Assessment of the Effects of Ultrasonics and Pulsed Electric Fields on Nutritional and Rheological Properties of Raspberry and Blueberry Purees

The impact of pulsed electric fields (PEF) in continuous, ultrasonication (US), and combined methods was evaluated in red raspberry (Rubus strigosus) and blueberry (Vaccinium corymbosum) purees in order to assess their effects on nutritional quality and rheology. Nonenzymatic browning was inhibited, but only US and combined methods were capable to inactivate polyphenol oxidase (PPO) in a considerable extent (p < 0.01). High recovery of biocompounds was observed, with a significant extraction (p < 0.01) of flavonoids (+20 %) and anthocyanins (+30 %) in raspberry and blueberry purees, respectively. Ascorbic acid was preserved, and the gentle effect of nonthermal technologies in antioxidant capacity was confirmed by DPPHaEuro cent scavenging value, which significant increased for raspberry (p < 0.01). The rheology of purees was dramatically modified by US, especially in blueberry, showing a progressive shift from non-Newtonian to Newtonian model, accompanied with a reduction in apparent viscosity values. Overall, the enhanced nutritional quality makes both technologies suitable for berry treatment, although changes on rheological properties should be taken into account for process design.