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Effect of gamma irradiation on physicochemical, functional and pasting properties of some locally-produced rice (Oryza spp) cultivars in Ghana
Radiation Physics and Chemistry 130 (2017) 196–201
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Effect of gamma irradiation on physicochemical, functional and pasting properties of some locally-produced rice (Oryza spp) cultivars in Ghana Fidelis C.K. Ocloo a,n, Mavis Owureku-Asare a, Joyce Agyei-Amponsah a, Wisdom S.K. Agbemavor a, Martin N.Y.H. Egblewogbe b, Franklin B. Apea-Bah a, Adjoa Sarfo a, John Apatey a, Henry Doku c, Dora Ofori-Appiah a, Ernestina Ayeh a a Radiation Technology Centre, Biotechnology and Nuclear Agriculture Research Institute. Ghana Atomic Energy Commission, P.O. Box LG 80, Legon, Accra, Ghana b Department of Physics, University of Ghana, Legon, Accra, Ghana c Crop Research Institute, Council for Scientific and Industrial Research, P.O. BOX 3785, Kumasi, Ghana
H I G H L I G H T S
Effect of gamma irradiation on properties of some rice cultivars in Ghana was investigated. Gamma irradiation decreased pH and swelling power, whereas solubility increased. Gamma irradiation did not change the XRD pattern of the rice cultivars. Gamma irradiation decreased peak time for BAL and VNT rice cultivars. Gamma irradiation decreased PV, HPV, BDV, FV and SBV for all the rice cultivars.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 February 2016 Received in revised form 22 August 2016 Accepted 28 August 2016 Available online 29 August 2016
Rice (Oryza sativa L.) is a staple crop in Ghana and much of West Africa, where it serves as an important convenience food for urban consumers. The objective of this study was to determine the effect of gamma irradiation as insect disinfestation technique on some physicochemical, functional and pasting properties of selected locally-produced rice cultivars in Ghana. Four local rice cultivars and an imported (commercial) type were purchased, cleaned and irradiated at doses of 0.0, 0.25, 0.50, 0.75, 1.0 and 1.5 kGy. The irradiated rice cultivars were milled and their physicochemical, functional and pasting properties determined. There were reductions in pH and swelling power, as well as increase in solubility of rice cultivars after gamma irradiation. Gamma irradiation did not change the XRD pattern of the rice cultivars. Gamma irradiation significantly (Po 0.05) decreased peak time for BAL and VNT rice cultivars. Gamma irradiation significantly (P o 0.05) decreased PV, HPV, BDV, FV and SBV for all the rice cultivars. This study shows that flours from gamma irradiated rice cultivars have potential in food formulations that require low viscosity. & 2016 Elsevier Ltd. All rights reserved.
Keywords: Rice Gamma irradiation Characteristics XRD
1. Introduction Rice (Oryza sativa L.) has become a staple in Ghana and much of West Africa where it serves as an essential convenience food for urban people (Tomlins et al., 2007). Rice recorded the highest deficit (210,700 metric tonnes) on the domestic food supply and demand position for Ghana in 2008, with a per capita consumption of 15.1 kg/annum and an estimated national consumption of
n
Corresponding author. E-mail addresses: fi[email protected], ocloofi[email protected] (F.C.K. Ocloo). http://dx.doi.org/10.1016/j.radphyschem.2016.08.025 0969-806X/& 2016 Elsevier Ltd. All rights reserved.
353,300 metric tonnes (Ayittey and Banini, 2009). In Ghana, rice is utilized in a broad range of food products; the most common include ‘jollof rice’, ‘rice balls’, rice porridge, fried rice and plaincooked rice. Although rice forms a major part of the Ghanaian diet, locally grown rice is not patronized due to its variable quality. Several factors account for the variability in rice quality, and the most prominent factors being poor sensory and physical qualities (Tomlins et al., 2005). These quality defects arise not only from inappropriate post-harvest handling, but also from poor planting materials and poor agronomic practices (Gayin et al., 2009). Due to its chemical composition and production chain, rice is susceptible to infestation by insects which reduces the economic
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Table 1 Effect of gamma irradiation on some physicochemical and functional properties of rice cultivars.† Cultivar/ Type
Dose (kGy)
Moisture (%)
pH
Bulk density (g/ml) Solubility (%)
Swelling power (g/g)
Water Absorption capacity (ml/g)
Oil absorption capacity (ml/g)
BAL
0 0.25 0.50 0.75 1.0 1.5
12.7de 7 0.1 12.7de 7 0.1 12.5de 7 0.2 12.4de 7 0.1 12.8e 7 0.1 12.6de 7 0.1
6.10l 7 0.00 6.70r 7 0.00 6.04i 7 0.00 6.05j 7 0.00 6.05j 7 0.00 6.05j 7 0.00
0.91efgh 7 0.02 0.89cdef 70.01 0.85bc 7 0.04 0.89cdef 70.07 0.91efgh 7 0.03 0.82ab 70.03
7.3abcdefg 71.0 8.2abcdefgh 7 3.2 9.6efghi 7 1.5 9.0defgh 7 2.0 9.3defghi 7 2.6 7.0abcdef 7 0.6
8.6fg 7 0.6 8.5fg 7 0.4 8.8g 7 0.4 8.2efg 7 0.7 7.8def 7 0.1 7.9defg 7 0.2
1.5efg 7 0.1 1.4def 7 0.0 1.4def 7 0.0 1.4def 7 0.0 1.3cde 70.1 1.2bcd 7 0.0
1.2bc 7 0.2 1.2bc 7 0.2 1.3cd 7 0.1 1.3cd 7 0.2 1.3cd 7 0.2 1.4de 70.1
VNT
0 0.25 0.50 0.75 1.0 1.5
11.8abcde 70.0 12.3de 7 0.1 12.3de 7 0.0 11.7abcd 7 0.1 11.7abcd 7 0.1 12.1cde 7 0.1
5.95h 70.00 5.93g 7 0.00 5.92f 7 0.00 5.93g 7 0.00 5.92f 7 0.00 5.93fg 7 0.00
0.89cdef 70.05 0.86bcd 7 0.02 0.88cde 7 0.02 0.91efgh 7 0.01 0.85bc 7 0.02 0.88cde 7 0.02
6.8abcde 70.1 6.9abcdef 7 0.4 12.0ijk 72.0 15.0lmn 7 1.2 16.3mn 7 0.5 6.0ab 71.0
7.5cde 70.6 7.7def 7 0.8 7.0bcd 7 0.4 7.9defg 7 0.5 7.8def 7 0.2 7.9defg 7 0.8
1.3cde 70.1 1.4def 7 0.2 1.4def 7 0.1 1.2bcd 7 0.1 1.4def 7 0.0 1.3cde 70.1
1.4de 70.1 1.4de 70.1 1.1ab 7 0.1 1.2bc 7 0.1 1.2bc 7 0.2 1.1ab 7 0.1
VNS
0 0.25 0.50 0.75 1.0 1.5
12.6de 7 0.1 12.5de 7 0.0 12.3de 7 0.1 12.5de 7 0.1 12.0bcde 7 0.0 12.5de 7 0.1
