Extraction, Characterization and application of Antioxidant from Cashew (Anacardium occidentale L.) Leaves

Abstract

Optimization of extraction of antioxidative phenolic compounds from cashew (Anacardium occidentale L.) leaves was performed using response surface methodology (RSM) with 80% ethanol as the solvent. The central composite design (CCD) was used to establish treatments based on three independent variables, including extraction temperature (30-50 °C), time (60-180 min) and ethanol-to-solid ratio (15:1-35:1 v/w). Optimal conditions for extraction were: extraction temperature at 34.7°C for 64 min with an ethanol-to-solid ratio of 18:1 (v/w). The highest extraction yield was 8.64% under the following optimized condition. Total phenolic content (TPC) was 564.60 mg GAE/g dry extract and DPPH, ABTS radical scavenging activities and Ferric reducing antioxidant power (FRAP) were 11.74, 5.56 and 8.11 mmol TE/g dry extract, respectively. Isoquercetin and catechin were predominant in the extract. Phenolic compounds with antioxidative activity from cashew leaves were also extracted using ultrasound-assisted process. RSM and CCD were used to optimize the extraction, based on two independent variables, including amplitude (30- 77%) and time (7-31 min) when ethanol-to-solid ratio of 18:1 (v/w) was used. The highest extraction yield was 23.61 ± 0.06 % when the optimal extraction condition (77% amplitude for 31 min) was implemented. This was approximately 3 fold higher than that obtained from typical solvent extraction method. TPC was 579.55 ± 6.82 mg GAE/g dry extract and DPPH, ABTS radical scavenging activities and FRAP were 11.85, 6.04 and 10.28 mmol TE/g dry extract, respectively. Isoquercetin and catechin were the major phenolics in the extract. Additionally, hydroquinin, gallic acid, tannic acid, rutin, eriodictyol, quercetin and apigenin were also found in the extract. Antioxidative activities of cashew leaf extracts with different extraction methods (solvent extraction and ultrasound-assisted methods) at different concentrations (0-0.2 mg/ml) were investigated. DPPH, ABTS radical scavenging activities and FRAP of both extracts increased when the concentrations increased up to 0.1 mg/ml (P<0.05). Both extracts had higher activities tested by all assays than BHT (P<0.05), but lower than catechin. Furthermore, both extracts had high thermal and pH stabilities. After heating at 60-100 °C for 60 min, the antioxidative activities were still remained. High antioxidant activities of the extracts were generally observed at the pH ranging from 6 to 8. When both extracts (50 and 100 ppm) were added into ẞ-carotene-linoleic acid and lecithin liposome systems, the formation of conjugated diene (CD), peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) were lowered, compared to the control (P<0.05). Nevertheless, their preventive effect toward oxidation was lower than BHT in both tested systems. When cashew leaf extract (CE) was used as antioxidant in fish oil enriched mayonnaise in comparison with BHT at levels of 100 and 200 ppm, oxidative stability during storage of 30 days at 30 °C was monitored. With addition of CE or BHT, the lipid oxidation of mayonnaise was retarded, especially at 200 ppm, as indicated by lowered PV, TBARS and AnV values. At the end of storage, a lower abundance of selected volatile compounds was found in mayonnaise added with 200 ppm CE, compared to that of the control. However, the addition of CE (200 ppm) decreased L* value but increased a*, b* and AE* values (P<0.05). Overall, CE at both levels were effective in retard the formation of rancid odor and fishy odor in the mayonnaise enriched with fish oil during the storage of 30 days at 30 °C. Therefore, cashew leaf extract, especially prepared by ultrasound- assisted process, was rich in phenolics. It could be used as natural antioxidant to prevent the oxidation of foods containing lipids including food emulsion.