Isoflavone profile and protein quality during storage of sterilised soymilk treated by ultra high pressure homogenisation.

The application of ultra high pressure homogenisation (UHPH) treatments is useful to obtain fine and stable soymilk emulsions. Changes of isoflavones, protein digestibility and lysine availability during 4 months of storage at 20 ± 2°C in soymilk treated by UHPH (300 MPa and 75°C of inlet temperature) were studied in comparison to UHT-sterilised soymilk (142°C, 6s). Results indicated that although there was a significantly higher extractability of isoflavones in UHT (about 38%) than in UHPH-treated samples (about 15%), similar total contents were found at the end of storage. The interconversion of isoflavones into β-glucosides was faster in UHT than in UHPH-treated soymilk. Similar evolution of protein digestibility in both UHPH and UHT-treated soymilks was found, being slightly higher in the initial UHT (88.4%) than in UHPH-treated samples (83.3%). No great differences were observed in the % of blocked lysine among samples after treatments, neither in their evolution throughout storage.