Effect of Storage Conditions on Physical Properties, Lipid Oxidation, Isoflavones and Antioxidant Capacity of Flour Prepared from Soy Milk By-Product

Abstract

During the production of soy milk, a by-product is produced, which is typically treated as a waste material. This by-product has significant levels of dietary fibre, proteins, isoflavones and antioxidant capacity. As such, it has been recommended as an effective functional ingredient when milled to a flour after drying at 100 °C. The shelf-life stability of this dried by-product is relatively unknown when stored under different storage conditions (2 °C, 20 °C and 40 °C) and initial moisture content (9%, 12% and 14%), both packaged and exposed to immediate environments. This study investigated the impact of storage over ten weeks on the physical properties, lipid oxidation, antioxidant capacity and stability of isoflavones of this functional ingredient. The results showed that exposure significantly affected the stability of flour, especially on moisture content, water activity, isoflavone concentration and lipid oxidation. Different initial moisture contents significantly affected the initial and final colour, alongside final moisture and water activity when stored covered at 2 °C and 20 °C. Different storage temperatures were found to affect the moisture content, water activity, lipid oxidation, conversion of isoflavones and antioxidant capacity, with all tested initial moisture contents. Of note, higher conversion rates of malonyl isoflavones to β-glucosides were observed at high temperatures and longer times, while a minimum change in aglycone content occurred. In conclusion, the stability of this flour is least influenced by the initial moisture content but is more affected by high storage temperature and unpackaged conditions.