6.10l 7 0.00 6.11m 7 0.00 6.10l 7 0.00 5.81d 7 0.00 6.04i 7 0.00 6.08k 7 0.00
0.96i 7 0.02 0.91efgh 7 0.01 0.86bcd 7 0.01 0.87cde 7 0.02 0.90defg 7 0.02 0.86bcd 7 0.02
19.8o 72.0 13.1jkl 7 2.4 8.6bcdefgh 70.4 14.1klm 7 1.8 8.8cdefgh 7 1.4 10.0ghi 7 1.0
6.6bc 7 0.4 5.6a 7 1.3 6.1ab 7 0.5 6.6bc 7 0.2 7.1cd 7 0.5 7.0bcd 7 0.2
1.1abc 7 0.1 1.2bcd 7 0.1 1.2bcd 7 0.2 1.2bcd 7 0.0 1.1abc 7 0.1 1.0a 70.1
1.4de 70.1 1.4de 70.1 1.3cd 7 0.1 1.4de 70.0 1.4de 70.1 1.4de 70.0
VWR
0 0.25 0.50 0.75 1.0 1.5
12.6de 7 0.0 14.5f 73.5 12.7de 7 0.0 12.3de 7 0.1 12.6de 7 0.3 12.6de 7 0.0
6.31p 7 0.00 6.29o 7 0.00 6.23n 70.00 6.32q 7 0.00 5.89e 7 0.00 6.31p 7 0.00
0.87cde 7 0.02 0.88cde 7 0.02 0.78a 7 0.03 0.81a 7 0.03 0.92fgh 7 0.01 0.88cde 7 0.04
5.4a 7 0.3 8.0abcdefgh 7 1.6 6.7abcd 7 0.1 8.9defgh 7 1.6 8.5bcdefgh 70.8 9.7fghi 7 1.4
7.9defg 7 0.1 10.3h 7 0.2 8.6fg 7 0.3 8.5fg 7 0.8 8.8g 7 1.3 8.8g 7 0.7
1.1abc 7 0.1 1.2bcd 7 0.0 1.1abc 7 0.1 1.2bcd 7 0.1 1.2bcd 7 0.1 1.2bcd 7 0.1
1.2bc 7 0.1 1.0a 70.2 1.3cd 7 0.3 1.3cd 7 0.1 1.4de 70.2 1.3cd 7 0.1
JAS
0 0.25 0.50 0.75 1.0 1.5
11.1abc 7 0.1 11.0ab 70.1 10.0a 7 0.1 10.8a 7 0.2 11.1abc 7 0.3 10.9a 7 0.1
5.59b 7 0.00 5.61c 7 0.00 5.59b 7 0.00 5.58ab 70.00 5.58ab 70.00 5.58ab 70.00
0.86bcd 7 0.00 0.90defg 7 0.01 0.89cdef 70.02 0.90defg 7 0.02 0.90defg 7 0.01 0.93ghi 70.03
6.1abc 7 1.4 13.2kl 7 2.3 17.1no 7 1.2 14.4klmn 7 3.5 8.1abcdefgh 7 2.3 10.3hij 73.0
7.8def 7 0.8 8.4efg 7 0.6 7.5cde 70.3 8.2efg 7 0.3 7.9defg 7 0.4 8.1efg 70.3
1.6gh 7 0.1 1.3cde 70.1 1.2bcd 7 0.0 1.3cde 70.1 1.2bcd 7 0.0 1.3cde 70.1
1.1ab 7 0.1 1.4de 70.2 1.2bc 7 0.3 1.3cd 7 0.0 1.3cd 7 0.1 1.1ab 7 0.1
†
Each value represents the mean of three experiments 7 standard deviation. Values with different letters in a column are significantly different at P o 0.05.
value of local rice varieties. Gamma irradiation has been used for insect disinfestation and microbial decontamination of foods (Aldryhim and Adam, 1999; Loaharanu et al., 1971). The use of irradiation is however limited by its effect on rice quality. Irradiation has been reported to cause changes in colour, amylose content, water absorption, loss of solids during cooking, paste viscosity, cooked rice hardness and oxidative rancidity in rough and brown rice (Hayashi et al., 1998; Roy et al., 1991; Sabularse et al., 1992, 1991; Wang et al., 1983; Wootton et al., 1988). Similar effects have been reported when milled rice was irradiated (Bao et al., 2001; Loaharanu et al., 1971). Various gamma irradiation doses have been reported to maintain the sensory quality of irradiated rice. An acceptable limit below 3 kGy was recommended for Taiwanese rice (Wang et al., 1983) and up to 5 kGy for Indian rice (Roy et al., 1991). Bao et al. (2001) also stated that irradiation of milled rice for human consumption should be limited to a maximum dose of 2–4 kGy, due to its negative effect on rice colour and aroma. However, a maximum dose of 1 kGy was suggested for Australian rice and ordinary Thai rice (Loaharanu et al., 1971; Wootton et al., 1988). There is little information on the effects of gamma irradiation (for insect disinfestation) on the quality characteristics of the resultant flours obtained from local rice varieties. The objective of this study was to determine the effect of gamma irradiation as insect disinfestation technique on some physicochemical, functional and pasting properties of selected locally-produced rice cultivars in Ghana with the aim of preserving and widening the utilization of the rice cultivars.
2. Materials and methods 2.1. Materials 2.1.1. Collection and preparation of rice cultivars Four local rice cultivars, namely ‘Viwotor’ (VWR), ‘Viwonor’ short (VNS), ‘Viwonor’ tall (VNT) and ‘Balemi’ 1 (BAL) were bought from rice farmers in Kpong, Ghana. One imported rice type, Jasmine (JAS) was also purchased from a local market in Accra, Ghana. The paddy rice samples were sorted to remove any extraneous materials and defective rice seeds. The local rice cultivars were dehulled and then packaged into low density polyethylene bags (about 50 g each) along with the imported rice sample for gamma irradiation.
2.2. Methods 2.2.1. Gamma irradiation The five packaged rice samples (50 g each) were irradiated using a gamma irradiation facility, Cobalt 60 source (SLL-515, Hungary) at the Radiation Technology Centre (RTC) of the Ghana Atomic Energy Commission (GAEC). Samples were exposed to gamma irradiation doses of 0.0, 0.25, 0.50, 0.75, 1.0 and 1.5 kGy with a dose rate of 0.63 kGy/h. The absorbed dose was confirmed using Fricke's dosimetry system. The irradiated rice samples were milled into flour to pass through 250 mm mesh using a hammer mill (Brook Crompton Series 2000, England) and then packed into low density polyethylene bags prior to analyses.
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Fig. 1. a: Effect of gamma irradiation on XRD pattern and relative crystallinity of BAL rice cultivar, b: effect of gamma irradiation on XRD pattern and relative crystallinity of VNT rice cultivar, c: effect of gamma irradiation on XRD pattern and relative crystallinity of VNS rice cultivar, d: effect of gamma irradiation on XRD pattern and relative crystallinity of VWR rice cultivar, e: effect of gamma irradiation on XRD pattern and relative crystallinity of JAS rice cultivar.
2.2.2. Moisture determination The moisture content of gamma irradiated and un-irradiated rice samples was determined on their flours using the method described by AOAC (2000). Briefly, about 2 g of wellmixed rice flour was weighed into a weighed dish (previously heated to 130 °C and cooled). The dish with the flour sample was placed in the air-oven (Gallenkamp, United Kingdom) for 1 h at 130 °C. The dish with the dried flour was covered while still in the oven and then transferred into a desiccator to equilibrate. The cooled flour was then weighed and the moisture content determined.
