Optimizing of production conditions of jelly using pectin extracted from potato peel and examining its texture, physicochemical and sensory properties comparison with commercial pectin’s

Introduction: Nowaday, the demand for low calorie food based and keeping primary features including texture and taste is increasing. Jelly is one of low calorie products produced from fruits and other components, and its consumption is increasing for human health. Jelly is semi-solid and transparent product that prepared with the use of sugar or juice and pectin or gelatin and flavor and color may also be added. Potato peels contain valuable substances such as pectin. Using potato peels to produce pectin with appropriate properties can solve the environmental issue resulting from these wastes in addition to make value added product. Pectin is a complex polysaccharide that is found in the wall of early plant texture and in the intercellular layer. Pectin contains a group of rich polysaccharides of galacturonic acid units with lower amounts of different sugars (Baiano, 2014). Two commercial forms of pectin are available: high-methoxyl and low-methoxyl pectin (high ester and low ester pectin). High-ester pectin forms a gel in a solutions containing high soluble solids and acidic systems, whereas low-ester pectins form more gel at wider pH and range of solids content but they do require divalent cations to form the gel (Kratchanova et al., 2012). In the food industry, pectin is used as a jelly-making agent, especially in the production of jellies and jams. Pectin is also used in fillers, medicine, pastries, bakery products and also as a stabilizer in juices and beverages, as well as in dietary fiber (Sharma, 2006). Pectin also has therapeutic benefits such as lowering blood cholesterol levels, removing heavy metal ions from the body, stabilizing blood pressure and facilitating intestinal activity (Ptichkina et al., 2008). Temperature, pH, and acid extraction time are the most important factors affecting the extraction yield and quality of produced pectin (Yapo et al., 2007). Currently, almost all commercial pectins are produced from citrus or apple peels, both of which are juices by-products (Thirugnanasambandham et al., 2014). Therefore, the main objective of this study was to optimize the conditions of extraction of pectin from potato peel by response surface methodology and to compare the physicochemical properties of Jelly produced from potato peel under optimum conditions with Jelly produced from apple and citrus   Material and methods: Potato of Granola variety was purchased from the local market in Ardebil. The chemicals used for the tests include: citric acid, sodium hydroxide, phenolphthalein, and Calcium chloride were purchased from Merck Company (Germany). The method of Hoseeni et al (2017) was used for jelly production with slight modification as follows. In the First step,0.5 and 1% pectin extracted from potato peelings, 30 % Sugar, 0.014 % Cherry edible color and 0.75 % Cherry essential oil were mixed then 100 CC Boiling water was added to the mixture and mixed again. After the sugar was completely dissolved, 15, 30, and 45 mg of calcium chloride was added per gram of pectin. The pH of the samples was regulated by citric acid solution on 2.5 and 4. The heating of the samples was continued until the brix of the treated treatments was set to 42. The prepared samples were kept at room temperature for half an hour. The treatments were then refrigerated for 2 to 3 hours to complete the jelly closing process. For this purpose some jelly characteristics such as texture properties, physico-chemical (pH, acidity, brix, moisture and Drainage) and sensory properties of samples were investigated using five point hedonic scale. A one-way analysis of variance and Duncan test (P≤ 0.05) in three replications were used to establish the significance of differences in the experimental data. The results were analyzed using the Minitab version 16.   Results & Discussion: Results showed that by increasing calcium chloride, pH and Pectin concentration had a significant effect on increasing the hardness of the gel and the strength needed to make the gel brittle (P≤0.05).The highest hardness of the gel in pectin emulsion extracted from potato peel was 30.0959 N and highest force required to break the gel was 27.3431 N in the most severe extraction conditions at Calcium chloride 35.2286 mg/g, Pectin concentration 1% and pH 4. Results of physico-chemical properties showed that there was no significant difference between pH, acidity, brix and moisture of jelly made from apple pectin and citrus and apple commercial pectin. The results of the syneresis showed that the syneresis by the jelly of potato pectin is not similar with jelly from apple pectin and citrus and apple commercial pectin significantly different. Also Results of sensory properties showed that it was no significant difference between jelly from apple pectin and citrus and apple commercial pectin. The results of this study showed that by optimizing the production conditions, potato pectin can be used in jelly formulation and jelly can be produced with desirable and comparable quality compared to the commercial pectins