Effects Of Different Heating Methods On The Quality Changes Of Three Grape Juice Concentrates

In this study,Kyoho,Munage,Summerblack grape were used as raw materials,and the juice was squeezed.The three grape juices were concentrated by different methods such as electromagnetic heating concentration,Oil bath heating and concentration,and heating plate heating and concentration.The pH value,titratable acid,rheological properties,Browning index,color index,reducing sugar,amino acid,5-hmf and volatile compounds of concentrated grape juice under different heating conditions were determined.The study obtained the following basic conclusions:(1)Concentration method and concentration temperature have no significant effect on the pH value of grape juice concentrate(p>0.05),pH is only related to grape varieties;There is a significant correlation between the titratable acid content and the concentration temperature,and there is no significant relationship with the concentration method.The shear stress of grape juice and concentrated juice increased with the increase of shear rate.There was no thixotropic ring in grape juice and concentrated juice,and the viscosity also decreased with the increase of shear rate.It is a typical pseudoplastic fluid,independent of the grape variety,the way of concentration and temperature.(2)Concentrated grape juice has increased browning compared to raw juice;increased content of5-HMF;L~*value,white index WI is decreasing,a~*value,b~*value,chroma C~*,yellow index YI are increasing;The concentrated juice slowly forms a reddish brown.The higher the temperature,the higher the browning degree of the grape juice concentrate,the more the amount of 5-HMF is produced,the L~*value is decreasing,and the color of the grape juice concentrate is darker and darker.The browning degree of grape juice concentrate and the amount of 5-HMF produced at 100°C and 130°C are similar.The degree of browning of the grape juice concentrate and the amount of 5-HMF produced at 160°C were greater than those of the grape juice concentrate at 100°C and 130°C.(3)There is a certain difference between the type of volatile compounds in the grape juice concentrate and the original juice,but the manner and temperature of concentration do not significantly differ between the types of volatile compounds in the grape juice concentrate.Common substances in grape juice concentrate are:Phenylethanol,benzyl alcohol,1-[4-(2-hydroxypropan-2-yl)phenyl]ethanone,hexadecane,2,4-di-tert-butylphenol,oleic acid amide,1,3-two Acetylbenzene,N-phenyl-2-naphthylamine;The concentrated grape juice in the sandwich pot has the following substances:Phenylethanol,3,3-dimethylhexan-2-one,-2H-pyran-2,6-(3H)-dione,eicosane,hexadecane,2,6,10-trimethyl Pentadecane,2,4-di-tert-butylphenol,eugenol,5-hydroxymethylfurfural.The relative content of each volatile component does not have a significant tendency during the heating process,and has little effect on the heating mode and temperature.