The Effect Of Microwave Heating On The Dielectric And Physical Properties Of Potato Starch

Microwave is widely used in the field of food processing and reheating for its efficientand fast processing characteristics. As a complex food macromolecule, starch plays animportant role in the microwave food field. At present, most research focus on thegelatinization phase of the starchy material and the application of the starchy food. As thedielectric properties of material determine the effect of microwave heating, lack of study onthe dielectric properties of starch under microwave heating is not conducive to cognitive thechanges in physical properties during the processing, also hinder the development ofmicrowave technology in the food industry.In this paper, we selected the typical B-type crystal starch-potato starch as the object,for it has regular shape and wide application. Based on the characteristics of the microwaveheating process, we established a rapid heating process model, which was highly fitted withthe microwave heating process; meanwhile, a conventional heating process was established asa reference. Moreover, the influence on the dielectric properties, morphology, thermalcharacteristics and the water state of potato starch during microwave heating was studied toclear the main mechanism of microwave heating. The major results of the study are asfollows:(1) The effect of microwave heating on the dielectric properties of potato starchThe network analyzer was applied to research the dielectric properties of potato starch.The study found that microwave heating induced the dipole moment of the main componentsin the starch-water system tend standardized, make the starch-water system exhibit a morestable dielectric response in the1.7-2.6GHz range; During microwave heating, the dielectricproperties variation with temperature is relatively stable under the conditions of2450MHz,during40oC-50oC, the polar molecules of starch-water system heated with microwave was toolate to response, which made the dielectric constant, dielectric loss factor and loss angletangent values were lower than the conventional heating. The rapid heating impact ofmicrowave played a leading role in the low temperature region;(2) The effect of microwave heating on the physical properties of potato starchThe optical microscopy (OM), polarizing microscope (PM), scanning electronmicroscope (SEM) and laser particle size distribution analyzer were applied to research theeffect of microwave heating on the polarization cross, morphology, microscopic morphologyand grain size of starch granule. The results showed that the thermal effects and special effectsof microwave was counterproductive, so that the change degree of microwave heated samplewas between rapid conventional heating and conventional heating. Besides, the microwavespecial effects lead to the surface of the potato starch show shallow nicks and grooves in thelow-temperature phase.The differential scanning calorimetry (DSC) and thermal gravimetric analysis (TG) wereapplied to research the effect of microwave heating on the pasting parameters and thermalstability. The results showed that microwave heating had an effect on the endothermicproperties and thermal stability of potato starch. At the early stage of the gelatinization, thespecial effects of microwave played a leading role while the thermal effects of microwave gradually began to occupy the absolute dominance after gelatinization.The low-field nuclear magnetic resonance (1H NMR) technology was applied to researchthe effect of microwave heating on the water state of potato starch. UseCarr-Purcell-Meiboom-Gill (CPMG) pulse sequence to get the original relaxation data. Bymeans of principal component analysis (PCA) the variation pattern of original relaxation datawas obtained, and the transverse relaxation time (T2) was calculated throughmulti-exponential regression to analysis the moisture change information in the potato starch.The results showed that microwave heating had a significant impact on the moisturedistribution within the potato starch particles. The thermal effects of microwave had aninhibitory impact on the destruction of the hydrogen bonds between starch molecules andstarch-water, while the special effect of microwave showed acceleration on the destruction ofthe hydrogen bonds.Microwave always produce different levels of influence on the potato starch-watersystem throughout the heating process. The thermal effect of microwave showed an absoluteadvantage after gelatinization while the special effects of microwave were taken an effectbefore or in the beginning stages of gelatinization, which influenced the dielectric properties,morphology, thermal characteristics and the water distribution of the potato starch granule.