Ultra high pressure homogenization of soymilk:: Microbiological, physicochemical and microstructural characteristics

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa on soymilk was studied. A soymilk base product (BP) and ultra high temperature (UHT) treated soymilk were compared with UHPH treated soymilk. UHPH at 200 and 300 MPa reduced initial counts, spores and enterobacteria counts. Particle size analysis evidenced the intense reduction of particle size caused by UHPH, although the formation of aggregates was detected at 300 MPa. Colour differences between UHPH and BP or UHT soymilks were found. Treated soymilk (300 MPa) showed the lowest values of L*, a* and b* coordinates. UHPH processed samples were more stable (showed less particle settling) than BP and UHT soymilks and these differences were also observed at days 30 and 60 of storage at 4 degrees C. Differential scanning calorimetry analysis indicated that soymilk proteins were partially denatured by 200 MPa, whereas UHPH treatment at 300 MPa showed the same extent of denaturation as UHT soymilk. Images of transmission electron microscopy showed the distribution and general characteristics of the colloidal particles and structures of UHPH, BP and UHT which were generally in accordance with the physicochemical parameters studied. (c) 2007 Elsevier Ltd. All rights reserved.