Soy protein selectively accumulates formaldehyde

Abstract

Soy protein (SP) is easily obtained from defatted soybeans that have had soybean oil removed. Therefore, the materials consisting of soy protein are not only environmentally benign but also sustainable materials. We prepared the SP - GPTMS composite materials by mixing the SP and a silane coupling reagent, 3-glycidoxypropyltrimethoxysilane (GPTMS), and demonstrated the accumulation of various aldehydes, such as formaldehyde (HAld), acetaldehyde (AcAld), butyl aldehyde (BuAld), and benzaldehyde (BnAld), by the SP - GPTMS composite materials. As a result, when the composite materials were incubated in an aqueous multi-component solution containing four aldehydes, these materials effectively accumulated the aldehydes. The accumulated amounts of the aldehydes were BnAld < BuAld < AcAld < HAld and the amount of HAld was three times higher than that of BnAld, which had the lowest accumulated amount. These results suggested that the SP - GPTMS composite materials indicated a molecular selectivity for HAld. In addition, the accumulated amounts of HAld further increased under acidic conditions. Furthermore, according to the IR measurements, the HAld-accumulated SP - GPTMS composite materials showed the formation of Schiff base bonds. Therefore, the molecular selectivity of HAld in the SP - GPTMS composite material was due to the high electrophilicity of HAld and the low steric hindrance.

Keywords: Aldehydes; Formaldehyde; Selective accumulation; Soy protein; Sustainable bio-resources.

Fig. 1

Molecular structure of 3-glycidoxypropyltrimethoxysilane (GPTMS).

Fig. 2

Molecular structures of formaldehyde (HAld), acetaldehyde (AcAld), butyl aldehyde (BuAld), benzaldehyde (BnAld), and azulene-1-carboxaldehyde (AzAld).

Fig. 3

Photographs of (a) SP − GPTMS composite material in water and (b) AzAld-accumulated SP − GPTMS composite material in ethanol. Each scale bar represents 10 mm.

Fig. 4

The swelling ratios of the SP − GPTMS composite material in a water-ethanol (v/v) mixed solution. The swelling ratios were calculated using Eq. (1). The ethanol concentrations were 0 − 100%. Each of the values represents the mean of three separate determinations ± standard deviations.

Fig. 5

Accumulated amounts of (closed circle) HAld, (closed square) AcAld, (closed triangle) BuAld, and (closed diamond) BnAld by the SP − GPTMS composite material in an aqueous single-component solution for various incubation times. Each concentration of the aldehydes was 1 ppm. Each of the values represents the mean of three separate determinations ± standard deviations.

Fig. 6

Accumulated amounts of (closed circle) HAld, (closed square) AcAld, (closed triangle) BuAld, and (closed diamond) BnAld by the SP − GPTMS composite material in an aqueous single-component solution for various concentrations. The incubation time was 6 h. Each of the values represents the mean of three separate determinations ± standard deviations.

Fig. 7

Maximum accumulated amounts of HAld, AcAld, BuAld, and BnAld in (green bars) aqueous single-component solution and (blue bars) aqueous multi-components solution. Error bars showed standard deviations.

Fig. 8

Accumulated amounts of (closed circle) HAld, (closed square) AcAld, (closed triangle) BuAld, and (closed diamond) BnAld by the SP − GPTMS composite material in an aqueous multi-components solution for various concentrations. The incubation time was 6 h. Each of the values represents the mean of three separate determinations ± standard deviations.

Fig. 9

IR spectra in 800–1800 cm⁻¹ region of HAld-accumulated SP − GPTMS composite material. The concentrations of the aqueous HAld solution are (a) 0 ppm (no HAld in water), (b) 4000 ppm, and (c) 8000 ppm. The dashed lines are the 1076 cm⁻¹ 1058 cm⁻¹, and 1045 cm⁻¹ peaks. The scale bar indicates a transmittance of 10%. Similar results were obtained for the triplicate experiments.

Fig. 10

Maximum accumulated amounts of HAld, AcAld, BuAld, and BnAld from an aqueous single-component solution at pH 5.5 (red bars) and pH 7.0 (blue bars). The insert in the figure shows the accumulated maximum amounts from an aqueous multi-component solution at pH 5.5 (red bars) and pH 7.0 (blue bars). Error bars showed standard deviations.