• Users Online: 98
  • Print this page
  • Email this page


 
 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 7  |  Issue : 2  |  Page : 97-104

First-order kinetic study-based comparative shelf-life assessment of Raw Vetas (Salix alba L. stem bark) and Vetas Ghana (a semisolid form of Salix alba L. stem bark aqueous extract)


1 Department of Chemistry, Central Ayurveda Research Institute, Jhansi, Uttar Pradesh, India
2 Department of Microbiology, Central Ayurveda Research Institute, Jhansi, Uttar Pradesh, India
3 Department of Ayurveda, Central Ayurveda Research Institute, Jhansi, Uttar Pradesh, India
4 Department of Chemistry, Central Council for Research in Ayurvedic Sciences, New Delhi, India
5 Department of Ayurveda, Central Council for Research in Ayurvedic Sciences, New Delhi, India

Date of Submission24-Jan-2022
Date of Acceptance06-Feb-2022
Date of Web Publication14-Sep-2022

Correspondence Address:
Dr. Vijay Kumar
Department of Chemistry, Central Ayurveda Research Institute, Jhansi 284003, Uttar Pradesh
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdras.jdras_10_22

Rights and Permissions
  Abstract 

BACKGROUND: Shelf-life is an important aspect of raw as well as finished drugs. Recently, shelf-life parameters have been included in the Ayurvedic Pharmacopeia of India (API). The aim of this study to evaluate the comparative long-term shelf-life study of Raw Vetas (Salix alba stem bark) and Vetas Ghana (a semisolid form of Salix alba Stem bark aqueous extract). METHODS: A stability chamber with environmental conditions 30°C ± 2°C/60% RH ± 5% was used for the long-term shelf-life study of Raw Vetas and Vetas Ghana. Physicochemical parameters like loss on drying, pH, total ash, acid insoluble ash, water extractive value, and alcohol extractive value were evaluated at a regular frequency (0th, 3rd, 6th, 9th, and 12th months). RESULTS: There are significant changes that have been observed w.r.t. physicochemical parameters analysis. Physicochemical parameters revealed that the shelf-life of Raw Vetas ranged from 31 to 66 months and the shelf-life of Vetas Ghana ranged from 38 to 62 months. CONCLUSIONS: The average shelf-life of Raw Vetas and Vetas Ghana was 41.83 and 47.50 months, respectively. This study may help to understand the shelf-life of various Ayurvedic formulations consisting of Raw Vetas and Vetas Ghana.

Keywords: API, Salix alba, shelf-life, Vetas, Vetas Ghana


How to cite this article:
Verma R, Jain V, Rawat H, Kushwaha V, Gandhi Y, Mishra SK, Kumar V, Tandon S, Charde V, Jagtap C, Babu G, Singh A, Singh R, Sharma BS, Srikanth N. First-order kinetic study-based comparative shelf-life assessment of Raw Vetas (Salix alba L. stem bark) and Vetas Ghana (a semisolid form of Salix alba L. stem bark aqueous extract). J Drug Res Ayurvedic Sci 2022;7:97-104

How to cite this URL:
Verma R, Jain V, Rawat H, Kushwaha V, Gandhi Y, Mishra SK, Kumar V, Tandon S, Charde V, Jagtap C, Babu G, Singh A, Singh R, Sharma BS, Srikanth N. First-order kinetic study-based comparative shelf-life assessment of Raw Vetas (Salix alba L. stem bark) and Vetas Ghana (a semisolid form of Salix alba L. stem bark aqueous extract). J Drug Res Ayurvedic Sci [serial online] 2022 [cited 2023 Mar 28];7:97-104. Available from: http://www.jdrasccras.com/text.asp?2022/7/2/97/356049

Ravi Verma, Vipin Jain, Hemant Rawat, Vikram Kushwaha, Yashika Gandhi, Sujeet K. Mishra, Vijay Kumar, Smriti Tandon, Vaibhav Charde, Chandrashekar Jagtap; Equal contribution





