Study On The Effects Of Phenolic Compounds From Yugan Euryale Ferox Salisb On Its Starch Digestion

Euryale ferox is not only an valuable food resource,but also a precious traditional Chinese medicinal material,which grows in China,Russia,North Korea,Japan and India and now is widely used in foods or medicines,which can nourish blood and tranquilize,supplement the kidney to control the nocturnal,invigorate the spleen and also dehumidify Previous studies in our laboratory have shown that the digestion rate of Yugan Euryale ferox starch was slower,but the mechanism was still unclear.In this paper,the differences in Euryale ferox between Yugan and other areas’were compared from the aspects of appearance,nutrients,active substances and mineral elements.The physicochemical properties and digestibility of the dried starch were systematically tested and analyzed,and the polyphenols were extracted and identified from the seeds.On the basis of this,the effects of its polyphenols on the digestion of starch in vitro were studied.The mechanism of slow digestion of dried starch was explored from inhibition of starch digestion-related enzyme activity and interaction within starch.The main results and conclusions are as follows:（1）Main features and quality evaluation of Yugan Euryale ferox:The appearance were significantly different in Euryale ferox from Yugan and other places.Yugan Euryale ferox was small and black but with a higher rate of kernel and the fruit shape was biased to a long circle.The shell of it was thin,firm and brittle,and it was easy to shell.In terms of main components,the content of dried starch was higher（72.97⁷6.53%）,and also the fat content（0.66%）was significantly higher than those from other places.The results of HPLC measurement showed that the alcohol-soluble components of Yugan Euryale ferox were basically consistent with those from other places,but there were some differences in the content of each component.（2）Structure,physicochemical properties and digestive properties of Yugan Euryale ferox:The Yugan Euryale ferox starch was extracted and purified by water milling method.The results showed that the starch contained 45.85%amylose;the starch granules were mostly irregular polyhedrons with smooth surface and particles were intact with no cracks,the average particle size is 3μm;The crystal structure was type A,and crystallinity was38.84%.At 95°C,the solubility of 2%Yugan Euryale ferox starch was 9.76%and the degree of swelling was 22.54%,which was a restricted type of expanded starch;The fast viscosity measurement curve showed that the gelatinization temperature of this starch was higher（82.30°C）and the starch digestion experiment in vitro showed that the seed coat had a strong inhibitory effect on the digestion of Yugan Euryale ferox starch.（3）Extraction and identification of polyphenols from the seed coat:The main process parameters of ultrasonic-assisted extraction of medicinal polyphenols were optimized.The optimized parameters were as follows:extract was 60%acetone,ratio of material to liquid was 1:60（W:V）,extraction temperature was 55℃,and the extraction time was 50 min,Under the optimized conditions,the extraction yield of polyphenols from the seed coat was1.485%.The polyphenol extract was determined by HPLC-Q-TOF.The polyphenols in the extract mainly contained gallic acid,galactosyl hexose,and epicatechin gallate,and the content was 190.87μg/g,114.61μg/g,301.62μg/g,respectively.（4）Effect of polyphenols from the seed coat on starch digestion-related enzyme activities:In vitro digestion test showed that the polyphenol extract and its high content fraction（gallic acid,epicatechin gallate）could both significantly inhibit the activity of a-amylase,a-glucosidase and glucoamylase.The IC₅₀0 values of the crude polyphenol extractions for a-amylase,a-glucosidase and glucoamylase were 1.36 mg/mL,3.25μg/mL and 2.90 mg/mL,respectively,and the gallic acid and epicatechin gallate were important component of inhibition.（5）The effect of polyphenols on the morphology and structural characteristics of starch granules:The results of iodine binding,electron microscopy,X-ray diffraction and also the Fourier transform infrared spectroscopy indicated that polyphenols could inhibit the formation of ramie starch-iodine complex,which could reduce the pores on the surface of starch retrograding crystals,with smooth surface and tight structure.The interaction between polyphenols and starch was mainly hydrogen bonding.The above research results shown that Yugan Euryale ferox had distinct characteristics and good quality.Its seed coat contained polyphenols such as gallic acid,bis-gallohexanoside and epicatechin gallate,which had a strong inhibitory effect on starch-digesting enzymes.The polyphenol extract of the seed coat has higher inhibitory activity on the active a-glucosidase than acarbose;in addition,the polyphenol and the starch could interact with each other through hydrogen bonds,which in turn changed the morphology and structural characteristics of the starch.It could be seen that the slow digestion characteristics of Euryale ferox starch were caused by the inhibition of the activity of starch digestive enzymes by the polyphenols and also the changes in the morphology and structure of the starch molecules.