Effects of Drying and Frying Process on Characteristics of Popped Rice

Effects of Drying and Frying Process on Characteristics of Popped Rice
Samatcha Phanitcharoen, Anon Maliket and Prasong Siriwongwilaichat*
Department of Food Technology, Faculty of Engineering and Industrial Technology, Silpakorn University,
Amphur Mueng, Nakhon Pathom 73000 *Email: deersong1@yahoo.com

Abstract


The objective of this study was to investigate the effect of drying time and frying
time on the characteristics of popped rice to be used as ingredient base for snack bar. The
broken sticky rice was steam-cooked before drying at 65 oC for 2,3 and 4 hours. The
popped rice was prepared by deep fat frying dried rice at 210 oC for 5, 10 and 15 seconds.
The product quality was evaluated for moisture content, water activity, color, texture and
sensory perceptions. It was found that the drying time significantly effected the product
color (p<0.05). However, the effect of frying time on final product quality was not
significant at a given drying time (p>0.05). The color of fried product obtained from
cooked broken sticky rice dried for 2 hours was significantly lighter than that dried for 3
and 4 hours. The hardness of product measured as peak compression force increased with
increasing drying time. Sensory evaluation indicated that the product obtained from drying
cooked sticky rice for 3 hours, followed by deep fat frying for 10 seconds was the most
acceptable.

Keywords: Popped rice snack, Drying, Frying, Textural characteristics

Introduction


Sticky rice is produced and widely consumed in Thailand. Nevertheless, the
broken sticky rice has not been fully developed to value added products. Popped rice is
one of the most well known puffed snacks in Thailand. It could be also used as an
ingredient base for various snack bars, thus considered for this study. The main process of
popped rice preparation includes steaming, drying and frying (Niyomwit, 1989). Initial
moisture content of rice before frying is a major factor influencing final product quality.
With lower initial moisture content, the lower oil content is absorbed inside the fried
product (Sharma, 2000). Frying time also influences the product characteristics,
especially texture and color.

The objective of this study was to investigate the effect of drying time and frying
time on the characteristics of popped rice to be used as ingredient base for snack bar.

Materials and Methods

Materials: Broken sticky rice, Palm oil, Sucrose, Salt, Water
Equipments: Thermometer, Deep fat fryer, Tray dryer, Texture analyzer, Color-view
Spectrophotometer, Water activity meter (thermoconstanter), hot air oven
Methods: Sticky rice of 200 g was washed and soaked in water for 1 h, then drained
before steaming at 100 oC for 30 min. The steamed rice was dried in tray dryer at 65 oC.
Two variables, drying time and frying time, were included in this study. Drying time was
varied at 2, 3, and 4 h. Frying time was varied at 5, 10 and 15 s, respectively. Each
experiment was repeated one time. The fried popped rice was evaluated for moisture
content, water activity, color, texture (probe p/100, compression plate) and sensory
perceptions. For sensory evaluation, popped rice bar was prepared using binding syrup
comprising 2 g of salt, 175 g of sucrose and 175 g of glucose syrup with 650 g of popped

1

---

rice. Out of six treatments, top three samples were selected using ranking test with 40
untrained panels as tasters. Hedonic scale (from 1-extremely dislike to 9-extremely like)
was also applied with 40 untrained panels as tasters for product acceptance evaluation.

Results and Discussion

• Rice Steaming and Drying Preparation


Steamed rice was prepared and dried before frying to obtain popped rice. During
drying, samples were collected at 2, 3 and 4 hours for moisture content determination. The
results are presented in Table 1. Rice moisture content decreased with increasing drying
time. The samples with varied levels of moisture content were then used for frying
experiments.

Table 1 Moisture content of dried rice
Moisture content (% dry basis),
Drying time at 65 oC (h)
mean±s.d.
2
9.85±0.02
3
5.45±0.01
4
3.47±0.01

• Rice Frying

Rice frying experiments were conducted to examine the effect of initial moisture
content of rice before frying and frying time on popped-rice characteristics. After frying,
product’s water activity was varied between 0.3-0.4. It was found that the color of popped-
rice as indicated by L*, a*, and b* (Table 2) became darker yellow when initial moisture
content of rice was lower (longer drying time). However, only popped rice dried for 2
hours with the highest initial moisture content gave significantly different color from that
of rice dried for 3 and 4 hours (p<0.05).


2

---

Table 2 The effect of drying and frying time on popped rice color
Color1
Frying time

(mean±s.d.)

Drying time (h)
(S)
L*
a*
b*
5
74.12 ± 4.21 a 2.49 ± 1.61 b
20.33 ± 2.10 c
2
10
72.96 ± 2.00 a
2.96 ± 1.63 b
22.86 ± 2.58 c
15
72.73 ± 3.52 a
3.94 ± 1.84 b
22.57 ± 2.02 bc
5
65.16 ± 0.26 b
8.51 ± 0.91 a
26.97 ± 0.22 a
3
10
64.94 ± 1.59 b
7.29 ± 0.58 a
24.57 ± 0.61 ab
15
64.44 ± 0.45 b
8.05 ± 0.87 a
26.79 ± 1.01 a
5
62.69 ± 0.56 b
8.47 ± 0.85 a
26.92 ± 0.98 a
4
10
62.38 ± 0.04 b
7.96 ± 0.44 a
27.33 ± 0.69 a
15
61.234 ± 0.58b
8.04 ± 0.68 a
27.025 ± 1.02 a
Note: 1Letter a, b, and c indicate the significant different mean values in the same column.

Texture of popped rice was measured as peak compression force as shown in
Figure 1. The results indicated that at a given drying time, the peak compression force of
fried product tended to be maximum at 10 minutes of frying. However, the peak
compression force increased with increasing drying time or when the initial rice moisture
content was lower.

10,000.00
)
r
c
e

(
g
o
8,000.00

F
n
Drying 2 hours
r
e
s
s
i
o
6,000.00
p
m
Drying 3 hours
o
b

C
b
a
Drying 4 hours
e
a
k
4,000.00
b
a
e

P
a
e
r
a
g
v
2,000.00
A
0.00
0
2
4
6
8
10
12
14
16
Frying Time (seconds)

Note: Letter a and b indicate the significant difference of mean values of the same line.

Figure 1. Effect of rice drying and frying time on popped rice hardness

3

---

Three product treatments including drying 2 hours, frying 10 seconds, drying 2
hours, frying 15 seconds, and drying 3 hours, frying 10 seconds were chosen by ranking
preference test. To evaluate the consumer’s liking of the popped rice, plain rice snack bar
was prepared. Hedonic score was employed. The results shown in Figure 2 indicate that
the product prepared from 3 hours of drying followed by 10 seconds of frying received the
highest overall liking score (p<0.05). It was noticed that the most acceptable product also
provided the highest color and texture liking scores. Nevertheless, the crispiness liking
scores of all samples were not significantly different (p>0.05)


9


8

7


b
b
a
6

ab
r
e
a
o
a

b
a
a

s
c
5
a
a
g
i
n

b
i
k
L
4


3


2

1


0

Color Biking hardness Crispiness Overall liking



Drying 2 h, frying 10 s
Drying 2 h, frying 15 s
Drying 3 h, frying 10 s



Figure 3 Liking score of popped rice snack bar


Conclusions

The experimental results showed that popped rice characteristics were associated
with the initial moisture content prior frying and frying time. According to this study,
drying cooked rice for 3 hours (moisture content of about 3.47%d.b.) followed by 10
seconds of deep-fat frying was the best condition for popped rice preparation.

Acknowledgements

This research was sponsored by Research and Development Institute, Silpakorn
University, Thailand.






4

---

References
Niyomwit, N. (1989). Rice processing. (Lecture). Seminar on Food Processing and
Consulting Clinic; 27-28 June, 1989; Industrial Development Center, Department
of Industrial Promotion, Bangkok, Thailand, p. 1-13.
Sharma, S.K., S.J. Mulvancy and S.S.H.,Rizvi (2000). Food Processing Engineering
Theory and Laboratory Experiment. John Wiley & Sons, Canada, p. 259-265.



5

---