Structure Characterization Of Cowpea Polysaccharide And Its Blend With Potato Starch

Cowpea(Vigna unguiculata)is a leguminous plant,which is rich in protein and nutrients.Cowpea can not only be eaten as a vegetable,but also as a staple food(bean flour)in Northwest China.Cowpea,as a staple food of coarse cereals,has been rarely studied.At present,it has only been reported in antioxidant and hypoglycemic aspects of its active components.Cowpea is rich in polysaccharides,so a comprehensive study on its composition,structure and function will help to improve its application in staple food.Four cowpea polysaccharides(CPP-60,CPP-70,CPP-80 and CPP-90)were precipitated by 60-90 % ethanol.The differences of Four CPPs in composition and structure were studied,and the effects of CPP and potato starch on the physicochemical properties of starch were studied.The main results are as follows:1.The ultrasonic assisted extraction of CPP was optimized.Firstly,the ultrasonic time is5 min and the ultrasonic power(750W)is 50% of the rated power.Under ultrasonic conditions,response surface method was used to optimize the extraction temperature,extraction time and solid-liquid ratio on the yield of polysaccharides.The optimal extraction conditions were as follows: extraction time 2 h,extraction temperature 93 ?,solid-liquid ratio 1:42.Under these conditions,the yield of polysaccharide was 7.65 %,which was significantly higher than that of conventional hot water extraction.2.The structures of the four polysaccharides obtained by 60-90 % alcohol precipitation were compared.The results of monosaccharide composition showed that CPP had the same type of monosaccharide,but the content of monosaccharide was different.The results of infrared spectrum showed that all the polysaccharides had the characteristic absorption peak.The crystal state of the four polysaccharides was significantly different.The particle size and potential results showed that CPP was a anion polysaccharide,and the particle size range of polysaccharide was 120.5-679.3 nm.The scanning electron microscope(SEM)results showed that CPP had the characteristics of polysaccharide the states are different.3.The effects of CPP on starch properties were studied by RVA,XRD,DSC and SEM.All the four CPPs decreased the solubility and swelling of starch and promoted the short-termsedimentation of starch;RVA results showed that CPP increased the viscosity of the blend and delayed the gelatinization of starch.DSC analysis showed that the enthalpy of the blends decreased significantly and the gelatinization temperature increased.XRD results showed that the addition of polysaccharides did not change the crystalline region of the raw starch.Scanning electron microscopy showed that the gel surface of the blends became rough after gelatinization.To sum up,the monosaccharide composition of the Four polysaccharides obtained by fractional alcohol precipitation has no difference,but their structure and morphology are significantly different.The Four polysaccharides samples can delay the gelatinization of starch and promote the short-term sedimentation of starch,so they have the application potential of starch based food film.