Effect of high hydrostatic pressure on microbial inactivation and quality changes in carrot-orange juice blends at varying pH

This study investigates the effect of high hydrostatic pressure, also known as high pressure processing (HPP), on microbial inactivation and changes in physicochemical characteristics of carrot-orange juice blends at different pH values. HPP conditions (200-400 MPa, up to 5 m) were evaluated to reach at least 5-log inactivation of L. innocua (ATCC 51742) in each blend. HPP at 300 MPa for 2 m, 400 MPa for 1 m, and 400 MPa for 3 m achieved more than 6-log reduction of L. innocua in pH 4, pH 5, and pH 6 blends, respectively. Ascorbic acid (16-45 mg/ 100g), total carotenoid (66-241 mg/L), and total phenolic (30-44 mg/L) contents did not significantly change after HPP compared to the corresponding untreated blends. The natural microbiota (i.e. aerobic mesophilic bacteria) was kept below 2-log CFU/mL for 28 d of storage. pH and total soluble solids remarkably changed for untreated blends in 10 d while HPP-treated blends were more stable during 28 d. Color attributes (L*, a*, b*) were retained after HPP and during storage. This study identified less intense high pressure processes for carrotorange juice blends compared to commercially applied pressure levels (i.e. 600 MPa) to produce microbiologically stable blends with preserved quality attributes depending on pH and blend proportion.