FST CMU Research Exercise 2016
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Physicochemical properties of dried rice supplemented with
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tomato juice
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Nuntarat Boonlao and Sirada Kamprasit
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Division of Food Science and Technology, Faculty of Agro-Industry, Chiang Mai University, Chiang Mai 50100,
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Thailand
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* Corresponding author, e-mail:
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Received: / Accepted: / Published:
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Abstract
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Rice is rich with beneficial nutrients, but lack with antioxidant compounds. Therefore, this
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study was aimed to have added value dried rice by infusing it with antioxidant compounds. Raw rice
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was cooked with 0, 20 or 50% (v/v) tomato juice. The cooked rice was then dried using a microwave
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at 850 watts for 3 min, followed with a hot air oven at 50ºC for 3 h. Different levels of tomato juice
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did not significantly affect water activity, L* value, hardness, density, volume increase and moisture
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content of the dried rice samples (p>0.05). On the other hand, higher levels of tomato juice were
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University, Chiang Mai, 50100 Thailand.
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significantly increased a* value, b* value, rehydration ratio, total acidity, β-carotene and lycopene of
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the final product (p<0.05).
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Keywords: Dried rice, tomato juice, β-carotene, lycopene
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1. Introduction
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Thai people consume rice as a main dish. Rice is a source of carbohydrate that
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body use and change to energy. Rice is rich with beneficial nutrients, but still lack with
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antioxidant compounds. (Nuttapol,2016)
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Tomato has been referred to as a “functional food”, which is good food that
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goes to beyond providing just basic nutrition. Tomatoes play a role in preventing chronic
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disease and deliver other health benefits (Ware,2012).
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Tomatoes contain high levels of β-carotene, an antioxidant that supports the
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immune system and helps maintain healthy skin and tissue lining. They are packed with
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antioxidant flavonoids and vitamin E, both of which are essential for heart health, and
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are a good source of potassium. One medium size tomato provides 50 per cent of the
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recommended daily dose of vitamin C. In addition, they do not contain saturated fatty
FST CMU Research Exercise 2016
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acids, are low in salt, starch and sugars, high in dietary fibre and have a low glycemic
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index (Rhodes,2008).
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Furthermore, tomatoes are the richest source of an exceptionally potent
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antioxidant compound, called lycopene. This is the pigment that gives the vegetable
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their deep red color. A single lycopene molecule can neutralize 13 free radicals which, if
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allowed to build up, can cause cell damage and trigger cancer. This benefit is twice the
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free radical busting power of β-carotene, another powerful antioxidant (Rhodes,2008).
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Thermal processing is the most common method for extending shelf life of food
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products. In this study, an application of microwave at 850 watts for 3 min and a hot air
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oven at 50ºC for 3 h was carried out to reduce moisture contents of rice samples. At
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low moisture content, rice samples could inactivate activities of microorganisms and
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enzymes. Unfortunately, heat treatments could also reduce nutritional qualities of food
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products (Braddock, 1999). Since consumer demands for healthy and nutritious food
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products with a fresh liked appearance, heat treatment application should consider
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changing in the physicochemical properties of food products. This research was aimed
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to improve antioxidant properties of rice grains by supplementing the rice with
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components from tomato juice.
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University, Chiang Mai, 50100 Thailand.
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2. Material and method
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2.1 Raw materials
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Thai Jasmine rice and fresh Queen tomatoes were purchased from a local
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market, Ton Payom market, in Chiang Mai, Thailand. For the tomatoes, the fruit was
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washed with tap water, blended in a kitchen blender (Tefal,China) and filtered with a
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cleaned white cheese cloth. Some physicochemical characteristics of the raw materials
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are shown in Table 1.