  Introduction Top


Salix alba L. is a medicinal plant widely used in the treatment of musculoskeletal and inflammation-related diseases.[1],[2],[3] In Ayurveda, the stem bark of Salix alba L. is considered to be a medicinally important part. In Ayurveda, Salix alba L. is known as Vetas and a semisolid form of Salix alba (Stem bark) aqueous extract is known as Vetas Ghana (VG). VG is an intermediate or precursor of various Ayurvedic formulations.[4] The phytochemicals like salicin, isosalicin, salicylic acid, catechin, epicatechins are the major constituents of Salix alba L. responsible for biological activities including anti-obesity, anti-migraine, anti-inflammation, cardiovascular potency, antioxidant, anti-acetylcholinesterase, anti-rheumatoid arthritis, anti-cancer, etc.[5],[6],[7],[8],[9],[10]

Shelf-life is termed as Virya, which means the potency of any drug.[11] Shelf-life and expiry date are different concepts, but these terms are interrelated to each other. Expiry of any drug depends upon the shelf-life of the product. In classical literature, it is in practice since the twentieth century AD.[11] To maintain the safety regulations, International Conference on Harmonisation (ICH) has issued the shelf-life guidelines.[12],[13],[14],[15],[16],[17] Recently, in 2016, the Indian government amended Drugs and Cosmetics (Amendment) Rules, 1940 to meet the international standards and shelf life of various dosage forms used in Ayurveda have been introduced in the regulatory provisions for ASU drugs.[18] The basic parameters for shelf-life studies included in API were evaluation of physicochemical parameters and biological testing. The examination of shelf-life of traditional or herbal drugs is a tedious and cumbersome job. The Shelf-life of a polyherbal formulation (tablet (vati), and powder (churna) consisting of more than three ingredients may depend on various factors. One contaminated ingredient, having contamination such as microbial load, aflatoxins, pesticide residues, or heavy metal, may spoil the whole formulation. Microbial contaminations (microbial load or aflatoxins) exert a prime effect on the shelf-life of herbal drugs. Environmental factors including temperature and humidity, storage, handling, and transportation play a vital role in the shelf-life of any product.[19],[20],[21],[22]

There is no report on the shelf-life study of Vetas and VG available yet which is the aim of this study. The aim of this study was to evaluate the comparative long-term shelf-life study of Raw Vetas (RV) (Salix alba stem bark) and VG (a semisolid form of Salix alba Stem bark aqueous extract).


  Experimental Top


Materials and methods

Standards of metal ions lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) of analytical grade and purity >98% were purchased from Merck Ltd India. Agar (MacConkey, Bismuth sulfite, Mannitol Salt, and Soyabean casein) and standard chloramphenicol were of AR grade purchased from HiMedia. The microorganisms with MTCC numbers were purchased from CSIR – Institute of Microbial Technology Chandigarh, India. The authentic material of RV (Salix alba L. stem bark) was collected from Kashmir, India by the Botanist of Kashmir University (Herbarium Number: 3160-KASH). VG was prepared in the in-house pharmacy of Central Ayurveda Research Institute Jhansi.

Long term shelf-life studies

The dried RV and VG samples were packed in seal packs in December 2020 and were kept in food grade HDPE containers. The containers were placed in a stability chamber for long term shelf-life studies at 30°C ± 2°C/65% RH ± 5% RH.[14] A control sample was kept in a deep freezer at 0°C.

Quality control parameters assessment

Quality control parameters like loss on drying (LOD), pH, total ash, acid insoluble ash, water extractive value, and ethanol extractive value were performed at a regular frequency (0th, 3rd, 6th, 9th, and 12th months) as per the protocols mentioned under the API.[23],[24],[25]

Kinetic analysis

The results of quality control parameters were fitted in first-order kinetic model =by plotting log Ct vs. time (t) and a straight line was observed. The differential and integrated rate law for first-order-kinetics is represented by





The 10% degradation time, t0.9 (where Ct = 0.9C0) was calculated from the first-order integrated rate law. The equation for time required for 10% decomposition is as follows:





The rate constant (kobs) is the slope obtained from the linear plot of log Ct vs. time (t).

Safety and toxicological parameter analysis

Heavy metal analysis

Heavy metals like lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As) were analyzed by using the inductively coupled plasma-optical emission spectrometry (ICP-OES) instrument (Agilent 5800, USA). The samples were digested by using an automatic microwave sample digestor (Microwave 130000 Multiwave GO Plus 50Hz).

