NADES-Extracted SunGold Kiwifruit Polyphenols as Functional Ingredients in Antioxidant-Enriched Yoghurt

Natural deep eutectic solvents (NADES) offer a potentially food-compatible alternative for extracting plant polyphenols, although their direct application in yoghurt remains limited. This study evaluated the antioxidant and physicochemical properties of yoghurt fortified with SunGold kiwifruit extracts obtained using a selected choline chloride and glycerol NADES, with water extraction used for comparison. The phenolic profile of the NADES extract was characterised using LC-MS/MS. Both extracts were incorporated before (PRE) or after (POS) fermentation at concentrations of 10%, 20%, and 30% (v/v). The extracts and fortified yoghurts were analysed for total phenolic content (TPC), total flavonoid content (TFC), DPPH radical scavenging activity, FRAP, CUPRAC, and physicochemical properties. LC-MS/MS tentatively annotated several phenolic compounds in the NADES extract, with catechin showing the largest peak area among the annotated compounds. The water extract showed higher TPC and DPPH activity, whereas the NADES extract showed higher TFC, FRAP, and CUPRAC values. Increasing extract concentration generally increased the measured bioactive properties of the yoghurts, although the magnitude of change varied among assays and treatments. Water extract-fortified yoghurts generally showed higher TPC and DPPH values, while NADES extract-fortified yoghurts showed higher TFC, FRAP, and CUPRAC values. Extract type, fortification stage, and concentration also influenced pH, °Brix, viscosity, colour, and syneresis. Higher fortification concentrations reduced viscosity and increased syneresis, while low-concentration NADES extract-fortified yoghurts retained physicochemical properties closer to those of the control. Overall, the NADES extract showed potential as an ingredient for yoghurt fortification. Further studies are required to evaluate sensory acceptability, storage stability, starter culture viability, and gastrointestinal bioaccessibility.