Study On The Preparation Of Rice Protein-pea Proteins Hydrophilic Complexs And Foaming Properties

Rice proteins(RPs)and pea proteins(PPs)are high quality plant proteins with reasonable amino acid composition,low allergenicity and high nutritional value.Although RPs and PPs are attracting more and more attention,both proteins are yet to fully meet the manufacturing,consuming,and marketing demands at large due to extremely low water solubility of RPs(<2%)and low digestibility of PPs.There are many methods for protein modifications,but they have a profound impact on the integrity of molecular structures,nutritional completeness,and functional properties.In response to the above problems,the pH cycle method was used to prepare hydrophilic binary composites based on RPs and PPs(Rice protein-pea proteins,RPPPs),and the interaction mechanism was explored;The nutritional characteristics and foaming properties of the RP-PP composites were characterized.Finally,starch nanocrystallines(SNCs)were used to improve the foaming stability of RP-PP composites,and the mechanism was studied from perspective of protein-SNCs interactions,interfacial properties,and rheological properties.The detailed results were as follows:Firstly,the interaction mechanism between RPs and PPs was explored.RPs and PPs were mixed and stirred at a pH of 12.0 at different mass ratios(RPs/PPs=1:0.01?1:1),followed by neutralization,and then the RP-PP binary composites were obtained.Compared with RPs,the solubility of RPs in the protein composites increased to 94.4%.The results of SDS-PAGE showed that the RP-PP composite completely retained the primary structures of RPs and PPs.TEM and AFM studies indicated that the RP-PP composite had a relatively swollen structure after the pH cycle.Light scattering results showed that the degree of swelling increased with the increase of PP content.The folding kinetics of the RP-PP composites during acidification process was studied by spectroscopy.At pH 12.0,RPs and PPs began to interact and combined to form the composite structure,which obatined considerable structural strength and could resist acid-induced conformational folding.The higher the proportion of PPs,the stronger the antifolding ability was gained.Zeta-potential and hydrophobicity data indicated that RP-PPs were surface repulsive during the neutralization process to maintain the colloidal stability of the system,leading to improved solubility of the proteins.Secondly,the nutritional characteristics and foaming properties of RP-PP composites were characterized.The results of amino acid analysis showed that the RP-PP composites obtained a more reasonable amino acid composition,which solved the lysine deficiency in RPs and deficiency of sulfur-containing amino acid in PPs.Moreover,the amino acid content reached the recommended standards of FAO/WHO.The results of in vitro digestion experiments and SDS-PAGE showed that the digestion rate of complexed proteins was higher than that of individual RPs or PPs,indicating that the digestibility of protein complexes was improved compared with single proteins.This is due to the unfolding of the conformation,exposing more reaction sites to promote pepsin hydrolysis.In addition,the effects of different RPs/PPs ratios and different pH on the foaming properties of the protein composites were studied.The foaming properties of the composite proteins were significantly improved compared to the those of single proteins;when RPs/PPs=1:1(w/w),the foaming ability was the best,reaching 320%.Among different pH,the foaming ability was the highest at pH 7.0,where,however,the foam stability was weak.Finally,SNCs were applied to improve the foaming stability.The foaming stability of the secondary complexes of RP-PP and SNCs was significantly improved compared to RP-PPs.When RP-PPs/SNCs=1:1(w/w),81.7% of the foams could be maintained after storage for 12 h.The interaction of SNCs and RP-PPs were driven by hydrogen bonding.With the increase of the proportion of SNCs,the surface tension and apparent viscosity increased,which was conducive to the adsorption of proteins on the interface and the formation of elastic film,thus improving the stability of foams.The above results indicated that the composite proteins,formed by embedding structures of binary proteins in a homogeneous matrix,had good solubility,and the nutritional and functional properties of both proteins were improved.At the same time,SNC had strong mechanical properties to improve the foam stability of the complexed proteins.This study provides new research concepts for the preparation of novel protein materials,which will help to further expand the application of plant proteins such as RPs and PPs in food industry.