| Curcumin(Cur)is a typical fat-soluble polyphenolic compound with various physiological activities such as antioxidant,antibacterial,and antitumor.However,the application of curcumin in the food field is limited by its low water solubility and poor stability.Embedding curcumin in a suitable carrier(wall material)by encapsulation technology is an effective way to solve the above problems.At present,protein has attracted much attention in many enclosing wall materials because of its high nutritional properties,better functional properties and better affinity for fatsoluble active ingredients.Soy protein(SP)is a plant protein with low cost and balanced amino acid composition,which has broad application prospects in the field of encapsulation.So far,a large number of protein-based encapsulation systems have been reported,but the complexity,low encapsulation efficiency,high energy consumption,and the use of organic solvents in existing processes limit their application in practical production.Therefore,it is urgent to develop a simpler and more convertible protein-based encapsulation method.In this paper,the de-folding and re-folding processes of soy protein treated by the pH-shift method were characterized systematically,and the effects of soy proteinbased nanoparticles on the loading effect and stability of curcumin were investigated.Secondly,the critical pH for the structural unfolding of soy protein induced by pHshift method was determined,the delivery carrier of 7S and 11 S protein-curcumin nanocomposite was constructed,and the encapsulation effect of curcumin was evaluated.Then,the controllable unfolding of soy protein structures induced by disulfide bond breakage was developed,revealing the effect of soy protein unfolding on curcumin encapsulation.A new method for inducing conformational changes in soy protein by disulfide bond cleavage in conjunction with critical pH treatment was further established,and the potential for encapsulation and protection of hydrophobic curcumin was evaluated.Finally,the effects of different drying methods on the stability and bioavailability of the soy protein-curcumin complex were studied.The main research content and results of this article are as follows:1.Study on the induction of soy protein unfolding based on pH-shift method and its encapsulation effect and mechanism on curcuminThe SP-Cur composite nanoparticles were prepared by the pH-shift method,and the encapsulation and protection potential of SP to Cur were evaluated.SP structure underwent a typical path from de-folding to re-folding during the pH-shift,and pH 10 was found to be a critical point of protein structure unfolding.The combination of Cur and SP was a spontaneous thermal reaction,hydrophobic action was the main driving force to promote the interaction between SP and Cur,and hydrogen bonds were also involved.In addition,the encapsulation efficiency of SP on Cur exhibited a concentration-dependent manner,and when the mass ratio of SP to Cur was 10:1,the encapsulation efficiency of Cur could reach as high as 97.43%.The morphology of SP-Cur did not exhibit a typical core-shell structure,and Cur was uniformly distributed in the protein.Moreover,the SP-Cur composite showed higher thermal stability and photostability.2.Determination of the critical point of 7S and 11 S protein unfolding induced by the pH-shift method and its effect on curcumin encapsulationThe critical point of 7S and 11 S protein unfolding and its encapsulation effect on Cur during pH-shift were investigated,and the critical pH of SP structure unfolding induced by pH-shift was determined.In the pH-shift process,the critical point of structural unfolding in 7S was pH 10.5,and the critical point of structural unfolding in11 S was pH 10.3,and the unfolding degree of protein structures at critical pH was increased and disorder was higher.The unfolding of the 7S and 11 S protein structure at critical pH was mainly due to increased electrostatic repulsion,weakened hydrogen bonding and hydrophobic interactions.The encapsulation efficiency of 7S at the critical pH-shift increased by 8.75%,and that of 11 S at the critical pH-shift increased by 15.24%,indicating that the critical pH-shift treatment could indeed improve the encapsulation effect of Cur.Therefore,SP could choose pH 10.5 as the critical pH for structural unfolding for subsequent research.3.Disulfide bond breakage induced soy protein unfolding and its encapsulation effect and mechanism on curcuminA simple method for encapsulating Cur was proposed and its feasibility was verified,which involved inducing protein structure unfolding by breaking disulfide bonds,and then encapsulating Cur in SP.The disulfide bond cleavage promoted the unfolding of protein structure,and the unfolding degree increased with the increasing reductant concentration.Compared with the control,the SP with disulfide bond cleavage exhibited higher surface hydrophobicity,promoting its binding with Cur.When the mass ratio of Cur to SP was less than 1:10,the encapsulation efficiency of more than 90% was successfully obtained.Therefore,it was feasible to achieve the encapsulation of Cur by breaking the disulfide bond and inducing soy protein to unfold,and the Cur encapsulated by this method showed higher thermal stability and photostability.4.Disulfide bond cleavage and critical pH induced unfolding and assembly of soy protein and its encapsulation effect and mechanism on curcuminThe Cur was encapsulated by inducing SP unfolding through the synergistic disulfide bond cleavage and critical pH.The conformation of SP was changed by the cooperative treatment.The disulfide bond was broken,leading to the transformation of large protein particles into small ones.The electrostatic repulsion was increased,and the internal hydrophobic and hydrogen bonds were weakened,thus exposing the hidden hydrophobic regions.This method could achieve high encapsulation efficiency of the composite at a higher mass ratio of core material to the encapsulation wall material.When the mass ratio of Cur to SP further increased to 1:1,the encapsulation efficiency of Cur in the composite obtained by the disulfide bond breaking synergistic critical pH-shift method(85.36%)was significantly higher than that obtained by the pH-shift(pH 7-12-7)method(61.82%)and disulfide bond breaking method(66.38%).Compared with SP treated with disulfide bond breaking alone and critical pH-shift alone,SP obtained by disulfide bond breaking synergistically with critical pH-shift showed a better protective effect on Cur.5.Effect of different drying techniques on the commercialization of soy proteincurcumin complexThe encapsulated complex solution was transformed into powder by freezedrying and spray-drying technology,and the stability,antioxidant activity,digestive characteristics and bioavailability of SP-Cur complex prepared by different methods were discussed.The results showed that encapsulation technology improved the stability,antioxidant capacity,and in vitro and in vivo bioavailability of Cur.The protective effect of freeze-drying technology on Cur was better than that of spraydrying technology,and the powder prepared by freeze-drying technology showed higher bioavailability,while the powder prepared by spray-drying technology had higher sustained release performance.After forming the compound of Cur and SP,the antioxidant activity of Cur was significantly increased,and the antioxidant capacity of Cur in freeze-dried powder particles was higher than that of spray-drying.The stability,antioxidant capacity and bioavailability of the complexes formed by breaking disulfide bonds combined with critical pH-shift were higher than those formed by other methods.Therefore,with SP as the wall material,it is recommended to select the breaking disulfide bond combined with the critical pH-shift method for encapsulating Cur. |
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