• Users Online: 335
  • Home
  • Print this page
  • Email this page
Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 


 
 Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 1  |  Issue : 1  |  Page : 16-20

Determination of Electrical Conductivity of Cadaver Skeletal Muscle: A Promising Method for the Estimation of Late Postmortem Interval


Department of Forensic Medicine, Forensic Medicine Institute, Henan University of Science and Technology, Henan, China

Date of Web Publication29-May-2015

Correspondence Address:
Yaonan Mo
Forensic Medicine Institute, Henan University of Science and Technology, No. 31 Anhui Road, Jianxi District, Luoyang, Henan 471003
China
Login to access the Email id

Source of Support: Basic & Frontier Study of Technology Project of Henan Province (Grant No. 112300410082), the Doctor Foundation and the Youngs’ Foundation of Henan University of Science and Technology (Grant No. 09001309, 13000914 and 13000696).., Conflict of Interest: None


DOI: 10.4103/2349-5014.155554

Rights and Permissions
  Abstract 

The electrical conductivity (EC) of extracted muscle fluid has been extensively used to evaluate meat freshness and shelf life in the field of food sanitation for decades. The opposite of freshness is the corruption that increases with time. Based on the freshness/corruption principle, we investigated the relationship between long postmortem intervals (PMIs) and EC in cadaver skeletal muscle. EC values of extracted fluid from rat muscles were measured at different PMIs for 10 days. The results indicate that there was a significant correlation between PMI and EC, and the data fit well to the cubic polynomial regression equation y = - 0.01x 3 + 0.264x 2 -13.657x + 1769.148 (R 2 = 0.925). In addition, the EC of different dilutions of these muscle extracts showed strict quadratic correlation (R 2 = 1) with the dilution ratios, suggesting that EC can be measured with very small quantities of muscle sample. Our study suggests that determination of the EC of cadaver skeletal muscle extracts may be a useful method for estimating long PMIs.

Keywords: Electrical conductivity, forensic science, muscle extraction liquid, muscle fluid extract, postmortem interval estimation


How to cite this article:
Xia Z, Zhai X, Liu B, Mo Y. Determination of Electrical Conductivity of Cadaver Skeletal Muscle: A Promising Method for the Estimation of Late Postmortem Interval. J Forensic Sci Med 2015;1:16-20

How to cite this URL:
Xia Z, Zhai X, Liu B, Mo Y. Determination of Electrical Conductivity of Cadaver Skeletal Muscle: A Promising Method for the Estimation of Late Postmortem Interval. J Forensic Sci Med [serial online] 2015 [cited 2019 Aug 26];1:16-20. Available from: http://www.jfsmonline.com/text.asp?2015/1/1/16/155554


  Introduction Top


Estimating the postmortem interval (PMI) is a major challenge for death investigations in forensic science. PMIs as used in forensic practice are usually based on postmortem changes, such as hypostasis, rigor mortis, rectal temperature, or different supravital reactions. [1] Although numerous studies have been conducted to develop more accurate methods, no single method can be used to accurately estimate PMIs, especially after long PMIs and in more extensively decomposed corpses. Due to the inherent limitations of preserving biological materials, there are still no practical and appropriate methods that can be used as prompt and accurate PMI estimators at crime scenes. [2]

Bodies undergo postmortem changes in several stages. The changes begin at the molecular level and sequentially progress to changes in microscopic and macroscopic morphologies. [3],[4] As bacteria grow in muscle tissues, their metabolic products, most of which are ionic, start to accumulate. [5] The decomposition of macromolecules such as proteins and DNA into smaller, charged molecules results in an effective increase in conductivity; thus, the electrical conductivity (EC) of cadaver muscle could provide a novel basis for estimating longer PMIs.

EC analysis is a rapid, relatively accurate, and economical method for estimating meat freshness for different kinds of animals and has been extensively used in the field of food sanitation for decades. [6],[7],[8] The opposite of freshness is the corruption that increases with time. However, few studies using EC have been reported in the field of forensic science. As there are great similarities between PMI estimation and meat shelflife evaluation which are both mainly dependent on degrees of protein decomposition caused by bacteria, we designed the present study in order to establish a method for estimating long PMIs.


  Materials and Methods Top


Forty-eight healthy Sprague-Dawley rats of either sex, weighing 260-380 g, were euthanized by cervical vertebrae dislocation. The cadavers were randomly divided into 16 groups of three rats each and kept at 19 ± 1°C. The muscles of the left lower hind limbs of the rats were removed at PMIs of 0 h, 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 48 h, 72 h, 96 h, 120 h, 144 h, 168 h, 192 h, 216 h, and 240 h. The muscles removed were immediately sent to the laboratory for EC testing.

The extracted muscle fluid was processed using the method described by Ekanem and Achinewhu, [9] with some modifications. Muscle in 5 g was homogenized with 50 mL of Mili-Q water and stirred while dynamic EC was determined in the liquid. The mixture was filtered until dynamic EC reached the maximum. The EC of extracted muscle fluid under the precisely controlled temperature of 25°C was measured with a conductivity meter (DDS-11A, Qiwei Instrument Co. Hangzhou, China). With PMI as the independent variable and EC at 25°C as the dependent variable, the data were evaluated by regression analysis ( SPSS version 13.0, IBM , Chicago, USA).

Temperature compensation coefficients (TCCs) were calculated for the same fluids at 20°C and 18°C using the formula α = (κt - κ25 )/[κ25 (t - 25)]. [10] TCCs in the groups at 20°C and 18°C were separately averaged and the results are indicated as α20 and α18 . All the EC values at 20°C and 18°C were compensated for using the formula κc = κt [1+ (25 - t)α] [10] ( Microsoft Office Excel 2007, Microsoft Corporation). Paired-sample t-tests were separately performed using EC values at 25°C and the compensated ones at 20°C and 18°C (SPSS version 13.0). The overlapping curves of all the uncompensated and compensated values at different PMIs were drawn using OriginLab OriginPro version 8 software (OriginLab Corporation, Massachusetts, USA).

Fluids extracted at 0 h, 120 h, and 240 h were separately diluted 5, 10, 30, 40, 50, 60, 70, 80, 90, and 100 times with ultrapure water and the EC was determined in each diluent. Regression curves between EC values and dilution ratios were drawn using OriginLab OriginPro version 8. With the dilution ratio as the independent variable and EC as the dependent variable, the data were evaluated by regression analysis (SPSS version 13.0).


  Results Top


EC values at 25°C at different PMIs

EC values at 25°C at different PMIs are shown in [Table 1]. The data were best fit to the cubic polynomial regression equation y = - 0.01x 3 + 0.264x 2 -13.657x + 1769.148 (R 2 = 0.925). The regression curve is shown in [Figure 1].
Figure 1: The regression curve between PMI and EC (25°C).

Click here to view
Table 1: EC (25°C, 20°C, and 18°C) at Different PMIs


Click here to view


EC values at 20°C and 18°C at different PMIs and TCCs

EC values at 20°C and 18°C are shown in [Table 2], and the EC values at 25°C are also included for comparison. These data show that EC values decreased as fluid temperature decreased. The averages of TCCs were α20 = 1.9912 percent per degree centigrade and α18 = 1.9791 percent per degree centigrade [Table 2]. For simplicity, the final TCC for all extracted fluids was determined to be α = 2.0 percent per degree centigrade.
Table 2: The TCCs


Click here to view


Compensated EC values at 20°C and 18°C are shown in [Table 3]. The paired-sample t-test results showed no significant differences between EC at 25°C and the compensated EC at 20°C and 18°C. Overlapping curves show good agreement between the data after compensating for the EC values at 20°C and 18°C [Figure 2] and [Figure 3].
Figure 2: The curves between PMI and EC (25°C, 20°C, and 18°C) with no temperature compensation.

Click here to view
Figure 3: The curves between PMI and EC (25°C, 20°C, and 18°C) with TCC 2 percent per degree centigrade.

Click here to view
Table 3: Compensated EC (20°C and 18°C) at Different PMIs


Click here to view


EC values of different dilution ratios

The experiments using different dilution ratios of the extracted muscle fluids indicated that the EC values decreased with increasing dilution factor [Table 4]. The curves between EC and different dilution ratios indicate that EC increased smoothly as the concentration of diluents increased [Figure 4]. Regression analysis revealed a strict quadratic correlation between relative concentration and EC values. The equations are y = - 208.19x 2 + 1096.694x + 5.402 (R 2 = 1), y = - 401.713x 2 + 1800.309x + 5.304 (R 2 = 1), and y = - 863.727x 2 + 2998.874x + 4.360 (R 2 = 1).
Figure 4: The tendency curves between EC and relative concentrations of multiple diluents.

Click here to view
Table 4: EC of Different Concentrations of Multiple Diluents


Click here to view



  Discussion Top


EC is used to measure how well a solution conducts electricity and has been widely employed in many fields such as food science, geology, [11],[12],[13] clinical medicine, [14],[15] and forensic environmental science. [16],[17] To the best of our knowledge, this is the first report showing the application of the EC of extracted muscle fluid to PMI estimation in forensic science.

Electrochemical studies have shown that the conductivity of an electrolyte solution is positively correlated with the temperature, with a significant increase by 1.5-5.0% per degree centigrade {Taghizade Mortezaee, 2014 #2}. To eliminate potential discrepancies caused by measuring EC at different temperatures, conductivity readings are commonly converted to the values at the same reference temperature, typically 25°C.

EC was used in our study because it reflects the total dissolved conductive substances from the cadaver muscle tissue. To simplify the study, EC values were measured with the extracted fluid maintained at 25°C. Our results show that EC values increased more significantly after a PMI of 24 h than within 24 h. For the first 24 h, the EC values showed no obvious change. However, EC started to increase slowly during the next 48 h, and rapidly from 72 h (day 3) to 192 h (day 8), after which it reached the peak value and plateaued. Rectal temperature has been considered a useful parameter for estimating short PMIs. Currently, there is no objective, accurate method for estimating long PMIs. Therefore, estimation of long PMIs in forensic practice is more challenging compared to short PMIs. We believe that measurement of the EC of cadaver skeletal muscle is likely to become a useful method for the estimation of long PMIs.

It is not only time-consuming but also unsatisfactory to control the temperature of the extracted fluids for prompt PMI estimation at the crime scene. Knowing the TCC makes it possible to determine EC at any temperature by merely adjusting the default TCC on conductivity meters; EC values in the present study were determined at 20°C and 18°C to acquire this important coefficient. Interestingly, the calculated coefficient was nearly identical to the default one (2 percent per degree centigrade) on the conductivity meter.

Estimating PMIs in forensic science is as important as evaluating meat freshness in food science. Some improvements in preparing the extracted muscle fluid were made on a method previously reported by Ekanem and Achinewhu. [9] Dynamic monitoring of EC was performed to save time and ensure that the conductive substances in the muscle were fully extracted in the water. In addition, to experimentally mimic situations in which PMIs are estimated using small amounts of cadaver tissue from bodies in more advanced stages of decomposition, we measured the EC values of different concentrations of diluted muscle extract. Our results indicate that EC can be determined in trace amounts of tissue sample and used to estimate PMI, if care is taken to maintain the precision of electronic EC meters.

EC has been mainly applied in the field of food sanitation to estimate the freshness and shelf life of meats such as fish, [6],[18] pork, [19],[20] beef, [21],[22] lamb, [23] and poultry, [24] . However, forensic PMI estimation involves multiple factors. Of these, environmental temperature has been identified as one of the most decisive factors in cadaver decomposition. [25] Further study is needed to measure the EC of human cadaver skeletal muscle to determine the correlation between the PMI and the EC at different temperatures.


  Conclusion Top


In conclusion, the determination of EC of cadaver skeletal muscle may be a useful method for the estimation of long PMIs.

 
  References Top

1.
Kaliszan M. Studies on time of death estimation in the early post mortem period - application of a method based on eyeball temperature measurement to human bodies. Leg Med (Tokyo) 2013;15:278-82.  Back to cited text no. 1
    
2.
Li ZQ1, Zuo WD, Zhang F, Li DR, Wang HJ. Latest progress in postmortem interval estimation. Fa Yi Xue Za Zhi 2012;28:287-92.  Back to cited text no. 2
    
3.
Hong H, Luo Y, Zhou Z, Shen H. Effects of low concentration of salt and sucrose on the quality of bighead carp (Aristichthys nobilis) fillets stored at 4°C. Food Chem 2012;133:102-7.  Back to cited text no. 3
    
4.
Lee S, Norman JM, Gunasekaran S, van Laack RL, Kim BC, Kauffman RG. Use of electrical conductivity to predict water-holding capacity in post-rigor pork. Meat Sci 2000;55:385-9.  Back to cited text no. 4
    
5.
Ekanem EO, Achinewhu SC. Effects of shucking method on opening, meat yield and selected quality parameters of west african clam, galatea paradoxa (born). J Food Process Preserv 2000;24:365-77.  Back to cited text no. 5
    
6.
Fan H, Luo Y, Yin X, Bao Y, Feng L. Biogenic amine and quality changes in lightly salt- and sugar-salted black carp (Mylopharyngodon piceus) fillets stored at 4°C. Food Chem 2014;159:20-8.  Back to cited text no. 6
    
7.
Zhang H, Taxipalati M, Que F, Feng F. Microstructure characterization of a food-grade U-type microemulsion system by differential scanning calorimetry and electrical conductivity techniques. Food Chem 2013;141:3050-5.  Back to cited text no. 7
    
8.
Fosgate GT, Petzer IM, Karzis J. Sensitivity and specificity of a hand-held milk electrical conductivity meter compared to the California mastitis test for mastitis in dairy cattle. Vet J 2013;196:98-102.  Back to cited text no. 8
    
9.
Ekanem EO, Achinewhu SC. Mortality and quality indices of live west african hard-shell clams (galatea paradoxa born) during wet and dry postharvest storage. J Food Process Preserv 2006;30:247-57.  Back to cited text no. 9
    
10.
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China. GB/T 11007-2008. Test method of electrolytic conductivity analyzers [S].  Back to cited text no. 10
    
11.
Sifré D, Gardés E, Massuyeau M, Hashim L, Hier-Majumder S, Gaillard F. Electrical conductivity during incipient melting in the oceanic low-velocity zone. Nature 2014;509:81-5.  Back to cited text no. 11
    
12.
Bachand PA, Bachand S, Fleck J, Anderson F, Windham-Myers L. Differentiating transpiration from evaporation in seasonal agricultural wetlands and the link to advective fluxes in the root zone. Sci Total Environ 2014;484:232-48.  Back to cited text no. 12
    
13.
Pozzo M, Davies C, Gubbins D, Alfè D. Thermal and electrical conductivity of iron at Earth's core conditions. Nature 2012;485:355-8.  Back to cited text no. 13
    
14.
Schaupp L, Feichtner F, Schaller-Ammann R, Mautner S, Ellmerer M, Pieber TR. Recirculation-a novel approach to quantify interstitial analytes in living tissue by combining a sensor with open-flow microperfusion. Anal Bioanal Chem 2014;406:549-54.  Back to cited text no. 14
    
15.
Grychtol B, Adler A. Choice of reconstructed tissue properties affects interpretation of lung EIT images. Physiol Meas 2014;35:1035-50.  Back to cited text no. 15
    
16.
Pringle JK, Jervis JR, Hansen JD, Jones GM, Cassidy NJ, Cassella JP. Geophysical monitoring of simulated clandestine graves using electrical and ground-penetrating radar methods: 0-3 years after burial. J Forensic Sci 2012;57:1467-86.  Back to cited text no. 16
    
17.
Praveena SM, Siraj SS, Aris AZ, Al-Bakri NM, Suleiman AK, Zainal AA. Assessment of tidal and anthropogenic impacts on coastal waters by exploratory data analysis: An example from port dickson, strait of Malacca, Malaysia. Environ Forensics 2013;14:146-54.  Back to cited text no. 17
    
18.
Yao L, Luo Y, Sun Y, Shen H. Establishment of kinetic models based on electrical conductivity and freshness indictors for the forecasting of crucian carp (Carassius carassius) freshness. J Food Eng 2011;107:147-51.  Back to cited text no. 18
    
19.
Van De Perre V, Ceustermans A, Leyten J, Geers R. The prevalence of PSE characteristics in pork and cooked ham-effects of season and lairage time. Meat sci 2010;86:391-7.  Back to cited text no. 19
    
20.
Popp J, Wicke M, Klein G, Krischek C. The relationship of pork longissimus muscle pH to mitochondrial respiratory activities, meat quality and muscle structure. Animal 2015;9:356-61.  Back to cited text no. 20
    
21.
Banach JK, ¯ywica R. The effect of electrical stimulation and freezing on electrical conductivity of beef trimmed at various times after slaughter. J Food Eng 2010;100:119-24.  Back to cited text no. 21
    
22.
Zeng J, Price GW, Arnold P. Evaluation of an aerobic composting process for the management of Specified Risk Materials (SRM). J Hazard Mater 2012;219-220:260-6.  Back to cited text no. 22
    
23.
Jandasek J, Milerski M, Lichovnikova M. Effect of sire breed on physico-chemical and sensory characteristics of lamb meat. Meat sci 2014;96:88-93.  Back to cited text no. 23
    
24.
Blacha I, Krischek C, Klein G. Influence of modified atmosphere packaging on meat quality parameters of turkey breast muscles. J Food Prot 2014;77:127-32.  Back to cited text no. 24
    
25.
Vass AA. The elusive universal post-mortem interval formula. Forensic Sci Int 2011;204:34-40.  Back to cited text no. 25
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

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


This article has been cited by
1 Are soil testate amoebae and diatoms useful for forensics?
Manfred Wanner,Elisa Betker,Satoshi Shimano,René Krawczynski
Forensic Science International. 2018; 289: 223
[Pubmed] | [DOI]



 

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
Materials and Me...
Results
Discussion
Conclusion
References
Article Figures
Article Tables

 Article Access Statistics
    Viewed2312    
    Printed141    
    Emailed1    
    PDF Downloaded424    
    Comments [Add]    
    Cited by others 1    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]