| Compared with traditional emulsifiers,Pickering emulsifier has great potencial to resist emulsion droplet polymerization and make emulsion more stable.Starch is a highly potential Pickering emulsifier material due to its wide range of sources,biodegradability,ease of production,and low cost.However,the emulsification performance of natural starch is poor because of its large particle sizes and poor hydrophobicity,which requires modification treatment.With the development of the times,Clean-Label food additives have become more popular among consumers.Enzymatic modification and ball milling modification are both green and safe methods for Clean-Label modification.In this study,quinoa starch with small particle sizes was selected as the raw material.On the basis of single modification by enzymatic hydrolysis and ball milling,enzymatic hydrolysis and ball milling composite modification were used to further improve the emulsification ability of quinoa starch,and the improvement mechanism of quinoa starch emulsification performance was studied.This study is expected to provide a new type of starch-based Clean-Label Pickering emulsifier,which has good application prospect in the processing of food emulsion system and the emulsion-based delivery system for functional ingredients.The main results of the paper are as follows:(1)The effect of different proportions of amylase(AM)and glucoamylase(AMG)on the structure and emulsifying properties of quinoa starch was studied.Compared with the natural starch,the starch particle sizes and relative crystallinity decreased,and the contact angle increased after being treated with different proportions of composite enzymes.After enzymatic hydrolysis modification,the protein and fat content of quinoa starch were significantly reduced,which could exclude the influence of hydrophobic groups present in proteins and lipids on the emulsification performance of EMQS.For EM-8:1～EM-2:1,with the decrease of AM:AMG ratio,the average particle sizes of starch gradually decreased,and the emulsification index of its emulsion also gradually increased.For EM-1:2～EM-1:8,with the further reduction of AM:AMG ratio,the average particle sizes of starch gradually increased,the emulsification performance of its emulsion still gradually increased.It can be inferred that the hydrophobic property of starch had a greater impact on the emulsification performance of starch than the particle sizes.Although the average particle sizes of EM-1:1 were larger than other composite enzymatically modified starch,its contact angle was larger,so the emulsification performance was also good.Rheological results showed that all emulsions exhibited shear thinning phenomena.In the frequency range of 0.01 Hz-1 Hz,the emulsion modulus had a low dependence on frequency.With the further increase of frequency,the G ’and G’ ’values increased,and the viscoelasticity of emulsion increased.At the same shear rate,the viscosity of emulsion stabilized by EM-1:1～EM-AM showed a general downward trend with the increase of AM content,and the viscosity of emulsion stabilized by EM-1:1～EM-1:8 showed an upward trend with the increase of AMG content.The viscosity of emulsion had a positive significance in inhibiting the movement and aggregation of oil droplets,which was conducive to maintaining the stability of emulsion.The emulsion stabilized by EM-AMG had the highest emulsification index of 92.14%±2.02%which showed the smallest change with storage time,and it had the smallest and most stable emulsion droplets.(2)The effect of ball milling treatment on the structure and emulsification performance of quinoa starch for 0.5h.1h,and 2h were studied,respectively.After ball milling,the protein content of quinoa starch increased,but there was no significant change in fat content.Ball milling did not change the crystal form of starch,but the relative crystallinity decreased,the lamellar structure was destroyed,the average repetition distance increased,and the lamellar structure of BM-2h was completely destroyed.After ball milling,the particle sizes of starch were smaller than that of natural starch,but it decreased first and then increased with the increase of ball milling time.After ball milling,the contact angles of starch increased,and the hydrophobicity of starch also increased.The increase of starch hydrophobicity was related to the increase of protein content,amylose double helix structure,and short-range order degree.After ball milling,the emulsification performance of starch was enhanced.BM-1h had better emulsification performance than BM-0.5h,which was due to the dual effects of particle sizes reduction and enhanced hydrophobicity;the BM-2h had the best emulsification performance and stability,mainly due to its enhanced hydrophobicity.G" of emulsions stabilized by BMQS decreased first and then increased with the increase of frequency,and in the low frequency range(<0.16Hz),the G" value of emulsions decreased with the increase of ball milling time at the same frequency,but the G" value of the emulsion stabilized by BM-2h was higher than that of the emulsion stabilized by BM-1h when the frequency is greater than 0.16 Hz,indicating that the viscosity of the emulsion stabilized by BM-2h at high frequency was higher than that of the emulsion stabilized by BM-1h.(3)The single modified sample was set as control samples,composite modified quinoa starches with different modification orders(ball milling followed by enzymatic hydrolysis and enzymatic hydrolysis followed by ball milling)were prepared,and the effects of composite modification on the structures and properties of single modified starches were studied.The particle sizes of composite modified starches were smaller than that of single modified starch.The composite modification destroyed the double helix structure of enzymolysis starch,resulting in the decrease of the relative crystallinity of the sample with the increase of milling time.Before enzymatic hydrolysis,starch might undergo partial-gelatinization during ball milling for 2 hours.During the subsequent enzymatic hydrolysis and drying processes,the molecular chains were recombined and arranged to form new crystalline and layered structures,resulting in an increase in relative crystallinity.This might enhance the hydrophobicity of starch and further improve the emulsification performance of ball milled starch.The ratios of 1047 cm-l/1022 cm-1 decreased with the prolongation of ball milling pretreatment time before enzymatic hydrolysis,and were lower than that of starch samples that underwent enzymatic hydrolysis followed by ball milling at the same time,and the decline was even greater.This indicated that ball milling followed by enzymatic hydrolysis had a more significant impact on the short-term order of quinoa starch.The adhesion of droplets and the dispersed starch around the oil droplets shown in the CLSM diagram were conducive to increase the spatial hindrance of oil droplet aggregation,thus enhancing the stability of emulsion.The contact angles of the BE group were greater than that of the BM group,indicating that enzymatic hydrolysis can further improve the hydrophobicity of ball milled starch.The contact angles of the EB group were smaller than that of the EM-AMG,which might be related to the combined exposure of starch hydrophilic groups and protein hydrophobic groups during ball milling.For all modified starches,BE-2h and EB-2h had better emulsification effect,which benefited from the dual effects of particle size reduction and hydrophobicity increase.The rheology results showed that the emulsion stabilized by the composite modified starch had higher viscosity than the emulsion stabilized by the BM group,which was conducive to inhibiting oil droplet aggregation.CLSM showed that a large amount of starch was dispersed between BE-2h oil droplets,and the spatial hindrance of oil droplet aggregation increased,which were also conducive to maintain the stability of the emulsion. |
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