This study achieved maximum removal of ochratoxin A (OTA) during the grape juice clarification process with minimal reduction in antioxidant compounds (phenolic acid, flavonoids, and antioxidant capacity by FRAP) by the RSM method. Independent variables included three types of clarifiers—gelatin, bentonite, and diatomite (diatomaceous earth)—at a concentration level of 0.25–0.75% and clarification time of 1–3 h. OTA was measured by high-performance liquid chromatography with fluorescence detection. Clarifying agent concentration and clarification time affected the reduction amount of OTA and antioxidant compounds in grape juice. There was a direct linear correlation between the reduction amounts of OTA and antioxidant compounds and capacity with the concentration of bentonite, gelatin, and diatomite, and the clarification time. The reduction amount of OTA and antioxidant capacity followed the linear mode. However, the decreased phenolic acid and flavonoid values followed the quadratic model. The study results showed that if the concentrations of bentonite, gelatin, and diatomite and clarification time were 0.45, 0.62, 0.25%, and 1 h, respectively, the maximum amount of OTA reduction (41.67%) occurred. Furthermore, the phenolic acid, flavonoid, and antioxidant activity decrease amounts were at their lowest levels, i.e., 23.86, 7.20, and 17.27%, respectively.
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