Microbial load, specific pathogens

Microbial assay like microbial load and specific pathogens (Aspergillus niger,  Escherichia More Details coli, Pseudomonas aeruginosa,  Salmonella More Details typhi, and Staphylococcus aureus) were analyzed as per protocols mentioned in API and were found to be within limits.

Pesticides residues analysis and Aflatoxin analysis

The analysis of aflatoxins (B1, B2, G1, and G2) and pesticide residues (organochlorine, organophosphate, and pyrethroid pesticides) were carried by Delhi Test House, Delhi. The gas chromatography tandem mass spectrometry (GC-MS/MS) based QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure was used to analyze the pesticides residues.[26] The quantification of aflatoxins was done by using the high-performance liquid chromatography (HPLC) method.[21]


  Results and Discussion Top


The results of the long-term shelf-life study of RV and VG are mentioned in [Table 1] and shown in [Figure 1]. [Figure 1] shows that, in RV, after 12 months, pH, LOD, water extractive value (WEV), ethanol extractive value (EEV), total ash (TA), and acid insoluble ash (AIA) were changed by 4.34%, 8.69%, 8.59%, 7.66%, 6.77%, and 9.43%, respectively. In the case of VG, after 12 months, 6.16%, 7.96%. 4.70%, 8.25%, 6.57%, and 5.13% changes were noticed for pH, LOD, WEV, EEV, TA, and AIA parameters. After 12 months, significant changes (at P < 0.001) were observed as compared to the initial day (0th month) results.
Table 1: Shelf-life data of raw Vetas (RV) and Vetas Ghana (VG)

Click here to view
Figure 1: % change in parameters of Raw Vetas (RV) and Vetas Ghana (VG) with time (months) (LOD = loss on drying, WEV = water extractive value, EEV = ethanol extractive value, TA = total ash, AIA = acid insoluble ash)

Click here to view


The toxicity and safety parameters of RV and VG were analyzed and have been mentioned under [Table 2] and [Table 3]. The microbial load (cfu/g) w.r.t. total bacterial count (TBC) and total fungal count (TFC) was increased as compared to initial day (0th month) results [Table 2]. The observed TBC values for RV and VG changed from 112 to 436 cfu/g and from 32 to 387 cfu/g, respectively. Similarly, TFC values for RV and VG changed from 123 to 311cfu/g and from 21 to 287cfu/g, respectively. Specific pathogens viz. A. niger, E. coli, Salmonella, S. aureus, and P. aeruginosa were not observed in RV and VG samples throughout the examination period, that is, from 0th to 12th month. The aforementioned results were quite within limits as per prescribed limits of API as well as the World Health Organization (WHO). The observed results for aflatoxins B1, B2, G1, and G2 were well within tolerance limits as none of the aflatoxin was detected in the whole period of shelf-life analysis [Table 2]. The analysis for heavy metals and pesticides residues were done at the initial day (0th month) where no pesticide residues and heavy metals were detected [Table 4]. The analysis of pesticide residues and heavy metals was carried out as numerous reports on heavy metal toxicity and pesticides contaminations of herbs or raw drugs have been published till date.[21],[22],[27],[28] In this study, RV was collected from natural resources and that might be the reason that there is no heavy metal toxicity and pesticides residue detected in RV.
Table 2: Microbial load and test for specific pathogens in Raw Vetas (RV) and Vetas Ghana (VG)

Click here to view
Table 3: Pesticides residues and heavy metals in Raw Vetas (RV) and Vetas Ghana (VG)

Click here to view
Table 4: Kinetics study data of Raw Vetas (RV) and Vetas Ghana (VG)

Click here to view


Kinetic results of the shelf-life study are tabulated under [Table 4] and shown in [Figure 2]. Various kinetic models were applied to the obtained data and finally, first-order kinetics was found to be the most suited where linear plot of log Ct vs time (t) with regression coefficient r2 > 0.95 was observed [Figure 2]. The shelf-life period w.r.t. 10% degradation was calculated. The shelf-life period of RV w.r.t. LOD, pH, WEV, EEV, TA, and AIA parameters was calculated to be 34, 66, 35, 39, 46 and 31 months, respectively. Similarly, shelf-life period of VG w.r.t. LOD, pH, WEV, EEV, TA, and AIA parameters was calculated to be 39, 44, 62, 38, 44 and 58 months, respectively.
Figure 2: Linearity plot log (Ct) vs. time (t in months) of shelf-life data of Raw Vetas (RV) and Vetas Ghana (VG) (LOD = loss on drying, WEV = water extractive value, EEV = ethanol extractive value, TA = total ash, AIA = acid-insoluble ash)

