Basic Structural And Rheological Characteristics Of Polysaccharide From Okra(Abelmoschus Esculentus(L.)Moench) And The Effect Of High Pressure Homogenization On Its Structure

Okra?Abelmoschus esculentus?L.?Moench?is also named as Vietnamese sesame,croissant kidney fruit,etc.It is an annual herbaceous plant of Malvaceae family.As a new type of health-promoting vegetable,okra possesses anti-oxidation,anti-tumor,anti-fatigue,anti-inflammatory and analgesic activities.Okra polysaccharide is a kind of acidic polysaccharide,which is composed of rhamnose,galactose,glucose,galacturonic acid and glucuronic acid.Recent researches mainly focus on the mixed extraction of okra polysaccharide from the fruit.However,effects of different parts of the fruit,including peel,pulp and seeds,on the polysaccharide structure and functional properties have not been reported.In this paper,polysaccharides were extracted from different parts?peel,pulp and seeds?of okra by hot water,boiling water or acid solution.The basic structural characteristics and antioxidant activity of the obtained okra polysaccharides were investigated and compared,respectively.Meanwhile,rheological properties of the main polysaccharide OPWE-60 from the okra peel were studied.Furthermore,effects of high pressure homogenization on the structural and solution characteristics of OPWE-60 were investigated.The main contents and conclusions are as follows:1.The basic structures and antioxidant activities of polysaccharides from different parts of okra were analyzed.Okra was divided into three parts as peel,core and seed,which were applied for polysaccharides extraction.As the low yields of polysaccharides from okra core and seed,the structure and antioxidant activity of polysaccharides from okra peels were mainly studied in our study.Results showed that main polysaccharides in the okra peel were OPWE-60?hot water extraction,60^oC?and OPWE-100?boiling water extraction?,which were obtained by water extraction followed by ethanol precipitation.At the same time,the polysaccharide extracted by acid method?OPAE-60?had the lowest yield.These above three polysaccharides were pectic,of which OPWE-60 mainly consisted of type I rhamnogalacturonan?RG-I?.Both homogalacturonan?HG?and RG-I pectin were existed in OPWE-100 and OPAE-60.In addition,there were some differences in apparent viscosity and antioxidant capacity among the three okra polysaccharides.OPWE-60 possessed the strongest antioxidant activity and highest viscosity.2.Effects of different concentrations,standing time,temperature and ionic strength on steady flow behavior and dynamic viscoelastic behavior of OPWE-60were systematically investigated.Meanwhile,its effects on apparent viscosity and gelling properties of three different kinds of food hydrocolloids were preliminary studied.Results showed that OPWE-60 was a pseudoplastic fluid with weak gel properties.After standing at room temperature for 12 h,the apparent viscosity of OPWE-60 was reached at a constant value.Its apparent viscosity was not sensitive to the temperature,showing slight reduction as temperature increasing.Furthermore,the apparent viscosity and the gelling property were decreased after the addition of NaCl or CaCl₂.OPWE-60 could significantly increase the apparent viscosity of konjac gum,xanthan gum and guar gum,and improve their geling properties,especially for konjac gum.3.The effects of high pressure homogenization?HPH?were investigated on structural characteristics and solution properties of OPWE-60.Results showed that HPH caused notable decreases in molecular weight and apparent viscosity.However,it had no obvious effect on monosaccharide composition,functional group,surface morphology,solution properties and other indexes.The promotion of HPH on the scavenging effect against hydroxyl radical of okra polysaccharides might be related to the reduced molecular weight.