2.2.3. pH pH of flours from gamma irradiated and un-irradiated rice samples was determined using the method described by AOAC (2000). In brief, about 10.0 g of the sample was weighed into a clean, dry Erlenmeyer flask and 100 ml of distilled water added. The mixture was shaken until particles were evenly suspended and free of lumps. The mixture was then allowed to stand for 10 min for the particles to settle. The supernatant was decanted into a 250 ml beaker, and the pH was determined, using pH metre (Mettler Toledo, Switzerland). Prior to the pH determination, the pH metre was calibrated using buffer solutions of pH 7.0 and 4.0.
F.C.K. Ocloo et al. / Radiation Physics and Chemistry 130 (2017) 196–201
Table 2 Effect of gamma irradiation on relative crystallinity of the rice cultivars.† Cultivar/Type
Dose (kGy)
Relative crystallinity (%)
BAL
0 0.25 0.50 0.75 1.0 1.5
29.0abcd 71.4 31.5cd 7 0.7 28.0abcd 70.0 25.0a 7 0.1 30.5bcd 7 0.7 28.0abcd 70.0
VNT
0 0.25 0.50 0.75 1.0 1.5
32.0cd 7 5.7 28.0abcd 70.0 29.5abcd 72.1 30.5bcd 7 0.7 29.5abcd 70.7 30.0bcd 7 1.4
VNS
0 0.25 0.50 0.75 1.0 1.5
30.0bcd 7 4.2 29.0abcd 72.8 32.5d 7 4.9 28.5abcd 72.1 31.5cd 7 3.5 30.5bcd 7 3.5
VWR
0 0.25 0.50 0.75 1.0 1.5
27.5abc 7 2.1 28.0abcd 72.8 29.0abcd 70.0 29.5abcd 72.1 31.0bcd 7 2.8 30.0bcd 7 2.8
JAS
0 0.25 0.50 0.75 1.0 1.5
32.5d 7 0.7 28.5abcd 72.1 30.0bcd 7 1.4 29.5abcd 70.7 30.0bcd 7 1.4 26.5ab 7 1.4
† Each value represents the mean of three experiments 7standard deviation. Values with different letters in a column are significantly different at P o 0.05.
2.2.4. Bulk density The bulk density of flours from gamma irradiated and un-irradiated rice samples was determined using the method described by Narayana and Rao (1984). In brief, a calibrated centrifuge tube was weighed and filled with the flour samples to the 5 ml mark by constant tapping until there was no further change in volume. The contents were weighed and the difference in weight was taken. The bulk density of the sample was calculated by dividing the difference in weight by the volume of the sample. 2.2.5. Water and oil absorption capacities Water and oil absorption capacities of the flours from gamma irradiated and un-irradiated rice samples were determined using the method described by Sathe and Salunkhe (1981) as modified by Adebowale et al. (2005). In brief, about 1.0 g (dry basis) of the sample was dispersed in 10 ml distilled water or oil (Soybean oil) and the suspension stirred using a magnetic stirrer for 5 min. The suspension was centrifuged at 3500 rpm for 30 min and the supernatant water or oil measured in a 10 ml graduated cylinder. The densities of water and the refined oil were taken as 1.0 g cm 3 and 0.889 g cm 3, respectively. The water and oil absorption capacities were expressed as percentage water or oil absorption based on the original weight. 2.2.6. Solubility and swelling power Solubility and swelling power of flours from gamma irradiated and un-irradiated rice samples were determined based on the modifications of the method described by Leach et al. (1959). About 1 g of rice flour samples was weighed into a previously weighed 40 ml centrifuge tube and 40 ml of distilled water added. The suspension was stirred uniformly and gently avoiding excess
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force that might rapture the starch granules in the flour. The suspension was heated in a thermostatically controlled water bath (OLS 200 Grant, England) at 85 °C for 30 min, with constant stirring. The tube was removed from the water bath, wiped and allowed to dry and cool to room temperature. The supernatant was then poured into a weighed crucible and evaporated to dryness in an oven (Gallenkamp, United Kingdom) at 105 °C. The weight of dried supernatant after cooling and the weight of the sediment paste were used to calculate the solubility and swelling power, respectively. 2.2.7. X-ray diffraction (XRD) The crystal patterns and relative crystallinity of gamma irradiated and un-irradiated rice samples were determined on their flours using X-ray diffraction (XRD) (PANanalytical Empyrean diffractometer) (Eindhoven, the Netherlands). The powdered rice samples were equilibrated at 95% relative humidity (using a 22% glycerol solution) (Darfour et al., 2012) for 5 days at about 25 °C. The XRD operating conditions were: 45 kV, 40 mA and Cu Kα1 (0.154 nm). Samples were scanned from 5° to 40° (2θ) with a step size of 0.20° and a step time of 10 s. The relative intensity peaks were then plotted against 2θ peaks. Relative crystallinity of the flour samples was calculated as percent integrated area of crystalline peaks to the total integrated area above a straight baseline (Cheetham and Tao, 1998). 2.2.8. Pasting properties Pasting properties of gamma irradiated and un-irradiated rice samples were determined on their flours using a Rapid Visco Analyser (RVA Model 3D) (Newport Scientific, Warriewood, Australia). The method described by D'Silva et al. (2011) was used. Briefly, 3 g (db) of rice flour was suspended in distilled water and the weight adjusted with water to 28 g. The flour suspension was initially stirred with a speed of 960 rpm at 50 °C for 30 s and then stirred at 160 rpm for the entire period thereafter. The temperature was increased at a rate of 5.5 °C/min to 91 °C (since water boils at 95 °C in Pretoria, South Africa) and held at this temperature for 5 min. The paste was then cooled to 50 °C at a rate of 5.5 °C/min. The viscosity values were recorded in rapid visco units (RVU). The parameters evaluated from the curve were: peak viscosity (PV), trough/ hot paste viscosity (HPV), final viscosity (FV), setback viscosity (SBV), breakdown viscosity (BDV) and Peak time (time required to reach peak viscosity, PTime). 2.2.9. Statistical analysis Apart from pasting properties which were determined in duplicates, all other analyses were done in triplicates. A multifactor analysis of variance (ANOVA) was used to determine the effects of rice variety and irradiation dose on dependent variables. Fisher's least significant difference (LSD at Po0.05) was used for mean separation, to ascertain where differences existed. MINITAB statistical software (Minitabs Release 14.13, Minitab Inc., USA) was used for the statistical analysis.
3. Results and discussions 3.1. Physicochemical properties The moisture contents for gamma irradiated and un-irradiated JAS rice were significantly (P o0.05) lower than the local cultivars (BAL, VNT, VNS and VWR) (Table 1). Gamma irradiation did not significantly influence the moisture contents of the rice cultivars. Moisture content values for all the rice samples were low, indicating better storage stability of rice as well as its starch keeping quality (Maeda et al., 2004).
