Preparation Of Lemon Pectin And Its Application In Formulated Acidic Milk Beverage

Lemon pomace is a waste of lemon processing with a pectin content of 30% in its dry basis.Compared with pectin from other sources,pectin from lemon pomace has strong gelation,high esterification degree and high molecular weight.It is a good raw material for producing pectin.At present,there are some problems in pectin production,such as low pectin yield,high energy consumption,long extraction period and poor product quality.Based on the current situation of pectin production,from the view of economic point,combined with new technology,a comprehensive research had been conducted on lemon peel residue drying,pectin extraction,concentration,precipitation,drying process and lemon pectin as stabilizer on the quality of the acidic milk beverage(AMB),which aims to provide reference for the development of pectin industry.The main results are as follows:1.In order to select low drying energy consumption process and prepare high quality pectin lemon dried,dry lemon peel for extracting pectin was produced with fresh lemon pomace by using different drying methods including hot air drying,air gradient drying,vacuum drying,freeze drying,microwave drying,microwave-air drying and freeze-air drying.Results showed that different drying methods had a significant effect on indexes,such as sensory score,drying energy consumption and pectin yield(p<0.05),the one with highest comprehensive score was hot-air drying with a two-stage drying temperature conducted at 70 ? drying to peel with(40±2)% moisture content and 50 ? to 8%-10% moisture content,respectively.2.In order to explore yield and physicochemical properties of lemon pectin extracted by different methods,indexes such as lemon pectin yield,esterification degree and galacturonic acid content of lemon pectin among different extracting methods were measured,the extraction process of isolate pectin by five methods including acid,microwave,ultra-high pressure,enzymatic and ultrasonic was optimized by orthogonal test.Microwave-assisted extraction had the highest weighted comprehensive score among the five extraction methods,and acid extraction required 150 minutes can be shortened to 8 minutes,significantly increased lemon pectin extraction rate.The optimal process was as follows: solid/liquid ratio1:22,extracting pH 2.3 and 320 W extracted for 8 min.The extraction yield of pectin on dry basis was18.22%,the esterification degree and the galacturonic acid content of pection was 69.91% and 82.79%,respectively.3.The objective was to ascertain the optimum technological conditions of concentration,precipitation and drying of pectin solution.The optimal process was as follows: The pectin solution was concentrated to1/2 of the original volume at 60 ?,then precipitated with 90% ethanol for 45 min with the ratio of material-to-ethanol 1:2,and then washed 4 times with absolute ethanol,and dried at 60 ? under vacuum until constant weight.The galacturonic acid,esterification degree,unit energy consumption,activation energy,particle size,emulsifying activity and emulsion stability of the obtained lemon pectin were83.441%,73.283%,28.132 kJ/g,20.458 KJ/mol,1.568 ?m,93.329 m2/g and 138.964 min,respectively.Different drying methods had significant impact on physicochemical,rheological and emulsifying properties of lemon pectin(p<0.05).All pectins,galacturonic acid content exceeded the national standard of65%,and the esterification degree was higher than 50%,indicating that lemon pectin was a kind of high methoxyl pectin.Fourier Transform Infrared Spectrometry showed that pectin dried by different methodshad pectin characteristic functional groups,indicating that the drying methods adopted would not affect the pectin structure.The apparent viscosity of pectins dropped with the increase of shearing rate and temperature,which belonged to pseudo-plastic fluid behavior of typical non-newtonian fluid.Except for vacuum drying at 70 ?,vacuum drying at 80?and hot air drying at 70 ?,the pectin obtained by other drying methods increases of angular frequency has a point of less than 1 in tan?,showing gelatability and better storage stability.With the increase of pH(3-7),the absolute value of Zeta potential increased first and then remained constant,indicating that the change rule of pectin with pH was consistent at different pH values,Under the same pH condition,the stability of freeze-dried pectin is the best.The results of emulsion stability showed that all pectin samples have good emulsifying activity and stability.The one with highest comprehensive score was the pectin vacuum dried at 60?,which has good physicochemical,rheological and emulsifying properties,which provided a basis for further application of lemon pectin in food industry.4.Using the lemon pectin obtained by the optimum process as a stabilizer,the two common stabilizers,carboxymethyl cellulose(CMC)and propylene glycol alginate(PGA)were selected as controls,the stability effect of lemon pectin on AMB during its shelf life was studied.Results showed that stabilizing effect of the stabilizer on the AMB is macroscopically characterized by high sensory score,decreased precipitation rate,and stable R value.The microscopic properties show that the particle size of the product decreases,the water mobility decreases,and the absolute value of the zeta potential rises.Moreover,no significant changes were observed in each index with the increase of storage time.Overall,lemon pectin has the best stabilizing effect and is an ideal stabilizer in AMB.When pectin was used as stabilizer,all indexes of AMB with the optimal processed pectin were higher than those of commercial lemon pectin,indicating that pectin characteristics can be improved,taste and stability of AMB could be elevated by optimizing pectin production process.