Click here to view


Recently, a number of studies on the shelf-life study of herbal drugs have been reported by few researchers, which shows the keenness of scientific community on herbal drugs shelf-life study. Few shelf-life reports on Ayurvedic drugs like churna, avaleha, ghrita, kwath churna, and herbo-minerals have been reported.[21],[24-26],[29–35] It has been observed that herbal or polyherbal drugs contain a wide class of phytochemicals and act as good inhibitors for microbes and aflatoxins.[21],[24-26],[29-35] For the better understanding of shelf-life, the terms like “true shelf life,” “estimated shelf life,” “supported shelf life,” “maximum shelf life,” and “labelled shelf life” have been well mentioned in literature.[36] Few researchers have experimentally claimed that shelf-life and expiry are even more than 10 years as labelled shelf-life.[37] This shows that potency of drug does not depend upon a single parameter or single phytochemical. The average shelf-life of RV and VG was found to be 41.83 and 47.50 months, respectively. The lower shelf-life of RV as compared to VG might be due to preparation of VG in controlled conditions. VG was prepared in pharmacy and packed for shelf-life study whereas RV was used as collected from natural resources. Stem bark sample of RV might contain high moisture content and high microbial load which attributes to lower shelf-life period. To obtain the highest level of homogeneity in results and global acceptance of herbal drug, it is important to follow the same methodology as prescribed by ICH[38] and followed by Govt. of India. For the better understanding of shelf-life of herbal drugs, the shelf-life of raw drugs and intermediate is an importance aspect that needs to be covered by researchers while performing their shelf-life study experiments.


  Conclusions Top


This is the first kinetics-based shelf-life study where an Ayurvedic raw drug and its intermediate was assessed. Overall, first-order kinetic model was fitted to shelf-life experiments of RV and VG. Good linearity was maintained with r2 more than 0.95. The average shelf-life of RV and VG was found to be 41.83 and 47.50 months, respectively. This study may help to understand the shelf-life of various Ayurvedic formulations consisting of RV and VG.

Acknowledgement

DG-CCRAS is highly acknowledged for funding and facilities at CARI, Jhansi (Uttar Pradesh). RARI, Jammu is highly acknowledged to collect Salix alba L. stem bark sample from Kashmir University.

Financial support and sponsorship

This work was supported by the CCRAS, Ministry of Ayush under IMR Project.

Conflicts of interest

There are no conflicts of interest.

Ethics approval and consent to participate

Not applicable.





 
  References Top

1.
Mukladaa H, Davidovich-Rikanati R, Wilkerson DG, Klein JD Genotypic diversity in willow (Salix spp.) is associated with chemical and morphological polymorphism, suggesting human-assisted dissemination in the Eastern Mediterranean. Biochem Systemat Ecol 2020;91:104081.  Back to cited text no. 1
    
2.
Tawfeek N, Mahmoud MF, Hamdan DI, Sobeh M, Farrag N, Wink M, et al. Phytochemistry, pharmacology and medicinal uses of plants of the genus salix: An updated review. Front Pharmacol 2021;12:593856.  Back to cited text no. 2
    
3.
Piatczak E, Dybowska M, Płuciennik E, Kosla K, Kolniak-Ostek J, Kalinowska-Lis U Identification and accumulation of phenolic compounds in the leaves and bark of salix alba (L.) and their biological potential. Biomolecules 2020;10:1391.   Back to cited text no. 3
    
4.
Anonymous. Ayurvedic Formulary of India. Part I to II. New Delhi, India: Ministry of Health and Family Welfare, Government of India; 2007.  Back to cited text no. 4
    
5.
Zaiter A, Becker L, Petit J, Zimmer D Antioxidant and antiacetylcholinesterase activities of different granulometric classes of Salix alba (L.) bark powders. Powder Technol 2016;301:649-56.   Back to cited text no. 5
    
