Changes of isoflavones and protein quality in soymilk pasteurised by ultra-high-pressure homogenisation throughout storage

• Changes of isoflavones in ultra-high-pressure homogenised (UHPH) soymilks under refrigerated storage.
• Aglycone formation was lower in UHPH than in heat-processed samples.
• In-vitro protein digestibility was similar during storage in heat-pasteurised and UHPH soymilks.
• Blocked lysine was higher during storage in heat-pasteurised than in UHPH soymilks.

Ultra high pressure homogenisation (UHPH) is an emerging technology to obtain fine and stable soymilk emulsions. Very little information is available about the stability of this kind of product during storage. Changes of isoflavone profile, protein digestibility and lysine availability in pasteurised-UHPH soymilks were studied for 21 days at 4 °C in comparison to heat-pasteurised soymilks. Neither heat nor UHPH treatments affected the isoflavone profile, as the percentage of each chemical form, in comparison with unprocessed-soymilk. During storage, there was a conversion of isoflavone forms to aglycones, being higher in heat-processed samples. In addition, UHPH samples showed a lesser percentage of blocked lysine during storage. No differences were observed in the evolution of protein digestibility among samples. Therefore, UHPH treatment seems to produce a better product, due to lower amounts of aglycones, and higher protein nutritional quality than heat treatment.