Antioxidant of tamarindus indica seed coat extracts and application for skin product

Abstract

Methanolic extracts from seed coats of certain types of Thai tamarinds including sweet-type: “Srichomphu”, “Sithong-nak”, “Sithong-bao” and “Khanti” and sour-type: “Priao-yak” cultivated in Petchabun province, Thailand were studied for their phenolic compounds contents and antioxidative properties. Phenolic compounds including total phenols, tannins and proanthocyanidins contents were investigated. The highest total phenol was found in tamarind seed coat extracts (TSCEs) sweet-type such as “Khanti” and “Sithong-bao” (p < 0.05). All sweet and sour tamarinds showed high tannins contents while proanthocyanidins were low. The highest tannins content was found in “Priao-yak”. Proanthocyanidins were found in the following order: “Khanti” = “Sithong-bao” > “Priao-yak” = “Sithong-nak” > “Srichomphu”. Antioxidative activities were evaluated by using different methods including reducing power assay, anti-lipid peroxidation, hydroxyl radical scavenging activity and scavenging activity on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. “Priao-yak” and “Sithong-bao” showed increased reducing powers with increased concentration of TSCEs. All tested cultivars showed anti-lipid peroxidation activity in a dose-dependent manner. “Sithong-bao” exhibited high anti-lipid peroxidation particularly at concentration 100-500 µg/mL and its EC₅₀ value (62.19±7.13 µg/mL) was significantly lower (p < 0.05) than that of positive control, vitamin C (263.93±8.03 µg/mL). “Priao-Yak” showed the lowest lipid peroxidation inhibition at concentration 10 to 500 µg/mL. All tamarind cultivars exhibited good scavenging activity against hydroxyl radical. But this activity is lower than butylated hydroxyanisole, a positive control. This activity was found in the following order: Butylated hydroxyanisole (94.65 ± 1.41) > “Sithong-bao” (77.54 ± 4.81) > “Priao-yak” (76.47 ± 1.41) > “Khanti” (73.26 ± 1.93) > “Sithong-nak” (68.45 ± 0.53) > “Srichomphu” (60.96 ± 0.53) at 500 µg/mL concentration, with the EC₅₀ value inversely correlated with their total phenols and proanthocyanidins contents. All cultivars showed high DPPH radical scavenging activity. Furthermore, “Khanti” showed the strongest scavenging activity against DPPH. However, EC₅₀ values of “Khanti” (70.10 ± 1.75 µg/mL) and vitamin C (138.29 ± 5.54 µg/mL) showed no significant difference (p ≥ 0.05). The TSCE from “Sithong-bao” was used as a natural antioxidant for gel preparation according to its high antioxidative activities. Gel preparation for topical use containing TSCE was prepared by using polysaccharide gel (PG) from durian-rind or tamarind seed polysaccharide (TSP) from tamarind seed kernel as a gelling agent. Physical properties including viscosity, pH and rheology study of TSCE-PG gel products and TSCE-TSP gel preparations were determined. The satisfactory physical properties of TSCE-PG gel preparations were obtained. In contrary, unsatisfied TSCE-TSP gel preparations were found. Lipid peroxidation inhibition activity of TSCE-PG gel preperations at ambient temperature (28±5 ℃) was tested in vitro by lipid peroxidation assay using lipid in egg yolk as a substrate. It was found that the activity increased with increasing concentrations of TSCE. Accelerated stability test at 45 ℃ decreased anti-lipid peroxidation activity of TSCE-PG gel preparation