Preparation Of Starch Spherulites And Its Application In Pickering Emulsions

Pickering emulsions are a kind of emulsions with solid particles as stableilizers.Due to its good emulsion stableility and low-added amount of emulsifier,Pickering emulsions have attracted increasing attention recently.Starch is a natural renewable carbohydrate polymer with advantages of inexpensive,aboundant,and wide varieties of sources,therefore it is an ideal particle to stableilize Pickering emulsions.In this work,starch spherulites were prepared by combining methods of enzymatic recrystallization,octenyl succinic anhydride(OSA)hydrophobicity modification and high-speed shear dispersion,which could effectively reduce the particle size and enhance the yield of spherulites.Starch spherulites were then applied to prepare Pickering emulsions.The effects of different factors on physicochemical property and emulsion stableility of the emulsions were investigated.Finally,starch spherulites were used for preparing moisturizers.The main index of the moisturizers were evaluated.These results obtained would provide an important references for preparing novel starch-based emulsifier to stableilize Pickering emulsions and also expand the application fields of starch.The main results were as follows:1.Effects of added amount of enzyme on degree of branching of starch and starch spherulites were investigated.Degree of branching of starch decreased from 5.8%(native starch)to 0 as increasing added amount of isoamylase in the range of 5~25 U/g.When the amount of isoamylase was 25 U/g,waxy corn starch was entirely debranched.With the increasing of recrystallization time from 0.5 h to 24 h,the yield of starch spherulites increased from 56.9% to 76.6%.The volume average particle size(D[4,3])of starch spherulites was about 0.8 ?m,but the aggregation phenomenon of starch spherulites happened significantly.After 24 h of recrystallization time,D[4,3] was increased to 35 ?m,the crystallinity increased from 44.2 to 51.1%,and the gelatinization temperature increased from 71.99 to 75.09 ?.In addition,the yield,crystallinity and gelatinization temperature of starch spherulites did not change obviously after 16 h of recrystallization time.The average degree of polymerization of starch spherulites was 26.7(the chain length of the starch spherulites was 10 or more),which was larger than that of waxy maize starch.2.Effects of physical treatment on the debranched starch recrystallization were investigated.D[4,3] of starch spherulites decreased from 35.95 ?m to 12.18 ?m with the stirring rate changing in the range of 0~500 rpm.Moreover,D[4,3] of starch spherulites decreased gradually with increasing the intermittent ultrasonic time and power.When the ultrasonic power was 300 W and ultrasonic time was 90 min,D[4,3] decreased to 8.54 ?m.The results indicated that physical treatment could significantly reduce its particle size,but it also affected the orderly accumulation of short-chain amylose and failed to completely solve aggregation.The frozen grinding caused a decrease of D[4,3] from 35.95 ?m to 17.22 ?m,but the micronized effect was poor.In addition,different drying methods were applied to starch spherulites.D[4,3] of undried,frozen-dried and oven-dried starch spherulites were 4,35.95 and 8,respectively.Results indicated that drying process was the main reason for the agglomeration of starch spherulites.Because frozen-dried starch spherulites appeared loose and porous structures on the surface,particles between the larger contact areas was bigger which was easy to agglomerate into larger particles.Finally,starch spherulites were dispersed in water and homogenized by a high speed shear at 23,000 rpm for 2 min.The D[4,3] of oven-dried starch spherulites was decreased to 4.0 ?m which was easier to be dispersed compared to freeze-dried starch spherulites.3.OSA-modified starch spherulites were chosen as particle emulsifiers to stableilize Pickering emulsions.Rice starch,waxy corn starch and potato starch were used as the control.Results showed that the stableility of the emulsions were decreased in the order of starch spherulites > rice starch > waxy corn starch > potato starch.With the increasing of concentrations of starch spherulites(1~5%,w/w),the emulsions became more stable and its D[4,3] gradually decreased.The visocosity and stableility of the emulsions increased with increasing the oil volume fraction(5~50%,v/v).The pH exhibited no significant effect on the emulsion stableility;The addition of NaCl resulted in the decreasing of the surface charge and promoted emulsion creaming.But emulsification index(EI)were not changed greatly with increasing the NaCl concentrations(100~500 mmoL/L),and the EI kept above 60% after 30 d of storage.Due to high onset temperature of starch spherulites,Pickering emulsions exhibited good stableility below 80?.When the starch spherulites concentration was 4%,the oil volume fraction was 40%,the pH value was 5~6 and the temperature was about 50?,the prepared emulsions exhibited good stableility.4.The modified starch spherulites were used to replace the traditional surfactant in the moisturizer.Results showed that compared to commercial moisturizer,heat/cold and centrifugal stableilities of moisturizer stableilized by the modified starch spherulites was comparable.When the humidity was 43% or 75%,its moisture resistance was even better than commercial moisturizer.Sensory evaluating results showed that the mucosity and spreadability of moisturizer stableilized by the modified starch spherulites were weaker than commercial products.But its stableility,moisture resistance and permeability were better,and could effectively reduce the irritation of the products.