Printer Friendly

Effect of electromagnetic waves (cold pasteurization) on yolk liquid stored at different time on the logarithmic count of mesophilic aerobic bacteria.

Introduction

Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food. Pasteurization has two main purposes, a) General hygienic aspect, for providing safe food products by destroying all pathogen bacteria which may be dangerous for human's health. b) Storage quality aspect (improving foods storage quality). Also; Pasteurization inactivates some of undesirable enzymes, this method extends shelf life of liquid egg yolk around 7 days, 10 days, 14 days and even 16 days. It depends on relation between thermal processing temperature and length of time [23]. Pasteurization is defined as "a process of heating food for the purpose of killing harmful organisms such as bacteria, viruses, protozoa, molds, and yeasts." [15]. The process was named after its inventor, French scientist Louis Pasteur.

Pasteurization of egg product in USA was begun since 1926. The purpose of this operation was reduction and elimination of pathogenic bacteria. The first used instrumentals as Pasteurizer were very small and they were used as batch-type pasteurizers which they were operated above 60[degrees]C. After them plate-type high-temperature-short-time (HTST) pasteurizers were used. In Europe approximate 30 years ago liquid whole egg was successfully pasteurized in continue commercial instrumentals [22].

There are a number of techniques which are known for pasteurizing and processing liquid egg. The more popular approaches involve the use of conventional plate heat exchangers, steam infusion systems, or combinations of both. However, these techniques have limitations because of the physical nature of liquid egg. Plate heat exchangers are very popular in that they are very efficient and relatively simple to use. However, plate heat exchangers are limited in the amount of heat that they can convey to liquid eggs without causing irreparable harm such as undue coagulation, scorching, caking on the plate, and the like [20].

A process has been developed for the non-thermal treatment of liquid food products which results in a significant reduction in the microbial population, thus reducing spoilage and extending shelf life. The novel process involves the rapid application of electromagnetic energy (EME), such as microwave or radio frequency energy, and the simultaneous removal of any thermal energy which may be generated by the process through the use of circulating cooling medium and an efficient heat exchanger. Pasteurization, or controlled heat, has been a particularly beneficial treatment from a food safety standpoint and is now required for many liquid foods such as milk and fruit and vegetable juices [13].

In egg yolk because of low pH and higher solids content, Egg yolk is an excellent media for the growth and multiplication of bacteria and bacteria are able to grow faster than whole egg and albumen, so egg yolk pasteurization temperature must be higher than pasteurization temperature for egg and albumen [22].

Proteins are highly heat sensitive components of the egg. The functional properties like whipability, foamability, foam stability etc. which make the eggs an inevitable ingredient of various food products are severely affected by high temperatures. Also experimentally it is found that the egg yolk needs to be heated to a higher temperature than the albumen [3]. Since yolk pasteurization changes the amount of solid substances, it is effect on stability and resistance of the emulsifier, also in consequence of thermal process, proteins will be denaturised and formed disulfide bonds that will cause to release sulphur gas and make a bad smell [9].

Heating leads to death in foodstuff bacteria, either it is effect on aroma, flavour, texture and nutritional value of processed food. Among different methods of antisepticising of food, because of protection nutritional value of product, improve the quality of food and decrease of its cost that it is important for customer the non thermal methods which results in significant reduction in microbial count, and decreasing of spoilage and increasing shelf life of food products these methods have been received more attentions [8,10].

It is confirmed that microwave heating has some Enormous advantages in comparison with current method in reduction of process time and improving foods quality [25]. Because of the lack of essential information's about dielecterical properties of foodstuffs and also higher cost of equipments of the technology, it hasn't been industrialized, and therefore food industry has no desire to investment in this way [8].

This study examined the effect of cold pasteurization by electromagnetic waves (microwave) on liquid egg yolk and reduction of logarithmic amount of present aerobic mesophilic micro-organisms in samples, and compare it with current thermal methods (regular pasteurization).

Materials And Methods

Sample preparation:

Samples were selected from a fresh and healthy batch of egg and it was broken by egg breaker equipment, and was separated (yolk and white egg), was filtered (to separate crust and small particles) and was homogenized. These was performed by selecting fifty 100 g samples from 100kg liquid yolk randomly and they were filled in special poly ethylene bags automatically after filtering and they were stored at 0 to 4[degrees]C until experiments.

