RHEOLOGICAL STUDY

Human milk (LH) is the gold standard in neonatal nutrition, especially in preterm infants. The concentration of LH by route-evaporation aims to increase caloric-protein density, since neonates have a high energy demand and a low gastric capacity. High-intensity ultrasound (US) stands out as a non-thermal technology capable of preserving sensitive lipid and protein fractions, improving colloidal stability and the rheological profile of LH. The present study aims to evaluate the effects of LH pretreatment with US on its rheological behavior, with emphasis on the parameter of consistency (k), flow index (n) and colloidal stability before and after LH concentration. For the study, a pool of samples from the Human Milk Bank (<800 kcal/L) was used, being a control sample (without US) and a sample pretreated with tube US (20 kHz, 60% amplitude, 30 min). Then, both were pasteurized (60 °C/30 min) and concentrated in a rotator-evaporator up to 60% humidity. The rheological analyses were conducted in a rheometer with parallel plates (diameter of 50 mm), applying three shear rate variation ramps, at intervals from 0.01 to 200 s⁻¹. The data from the third ramp were used to fit the Ostwald-de-Waele model, to determine K and n. Before concentration, US reduced the k parameter by 64.5%, from 0.0062 Pa·sⁿ to 0.0022 Pa·sⁿ. In addition, an increase of n was observed by 14.9% (0.94 to 1.08), values that are close to a Newtonian behavior, with lower resistance to flow