Sunflower meal protein (SMP) has been considered as a high-quality source of plant protein. However, because the chlorogenic acid (CA) contained in sunflower seed meal was prone to oxidation reactions under traditional alkali extraction conditions, the extracted protein has a dark color and some poor functional properties. To this end, this study used ultrasound-assisted macroporous resin treatment to extract SMP. The improvement effects and potential mechanisms of ultrasonic-assisted macroporous resin treatment with different powers (100, 300, and 500 W) on the color and functional properties of SMP were studied. The results showed that compared with untreated sunflower meal protein (USMP), the lightness value (L*), solubility, emulsification, and gel elasticity were significantly enhanced when treated with 100 W and 300 W ultrasonic-assisted macroporous resin. However, when the ultrasonic power was increased to 500 W, the L* value, solubility, emulsification, and gel elasticity decreased instead, indicating that lower power (100 W and 300 W) ultrasonic-assisted macroporous resin treatment significantly improved the color and functional properties of SMP. Further research found that ultrasound-assisted macroporous resin treatment changed the secondary and tertiary structures of SMP, transformed β-sheet into α-helix and β-turn through rearrangement, and significantly improved surface hydrophobicity. It shows that ultrasonic-assisted macroporous resin treatment expands the SMP structure and exposes hydrophobic groups, thereby improving the color and functional properties of SMP. This study provides a potential strategy for extracting SMP with light color and good functional properties. It also provides a theoretical basis for the wide application of SMP in food processing.

Umami peptides were derived from enzymatic hydrolysis of sunflower seed protein, followed by isolation and identification. The flavourzyme-enzymatic hydrolysates exhibited the highest umami intensity value of 10.72 ± 0.05 and the lowest bitterness, when pH was adjusted to 7.0, the flavorzyme was added at enzyme-to-substrate (E/S) ratio of 1:25 (w/w), then incubated in a temperature-controlled water bath at 55°C, and the hydrolysis time was 480 min. Ultrafiltration, gel filtration chromatography, and reversed-phase high-performance liquid chromatography (RP-HPLC) were used to isolate the umami peptides of sunflower seed. Five fractions were obtained after ultra-filtration, fraction with molecular weight 1-3 kDa showed highest umami intensity value 13.93 ± 0.06. Fraction F1, which was purified via sephadex gel filtration chromatography, exhibited high umami value (12.21 ± 0.06), and low bitterness (4.57 ± 0.06). Seven sub-fractions were purified by RP-HPLC, and the umami taste value of F1-4 was the highest (14.16 ± 0.05), which was 1.32 times stronger than that of sunflower seed protein hydrolysates without any purification. Furthermore, the structure of fraction F1-4 was characterized by mass spectrometry, and three peptide fractions were identified, with amino acid sequences of DVNNPANQLD, NNENQLDEYQR, and EFEGGSIEH, respectively.

In order to improve the color and functional properties of sunflower seed protein, low-temperature defatted sunflower seed meal was used as the raw material to study the effects of limited enzyme hydrolysis combined with macroporous resin adsorption decolorization technology on the color and functional properties of sunflower seed protein. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD), particle size, intrinsic fluorescence intensity, surface hydrophobicity (H₀) and scanning electron microscopy (SEM) were used to analyze the influence on its structure. The results showed that the molecular weight of sunflower seed protein was reduced after limited enzyme hydrolysis combined with macroporous resin decolorization; the content of α-helix and β-turn was significantly reduced, and the content of β-sheets and random coils was significantly increased; the average particle size was reduced; the fluorescence intensity was increased and the red shift phenomenon occurred. H₀ also increased, SEM results showed that the surface of sunflower seed protein changed from a smooth large sheet-like structure to an irregular fragmented fast-like structure. Solubility, foamability, emulsification and emulsification stability were all significantly improved (p < .05), while foam stability and oil retention were reduced. The above results indicate that limited enzyme hydrolysis combined with macroporous resin adsorption and decolorization changes the structure of sunflower seed protein, and then improve its functional properties.