Study On Citrus Fruit Peels Hemicellulosic Hydrolysate For Production Of Xylitol By Fermentation

Xylitol is a polyol,with a sweetening power similar to sucrose and a calorie similar to glucose. It is used as a nutrition and a cure for diabetes patients because it can regulate abnormity of metabolism.It is also used for salvaging acetone-body patients because of its resisting acetone-body effect.It can slower the productivity of fatty acid in plasma,but cannot result in the rise of bloodsugar.It is also used as a medicine for protecting liver.It has good heat-stability and never reacts with amino acids under heating,so it is confected all kinds of preparations for nutrition medicines together with amino acids.As a food,it can defend decayed tooth.Besides,it is applied abroadly in national defence,plastic and light industry.At present,xylitol is produced by chemical method in industry.But chemical method has high cost of production and serious pollution inenvironment.The production of xylitol by fermentation of hemicellulosic hydrolysates becomes a hotspot.The discourse studies the preparation of citurs fruit peels hemicellulosic hydrolysate for production of xylitol by fermentation.Firstly,hydrolyze citurs fruit peels hemicellulose with sulfuric acid.Then,detoxicate citurs fruit peels hemicellulosic hydrosate with S-8 macroporous adsorption resin and calcium hydroxide.Finally,studied the production of xylitol fermentation technology,identified the optimum operating parameters.Study results are as follows:1.Determined pentosan content of orange peels of different area.Among those areas,polemo peels produced in Chongqing Liangping has the highest pentosan content in those polemo peels.Orange peels Orange peels produced in Sichuan Rongxian has the highest pentosan conten in those orange peel.2.Firstly,on the basis of single factor experiment of four factors which are sulphuric acid concentration,hydrolysis temperature,reaction time and liquid-solid ratio,the optimal hydrolysis condition established by perpendicular design is sulphuric acid concentration 3%,liquid to solid ratio(mg/L)7.5:1,reaction time 2h,hydrolysis temperature 115℃.Under the condition,xylose yield of polemo peels produced in Chongqing Liangping hemicellulosic hydrolysis is 69.67%, xylose yield of orange peels produced in Sichuan Rongxian hemicellulosic hydrolysis is 65.83%.3.Through the single factor experiment,respectively inspected the effect of temperature,pH, reaction time and liquid-solid ratio on detoxication.The influence of temperature,pH,reaction time and liquid to solid ratio on detoxification of hydrolysate by S-8 macroporous adsorption resin isconsidered.The detoxification condition by S-8 macroporous adsorption resin is:adjust the pH of cellulosic hydrolysis to 10～11 by Ca(OH)2 powder,centrifuges it within 10min at the rate of 4000r/min,adjust the pH of supematant fluid to 6.0 with phosphoric acid,centrifuges it within 10min at the rate of 4000r/min.Then added the S-8 macroporous adsorption resin at the liquid-solid ratio of 5:1,35℃dealt with under 10h.Under these conditions,the polyphenol compounds, single-phenol compounds and the removal of furfural were 89.3%,92.7%and 58.1%,xylose loss rate of 15.2%.The results showed that this process can effectively remove the economic inhibitor.4.Conducted a preliminary study on fermentation of detoxified hydrolysates.The detoxified hydrolysates are fermented which are obtained with calcium hydroxide followed by S-8 macroporous adsorption resin.Examined the effect of inoculum age,inoculum concentration, culture medium volume,initial pH,fermentation temperature,sorts and addition of nitrogen source, sorts and addition of carbon source,sorts and concentration of salts on xylitol production.Concluded the best fermentation process as follow:inoculum age 10h,inoculum concentration 10mL,culture medium volume 125mL,initial pH 7.0,fermentation temperature 28℃, sorts and addition of nitrogen source:mixture of yeast extract(20g/L)and tryptone(40g/L),carbon source glucose(4g/L),NaCl addition 6g/L.Under these conditions,the higest concentration of xylitol is 28.6g/L,the percentage xylose conversion is 72.4%.