6.
Lavola A, Maukonen M, Julkunen-Tiitto R Variability in the composition of phenolic compounds in winter-dormant salix pyrolifolia in relation to plant part and age. Phytochemistry 2018;153:102-10.  Back to cited text no. 6
    
7.
di Giacomo V, Ferrante C, Ronci M, Cataldi A, Di Valerio V, Rapino M, et al. Multiple pharmacological and toxicological investigations on tanacetum parthenium and Salix alba extracts: Focus on potential application as anti-migraine agents. Food Chem Toxicol 2019;133:110783.  Back to cited text no. 7
    
8.
Dou J, Heinonen J, Vuorinen T, Xu C, Sainio T Chromatographic recovery and purification of natural phytochemicals from underappreciated willow bark water extracts. Sep Purif Technol 2021;261:118247.   Back to cited text no. 8
    
9.
Ingemarsson A, Nilsson M, Pedersen JR, Olsson JO Slow pyrolysis of willow (Salix) studied with GC/MS and GC/FTIR/FID. Chemosphere 1999;39:103-12.  Back to cited text no. 9
    
10.
Harbourne N, Marete E, Jacquier JC, O’Riordan D Effect of drying methods on the phenolic constituents of meadowsweet (Filipendulaulmaria) and willow (Salix alba). LWT– Food Sci Technol 2009;42:1468-73.  Back to cited text no. 10
    
11.
Bansal G, Kaur J, Suthar N, Kaur S, Negi RS Stability testing issues and test parameters for herbal medicinal products. In: BajajS, SinghS, editors. Methods for Stability Testing of Pharmaceuticals. New York: Springer; 2018. p. 307e33.  Back to cited text no. 11
    
12.
Anonymous. The Ayurvedic Pharmacopeia of India, Part-I. 2nd ed. New Delhi: Ministry of Health and Family Welfare, Department of AYUSH, Government of India; 2003. p. 119.  Back to cited text no. 12
    
13.
Anonymous. The Ayurvedic Pharmacopeia of India, Part-II (Formulations), Volume I, 1st ed. New Delhi: Ministry of Health and Family Welfare, Department of AYUSH, Government of India; 2007. p. 79-89.  Back to cited text no. 13
    
14.
Anonymous. ICH Harmonised Tripartite Guideline. Stability Testing of New Drug Substances and Products–Q1A (R2). 2003. Available from: https://www.ich.org/page/quality-guidelines. [Last accessed on 19 Dec 2021].  Back to cited text no. 14
    
15.
EMEA. Reflection paper on stability testing of herbal medicinal products and traditional herbal medicinal products. United Kingdom: European Medicines Agency; 2010.  Back to cited text no. 15
    
16.
WHO. Global Atlas of Traditional, Complementary and Alternative Medicine. Vols. 1 and 2. Geneva: World Health Organization; 2005.  Back to cited text no. 16
    
17.
EMEA. Guidelines on Quality of Herbal Medicinal Products/Traditional Medicinal Products. EMEA/CVMP/814OO Review. London: European Agency for the Evaluation of Medicinal Products (EMEA); 2005.  Back to cited text no. 17
    
18.
Anonymous. Drugs and Cosmetics (8th amendment) Rules. New Delhi: Ministry of Health and Family Welfare, Govt of India; 2016.  Back to cited text no. 18
    
19.
Singh BK, Tiwari S, Maurya A, Nawal SK, Dubey K Fungal and mycotoxin contamination of herbal raw materials and their protection by nanoencapsulated Essential oils. Biocatal Agric Biotechnol 2022;39:102257.  Back to cited text no. 19
    
20.
Han TY, Yang Z, Yu C, Xing JJ Effect of acidity regulators on the shelf life, quality, and physicochemical characteristics of fresh wet noodles. J cereal Sci 2022;103:103409.  Back to cited text no. 20
    
21.
Muller P, Basedow T Aflatoxin contamination of pods of Indian Cassia senna L. (Caesalpinaceae) before harvest, during drying and in storage: Reasons and possible methods of reduction. J Stored Prod Res 2007;43:323-9.  Back to cited text no. 21
    
22.
Donsingha S, Assatarakul K Kinetics model of microbial degradation by UV radiation and shelf life of coconut water. Food Control 2018;92:162-8.  Back to cited text no. 22
    
