Received date: January 16, 2013; Accepted date: April 25, 2013; Published date: April 30, 2013
Citation: Kamel SM (2013) Effect of microwave treatments on some bioactive compounds of parsley (Petroselinum Crispum) and dill (Anethum graveolens) leaves. J Food Process Technol 4:233. doi:10.4172/2157-7110.1000233
Copyright: © 2013 Kamel SM. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Visit for more related articles at Journal of Food Processing & Technology
The aim of the present study was to evaluate the effect of microwave heating, (for one, two and three minutes) on some bioactive compounds of parsley (Petroselinum crispum) and dill (Anethum graveolens) leaves blended in water. The effect of microwave drying process of parsley and dill leaves was also studied. Total phenols, antioxidant activity, chlorophyll, caroteoids and color indices were determined in this study. According to the obtained results, dill leaves contain higher total phenols, antioxidant activity and carotenoids (1287.00 mg as gallic acid / 100g, 48.14% and 45.98mg/kg, respectively) than parsley leaves (1031.39 mg as gallic acid/100g, 40.10% and 40.00mg/kg, respectively). Total phenols, antioxidants activity and carotenoid contents of parsley and dill heated samples significantly (p<0.05) increased after one minute of heating. Then gradual decrease was observed in the same parameters after 2 and 3 minutes in both parsley and dill. Significant decrease in all tested parameters was observed in microwave dried samples compared to the fresh state. Antioxidant activity decreased 20% in dried parsley and 30.3% in dried dill compared to fresh samples. This work indicated that the tested bioactive compounds of parsley and dill was stable only after one minute of microwave heating, however, after 3min of heatinf 32.3 to 80% decrease was observed in these parameters.
Microwave; Green vegetables; Antioxidant activity; DPPH; Pigments
Recently special attention has been paid towards edible plants that are rich in secondary metabolites (frequently called phytochemicals) and there is now increasing interest in antioxidant activity of such phytochemicals present in the diet. Phenolic compounds are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of plants, with more than 8,000 phenolic structures currently known, ranging from simple molecules such as phenolic acids to highly polymerized substances such as tannins. Plant phenolics are generally involved in defense against ultraviolet radiation or aggression by pathogens, parasites and predators, as well as contributing to plants’ colors. They are ubiquitous in all plant organs and are therefore an integral part of the human diet. Phenolics are widespread constituents of plant foods (fruits, vegetables, cereals, olive, legumes, chocolate, etc.) and beverages (tea, coffee, etc.), and partially responsible for the overall organoleptic properties of plant foods. Antioxidants are important in prevention of pollution damage of plants, disease prevention in both plants and animals and play a very important role in the body defense system and reactive oxygen species . The bioactive compounds including polyphenolic and photosyntethtic pigments like chlorophylls and carotenoids have been shown to have possible health benefits with antioxidative, anticarcinogenic, antihypertensive, antimutagenic, and antimicrobial activities. Based on the scientific arguments, supplementation of diet with various herbs is recommended among individual consumers, both for its healing properties and nutritive value . The biological importance of carotenoids lies is the fact that carotenoids can also serve as antioxidants, and many reports indicated that carotenoids may possess some anticarcinogenic properties, which may be related to their ability to interact with and quench various radical species that can be generated within cells . Deep-coloured vegetables and fruits are known to be good sources of phenolics, including flavonoid, anthocyanin, and carotenoids . Green leafy vegetables are popularly used for food in many countries of the world, being a rich source of ß-carotene, ascorbic acid, minerals and dietary fiber [5-8].
Parsley (Petroselinum crispum) and dill (Anethum graveolens L.), annual herbs of the parsley family (Apaceae or Umbelliferae), are popular herb widely used in many regions find their applications as culinary herb or as minor adjuncts to salads (fresh herbs) and herbal teas (dry leaves/shoots) and as aromatic agents in the food, pharmaceutical, perfumery and cosmetic, functional food and nutraceuticals industries .
Many investigations point out to the antioxidant properties of parsley. The flavonoid apigenin, one of the components of parsley plant, was shown to express strong antioxidant effects by increasing the activities of antioxidant enzymes and related to that, decreasing the oxidative damage to tissues. Potential for anticancer activity by parsley was reported as well [10,11]. Dill contains range of phytochemicals, such as vitamin C and polyphenols, which significantly contribute to their total antioxidant activity .
The popular thinking is that fresh fruits and vegetables are better for us than cooked ones nutrition wise. Despite this thinking, most vegetables are usually cooked before consumption. These cooking processes could bring many changes in physical characteristics and chemical composition of vegetables [13,14]. However, processing can also lead to disruption of the food matrix, increasing the inaccessibility of many phytochemicals and thus improving the nutritional quality of vegetables . Moreover, the attention should be also paid to the processing methods in order to preserve the desirable antioxidant properties of foods .
The use of the microwave oven increased constantly, both at home and in the industry sector, due to its advantages, that includes capacity to rapidly transmit heat [17,18], convenience, ease of use [19,20] and time and energy savings . Another reason to use of the microwave oven is the tendency of the industry to produce pre-prepared food products especially to defrost heat or cook . The microwave heating process could accelerate oxidative reactions which promote the involvement of free radicals .
The effects of microwave on food constituents , including in lipid fraction of animal fats, vegetable oils and some raw and cooked vegetables [23-26] have been studied. The objectives of this study were to confirm the effect of different microwave heating times on the total phenols, antioxidant activity, carotenoids, chlorophylls and color indices of two green leafy vegetables, parsley and dill, are popularly used in many countries of the world as spices to flavor food and also in medicinal purposes. The effect of microwave drying process on the same parameters has been studied also on the same parameters.
Sample preparation for microwave heating
Fresh plant materials of parsley and dill were purchased from local supermarket in Cairo, Egypt. Samples were washed under tap water and inedible parts and stems were removed. The edible parts of the vegetables (3g) were homogenized with 50 ml distilled water in a laboratory blender, Poured in 100 ml glass beaker (four for each plant). One beaker left as control (corresponding to 0 min) and the second, third and fourth beakers were heated in Panasonic microwave oven at full power (750 W) for 1, 2 and 3 min, respectively. The samples were then cooled for a few minutes at room temperature, filtered and adjusted to 100ml.
Microwave drying process
The edible parts of parsley and dill leaves were dried using a microwave-oven. The characteristic parameters of drying program were as follows: rotation speed - 6 rpm; product mass per load-3 g; drying time-1 min for dill and 2min for parsley (Table 1).
|Parsley leaves||Dill leaves|
|Weight of sample(g)||5||5|
|Moisture content (%)||6.65||5.93|
Table 1: Different methods of drying.
Determination of total content of phenolic compounds
The total content of phenolic compounds (TPC) in samples was determined according to the method reported by Boyer and Hai Liu . One ml of extract was mixed with 5 ml of 10% Folin-Ciocalteu reagent in distilled water and 4 ml of 7.5% sodium carbonate solution. After incubation of samples with reagent at room temperature for 30 min with periodical mixing, the absorbance at 765 nm was measured. The calibration curve was constructed within the concentration range 0.075-0.6 mg/ml of Gallic acid. Mean values were calculated from three parallel analyses. Results were calculated as Gallic Acid Equivalents (GAE) in mg/100 g of dry plant material using the following equation:
C = a× γ× (V/m) ×100,
Where: C - total amount of phenolic compounds, mg GAE/100g; a - dilution number; γ - concentration obtained from calibration curve, mg/ml; V - volume of aqueous ethanol used for extraction, m; m - weight of sample (g).
DPPH free radical scavenging ability
The free radical scavenging ability of samples against DPPH (1, 1-diphenyl-2 picryl hydrazyl) free radical was evaluated as described by Zhang and Hamauzu . One ml extracts was mixed with 1ml of 0.4 mmol l-1 methanolic solution containing DPPH radicals. The mixture was left in the dark for 30 min and the absorbance was measured at 516 nm. The DPPH free radical scavenging ability was subsequently calculated with respect to the reference (which contains all the reagents without the test sample).
Objective color measurements were made by using a Hunter colorimeter (Hunter Associates Laboratory Inc., Reston, USA) on the basis of three color values, namely L, a and b. The instrument (45°/0° geometry, D25 optical sensor, 10° observer) was calibrated against a standard white reference tile (L.90.55, a. ± 0.71, b.0.39). A glass cell containing the microwave-treated or untreated samples was placed above the light source and covered with a white plate and L, a and b values were recorded .
Chlorophylls and carotenoids content
Following the procedures described by Mosquera et al.  the chlorophyll fraction was measured in a UV spectrophotometer at 670 nm and the carotenoid fraction at 470 nm.
All determinations were conducted in triplicate. Differences between means of data were compared by least significant difference (LSD) calculated using the SAS for Windows 2000 Version 8.2 .
Effect of microwave heating on total phenols, antioxidants activity, chlorophyll and carotenoid contentsof parsley and dill leaves
The total phenols content of the liquor from microwaved parsley and dill leaves were presented in table 2. The data revealed that total phenols in parsley leaves increased from 1031.39mg/100g prior to microwave heating to 1371.84mg/100g after one min. Dramatic decrease to 482.81and 204.60 mg/100g was recorded after two and three min, respectively. Total phenols in dill leaves increased from 1287.00 to 1636.80 after one min then decreased to 981.75 and 861.63 mg/100g after two and three min, respectively.
|Treatments||Total phenols (as mg gallic acid / 100g)||Antioxidant activity (%)||Chlorophyll (mg /kg)||Carotenoids (mg /kg)|
|Dill (0 min)||1287.00ab||48.14ab||33.97a||45.98a|
Table 2: Effect of microwave heating on the total phenols, antioxidant activity, chlorophyll and carotenoid contents of parsley and dill.
Data in same table showed that antioxidants activity of parsley and dill leaves significantly (p < 0.05) increased from 40.10 to 51.83% and from 48.14 to 50.71%, respectively after 1min of heating. However, gradual decrease was recorded after 2 and 3 min of heating in antioxidant activity. Heating or cooking in water seems to cause a leakage of vegetable antioxidants like phenols into the cooking water. Then degradation of these antioxidant compounds may take place with prolonged time to microwave heating. Gahler et al.  reported an improvement in the antioxidant activity of tomatoes after heat treatment than in raw tomato.
These results are in agreement with Wachtel-Galor et al.  who concluded that microwaving led to a greater loss of antioxidants into the liquor than did boiling. Our results in a line with Turkmen et al.  who found that after 1.5 min microwaving the antioxidant activity increased by 15.90% and 16.68% in some fresh vegetables. These results are also in accordance with Jimnez-Monreal et al.  who evaluate the influence of cooking methods on antioxidant activity of vegetables. They found that the scavenging capacity decreased between 30% and 50% when they were submitted to microwaves. The same trend was appeared with caronenoids contents (Table 2). Carotenoids content increased after one min then decreased about 27% in parsley and 76% after 3min in dill leaves. The increase after one min may be due to the heat treatment that enhances the libration and the bioavailability of carotenoids as investigated by Rock et al. . In the same table chlorophyll contents decreased significantly (p < 0.05) after, 2 and 3min in parsley and after 3min in dill. The same findings were stated by Pellegrini et al.  who found that total chlorophyll content of raw fresh broccoli, was significantly decreased by all the cooking methods include microwaving except for oven steaming.
Effect of microwave heating on the color indices of parsley and dill leaves
Hunterlab colorimeter was used here to assess the effect of microwave heating on the change of color in parsley and dill leaves. Data in table 3 showed that microwave heating for 1, 2 and 3min induced significant decrease in L-value for parsley and dill. Loss of greenness (-a) was recorded in both parsley and dill leaves after all heating time. Yellowness (b-value) increased after 1min of cooking from 1.98 to 2.68 and 2.07 in parsley and dill leaves, respectively. However after 3 min of cooking the yellowness decreased. Conversion of chlorophylls to pheophytins during thermal processing seemed to be the main reason of the darkening and the decrease in greenness. These results are in a line with Pellegrini et al.  who studied the effect of different cooking methods on color, phytochemical concentration, and antioxidant capacity of raw and frozen Brassica vegetables and their results showed loss of greenness (-a) in microwaved vegetables. The increase in Yellowness may be referring to the liberation of carotenoids after 1min. Then degradation of carotenoids with increasing the exposure time led to decrease in yellowness. In agreement with these results microwaving induced a significant decrease of both lutein and β-carotene was recorded by Zhang and Hamauzu .
|Brightness (L)||Greenness (–a)||Yellowness (+b)|
|Dill (0 min)||24.25bc||-1.50a||2.32ab|
Table 3: Effect of microwave heating on the color Indices of parsley and dill leaves.
The present results are in accordance with Rocha et al. and Ihl et al. [36,37] who stated that the color changes from bright green to olivebrown during thermal and microwave processing are caused by the conversion of chlorophylls to pheophytins.
Effect of microwave drying process on total phenols, antioxidants activity, chlorophyll and carotenoid contents of parsley and dill
Data in table 4 revealed that total phenols were affected obviously with the microwave drying process in both parsley and dill leaves. Significant decrease (P>0.05) was observed in total phenols content of both microwave dried samples compared to the fresh state (12.73% in parsley and 12.18% in dill). Antioxidant activity decreased 20% in dried parsley and 30.3% in dried dill compared to fresh samples. This decrease may due to the decrease in total phenols and the thermal labile components content of samples such as carotenoids, (table 4). Data in the same table showed a noticeable decrease in chlorophyll content in dried parsley and dill compared to fresh samples (on dried weight). This data are in parallel and ensure the data above. The same results were obtained by Annamalai (2011)  who found a significant reduction in antioxidant property for microwave dried plant material when compared to other drying treatments. Bejar et al.  studied the effect of microwave drying on orange peel and leaves and stated that microwave drying decreased the total phenol content of the dried leaves compared to the fresh one.
|Samples||Total phenols (as mg gallic acid / 100g)||Antioxidant activity (%)||Chlorophyll (mg /kg)||Carotenoids (mg /kg)|
Table 4: Effect of microwave drying on some parameters of parsley and dill leaves.
Effect of microwave drying process on the color Indices of parsley and dill
The effect of microwave drying on color parameters was showed in table 5. Compared to the fresh state of parsley, the applied microwave drying process has no significant effect on degree of brightness (L) however, significant decrease was noticed on a (P>0.05) and b (P>0.05) as greenness and yellowness degree, respectively. In dill sample the degree of brightness and greenness were significantly (P>0.05) decreased but microwave drying has not a significant effect on b (P>0.05). This decrease can be explained by Maillard and the nonenzymatic browning reactions occurred essentially during microwave drying and the degradation of carotenoids and chlorophyll pigments responsible of the leaves color. These results are in parallel with that by Dwivedy et al.  their study indicated that the therapeutic values (total phenols and antioxidant activity) of dried Indian Borage (Coleus aromaticus) leaves were significantly less than that of fresh leaves.
|Brightness (L)||Greenness (–a)||Yellowness (+b)|
Table 5: Effect of microwave drying on the color Indices of parsley and dill leaves.
The present work showed that microwave heating induces significant loss in some bioactive components and their activities in parsley and dill. However the appearance quality as brightness and greenness does not extremely affected. More research should be investigated in more foods in order to better guide food preparation methods that preserve food of their rich bioactive components and antioxidant capacity.
The authors would like to thank all members in Food Technology Research Institute, ARC, Giza, Egypt and the Faculty of Agriculture and Food Science, KFU, Saudi Arabia, for the laboratory facilities.