Study on radiation preservation of frozen egg liquid

Li Fengmeia,*, Gu Yongbaoa, Chen Dianhuab

aInstitute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875, People's Republic of ChinabChina Isotope and Radiation Association, P.O. Box 2102(30), Beijing 100822, People's Republic of China

Abstract

In this paper the preservation process of g-irradiated frozen egg liquid has been studied. It shows that the proper

absorbed dose is 2 kGy and there is no signi®cant di�erence in nutrient components, vitamins content between theirradiated frozen egg liquid and the control. A study of a diet including g-irradiated frozen egg liquid was carriedout with 58 volunteers who, during a 70-day test, indicated that the frozen egg liquid exposed to radiation is

hygienic and safe. # 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Frozen egg liquid; g-Irradiation; Trial diet for human body; Health safety

1. Introduction

Studies on killing microorganisms and controlling

its growth in food by irradiation started in 1940s.Until 1995, 224 kinds of irradiated food have been

approved in 38 countries (FAO, IAEA, WHO, 1995).At present the sterile standard for eggs and egg pro-

ducts has been approved only in Croatia, France,

Mexico, South Africa, while studies on preservationof frozen egg liquid exposed to radiation has not

been reported. The traditional preservation method ofspecial processed frozen egg liquid is high tempera-

ture pasteurization. In order to control microorgan-

isms in frozen egg liquid and keep its physicalproperty and nutrients without change, the frozen egg

liquid was exposed to 60Co g rays under frozen con-dition. The experiment shows that this process is feas-

ible and safe for food process.

2. Material and method

2.1. Sample preparation

10 kg of frozen egg liquid was supplied by Beijing

Egg Process Factory. The egg liquid was rapidly frozento ÿ308C and stored at temperature of ÿ158C. Theinner packing material was polyethylene plastic bagand the outer packing was a 20 � 20 � 30 m card-

board box.

2.2. Bacterium test

Samples were taken at random (more than 3samples). The test was carried out for inspection oftotal number of bacterium, the number of bacillus coli

and pathogenic bacteria for frozen egg liquid beforeand after irradiation in accordance with the nationalTest Method of Food Hygiene (P.R.C.).

2.3. D10 determination of bacillus coli

Samples were prepared with a bacteria concentration

Radiation Physics and Chemistry 57 (2000) 341±343

0969-806X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PII: S0969-806X(99 )00401-6

www.elsevier.com/locate/radphyschem

* Corresponding author. Tel.: +86-10-62208246; fax: +86-

10-62231765.

E-mail address: wuyug@sun.ihep.ac.cn (L. Fengmei).

of 13 � 108 cfu/ml, which were exposed to radiation atvarious doses; the survival bacteria number was deter-

mined, a dose±survival cure was drawn. The relativecoe�cient and D10 value were obtained by means of lin-ear regression (Wang Weiguo et al., 1988).

2.4. Irradiation

60Co g-ray source with a source strength 3700 TBq

was used. Absorbed dose rate was 40 Gy/min. Sampleswere kept at a temperature of ÿ158C and irradiationwas carried out at temperatures less than 158C. Thesamples were irradiated from both sides by g-rays.

2.5. The absorbed dose determination

The absorbed dose was determined by using alanine/ESR and glucose/ESR dosimeters and FWT-60 radio-chromic dye ®lms. The calibration between alanine/ESRand IAEA standard dosimeter has been carried out

(Wang Weiguo et al., 1989).

2.6. Nutrients

1. Water: dry method.2. Total protein: Kartal nitrogen determination method.3. Total lipid: acid hydrolysis.

4. Fatty acid: gas chromatography (Shimadzu GC-9Achromatograph).

5. Amino acid: high-pressure liquid chromatograph(HITACHI 835-50) Amino Acid Auto-Analyzer.

2.7. Diet test

In this test, each volunteer had lunch with food con-taining 100 g frozen egg liquid. The physiological index,peripheral blood, all cell count, chromosome, biochemi-

cal and endocrine index were then determined.

