**3.5 Reducing power capacity assessment of crystal compound isolated from black pepper**

The reducing power of plant material and standard material had been evaluated through the method of Oyaizu (1986) [44]. During this assay, the color of sample has


**Table 5.**

*Superoxide radical scavenging data analysis for standard catechin and crystal compound.*

**Figure 7.**

*Graphical representation for in vitro data analysis (DPPH radical scavenging test, hydroxyl radical scavenging test, superoxide radical scavenging test) regarding crystal compound found in black pepper and standard catechin.*

altered to various shades of green and blue color based on the reducing capacity of the samples. The antioxidant compound actually served as reductant, and it induces reduction of the ferriccyanide to the ferrous form by releasing an electron. The overall reaction has been examined by monitoring the appearance of Perl' s Prussian blue at 700 nm.

Fe<sup>3</sup><sup>þ</sup> � ferricyanide <sup>þ</sup> <sup>e</sup> ! Fe<sup>2</sup><sup>þ</sup> � ferrouscyanide

Reducing power was investigated using the method developed by Oyaizu (1986). 2.5 ml of phosphate buffer (200Mm, p<sup>H</sup> 6.6) and 2.5 ml 1% potassium ferricyanide had been incorporated into 2.5 ml of sample (crystal compound). The mixture was transferred into a water bath for maximum 20 min at 50°C followed by rapid cooling after warm-up. After that, 2.5 ml of 10% trichloro acetic acid was added, and it has centrifuged at 3000 rpm for 10 min. From the supernatant, 5 ml had been collected and being dispersed it into 5 ml of distilled water and 1 ml of ferric chloride, and absorbance has been taken, which reflects that higher the absorbance value, stronger the reducing capability. According to **Table 6**, the absorbance of crystal has increased with increasing concentration, which was close to similar with standard ascorbic acid.
