Dissolution Mechanisms Of Yeast ?-D-glucan Modified By The Ionic Liquid Combined With High Pressure Microfluidization

Yeast ?-D-glucan(YG)has good immunomodulatory activity,and had been listed as “New Resource Food” by Ministry of Health.However,YG exists as a compact triple helix conformation,which makes it hardly soluble in water and other common organic solvents,thereby severely limiting its applications.The ionic liquid 1-butyl-3-methylimidazolium acetate(EmimAc)combined with high pressure microfluidization(HPM)can be applied to solubilize YG.Nonetheless,the underlying solubilization mechanisms are not clear.In this work,the structural and physiochemical properties of YG during the modification were investigated,and the mechanisms of YG solubilization were elucidated.Finally,EmimAc-HPM was also employed to solubilize curdlan.The elevated water-solubility of YG would expand its applications in food industry,cosmetics,biomedicine,and yeast processing industry effectively.The modification parameters on YG solubilization by EmimAc-HPM were optimized.Specifically,the YG concentration was 2 wt%,the HPM pressure was 24000 psi,the HPM pass was eight times,and EmimAc was recycled and reused for five times.Under the optimum process conditions,the water-solubility of ?-D-glucan treated by EmimAc(EYG),and modified ?-D-glucan by EmimAc–HPM(EMYG)reached 75.53 ± 0.49%,and 85.01 ± 0.45%,respectively.These suggested that EmimAc had superior dissolution ability to YG with branched chains,and EmimAc–HPM could significantly improve YG's solubility.The molecular weights(Mw),rheological characteristics and thermal properties of ?-D-glucan during the modification were investigated.Specifically,YG's Mw was 598300 g/mol,while that of EYG and EMYG decreased to 528000 and 171300 g/mol,respectively;on the contrary,the polydispersity index(Mw/Mn)of ?-D-glucan increased from 1.213 to 2.187,which indicated that EmimAc and HPM treatment lowered YG's Mw,and depolymerized it into small fractions,so the solubility of regenerated ?-D-glucan was elevated.In addition,the rheological properties of ?-D-glucan were changed after modification.Specifically,the loss modulus(G'')of YG with high concentration solutions was higher than that of low samples,while the storage modulus(G')was lower than that of low concentration solutions.By contrast,the G' and G''of EMYG with high concentrations were both lower than those of low concentration ones,which might be ascribed to the dynamic viscoelastic change of modified ?-D-glucan caused by its elevated solubility.Moreover,?-D-glucan's thermal transition temperature significantly declined after treatment,and its thermal stability gradually decreased.The structural and conformational changes of ?-D-glucan during the modification were clarified.The compact triple helix conformation of YG was transformed to irregular chains after EmimAc–HPM treatment.Besides,YG possessed moderate absorption at 9.5° and 31° while such absorption peaks apparently vanished after treatment,which indicated that YG's crystallinity was reduced after treatment.This was due to the disruption of YG's native triple helix conformation.Additionally,?-D-glucan's negative absorption peak at 185 nm was gradually red-shifted to 187.5 nm after EmimAc-HPM treatment.The results revealed that YG's triple helix structure was broken,and changed to ?-sheet-like structure.EmimAc-HPM treatment did not destruct the essential structural of ?-D-glucan,and it was still linked by ?-(1?3)-glycoside bonds.Furthermore,the potential mechanisms of YG solubilization by EmimAc-HPM were deduced.New H-bonds between EmimAc cation and hydroxyl groups in ?-D-glucan formed,thereby disrupting YG's native strong H-bonds networks.Meanwhile,HPM disrupted YG's native triple helix structure,and lowered its Mw,thereby elevating its water-solubility.EmimAc–HPM was also applicable to solubilize curdlan.After regeneration,the water-solubility of curdlan treated by EmimAc(RC),and modified by EmimAc–HPM(RMC)attained 74.41 ± 0.63%,and 83.11 ± 0.56%,respectively,which implied that EmimAc also had dissolving ability to linear curdlan.Results showed that RC possessed loose and uniform structure after regeneration,and curdlan's native triplex conformation was broken,leading to its decreased crystallinity and thermal decomposition temperature.Novel H-bonds between EmimAc cations and curdlan formed,which disrupted extensive intra-and intermolecular H-bonds in curdlan,thereby resulting in RC's elevated solubility.