EFFECTS OF OHMIC HEATING PRETREATMENT, CLONAL VARIETY, AND PRODUCTION SOURCE ON TOTAL PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF COCOA BEAN SHELL EXTRACTS

Roasted cocoa bean shells (CBS) are phenolic-rich by-products that may be valorized through ohmic heating (OH) pretreatment. This study evaluated the effects of OH pretreatment conditions (temperature and voltage), clonal variety (CCN51 and PS1319), and production source (producers A and B), as well as their interactions, on total phenolic content (TPC) and antioxidant activity (AA) of CBS extracts. CBS were pretreated with OH in an aqueous medium (1:30, w/v) at 60 and 70 °C under voltages of 100, 150, and 200 V, with a 10-min holding period at the target temperature. Subsequently, 30 mL of absolute ethanol was added to the 30 mL aqueous medium to obtain a 50% (v/v) hydroethanolic solution, followed by extraction at 40 rpm for 60 min and concentration by rotary evaporation. TPC was determined by Folin–Ciocalteu (mg gallic acid equivalents g⁻¹ CBS), and AA by FRAP (µmol Fe²⁺ equivalents g⁻¹ CBS) and DPPH (mg Trolox equivalents g⁻¹ CBS), using spectrophotometric measurements. Data were subjected to factorial ANOVA, including interaction effects, and Tukey-adjusted mean comparisons (α = 0.05), using R software. TPC and FRAP exhibited significant source × temperature × voltage interactions (p < 0.001). Averaged across varieties, at 60 °C, increasing voltage from 100 to 200 V decreased TPC from 0.99±0.05 to 0.89±0.07 and FRAP from 300.15±48.63 to 250.89±29.75 for producer A (p < 0.05). Conversely, for producer B, TPC increased from 0.51±0.12 to 0.65±0.11 and FRAP from 159.61±36.29 to 210.61±32.39 (p < 0.05). At 70 °C, the same voltage increase raised TPC from 1.00±0.07 to 1.16±0.05 for producer A (p < 0.05). For producer B, TPC was higher at 150 V (0.64±0.15) and 200 V (0.63±0.14) than at 100 V (0.61±0.21; p < 0.05), with no difference between the higher voltages. FRAP did not differ among voltages at 70 °C for either producer (p > 0.05). DPPH scavenging activity exhibited a significant clonal variety × temperature × voltage interaction (p < 0.001). Averaged across producers, CCN51 showed higher activity at 150 V (24.28±4.48; p < 0.05) than at 200 V (20.36±6.46) at 60 °C; at 70 °C, 200 V (19.56±3.39; p < 0.05) exceeded 100 V (13.34±4.39) and 150 V (13.12±2.51). For PS1319, 100 V (17.64±4.24; p < 0.05) exceeded 150 V (12.39±3.66) at 60 °C, whereas 150 V (14.16±2.14) exceeded 200 V (9.88±1.70) at 70 °C (p < 0.05). These findings indicate that the effects of OH pretreatment conditions (temperature and voltage) on TPC and AA depend on raw material characteristics. The differing TPC and AA responses suggest that increased phenolic recovery is not necessarily accompanied by greater antioxidant activity. Therefore, OH conditions should be selected according to CBS source, clonal variety, and the target response.