Isolation of pectin from vegetable waste and study of its physical and chemical properties

. Currently, the deterioration of the environmental situation is due to the fact that tens of thousands of substances are introduced into the environment every year, which are characterized by toxic properties for humans and affect the change in the nutritional status of the population. A significant part of substances with carcinogenic and mutagenic effects enter the human body with water and food. As known, pectin has the ability to bind these substances and remove them from the body. This principle is based on the use of pectin as an additive in various products for therapeutic and prophylactic purposes, as well as for the manufacture of medicines. This article presents the results of the extraction of food pectin from carrot and pumpkin cake, its hydrolysis, as well as the study of the physicochemical properties of pectin. The paper presents the results of IR spectroscopy and pectin substances of carrot cake, determination of their molecular weight.


Introduction
Currently, among the urgent problems are the rational use of primary raw materials, complex processing and safe disposal of secondary raw materials. To solve it, it is necessary to build up the production base of the processing industry, as well as improve the use of raw materials through the development and creation of new progressive, energysaving technologies for the complex processing of valuable secondary raw materials based on the latest achievements of science and technology [1,2].
The problem of increasing the production of high-quality pectin substances and expanding their range is part of the solution to this problem. The development of industry, especially chemical, petrochemical, pharmaceutical, nuclear, as well as all branches of engineering, has led to a sharp deterioration in the environmental situation. Every year, environmental pollution is growing with various industrial emissions, vehicle exhaust gases containing salts of heavy metals, radionuclides and other substances toxic to the animal and plant world [3,4].
Pectin has the ability to bind these substances and remove them from the body. This principle is based on the use of pectin as an additive in various products for therapeutic and prophylactic purposes, as well as for the manufacture of medicines [5].
In the food industry, pectin is used as a gelling agent in the manufacture of various marmalade products, jams and jams. In addition, the diversity of pectin makes it possible to use it as a stabilizer for wines, juices and drinks, emulsifiers in the manufacture of food emulsions and whipped oils, a thickener for fruit and vegetable pastes and sauces, and in many other cases [6,7].
Pectin substances are high-molecular compounds of carbohydrate nature. The main component of pectin substances is polygalacturonic acid, part of the carboxyl groups of which are esterified with methoxyl groups [8]. The degree of esterification or methoxylation is an important indicator of pectin and is expressed as the ratio of the number of methoxylated groups to their total number in pectin substances [9,10].
In the cell walls of plants, pectin is found in the form of protopectin chemically bound to cellulose fibrils and hemicelluloses [11]. The role of pectins lies in the fact that together with hemicelluloses they form a matrix of the cell membrane that holds the cellulose fibrils together into a rigid structure [12].
Very valuable in practical terms, the property of pectin is their ability to form jellies in the presence of sugar, acid, metal ions [13]. During gelling, the filamentous pectin molecules form a three-dimensional framework.

Materials and methods
Pectin substances are contained in the cell membranes of all higher plants, but traditionally, various wastes from the processing industries of the agro-industrial complex are used to obtain pectin.
Modern economic relations in the sphere of production contribute to the introduction of new technologies for the rational use of primary raw materials, complex processing and waste-free disposal of secondary raw materials based on the achievements of science and technology. This will ensure the release of high quality, competitive products at low prices.
The work was carried out on vegetable waste (carrots and pumpkins). Methods were used to isolate pectin substances from carrots and pumpkins; hydrolysis of pectin substances was carried out by the method of acid hydrolysis. The viscosity of pectins was determined by the Oswald method. The structure of the studied pectins was established using the IR spectroscopy method.

Results and discussion
Pectin substances are part of the cell wall of the middle plates, the cytoplasm of plant cells. They are present in almost all higher plants. Performing, due to their specific properties, a number of important functions (regulation of the water regime of tissues, transport of water current, and others), they participate in the processes of cell wall stretching.
According to modern concepts, pectin has a linear structure. The basis of pectin substances is a molecular chain of D-galacturonic acid residues having a pyranose configuration and connected by a 1.4-α-glycosidic bond.
The multifaceted range of properties inherent in pectin determines its widespread use in the medical and food industries. Its most promising use is in the manufacture of products for medical and preventive purposes. The production of pectin is based on the use of apple pomace and beet pulp.
Our task was to study carrot and pumpkin cake, which is a secondary raw material for the industrial processing of vegetables into juice and puree, as a source of food pectin.
Physico-chemical properties of pectin, its further use depend on the quality of the plant raw materials used, the conditions for extracting pectin from this raw material, and also on the balance of functional groups.
To isolate pectin substances from carrot cake, 18 g of waste was extracted twice with a mixture of 0.5% solutions of oxalic acid and ammonium oxalate, taken in a ratio of 1:1. The extraction was carried out at 80-85 0 C, constantly stirred for 2 hours. The extractant was used in amounts of 450 and 400 ml. The extracts were combined, evaporated to 100 ml and precipitated with 5 volumes of 90 ° alcohol, the precipitate was separated by filtration, washed to neutral 90 ° with alcohol, and dried with 96 ° alcohol. The yield was 1.91 g (10.6%).
To isolate pectin substances from pumpkin cake, 23 g of pumpkin cake were also extracted twice with a mixture of equal volumes of 0.5% solutions of oxalic acid and ammonium oxalate (500 and 450 ml) at 80-85 °C with constant stirring for 1.5-2 hours. Then the extracts were combined, evaporated to 150 ml and precipitated with 600 ml of alcohol. The precipitate that formed was separated by filtration, washed until neutral with 90 % alcohol, and dried with 96 % alcohol. Yield was 2.2 g or 9.56% 0.1 g of HP from carrot and pumpkin cake was hydrolyzed with 4 ml of 2nH2SO4 for 24 hours at 100 0 in a sealed ampoule. Then the ampoule was opened, the contents were transferred into a beaker and neutralized with barium carbonate (BaCO3), then the solution was filtered and deionized with a KU-2(H+) cation exchanger to remove barium. Next, the filtrate was separated from the cation exchanger, evaporated and analyzed by paper chromatography in a descending manner. Paper -Filtrak-FN-18. For chromatography, the system butanol-1-pyridine-water (6:4:3) was used. Chromatography time -18 hours. The chromatogram after this time was removed from the chamber, dried, sprayed with acid aniline phthalate developer.
Then the paper was dried and heated in an oven at 105 0 C for 3-4 minutes. In this case, the manifestation of monosaccharides in the test sample occurs.
Known sugars were used as controls: galacturonic acid, galactose, glucose, arabinose, xylose, rhamnose:  Pentosugars: arabinose and xylose appear as pink spots  Hexoses: galactose and glucose appear as brown spots. Rhamnose also appears. Galacturonic acid appears as patches of a pink tint. The monosaccharide composition of the PV of carrots is represented by acidic galacturonic acid) and neutral sugars (galactose and arabinose prevail, glucose, xylose and rhamnose are in smaller quantities).
The monosaccharide composition of pumpkin HP is also characterized by an increased content of galacturonic acid, galactose and arabinose, compared with glucose, xylose and rhamnose, which are found in smaller quantities (Table 1). Next, the esterified carboxyl groups were determined. For this, 10 ml of 0.1 N NaOH was added to the reaction mixture and left for saponification for 2 hours, then 10 ml of 0.1 N HCI was added, stirred and titrated with 0.1 N NaOH until a pink color appeared, using the indicator phenolphthalein. The consumption of 0.1 n NaOH is 4.5 ml for carrots and 2.6 ml for pumpkins. The number of esterified carboxyl groups was determined by the formula: Ke carrot = 0,45х45 0,25 8,1% Ke pumpkin = 2,6 х 0,45 0,25 = 4,6% The total number of carboxyl groups in this case is: Kо = Kc + Ke Ko carrot = 1.98 + 8,1 = 10,08% Ko pumpkin = 1,98 + 4,6 = 6,58% From the total number of free and esterified groups (Kc and Ke), the total number of these groups in the sum Ko and the degree of esterification -λ were determined. Thus, the pectin obtained from carrot waste is a highly esterified polymer, the main chain of which is D-galacturonic acid residues connected by α-1.4 -glycosidic bonds. The monosaccharide composition of pumpkin HP is characterized by an increased content of galacturonic acid, galactose and arabinose, compared with glucose, xylose and rhamnose, which are found in smaller quantities (Table 2). As in all IR spectra of polysaccharides, in the spectrum of carrot HP we note absorption bands of hydroxyl groups 3518-3322 cm -1 . Absorption in the region of 2935 cm -1 is typical for stretching vibrations of hydroxyls involved in hydrogen bonding (Fig. 1). In the IR spectrum of HP there is an absorption band at 953 cm -1 , which shows deformation vibrations of methyl and methylene groups. And the triplets of pyranose rings 917, 870 and 830 cm -1 indicate the presence of another α-1→ 4 glycosidic bond, which is in the α position between the residues of D-galacturonic acid. Thus, the results of HP IR spectroscopy show that the studied biopolymer is an esterified acidic polysaccharide, which is consistent with the data of titrimetric analysis.
The presence of carboxyl groups in HP, both free and esterified, gives a number of bands in the IR spectra. But, nevertheless, there are areas of absorption that characterize this pectin.
The absorption region 2851-3579 cm -1 characterizes the functional groups OH.CH. Of these bands, the absorption bands at 3221 and 3292 cm -1 are characteristic of the frequencies of the stretching vibrations of the OH groups associated with -CH, indicating intramolecular hydrogen bonds. The absorption band at 2918 cm -1 characterizes the stretching vibrations of hydroxyls involved in hydrogen bonds (Fig. 2). 2851 cm -1 -bands of stretching vibrations -CH2, -CH are expressed. The C=0 stretching vibrations of the carboxyl anion bond are located in the region of 1745 and 1638 cm -1 . Ionized carboxyl bound to the metal (Na) appears at 1409 cm -1 etherified carboxyl (methylated) is reflected by absorption bands at 1440 and 1370 cm -1 . Absorption bands 1146, 1104, 1018, 1051 are characteristic of a number of functional groups, primarily they reflect the pyranose ring, as well as C-C, C-O, CH2.
The absorption band at 950 cm -1 shows the bending vibrations of the methyl and methylene groups. Pectins are a biopolymer based on D-galacturonic acid. Acids connected to each other by α-1→4 glycosidic bonds. The foregoing is reflected in the IR spectra of HP by absorption bands at 830 and 890 cm -1 .

Conclusions
Thus, as a result of the studies, pectin substances from the cake of carrots and pumpkins were isolated by us in the amount of 10.6 and 9.56%, respectively. In the course of acid hydrolysis, when determining the qualitative monosaccharide composition of carrot HP, it turned out that galactouronic acid and galactose and arabinose prevailed, while glucose, xylose and rhamnose were present in smaller amounts. When studying the monosaccharide composition of pumpkin HP, an increased content of galacturonic acid, galactose and arabinose was revealed, compared with glucose, xylose and rhamnose, which are in smaller quantities, relative viscosity values were obtained equal to 84.84 and 31.9, respectively.
The data of titrimetric indicators made it possible to attribute the studied PVs to highly etirified ones (PV carrot, PV pumpkin). Using IR spectroscopy, the structure of the studied PVs was established, in which the main chain is D-galacturonic acid residues connected by α-1→4 glycosidic bonds.
The results obtained by our studies make it possible to recommend the use of carrot HP and pumpkin HP for food purposes in the manufacture of confectionery products (drinks, marmalade, jelly, marshmallows, bakery products) and for medical purposes (adsorbent for heavy metal poisoning, radionuclide exposure).