It suggested that more disulfide bonds of feather keratin were
destroyed with higher mass ratio. Nevertheless, it also showed that
the yield did not have significant increase when the mass ratio surpassed
1.0. This effect could be because all the disulfide bonds of
feather keratin were reduced when excessive NaHSO3 was supplied.
In the reaction system without NaHSO3, the yield of extracted
keratin was up to 7.86% only relying on the hyper polarity of ionic
liquid [BMIm][NTf2]. Therefore, the optimal mass ratio was 1:1
considering both the yield of keratin and the production costs.