Effects Of Micronized Macromolecules On Texture Formation Of Freeze-dried Strawberries

Texture is an important quality evaluation index for dried fruit and vegetable products,which would greatly affect the consumers’sensory perception.The formation of texture is affected by the drying process and the tissue structure of the material,and changing the composition of the tissue cell matrix of fruits and vegetables is an effective way to control the texture of dried fruit and vegetable products.At present,small molecular sugars have been used to change the composition of the cell matrix to improve the texture quality of dried fruit and vegetable products.Macro-molecular substances are difficult to enter into tissue cells due to their large molecules or agglomeration.Therefore,research on texture regulation by changing the macro-molecular matrix has not been report yet.In this paper,four macro-molecular substances in fruit and vegetable cells were selected:arabinoxylan（AX）,protein（WP）,starch（PS）,and pectin（PE）.They were micronized by dynamic high pressure microfluidization（DHPM）method.And the basic properties and structure of the macro-molecular substances changed before and after the DHPM process were studied.And the micronized macro-molecular substances were added to the freeze-dried（FD）strawberry slices by vacuum impregnation.By studying the changes in the micro-structure,moisture migration and texture properties of strawberry slices during the drying process,the influence mechanism and key influencing factors of different macro-molecular substances on the texture formation process of FD strawberry slices were investigated.The main contents are as follows:（1）The four macro-molecular substances were homogenized by DHPM,and the particle size,scanning electron microscope（SEM）,X-ray diffraction（XRD）,ultraviolet absorption spectrum,Fourier transform infrared spectrum（FT-IR）,and apparent viscosity measurement of the macro-molecular substances before and after treatment were analyzed to study the effect of DHPM on the basic structure and properties of macro-molecular substances.The results found that the particle sizes of AX,WP,PS,and PE were decreased after DHPM treatment,and the average particle size decreased by 79%,31%,68%,and 63%,respectively.The surface of macro-molecular particles was sheared and broken to different degrees under the action of shear force,the apparent viscosity of AX and PS increased,and the apparent viscosity of WP and PE decreased.The results of FT-IR and XRD showed that the shearing treatment resulted in a red shift of some absorption peaks,and the peak width of the characteristic absorption peaks of AX,PS and PE in the O-H hydrogen bond association stretching vibration increased,theα-helix of WP secondary structure disappeared,the content ofβ-sheet reduced,and the original crystal structure of WP,PS and PE was destroyed,and the crystallinity decreased.（2）The macro-molecular particles were vacuum-impregnated into FD strawberry slices,and the microstructure,water migration and mechanical properties of the samples before（BD）,during（DD）and after（AD）FD were analyzed.The results showed that the addition of macro-molecular particles promoted the thickening of the cell wall of strawberry slices,and the cells shrunk or swelled to varying degrees.During the drying process,the cell area and diameter gradually increased,and the coefficient of variation and fractal dimension also increased.The cells in the AX group were more severely broken,while the PE group had higher cell integrity and the thickest cell wall.The macro-molecular particles slowed down the water loss of strawberry slices during the FD process,and the elastic modulus,hardness and total work increased,and the elasticity decreased.The formation of strawberry slice texture during the whole drying process mainly occurred in the late drying period.（3）After adding macro-molecular substance particles,the increase of macro-molecular substance in dry basis,microstructure,porosity and texture characteristics of strawberry chips were studied.The results showed that the increase in dry basis of macro-molecules in strawberry chips were increased with the trends of AX>WP>PE>PS（p<0.05）.Various staining observations and SEM results showed that the macro-molecular particles were mostly aggregated in the intercellular space,which made the cell structure denser and the cell uniformity decreased.The PE group had the thickest cell wall and showed a neat frame structure.The addition of macro-molecular particles also made the cracking distance of strawberry chips basically decreased significantly（p<0.05）,and the compression hardness,brittleness slope and texture property index increased significantly（p<0.05）.The porosity of strawberry chips in WP,PS and PE groups were significantly decreased（p<0.05）.Among them,the strawberry chips in PE group had the lowest porosity,reaching 60.57±1.36%,moderate hardness（6,440.67±386.62 g）,the shortest rupture distance（0.53±0.06 mm）,the largest brittleness slope（4,575.25±77.28 g/s）,the smallest cracking effort（906.10±256.78 g·s）,and the highest texture property index（0.98±0.05）,which represented the most suitable texture;（4）Correlation analysis and principal component analysis（PCA）were carried out on the microstructure,water migration,porosity,elastic modulus,texture characteristics and other indicators of strawberry chips.The results showed that the texture properties of strawberry chips were mainly related to their hardness,cell structure,and porosity.The PCA extracted two principal components,which explained 57.51%and 25.57%of the total variables respectively.The score calculated according to the principal component equation showed that adding macro-molecular particles could improve the texture quality of strawberry chips,and the PE group had the best texture quality and the highest PC₁score and composite score.It was found that AX was related to the pore size of the sample,WP was related to the hardness of the sample,PS was related to the number of pores in the sample,and PE was related to the pore regularity and brittleness of the sample through the analysis of the scores of each group and the loadings of each index.