Instrumentals specifications:

Electromagnetic pasteurizer was used (model SCP150, Afra Sanat Kimia Mashhad co, Mashhad, Iran). This device was able to work in variety of temperature, times and frequencies.

Method:

Four Samples were selected randomly, then, one of them was retained as control sample and other three samples were treated under 3 frequencies (2950, 3950 and 4500 MHz). Each experiment replicate 10 times. Prepared packaged samples placed in the device chamber and it was set turn on and turn off magnetrons at specific times. It was considered 2 pulses, 6 sec ON and 8 sec OFF it means that the total exposure period was defined 12 sec and total procedure period was 20 sec. The storage time was defined according to avoid of egg yolk coagulation that it is the maximum time which 100 g liquid egg yolk could expose to electromagnetic waves at max 40[degrees]C without any damages or changes in its physical properties in comparison with fresh (control) sample. After setting pulses numerous and time switch the magnetron1 (frequency 1 ON and turn the system ON, and has taken out the sample, after the set time has finished and system turned OFF, second and third samples exposure to higher frequency by defined method respectively, then all samples treated under the same pasteurization method. In this method temperature of product center was below 40[degrees]C. Also egg yolk liquid samples were pasteurized at 65[degrees]C by regular pasteurizer and then automatically filled in airproof packages by filler and placed in refrigeration room. Then samples transferred to laboratory for cultivation with culture medium of plate count agar in 2 repeat, and cultivated in 30[degrees]C for 72 hours according to national standard NO. 5272, and Total Aerobic Mesophilic Count (TAMC) were determined. Results were compared with those which they are as control and thermal treated samples. After that treated samples which stored in suitable condition (0[degrees]C to 4[degrees]C) for 1, 3, 5, 8, 10, 15 days for studying the effect of storage time on TAMC, then cultivated and TAMC was determined again. Results were compared with permitted total count of mesophilic bacteria's in pasteurized egg, with consider to Iranian national standard (13248) [11,12].

Statistical analysis:

Each treatment was analyzed as randomized complete block design with ten replications and the data were assessed by analysis of variance (ANOVA) and Duncan s multiple range test using MSTAT-C software program. Differences among treatments were tested with least significant difference (LSD) test (P<0.05). Besides, correlation analyses were preformed to clarify the relations among parameters considered in this study. Microsoft Excel 2007 was used to plot apparent.

Results And Discussion

Effect of different electromagnetic frequencies (microwave) and different storage time on logarithmic count of aerobic mesophilic bacteria:

In this research, effect of three frequencies (2950 MHz, 3950 MHz and 4500 MHZ) was studied in 12 sec constant operation time on reduction of aerobic mesophilic bacteria in egg yolk liquid. Results showed that pasteurization by electromagnetic waves had reduced count of aerobic mesophilic bacteria in egg yolk liquid at least 0.30 to 0.46 logarithmic cycles instantly after cold pasteurization in compare with control samples. Microwaves can be used to raise the temperature of in-shell eggs to the required pasteurization temperature in minutes. It is also a proven fact that microwave enhances the thermal destruction of microbes [24].

Microwaves have the ability to generate heat from within the substance that is exposed to it. Theoretical mathematical studies have shown that even though albumen exhibits better dielectric properties than yolk, the egg's curvature has a focusing effect which leads to a suitable power distribution [2]. The shell egg appears ideally suited for pasteurization in a microwave environment [4,18].

The results confirmed with results of kozempel et al. [13] which reported microwave energy has a significant effect on reduction of microbial population in egg yolk liquid [13]. Results also agreed with results of Dev et al. [3] which showed, in this study, microwave heating has been considered for in-shell egg pasteurization. First of all, the effects of temperature (0-62[degrees]) and frequency (200 MHz to 10 GHz) on the dielectric properties of egg components were investigated. Laboratory trials on microwave heating of in-shell eggs indicated that the heating rates of both albumen and yolk were similar. Therefore, microwave heating appeared perfectly suited for in-shell egg pasteurization [3].

According to results, that obtained from statistical analyzes, effect of adding frequency variants (P<0.05) and pasteurized product durability (P<0.01) on reduction of total aerobic mesophilic count in liquid egg yolk in a level was 0.05 (95% probability) and it was statistically significant, but no interaction was observed between studied variants in cold pasteurization process. Storage time which was studied up to 15 days has a higher effect on TAMC than various frequencies applied during so the value of increasing TAMC was higher than reduction of it during yolk liquid pasteurization process by different electromagnetic waves.

Comparing averages of three types frequencies was used in liquid egg yolk cold pasteurization and reduction of TAMC, showed that killing ability of waves has decreased by increasing frequency from 2950 MHz to 3950 MHz, and then by increasing frequency to 4500 MHz efficiency of electromagnetic method in reduction of microbial population in pasteurized product significantly increased (figure. 1). As shown in figure 1, minimum TAMC was in samples which treated by frequency 4500 MHz that it was 3.68 cfu/mL, that a reduction was found around 1.2 logarithmic cycles in comparison with control samples were occurred. The least lethal effect was in 3950 MHz that it has a decline around 0.97 logarithmic cycles comparing with control sample. Lethal ability of microbial population at 2950 MHz frequency was medium, however it was better than 3950 MHz frequency (by reduction around 1.1 logarithmic cycles) but it was not statistically significant.

Therefore it has been confirmed that in a way of better functionality and higher Lethal ability frequencies can show with this order: 3950 MHz <2950 MHz <4500 MHz which it had confirmed by result of Tang et al. (2002) that it showed 2450 MHz frequency is better than 915 MHz frequency in pasteurization and sterilization, and higher frequencies will increase killing effects (Tang et. al.,2002), but 3950 was an exception which it has a lower killing effects. Lakinz et al., [14]succeeded to decrease salmonella population from 100000 per gram to 100 per gram [14].

Results show that by increasing storage time of pasteurized product from 0 days to 15 days, TAMC rise rapidly, depend on intensity of treatments, increased by different growth rates (figure. 2). TAMC immediately after pasteurization by 4500 MHz was 3.17 cfu/mL and went up to 4.38 cfu/mL in 15th day. TAMC instantly after pasteurization (zero time) for 2950 MHz and 3950 MHz was 3.27 cfu/mL and 3.33 cfu/mL, respectively which in 15th day it reached 4.42 cfu/mL and 4.50 cfu/mL respectively. This agreed with Sevcan et. al. Studies on variation in dielectric Content of fresh egg in storage period and relation of it with egg freshness and either confirming that e' (dielectric properties rate) and e" (dielectric lose factor rate) in egg yolk, will increase during storage [21].

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Comparison Between Liquid Egg Yolk Cold Pasteurization, Electromagnetic Method And Pasteurization By Thermal Treatment:

Results showed that in zero time (immediately after treatment), thermal pasteurization can decline TAMC around 0.52 and pasteurization by electromagnetic method can decrease TAMC nearly 0.3 to 0.46 logarithmic cycle comparing with initial Control samples (Table 1). Thermal pasteurization method was more effective in destroying bacteria in comparison with cold pasteurization in zero time, but because of high advantages of non thermal methods, this difference is connive. Therefore, results of this study, confirmed different studies, include Goldblith and wang [7], Mudgett [16] and Fujikawa et al. [6] welt et al. [28] showed that there isn't a significant difference between microwave heating and regular heating [7,16,6,28].

Results generally showed that both treatment, include thermal and electromagnetic have significantly decreased microbial amount in comparison with blank samples, and this difference was observed during product storage days. According to results, cold pasteurization by electromagnetic waves decreased mesophilic bacteria population more than regular methods, especially during storage days, product which had been treated by waves, had less increasing microbial amount (figure. 3). As it could be observed, even worst electromagnetic treatment (in 3950 MHz) has better worked in comparison with thermal treatment (thermal treatment<3950 MHz<2950 MHz<4500 MHz).

