Research On Enzymatic Preparation Of LR-CD And Its Effect On Starch Gelatinization-Retrogradation Behavior

Large-ring cyclodextrin（LR-CD）has a wide range of application in food processing because of its unique advantages such as high solubility,large cavity,difficulty to retrogradation,safety and non-toxicity.Natural starch usually shows some shortcomings,such as insolubility in cold water,high viscosity after gelatinization,and ease to retrogradation in food processing,which greatly limits the processing of starch-based foods.Therefore,it is of great significance to modify starch to meet the performance requirements in different application scenarios.Adding exogenous substances to starch is one of the common means of starch modification.Therefore,this research took LR-CD prepared by enzymatic method as the object to explore its influence on the gelatinization-retrogradation behavior of starches,summarized the mechanism of LR-CD in the process of starch granule gelatinization-retrogradation,and verified the regularity of the effect of LR-CD on the gelatinization behavior of large starch granules.The main research contents were as follows:（1）Enzymatic preparation of LR-CD.LR-CD was prepared by 4-α-glucosyltransferase from Thermoproteus uzoniensis（TuαGT）.Sample LR-CD（PS）was prepared by TuαGT（10U/g starch）from potato starch for 10 h at 75℃,p H 6.0.The yield was 20.67%.The LR-CD sample was identified as CD₁₅-CD₃₆ by HPAEC-PAD and TOF-MS.（2）Effect of LR-CD on starch gelatinization-retrogradation behavior.After mixing LR-CD with potato starch（PS）,cassava starch（CAS）,corn starch（CS）,waxy corn starch（WCS）and pea starch（PEAS）,the effects of LR-CD on starch gelatinization,swelling,retrogradation and rheology were investigated.DSC showed that LR-CD had a stronger inhibitory effect on the long-term（7 d）retrogradation of starch.FTIR indicated that LR-CD could inhibit the short-range ordering of starch,especially for PS,PEAS and CAS.The swelling power results showed that LR-CD could limit the swelling of PS and CAS.The results of dynamic rheology revealed that LR-CD had a great effect on the G’of starch.The results of static rheology indicated that the addition of LR-CD reduced the viscosity and shear stress of PS and CS,and“K”vaule significantly decreased.In particular,the RVA showed that the addition of 5%（w/v）LR-CD significantly reduced the peak viscosity of PS by 40.83%at 7%（w/v）starch concentration,but had little effect on other starches.（3）The mechanism of LR-CD affecting starch granule gelatinization-retrogradation.Compared with CAS（13.24μm）,CS（13.84μm）,WCS（15.12μm）and PEAS（24.75μm）,PS（39.53μm）had the largest granule size and more branch chains.Based on the above research,the mechanism of LR-CD affecting the gelatinization-retrogradation of starch granules was analyzed.The starch granules expanded during gelatinization,the amylose leaching accompanied by LR-CD into the starch granules,and LR-CD could participate in the rearrangement of starch molecules to form finite double helix because of its large and flexible structure.As a result,the molecular entanglement between starch was partially inhibited,resulting in a significant decrease in gelatinization viscosity.Subsequently,LR-CD will continue to participate in starch molecular rearrangement,thereby inhibiting the retrogradation.（4）Verification of the effect of LR-CD on starch gelatinization behavior based on large granular starch.According to previous research,LR-CD was more likely to affect the gelatinization behavior of large granule starches.In order to verify the hypothesis and explore how LR-CD affected the gelatinization behavior of large granule starches,other large granule starches were selected:canna edulis ker starch（CKS）,lotus root starch（LRS）,sweet potato starch（SPS）and potato starch extracted from 7 varieties of potatoes（PS-1 to PS-7）.All potato starches（PS-1 to PS-7）and CKS had larger granule size and wider chain length distribution.RVA showed that the peak viscosity of all potato starches（PS-1 to PS-7）and CKS significantly decreased by 41.66%after adding LR-CD,while LRS and SPS had little change.The results of swelling power revealed that LR-CD could reduce the swelling of all large granule starches.The dynamic rheology results showed that LR-CD could effectively reduce the G’of large granule starch gels and improve the gels’structure during retrogradation.The results of static rheology indicated that LR-CD decreased the shear stress,viscosity and“K”of large granule starches.The static rheological results show that LR-CD could affect the shear stress and viscosity of large particle starches,and decrease“K”vaule.