Process Development On The Co-production Of The Essential Oils And Pectin Navel Orange Peel

With the increasing production of citrus,the citrus processing industry has become an important way to use the fresh citrus fruits.Canned oranges,juice drinks or preserves are the main processed products of citrus in China.In these production processes,a large amount of orange waste peel will be produced,which will cause the difficulty and high cost in waste treatment,resulting in a series of problems such as environmental pollution and waste of resources.Extracting functional active ingredients from citrus peel is one of the main resource utilization and treatment methods for wastes generated from the citrus processing industry.As two important active substances in the citrus peel,essential oils and pectins have excellent specially functional properties.However,the extraction of orange peel essential oil in the industry is usually carried out by the lime soaking pressing method.Due to the destruction of the pectin by the alkaline lime water,theremaining orange peel after the extraction of the essential oil cannot continue to be used for pectin extraction,resulting in the low utilization level of citrus pomace.In this study,navel orange was selected as the research object.The co-production process of the essential oil and pectin from orange peel was explored and the quality and structural characteristics of the products were compared and analyzed.The main results are as follows:(1)Study on the extraction process of orange peel essential oilBy analyzing the applicability of four common calcium salts,including the calcium chloride,calcium lactate,calcium sulfate and calcium nitrate,as the orange peel hardener,calcium chloride was selected as the optimum orange peel hardener.The extraction parameters of orange peel oil were optimized by single factor experiment and the optimum extraction conditions are as follows:the calcium chloride solution with 0.5%mass fraction was used as hardener and the orange peel was soaked for 4 h at the room temperature.The viscosity of the obtained press liquid from the co-production process was lower and the extraction rate of orange peel essential oil was higher when compared to the control.Furthermore,the extraction rate of essential oils generated from the co-production process was higher,and the aroma and color quality were better,when compared with the control.The relative density,refractive index,acid value,ester value and non-volatile matter were similar of both processes.(2)Analysis of volatile compounds in navel orange essential oilsThe volatile components in the navel orange essential oil extracted by the co-production process were determined by HS-SPME-GC-MS method.A total of 42 volatile compounds were detected,among which the terpenoids(23 species)were the main components.Among the volatile monoterpenes,D-limonene content is the highest,and α-pinene is another important characteristic component.(3)Study on the extraction process of pectinfrom the navel orange peelBy investigating the role of three inorganic acids,including the sulfuric acid,hydrochloric acid and nitric acid,in pectin extraction,it was found that the extraction rate of pectin obtained by sulfuric acid as acidifier was the highest.The optimum extraction parameters for co-production process were as follows:ratio of material to liquid:4,extraction time:60 min,extraction temperature:90 ℃,pH value of the extraction solution:2.2.Furthermore,the extraction rate of co-production pectin was significantly increased by 11.11%compared with the control.Gelatinity,contents of galacturonic acid,ash,acid insolubles,sulfur dioxide,moisture and other indicators are in line with national standards.(4)Study on the structural characteristics of pectin extracted by co-production processThe molecular weight of pectin obtained in the co-production process was significantly reduced,but its polydispersity coefficient was slightly increased,indicating that the co-production process produced more smaller molecules.Degree of esterification and acetylation of pectin obtained in the co-production process were increased,and the variation was mainly caused by the different types of acidifier.Types of monosaccharide composition of two pectin samples are the same and include rhamnose,galacturonic acid,galactose,arabinose and fucose.The content of Rhamnogalacturonan I(RG-I)in the co-production of pectin is significantly increased,but neutral sugar residues were degraded and the arabinose content was significantly decreased.On the other hand,the co-production process could preserve the Gal in the RG-I region,which could positively affect the bioactivity of pectin.The infrared spectrum results showed that the pectin extracted by the co-production process and the traditional process had similar basic chemical structure,which is consistent with the results of high performance liquid chromatography analysis.