Studies On Debittering Of Citrus Juice With Biological Enzyme

Citrus is the word's largest fruit.Its planting area in China has been the first place on the earth,with an annual output occuping second in the world.Along with the increasingly floushing development of citrus juice processing industry,the problem of bitter taste has become critical difficulties.Especially in China,where the problem has become even worse,because of the loose selection of raw materials.At present, research aiming at bitterness of orange juice has focused on debittering by bio-enzymatic method.Compared with adsorption debittering and shielding debittering,which have been commonly used in the current production,bio-enzymatic will become the main direction of citrus juice debittering in the future,due to its characteristics of high specificity, preferable reservation of juice flavor and nutrients,good effect,low cost and so on.However,studies on the problem by bio-enzymatic are still at the starting stage in China.This paper made a study on debittering method of bitter substances,content of bitter materials in citrus juice of different varieties,parameters of debitterize enzyme and comparison between enzymatic debittering and macroporous resin adsoption debittering.The main findings are as follows:1.Comparing the current commonly used determination methods of naringin and limonin,the results showed that,in the naringin and limonin analysis,HPLC method was easy and fast.By optimizing chromatographic conditions,testing conditions of naringin were confirmed:mobile phase methanol-water(volume ratio 40/60),flowing rate 0.9 mL/min,column temperature 35℃and detection wavelen- -gth 284 nm.Meanwhile,measurement conditions of limonin were difined: mobile phase acetonitrile-water(volume ratio 42/58),flowing rate 1.0 mL/min,column temperature 35℃and detection wavelength 215 nm. By optimizing sample pretreat- -ment conditions,it was dicided that in the determination of naringin,samples were precipitated by methanol of same volume and treated with ultrasonic waves;in the measurement of limonin,samples were precipitated by acetonitrile of equal volume and treated with ultrasonic waves.2.In this paper,we systematically analyzed 28 citrus samples, including sweet orange,citrus reticalata,hybrid citrus,pomelo,citrus aurantium and other citrus types.It was found that the content of naringin,hesperidin and limonin in different tissues if citrus fruit was higher in peels and seeds,and lower in mesocarps.In the same organ or tissue,their content varied due to different species and varieties. Varieties with high level of hesperidin were generally low in naringin amount.On the contrary,varieties with high content of naringin were low in hesperidin amount.The relationship between naringin concentration and hesperidin amount was mutually exclusive.Moreover, the content of limonin in orange juice of tested varieties was all increased under heating treatment.3.Using quadratic general rotary unitized design,we studied debittering process technology of citrus aurantium juice by means of naringinase,established the mathematical model of influnencing factors and debittering rate:y=-387.2464583+153.6125x₁+2.5064167x₂+ 65.6775x₃+6.4036667X₄+0.7825x₁ ^*x₂+ 19.025x₁ ^*x₃+0.1935x₂^*x₃+175x₃ ^*x₄-228.2291667x₁ ²-0.0203917x₂²-11.8791667x₃²-0.0704917x₄²,also,pro graining solved and test verified this model.It was indicated that the most influnential fator on the debittering rate was enzyme amount(x₁), next was pH value of the juice(x₃),then juice temperature(x₄),last was enzymatic time(x₂).As well,we determined the optimal process conditions:enzyme 0.69 g/L,time of enzymatic hydrolysis 95 min, enzyme solution pH 4.5 and nzymatic hydrolysis temperature 51℃. Verifying by experiments,the debittering rate of citrus aurantium juice under this condition was(95.073±0.627)%(n=3),consistent with the theoretical value of 95.70%.As a result,this regression model could preferably predict the enzymatic dibittering rate.4.Citrus aurantium juice debittering with macroporous adsorption resin was studied in this article.The results showed that:as macroporous resin LX-900 had larger pore size and specific surface area,it performed well in adsorbing and seperating naringin and limonin,so that it could be used in debittering of citrus aurantium juice.The adsorption equilibrium time of naringin and limonin in macroporous resin LX-900 was 4 h,which could be described well by the Freundlich equation.Static saturated adsorption capacity of macroporous resin LX-900 for naringin was about 92.2 mg/g,for limonin about 7.8 mg/g.It was aslo found that juice acidity had little effect on the adsorption of bitter substances,and the best adsorption temperature was 25℃- at room temperature. Through dynamic adsorp- -tion experiments,flowing rate was difined as 1.0 mL/min,and the elution rate was higher as choosing 80%ethanol aqueous at eluting time.5.The methods of enzymatic and macroporous resin debittering were compared.The results indicated that,the content of bitter substances in citrus aurantium juice was resuced to threshold hereabout using both methods.By means of macroporous adsorption resin,the content of naringin and limonin was far below the threshold,while the removal ratio of naringin was higher through enzymatic,but its effect of removing limonin was not very well.Compared with enzymatic method, resin adsorption method had a greater influnence on the citrus aurantium juice nutrients:total sugar loss rate was 6.7%,total acid loss rate was 17.9%,total carotenoid loss rate was 25.6%,vitamin C loss rate was 25%and soluble solids loss rate was 10.1%,among which,the loss rate of the major nutrient composition-total carotenoids and vitamin C was highest,while the enzymatic debittering hardly affected the nutritional quality of orange juice.Analyzing 1 ton of citrus aurantium juice,costs of enzymatic treatment were far lower than costs of the resin adsorption method.