Study On The Dolichos Lablab L.protein Extraction And Functional Properyties Of Its Polyphenol Complex

Dolichos lablab L.is an annual entangled herbaceous vine of the genus Leguminous hyacinth beans,which has been widely planted in China for a long time.Although Dolichos lablab L.has high in nutritional value and multiple biological activities,it has not been fully emphasized and exploited.At present,the Dolichos lablab L.is mainly directly and simply packaged and even sold in bulk on the market with poor economic benefits.The Dolichos lablab L.protein(DLP)accounts for18%-25% of the dry weight of Dolichos lablab L.,at present,the research on DLP is relatively few and mainly focused on traditional alkaline extraction and functional peptides.Therefore,in this study,an efficient preparation technology was established,and the structural and functional characteristics of DLP extracted by ultrasonic-assisted extraction were systematically investigated.On the basis,the DLP-polyphenol compound was prepared,and the combination mechanism was further discussed.A theoretical and scientific basis was expected to be laid for research of DLP.The main research contents and results are as follows.(1)Optimization of ultrasonic-assisted extraction of Dolichos lablab L.proteinPlackett-Burman design(PBD)was used to screen the single factors and the response surface methodology was used to optimize the parameters of ultrasonic-assisted extraction of DLP by Box-Benken design.Wherein the optimal parameters were as follows: ultrasonic time 30 min,p H 10.0 and solid-liquid ratio 1:60 g/m L.Under these conditions,the extraction rate of the DLP reached 69.98%,which was obviously higher than that of traditional method(40.95%).(2)Study on the structural and functional properties of Dolichos lablab L.proteinNine DLPs were obtained(UDLP,TDLP,20 kHz,40 kHz,60 kHz,20/40 kHz,20/60 kHz,40/60 kHz and 20/40/60 kHz,respectively)by ultrasonic-assisted alkaline extraction,traditional alkaline extraction and frequency ultrasonic-assisted modification.The structural,functional properties and antioxidant capacities of DLP were compared by physicochemical analysis,spectral analysis and in vitro antioxidant evaluation.Structural characteristics: compared with TDLP,the particle size of DLP in UDLP and 20/40 kHz groups significantly decreased,while the surface hydrophobicity increased significantly(p<0.05).Fourier transform infrared spectroscopy showed that the variation trend of secondary structure of different ultrasonic treatments was basically same,and the proportion of disordered structure decreased(the relative content of random coil and ? helix decreased by nearly 50%).The amino acid analysis showed that the total amino acid content of DLP in UDLP and 20/40 kHz treatment groups was significantly higher than that of TDLP(p <0.05).Functional characteristics: Compared with TDLP,the emulsion of UDLP and20/40 kHz treatment group was more stable(p < 0.05),and the water holding capacity of UDLP was increased by 40%.The oil holding capacity of DLP in 20/40 kHz treatment group was about 20% higher than that of TDLP.The solubility of UDLP and 20/40 kHz treated DLP was 1.25 and 1.17 times that of TDLP.In addition,ultrasonic treatment also improved the denaturation temperature of DLP,in which UDLP,60 kHz and 20/60 kHz respectively increased from 69.83? to 78.63?,81.47?and 75.57?.Antioxidation capacity: The results of ABTS,DPPH,reducing power,FRAP and Cuprac analyses showed that,compared with TDLP,the antioxidant capacity of DLP treated by different ultrasonic methods was increased by 0.4-1.8 times,suggesting that different ultrasonic treatments can improve the properties of DLP,among which UDLP had the greatest impact.(3)Study on the interaction and functional properties of Dolichos lablab L.protein-polyphenols complexThe interaction mechanism between nine different DLPs and tea polyphenols(EGCG,ECG,EGC)were studied by fluorescence spectroscopy and Fourier transform infrared spectroscopy.After adding polyphenols,the fluorescence quenching of protein was obvious,and it was static quenching.DLP provided 1-2binding sites for EGCG and ECG,while the number of sites with EGC was less than 1.The binding sites were closer to tyrosine residues,and mainly bound by hydrophobic action or van der Waals force and hydrogen bond.The changes of antioxidant capacity and bioaccessibility of polyphenols were evaluated by in vitro antioxidant experiment and simulated digestion combined with chromatographic analysis.It was confirmed that DLP combined with tea polyphenols could significantly enhance the storage stability,thermal stability and bioaccessibility of tea polyphenols.