Physicochemical Properties Of Polysaccharides From Orange Peel And Their Application In Acidic Milk Drink

Orange peel,a byproduct in the processing of food industries,is dumped randomly into the environment and cause serious pollution.Extracting the polysaccharides from orange peel can provide a reasonable way to take advantage of orange peel resource and protect the environment for it is rich in polysaccharides.In this study,six polysaccharides?HBOP,CHOP,DAOP,CAOP,AEOP and CHOP?were separately extracted from orange peel using hot buffer,chelating agent,dilute alkaline,concentrated alkaline,acid and enzyme extraction,respectively.The physicochemical properties of the six polysaccharides were compared,and their applications in acidic milk beverages were studied.The main results were as follows:?1?Optimal extraction conditions of AEOP:Based on single-factor experiments,response surface methodology was employed to obtain the optimum conditions for the extraction of AEOP polysaccharide.The effect of pH,extraction time and liquid-solid ratio on the yield of AEOP were investigated.The optimum extraction conditions were pH 3.3,extraction time 56.35 min and liquid-solid ratio of 15 mL/g,and the yield of AEOP was 14.23%.Optimal extraction conditions of EEOP:Based on the same as above optimal method,the effects of liquid-solid ratio,enzymatic hydrolysis temperature and enzyme dosage on the yield of EEOP were studied.The optimal extraction conditions were liquid-solid ratio of 39.41 mL/g,enzymatic hydrolysis temperature of 41.79? and enzyme dosage of 0.74 mg/mL.The maximum yield of EEOP was 17.20%.Under the same conditions of EEOP,the yield of HBOP was 2.54±0.09%,the extraction rate of CHOP was 10.6±1.62%,the extraction rate of DAOP was 12.09±1.06%,and the extraction rate of CAOP was 2.7±0.10%,respectively.?2?Physicochemical properties of orange peel polysaccharides:The high total carbohydrate was between 89.74-98.08%,galacturonic acid content was ranging from 8.95-33.16%and little proteins?<2%?in six polysaccharides.The esterification degree in EEOP and AEOP was higher than the others.The six orange peel polysaccharides were mainly composed of rhamnose,arabinose,galactose and glucose by the monosaccharide composition analysis.The microstructure of CAOP and AEOP was observed to be irregular by scanning electron microscopy.Thermal analysis showed that CHOP has the highest stability.?3?Rheological properties of orange peel polysaccharides:The six orange peel polysaccharide solutions were all pseudoplastic fluids.The apparent viscosity of DAOP was higher than CAOP.It is speculated that DAOP has less branched structure than CAOP.DAOP has good pseudoplasticity and can be used as a promising thickener.The six orange peel polysaccharides showed different viscosities after the addition of Ca²⁺.The viscosity of the CHOP,AEOP and EEOP solutions increased first and then decreased with increasing Ca²⁺ concentration.?4?Emulsifying properties of orange peel polysaccharide:The effect of concentration,pH,Ca²⁺ concentration and temperature on orange peel polysaccharide emulsion was investigated.As the concentration increased,the emulsifying activity and emulsion stability of the six orange peel polysaccharides increased,while the flocculation index decreased.The emulsion stability of the six orange peel polysaccharides reached a maximum at pH5.The flocculating index of the emulsions was higher under acidic or alkaline conditions.Zeta potential increased with the increase of pH value.The emulsifying activity of CHOP reached maximum under strong acid.The emulsification activity and emulsion stability of AEOP remained stable and the largest in weak acid.However,the emulsion stability and zeta potential of the six kinds of orange peel polysaccharide emulsions decreased with the increase of Ca²⁺ concentration,while the flocculation index increased gradually.The Ca²⁺ had little influence on the emulsifying activity and emulsion stability of HBOP.Temperature had more effect on the emulsifying property of polysaccharides emulsions and showed random,except DAOP.?5?Application of orange peel polysaccharides in acid milk drink:AEOP and EEOP had good effect in stabilizing the acidic milk beverages by comparing the centrifugal precipitation rate,turbidity of supernatant,particle size and zeta potential of the emulsions.The cream layer appeared in AEOP and EEOP milk systems under the neutral condition,whereas the CHOP and DAOP milk systems remained stable,indicating that CHOP and DAOP were beneficial to inhibit the fat ball from floating.The rough surface microstructure was observed in the orange peel polysaccharide milk systems by a Confocal Laser Scanning Microscope.The particle size became smaller as pH increased.The phase diagram showed that too low or too high polysaccharide concentration will cause the stratified milk system.