Abstract:

The antioxidant activity of small black soybean is closely related to its contents of phenolic compounds and
anthocyanins; however, these substances are easily affected by different thermal processing conditions. Roasting condition
has a significant effect on the antioxidant activity of small black soybean. In this study, the effect of roasting temperature and
time on the total phenolic, anthocyanins contents and antioxidant activity of small black soybean from Yanchi and Fugu was
investigated. Our results indicated that the small soybean roasted at 150 ℃ showed the lowest content of total phenols, while
that roasted at 200 ℃ had the highest content of total phenols. The content of total anthocyanins markedly declined with
increasing roasting temperature and time. The hydroxyl radical scavenging activity of small black soybean became lower
with increasing roasting temperature, and the roasted sample had superoxide anion radical scavenging activity significantly
lower than that of the unroasted one (P < 0.05). The roasted small soybean at 150 ℃ irrespective of the geographical origin
exhibited the lowest content of total phenols, total antioxidant capacity (ferric-reducing ability of plasma, FRAP), and radical
scavenging activity against DPPH and superoxide anion radicals. Moreover, the Yanchi small soybean roasted at 200 ℃ for
30 min showed the highest total phenol content and DPPH radical scavenging activity, while the small black soybean from
Fugu roasted at 200 ℃ for 40 min exhibited the highest total phenol content and had the highest anthocyanint content, FRAP
value and DPPH radical scavenging activity when roasted at 100 ℃ for 20 min.

Key words: small black soybean, roasting, antioxidant activity, total phenols, anthocyanins