23.
Kaur J, Bansal G WHO prescribed shelf life assessment of Syzygium Cumini extract through chromatographic and biological activity analyses. J Ayurveda Integr Med 2020;11:294-300.  Back to cited text no. 23
    
24.
Gurav NS, Gurav SS, Sakharwade SN Studies on ashwagandha ghrita with reference to murcchana process and storage conditions. J Ayurveda Integr Med 2020;11:243-9.  Back to cited text no. 24
    
25.
Verma P, Galib, Patgiri B, Prajapati PK Shelf-life evaluation of rasayana churna: A preliminary study. Ayu 2014;35:184-6.  Back to cited text no. 25
    
26.
Beneta A, Pavlović DM, Periša I, Petrović M Multiresidue GC-MS/MS pesticide analysis for evaluation of tea and herbal infusion safety. Int J Environ Anal Chem 2018;98:987-1004.  Back to cited text no. 26
    
27.
Kumar V, Singh S, Singh S, Datta S, Dhanjal DS, Singh J Methods and techniques for the chemical profiling and quality control of natural products and natural product-derived drugs. In: SinghJ, MeshramV, GuptaM, editors. Bioactive Natural Products in Drug Discovery. Singapore: Springer; 2020. p. 585-98.  Back to cited text no. 27
    
28.
Kumar V, Singh S, Singh A, Subhose V, Prakash O Assessment of heavy metal ions, essential metal ions, and antioxidant properties of the most common herbal drugs in Indian Ayurvedic hospital: For ensuring quality assurance of certain ayurvedic drugs. Biocatal Agric Biotechnol 2019;18:101018.  Back to cited text no. 28
    
29.
Prajapati DKD, Ruknuddin G, Bedarkar P, Patgiri B, Prajapati PK Shelf life evaluation of shirishavaleha and its granules: A preliminary study J Drug Res Ayurvedic Sci 2019;4:159-66.  Back to cited text no. 29
    
30.
Khemuka N, Galib R, Patgiri BJ, Prajapati PK Shelf-life evaluation of kaṃsaharītakī avaleha and its granules: A preliminary study. Anc Sci Life 2015;35:96-100.  Back to cited text no. 30
    
31.
Unnikrishnan V, Nishteshwar K, Patel BR Shelf life evaluation of Hridya Yoga Churna. Pharmacogn J 2016;8:234-8.  Back to cited text no. 31
    
32.
Shweta M, Shivshankar R, Galib, Vaghela DB Shelf life evaluation of Laghu Sutashekhara rasa: A preliminary assessment. J Ayurveda Integr Med 2020;11:213-6.  Back to cited text no. 32
    
33.
Bhushan S, Yadav KD, Chaudhary A Anti-aflatoxin and anti-oxidant activity of Sahaj vati: A novel herbomineral formulation as shelf-life enhancer. J Ayurveda Integr Med 2018;9:S18.  Back to cited text no. 33
    
34.
Chung KT, Wong TY, Wei CI, Huang YW, Lin Y Tannins and human health: A review. Crit Rev Food Sci Nutr 1998;38:421-64.  Back to cited text no. 34
    
35.
Prosena H, Pendry B Determination of shelf life of Chelidonium majus, Sambucus nigra, Thymus vulgaris and Thymus serpyllum herbal tinctures by various stability-indicating tests. Phytochem Lett 2016;6:311-23.  Back to cited text no. 35
    
36.
Capen R, Christopher D, Forenzo P, Ireland C, Liu O, Lyapustina S, et al. On the shelf life of pharmaceutical products. AAPS Pharmscitech 2012;13:911-8.  Back to cited text no. 36
    
37.
Gikonyo D, Gikonyo A, Luvayo D, Ponoth P Drug expiry debate: The myth and the reality. Afr Health Sci 2019;19:2737-9.  Back to cited text no. 37
    
38.
Kim JH, Lee K, Jerng UM, Choi G Global comparison of stability testing parameters and testing methods for finished herbal products. Evid Based Complement Alternat Med 2019;2019:7348929.  Back to cited text no. 38
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

 
  In this article
Abstract
Introduction
Experimental
Results and Disc...
Conclusions
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed504    
    Printed28    
    Emailed0    
    PDF Downloaded107    
    Comments [Add]    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]