3. Results and discussion

3.1. Contamination of frozen egg liquid and irradiationresistance of bacillus coli

In various seasons 53 samples in 6 batches were

taken. The tests showed that bacillus coli is a major ir-

Table 1

Initial test results of contaminated samples

Batch Sample no. Total number of bacteria (cfu/g) Bacteria coli number (cfu/100 g) Pathogenic bacteria

1 10 1 � 104±8 � 104 103±105 Not found

2 9 44 � 103±9 � 104 104±105 Not found

3 9 1 � 104±1 � 105 103±106 Not found

4 5 1 � 104±8 � 104 102±105 Not found

5 15 1 � 104±38 � 103 103±105 Not found

6 5 1 � 104±3 � 104 104±105 Not found

Table 2

Relationship between bacteria coli survival number and dose

D (absorbed dose kGy) 0 0.3 0.6 0.9 1.2 1.5 2.0 2.5

N (bacteria coli survival number/ml) 13 � 108 33 � 107 22 � 106 11 � 105 26 � 104 26 � 102 10 3

Table 3

Pre-pasteurization Post-pasteurization

Total bacteria number (cfu/g) < 106 < 5000

Bacillus coli number (cfu/100 g) < 1.1 � 107 < 1100

Pathogenic bacteria Not found Not found

Li Fengmei et al. / Radiation Physics and Chemistry 57 (2000) 341±343342

radiation resistance bacteria in the contaminated bac-teria in frozen egg liquid; the highest number of con-taminated bacteria is 106 cfu/100 g. The total number

of bacteria was 1 � 105 cfu/g (Table 1). There was nopathogenic bacterium. D10 of the bacteria coli in con-taminated egg liquid was obtained from data shown inTable 2. The correlation between absorbed dose D and

the bacteria survival number N is as follows:D=A+BlogN, then co-relation coe�cient is obtained:r= 0.989, A= 24.56, B=ÿ1.120, D10=0.258 kGy.

3.2. Absorbed dose

In accordance with national hygiene standards, theacceptable bacterial number in the frozen egg liquidbefore and after pasteurization is as shown in Table 3.D=D10logN/N0 N0=initial contaminated number,

N= survival bacteria number (Wang Weiguo et al.,1989). It is usually assumed that pasteurization can beachieved by irradiation with 4D10 value. If irradiation

is conducted with 8D10, the sterile e�ect will beenhanced greatly. Therefore, it is safer and healthier toconduct irradiation with 8D10, the best absorption

doses, i.e. 8 � 0.258=2 kGy.When the absorbed dose is equal to 2 kGy, not only

can be met sterile requirements fully but also the irra-

diated frozen egg liquid at this dose can be stored atÿ158C for 2 years without variation in hygiene level.

3.3. Control of absorbed dose

A 5-mm thick Plexiglas box, the size of which wasexactly as large as that containing frozen egg liquid

(20 � 20 � 30 cm) was killed with trash ice. Dosemeters were also placed at six points on the plane pas-sing through the central line. On each point, three

kinds of dose meter were placed, two for each kind.

The results demonstrate that irradiation is evenly dis-tributed and the relative deviation is <2%. The mini-

mum distribution zone of irradiation was located atthe center.

3.4. Nutrients

Experiments demonstrate that there is no signi®cantdi�erence in contents of nutrients, 18 kinds of amino-acids, Vitamin A, B1, B2 carotene, viscosity between

the un-irradiated frozen egg liquid and that irradiatedat a dose of 2 kGy (Wang Weiguo et al., 1990) (Table4).

3.5. Diet test

Diet tests were conducted in 58 healthy volunteersfor 70 days (Zhou Mei et al., 1990). Among these vol-unteers 31 were male, 27 female and the age range was

from 18 to 42 years old. The volunteers were randomlydivided into two groups: test and control. The resultsdemonstrate that the health of the tested volunteers is

good and there is no signi®cant di�erence between thetest and the control group. The irradiated food can beaccepted and there is no harmful e�ect on appetite,body weight, physiological, biochemical, endocrine and

chromosome indexes of the volunteers.The above mentioned tests demonstrate that frozen

egg liquid exposed to radiation of 2 kGy is a healthy

and safe food.

References

FAO, IAEA, WHO, 1995. Published on 25 September.

Wang Weiguo, et al., 1988. The e�ect of irradiation on

Beijing roast duck. Radiat. Phys. Chem. 32, 747±749.

Wang Weiguo, et al., 1989. Irradiation preservation study on

Beijing roast duck by low dose. Radiat. Res. Radiat.

Process. 7, 51±56.

Wang Weiguo, et al., 1990. The e�ect of irradiation on

Beijing roast duck. In: Seminar on Food Irradiation

Development in China, pp. 107±113.

Zhou Mei, et al., 1990. A study on irradiated frozen duck and

egg liquid as a human diet. In: Seminar on Food

Irradiation Development in China, pp. 203±209.

Table 4

Nutrients of frozen egg liquid

Sample Lipid Protein Water

Control 13.01 13.71 70.92

Irradiation (kGy) 13.12 14.11 70.65

Li Fengmei et al. / Radiation Physics and Chemistry 57 (2000) 341±343 343