Comparative Optimization of Hot Water and Ultrasound-Assisted Extraction of Crude Polysaccharides from Oat (Avena sativa L.) for Structural Characterization and Functional Properties

This study aimed to evaluate the efficacy of crude polysaccharide extraction from Thai-cultivated oats (Avena sativa L.) utilizing hot water extraction (HW) and ultrasound-assisted water extraction (UW) methods. Optimal conditions were determined by a response surface methodology (RSM). The influence of solid-to-liquid ratio, temperature or %amplitude, and extraction time on %yield and beta glucan content was investigated. Under optimal conditions, UW produced a superior %yield (82.72 ± 2.19%) and beta glucan content (1.75 ± 0.87 g/100 g extract) compared to HW (41.32 ± 0.98% and 1.25 ± 0.27 g/100 g extract). This finding may occur from acoustic cavitation, which effectively dismantles the cellular wall structure, supported by FTIR analysis finding more distinct β-glycosidic linkage peaks. SEM analyses indicated a greater surface area dispersion and porosity in UW extract relative to HW extract. Analysis of monosaccharide composition supported the properties of both crude extracts, demonstrating glucose as the predominant component. However, the functional and bioactive characterization demonstrated a distinct trade-off between the two extraction methods. HW extract demonstrated superior swelling capacity (6.2 vs. 2.7 g/g at pH 6.5), enhanced antioxidant activity compared to both ABTS (0.67 ± 0.04 vs. 0.58 ± 0.06 μmol TE/g), DPPH (0.53 ± 0.06 vs. 0.35 ± 0.06 μmol TE/g), and FRAP (0.05 ± 0.02 vs. 0.03 ± 0.01 μmol TE/g), total phenolic content (98.33 ± 7.68 vs. 87.79 ± 3.07 mg GAE/g). The crude extracts from the two methods had selective enzyme inhibitory activity, exhibiting considerable inhibition of α-glucosidase and markedly reduced inhibition of α-amylase. UW demonstrated slightly superior inhibitory activity compared to HW for both enzymes. The findings indicate that the determination of crude polysaccharides should principally take into account the purpose of the final product. UW is preferable for optimizing %yield and beta glucan content. Nevertheless, if the emphasis is on functional attributes like water absorption and antioxidant efficacy, HW has advantages that merit a consideration. This research provides a framework for identifying optimal extraction methods aimed at extracting crude polysaccharides from Thai-cultivated oats for use as a functional ingredient in health food products.