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Table 3 Effect of gamma irradiation on RVA pasting properties of rice cultivars.† Cultivar/Type
Dose (kGy)
PTime (min)
PV (RVU)
HPV (RVU)
BDV (RVU)
FV (RVU)
SBV (RVU)
BAL
0 0.25 0.50 0.75 1.0 1.5
12.2fgh 7 0.1 11.9def 7 0.1 13.0k 7 0.0 12.8ijk 7 0.1 12.3gh 70.4 10.9a 7 0.1
318.5mn 7 2.3 283.5k 7 0.8 263.8ij 715.1 295.5kl 7 7.1 249.4ghi 7 0.3 243.3gh 715.0
289.6no 7 1.0 256.1ijk 7 0.5 246.0hij 714.2 273.0lmn 77.7 230.7fgh 7 2.1 216.8ef 7 12.2
28.9hi 7 1.3 27.4ghi 7 0.3 17.7cde 70.9 22.5efg 7 0.6 18.7cde 71.8 26.5ghi 7 2.8
414.5no 71.9 359.2lm 7 4.3 330.3ijk 7 17.0 372.0m 7 4.7 329.3ijk 7 0.1 312.2hi 7 15.0
124.9n 7 0.9 103.1kl 7 4.8 84.2def 7 2.8 99.0ijk 7 3.1 98.5ijk 7 2.2 95.4hij 72.8
VNT
0 0.25 0.50 0.75 1.0 1.5
12.8ijk 7 0.3 13.0k 7 0.0 12.6hij 7 0.3 13.0k 7 0.0 12.8ijk 7 0.1 12.5hi 70.1
295.4kl 7 6.2 294.0kl 7 3.8 282.6k 7 1.4 222.0ef 7 3.2 231.0fg 710.0 193.3d 7 2.6
272.6klm 7 6.4 273.8lmn 71.5 257.9jkl 77.9 210.5e 7 3.0 218.7ef 7 10.4 183.2d 7 2.2
22.8efg 7 0.1 20.2def 7 2.3 24.7fgh 7 6.5 11.5ab 7 0.2 12.3ab 7 0.5 10.2a 7 0.4
365.4m 7 8.0 363.9lm 78.8 339.1jk 7 8.5 291.9fg 7 1.6 301.5gh 710.5 256.7e 7 2.0
92.8ghi 7 1.6 90.2fgh 7 7.3 81.2d 70.6 81.4d 71.4 82.8de 7 0.1 73.5c 7 0.2
VNS
0 0.25 0.50 0.75 1.0 1.5
13.0k 7 0.0 13.0k 7 0.0 13.0k 7 0.0 12.9jk 7 0.1 13.0k 7 0.0 13.0k 7 0.0
204.5de 7 18.0 167.7c 7 4.7 147.7b 73.6 167.5c 7 21.4 169.6c 7 6.4 121.6a 71.5
184.3d 7 15.8 148.8c 72.8 131.5b 7 2.5 149.8c 722.6 146.7bc 71.0 109.8a 7 1.6
20.1def 7 2.2 18.9cde 71.8 16.2bcd 7 1.1 17.7cde 71.2 22.9efg 7 5.4 11.9ab 7 0.2
211.1d 7 21.4 171.4bc 74.6 152.2b 71.9 177.0c 7 24.9 174.2c 7 1.4 131.3a 7 1.5
26.8ab 7 5.7 22.6ab 7 1.8 20.7a 7 0.5 27.2b 7 2.4 27.5b 7 0.4 21.6ab 70.1
VWR
0 0.25 0.50 0.75 1.0 1.5
11.0a 70.2 11.1ab 7 0.2 11.4bc 7 0.0 11.1ab 7 0.2 10.9a 7 0.2 11.2abc 7 0.2
352.8p 7 15.8 339.9op 74.4 319.1mn 7 14.7 285.3k 7 8.6 294.3kl 7 7.4 252.8hi 7 3.9
297.3o 7 9.9 291.0o 75.1 280.8mno 7 12.7 245.2hij 75.4 244.1hij 77.1 221.9ef 7 3.1
55.6n 7 5.9 49.0m 7 0.8 38.3kl 7 2.1 40.0l 7 3.2 50.3m 7 0.4 31.0ij 7 0.8
447.3p 7 14.5 424.5o 72.4 397.7n 7 14.8 367.0m 7 8.1 364.1lm 7 2.9 326.0ijk 7 8.0
150.1p 7 4.6 133.5o 7 2.8 116.9m 7 2.1 122.7mn 7 2.8 120.0mn 7 4.2 103.9kl 7 4.8
JAS
0 0.25 0.50 0.75 1.0 1.5
11.5c 7 0.1 11.5cd 7 0.2 11.6cde 7 0.0 12.2fgh 7 0.3 11.9ef 7 0.0 12.0efg 70.4
329.4no 73.1 308.3lm 7 5.7 279.5jk 7 0.6 257.6hi 7 8.4 242.9gh 70.6 204.8de 7 13.6
293.3o 7 0.0 274.0lmn 70.5 251.8ij 7 0.1 239.4ghi 76.2 224.6efg 7 1.0 190.1d 7 14.1
36.0jkl 7 3.1 34.3jk 7 5.1 27.7ghi 7 0.6 18.2cde 72.2 18.3cde 71.6 14.7abc 7 0.5
419.4o 71.1 395.0n 72.4 369.3m 7 0.4 345.2kl 710.1 324.3ij 73.1 277.9f 7 13.1
126.1n 7 1.1 121.0mn 7 2.9 117.5m 7 0.4 105.8l 73.8 99.7jkl 7 4.1 87.8efg 7 0.9
PTime ¼Peak Time; PV ¼Peak viscosity; HPV¼ Hot paste viscosity; BDV ¼ Breakdown viscosity; FV ¼Final viscosity; SBV ¼ Setback viscosity; PS ¼Paste stability. †
Each value represents the mean of two experiments 7standard deviation. Values with different letters in a column are significantly different at p o0.05.
parameter for determining packaging requirement and material handling in the food industry (Falade et al., 2014). Gamma irradiation significantly (P o0.05) decreased water absorption capacity and swelling power as well as increased the oil absorption capacity and solubility of the rice cultivars (Table 1). The above changes due to gamma irradiation have been attributed to depolymerisation of amylopectin chains in the starch molecules (El Saadany et al., 1979; Liu et al., 2012). 3.3. X-ray diffraction (XRD)
Fig. 2. A representative RVA pasting curve of flour from local rice cultivars compared with imported (commercial) type.
pH values for JAS were significantly (Po0.05) lower than the local cultivars (BAL, VNT, VNS and VWR) (Table 1). pH values decreased with increase in gamma irradiation dose. The decreases in pH, due to gamma irradiation were not in dose-dependent manner. The non-dose dependence effect observed could be due to the low doses used in the present study. The decreases in pH observed could be attributed to partial break down of starch molecules by the gamma rays, causing the formation of carboxylic acid (COOH) (Sokhey and Chinnaswamy, 1993). 3.2. Functional properties There were generally, varietal differences in the functional properties of the rice samples (Table 1). Gamma irradiation did not significantly (P 40.05) influence the bulk density values for all the rice cultivars (Table 1). Bulk density, is considered a useful
The X-ray diffractograms and relative crystallinity for gamma irradiated and un-irradiated rice cultivars are shown in Fig. 1a–e and Table 2, respectively. All the rice cultivars (irradiated and unirradiated) had major peak intensities at 2θ E15°, 17°, 18° and 23°. These 2θ peaks have been attributed to the presence of A-type crystal starches. Minor peak intensities were also observed at 2θ E20 and 27°. The peak observed at 2θ E20° indicates the presence of some V-type starch crystals in the rice cultivars. Gamma irradiation did not change the crystal type (XRD pattern) of the rice cultivars (Fig. 1a–e). Bao et al. (2005) reported an A-type X-ray diffraction pattern for flour and starch isolated from irradiated and un-irradiated white rice. Strong reflections at 2θ E15°, 17°, 18°, and 23° have also been reported by Yu et al. (2012). The relative crystallinity values for un-irradiated rice cultivars ranged from 29.0% to 32.5% (Table 2). There were no significant differences (P 40.05) between the relative crystallinity values for all the rice cultivars. Gamma irradiation had no significant (P 40.05) effects on the relative crystallinity of the rice cultivars (Table 2). Bao et al. (2005) reported relative crystallinity value of 31.5% for flour from un-irradiated white rice.
