Abstract

This study examined the effects of Kratom (Mitragyna speciosa) leaf polyphenol extract (KPE) on myoglobin oxidation in frigate mackerel (Auxis thazard) muscle at 4 °C using a two-stage design. First, Mb solutions were incubated for 30 min with KPE (0–150 ppm) to screen dose-dependent effects and select an effective concentration. Ascorbic acid (AA, 5% w/v) was included as a commercial benchmark (positive reference). Spectrophotometric analysis revealed a dose-dependent reduction in metmyoglobin, with 150 ppm KPE reducing levels by ~ 40% (p < 0.05), accompanied by a red shift in the Soret band and diminished 630-nm peak. These changes suggest KPE modulated myoglobin redox transitions, likely via polyphenol-myoglobin interactions. KPE slightly decreased pH but was less acidic than AA (p < 0.05). Color parameters significantly improved with KPE. Second, the selected condition (150 ppm KPE) was further evaluated in a time-course experiment for up to 180 min at 4 °C to assess redox stability over storage time. During 180-min storage, both 150 ppm KPE and AA increased ferrous and decreased ferric myoglobin within 90 min, with KPE maintaining redox stability thereafter. These findings support the use of KPE (150 ppm) as a natural antioxidant to preserve myoglobin stability and color in dark-fleshed fish, with AA serving as a reference benchmark rather than a concentration-matched potency comparator, in line with green preservation trends.