overall, OH seems an interesting technology to be used in high protein dairy foods, with important physical changes relevant for consumers, besides its ability to reduce energy expenditure.