Results of this research showed that usage of both heat and waves could have stronger effect on lethal factor that it confirmed Kozmpel et al. which demonstrated that microwave energy may complete or strength thermal effects [13]. Such that Sanvo co. (2010) used microwave method combine with 65[degrees]C heating and claimed that this methods very quickly and total time of operations is only a part of second and product heated to only coagulation and coacolation point and consequently the product was completely like fresh egg. This process decreases total amount of bacteria 10 times more than regular pasteurization methods. Studies showed that the method will protect egg functional properties 20% more than regular methods [1]. In different studies have severally referred to damages to egg yolk physical and functional properties in temperatures above 60[degrees], for instance Wang et al. [27] showed that thermal denaturation was affected by dielectric properties and polar compounds in egg, and these changes (higher loss coefficient) occur in temperatures higher than 60[degrees]C which is effective on egg yolk functional properties and results in losing some of this properties [27]. Therefore insignificant differences in killing rate in zero time (immediately after processing) in using method in this study (pasteurization by waves) and regular method (thermal method) is not important. There are significant reduction in process time which is important in results of other studies, also in this study confirmed total time of process is only 20 sec that it is very short comparing with 120 sec time of thermal pasteurization. Tang and others [25] Showed that it is possible to reduction packaged food pasteurization time from 1.1 to 1.4 in compared with regular methods [26]. In comparison with regular methods for heating foodstuffs, pasteurization by microwave potentially could improve organoleptic properties, appearance and nutritional value. Ohlson [17] reported that very short time length in microwave process causes to producing a product with very higher grade and quality comparing with products obtained from regular heating methods [17]. Also David Reznik [20] showed that there are many obstacles in egg pasteurization because of its unique properties. Because of these contortions and according to trading practical respects, yolk liquid thermal pasteurization is very difficult [20].

During storage time minimum amount of aerobic mesophilic bacteria was determined in samples treated by waves and since first day it was observed that increased amount of aerobic mesophlic bacteria in thermal treatment. It was much higher than treatments by waves (Table 1) for example in 4500 MHz frequency logarithmic number of bacteria increased from 3.17 at the first moment after process to 4.38 in 15th day,(i.e it has increased 1.21 logarithmic cycle), whereas in thermal treatment from 3.11 immediately after process reached to 4.99 in 15th day (i.e. it has increased 1,88 logarithmic cycle). As it has shown in figure 3, logarithmic number of bacteria in 4500 frequency which was equal to 3.68 cfu/mL during storage days as it showed reduction around 1.2 logarithmic cycles in comparison with control sample. Minimum killing effect was in 3950 MHz which had a reduction around 0.97 logarithmic cycles. Killing effect of 2950 MHz was halfway and it was almost 1.1 logarithmic cycles and in thermal treated samples, total aerobic mesophilic bacteria was equal to 4 cfu/mL and killing effect was around 0.74 logarithmic cycle. Results showed that, however thermal pasteurization was better on destroying bacteria than cold pasteurization at the first time, microbial amount increase more rapidly during storage time.

3.3. Determination pasteurized sample's storage time according to Iranian national standard limit

Microwave energy inactivates micro-organisms through thermal kill. It also has the potential to cause biological damage as well as alteration of the cell membrane and metabolic functions. This injurious effect on the living organisms may very well induce additional lethality and impaired recovery from injuries by them during the subsequent time period of product storage [10].

Maximum authorized logarithmic amount of liquid egg pasteurized mesophilic bacteria at 0[degrees]C--4[degrees]C is 4.47cfu/mL and it was defined 30000 pcs/mL according to Iranian national standard. At the end of third day, results showed that logarithmic amount of mesophilic bacteria in control samples (nonpasteurized) is 4.72 cfu/mL (Table 1). Therefore, maximum storage time of non-pasteurized liquid egg is two days. At the end of 8th day, results confirmed that total aerobic mesophilic count in thermal treated samples is 4.45 cfu/mL (Table 1). Therefore, maximum storage time of liquid egg pasteurising by regular thermal method is 7 days. At the end of 15th day results showed that number of aerobic mesophilic bacteria in cold pasteurized samples is 4.38- 4.5 cfu/mL (Table 1). Therefore, maximum storage time of liquid egg which pasteurized by waves method is 14 days. Finally it was observed that the rate of increasing total aerobic mesophilic count in product that was pasteurized by this method (cold pasteurization in electromagnetic method) was much slower than regular thermal method. Therefore results of the study, confirmed Sanvo co. reports (2010) that invented commercial system for using waves in egg pasteurization, and announced that pasteurization by waves can increase eggs shelf life and protect its functional properties [1]. Tang et al. [25] in Washington university by similar studies on bean showed that the product was processed by microwave had better color and taste than those pasteurizing by regular method in cans and shelf life of sterile product by microwave will increase [25].

