Evaluating the total antioxidant capacity of processed milk: utilising applicable antioxidant assays and key antioxidant components

Summary Total antioxidant capacity (TAC) holds immense importance in evaluating the milk quality. However, achieving accuracy and comparability in TAC measurement requires a thorough examination of detection methods and the constituents of antioxidants. This research focussed on developing TAC evaluation system tailored for processed milk, and the applicability of four assays (ABTS, FRAP, DPPH and ORAC) was examined, considering their compatibility with antioxidants. For fractionated milk, defatting and deproteinisation processes targeted reduced fat‐soluble (phospholipids by 88.75%) and water‐soluble (ascorbic acid and riboflavin by 55.22% and 63.85%) components, respectively. ORAC assay proved effective for detecting deproteinised milk, whereas DPPD assay displayed heightened sensitivity to alterations in milk fat antioxidants. Regarding pressure‐ and heat‐treated milk, homogenisation increased the availability of phosphatidylcholine (36.59–57.53 mg/L) and sphingomyelin (5.56–10.35 mg/L). However, the TAC of heat‐treated milk experienced a significant reduction due to the degradation of various fat‐soluble antioxidants. ORAC and ABTS assays were found suitable for assessing homogenised and heat‐treated milk, respectively. The peroxide value of reconstituted processed milk fell within the range of 98.48%–104.57% compared to untreated whole milk, affirming the accuracy of key antioxidants and detection methods. This study provides valuable insights for the meticulous assessment and enhancement of antioxidant capacity in milk.