The Effect Of Dynamic High-pressure Microfluidization On The Structure And Physicochemical Properties Of Lotus Seed Starch

Lotus seed is an important cash crop in China.Starch accounts for more than 50%of the total dry matter content of lotus seeds,of which amylose content is as high as 42%,making lotus seed starch a specific starch with high amylose content.Generally,the industrialization of lotus seed production is constrained by their low solubility,poor stability and aging easily.Dynamic high-pressure microfluidization?DHPM?treatment is a new physical modification method that has been successfully used in the food industry,for heating,mixing,ultra-fine crushing,etc,which can modify starch structure and physicochemical properties safely and effectively.Therefore,the purpose of this study was to explore the influence of DHPM treatment?at different pressure or with different times?on structural and physicochemical properties of lotus seed starch before and after retrogradation,with a view to providing a reference for applying DHPM in starchy foods production.The main findings were as follows:?1?Effect of dynamic high-pressure microfluidization time on the structural characteristics of lotus seed starchThe structural characteristics of the non-retrogradation group?LS?and the retrogradation group?LRS?were studied after DHPM treatment with different times.The results showed that the lotus seed starch deformed under a high pressure of DHPM and lost its original shape in the LS group.The particles of LS-7 and LS-9?DHPM with 7 and 9 times?were severely deformed,with dents on the surface.Meanwhile,the particles of the LRS group were regenerated after gelatinization,which aggregate together to form big blocks.Based on the particle size and molecular weight of startch in the LS group,5 times was chosen as optimal DHPM treatment conditionyield the best overall performance.The area average diameter and volume average diameter decreased from11.93?m and 20.17?m to 10.80?m and 12.00?m,respectively.The diameter and molecular weight of the particles first decreased then increased with the increasing DHMP times,indicating DHPM play a role in the degradation of lotus seed starch.However,when DHPM times further increase,lotus seed starch was partially gelatinized and small particles was aggregated on the surface of large particles.X-ray diffraction analyses was also used to detect the crystalline region of lotus seed starch,which revealed that the crystal structure of the LS group was still C-type starch,but the characteristic peaks were significantly attenuated.The crystallinity decreased significantly as the high-pressure shear force intensified,and the lowest crystallinity was observed in LS-5sample;while in the LRS group retrogradation after DHPM treatment has strong impact on the crystal type of the LRS group,changing it from C-type to B-type crystals.The results were consistent with the measurements of Solid-State NMR and FTIR.The low-field NMR water distribution study showed that the bound water in the LS group gradually moves towards immobile water and free water;while the bound water and free water in the LRS group increase slightly,indicating that DHPM treatment leads to the water transfer between the different phases.?2?Effect of dynamic high-pressure microfluidization time on the physicochemical properties of lotus seed starchThe physicochemical properties of the LS and LRS groups were studied after DHPM treatment with different times.DSC analyses demonstrated the gelatinization temperature value and gelatinization enthalpy first showed a decreasing trend and then increased.The gelatinization temperature and enthalpy of LS-5 were the lowest.Compared with LS-0,the gelatinization temperature of LRS-0 was higher,which was due to the fact that B-type crystal structure of LRS-0 was relatively stable,and required more energy for gelatinization.Among LRS samples,LRS-5 exhibited the most obvious change.The RVA results also showed the viscosity characteristic values of the LS and LRS groups both first decreased and then increased,indicating that DHPM has a certain anti-aging effect.The results of sedimentation stability,solubility and swelling degree indicated that 5 times led to the most obvious change.DHPM may increased the binding between starch molecules and water molecules by reducing the size of starch particles,thereby enhanced its water holding capacity.As a result,the starch particles in the starch solution were not easily separated by centrifugation,which the molecular chains were degraded.Therefore,LS-5 and LRS-5 showed better effect,which were also by supported by transmittance measurements.The freeze-thaw stability was also augmented to a certain extent,with LS-5having the lowest syneresis rate,followed by LS-3 and LRS-5 