Alternative application approach on black bean: hair coloring product

Abstract

Abstract Background Black bean is one of the important beans as the second most consumed bean globally after soybean. It has been reported as a sustainable source of anthocyanins, important natural colorants used in food and consumer products. However, industrial uses of black bean anthocyanins in pharmaceutics and cosmetics have rarely been explored. Thus, here, a black bean anthocyanin extract was prepared, quality controlled and developed into an efficient hair coloring product. Results Black bean was macerated in hydrochloric ethanol to produce a dark-reddish 1.85 ± 0.04% dry extract with total anthocyanin content (TAC) of 1.24 ± 0.48 µg/ml cyanidin-3-glucoside. The extract was readily dissolved in propylene glycol (25%), giving a reddish to red-brownish solution at pH of 4.00–7.00. The addition of antioxidant significantly (p = 0.000) enhanced the stability of the extract in an accelerated stability test (90.34 ± 5.32 from 67.83 ± 3.45% TAC remaining). Three base hair gels containing different thickeners were developed to yield clear gels with a viscosity of 101,666.67–447,333.33 cps and a pH of 4.80–4.97. The gel base with the best hair application properties was chosen to mix with 8, 10 and 12% black bean extract to produce similar visually assessed red-brown gels (L* = 33.25–33.76, a* = 0.06–0.09, b* = − 0.45–0.38 and h* = 277.54–283.31) at 73,733.33–99,666.67 cps and a pH of 5.00–5.01. All of the black bean hair coloring gels were stable under the accelerated test. The 10% hair gel was tested for its hair staining efficacy. The black bean hair coloring gel was found to efficiently color hair, and the color was maintained through four washings. Conclusions An alternative application approach of using black bean as a natural colorant is presented here, including its basic requirements for preparation and quality control from an industrial aspect. The efficient semi-permanent hair coloring product containing black bean is an innovative natural product and is considered as one progress towards a sustainable bio-based economy using a readily available industrial crop, black bean.