Enzymatic Preparation Process And Characterization Of Low-methoxy Pectin

Pectin is a natural non-toxic food additive. As an important component of plant cell wall, it is widely existed in nature. The commercial pectin is mostly divided into two kinds:high-methoxy pectin (HMP) and low methoxyl pectin (LMP). The pectin in most plants is the high methoxyl pectin, so the low-methoxy pectin has to be prepared by reducing the degree of esterification. Now the more widely applied method in industry is low-temperature alkaline process, but the method would result inβ-elimination reaction with pectin molecules in the productive process, decreasing the molecular weight and gel properties of pectin. The enzymatic preparation of low methoxyl pectin was focuses on in this paper. Extraction of pectin from sour orange peel, the process of low methoxyl pectin by enzymatic method and the comparison of the alkaline and enzymatic process were studied. The use of exogenous pectin esterase for low methoxyl pectin, improving the defects like susceptible to occurβ-elimination reaction and the pectin quality reduced in traditional alkaline process were explored. All these provided a theoretical reference to the high-quality low methoxyl pectin. The main conclusions of this paper are as follows:1. The pretreatment and pectin content of the sour orange peel were studied. The acid extraction widely applied in industrial production was used for the preparation of pectin from lime peel. The results showed that: the pectin content in sour orange peel is 16.22%; under the condition of pH1.5, temperature 90℃, liquid-solid ratio of 20:1, reaction time 90min, the pectin extraction rate reached 84.90%, with the loss on drying of pectin 4.91%, meeting the merchandise pectin requirements.2. Adding exogenous pectin esterase to the acid pectin extraction was prepared for low methoxyl pectin. The optimum parameters for the enzymatic preparation of low-methoxy pectin were determined by the Box-Behnken design of Design Expert 7.0 software and response surface analysis based on the single-factor testbased on the single-factor tests. Under the conditions of 1000-fold diluted pectin esterase 5.39mL, reaction time 50min,42.71℃, pH4.61, the esterification degree of pectin was reduced from 67.83% to 42.55%. Model was significant (P<0.0001); lack of fit P=0.0688>0.05, was not significant; the determination coefficient R2=0.9818, showed that the model could fit the data at 98% level. The model could be used to analyze low methoxyl pectin by the addition of exogenous pectin esterase.3. The qualities of pectin prepared by the enzymatic process and the currently applied low-temperature alkaline process in industrial production were compared, including extraction rate of pectin, galacturonic acid content, degree of esterification, viscosity-average molecular weight. The results showed that:as low methoxyl pectin by alkaliβ-elimination reaction took place, so that some galacturonic acids in pectin macromolecules were dissociated, pectin extraction yield, galacturonic acid content and viscosity-average molecular weight were lower; the low methoxyl pectin by enzymatic preparation with the higher esterification degree. In consequence, theβ-elimination reaction in alkaline process could be improved and higher molecular weight pectin was obtained in enzymatic preparation for low methoxyl pectin; however, higher esterification degree was got by enzymatic preparation, which may affect the speed of the pectin gel, pending further study.