Octanal

HMG was synthesized according to the method described in our previous report [14 (link)]. Gelatin (type B) (Sigma-Aldrich Co., St. Louis, MO, USA) was dissolved in phosphate-buffered saline (pH 7.4, 200 mL, 3% (w/v)) by heating. Ethanol (99.8% (v/v)) was added to the solution in a volume ratio of 5 (ethanol) to 7 (polymer solution), and the resulting solution was cooled to room temperature. After mixing with fatty aldehydes (butanal (C4), hexanal (C6), octanal (C8), or dodecanal (C12); Wako Pure Chemical Industries, Ltd., Osaka, Japan) dissolved in a small amount of ethanol, the solution was gently stirred for 6 h to form imine bonds between the amino groups of gelatin and the aldehyde groups of the fatty aldehydes. Table 1 shows the feed molar ratios of fatty aldehydes to free amino groups in the gelatin. 2-methylpyridine borane (1.7 g) (Junsei Chemical Co. Ltd., Tokyo, Japan), a reductant, was then added to the solution, which was stirred for a further 24 h for reductive amination. HMG was precipitated by adding a large amount of ethanol, collected by centrifugation, and lyophilized. The degree of substitution (DS) values of the alkyl groups were estimated by determining the number of unmodified amino groups in the HMG using the trinitrobenzene sulfonic acid method [15 (link)]. The solid HMG was ground to obtain fine particles.

Granule-type soy-based TVP was purchased from Marukome Co. Ltd. (Nagano, Japan). CGT (Amano Enzyme Inc., Nagoya, Japan) is a commercially available food-grade product. α-CD, β-CD, and γ-CD were obtained from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan). Potato starch was purchased from Nippon Star Chemical Co. Ltd. (Osaka, Japan). Hexanal, heptanal, octanal, nonanal, 2-octenal, 2-nonenal, benzaldehyde, 1-hexanol, 1-octen-3-ol, pyrazine, acetic acid, 2-pentylfuran, and furfural were obtained from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan).