alexa Impression of Instinctive Cookery Methods along with Altered Processing Time on the Potential Antioxidants, Color, Texture, Vitamin C and β-Carotene of Selected Vegetables | Open Access Journals
ISSN: 2157-7110
Journal of Food Processing & Technology
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Impression of Instinctive Cookery Methods along with Altered Processing Time on the Potential Antioxidants, Color, Texture, Vitamin C and β-Carotene of Selected Vegetables

Ali M1*, Khan MR2, Rakha A2, Khalil AA2, Lillah K2 and Murtaza G2

1School of Food Science and Biotechnology, Key Laboratory of Fruits and Vegetables, Zhejiang Gongshang University, Hangzhou, China

2National Institute of Food Science and Technology, Fruits and Vegetables Processing Laboratory, University of Agriculture Faisalabad, Pakistan

*Corresponding Author:
Maratab Ali
School of Food Science and Biotechnology
Key Laboratory of Fruits and Vegetables, Zhejiang
Gongshang University, Hangzhou 310018, China
Tel: +86-13221002007
E-mail: [email protected]

Received date: March 09, 2017; Accepted date: March 28, 2017; Published date: April 03, 2017

Citation: Ali M, Khan MR, Rakha A, Khalil AA, Lillah K, et al. (2017) Impression of Instinctive Cookery Methods along with Altered Processing Time on the Potential Antioxidants, Color, Texture, Vitamin C and β-Carotene of Selected Vegetables. J Food Process Technol 8:666. doi: 10.4172/2157-7110.1000666

Copyright: © 2017 Ali M, et al. 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.

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Abstract

In the current millennium, consumers are becoming more conscious about their dietary patterns with special concern to nutrient retention during cooking methods. There is a need to assess the most convenient and nutritionally better thermal cooking method which causes the least nutrient abuse. The current study investigated the consequence of three cookery methods viz. conventional boiling, steaming and microwave cooking on the physical parameters, β-carotene, vitamin C, total phenolic contents (TPC), total flavonoid contents (TFC) and antioxidant activity (DPPH%) of the particular vegetables. Results revealed that both cooking methods and length of time exerted positive and negative influence on nutritional composition of vegetables. L*, a* and b* values decreased in all samples. In texture analysis, highest force N (Newton) determined in control and microwave cooked samples followed by steaming and boiled samples. Cooking of vegetable by microwaving had the maximum retention for vitamin C, TPC and DPPH% after control. While, ß-carotene contents increased in microwave cooking than control. Total flavonoid contents were tending to a decreasing trend in all cooking methods but highest contents were retained in boiling cooking. Amongst the three cookery methods adopted, microwave cooking method emerged as the most appropriate method in terms of retention of nutrients in vegetables.

Keywords

Carrot; Cabbage; Cooking; Boiling; Steaming; Microwave

Introduction

In current era, there is a mounting trend towards the assessment of beneficial phytochemicals and efficient ingredients from natural dietetic sources like fruits and vegetables [1,2]. Fresh vegetables contain nutritional constituents including phytochemicals, vitamins and minerals. However, these are extremely perishable [3]. Numerous epidemiological investigation has showed the defensive impacts of vegetable utilization against the danger of several age-related illnesses like tumor, cardiovascular diseases, cataract and muscular disintegration [4,5]. Carrot and Cabbage are usually consumed after adopting the cooking procedures such like boiling, steaming and microwave before use. These vegetables are consisting of various bioactive components like phytochemicals, carotenoids, vitamin C and minerals. In this way, these compounds prevent the people from certain diseases like hypertension, stroke and heart disorders [6]. The role of carrot carotenoids as the precursors of vitamin A and excellent antioxidants source has been generally known [7,8]. Cabbage is a cruciferous green leafy vegetable, which contains high amounts of fibre, vitamins, and minerals [9,10]. Cabbage also attains beneficial phytochemicals and carotenoid contents in significant amounts [11].

The nutritional profile of vegetables is highly dependent on handling and processing techniques. Even minor thermal treatments, like blanching exert detrimental effects on functional constituents [12]. Cookery methods initiate substantial alteration in natural composition, manipulation in chemical concentration and bio-accessibility of bioactive component in vegetables. Alternatively, impacts of both aspects, positive and negative have been accounted which are dependent upon changes in process conditions, morphological parameters and dietary properties of vegetables [13]. Defective cooking methods expressively affect the physical parameters, ß-carotene, vitamin C, TPC, TFC and DPPH% of vegetables. Such cooking methods alter the antioxidant and anti-nutrient components [14]. While, the degree of alteration largely depends upon length of time and adopted cooking methods [15]. Cookery methods can also lead to interruption of the food matrix, growing the bio-accessibility of many phytochemicals and therefore improve the nutritional quality of vegetables [16].

After processing, vegetables quality was gradually lowered as the result of nutrient loss. The result of these changes shows poor acceptability [17]. Hence, the influence of different cooking methods on qualitative and quantitative values of nutrients should be investigated. Therefore, current study was planned to inspect the values of nutritionally active components and physical characteristics of carrot and cabbage before and after boiling, steaming and microwave cooking protocols.

Material and Methods

Research was conducted in National Institute of Food Science and Technology, University of Agriculture Faisalabad.

Chemicals

All chemicals used were of analytical grade supplied by Merck and Sigma. All the measurements were done in triplicates.

Procurement of raw material

The vegetables cabbage and carrot were purchased from the local market of Faisalabad, Pakistan.

Preparation of raw material

The vegetables were subjected to washing, peeling and dicing prior to subjecting for cooking process.

Cooking methods

Conventional boiling, microwave and steam cooking methods were adopted to cook the vegetable [12]. In all cooking methods, 500 g of each vegetable was taken. In conventional cooking method, vegetables were subjected to boiling in sufficient volume of water. While in steam cooking, vegetables were subjected to a domestic steamer. After cooking, vegetables were drained using a strainer. For microwave cooking, vegetables samples were subjected to a microwave oven (Panasonic 600 W power) in which no added water was used. All vegetable samples were cooked for both 10 min and 15 min separately. The cooked material was packed in polythene zip bags and stored at (-42°C) for further analysis

Treatments

Raw vegetables were taken as Tₒ showing no cooking treatment employed, T1 and T2 showed vegetables subjected to boiling for 10 and 15 minutes, T3 and T4 showed vegetable subjected to steaming for 10 and 15 minutes while T5 and T6 showed vegetables subjected to microwave cooking for 10 and 15 minutes.

Physicochemical Analysis

Color analysis

The color measurements of cooked vegetables were determined using ColorTec-PCMTM spectrophotometer (Accuracy Microsensors, Inc. Pittsford, New York, USA) method [17]. The color was expressed in terms of L*, a* and b*.

Texture analysis

Textural analyses of all the samples were determined using the texture analyzer (TA-XT2, Stable Microsystems, Surrey, UK) method [18].

Determination of ascorbic acid

Vegetables samples were assessed for evaluating the ascorbic acid content by the method of Association of Vitamin Chemists [19]. The blue color created by the reduction of 2,6-dichlorophenyl indophenols dye by ascorbic acid was recorded calorimetrically.

Determination of ß-carotene

Beta-carotene contents were analyzed by the spectrophotometer method [20]. In this method, 500-gram sample was taken in a pestle and mortar, grinded using acetone. Extraction procedure was repeated for 2-3 times. The extract was collected and subjected to filtration process. The filtrate was shifted to separating funnel and mixed with 10-15 mL of petroleum ether. The pigments were shifted into the petroleum ether phase. The staying period was given to separate the extract thoroughly. After staying time the bottom layer was drained off while top layer extract was collected into a 250 mL conical flask. The absorbance of the extract was estimated at 452nm by spectrophotometer.

Preparation of extract

Extract was prepared by mixing the 5 grams of each sample into 50 mL 80% methanol by using ultrasonic bath for 20 minutes. An aliquot (2 mL) of the extracts was ultracentrifugated for 15 minutes at 2200 rpm at room temperature. The clear extract solution was analyzed for the estimation of TPC, TFC and antioxidant activity.

Determination of total phenolic contents

The TPC of sample extract was estimated by using Folin- Ciocalteu’s reagent method [21]. In this method, 1 mL of extract was mixed with 9 mL of distilled water. Latterly, 1 mL of Folin-Ciocalteu’s phenol reagent was incorporated with extract. After time interval of 5 min, 10 mL of 7% Na2CO3 was incorporated. Final volume was made up to 25 mL with the incorporation of 4 mL of distilled water. After 90 min of incubation period at room temperature, the absorbance was recorded at 750 nm by using spectrophotometer. The total phenolics were stated as mg of gallic acid equivalents (GAE)/g fresh matter of vegetable (mg/g sample).

Determination of total flavonoids contents

The TFC of vegetables extract was estimated according to the aluminium chloride colorimetric method [22]. In this method, 1 mL of extract was added in 4 mL of distilled water and incorporated with 0.3 mL 5% NaNO2. 0.3 mL of 10% AlCl3 was mixed after time interval of 5 min. This mixture was agitated thoroughly with 2 mL of 1 M NaOH for 6 min. After it final volume of mixture was made up to 10 mL by distilled water incorporation. At wavelength of 510 nm, the reaction mixture absorbance was recorded. The findings were stated as mg of quercitin equivalent (QE)/g fresh matter of vegetable.

Determination of antioxidant activity (DPPH%)

The antioxidant activity of extract was estimated by adopting the spectrophotometer method [23]. In this method, 200 μL of extracts and 0.8 mL methanol was incorporated in 2 mL of 0.1 mM DPPH methanol solution. Then, final mixture was agitated systematically and placed in the dark place for 60 min at room temperature. The control was prepared by the incorporation of 2 mL of DPPH with 1 mL of methanol. Finally, absorbance was estimated at 517 nm. Percent inhibition was calculated by using the following formula;

Reduction in absorbance (%) = [Abs control - Abs sample / Abs control] × 100

Statistical Analysis

Statistical analysis was carried out by using two factor factorials under completely randomized Design (CRD) to determine the level of significance [24].

Results and Discussion

Color

Statistical results regarding color values of vegetables are presented in Table 1. Highest L* (lightness), a* (red color) and b* (yellow color) values were noticed in T5 after Tₒ followed by T6, T3 and T4. Lowest values were recorded in T2 and T1. The decreasing trend of L* a* and b* value in boiling cooking was observed due to the fact of degradation of chlorophyll pigments mainly in cabbage and carotenoid contents in carrot. The deteriorated effect of heat along with leach down effect of boiling cooking was the major reason of color lessening. α- and β- carotene contents collectively resolute the final color of cooked vegetables. However, such carotene compounds were identified as moderately heat sensitive. So, these compounds isomerize into numerous cis-isomers during cooking. The reduction in L*, a*, b* values observed in all treated vegetables which may be related to α- and β- carotene decrease and their isomerization [25]. Heat induces modifications on carotenoid pigment which results in color variation in vegetables. The results were parallel with the findings of Miglio [13], Nwanekezi [26] who noticed pronounced L*, a*, b* values in vegetables during different cooking methods.

97.27 ± 2.74f
Treatment L*-value a*-value b*-value Texture (N)
 Carrot
T0 57.50 ± 1.75a 33.57 ± 1.06a 42.41 ± 1.76a 151.82 ± 2.16a
T1 42.59 ± 1.17ef 13.63 ± 1.11de 29.64 ± 1.27c 122.48 ± 2.02e
T2 40.16 ± 1.47f 11.92 ± 1.04e 24.81 ± 1.51d 117.82 ± 2.26f
T3 48.50 ± 1.38cd 17.05 ± 1.11d 36.41 ± 1.20b 132.48 ± 2.02d
T4 45.83 ± 1.52de 14.67 ± 1.45de 32.19 ± 1.45c 126.15 ± 2.72e
T5 54.50 ± 1.75ab 26.17 ± 1.38b 41.81 ± 1.01a 142.82 ± 2.49c
T6 51.84 ± 1.62bc 22.28 ± 1.72c 38.55 ± 1.37ab 147.48 ± 2.74b
 Cabbage
T0 52.82 ± 1.55a -6.59 ± 0.06b 8.69 ± 0.43a 105.82 ± 2.50b
T1 35.47 ± 1.23e -1.64 ± 0.60a 5.36 ± 0.81de 67.48 ± 2.74f
T2 31.51 ± 1.11f -1.53 ± 0.55a 4.86 ± 0.60e 62.41 ± 3.00c
T3 41.83 ± 1.21cd -5.93 ± 0.53b 6.69 ± 0.51bcd 77.43 ± 2.01d
T4 39.68 ± 1.25d -5.73 ± 0.57b 6.09 ± 0.95cde 69.67 ± 0.78ab
T5 45.67 ± 1.08b -6.53 ± 0.97b 8.23 ± 0.39ab 93.15 ± 2.02f
T6 43.28 ± 1.04bc -6.13 ± 0.50b 7.90 ± 0.62abc

Table 1: Effects of different cooking methods on the physical characteristics of vegetables.

Texture

Different thermal cooking methods influence the texture attributes of vegetables. Firmness of cooked samples significantly decreased relative to the control sample. The statistical results are presented in Table 1. Highest shear force N (Newton) was taken by T6 after Tₒ followed by T5, T3 and T4. While the Lowest shear force was gained by T2 and T1. Cooking of vegetables triggered a decrease in the force required to shred the vegetable. Heat effect of cooking represents the decrease of softness and consequently softening of the vegetable internal and external structures. The findings of this study were covenant with Miglio [13], Maria [18] who studied the effect of microwaving and conventional cooking methods on nutrient profile and textural analysis of different vegetables (Table 1).

ß-Carotene content

Statistical values regarding ß-Carotene content are presented in Table 2. Highest β-carotene content was observed in T6 followed by T5, Tₒ, T1 and T2. Lowest β-carotene contents were determined in T4 and T3. Steaming caused major losses due to the oxidation of conjugate double bonds in β-carotene along with higher temperatures degradation. It was observed that heating triggered the both coloring pigment deprivation and an extractability upturn due to the breakdown of proteincarotenoid complexes: in the skin the first outcome prevailed as of the thinness of soft tissue, which permitted easy and fast heat transmission and results in extreme water leaching [27]. Results of beta carotenoid contents during the study of different cooking treatment in different vegetables were in similarity with the findings of some previous studies [13,20,28,29].

Vitamin C

Different cooking methods showed significant variation on vitamin C contents of vegetables. Statistical values of all treatments are presented in Table 2. The highest vitamin C contents were recorded in T5 after Tₒ followed by T6, T3 and T4. Unlike to that, maximum loss of vitamin C content was seen in T2 and T1. Consequently, microwaving did not far destroy the vitamin C as compared to boiling and steaming [30]. Boiling largely decreased the vitamin C content when vegetable was subjected for 15 minutes. In boiling cooking, decreasing trend of vitamin C occurred due to the oxidation of vitamin C in the presence of molecular oxygen initiated by inherent enzymes (vitamin C oxidase and peroxidase). The findings of this study regarding vitamin C concentrations were similar with Lee SK [31] who determined the ascorbic acid contents decreased in vegetables from 3.02 mg/100 g to 2.47 mg/100 g during different cooking methods. Lower content of vitamin C during cooking were also determined [20,28] (Table 2).

Treatment β – Carotene (mg/100g) VitaminC (mg/100g) β-Carotene (mg/100g) VitaminC (mg/100g)
Carrot Cabbage
T0 55.36 ± 2.88bc 30.56 ± 1.31a 1.63 ± 0.02b 18.11 ± 1.88a
T1 53.58 ± 2.05c 19.14 ± 0.22d 1.57 ± 0.01c 12.02 ± 1.42de
T2 51.66 ± 2.07c 18.18 ± 0.27d 1.54 ± 0.01cd 10.60 ± 1.87e
T3 47.56 ± 2.17d 26.11 ± 1.27bc 0.52 ± 0.03de 14.44 ± 1.34bc
T4 45.56 ± 2.78d 24.26 ± 1.52c 0.49 ± 0.01e 13.11 ± 1.27cd
T5 57.83 ± 1.63ab 29.21 ± 0.33ab 1.67 ± 0.03a 17.44 ± 0.37ab
T6 59.42 ± 1.06a 28.17 ± 1.90b 1.69 ± 0.01a 16.11 ± 0.51ab

Table 2: Effects of different cooking methods on the β – Carotene and Vitamin C contents of vegetables.

Total phenolic content

It is obvious from the results that the total phenolic contents were highly significantly affected due to the differences in cooking methods and different cooking time length. Statistical values regarding total phenolic content of vegetables are presented in Table 3. This indicated that the maximum TPC were recorded in T6 after Tₒ followed by T5, T3 and T4. The lowest TPC were observed in T1 and T2 in both vegetables. The total phenolic contents were effect significantly by the cooking methods and water contents. Low moisture contact results in lowest losses of total phenolic contents. Application of thermal treatment regulates firmness and break down of cellular structures with consequential discharge of these components into the hot water. The higher degree of softness was recorded for boiled samples, which clarifies the maximum loss of phenolic compounds in boiling as compared to steamed and microwave samples. The results were in conformity with the findings of Miglio [13] who observed that the TPC decreased in vegetables during different cooking methods. Changes of TPC during different cooking methods were also in conformity with the research findings of Hunter [30] and Ismail [32] showed that TPC decreased during different cooking methods. Our results of this study were also in matching with the conclusions of Sahlin [33].

Treatment TPC (mg GAE/100 g) TPC (mg GAE/150 g) TFC (mg QE/100g) DPPH%
Carrot
T0 13.55 ± 1.84a 5.79 ± 0.15a 73.67 ± 2.14a
T1 8.21 ± 1.03d 5.40 ± 0.21b 62.35 ± 2.57c
T2 7.96 ± 0.81d 5.04 ± 0.10c 56.42 ± 2.91d
T3 10.55 ± 1.28bc 5.32 ± 0.10b 69.15 ± 0.56b
T4 9.21 ± 1.06cd 4.94 ± 0.04c 64.82 ± 2.24c
T5 11.88 ± 1.01ab 4.01 ± 0.02d 70.16 ± 1.07b
T6 12.1 ± 1.06ab 3.97 ± 0.04d 72.01 ± 1.02ab
Cabbage
T0 16.70 ± 1.11a 10.91 ± 0.49a 64.10 ± 1.80a
T1 9.36 ± 0.52de 9.29 ± 0.15b 47.95 ± 1.92e
T2 8.03 ± 0.11e 8.18 ± 0.11c 44.10 ± 1.57f
T3 11.36 ± 1.04cd 8.42 ± 0.20c 55.67 ± 1.23c
T4 10.41 ± 0.58de 7.37 ± 0.04d 52.89 ± 1.00d
T5 13.04 ± 1.81ab 6.77 ± 0.18e 58.25 ± 1.41c
T6 15.63 ± 1.14bc 6.34 ± 0.19e 61.30 ± 1.80b

Table 3: Effects of different cooking methods on the TPC, TFC and DPPH% of vegetables.

Total flavonoid content

Cooking had both positive and negative influence on TFC depending on the kind of vegetables [34,35]. Statistical values regarding total flavonoid content of both vegetables are presented in Table 3. This indicated that the highest total flavonoid contents were recorded in T1 after Tₒ followed by T3, T2, T4, and T5. While the lowest total flavonoid contents were identified in T6. Decreasing trend of TFC in all cooking methods was due to the fact of food processing, like cutting action of the vegetable tissues and influence of employed temperatures. This can lead to cellular destruction and separation of some flavonoids compounds from cellular assemblies such as lignin and causing them to be highly extractable and freely identified [36]. The TFC was found to decrease highly in microwave cooking due to the application of dry heat, which leads to the maximum moisture reduction along with oxidation of volatile compounds in the presence of light and oxygen. Commonly, thermal actions have damaging influence on the flavonoid and phenolic compounds as they are extremely heat sensitive compounds [32]. The results were parallel with the findings of Khwairakpam B [20] who observed that the total flavonoid contents decreased in vegetables from 5.7 to 4.5mg QE/100g during different cooking methods.

Antioxidant activity (DPPH%)

Statistical values regarding antioxidant activity (DPPH%) of both vegetables are described in Table 3. This indicated that the maximum antioxidant activity (DPPH%) was observed in T6 after Tₒ followed by T5, T3, T4 and T1. While the lowest antioxidant activity (DPPH%) was observed in T2. The decreasing trend of antioxidant activity (DPPH%) was due to the fact of reduction and extractability of total phenolic compounds in cooking methods. No association was establish between TPC and antioxidant activity (DPPH%) in the study by Kahkonen MJ [37] on some vegetable extracts having phenolic contents. While the current study showed a strong correlation between phenolic contents and DPPH radical scavenging activity. antioxidant activity (DPPH%) was found to decrease by cooking irrespective of the leach down of high extent of total phenolic contents caused by thermal damage of cellular and sub-cellular compartment walls and radical exclusion by heat and chemical reaction. Overall microwave cooking was identified as an optimum method of cooking which resulted in highest DPPH% inhibition. The results were in accordance with the findings of Khwairakpam [20] who observed that the antioxidant activity increased from 11.20% to 13.75% during microwave cooking method. Changes of antioxidant activity during different cooking treatments were also in conformity with the findings of Faller ALK [38-40] (Table 3).

Conclusion

Certain nutrients are lost during processing of vegetables. Vegetables were cooked by boiling, steaming and microwave cooking methods. Physical characteristics of cooked vegetables were highly affected by all adopted cooking methods. Vitamin C, beta carotene, TPC, TFC and antioxidants activity (DPPH%) significantly decreased by thermal action of applied cooking methods along with longer time of cooking. Short time length of cooking significantly reduced the nutrient loss. Overall, microwave cooking method was recognized the optimum cooking method which resulted in highest retention of vegetables constituents. Consequently, it is suggested that cook the vegetables for short time up to just softening the tissue to improve their digestibility and reserve maximum nutritional profile.

Acknowledgement

I am so grateful to Dr. Moazzam Rafiq Khan for providing research material and keen guidance throughout the completion of research project.

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