**3. Results**

*3.1. PRHE Possesses Antioxidant Capacity and Contains Protocatechuic Acid and Cyanidin-3-Glucoside as Major Phenolic-Based Compounds*

Initial screening of phytochemical elements in PRHE revealed the presence of phenolics (98.66 ± 0.003 mg gallic acid equivalents/g extract), flavonoids (64.26 ± 0.002 mg quercetin equivalents/g extract), and anthocyanins (7.90 ± 0.030 mg cyanidin-3-glucoside equivalents/g extract). DPPH and ABTS radical scavenging assay demonstrated the antioxidant power of PRHE, being 12.42 ± 0.16 mg gallic acid equivalents/g extract and 152.96 ± 0.77 mM Trolox equivalents/g extract, respectively. HPLC further revealed a variety of phenolic acids (Figure 1) and anthocyanins (Figure 2), where protocatechuic acid (PCA) and cyanidin-3-glucoside (C3G) appeared to be the major phenolic acid and anthocyanin found in PRHE, respectively.

**Figure 1.** HPLC chromatogram at 280 nm showing major phenolic acids of purple rice husk extract. (**a**) Reference standards; (**b**) purple rice husk extract. The chromatographic peaks of the extract were confirmed by comparing their retention time and UV spectra with those of the reference standards. Numerical values denote the amount of individual compounds detected. Data (mean ± SD, *n* = 3) are expressed in mg/g of the extract.

**Figure 2.** HPLC chromatogram at 520 nm showing major anthocyanins of purple rice husk extract. (**a**) Reference standards; (**b**) purple rice husk extract. The chromatographic peaks of the extract were confirmed by comparing their retention time and UV spectra with those of the reference standards. Numerical values denote the amount of individual compounds detected. Data (mean ± SD, *n* = 3) are expressed in mg/g of the extract.

#### *3.2. PRHE Improves Diabetes-Induced Metabolic Alterations*

The diabetic control group (DMV) showed significant body weight gain along with increased visceral fat, serum cholesterol, and triglycerides compared to the nondiabetic group (NDV), though the energy intake was comparable (Table 1). A significant increase in fasting blood glucose and insulin, including HOMA-IR, was also observed in the DMV group compared to the NDV group. Diabetes-induced metabolic alterations were significantly diminished in the PRHE-treated group (DME). Interestingly, treatment with PRHE was as effective as metformin alone (DMM) or metformin plus PRHE (DMME).

**Table 1.** Effects of purple rice husk extract (PRHE) and metformin on metabolic indexes.


Values are the mean ± SD (*n* = 6). NDV: vehicle-treated normal group; DMV: vehicle-treated diabetic group; DMM: metformin-treated diabetic group; DME: PRHE-treated diabetic group; DMME: metformin plus PRHE-treated diabetic group; BW: body weight; VF: visceral fat; HOMA-IR: homeostasis model assessment of insulin resistance. a–c Mean values with different letters in the same row are significantly different (*p* < 0.05).
