Effect Of Pulsed Electric Fields Treatment On Kumquat Cell Wall Structure And Its Application

At present,a large amount of literature had studied the effect of pulsed electric field?PEF?on the structure of cell membranes,and the theory of"electroporation"of cell membranes is highly recognized,but few have studied the changes of cell wall structure.In this paper,the effect of PEF on the cell wall structure of kumquat was studied.The posssible mechanism of electroporation on kumquat epidermis cell wall and the application of cell wall structure changes in soaking and quality improvement of kumquat were investigated.The main conclusions are listed as follows:1. The treatment of PEF on kumquat caused an effective epidermal perforation of the kumquat skin.Under the condition of PEF treatment for one time?1.0 kv/cm,10 pulses?,17big holes and 22 small holes were formed in the microscopical field of vision.The structure of kumquat epidermis essential oil cavity was fluffy,forming cracks.2. By studying the effect of PEF treatment on the structure of components of cell wall of kumquat,it was found that the treatment of PEF results in the change of the structure of cellulose in the primary and secondary wall layer:the hydrogen bond between cellulose chains was weakened,the crystallinity,crystallinity index and crystallinity size were reduced,the distance between large fibrils was increased,the surface structure was rough,and the filamentous micro fibrils were exposed.With the increase of electric field intensity to 2.0kv/cm,30 pulses,many voids appeared on the surface of cellulose,and the strength of cytoskeleton was decreased.The supporting effect of cellulose on cells was weakened and the rigidity was reduced.Under the PEF treatment intensity of 2.0 k V/cm for 30 pulses,the hydrogen bonding force between the half-fiber chains in the cell wall was significantly reduced,the water adsorption performance was weakened,the C₁-H bending vibration was enhanced,the spatial structure was changed,and the molecular chain was shortened.The hemicellulose changed from a regular ring structure to small disordered particles,the structure collapsed,and the surface zigzag structure became a needle-shaped structure,so the connection effect of hemicellulose on the surface of the microfibers was weakened,resulting in the destruction of the hard network structure skeleton of the cell wall.Under the PEF treatment intensity of 2.0 k V/cm for 30 pulses,the hydrogen bonding stretching vibration peak of the intercellular pectin molecules in the cell wall was enhanced,the hydrophilic property was increased and the molecular weight was reduced.The viscosity of pectin decreased with increasing PEF strength,and the mutual adhesion force between the cell walls was weakened,resulting in the loosening of the cell wall skeleton and the enlargement of the voids,thereby causing the perforation of the kumquat skin.3. The cell wall tissue structure determines the texture characteristics of plant-based foods.It was found that after the PEF treatment intensity of 2.0 k V/cm for 30 pulses.The hardness and the adhesion decreased by 78.89%and 71.06%,respectively,and the chewability decreased from 367.63 to 157.46.When the pulse processing intensity was 1.5k V/cm,the elasticity,cohesion and recovery of fresh kumquat were increased by 50.86%,60.37%and 104.70%respectively.4. Based on the study of pulsed electric fields perforation,PEF technology was applied to the manufacturing process of kumquat preserves to improve the impregnation rate.The results showed that the electric field strength was 1.5 k V/cm,40 pulses and treated 4 times was the best parameter to increase the kumquat impregnation rate.Under this condition,the kumquat impregnation rate was at least 78.49%higher than the traditional process.Shorten by6-7 days.5. The results of PEF treatment on the quality of kumquat preserves showed that under the PEF treatment intensity of 1.0 k V/cm for 10 pulses could significantly improve the chewability and elasticity.Compared with the traditional process,the elasticity and chewability increased by 15.33%and 76.36%on the 10th day of dipping,respectively.The PEF treatment reduced the spiciness and bitterness of kumquat,and improved palatability.In addition,PEF treatment affected the content of polysaccharides,vitamin C,and protein in the kumquat peel.The polyphenol content was significantly increased at the electric field strength of 0.5 k V/cm,and the vitamin C content in the kumquat pulp was maintained well;as the intensity of the PEF treatment increased,the content of polyphenols,polysaccharides,and protein showed an increase and then a decrease,with the highest content at the pulse electric fields intensity of 1.0 k V/cm.Based on factors such as impregnation rate,palatability,color and nutrient content of kumquat preserves,the optimal parameter range for PEF treatment of kumquat is:electric field intensity 0.5?1.0 k V/cm,30?40 pulses.