Hydrophobic Modification Of Sodium Caseinate And Its Application In Food Delivery Systems

Edible protein,with rich sources and high nutritional value,is widely used in food industry.Casein accounts for 80 to 82%(w/w)of total milk protein and contains 8 essential amino acids.Its sodium salt known as sodium caseinate(Na Cas)is widely used in food industry due to its desirable physico-chemical and functional properties(solubility,thickening property,foaming property,etc.).Recently,Na Cas was also used as the carrier material for food delivery systems.However,due to its excellent water solubility,some properties of food delivery systems based on Na Cas as the carrier material are not desirable to meet the food application.In order to develop new carrier materials with improved properties,nonpolar alkyl groups were incorporate into Na Cas molecules by using mild methods.N-succinimidyl esters(n C-NHS,n=12,14,18,20)with different alkyl chain lenghths were firstly synthesized,and then n C-NHS reacted with?-NH₂ of lysine residues in Na Cas under alkaline condition to obtain alkyl conjugated caseinate derivatives(n C-caseinate,n=12,14,18,20).By controlling the feed mole ratio of?-NH₂ of lysine residues to n C-NHS,n C-caseinates with different substitution degrees of alkyl groups(3.01 to26.71%)were obtained.Compared with the unmodified Na Cas,the hydrophobicity index of n C-caseinate increased with the increase of the alkyl substitution degree.In addition,it was found that the critical micelle concentration(CMC)of 16C-caseinate was much lower than that of the unmodified Na Cas,and the CMC value of 16C-caseinate decreased with the increase of alkyl substitution degree.This results indicates that 16C-caseinate has better self-assembly property and it can be further applied as encapsulation materials for hydrophobic food ingredients.In addition,two Na Cas derivatives(Cross-linked caseinate,CCA&Octyl conjugated caseinate,OCA)catalyzed by microbial transglutaminase(MTGase)were also investigated as the stabilizer for Zein nanoparticles.The results showed that CCA-Zein and OCA-Zein nanoparticles have desirable redispersibility and storage stability in water,Na Cl solution and sucrose solution after re-dispersing,which indicate that both CCA and OCA can be used as the stabilizer for Zein nanoparticles.