Change in Quality of Brown Rice Packaged in Polymeric Films (1)Change in Quality of Brown Rice Packagedin Polymeric Films (1)- Prediction of Change of Germination Rate Yutaka ISHIKAWA*, Patcharee TUNGTRAKUL** , Toshiaki SHIMIZU*** ,Hidechika TOYOSHIMA*, Yoshinori HASEGAWA****and Takasuke ISHITANI** ***Germination rate is one of the quality-control indexes for brown rice. The effects of moisture content, temperature and storage time on the germination rate of brown rice were investigated and changes of germination rate during storage were predicted.
The relationship between the germination rate and time was expressed exponentially andthe time coefficient kept constant, independent of temperature and moisture content. The relationship between the germination rate and temperature was likewise expressed exponentiallyand the temperature coefficient kept constant, independent of moisture content. In the relationship between germination rate and moisture content, the germination rate decreased markedly
when the moisture content exceeded 15.5% and the exponential function was adapted. The germination rate was then expressed as a function of moisture content, storage temperature andsto rage time.
The mathematical model thus developed predicted the change in the rice germination rate
in storage at ordinary temperatures.
Keywords : Brown rice, Germination rate, Storage, Predictionb y r e s p i r a t i o n . 1 , 2 ) G e r mi n a t i o n r a t e i s u s e d
as an index for objectively evaluating quali-

1. Introduction
Prolonged brown rice storage must en su rethat physiological activity is appropriately
controlled and that the quality at harvest ismaintained. The negative correlation between brown rice germination and respiration rates suggested that decreased germination was caused by self-consumption inducedty. 3 , 4 ) The decrease of rice - seed germination depends on moisture content and storage te mp erature. 5 ) Many reports have dealt
q u a n t i t a t i v e l y w i t h h o w mo i s t u r e c o n t e n t ,temperature, and period of viability dependence relate to the germination rate.6,7,8) If
the moisture content and temperature of the*National Food Research Institute, Ministry of Agriculture, Forestry and Fisheries, Kannondai, Tsukuba, Ibaraki
3 0 5**Institute of Food Research and Product Development, Kasetsart University, Kasetsart, Bangkok 10903, Thailand***OKURA INDUSTRIAL CO. , LTD. , Nakatsu-cho, Marugame, Kagawa 7 6 3****Shikoku National Agricultural Experiment Station, Ministry of Agriculture, Forestry and Fisheries, Ikuno-cho,Zentsuji, Kagawa 765*****Tohoku National Agricultural Experiment Station, Ministry of Agriculture, Forestry and Fisheries, Akahira,Shimo-kuriyagawa,Iwate 0 2 0 - 0 1- 7 1 -J. Pack. Sci. Technol. Vol. 7 No. 2 (1997)

brown rice is known, it is possible to predict
the expected life of the rice.
Our objectiv es were to inv estig ate ho w
moisture content and temperature influenced
the germination rate and to develop amathematical model that predicted changes
in the ge rmi n a tion ra te .

within pouches was ambient air.

2.4 Germination rate
100 grains of rice were soaked in 1%
sodium hypochlorite solution for 30 minutes,
then washed 3-4 times using distilled waterand placed on wet filter paper in a petri dishat 20°C. The germination rate was measured

2. Materials and Methods
2.1

by counting the number of grains germinated within 7 days.

RiceBrown rice of the Ko shihikari v ariet y,japonica rice produced in Ibaraki prefecture,
Japan, was used. The rice was placed in ane nvi r on me n t al ch a mb er k ep t at 1 5 ° C an d
95% RH to set the moisture content at
16%, then transferred to the environmental
chamber kept at 21°C and 35% RH to dehumidify the moisture content below 16% ofsamples for this experiment. Thus, rice of
14.0, 14.5, 15.0, 15.5 and 16.0% moisture
content was prepared.

3. Results and Discussion
3.1 Storage time and germination rate
Changes in germination rate are shown in
Fig. 1. The germination rate was kept constant at 10°C, decreased slightly at 20°C, anddecreased greatly at 30°C, depending on themoisture content. Roberts 6 ) reported that acurve showing a frequency distribution of
the death points of individual seeds is asigmoid cumulative frequency-distribution.
And they confirmed that within the limits of2.2 Moisture content
Brown rice was crushed by a roller mill.
Moisture content of rice was measured by
the weight loss by drying at 135°C for 3
h o u r s . 9 )experi mental error the theoretical curves
provide a good fit to the experimental
data. 1 0 , 1 1 ) Their mathematical model, however, could not be predicted the viability ofrice stored at ordinary ambient temperature.
This was closely approximated by the following exponential function.

2.3 Packaging films and conditions
One hundred grams each of rice packaged
in low density polyethylene pouches 120 by
140 mm in size and 79.5 μm thick werestored in an environmental chamber at 10,20 or 30 °C fo r 6 mo nth s. The initial ga s

- 7 2 -

G= Go {exp(αt)- 1}+100
whereGt= germination rate (%)= storage time (months)(1)Change in Quality of Brown Rice Packaged in Polymeric Films (1)Fig. 1 Changes in rice germination rate(a) 10°C, (b) 20°C, (c) 30℃■1 4. 0 %, ● 1 4. 5 %, ▲ 1 5 . 0 %, ◆ 15. 5%, ▼ 16.0%

G０, α = coefficients
All approximate equations correlated wellwith experimental values. Coefficients G0and α were calculated by the least squares
method (Table 1). α remained almost constantly the same, independent of temperature and moisture content. G0 varied withtemperature and moisture content, however.
A time coefficient, α, of 0.55 was assumedby averaging.
temperature dependence in all samples, independent of moisture content.

