Subcritical Water Extraction of Kānuka (Kunzea ericoides): A Qualitative Analysis of Bioactive Profile Based on Antioxidant Properties

Kānuka (Kunzea ericoides) has been traditionally recognised for its health-promoting properties. However, limited comprehensive data on its bioactive profile hinders its potential industrial applications. Therefore, this study investigated the bioactive constituents of the kānuka subcritical water extract, exhibiting maximum antioxidant potential, using LC-MS/MS QTOF. Experiments were performed at different extraction temperatures and times to determine antioxidant content and capacity. The data were statistically analysed to select extracts with the maximum antioxidant response for bioactive screening. The highest recovery of polyphenolics and flavonoids occurred at 170 °C, 5 min (319.96 ± 22.67 mg GAE/g dw and 163.57 ± 9.7 mg QE/g dw), correlating with increased antioxidant activity (DPPH: 87.77 ± 1.74%; ABTS: 97.62 ± 0.12; FRAP: 166.43 ± 25.54 mg TE/g dw). Extracts obtained at 170 °C, 180 °C, 200 °C, and 220 °C with shorter extraction times (5, 10, and 15 min) were selected for bioactive screening using multivariate principal component analysis. Consequently, a rich composition of phenylpropanoids, including flavonoids, phenolic acids, stilbenes, and monolignols, was identified in the kānuka extracts using LC-MS/MS QTOF. Additionally, bioactives previously not found in kānuka extracts were identified, including 2',6'-Dihydroxy-4'-methoxydihydrochalcone, resveratrol, scopoletin, and naringin, underscoring its potential as a source of valuable metabolites to the pharmaceutical and food industries.