Interaction Of Phenolic Compounds In Cloudy Apple Juice With Gliadin

During the processing and storage of cloudy apple juice,precipitation has always been an important technical problem that perplexed juice production.After the precipitation of apple juice,it will not only affect the sensory value of the juice,but also make consumers resist the product in the mind.Scholars generally believe that the precipitation is mainly due to the interaction between polyphenols and proteins.In this paper,six characteristic apple varieties in western Liaoning were selected as the raw material.High-performance liquid chromatography(HPLC)was used to study the characteristic phenolic substances in cloudy apple juice.A simulation system was established to study the effect on temperature and pH changes in cloudy apple juice for phenol-protein complexes formation during processing.The structure and stability characteristics of phenol-protein complexes were analyzed by various physical and chemical means.This study could provide some theoretical basis on improving the stability of apple cloudy juice by analyzing the interaction between phenolic compounds in apple cloudy juice and proteins.The main conclusions reached are as follows:1.The result by comparing the extraction methods of mixed phenols and acidic/neutral phenols showed that,the mixed phenols extraction method is more comprehensive for the extraction of polyphenols.HPLC was used to simultaneous analysis on phenolic substance in cloudy apple juice.A reasonable mobile phase of acetonitrile and formic acid aqueous solution(2/98,v / v)was obtained by analysis on elution effect of HPLC;Different detection wavelengths were compared for juice of different apple varieties,and the better HPLC detection wavelength was 280 nm.Quantitative analysis of three characteristic phenols in turbid juice of different apples by HPLC found that,the chlorogenic acid content in cloudy juice of ‘Hanfu' apple reached 3.68 mg / L,and the chlorogenic acid content in cloudy juice of ‘Orin' apples was only 1.23 mg / L;Epicatechin was higher in ‘Ralls' apple turbid juice,while ‘Golden Delicious' apple turbid juice had a lower epicatechin content of only 0.36 mg / L;Gallic acid was relatively higher in ‘Golden Delicious' cloudy apple juice,while,which lowest content was in ‘Hanfu' cloudy apple juice.2.Fluorescence spectroscopy combined with ultraviolet spectroscopy was used to preliminarily explore the binding rules of three characteristic phenolic compounds with gliadin,and the effects of temperature and pH on their interactions.As the polyphenol concentration gradually increased,the fluorescence intensity of the protein bound to it gradually decreased.At different temperatures and pH,the quenching constants Ksv and Ka both changed.According to the Van't Hoff equation,among the binding reaction of three characteristic phenols with gliadin,the reactions of epicatechin and chlorogenic acid were exothermic reactions with ?H,?S,?G less than zero,and they formed the hydrogen bond and van der Waals force with gliadin;The gallic acid-gliadin complex was an exothermic reaction with ?H,?G less than zero,while ?S greater than zero,indicating that the gallic acid and gliadin are connected by hydrogen bonding,and occurred Hydrophobic interaction.3.The complex construction of epicatechin,chlorogenic acid,gallic acid with gliadin were analyzed,and their solution stability was also studied.Fourier transform infrared spectroscopy analysis showed that,the addition of phenolic compounds resulted in changing of the secondary structure of gliadin,such as,?-helix,?-sheet,?-turn,and random curl.The fluorescence spectrum showed that the complex formation of the three phenolic compounds with gliadin led to the fluorescence quenching of tyrosine or tryptophan in gliadin,which changed the amount of tyrosine or tryptophan.Ultraviolet spectrum showed that the formation of three phenol-gliadin complexes changed the structure of gliadin,which might cause more tryptophan and tyrosine groups to be exposed to surrounding solvents.Using field emission scanning electron microscopy,it was shown that there were grooves on the surface of the phenol-protein complex,which could form spheres,flakes,or irregular particles.Studies on the stability of phenol-protein solutions showed that,as the concentration of gallic acid increases,the phenol-protein solution changed gradually from negative charge to positive charge.As the concentration of phenolic compounds increased,the particle size of the solution gradually increased,and the turbidity also gradually increased.Multiple light scattering showed that the TSI value of the mixed phenol-gliadin solution was higher,indicating that the simultaneous combination of multiple phenols with gliadin decreased the solution stability.