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3.4. Pasting properties
References
The pasting behaviours of the rice cultivars varied (Table 3, Fig. 2). Significant (P o0.05) differences were found in peak time, peak viscosity, trough, breakdown viscosity, set back and final viscosities of the rice cultivars used in the present study. Similar variations have been reported by other authors (Asante et al., 2013). Gamma irradiation of the rice cultivars significantly (P o0.05) decreased peak time for BAL and VNT (Table 3). However, gamma irradiation did not change the peak time for VNS, VWR and JAS. Decreased pasting time has been reported for flours obtained from high proton beam irradiated rice cultivars (Kim and Kim, 2013). The current study indicates that gamma irradiation significantly (P o0.05) decreased the PV, HPV, BDV, FV and SBV for all the cultivars studied (Table 3). However the decreases were not dosedependent in most cases. The non-dose dependence effect observed, as stated earlier could be due to the low doses used in the present study. The decreases in these characteristic features (PTime, PV, HPV, BDV, FV and SBV) of rice flour upon gamma irradiation of the rice seeds could be due to depolymerisation of the rice starch molecules through chain scission. Gamma irradiation (0–3 kGy) of brown rice has been reported to decrease the peak viscosity, hot paste viscosity, final viscosity, breakdown viscosity and setback viscosity (Sabularse et al., 1992). Decreased viscosity has been attributed to degradation and uncoiling of starch chains as well as breakdown of hydrogen bonding within the starch molecules by irradiation (MacArthur and D'Appolonia, 1983). Also, decreased setback viscosity due to irradiation has been attributed to the breakdown of the starch molecules which were not able to produce longer helical structures and association between starch molecules, hence less starch retrogradation (Sabularse et al., 1992). Similar trends have also been reported by Bao et al. (2001) and Kim and Kim (2013) for flours obtained from gamma irradiated (2, 4, 8 and 12 kGy) and proton beam irradiated (0, 300, 500, 800, 1200 Gy) milled rice, respectively. The reductions in viscosities of the rice cultivars due to gamma irradiation suggest that irradiated rice may not be suitable for use as thickeners in foods. However, they can be used in children foods, such as soft porridge. Due to the low viscosity of the flours obtained from gamma irradiated rice, more solids could be added to enhance the production (preparation) of high energy porridges to support the child's nutritional requirements. The flours from gamma irradiated rice could also be used as starch matrix fillers.
Adebowale, K.O., Olu-Owolabi, B.I., Lawal, O.S., 2005. Functional properties of native, physically and chemically modified breadfruit (Artocarpus artilis) starch. Ind. Crops Prod. 21 (3), 343–351. Aldryhim, Y.N., Adam, E.E., 1999. Efficacy of gamma irradiation against Sitophilus granarius (L.) (Coleoptera: Curculionidae). J. Stored Prod. Res. 35, 225–232. AOAC, 2000. Official Methods of Analysis. AOAC International, Gaithersburg, MD, USA. Asante, M.D., Offei, S.K., Gracen, V., Adu-Dapaah, H., Danquah, E.Y., Bryant, R., McClung, A., 2013. Starch physicochemical properties of rice accessions and their association with molecular markers. Starch - Stärke 65 (11–12), 1022–1028. Ayittey, J., Banini, G., 2009. Country Stat Ghana – First Panorama Report. SRIDMoFA, Accra, Ghana, p. 45. Bao, J., Ao, Z., Jane, J., 2005. Characterization of physical properties of flour and starch obtained from gamma-irradiated white rice. Starch-Stärke 57 (10), 480–487. Bao, J., Shu, Q., Xia, Y., Bergman, C., McClung, A., 2001. Effects of gamma irradiation on aspects of milled rice (Oryza sativa) end-use quality. J. Food Qual. 24 (4), 327–336. Cheetham, N.W.H., Tao, L., 1998. Variation in crystalline type with amylose content in maize starch granules: an X-ray powder diffraction study. Carbohydr. Polym. 36 (4), 277–284. D’Silva, T.V., Taylor, J.R.N., Emmambux, M.N., 2011. Enhancement of the pasting properties of teff and maize starches through wet–heat processing with added stearic acid. J. Cereal Sci. 53 (2), 192–197. Darfour, B., Ocloo, F.C.K., Wilson, D.D., 2012. Effects of irradiation on the cowpea weevil (Callosobruchus maculates F.) and moisture sorption isotherm of cowpea seed (Vigna unguiculata L. Walp). Arthropods 1 (1), 24–34. El Saadany, R., Foda, Y., El Saadany, F., 1979. Improving of Egyptian rice by means of gamma irradiation. Starch-Stärke 31 (7), 230–234. Falade, K.O., Semon, M., Fadairo, O.S., Oladunjoye, A.O., Orou, K.K., 2014. Functional and physico-chemical properties of flours and starches of African rice cultivars. Food Hydrocoll. 39 (0), 41–50. Gayin, J., Manful, J., Johnson, P., 2009. Rheological and sensory properties of rice varieties from improvement programmes in Ghana. Int. Food Res. J. 16, 167–174. Hayashi, T., Okadome, H., Toyoshima, H., Todoriki, S., Ohtsubo, K., 1998. Rheological properties and lipid oxidation of rice decontaminated with low-energy electrons. J. Food Prot. 61, 73–77. Kim, S.K., Kim, H.Y., 2013. Effect of high proton beam irradiation on pasting properties of rice starch. J. Crop Sci. Biotechnol. 16 (2), 161–166. Leach, H.W., McCowen, L., Schoch, T.J., 1959. Structure of the starch granule. I. Swelling and solubility patterns of various starches. Cereal Chem. 36 (6), 534–544. Liu, T., Ma, Y., Xue, S., Shi, J., 2012. Modifications of structure and physicochemical properties of maize starch by γ-irradiation treatments. LWT - Food Sci. Technol. 46 (1), 156–163. Loaharanu, S., Sutantawong, M., Ungsunantawiwat, A., 1971. Sensory acceptability evaluation of irradiated rice,Oryzae sativa indica. Office of Atomic Energy for Peace, Bangkok, Thailand. MacArthur, L.A., D'Appolonia, B.L., 1983. Gamma radiation of wheat. I. Effects on dough and baking properties. Cereal Chem. 60 (6), 456–460. Maeda, T., Maryanto, Morita, N., 2004. Characteristics of java taro starches and physical properties of acid- and heat-treated taro starches. J. Appl. Glycosci. 