Effect Of Polysaccharides On The Thermal Stability And Infant In Vitro Digestive Characteristics Of Lactoferrin

Lactoferrin(LF)is a natural iron-binding globular glycoprotein with various biological functions such as antibacterial,antiviral,immunomodulatory and anti-inflammatory.LF plays a very important role in the prevention of neonatal infections,intestinal immune regulation,brain development,bone growth and iron absorption.Heat treatment is widely used in the processing of dairy products,which can lead to denaturation and aggregation of LF,thus affecting its physicochemical properties and functional activity.The interaction of polysaccharides with LF to form protein-polysaccharide complexes has been shown to be an effective method to improve the thermal stability of LF.In this study,three polysaccharides,carrageenan(CG),xanthan gum(XG)and locust bean gum(LBG),which are allowed to be added to infant formula,were selected to form protein-polysaccharide complexes with LF.The physicochemical properties and formation mechanism of the protein-polysaccharide complexes were analyzed,and their thermal stability and in vitro simulated infant digestion and absorption properties were studied.The specific results are summarized as follows:(1)Properties and interaction mechanism of LF-polysaccharide complexes.The optimal preparation conditions(pH and protein/polysaccharide mass ratio)for LF-polysaccharide complexes were LF-CG(pH 7,10:1),LF-XG(pH 8,5:1),LF-LBG(pH 7,15:1).Polysaccharide solution was treated by ultrasonic(270 w,20 min)and then mixed with LF,resulting in stable LF-polysaccharide complexes with small particle size.FTIR results showed that the complexes between LF and two anionic polysaccharides(CG,XG)were mainly formed by electrostatic interactions,while the complexes between LF and LBG mainly relied on hydrogen bonds or hydrophobic interactions.(2)Effect of polysaccharides on the thermal stability of LF.The structural changes of LFpolysaccharide complexes in liquid and powder forms at simulated industrial heat treatment temperatures(72 ℃,95 ℃)were systematically investigated.The results showed that the structural changes of LF were more severe with the increase of heating temperature and heating time.After heat treatment,the degree of changes in intrinsic fluorescence,surface hydrophobicity and secondary structure of LF-polysaccharide complexes were lower than those of LF.CG can significantly inhibit the loss of the α-helical structure of LF under heating conditions.The results of the circular dichroism spectra showed that the structure of LF changed slight after the heat treatment of the powder samples.Besides,LF-XG powder showed a higher stability than the other samples.(3)Effect of polysaccharides on infant in vitro semi-dynamic digestion and cell absorption of LF.In vitro infant semi-dynamic digestion model and Caco-2 cell uptake model were used to study the digestive characteristics and uptake of the three complexes under simulated conditions.The results showed that LF-polysaccharide complexes exhibited a protective effect on LF during the gastric digestion.LF-CG and LF-LBG significantly slowed down protein hydrolysis at the intestinal phase.LF,LF-CG and LF-XG had no adverse effect on the growth of Caco-2 cells in the LF concentration range of 10-300 μg/m L.XG facilitated the increase in uptake of LF by Caco-2 cells.In summary,pH and protein/polysaccharide mass ratio influenced the formation of soluble LF-polysaccharide complex.The electrostatic interaction of CG and XG with LF can obviously inhibit the loss of α-helix structure of LF under heating condition,and the powder sample had higher stability.In vitro digestion results showed that LF-CG and LF-LBG could protect LF in the gastric phase and slow down the degradation of LF in the intestine.XG was better beneficial to improve the uptake of LF by Caco-2 cells than the other groups.This study can provide technical support for the enhancement of thermal stability of LF during processing,and provide reference for the improvement of digestive stability and absorption of LF in the gastrointestinal environment of infants.It also provided information for the fortification of LF and other heatsensitive nutrients in infant food.