Physicochemical Properties of Oat (Avena sativa) Flour According to Various Roasting Conditions

This study was performed to investigate the physicochemical properties of raw and roasted oats for the production of processed goods. Changes in particle size, pH, moisture content, Hunter b value, polyphenols, proteins, flavonoids, lipid rancidity, ${\beta}-glucan$ content and sensory evaluation were compared between raw and roasted hulled oats (HO) and de-hulled oats (DO) after heating treatment at 0, 80, 120, 160 and $200^{\circ}C$. HO was more finely crushed than DO. The Hunter b value of HO was lower than that of DO, which increased sharply at $200^{\circ}C$. The pH range was from 6.2 to 6.6, with an average value of 6.4. In contrast to the protein contents of the two oat types, polyphenol content showed gradual decrease as roasting temperature increased. A comparison of the flavonoid content of HO with DO, indicated difference in the increase of flavonoids with increasing temperature. The protein content of HO was observed to be higher than that of DO. Furthermore, the protein level was slightly increased with increasing temperature. Malonidialdehyde (MDA) content was statistically identical from $0^{\circ}C$ to $160^{\circ}C$, but then increased sharply at $200^{\circ}C$. As expected, the ${\beta}-glucan$ content of HO was higher than that of DO. The ${\beta}-glucan$ content of HO was decreased at $80^{\circ}C$, but increased from $120^{\circ}C$ to $200^{\circ}C$. In contrast, the ${\beta}-glucan$ of DO increased constantly compared to the control. Variations in sensory characteristics such as color, taste, smell and overall preference were observed. There were statistically significant difference among the sensory characteristics of the two oat types heated at $0^{\circ}C$ and $120^{\circ}C$ and at $160^{\circ}C$ and $200^{\circ}C$ (p<0.05). Our collective results, including those for particle size, MDA, protein, ${\beta}-glucan$ content and sensory evaluation, indicated that HO would be more useful in the development of processed goods than DO, and that an optimum temperature for roasting oats is approximately $160^{\circ}C$ for 15 min. Moreover, our results indicate that suitable roasting temperatures and cultivars are necessary to produce high-quality processed oat goods.