51 (2), 109–113. Narayana, K., Rao, M.S.N., 1984. Effect of partial proteolysis on the functional properties of winged bean (Psophocarpus tetragonolobus) flour. J. Food Sci. 49 (3), 944–947. Roy, M.K., Ghosh, S.K., Chatterjee, S.R., 1991. Gamma irradiation of rice grains. J. Food Sci. Technol. 28, 337–340. Sabularse, V., Liuzzo, J., Rao, R., Grodner, R., 1992. Physicochemical characteristics of brown rice as influenced by gamma irradiation. J. Food Sci. 57 (1), 143–145. Sabularse, V.C., Liuzzo, J.A., Rao, R.M., Grodner, R.M., 1991. Cooking quality of brown rice as influenced by gamma irradiation, variety and storage. J. Food Sci. 56 (1), 96–98. Sathe, S., Salunkhe, D., 1981. Functional properties of the great northern bean (Phaseolus vulgaris L.) proteins: emulsion, foaming, viscosity, and gelation properties. J. Food Sci. 46 (1), 71–81. Sokhey, A., Chinnaswamy, R., 1993. Chemical and molecular properties of irradiated starch extrudates. Cereal Chem. 70, 260. Tomlins, K., Manful, J., Gayin, J., Kudjawu, B., Tamakloe, I., 2007. Study of sensory evaluation, consumer acceptability, affordability and market price of rice. J. Sci. Food Agric. 87, 1564–1575. Tomlins, K.I., Manful, J.T., Larwer, P., Hammond, L., 2005. Urban consumer preferences and sensory evaluation of locally produced and imported rice in West Africa. Food Qual. Prefer. 16, 79–89. Wang, U.P., Lee, C.Y., Chang, Y.L., Yet, C.L., 1983. Gamma radiation effects on Taiwan produced rice grains. Agric. Biol. Chem. 47, 461–472. Wootton, M., Djojonegoro, H., Driscoll, R., 1988. The effect of gamma irradiation on the quality of Australian rice. J. Cereal Sci. 7, 309–315. Yu, S., Ma, Y., Menager, L., Sun, D.-W., 2012. Physicochemical properties of starch and flour from different rice cultivars. Food Bioprocess Technol. 5 (2), 626–637.
4. Conclusions All the rice cultivars exhibited A-type crystallinity pattern, and varied pasting properties. Gamma irradiation did not change the XRD pattern of the rice cultivars. The pasting properties (viscosity) of the rice cultivars were reduced by gamma irradiation. The study shows that flours from gamma irradiated rice cultivars have potential in food formulations that require low viscosity, such as children foods.
Acknowledgement We are grateful to the Department of Food Science, University of Pretoria, South Africa for allowing us use their RVA. Thanks to Prof. Naushad M. Emmambux for his support. Thanks also go to the technicians and technologists at the XRD laboratory, Department of Physics, University of Ghana for helping us with the XRD analysis.
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Effect of gamma irradiation on physicochemical, functional and pasting properties of some locally-produced rice (Oryza spp) cultivars in Ghana Fidelis C.K. Ocloo a,n, Mavis Owureku-Asare a, Joyce Agyei-Amponsah a, Wisdom S.K. Agbemavor a, Martin N.Y.H. Egblewogbe b, Franklin B. Apea-Bah a, Adjoa Sarfo a, John Apatey a, Henry Doku c, Dora Ofori-Appiah a, Ernestina Ayeh a a Radiation Technology Centre, Biotechnology and Nuclear Agriculture Research Institute. Ghana Atomic Energy Commission, P.O. Box LG 80, Legon, Accra, Ghana b Department of Physics, University of Ghana, Legon, Accra, Ghana c Crop Research Institute, Council for Scientific and Industrial Research, P.O. BOX 3785, Kumasi, Ghana
H I G H L I G H T S
Effect of gamma irradiation on properties of some rice cultivars in Ghana was investigated. Gamma irradiation decreased pH and swelling power, whereas solubility increased. Gamma irradiation did not change the XRD pattern of the rice cultivars. Gamma irradiation decreased peak time for BAL and VNT rice cultivars. Gamma irradiation decreased PV, HPV, BDV, FV and SBV for all the rice cultivars.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 February 2016 Received in revised form 22 August 2016 Accepted 28 August 2016 Available online 29 August 2016
Rice (Oryza sativa L.) is a staple crop in Ghana and much of West Africa, where it serves as an important convenience food for urban consumers. The objective of this study was to determine the effect of gamma irradiation as insect disinfestation technique on some physicochemical, functional and pasting properties of selected locally-produced rice cultivars in Ghana. Four local rice cultivars and an imported (commercial) type were purchased, cleaned and irradiated at doses of 0.0, 0.25, 0.50, 0.75, 1.0 and 1.5 kGy. The irradiated rice cultivars were milled and their physicochemical, functional and pasting properties determined. There were reductions in pH and swelling power, as well as increase in solubility of rice cultivars after gamma irradiation. Gamma irradiation did not change the XRD pattern of the rice cultivars. Gamma irradiation significantly (Po 0.05) decreased peak time for BAL and VNT rice cultivars. Gamma irradiation significantly (P o 0.05) decreased PV, HPV, BDV, FV and SBV for all the rice cultivars. This study shows that flours from gamma irradiated rice cultivars have potential in food formulations that require low viscosity. & 2016 Elsevier Ltd. All rights reserved.
Keywords: Rice Gamma irradiation Characteristics XRD
1. Introduction Rice (Oryza sativa L.) has become a staple in Ghana and much of West Africa where it serves as an essential convenience food for urban people (Tomlins et al., 2007). Rice recorded the highest deficit (210,700 metric tonnes) on the domestic food supply and demand position for Ghana in 2008, with a per capita consumption of 15.1 kg/annum and an estimated national consumption of
n
Corresponding author. E-mail addresses: fi[email protected], ocloofi[email protected] (F.C.K. Ocloo). http://dx.doi.org/10.1016/j.radphyschem.2016.08.025 0969-806X/& 2016 Elsevier Ltd. All rights reserved.