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2.2 Production process of dried rice
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Thai Jasmine rice was washed with tap water and cooked in a rice cooker
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(Sharp,Japan) using fresh tomato juice with concentrations of 0, 20 or 50% (v/v). The
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ratio of rice and water was 1:1.5 (v/v). The cooking process took an approximately 15-
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20 min. Cooked rice was then cooled down at room temperature and dried using a
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combination of microwave (Samsung, Malaysia) and hot air oven (Moisture analyzer
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balance Precisa XM 60,Switzerland). The microwave at 850 watts was run for 3 min
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with a break after 90 s. Afterwards, the cooked rice was heated in the hot air oven at
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50ºC for 3 h to reduce the aw of the rice to be below 0.6. Dried rice samples were
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placed in plastic packaging and stored at refrigerator temperature until being analyzed.
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Each treatment was carried out in triplicate.
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Table1. Physicochemical properties of Thai Jasmine rice and tomato juice.
Thai Jasmine Rice(Hom Mali)
aw
0.509 ± 0.021
Moisture content (%)
9.64 ± 0.187
Queen tomato juice
L* value
27.37 ± 0.058
a* value
7.05 ± 0.818
b* value
8.15 ± 0.021
pH
4.12 ± 0.058
Total acidity
0.087 ± 0.021
(% citric acid)
Total soluble solid
6.67 ± 0.289
(°Brix)
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2.3 Water activity
Rice samples were determined for their aw values using an aw-meter
(AqualabLITE,USA).
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University, Chiang Mai, 50100 Thailand.
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2.4 Moisture content
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Moisture content of rice samples was determined by drying moisture cans at
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105±110ºC for 60 min. After the can was cooled down, the weight of moisture can was
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measured. Into the empty moisture can, an amount of 2±3 g rice samples was weighed
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then the can with its sample was placed back in a hot air oven (Moisture analyzer
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balance Precisa XM 60,Switzerland) at 105±110ºC for 4 h. The can and its content
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were cooled down before being measured for their final weight. The moisture content of
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rice samples was calculated based on Equation 1.
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Mn = ((Ww-Wd)/Ww) x 100
(1)
in which: Mn = moisture content of material (%)
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WW = wet weight of the sample (g), and
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Wd = weight of the sample after drying (g).
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2.5 Color measurement
Measurement of color values, in the term of L*, a* and b*, for rice and tomato
samples was carried out using a colorimeter (Konika Minolta CR 410, Japan).
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2.6 Total acidity
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The acid content of rice and tomato samples was determined by titrating a sample (a
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given volume) with a base such as sodium hydroxide solution to a phenolphthalein end
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point or alternatively, to a pH of 8.2. The titratable acidity was expressed as grams of
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citric acid per 100 ml.
% acid = ( N × V 1 × Eq.wt ) / ( V 2 × 10 )
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In which :
N is normal of NaOH
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V 1 is volume of NaOH
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Eq.wt is molecular weight divide ratio mole of NaOH per acid in sample
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V 2 is volume of sample
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2.7 pH value and total soluble solids
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Tomato juice was analyzed pH by pH meter and total soluble solid by Hand
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refractometer.
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2.8 Texture measurement
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Texture of rice sample, in the term of hardness, was performed using a texture analyzer
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(Stable micro systems texture analyzer, TA-XT plus,Vienna).
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University, Chiang Mai, 50100 Thailand.
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2.9 Density, rehydration ratio and volume increase (Waraporn pesert el al.,2009)
2.9.1. Density
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Rice sample was put in 100 ml cylinder and tapped for 25–30 times to allow
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uniform compacking of the grain. Afterwards, volume and weight of the rice sample in
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the cylinder were recorded. Density of rice samples was determined based on Equation
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2.
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Density = weight of dried rice (g)/ volume of dried rice (ml)
(2)
2.9.2. Rehydration ratio
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Rehydration ratio was determined using 10 g of dried rice that was added with
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100 ml drinking water (Singha Corporation Co., Ltd, Thailand), which was previously
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heated in a microwave (Samsung,Malaysia) for 6 min. After the hot water was mixed for
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5 min, excess water was drained. The rehydrated rice sample was then weighed. The
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rehydration ratio was calculated as weight of rice before and after cooking according to
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Equation 3.
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Rehydration ratio = weight of dried rice after cooking (g)/ weight of dried rice before
cooking (g)
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2.9.3. Volume increase
(3)
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Volume increase was measured by measuring the volume of 20 g of dried rice
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before and after cooking in a microwave (Samsung,Malaysia) for 6 min using graduated
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cylinders after being tapped for 25–30 times to allow uniform compacking of grain. The
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volume increase calculated as the volume of rice before and after cooking as in
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Equation 4:
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Volume increase = volume of rice after cooking (ml) / volume of rice before cooking (ml)
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(4)
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2.10 β-carotene and lycopene contents (Benakmoum et al., 2013)
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Briefly, into a beaker an amount of 10±15…. g dried or cooked rice sample was mixed
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with 100 ml of organic solvent mixture (hexane(Wolrdchemical Co., Ltd,Thailand),
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acetone (Wolrdchemical Co., Ltd,Thailand), ethanol (Wolrdchemical Co., Ltd,Thailand)
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at 50:25:25, v/v/v). The mixture was stirred for 1 h 30 min, filtered and poured in a
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separating funnel. The organic phase was washed three times before being separated
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and filtered through dry sodium sulphate (Wolrdchemical Co., Ltd,Thailand)The filtrate
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obtained was adjusted to 50 ml by addition of hexane. This extract was used for the
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determination of
β-carotene
and lycopene concentrations using a UV-Vis
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University, Chiang Mai, 50100 Thailand.
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FST CMU Research Exercise 2016 Volume: xx-xx
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spectrophotometer (Genesys10S UV-VIS,Germany) at 450 and 503 nm. Concentrations
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of β-carotene and lycopene were calculated using Equations 5 and 6, respectively,
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where A450 and A503 represented the absorbance at 450 and 503 nm, respectively.
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β-carotene (μg/ml)
= 4.624 x A450 – 3.091 x A503
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Lycopene (μg/ml) = 3.965 x A450 – 0.806 x A503
(5)
(6)
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3. Result and Discussion
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Table 2. Physicochemical properties of cooked rice added with different concentrations
of tomato juice.
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Physical parameters
Water activity ns
L* value
a* value
b* value
0% tomato juice
0.968 ± 0.020
74.37 ± 1.33 a
-1.46 ± 0.082 c
2.29 ± 0.098 b
20% tomato juice
0.978 ± 0.003
70.97 ± 0.595 b
1.003 ± 0.343 b
7.68 ± 0.268 a
50% tomato juice
0.975 ± 0.122
68.43 ± 0.988 c
4.39 ± 0.633 a
8.36 ± 0.741 a
1.40 ± 0.806
1.37 ± 1.231
1.98 ± 1.053
Chemical parameters
0% tomato juice
20% tomato juice
50% tomato juice
Moisture content (%) ns
63.80 ± 0.884
64.59 ± 0.388
63.42 ± 4.390
Total acidity
(% citric acid)
β-carotene (µg/ml)
Lycopene (µg/ml)
0.047 ± 0.005 b
0.044 ± 0.008 b
0.114 ± 0.008 a
0.047 ± 0.008 c
0.063 ± 0.004 c
0.215 ± 0.028 b
0.328 ± 0.024 b
0.407 ± 0.0029 a
0.635 ± 0.0023 a
Hardness (g force)
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a-c
ns
Significant differences (p
letters within each row.
ns Not significantly different.
˂
0.05) between samples are represented by different
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Table 3. Physicochemical properties of dried rice added with different concentrations of
tomato juice.
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Physical parameters
Water activity ns
L* value ns
a* value
b* value
0% tomato juice
0.325 ± 0.025
61.86 ± 4.628
-0.414 ± 0.308 c
5.010 ± 1.403 b
20% tomato juice
0.399 ± 0.068
59.32 ± 4.349
1.703 ± 0.337 b
8.220 ± 2.415 a
50% tomato juice
0.421 ± 0.081
61.11± 0.511
3.763 ± 0.766 a
10.673 ± 1.122 a
54.42 ± 2.775
43.33 ± 9.464
57.31 ± 10.516
Density (g/ml) ns
Rehydration ratio
Volume increase ns
Chemical parameters
0.636 ± 0.000
2.367 ± 0.111 b
2.179 ± 0.094
0% tomato juice
0.636 ± 0.000
2.997 ±0.0493 a
2.270 ± 0.238
20% tomato juice
0.627 ± 0.0156
2.910 ± 0.123 a
2.030 ± 0.052
50% tomato juice
Moisture content (%) ns
5.15 ± 2.25
5.50 ± 1.80
5.34 ± 1.83
Total acidity
(% citric acid)
β-carotene (µg/ml)
Lycopene (µg/ml)
0.000 ± 0.000 c
0.022 ± 0.00437 b
0.052 ± 0.0087 a
0.0315 ± 0.0035 b
0.038 ± 0.0056 b
0.0575 ± 0.0099 b
0.033 ± 0.0085 b
0.252 ± 0.318 a
0.332 ± 0.063 a
Hardness (g force)
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a-c
ns
Significant differences (p
letters within each row.
ns Not significantly different.
˂
0.05) between samples are represented by different
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3.1 Water activity and moisture content
Water activity indicates activities of water in which microorganisms can use to
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grow. Therefore, water activity affects shelf life of a food product. (Piotr P. Lewicki Piotr
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P. Lewicki,2004)
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Water activity of cooked rice added with different levels of tomato juice is shown
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in Table 1. The value of this water activity was extensively reduced in dried rice. This
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was happened because the rice samples passed a drying process, causing water in the
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rice to be removed by the heat and decreasing its water activity. The water activity of
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dried rice is displayed in Table 2. Different concentrations of tomato juice did not
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significantly affect the water activity of cooked and dried rice (p>0.05).
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Moisture contents of cooked rice with 0, 20 and 50% (v/v) tomato juice can be
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seen in Table 1. Since a drying process evaporated some moisture in rice samples, the
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moisture content of dried rice was lower than that of the cooked rice. The moisture
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contents of dried rice are presented in Table 2. Various concentrations of tomato juice
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supplemented in rice did not influence the moisture contents of cooked and dried rice
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samples. The moisture content of dried rice with tomato juice was lower than 5.50%.
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3.2 Color measurement
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Color is one of the physical parameters of rice that was measured in this study.
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The color measurement was conducted using L*, a* and b* values of the CIE system.
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Table 1 demonstrates the color values of cooked rice supplemented with different levels
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of tomato juice. The L* value of cooked rice without any addition of tomato juice (a
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control sample) had the highest lightness value. This L* value was significantly reduced
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in the cooked rice with 20 and 50% tomato juice (p<0.05). The finding was affected by
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the fact that the tomato juice had a low L* value, which was 27.37±0.06. Beside the L*
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value, the a* and b* values of the cooked rice were significantly increased with higher
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levels of tomato juice (p<0.05; Table 1). This result was due to high a* and b* values of
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tomato juice, which were 7.05±0.82 and 8.15±0.02, respectively. Processing the cooked
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rice with a thermal process caused a decrease in L* value (Tables 1 and 2). Table 2
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exhibits that different levels of tomato juice did not significantly affect the L* value of
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dried rice (p>0.05). On the other hand, tomato juice addition significantly affected the a*
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and b* values of dried rice (p<0.05). Higher a* and b* values were determined in the
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rice with higher levels of tomato juice.
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3.3 Hardness
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Texture is an important property of food products. In this study, texture of
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cooked and dried rice samples was determined in the term of hardness. The hardness
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of cooked and dried rice with tomato juice can be seen in Tables 1 and 2, respectively.
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University, Chiang Mai, 50100 Thailand.
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The hardness of cooked and dried rice was not significantly affected by different
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concentrations of tomato juice (p>0.05). This result might be affected by the same
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processing condition that was carried out for different rice samples. The hardness of
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dried rice was much higher than that of the cooked rice. This was due to removal of
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water during a drying process, causing an increase in the hardness of dried rice.
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3.4 Density, rehydration ratio and volume increase
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Density, rehydration ratio and volume were physical properties of dried rice. The
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measurement results of these parameters are shown in Table 2. From statistical
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analyses, it was found that the density and volume increase of different dried rice
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treatments were not significantly affected by addition levels of tomato juice (p>0.05).
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This finding could be due to a similar processing condition that was done for different
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rice samples. However, the rehydration ratio of dried rice was significantly affected by
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different concentrations of tomato juice (p<0.05). Higher rehydration ratio was found in
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the rice supplemented with the juice (Table 2). The higher rehydration ratio value
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indicated that the rice sample had a better water absorption capability. The result in this
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study could be affected by tomato juice components that were permeated into the rice
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samples. Tomato contained several nutritional components, including dietary fiber of
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lignin, cellulose, hemicelluloses and pectin. Lignin had a property of water absorption
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and hemicellulose had a characteristic of water holding capacity. ( Rattanapanon,2006)
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3.5 Total acidity content
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Tomato contained malic acid, citric acid and glutamate, therefore pH of tomato
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juice was 4.012±0.06 with a total acidity value of 0.087±0.021. An addition of tomato
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juice in rice significantly increased the total acidity of cooked and dried rice samples
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(p<0.05; Tables 1 and 2). The total acidity of rice samples was calculated based on
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citric acid. The highest total acidity was determined in the cooked and dried rice with
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50% supplementation of tomato juice. The finding was due to the highest amount of
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tomato juice added into the rice
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3.6 β-carotene and lycopene contents
β-carotene and lycopene are members of carotenoid family, which are highly
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pigmented (red, orange, yellow), fat-soluble compounds and naturally present in many
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fruits, grains, oils and vegetable (Ratanapanon,2006) .β-carotene and lycopene have
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University, Chiang Mai, 50100 Thailand.
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antioxidant properties, which contribute to protecting the body against the damaging
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effects of free radicals. Antioxidant can potentially decrease the risk of developing
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certain diseases, including cardiovascular diseases and cancer (Christian
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Nordqvist,2016).
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cooked and dried rice samples, respectively. It could be seen clearly that the
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supplementation of tomato juice significantly increased the levels of β-carotene and
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lycopene in the rice samples (p<0.05). The presence of β-carotene was 1.8 times
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higher when the dried rice was added with 20% tomato juice and it was increased to be
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8 times higher in the rice samples with 50% tomato juice (Table 2). A similar finding
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was also noticed for lycopene content. The dried rice supplemented with 50% tomato
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juice had 8.7 times more lycopene content than that of the control dried rice without any
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addition of tomato juice. The lycopene content of the dried rice with 20% tomato juice
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was not significantly differed than that of the control dried rice (p>0.05). Therefore, it
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could be determined that the initial concentration of tomato juice added into cooked rice
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and thermal processing affected the final levels of β-carotene and lycopene in dried
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rice. A low addition level of tomato juice would lead to low quantities of β-carotene and
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lycopene in the final product. Thermal processing of a microwave treatment at 850
Tables 1 and 2 shows the amount of β-carotene and lycopene in
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watts for 3 min and a hot air oven at 50ºC could also cause deterioration on β-carotene
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and lycopene in dried rice ( Siriwej,2014)
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Conclusion
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This study investigated physicochemical properties of dried rice supplemented
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with tomato juice. Dried rice samples had aw values in the range of 0.33-0.42 and
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moisture contents of 5.15-5.50%. L* value of dried rice was not significantly different
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between different treatments (p > 0.05), while a* and b* values of the rice was
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significantly increased at higher tomato juice concentration (p<0.05). Hardness, density
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and volume increase of dried rice were not significantly affected by different
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concentrations of tomato juice (p> 0.05). Total acidity, β-carotene and lycopene were
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significantly increased at higher concentrations of tomato juice added into cooked rice
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(p<0.05). Therefore, improving the nutritional value of dried rice could be done by
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cooking the rice with tomato juice, followed by a drying process to extend the shelf life
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of the rice.
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Acknowledgement
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The authors acknowledged partial funding from the Faculty of Agro-Industry,
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Chiang Mai University, Thailand, for the project. Thanks to be given to all staff and
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technicians of the Division of Food Science and Technology, Faculty of Agro-Industry,
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Chiang Mai University.
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