| Pectin is a linear macromolecule polysaccharide existing in plant cell wall.It has many applications in food,medicine and chemical industry.China has a large demand for pectin every year,but the yield of self-produced pectin is low and the quality is poor.It can only rely on imports from the United States,Denmark and other countries which increases production costs.Therefore,it is an urgent problem to improve the yield of pectin while maintaining the excellent quality of pectin.In this study,Pingshan pomelo peel was selected as the raw material,and the extraction technology of three different pectin extraction methods was optimized.The physicochemical properties and structural characteristics of pectin obtained by the three extraction methods were analyzed,and the possibility of using composite pectin film as food cling film investigated.The optimum conditions for acid extraction of pectin by intermittent microwave-assisted EDTA were as follows:microwave time 125 s(working time was 5 s and intermittent time was 5 s too),microwave power 550 W,EDTA content0.25%,pH 1.0,solid-liquid ratio 1:25 g/mL,and the yield of pectin was 38.48%.The optimum conditions for acid extraction of pectin by intermittent ultrasound-assisted EDTA were as follows:ultrasonic time 79 min(working time was 1 s and intermittent time was 1 s too),ultrasonic power 850 W,EDTA content0.25%,pH 1.0,solid-liquid ratio 1:25 g/mL,and the yield of pectin was 31.65%.The optimum conditions of EDTA-assisted acid extraction of pectin were as follows:extraction time 90 min,extraction temperature 90?,EDTA 0.25%,pH1.0,solid-liquid ratio 1:30 g/mL,and the yield of pectin was 33.11%.When using the same pomelo peel as raw material,the yield of pectin obtained by intermittent ultrasound-assisted EDTA method and EDTA-assisted acid method was less different.The yield of pectin obtained by intermittent microwave-assisted EDTA method is obviously higher than that of both methods,and it has the advantages of fast,high efficiency and energy-saving.The optimum technological conditions for the ethanol precipitation of pectin were as follows:the volume ratio of ethanol(80%ethanol)to pectin extraction liquid(15.32 mg/mL)is 3:2 and time of precipitation was 80 minutes.Under this condition,the precipitation rate of pectin can reach 99.64%Through FT-IR,XRD and SEM analysis,it was found that the solubility of pomelo peel pectin was affected by the microcosmic morphology and crystal structure.The solubility of three pectin was IUE>ED>IME.HPLC analysis showed that high Hg content indicated that there were more"smooth"areas in the three pectin structures,and IUE pectin was about 86.49%at most.At the same time,because of arabinopolysaccharide and other polysaccharides,pectin has a wide and long branch,so IME pectin can be used as a good emulsifier and stabilizer.DPPH antioxidant experiment showed that the DPPH clearance rate of IUE pectin with high galacturonic acid content and low esterification degree was significantly higher than that of IME pectin and ED pectin.By tape casting,the composite film was prepared with pectin and chitosan.The effects of pectin with different esterification degree and chitosan with different molecular weight on the quality of composite membranes were investigated by the determination of performance indexes.The results indicated that pectin and chitosan had a good compatibility,and the mechanical properties of pectin film were improved by adding chitosan in the film,and the water vapor permeability of the film was reduced.The composite film also maintained good swelling and in vitro degradation,which was suitable for food preservation film.According to the actual conditions,the optimum technological conditions were as follows:the mass ratio of low ester pectin to 200 kDa chitosan was 1:1,the glycerol content was0.3%,the calcium chloride concentration was 3%.The optimum properties of composite membranes are as follows:tensile strength 33.89±0.12 MPa,elongation at break 30.09±0.21%,water vapor permeability 382.66±0.18 g/(m~2·24h),composite membranes comprehensive score 95.42±0.28,which is close to the predicted value 95.54.The pectin/chitosan composite film was used to coat and seal strawberries.Compared with the control group,the physical and chemical indexes of strawberries were significantly improved,and the shelf extension period of strawberries could be effectively extended to 8 days.Low-ester pectin/200 kDa chitosan composite film can effectively reduce the rotting rate and weightlossness rate of strawberry,and hinder the decrease of VC and organic acid content of strawberry.Therefore,low-ester pectin/200 kDa chitosan composite film is suitable for strawberry fresh-keeping. |
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