353,300 metric tonnes (Ayittey and Banini, 2009). In Ghana, rice is utilized in a broad range of food products; the most common include ‘jollof rice’, ‘rice balls’, rice porridge, fried rice and plaincooked rice. Although rice forms a major part of the Ghanaian diet, locally grown rice is not patronized due to its variable quality. Several factors account for the variability in rice quality, and the most prominent factors being poor sensory and physical qualities (Tomlins et al., 2005). These quality defects arise not only from inappropriate post-harvest handling, but also from poor planting materials and poor agronomic practices (Gayin et al., 2009). Due to its chemical composition and production chain, rice is susceptible to infestation by insects which reduces the economic
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Table 1 Effect of gamma irradiation on some physicochemical and functional properties of rice cultivars.† Cultivar/ Type
Dose (kGy)
Moisture (%)
pH
Bulk density (g/ml) Solubility (%)
Swelling power (g/g)
Water Absorption capacity (ml/g)
Oil absorption capacity (ml/g)
BAL
0 0.25 0.50 0.75 1.0 1.5
12.7de 7 0.1 12.7de 7 0.1 12.5de 7 0.2 12.4de 7 0.1 12.8e 7 0.1 12.6de 7 0.1
6.10l 7 0.00 6.70r 7 0.00 6.04i 7 0.00 6.05j 7 0.00 6.05j 7 0.00 6.05j 7 0.00
0.91efgh 7 0.02 0.89cdef 70.01 0.85bc 7 0.04 0.89cdef 70.07 0.91efgh 7 0.03 0.82ab 70.03
7.3abcdefg 71.0 8.2abcdefgh 7 3.2 9.6efghi 7 1.5 9.0defgh 7 2.0 9.3defghi 7 2.6 7.0abcdef 7 0.6
8.6fg 7 0.6 8.5fg 7 0.4 8.8g 7 0.4 8.2efg 7 0.7 7.8def 7 0.1 7.9defg 7 0.2
1.5efg 7 0.1 1.4def 7 0.0 1.4def 7 0.0 1.4def 7 0.0 1.3cde 70.1 1.2bcd 7 0.0
1.2bc 7 0.2 1.2bc 7 0.2 1.3cd 7 0.1 1.3cd 7 0.2 1.3cd 7 0.2 1.4de 70.1
VNT
0 0.25 0.50 0.75 1.0 1.5
11.8abcde 70.0 12.3de 7 0.1 12.3de 7 0.0 11.7abcd 7 0.1 11.7abcd 7 0.1 12.1cde 7 0.1
5.95h 70.00 5.93g 7 0.00 5.92f 7 0.00 5.93g 7 0.00 5.92f 7 0.00 5.93fg 7 0.00
0.89cdef 70.05 0.86bcd 7 0.02 0.88cde 7 0.02 0.91efgh 7 0.01 0.85bc 7 0.02 0.88cde 7 0.02
6.8abcde 70.1 6.9abcdef 7 0.4 12.0ijk 72.0 15.0lmn 7 1.2 16.3mn 7 0.5 6.0ab 71.0
7.5cde 70.6 7.7def 7 0.8 7.0bcd 7 0.4 7.9defg 7 0.5 7.8def 7 0.2 7.9defg 7 0.8
1.3cde 70.1 1.4def 7 0.2 1.4def 7 0.1 1.2bcd 7 0.1 1.4def 7 0.0 1.3cde 70.1
1.4de 70.1 1.4de 70.1 1.1ab 7 0.1 1.2bc 7 0.1 1.2bc 7 0.2 1.1ab 7 0.1
VNS
0 0.25 0.50 0.75 1.0 1.5
12.6de 7 0.1 12.5de 7 0.0 12.3de 7 0.1 12.5de 7 0.1 12.0bcde 7 0.0 12.5de 7 0.1
6.10l 7 0.00 6.11m 7 0.00 6.10l 7 0.00 5.81d 7 0.00 6.04i 7 0.00 6.08k 7 0.00
0.96i 7 0.02 0.91efgh 7 0.01 0.86bcd 7 0.01 0.87cde 7 0.02 0.90defg 7 0.02 0.86bcd 7 0.02
19.8o 72.0 13.1jkl 7 2.4 8.6bcdefgh 70.4 14.1klm 7 1.8 8.8cdefgh 7 1.4 10.0ghi 7 1.0
6.6bc 7 0.4 5.6a 7 1.3 6.1ab 7 0.5 6.6bc 7 0.2 7.1cd 7 0.5 7.0bcd 7 0.2
1.1abc 7 0.1 1.2bcd 7 0.1 1.2bcd 7 0.2 1.2bcd 7 0.0 1.1abc 7 0.1 1.0a 70.1
1.4de 70.1 1.4de 70.1 1.3cd 7 0.1 1.4de 70.0 1.4de 70.1 1.4de 70.0
VWR
0 0.25 0.50 0.75 1.0 1.5
12.6de 7 0.0 14.5f 73.5 12.7de 7 0.0 12.3de 7 0.1 12.6de 7 0.3 12.6de 7 0.0
6.31p 7 0.00 6.29o 7 0.00 6.23n 70.00 6.32q 7 0.00 5.89e 7 0.00 6.31p 7 0.00
0.87cde 7 0.02 0.88cde 7 0.02 0.78a 7 0.03 0.81a 7 0.03 0.92fgh 7 0.01 0.88cde 7 0.04
5.4a 7 0.3 8.0abcdefgh 7 1.6 6.7abcd 7 0.1 8.9defgh 7 1.6 8.5bcdefgh 70.8 9.7fghi 7 1.4
7.9defg 7 0.1 10.3h 7 0.2 8.6fg 7 0.3 8.5fg 7 0.8 8.8g 7 1.3 8.8g 7 0.7
1.1abc 7 0.1 1.2bcd 7 0.0 1.1abc 7 0.1 1.2bcd 7 0.1 1.2bcd 7 0.1 1.2bcd 7 0.1
1.2bc 7 0.1 1.0a 70.2 1.3cd 7 0.3 1.3cd 7 0.1 1.4de 70.2 1.3cd 7 0.1
JAS
0 0.25 0.50 0.75 1.0 1.5
11.1abc 7 0.1 11.0ab 70.1 10.0a 7 0.1 10.8a 7 0.2 11.1abc 7 0.3 10.9a 7 0.1
5.59b 7 0.00 5.61c 7 0.00 5.59b 7 0.00 5.58ab 70.00 5.58ab 70.00 5.58ab 70.00
0.86bcd 7 0.00 0.90defg 7 0.01 0.89cdef 70.02 0.90defg 7 0.02 0.90defg 7 0.01 0.93ghi 70.03
6.1abc 7 1.4 13.2kl 7 2.3 17.1no 7 1.2 14.4klmn 7 3.5 8.1abcdefgh 7 2.3 10.3hij 73.0
7.8def 7 0.8 8.4efg 7 0.6 7.5cde 70.3 8.2efg 7 0.3 7.9defg 7 0.4 8.1efg 70.3
1.6gh 7 0.1 1.3cde 70.1 1.2bcd 7 0.0 1.3cde 70.1 1.2bcd 7 0.0 1.3cde 70.1
1.1ab 7 0.1 1.4de 70.2 1.2bc 7 0.3 1.3cd 7 0.0 1.3cd 7 0.1 1.1ab 7 0.1
†
Each value represents the mean of three experiments 7 standard deviation. Values with different letters in a column are significantly different at P o 0.05.
value of local rice varieties. Gamma irradiation has been used for insect disinfestation and microbial decontamination of foods (Aldryhim and Adam, 1999; Loaharanu et al., 1971). The use of irradiation is however limited by its effect on rice quality. Irradiation has been reported to cause changes in colour, amylose content, water absorption, loss of solids during cooking, paste viscosity, cooked rice hardness and oxidative rancidity in rough and brown rice (Hayashi et al., 1998; Roy et al., 1991; Sabularse et al., 1992, 1991; Wang et al., 1983; Wootton et al., 1988). Similar effects have been reported when milled rice was irradiated (Bao et al., 2001; Loaharanu et al., 1971). Various gamma irradiation doses have been reported to maintain the sensory quality of irradiated rice. An acceptable limit below 3 kGy was recommended for Taiwanese rice (Wang et al., 1983) and up to 5 kGy for Indian rice (Roy et al., 1991). Bao et al. (2001) also stated that irradiation of milled rice for human consumption should be limited to a maximum dose of 2–4 kGy, due to its negative effect on rice colour and aroma. However, a maximum dose of 1 kGy was suggested for Australian rice and ordinary Thai rice (Loaharanu et al., 1971; Wootton et al., 1988). There is little information on the effects of gamma irradiation (for insect disinfestation) on the quality characteristics of the resultant flours obtained from local rice varieties. The objective of this study was to determine the effect of gamma irradiation as insect disinfestation technique on some physicochemical, functional and pasting properties of selected locally-produced rice cultivars in Ghana with the aim of preserving and widening the utilization of the rice cultivars.
