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The combination of protein and flavonoids can ameliorate the problems of poor solubility and stability of flavonoids in utilization. In this study, soybean protein isolate pretreated by ultrasonication was selected as the embedding wall material, which was combined with luteolin to form a soybean protein isolate-luteolin nanodelivery system. The complexation effect and structural changes of soybean protein isolate (SPI) and ultrasonic pretreatment (100 W, 200 W, 300 W, 400 W and 500 W) of soybean protein isolate with luteolin (LUT) were compared, as well as the changes in digestion characteristics and antioxidant activity in vitro. The results showed that proper ultrasonic pretreatment increased the encapsulation efficacy, loading amount and solubility to 89.72%, 2.51 μg/mg and 90.56%. Appropriate ultrasonic pretreatment could make the particle size and the absolute value of ζ-potential of SPI-LUT nanodelivery system decrease and increase respectively. The FTIR and fluorescence results show that appropriate ultrasonic pretreatment could reduce α-helix, β-sheet and random coil, increase β-turn, and enhance fluorescence quenching. The thermodynamic evaluation results indicate that the ΔG 0, ΔH 0 and ΔS 0, so the interaction of LUT with the protein was spontaneous and mostly governed by hydrophobic interactions. The XRD results show that the LUT was amorphous and completely wrapped by SPI. The DSC results showed that ultrasonic pretreatment could improve the thermal stability of SPI-LUT nanodelivery system to 112.66 ± 1.69 °C. Digestion and antioxidant analysis showed that appropriate ultrasonic pretreatment increased the LUT release rate and DPPH clearance rate of SPI-LUT nanodelivery system to 89.40 % and 55.63 % respectively. This study is a preliminary source for the construction of an SPI nanodelivery system with ultrasound pretreatment and the deep processing and utilization of fat-soluble active substances.

High-pressure homogenization (HPH) can improve the functionalities of food proteins by forming soluble aggregates. This research aimed to determine the effects of thermal aggregation and high-pressure homogenization on the structural and emulsifying properties of kidney bean proteins. Results have shown that the soluble aggregates from heat-treated kidney bean proteins had markedly larger particle sizes and molecular weights than untreated proteins. This demonstrates that heat treatment could expose buried hydrophobic groups and free sulfhydryl groups, leading to SH/SS exchanges between protein molecules. Additionally, the viscosity, emulsifying activity, and emulsion stability of the thermally formed soluble aggregates increased substantially after heat treatment. HPH at a low pressure (30, 60 MPa) promoted the formation of disulfide bonds between molecules by hydrophobic interaction, leading to the formation of protein soluble aggregates. This increased the particle size, molecular weight, apparent viscosity, emulsion activity, and emulsion stability. HPH at high pressures (90, 120 MPa), on the other hand, has been shown to damage protein aggregates and break the disulfide bond, resulting in a decreased aggregate size, molecular weight, emulsion activity, and emulsion stability. Our findings showed that HPH at 60 MPa on thermally soluble aggregates of kidney bean protein could improve their physicochemical, structural, and emulsifying properties for potential beverage industrial applications.

The effects of sodium chloride (NaCl) and tert-butylhydroquinone (TBHQ) on 3-monochloropropane-1,2-diol (3-MCPD) ester and glycidyl esters (GEs) contents were investigated during long-term deep-frying (177 °C, 4 days). The properties of fried food probably affect the formation of 3-MCPD esters and GEs in frying oil. Less NaCl promoted lower 3-MCPD ester and GEs contents, contents of 3-MCPD ester and GEs in the extracted oils from Youtiao (0 mg/kg TBHQ) reduced from 1.272 to 0.360 mg/kg and 0.559 to 0.346 mg/kg, respectively, while the amount of NaCl in Youtiao reduced from 1.5 to 0.0 g/100 g. TBHQ possibly decreased the 3-MCPD ester and GEs contents by suppressing the formation of radical intermediates. The 3-MCPD ester and GEs contents in the extracted oils from Youtiao (1.5 g/100 g NaCl) decreased from 1.221 to 0.893 mg/kg and 0.534 to 0.312 mg/kg, respectively, while the amount of TBHQ in Youtiao increased from 0 to 300 mg/kg. The formation of 3-MCPD esters might be accompanied by decomposition, GEs were rarely generated but decomposed during long-term frying. 3-MCPD esters and GEs entered fried food through frying oil, and the 3-MCPD ester and GEs contents in the extracted oil from Youtiao were closely related to those in the frying oils.

The production of meat analogs using high moisture extrusion cooking is a complex process that depends on the properties of the protein ingredients. The aim of the study was to investigate the effect of different moisture and wheat gluten contents on the retention of volatile flavor substances, microstructure, moisture distribution, and secondary protein structures of meat analogs produced by the high moisture extrusion process. The high moisture extrusion trials were carried out using a soy protein concentrate with 0%, 10%, 20%, 30, and 40% added wheat gluten (by dry mass) or 50%, 60%, 70, and 80% moisture. The comparisons revealed that the retention rates of volatile flavor substances from large to small were generally represented by esters, alkanes, alkenes, phenols, aldehydes, and alcohols, under the same extrusion conditions. The wheat gluten and moisture contents affected the flavor characteristics of the meat analogs by affecting the microstructure, the binding capacity of internal proteins and water molecules, and the secondary structure of the proteins. The higher retention rates of the volatile flavor substances were observed in meat analogs produced by raw material with higher wheat gluten content and lower moisture content. Our findings show that wheat gluten and moisture contents of the raw material regulate the retention rate of volatile flavor substances by affecting the microstructure, water distribution, protein structure, and interactive force of the meat analogs, opening up a wide range of products for different consumer requirements.