Effects Of Polysaccharide-based Clarifying Agents And Membrane Separation Technology On Clarification And Quality Of Bayberry Juice

Bayberry(Myrica rubra Sieb.et Zucc.)is a subtropical fruit native to China,with a unique sweet-sour taste and attractive red appearance.It is rich in phenolic compounds such as anthocyanins and has various healthy functions.An effective way to use bayberry resources is to manufacture juice,thereby retaining the nutritious components of the original fruit and prolonging the shelf-life.In order to improve the quality of the juice and preventing precipitation during storage,investigating the clarification methods and technologies with high efficiency and mild conditions has become key problems in the production of bayberry juice.Effects of various polysaccharide-based clarifying agents(guar gum,locust bean gum,agar-agar,chitosan,xanthan gum and sodium alginate),different materials of microfiltration membranes(PES,Nylon,CA,PVDF,PTFE and PP)and membrane pore sizes(0.05,0.45 and 0.22 ?m and MWCO of 10,20,30,50,100 and 150 k Da)on the clarity,phenolic compounds and other physicochemical indexes of bayberry juice were investigated in this dissertation.The main research contents and results were as follows:1.The highest transmittance at 720 nm(%)and lowest turbidity(NTU)were obtained in the bayberry juice with 0.05 g/L xanthan gum,0.10 g/L chitosan,0.10 g/L sodium alginate,1.00 g/L agar-agar,1.00 g/L guar gum and 1.00 g/L locust bean gum,respectively.After clarified by six polysaccharide-based clarifying agents,the protein content(73.4-88.7%),total phenolic content(22.8-30.6%),and anthocyanins content(12.5-41.2%)of bayberry juice were significantly decreased.The polysaccharide-based clarifying agents could significantly improve the color of bayberry juice,and there was no significant difference in the p H of bayberry juice after clarification.The content of soluble solids decreased by 0.6-0.9 (?)Brix,and the acidity decreased by 0.1-0.17%.The formation rate and extent of the haze in juices depended on the clarifying agent added,sodium alginate and agar-agar were more effective than the other clarifying agents examined,in removing the haze-forming compounds from the bayberry juice.2.Among the six microfiltration membranes of different materials,Polypropylene(PP)membrane had the highest pure water flux and permeation flux of bayberry juice.All the microfiltration membranes can effectively improve the transmittance and reduce the protein content of bayberry juice.Microfiltration membranes of different materials had no significant effect on soluble solids,acidity and p H of bayberry juice(p>0.05),the effects on anthocyanins,total phenols and total flavonoids content and antioxidant activity were significantly different(p<0.05).The microstructure of these six membranes was different,and the surface of the membranes was obviously polluted after filtration.Nylon membrane was not suitable for clarifying bayberry juice because it had the largest adsorption on the active components and color of bayberry juice.3.The phenolic compounds in bayberry juice mainly included cyanidin-3-O-glucoside,three phenolic acids(gallic acid,protocatechuic acid and?-Hydroxybenzoic acid)and four flavonoid glycosides(kaempferol glycosides,myricetin-3-rhamnoside,quercetin-3-O-glucoside and quercetin-3-rhamnoside).When the MWCO was more than 100 k Da,there was no significant effect on phenolic compounds and other physicochemical indexes in bayberry juice,when MWCO was less than 50 k Da,the phenolic compounds,color,protein and soluble solids content in juice were mostly intercepted.While the membrane pore size had no significant effect on the acidity and p H of bayberry juice.4.Clarification with xanthan gum,microfiltration(0.22 ?m,PES)and ultrafiltration(100 k Da,PES)can effectively improve the transmittance of bayberry juice.The clarity,anthocyanins and color stability of bayberry juice during storage were less affected by clarification method,while temperature was the main factor affecting the stability of bayberry juice.The storage at 4 °C could effectively maintain the clarity and color stability,retard the formation of precipitation and the degradation rate of anthocyanins and extend the half-life of the degradation reaction of bayberry juice.Clarification method and storage temperature had no significant effect on the content of soluble solids,acidity and p H of bayberry juice.