Consequently, shelf life of pasteurized liquid egg yolk in electromagnetic method defined maximum 14 days which is more ideal comparing with shelf life of it in regular methods, 7 days, and control sample (non-pasteurized yolk liquid), 2 days.

[FIGURE 3 OMITTED]

Conclusion:

Liquid egg yolk cold pasteurization significantly decreased total aerobic mesophilic count of samples. Therefore this method can be used in liquid egg yolk manufacturing industry. Meanwhile present obstacles in use pasteurized yolk liquid in the country (because of changes in quality and functional properties comparing with fresh egg) will be eliminated and like other modern countries in the world, national legal organizations can persist on obligation of using pasteurized liquid egg in egg consumer units. Because raw egg consumption that includes a huge risk, will reduce in products such as mayonnaise sauce and therefore could effect on the usage of chemical preservative substances in these products. Also it was observed that product shelf life in this method has increased two times comparing with regular thermal method. It shows that in spite of initial amount of vegetative bacteria in regular thermal method was lower at the first time, it wasn't able to terminate bacteria spores equal to wave method, that this is very important for consumers and makes higher assurance for shopping and storage of product.

Acknowledgment

The authors are grateful staff of Narin co. for their helpful cooperative during this project. Special thanks to Dear Dr Khabazi as their helpful guides.

References

[1.] Colavitti, R. and E. Christoffer, 2010. there's more to shelf life than pasteurization. www.thornico.com/Sanovo-Technology-Group

[2.] Datta, A., G. Sumnu and G.S.V. Raghavan, 2005. Dielectric Properties of Foods. In Engineering Properties of Foods, edited by M. A. Rao and A. Datta. Boca Raton Florida: Taylor & Francis Publications.

[3.] Dev, S.R.S., G.S.V. Raghavan and Y. Gariepy, 2008. Dielectric properties of egg components and microwave heating for in shell pasteurization of eggs. Journal of Food Engineering., 86: 207-214.

[4.] Fleischman, G.J., 2004. Microwave pasteurization of shell eggs. In IFT Annual Meeting Las Vegas, USA: IFT.

[5.] Food & Drug Administration of Iran., 2009. Recipe of egg liquid pasteurization production.

[6.] Fujikawa, H., H. Ushioda and Kudo, 1992. Kinetics of Escherichia coli destruction by microwave irradiation. Journal of Appl Environ Microbiol., 58(3): 920-924.

[7.] Goldblith, S.A., and D.I.C. Wang, 1967. Effect of microwaves on Escherichia coli and Bacillus subtilis. Journal of Appl Microbiol., 15(6): 1371-1375.

[8.] Hasan zade, A, 2008. Application of electromagnetic in food pasteurization &sterilization" 18th National congress on food Technology, Mashhad Iran.

[9.] Hanson, H., L. Belle Lowe and G. Stewart, 1974. Pasteurization of Liquid Egg Products. Journal of Poult. Sci., 26(3): 277-283.

[10.] Huang, F., 1989. Method of treating liquid egg and egg white with microwave energy to increase refrigerated shelf life. -US Patent4853238

[11.] Institute of Iran Standard and Industrial Researches, Microbiology of food and animal feeding stuffs--Horizontal method for the enumeration of microorganisms--Colony count technique at 30[degrees]C, 2007. Standard no. of 5272, 1st revision

[12.] Institute of Iran Standard and Industrial Researches, Pasteurized Liquid Egg-Specifications and Test methods, 2010. Standard no. of 13248, 1st revision

[13.] Kozempel, M. Goldberg, NeilCook. Dallmer, Richar and Dallmer, Michael, 1999. Nonthermal energy treatment for the reduction of microbial population in liquid food products--US Patent., 5,962,054.

[14.] Lakins, D.G., C.Z. Alvarado, L.D. Thompson, M.T. Brashears, J.C. Brooks and M. Brashears, 2008. "Reduction of Salmonella Enteritidis in Shell Eggs Using Directional Microwave Technology". Journal of Poult. Sci., 87(5): 985-991.

[15.] Lewis, M.J., and J.H. Neil, 2000. Continuous Thermal Processing of Foods: Pasteurization and UHT Sterilization. Edited by M. J. Lewis and N. J. Heppell, Food Engineering Series Malden, MA, USA: Blackwell Publishing.