showing the lowest syneresis rate in the LRS group,followed by LRS-3.The above results confirmed the correlation between the structural characteristics and the physicochemical characteristics.Meanwhile,it showed that 5 times of DHPM treatment has significant effects on the structural and physicochemical characteristics of the LS and LRS groups.It has a certain anti-aging effect on the LS group and is beneficial for LRS group gel maintaining the original characteristics.?3?Effect of dynamic high-pressure microfluidization pressure on the structural characteristics of lotus seed starchBased on the study of different DHPM times on the structural and physicochemical properties of the LS and LRS groups,5 times were selected as the optimal processing parameter for the following chapters.In this chapter,the effects of different DHPM pressures on the structure of the LS and LRS groups were explored.The lotus seed starch granules were observed by FESEM.When the pressure reached 80 MPa,the starch granules aggregated,and some even cracked.When the pressure reached120 MPa,the granules were further agglomerated.When it exceeded 160MPa,the particles swelled and ruptured,most of which gelatinized into a bulk morphology.LRS-80 showed that the surface of the starch paste was rough,and LRS-200 starch absorbed large quantities of water and swelled,then gelatinized and returned to a smooth shape.The diameter analyses showed that the size of the LS group was uniform,mainly existed as small particles.The uniformity of LS-80 was the best,followed by LS-120,which moved to the direction of large particles as the pressure increased;however,the peak pattern of the LRS group shifted from unimodal to bimodal,indicating poor uniformity.Compared with other LRS samples,the particle uniformity of LRS-80 was the best,followed by LRS-120.The molecular weight of the LS group decreased initially followed by an increase with the increase in pressure.On the contrary,LRS group exhibited the opposite trend.The results of X-ray diffraction showed that the worst damage of crystal structure was found in LS-120sample,with its crystallinity reducing from 50.79%to 33.91%.Retrogradation weakened the characteristic diffraction peak of starch,the crystallinity of LRS-120 was reduced to the lowest value.The relative crystallinity of Solid-State NMR was reduced to a minimum at 120 MPa.FTIR analysis showed that the R_995/1022 and R_1047/1022 of LS-120 were the smallest,while LRS-80 was the best in the LRS group,followed by LRS-120.When the pressure exceeded 120 MPa,the ratio gradually increased,but still lower than LRS-0.The analysis of low-field NMR water distribution showed that the bound water content of LS-120decreased,while the immobile water and free water content increased.Compared with LRS-0,the bound water content of LRS-120 decreased significantly,the immobile water and free water content increased significantly.?4?Effect of dynamic high-pressure microfluidization pressure on the physicochemical properties of lotus seed starchThe effects of DHPM treatment at different pressures on the physicochemical properties of the LS and LRS groups were studied.DSC results showed that the gelatinization enthalpy tended to showed a U-shape pattern with DHPM pressure increasing.LRS-0 shows a higher gelatinization temperature compared to LS-0.When the pressure reached to 120 MPa,the gelatinization temperature value and gelatinization enthalpy were the lowest.The results of FESEM,particle size analysis,and GPC molecular weight test showed that the gelatinization critical point was between 120 and 160 MPa.The RVA results demonstrated that LS-120 in the LS group had a better effect than LS-80 with the viscosity characteristic value decreasing significantly.The viscosity characteristic value and the regenerative value of the LRS group first increased and then decreased.The determination of the sedimentation stability indicated that the DHPM could improve the solubility and expansibility of LS and LRS in water.The freeze-thaw stability of the LS and LRS groups was characterized by the syneresis rate.The syneresis rate of the treated samples was lower than untreated controls.After the first freeze-thaw,the syneresis rate was generally high,among which LS-120 and LRS-120were the lowest.The syneresis rate of the second freeze-thaw began to decreased,and reached equilibrium at the third freeze-thaw.In summary,DHPM technology can promote the freeze-thaw stability of the LS and LRS groups to a certain extent.According to the above results,120 MPa treatment has significant effects on the structural and physicochemical properties of the LS and LRS groups,which delays the regeneration rate and improves the solubility of the LS group;as well as improve the quality stability of the LRS group.