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International Journal of ChemTech Research CODEN (USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.10 No.3, pp 357-364, 2017
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Influence of Microwave Power on Physico-Chemical Characteristics of Aloe Vera (barbadensis Miller) During Microwave Drying
G. Srinivasan1, R.Baskar2,
1Department of Chemical Engineering,Erode Sengunthar Engineering College, Thudupathi, Perundurai, Tamil Nadu. India.
2Department of Food Technology, Kongu Engineering College, Perundurai,
Tamil Nadu.India.
Abstract : The objective of this present study is to evaluate the influence of different microwave power (180 – 900 W) with an interval of 180 watts on the physico-chemical properties of aloe vera samples during microwave drying. The results showed that,the color of the aloe vera samples were did not affected by the microwave treatment. On the other hand, the rehydration ratio, water holding capacity, shrinkage, total phenolic and flavonoid content was significantly affected by different microwave power level and it was decreased while increasing the microwave power level during drying. From the results, it was found that, the microwave treatment can increase the rate of mass transfer, and enhance the solvent penetration into the cells by disrupting the cellular walls and hydrophobic bonds in the cell membrane, it may lead to a high permeability of samples and decreased the rehydration ratio, water holding capacity, shrinkage, total phenolic and flavonoid content of dried aloe vera samples when compared with fresh materials.
Keywords : Microwave, Drying, Power, Physico-Chemical properties,Total phenol content,Total flavonoid content.
1.Introduction
Aloe vera is a succulent,which belongs to the Liliaceae family. It is one of the 250 known species of aloes, referred by the scientific terms of aloe vera and aloe barbadensis. The semi-tropical plant, aloe vera barbadensis miller from the Lily (Liliaceae) family has a long and illustrious history dating from biblical times. It has been mentioned throughout recorded history and was given a high ranking as an all purpose of herbal plant. Aloe's thick, tapered, spiny leaves grow from a short stalk near ground level. Aloe vera is an herbal plant species with the botanical name of aloe barbadensis miller. Aloe vera is well known for its marvelous medicinal properties. These plants are one of the richest sources of health for human beings comes from nature. It has been grown as Ornamental plant widely in India, it is found in Rajasthan, Andhra Pradesh, Gujarat, Maharashtra and Tamil Nadu. There are many products of the plant which is in the treatment of various ilments. It is a shrubby or arborescent, perennial, xerophyti, pea-green color plant belonging to Asphodelaceae (Liliaceae) family. Aloe vera (barbadensis Miller) is grown commercially for the health and moisturizing benefits found inside its leaves. An adult aloe vera plant reaches maturity at 1-2 years and can reach a height of 30 inches with up to 21 leaves. The leaves are green to grey-green in color and thick and fleshy. The fleshy portion of aloe vera leaves contain different phytochemicals and it has been used for medicinal and industrial purposes. The gel contains 97% water content and rest is made of lipids, sterols, glucomannans, amino acids
and vitamins. The middle layer consists of a bitter yellow sap and contains glycosides and anthraquinones. The outer thick layer synthesizes carbohydrates and proteins and has protective function.
In the food industry, aloe vera has been utilized as a resource of functional food, especially for the preparation of health food drinks and other beverages, including tea. The aloe gel is used as a moisturizer for skin care, hair care products and a healing agent in cosmetics. Medicinally it is used as antiseptic agents, natural antibiotic agent, calming agent, detoxifier and dilator to increases circulation and blood flow in the skin. It is also used as insect repellent, and a transparent pigment used in miniature painting. The cords and nets are made from the leaf fiber. The amount of aloe vera that finds its application in the pharmaceutical industry in not negligible as far as the manufacturing of topical ointments, gel preparations, tablets and capsules are concerned. Aloe vera gel also finds its application in the cosmetic and toiletry industries, where it is used as a base for the preparation of creams, lotions, soaps, shampoos and facial cleaners. Each aloe vera leaf has three layers; So large scale agricultural production of Aloe Vera is undertaken in several countries such as Australia, Bangladesh, Cuba, Dominican Republic, China, Mexico, Jamaica, Kenya, Tanzania , South Africa and United States of America . But, the shelf life of fleshy portion of aloe vera leaves are very limited. Hence, increasing shelf life of aloe vera pulp without affecting its nutritional and chemical composition is essential to meet out the global needs.
Drying is one of the most traditional methods to preserve food materials for longer storage purposes and its increase the self-life of the end product and it does not affects the nutritional value. It not only reducse the water content, but also affects physical and chemical properties, spoilage, shrinkage, rehydration capacity, and colour8. Its recently very popular in microwave drying as compared to other drying techniques, this technique has many advantages as it has higher thermal conductivity, lesser drying time, saves energy, space utilization for sanitation purposes, uniform energy distribution. In recent years microwave drying is popularly an alternate drying method for a wide variety of foods. So far microwave drying method was adapted by several researchers to dry different materials such as Mulberry3 ,Banana22., Plaster of pairs.32 , Mushroom35, Carrot33, Chilli18, Garlic36, Apple 15, Spinach 29 , Parsely 40 ,Potato 47, Mushroom35, Chilli peppers18, Mint 28, Okra 10.From the literature analysis, the influence of microwave power on physico-chemical properties of aloe vera samples under microwave drying has not been documented. Therefore, this present study has been planned to investigate the effect of different microwave power levels (180 - 900 Watts with an interval of 180 W) on the physico-chemical properties such as color parameters (chroma and hue angle), rehydration ratio, water holding capacity, shrinkage, total phenolic and flavonoid content of aloe vera samples during microwave drying.
2. Materials and Methods
2.1. Materials
Aloe vera leaves are purchased from local vendors, near perundurai, Erode, Tamilnadu, India. Thorns and hard layer present on the surface of aloe vera is removed, washed in tap water to remove surface contaminants and manually peeled off. The aloe vera is cleaned to remove the debris present. For that dematerialized water is used and is decanted. Gravimetric method is generally preferred for determining initial moisture content of aloe vera sample.
2.2. Experimental setup
A programmable multifunctional microwave drier with optimum technology and an output of 900 Watts and with manual microwave power adjustable system (180, 360,540,720 and 900 watts). The frequency 2450 MHz is used for the drying experiment. Electric power to microwave conversion inside microwave oven is done by an important part inside known as the magnetron . The dimensions of the microwave chamber provided is 327 X 370 X 207 mm . A fan is used to regulate the air flow inside chamber by fixing it inside the entire chamber. This fan helps to remove moisture from the drying chamber by passing it through the opening in the oven wall at the top to the outer surface. The oven is also equipped with a glass turn table along with a digital control facility for power adjustment. Five different power levels of 180, 360, 540, 720, 900 watts are taken into consideration for conducting this experiment. A digital balance with an estimated accuracy of 0.01 is fitted on top of the microwave oven which is directly connected with the turn table for weighing the sample without interrupting the drying throughout the project at any instance. The sample is initially placed on a plate on the rotating disk in the microwave oven. The losses of moisture from the sample is noted and recorded at
different intervals using Digital balance. As a function of time, three thin layer drying models are used to determine the moisture ratio. Since wide spread cultivation fields are the key source for aloe vera, fresh samples are collected from there.
Fig.1. Schematic illustration of the microwave drying set-up
2.3. Determination of colour coordinates
The colour measurements coordinate such as L (brightness or whiteness), a (redness or greenness) ,b (yellowness/blueness) of fresh and dried samples are determined with the help of a Chromameter (Minolta Chroma, CR-400, Japan). The total colour difference (ΔE) and hue angle (H) is attained from the following equations.
(1)
(2)
L0*, a0*, b0* – colour parameters of fresh aloe vera samples
2.4. Estimation of rehydration capacity
Rehydration capacity (RC) of dried samples are assessed by taking known amount (W1) of dried aloe vera samples which is immersed into boiling water for 2 min and then weight of the sample is measured (W2). The following equation is used to compute the rehydration ratio of the samples
(3)
2.5. Determination of shrinkage ratio
Water displacement method is used to determine the shrinkage ratio (SR) of the sample. The following equation is used to calculate the shrinkage ratio.
(4)
2.6. Estimation of water holding capacity (WHC)
WHC of the samples are estimated by centrifuging the known amount of rehydrated final samples (R1) at 6500 rpm for 15 minutes, the water is drained by using plastic mesh the weight of the sample is measured (R2). All measurements are done in triplicates the mean value is calculated and used to find out the WHC of the samples. The WHC is calculated according to the equation 5.
(5)
2.7. Determination of total phenolic content (TPC)
Folin-Ciocalteu method is described by 44 . It is used to determine the TPC of the extracts. 1 ml aliquots of dilute extracts (dilution with distilled water to adjust the absorbance within the calibration limits) is shaken for 1 min with 1.5 ml of the Folin–Ciocalteu reagent and 10 ml of distilled water. After the mixture is shaken, 6 ml of 10 % (w/v) sodium carbonate is added and the mixture is shaken again for 1 min. Finally, the solution is adjusted to 25 ml by adding distilled water. The absorbance are measured at 760 nm using spectrophotometer (Elico SL 244). From the calibration curve of gallic acid, results are calculated and expressed as gallic acid equivalents (mg GAE/g).
2.8. Estimation of total flavonoid content (TFC)
The sample (1 ml) is mixed with distilled water (4 ml) and 5 % (w/v) sodium nitrite solution (0.3 ml). After 5 min, 10 % (w/v) aluminum chloride solution is added in the solution and after 6 min, 2 ml of sodium hydroxide (1 M) solution is added in the sample solutions. The absorbance are measured at 510 nm and TFC is calculated from the standard curve of quercetin and expressed as quercetin equivalents (mg QE/g).
3. Result and Discussion
3.1.Influence of microwave power on color parameters
Determination of color difference (ΔE) and hue angle (H) is one of the best parameters to evaluate the sensory characteristic and expresses the color variation of any samples. Hence in this study, these parameters are evaluated and the results are depicted as in Figure 2.
Fig.2. Influence of microwave power on color and Huge angle.
From the results, it is observed that, the color parameters are not significantly differed from control sample. This is due to the fact that, the microwave drying does not cause surface overheating phenomena since it removes moisture on the surface by converting it directly to water vapor and preservation of product color seems good 26 had examined the color change in carrots at different microwave power levels and found that, very small noticeable color change was observed. Similar results were attained by39 for parsley leaves and coriander leaves6.
3.2. Influence of microwave power on RR and WHC
Rehydration ratio (RR) is one of the important parameters whether the dried materials could attain the original nature if they are immersed in the water.When the aloe vera is dried at 180 W it shows the have highest RR and WHC and when its dried at higher microwave power level of its shows the lower microwave power (900 W) in (Fig. 3) .This is attributed to the breakdown of the leaves during the drying process at lower microwave power is higher.
Fig.3.Influence of microwave power on rehydration ratio andwater holding capacity.
In addition to that, the time taken for drying of leaves at 180 W is higher than 900 W and it leads to damage and collapse the cells and tissues. Hence, more space could be created between the tissues and it absorbs more water and enhances the RR and WHC of the samples. The RR and WHC of aloe vera slices are found to have 35 to 25 % respectively under various drying conditions. Similar results on higher values of RR and WHC are reported in the literature by some researchers31,21.
3.3. Influence of microwave power on shrinkage
Drying is one of the preservation methods and leads to form shrinked materials. Hence in this study, shrinkage of the aloe vera samples during microwave drying is evaluated and presented as shown in figure.4.
Fig.4.Influence of microwave power on shrinkage
The shrinkage of aloe vera samples are 41.5 to 29 % respectively. Higher shrinkage is found at lower microwave level (180 W) than higher power level (900 W).This is attributed that the fact is, the time taken for attaining equilibrium moisture content of aloe vera sample at higher microwave power level is very low which is due to the fact that the slow sublimation due to extensive heat generation, accelerated removal of water from the tissue. So the cell and tissue damage is minimized and leads to produce low shrinked aloe vera samples.
3.4. Influence of microwave power on TPC and TFC
The total phenolic content (TPC) of aloe vera gel is also shown in Figure 5. A decreasing trend in TPC and TFC is observed in different power levels. TPC and TFC value is changed from the range of 3584.2 to 985.6 mg GAE/100 g d. m. due to different microwave power levels in the samples compared to 896.2 to 249.7 mg QE/100 g d. m. in the control sample.
Fig.5. Influence of microwave power on TPC and TFC
The MW treatment increases the permeability of the samples due to the change in the microstructure and it leads to evaporate the volatile compounds which are sensitive to heat. So the TPC and TFC of the dried samples are decreased.
4. Conclusion
Aloe vera samples are subjected to microwave treatment at different power levels (180,360,540,720 and 900 W with an interval of 180 W) and investigated its effect on physico-chemical properties such as color parameters (Chroma and hue angle), rehydration ratio, water holding capacity, shrinkage, total phenolic content and total flavonoid content of fresh and dried aloe vera samples. The samples dried at lower microwave power level (180 W) is shown at a higher rehydration ratio, water holding capacity, shrinkage, total phenolic content and total flavonoid content than samples dried at 900 W of microwave power level. From the results, it is found that, MW treatment does not significantly affect the color parameters of the samples. But it significantly decreases the rehydration ratio, water holding capacity, shrinkage, total phenolic content and total flavonoid content of the dried samples when compared with fresh samples. These results showed that,the microwave drying technique could be used to preserve the aloe vera samples, which would be highly beneficial for the production of a high quality ingredient.
References
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