Study On The Oxidized High-amylose Starch As A Novel Delivery Vehicle For:Preparation And Sustained Release Of Biologically Active Ingredients

Biologically active ingredients possess many bioacticities,including regulating the balance of intestinal flora,scavenging free radicals and enhancing immunity.However,their biological activities are easily lost due to the surrounding environment,such as processing,storage,and the human digestive environment,which have a great influence on the efficacy,as well as severely restrict the application of these biologically active ingredients in the food and pharmaceutical industries.An effective delivery system that can realize the effective encapsulation and targeted release of biologically active ingredients is desiderated to fully retain and play their bioacticities.Therfore,in this study,oxidized high-amylose starch(OHAS)was prepared using high-amylose starch(G80,HAS)to establish the two delivery systems of oxidized high-amylose starch macrogel(OHASM)and oxidized high-amylose starch emulsion(OHASE);then,the loading and sustained-release effects of the two delivery systems on biologically active ingredients were systematically explored.The establishment of delivery systems in this study suggests an attractive strategy for designing and developing new starch vehicles to encapsulate biologically active ingredients.The main research contents and results are as follows:(1)TEMPO media oxidation system,which can introduce carboxyl groups into starch,was used to prepare 4 kinds of OHAS(DO10/30/60/90-OHAS)with different oxidation degrees(DO or oxidation degree).The results of fourier transform infrared spectroscopy(FTIR)and the carboxyl content in OHAS demonstrated that the hydroxyl group on HAS was successfully converted to carboxyl groups,and the carboxyl content on OHAS increased with the increasing DO.Analysis by means of X-ray diffraction,thermogravimetric analysis and scanning electron microscope suggested that the molecular structure of starch has changed after TEMPO oxidation,and gradually loosened with the increase of DO.(2)OHAS with different DO crosslink Mg²⁺,Ca²⁺,Al³⁺,Fe²⁺,Fe³⁺,Cu²⁺,Zn²⁺and Ba²⁺to prepare OHASM using extrusion method.Further,the effects of OHAS with different DO and different kinds of metal ions with different concentrations on the structure,morphology and performance of the OHASM were studied,and then a delivery system for biologically active ingredients(probiotics,?-carotene,tea polyphenols)was fabricated.In the process of forming macrogels,the metal ion concentration,both kinds of metal ions and DO of OHAS were closely related to the crosslinking degree,affecting the morphology and sustained release characteristics of macrogels.Furthermore,the outstanding p H-responsiveness and resistance of OHASM against gastric acid,bile salt,and digestive enzymes were demonstrated by swelling and simulative digestive experiments in vitro.DO90-Zn²⁺macrogels,formed by Zn²⁺crosslinking DO90-OHAS,was suitable for biologically active ingredients,evidenced by62.4%,77.9%and 88.8%encapsulation efficiency(EE)for?-carotene,tea polyphenols and Lactobacillus paracasei,respectively.After continuous immersion in simulated gastrointestinal fluid for 5 h,the viable counts of Lactobacillus paracasei in free and encapsulated in DO90-Zn²⁺macrogels exhibited 9.2 and 3.0 log reductions in CFU(decreased by 97.8%and 32.6%),respectively.The percentage of?-carotene and tea polyphenols released from DO90-Zn²⁺and chitosan macrogels in simulated gastric fluid(SGF)at 2 h were only 24.8%and 63.9%,respectively;and that in simulated intestinal fluid(SIF)at 3h were 63.9%and 71.1%,respectively.It showed that DO90-Zn²⁺macrogels played a significant role in protecting and sustained-releasing?-carotene and tea polyphenols.Meanwhile,compared with free?-carotene(40.1±0.5%)and tea polyphenols(11.0±0.9%),the antioxidant activity of?-carotene(55.0±1.4%)and tea polyphenols encapsulated in DO90-Zn²⁺and chitosan macrogels have been improved.Hence,these results indicated that OHASM has an excellent protective effect on biologically active ingredients,and has a certain universality as a delivery vehicle.(3)HAS and OHAS with different DO were used to prepare G80 emulsion(G80E)and OHASE by high-speed shear emulsification method,respectively.Further,the effects of different DO90-OHAS concentration,oil phase mass fraction,p H,Na Cl concentration and temperature on the particle size,Zeta-potential and rheological properties of DO90-OHAS emulsion(DO90-OHASE)were explored.It was found that DO90-OHAS can produce stable gel-like O/W emulsions at fiber concentrations upon 5%(w/v)using 28%(w/w)oil.The DO90-OHASE is typical non-Newtonian fluid and its interfacial viscosity is not influenced obviously by changing p H from 3 to 7,ionic strength of Na Cl from 0.00 to 1.00 mol/L or temperature from-25 to 80?.And DO90-OHAS partition between the continuous phase and state of the droplets of emulsions were visualized by confocal laser scanning microscopy,confirming that in addition to Pickering stabilization,the DO90-OHAS-based network also contributed to stabilization of the emulsions.In addition,DO90-OHASE loaded with?-carotene was prepared under different p H conditions(p H=3,5 and 7),and the EE were about 72.5%.The percentage of?-carotene released from DO90-OHASE in SGF at 2 h were only 24.8%;and that in SIF at3h were 95.8±4.6%.In contrast,the release rate of?-carotene encapsulated in G80E in SGF was up to 100.2±2.7%.It indicated that DO90-OHASE has an excellent sustained-release effect on?-carotene.Meanwhile,the antioxidant activity of?-carotene(49.3±2.6%)encapsulated in DO90-OHASE was significantly higher than that of?-carotene(16.7±3.7%)encapsulated in G80E,showing that DO90-OHASE significantly improves its thermal stability.Therefore,these results indicated that DO90-OHASE has the potential to encapsulate and sustained release hydrophobic biologically active substances(?-carotene).This study will provide the certain theoretical base and scientific methods for establishing the delivery system of biologically active ingredients;at the same time,it may shed light on the application of starch in the food industries.