[16.] Mudgett, R.E. and H.G. Schwartzberg, 1982. "Microwave food processing: Pasteurization and sterilization" A review. AIChE Symposium Series vole., 78(218): 1-11.

[17.] Ohlsson, T., 1987. "Sterilization of foods by microwaves". Presented at Int" Sem. New Trends in Aseptic Processing and Packaging of Foodstuffs, 20: 22-23.

[18.] Rehkopf, A., 2005. Quality validation of a microwave-pasteurization process for shelleggs.

[19.] Paper read at IFT Annual Meeting, at New Orleans, Lousiana.

[20.] Reznik, D. and A. Knipper, 1997. "Method for rapidly cooling liquid egg"--US Patent., 5,670,198.

[21.] Unluturk, S., M.R. Atilgan, A.H. Baysal and C. Tari, 2008. "Use of UV-C radiation as a nonthermal process for (LEP) liquid egg product", Journal of Food Engineering, 85(4): 561-568.

[22.] Stadelman, W.J and J. Owen, 1995. "egg science and technology". Egg productes pasteurization. 4(12): 289-315.

[23.] Schlegel, W., 1992. "Commercial pasteurization and sterilization of food products using microwave technology". Journal of Food Technology, 46(12): 62-63.

[24.] Tajchakavit, S., 1997. "Microwave heating of fruit juices : kinetics of enzyme inactivation/microbial destruction and evaluation of enhanced thermal effects Bioresource Egg", McGill University, Ste Anne de Bellevue.

[25.] Tang, J., F. Hao and M. Lau, 2002. "Microwave heating in food processing" Department of Biological Systems Engineering, Washington State University Pullman, WA 99164-6120, USA2002; ch1:1-44

[26.] Tang, J., G. Mikhaylenko and J. Simunovic, 2003. "Microwave Sterilization Technology" Department of Food, Bioprocessing and Nutrition Sciences at North Carolina State University in Raleigh, NC

[27.] Wang, J., J. Tang, Y. Wang, B. Swanson, 2009. "Dielectric properties of egg whites and whole eggs as in uenced by thermal Treatments". Journal of LWT -Food Science and Technology, 42(7): 1204 -12.

[28.] Welt, B.A., J.A. Steet, C.H. Tong, J.L. Rossen, D.B. Lund, 1993. "Utilization of Microwaves in the Study of Reaction Kinetics in Liquid and Semisolid Media". Journal of Biotechnology Progress, 9(5): 481-487.

[1] F. Lotfian, [1] M. Hashemiravan, [2] E. Jahed, [2] M.H. Haddad Khodaparast, A. Mousavi Khaneghah [3]

(1) Department of Food Science and Technology, Islamic Azad University, Varamin-Pishva Branch, Iran

(2) Department of Food Science and Technology, Ferdowsi University, Mashhad, Iran

(3) Department of Food Engineering, Middle East University, Ankara, Turkey

Corresponding Author

Fahimeh Lotfian, Department of Food Science and Technology, Islamic Azad University, Varamin-Pishva Branch, Iran E-mail: nazi_lotfian@yahoo.com
Table 1: Average aerobic mesophilic bacteria's population, under
different treatments and different storage days

Blank     Heat      4500MHz   3950MHz   2950MHz   Storage day
        treatment

3/63      3/11       3/17      3/33      3/27          0
4/3       3/55       3/25      3/38      3/34          1
4/72      3/75       3/49      3/59      3/55          2
4/92      4/12       3/66      3/77      3/71          3
5/07      4/45       3/87         4      3/93          8
5/24      4/69       3/97      4/10         4         10
5/96      4/99       4/38       4/5      4/42         15
COPYRIGHT 2012 American-Eurasian Network for Scientific Information
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2012 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Original Article
Author:Lotfian, F.; Hashemiravan, M.; Jahed, E.; Khodaparast, M.H. Haddad; Khaneghah, A. Mousavi
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAN
Date:Feb 1, 2012
Words:4326
Previous Article:Enhancing yield and nitrogen use efficiency of Brassica napus L. using an integrated fertilizer management.
Next Article:The chemical composition of flower lipids of Cordia sebestina.
Topics:

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters