Electric fields and transglutaminase in preparing adzuki bean protein emulsion gel for plant-based steamed egg custard

Abstract

Alternating current (ACEF), direct current (DCEF) and pulsed (PEF) electric field (EF) were applied for adzuki bean protein (ABP) pretreatment to prepare substitutes of steamed egg custard. Emulsion gels of EF pretreated ABP dispersions with flaxseed oil were mediated by transglutaminase (TGase). The emulsion particle size and the oil droplet size increased with the oil portion. PEF and ACEF pretreatment significantly reduced the number of large droplets. With the increase of oil portion, the infrared spectra at 2854 and 1747 cm⁻¹ changed significantly and a new peak emerged in amide A zone. Three EF pretreatments all increased the β-sheets of ABP, ACEF pretreatment led to the random coils slightly higher than DCEF and PEF. DCEF pretreatment increased the α-helices significantly higher than ACEF and PEF. The EF pretreatments improved the emulsion gel texture in gel strength, hardness, and chewiness, and water holding capacity (WHC). The largest apparent viscosity and energy storage modulus were obtained in DCEF pretreatment and larger than PEF and ACEF pretreatments. The 0.15 % curcumin and 0.10 % β-carotene pigmentation of ABP-flaxseed oil emulsion gel gave the smallest difference in colour, and higher WHC, close springiness, slightly lower chewiness, and gel strength, compared with the real steamed chicken egg custard control.