| The enhancement of the stability of roselle anthocyanins is beneficial to improving the utilization rate of roselle anthocyanins in food and drug production.There are two ways to improve the stability of anthocyanins which were physical and chemical ways.In this study,roselle anthocyanins were extracted from dried roselle calyx by ultrasonic-assisted extraction and purified with macroporous resin.Soybean protein isolate,zein,gelatin and ?-cyclodextrin were used as wall materials,and roselle anthocyanin microcapsules were prepared by spray-drying method.The effects of different wall materials on encapsulation efficiency,microscopic morphology,thermal stability,antioxidant activity and hypoglycemic were investigated.Roselle anthocyanin was acylated by an enzymatic method with noctanoic acid as an acyl donor,and the acylation degree,acylation products,thermal stability,antioxidant activity and in vitro digestibility of acylated roselle anthocyanins were investigated.It is of great significance to develop natural food additives and improve the economic development of roselle planting areas.Wall materials were used individually to prepare microcapsules.Soybean protein isolate had the best embedding effect on roselle anthocyanins,the encapsulation efficiency was98.51%±0.45% which was measured by p H differential method,the encapsulation efficiency of gelatin and ?-cyclodextrin was 73.99%±2.66% and 89.75%±0.14%,respectively,while the encapsulation efficiency of zein was very low.The highest encapsulation efficiency was1.31%±0.12%,so zein was not considered when wall material was mixed.When two kinds of wall materials are used to prepare microcapsules,the encapsulation efficiency of gelatin +?-cyclodextrin was 99.59%±0.49%,and that of gelatin + soybean protein was99.95%±0.07%.The encapsulation efficiency of microcapsules prepared by soybean protein isolate + ?-cyclodextrin was 99.53%±0.48%.Fourier transform infrared spectroscopy(FTIR)was used to measure the purified roselle anthocyanin powder,all microcapsule samples and wall materials.The obtained spectra showed that ?-folding of the secondary structure of protein changed during spray drying.The microcapsules with ?-cyclodextrin and soy protein isolate as composite wall material showed the smoothest FTIR spectrum curve in the characteristic peak of anthocyanin.It was observed by scanning electron microscope that the particle size of the microcapsules formed was less than 10 ?m,and the microcapsules with gelatin as composite wall material had a smooth and non-concave surface structure.The acylation products of anthocyanins were determined by liquid chromatographymass spectrometry(LC-MS).The acylation degree and anthocyanins content were determined by potentiometric titration.The results showed that n-octanoic acid was linked to roselle anthocyanins by acylation,and the acylation product was cyanidin-3-(5"-n-octanoyl)sambudiglycoside.The acylation degree of anthocyanins modified by n-octanoic acid was9.69%±0.18%,and the total content of anthocyanins decreased by 57.30% from569.90±11.28 mg/100 g to 243.34±7.22 mg/100 g.Differential scanning calorimetry results confirmed that the endothermic peaks of microcapsules with gelatin + ?-cyclodextrin and soybean protein isolate as wall materials and roselle anthocyanins appeared at different positions,indicating the effect of embedding roselle anthocyanins was better.The microcapsule samples all had higher heat required for phase transition and showed good thermal properties.The antioxidant activity of the samples was evaluated,and it was found that the gelatin+?-cyclodextrin microcapsules had better antioxidant activity against DPPH and ABTS free radicals,with the highest scavenging rates of 72.03%±1.97%,and 90.62%±2.84%,respectively.The scavenging effect of hydroxyl radicals was not good(the highest scavenging rate was 13.45%±0.53%).The scavenging rates of SPI+gelatin microcapsules to DPPH,ABTS and hydroxyl radicals were31.75%±0.95%,66.83%±1.83% and 31.93%±0.93%,respectively.The scavenging rates of SPI+?-cyclodextrin microcapsules to DPPH,ABTS and hydroxyl radicals were38.42%±0.85%,60.62%±1.72% and 11.76%±0.31%,respectively.Acylation significantly reduced the fading rate of roselle anthocyanins in thermal environment.Compared with the microcapsule samples,the acylated roselle anthocyanins had better stability in the environment above 60 ?.The results of antioxidant activity showed that the acylation of noctanoic acid reduced the scavenging ability of roselle anthocyanins on DPPH and ABTS free radicals.Compared with unacylated roselle anthocyanins,acylation improved its scavenging ability to hydroxyl radicals.The hypoglycemic effect of the samples was investigated by simulating the digestive process of the gastrointestinal tract in vitro.Rice starch was used as control,gelatin +?-cyclodextrin microcapsules and acylated roselle anthocyanin were selected as sample groups with high encapsulation efficiency,good thermal stability and relatively smooth microcapsule surface structure.The hypoglycemic effect,total phenol content and antioxidant activity of the two microcapsules were investigated.Compared with the microcapsule sample,the acylated sample has a stronger hypoglycemic effect.According to the reducing sugar production rate curve,gelatin +?-cyclodextrin microcapsule delayed the production of reducing sugar,and the reducing sugar production rate gradually decreased in the second half of digestion,which was caused by the slow decomposition rate of digestive enzymes of gelatin and ?-cyclodextrin,which delayed the release of anthocyanins in Roselle.After digestion,the total phenolic content of the microcapsule group was the highest,and the antioxidant activity of the digested product was the best. |
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