3.2 Temperature and germination rate
Relationship between temperature andHikida et al. 1 2 ) reported that the relation-

germination rate after 6 months are shownin Fig. 2. Germination rate had markedly

ship between temperature and rice respiration rate closely fitted the Arrhenius' equa-declined under conditions of high temperature and moisture content, sho wing the sametion and Gore's equations. 1 3 ) The relation-

Table 1 Equation 1 coefficients obtained by least squares method

ture was also assumed to correlate highly because decreased germination was caused byship between germination rate and tempera-

self-consumption induced by respiration. 1 , 2 )Gore curve adapted to express the germination rate si mp l y is
100-G = G 1 ・exp (βT)

- 7 3 -(2)J. Pack. Sci. Technol. Vol. 7 No. 2 (1997)

whereTmination rate is expressed by the following= temperature (°C)

equation

G 1 , β = co efficien ts
Coefficients G １ and β were calculated by
the least squares method (Table 2). β re-:100-G = 3.79×10-9 - exp (1.42M) (3)wheremained almost constantly the same, indepen-

M = moisture content (%)

dent of mo isture content. G 1 va ried withA solid line (Fig. 3) calculated using

moisture content, however. A temperature

Equation 3 correlated well with experimen-coefficient, β, of 0.22 was assumed by avera g i n g .

tal data.

3.4 Germination rate as a function of time,
3.3 Moisture content and germination rate

temperature, and moismoisture content

Relationship between moisture content

In the relationship between moisture con-and rice germination rate stored at 20°C fortent and rice germination rate stored at 20°C

6 months are shown in Fig.3. Rice main-for 6 months expressed by Equ ation 3, G 1

tained a germination rate exceeding 60%,

was calculated as a function of moisture con-suggesting that rice stored at this temperature maintains a low respiration rate at atent by putting T 20 and equation 3 into

moisture content below 16%.

14)

The ger-equation 2, giving the following equation :100-G

4.54×10-11=・exp(1.42M)・exp(0.22T) (4)In the germination rate of rice stored for 6
months expressed by equation 4, G0 was
calculated as a function of temperature andmoisture content by putting t = 6 and equation 4 into equation 1, giving the following
equation:G = -1.78×10-12 ・exp(1.42M)
・exp (0.22T)・{exp(0.55t)-l}+100(5)In the relationship between the exp e r i me n t a l g e r mi n a t i o n r a t e a n d t h e v a l u e
calculated using equation 5 (Fig. 4), the highcorrelation coefficient of r = 0.975 suggested
that our mathematical model pre-- 7 4 -Change in Quality of Brown Rice Packaged in Polymeric Films (l)cisely predicted changes in the germination

mination rate stored at ordinary ambient

rate dur-ing storage.

temperature can be predicted precisely. Ourmathematical model was applicable over a

3.5 Verification

range of 12% to 17% moisture content. Ex-The validity of equation 5 was evaluated using rice stored at ordinary ambient tempera-

cessive low and high moisture content reportedly adversely affect germinationture from June ll for the ensuing 6 month.

activity 1 5 ) . Deterioration at a low moisture

Temperature change in storehouse arec o n t en t a p p e a r e d t o h a v e b e en c a u s e d b yelectrolyte leakage induced by loss of cellshown in Fig. 5. Temperature remained highuntil September and dropped markedly afterOctober.

m e mb r a n e i n t e g r i t y , 1 6 , 1 7 ) a n d d e t e r i o r a t i o n
at a high moisture content was presumably

The germination rate predicted by equa-

induced by microorganisms. 1 8 , 1 9 ) The mathe-tion 5 and experimental values (Fig. 6) de-matical model is not applicable under theseclined rapidly from month 1 to month 3 due

specific moisture content conditions.

t o h i g h s u m me r t e mp e r a t u r e s . T h e g o o d

Our mathematical model was applied only toagreement between the predicted and experimental values indicates that the rice ger-K o s h ih ik a ri r ic e. B eca u se re sp i ra ti o n r at e
and germination activity depend on the variety, coeffi cients in th e model presu mably
change with the variety 2 0 ) , so further experime n t a t i o n w i l l b e r e q u i r e d f o r p r e d i c t i n g
germination rates of different types of rice.
At this point, in any case, our mathematicalmodel can provide the optimum storage
temperature and moisture content based on
the tolerance limit of the germination rate.

- 7 5 -J. Pack. Sci. Technol. Vol. 7 No. 2 (1997)4.

( 1 9 6 0 ) .

Conclusion

7) W. V. Hukill, Proc. int. Seed Test.
T h e r i c e g e r mi n a t i o n r a te w a s e x p r e s s eda s a fun ction o f mo i stu re co n t en t , s to rag etemperature, and time. The mathematicalAss., 28, 871 (1963).
8 ) E . L . W a t s o n , Ca n . J . P l a n t S c i . , 5 0 ,107

(1970).

model we developed reliably predicted9) T. Nagahara and C. Tsutsumi, Rep.

changes in germination rate of rice stored atNatl. Food Res. Inst., 14, 77 (1959).

ordinary ambient temperatures. The math e-10) E. H. Roberts, Ann. Bot., 25, 381

matical model provides the optimum storage
temperature and moisture content based on
the tolerance limit of the germination rate.

( 1 9 6 1 ) .
ll) E. H. Robers and F. H. Abdalla, Ann.
Bot., 32, 97 (1968).

Mathematical model coefficients presumably

1 2 ) Y . H i k i d a , D . H . H a n a n d T . Ab e , J .

will change with the rice variety, and further

Jpn. Soc. Agric. Machin., 58 (2), 25

experimentation will be required for predict-( 1 9 9 6 ) .

ing germination rates of different types of13) S. Murata, K. Miyauchi and Y. Wang,J. Jpn. Soc. Agric. Machin., 55 (2), 69rice.

( 1 9 9 3 ) .

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