Mohammad Noshad; Mohammad Amin Mehrnia; Nasim Dehghan
Abstract
Introduction: Pectin is a type of water-soluble hetero-polysaccharide that is present in the primary cell wall of plant and is used as a jellying, thickening and stabilizing agent in various food products. The degree of esterification is the most important determinant of the use of pectin in the food ...
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Introduction: Pectin is a type of water-soluble hetero-polysaccharide that is present in the primary cell wall of plant and is used as a jellying, thickening and stabilizing agent in various food products. The degree of esterification is the most important determinant of the use of pectin in the food products, according to pectin is divided into two groups: high-esterification pectin (50% degree of esterification) and pectin with degree low esterification (degree of esterification less than 50 %(. Considering the high use of pectin in the food products, researchers are now looking for new sources of pectin extraction, among which the use of food waste has been considered high, because the waste of food factories is a major challenge for food manufacturers. Eggplant (Solanum melongena) belongs to the Solanaceae family, which is used extensively in the world. The plan species is believed to have originated in India, where it continues to grow in southern and eastern Asia. The skin and warhead of this product, which is discarded as waste, can be used as a valuable source for pectin extraction. The most commonly used methods for pectin extracting are the use of hot water, along with acids, which is a time-consuming process and the waste discard of this method is environmentally problematic. Therefore, the use of new methods such as ultrasound has been considered by researcher to minimize the limitations of the traditional method of pectin extracting. The purpose of this study was to extract pectin from eggplant waste using ultrasound and evaluate its physicochemical properties. Material and methods: The waste of eggplant from restaurant of agricultural sciences and natural resources university of Khuzestan were prepared. The waste was dried in an oven at 60 ºC to reach constant weight. The dried waste was powdered using a grinder and passed through the sieve. The ultrasound was used to extract pectin from eggplant waste (skin and warhead). For this purpose, the effect of ultrasound time (40-80 min) and dry matter /solvent ratio (1:10 – 1:30 g/ml) on extraction efficiency degree of esterification of extracted pectin were investigated. The FTIR (wavelengths scanned 4000-400 cm−1) and rheological behavior were studied to evaluate the performance characteristics of the extracted pectin. Analysis of variance (ANOVA) procedure followed by Duncan’s test using SPSS 16 (SPSS Inc., Chicago, IL, USA) software was applied to determine the significant difference (P < 0.05) between treatment means. Result & discussion: Based on results, increasing the extraction time had a significant effect (P<0.05) on the pectin extraction, so that the increase in extraction time from 40 to 60 min increased the extraction efficiency from 14.05 ±0.21 to 29.35±0.21 (%), which is probably due to the fact that the cavitation causes the cell wall to break down and more solvent penetrates the cell matrix, which results in increased extraction of pectin. The highest efficiency of pectin was obtained in the dry matter /solvent ratio (1:10 g/ml) and 60 min. The highest degree of esterification (84.18 ± 0.1 %) was obtained in the dry matter /solvent ratio (1:20 g/ml) and 60 min. Also, the degree of esterification of the obtained pectin varied from 67.69 ± 0.02 to 84.14 ± 0.1 %), which indicated the high quality of pectin was extracted. Due to the fact that the steric bonds are more unstable than acidic hydrolysis in comparison with glycosidic bonds, the higher degree of esterification indicates less damage to the pectin structure during the extraction process. FTIR showed all of the pectin's specific spectra and abundance of methoxy groups in extracted pectin. The FT-IR spectra show the characteristic absorption of -CH at the ranges of 3000-2800 cm-1 and at 1421 cm-1, while the wide band at 3406 cm–1 was assigned to the -OH stretching vibration. The wide band at the ranges of 1700-1600 cm-1 can be due to the stretching vibrations of the C=O bonds in the backbone of crude polysaccharide because of presence of uronic acid. Existence of a peak at 1200-900 cm-1 indicates that pectin contained multiple vibrations of glycosidic (C–O-C) and pyranoid (C=O) linkages due to the characteristic of the pyranose form of glucosyl residues. The apparent viscosity of the extracted pectin solution decreased with increasing shear rate (0.5 to 10 s-1) while in the higher shear rate (10 to 100 s-1), the apparent viscosity of the pectin solution remained almost constant. This process shows that the produced pectin solution at low shear rate exhibits pseudo plastic behavior, while at highest shear rate exhibits Newtonian behavior. These results indicated that eggplant waste could be used as a good source of high-performance pectin.
Hamed Saberian; Zohreh Hamidi-Esfahani; Hassan Ahmadi Gavghili; Mohsen Barzegar
Abstract
Introduction: Ohmic heating or direct resistance heating is one of the several electromagnetic based methods, occurs when alternating electrical current is passed through a conductive material, with the primary purpose of heating it due to the electrical resistance of the foods. There are many applications ...
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Introduction: Ohmic heating or direct resistance heating is one of the several electromagnetic based methods, occurs when alternating electrical current is passed through a conductive material, with the primary purpose of heating it due to the electrical resistance of the foods. There are many applications that can use ohmic treatment technology, such as blanching, evaporation, dehydration, fermentation, extraction, sterilization and pasteurization of foods (Saberian et al. 2015; Assiry et al. 2010). Pectins are complex heteropolysaccharides, consisting of α-1, 4-linked D-galacturonic acid units and interrupted by L-rhamnose residues with side chains of neutral sugars, mainly L-rhamnose, L-arabinose and D-galactose. In the industrial extraction process, pectin is usually extracted from waste plant material such as citrus peels, apple pomace, sugar beet pulp and sunflower head using hot water (60–100°C) acidified with a mineral acid (such as sulfuric, phosphoric, nitric, hydrochloric) or organic acid (especially citric acid) within the pH of 1.5–3 for 0.5–6 h. The aim of this study was to explore the effect of enzymatic extraction on the yield and quality properties (degree of esterification, Galacturonic acid, emulsifying properties and viscosity) of the pectin, and to compare this pectin with the pectins extracted by ohmic and conventional methods. Finally, the best extraction method was selected.
Materials and Methods: Extraction of pectin was done with the assistance of an ohmic heating system at working frequency of 50 Hz under different parameters including voltage gradient (7-15 V/cm), temperature (50-90°C), and time (5-30 min). Then, the effect of enzyme dose (0-20% v/w) of Celluclast and Rohament CL, solid/liquid ratio (S/L ratio) (1:10 to 1:50 g/ml) and extraction time (1-18 h) on the yield of the extracted pectin from orange waste was investigated.
After the time of extraction (enzymatically, ohmically or conventionally), the sample was cooled to room temperature and centrifuged (10000 rpm, 15 min), and the supernatant was precipitated with two volumes of 96% (v/v) ethanol at 4 °C for 1 h. The precipitated pectin mass was washed twice with 96% ethanol in order to remove impurities. The pectin was dried in a forced circulation oven at 55°C until a constant weight (14 h).
Galacturonic acid content was determined according to Scott (1979) with some modifications. The degree of esterification (DE) of pectin samples was determined by titrimetric method according to Santos et al. (2013).
Emulsifying activity and emulsion stability were measured according to the method described by Yapo et al. (2007).
The viscosity and the flow behavior of the selected pectin solutions (2%, w/v) extracted conventionally and ohmically at 90°C for 30 min (the optimum extraction condition) and the highest pectins extracted enzymatically, were measured at 25°C.
Pectin powder samples were mixed with KBr and pressed into KBr pellets before FTIR analysis. PerkinElmer FTIR spectra (PerkinElmer, Frontier model, USA) was applied at the transmission mode in the frequency range of 4000–400 cm-1 at a resolution of 1 cm-1.
Results were analyzed by analysis of variance (ANOVA) using SPSS 19 statistical software and the Duncan’s test with 95% confidence interval was used to compare the means of the tests. The results which were presented in this research, have been obtained from the average values of the minimal two replicate experiments.
Results and Discussion: first, the effect of enzyme dose, solid/liquid ratio (S/L ratio) and time of extraction on the yield of the extracted pectin from orange waste by using Celluclast and Rohament CL enzymes was studied. Then, the yield, of esterification, galacturonic acid, emulsifying properties and viscosity behavior of the pectins extracted in the optimum condition by enzymes were compared to the extracted pectins by ohmic and conventional methods. Results indicated that the highest yield of pectin was obtained by using Celluclast and Rohament CL enzymes at enzyme doses of 15 and 17.5%, S/L ratio of 1:20 and 1:40 (g/ml) and time of 3 h for both, which were 5.92 and 10.70 %, respectively. The highest yield of pectin by ohmic heating was obtained at the voltage gradient of 15 v/cm, the temperature of 90°C during 30 min (14.33%), which was higher than the amount obtained by conventional method (13.53%) may be due to the electroporation (disruptive pores which were made on the cell membrane by the electric field) (Cho et al., 1996). de Oliveira et al. (2015) reported that the moderate electric field (at 45°C, 50 and 100 V) extracted the pectin significantly (p < 0.05) more than the conventional extraction. The emulsifying activity of the extracted pectins by ohmic and conventional methods were 65.47 and 67.18%, respectively, although the pectins extracted by enzymatic method had not any emulsifying activity. It seems that during the pectin extraction, enzymes hydrolyzate the pectins. The viscosity of the pectins extracted by ohmic and conventional methods at the concentration of 2% was higher than those obtained from the enzymatic method. Therefore, pectin extracted by ohmic and conventional methods had the highest yield, emulsifying properties, and viscosity.