2. Materials and methods 2.1. Materials 2.1.1. Collection and preparation of rice cultivars Four local rice cultivars, namely ‘Viwotor’ (VWR), ‘Viwonor’ short (VNS), ‘Viwonor’ tall (VNT) and ‘Balemi’ 1 (BAL) were bought from rice farmers in Kpong, Ghana. One imported rice type, Jasmine (JAS) was also purchased from a local market in Accra, Ghana. The paddy rice samples were sorted to remove any extraneous materials and defective rice seeds. The local rice cultivars were dehulled and then packaged into low density polyethylene bags (about 50 g each) along with the imported rice sample for gamma irradiation.
2.2. Methods 2.2.1. Gamma irradiation The five packaged rice samples (50 g each) were irradiated using a gamma irradiation facility, Cobalt 60 source (SLL-515, Hungary) at the Radiation Technology Centre (RTC) of the Ghana Atomic Energy Commission (GAEC). Samples were exposed to gamma irradiation doses of 0.0, 0.25, 0.50, 0.75, 1.0 and 1.5 kGy with a dose rate of 0.63 kGy/h. The absorbed dose was confirmed using Fricke's dosimetry system. The irradiated rice samples were milled into flour to pass through 250 mm mesh using a hammer mill (Brook Crompton Series 2000, England) and then packed into low density polyethylene bags prior to analyses.
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Fig. 1. a: Effect of gamma irradiation on XRD pattern and relative crystallinity of BAL rice cultivar, b: effect of gamma irradiation on XRD pattern and relative crystallinity of VNT rice cultivar, c: effect of gamma irradiation on XRD pattern and relative crystallinity of VNS rice cultivar, d: effect of gamma irradiation on XRD pattern and relative crystallinity of VWR rice cultivar, e: effect of gamma irradiation on XRD pattern and relative crystallinity of JAS rice cultivar.
2.2.2. Moisture determination The moisture content of gamma irradiated and un-irradiated rice samples was determined on their flours using the method described by AOAC (2000). Briefly, about 2 g of wellmixed rice flour was weighed into a weighed dish (previously heated to 130 °C and cooled). The dish with the flour sample was placed in the air-oven (Gallenkamp, United Kingdom) for 1 h at 130 °C. The dish with the dried flour was covered while still in the oven and then transferred into a desiccator to equilibrate. The cooled flour was then weighed and the moisture content determined.
2.2.3. pH pH of flours from gamma irradiated and un-irradiated rice samples was determined using the method described by AOAC (2000). In brief, about 10.0 g of the sample was weighed into a clean, dry Erlenmeyer flask and 100 ml of distilled water added. The mixture was shaken until particles were evenly suspended and free of lumps. The mixture was then allowed to stand for 10 min for the particles to settle. The supernatant was decanted into a 250 ml beaker, and the pH was determined, using pH metre (Mettler Toledo, Switzerland). Prior to the pH determination, the pH metre was calibrated using buffer solutions of pH 7.0 and 4.0.
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Table 2 Effect of gamma irradiation on relative crystallinity of the rice cultivars.† Cultivar/Type
Dose (kGy)
Relative crystallinity (%)
BAL
0 0.25 0.50 0.75 1.0 1.5
29.0abcd 71.4 31.5cd 7 0.7 28.0abcd 70.0 25.0a 7 0.1 30.5bcd 7 0.7 28.0abcd 70.0
VNT
0 0.25 0.50 0.75 1.0 1.5
32.0cd 7 5.7 28.0abcd 70.0 29.5abcd 72.1 30.5bcd 7 0.7 29.5abcd 70.7 30.0bcd 7 1.4
VNS
0 0.25 0.50 0.75 1.0 1.5
30.0bcd 7 4.2 29.0abcd 72.8 32.5d 7 4.9 28.5abcd 72.1 31.5cd 7 3.5 30.5bcd 7 3.5
VWR
0 0.25 0.50 0.75 1.0 1.5
27.5abc 7 2.1 28.0abcd 72.8 29.0abcd 70.0 29.5abcd 72.1 31.0bcd 7 2.8 30.0bcd 7 2.8
JAS
0 0.25 0.50 0.75 1.0 1.5
32.5d 7 0.7 28.5abcd 72.1 30.0bcd 7 1.4 29.5abcd 70.7 30.0bcd 7 1.4 26.5ab 7 1.4
† Each value represents the mean of three experiments 7standard deviation. Values with different letters in a column are significantly different at P o 0.05.
2.2.4. Bulk density The bulk density of flours from gamma irradiated and un-irradiated rice samples was determined using the method described by Narayana and Rao (1984). In brief, a calibrated centrifuge tube was weighed and filled with the flour samples to the 5 ml mark by constant tapping until there was no further change in volume. The contents were weighed and the difference in weight was taken. The bulk density of the sample was calculated by dividing the difference in weight by the volume of the sample. 2.2.5. Water and oil absorption capacities Water and oil absorption capacities of the flours from gamma irradiated and un-irradiated rice samples were determined using the method described by Sathe and Salunkhe (1981) as modified by Adebowale et al. (2005). In brief, about 1.0 g (dry basis) of the sample was dispersed in 10 ml distilled water or oil (Soybean oil) and the suspension stirred using a magnetic stirrer for 5 min. The suspension was centrifuged at 3500 rpm for 30 min and the supernatant water or oil measured in a 10 ml graduated cylinder. The densities of water and the refined oil were taken as 1.0 g cm 3 and 0.889 g cm 3, respectively. The water and oil absorption capacities were expressed as percentage water or oil absorption based on the original weight. 2.2.6. Solubility and swelling power Solubility and swelling power of flours from gamma irradiated and un-irradiated rice samples were determined based on the modifications of the method described by Leach et al. (1959). About 1 g of rice flour samples was weighed into a previously weighed 40 ml centrifuge tube and 40 ml of distilled water added. The suspension was stirred uniformly and gently avoiding excess
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force that might rapture the starch granules in the flour. The suspension was heated in a thermostatically controlled water bath (OLS 200 Grant, England) at 85 °C for 30 min, with constant stirring. The tube was removed from the water bath, wiped and allowed to dry and cool to room temperature. The supernatant was then poured into a weighed crucible and evaporated to dryness in an oven (Gallenkamp, United Kingdom) at 105 °C. The weight of dried supernatant after cooling and the weight of the sediment paste were used to calculate the solubility and swelling power, respectively. 2.2.7. X-ray diffraction (XRD) The crystal patterns and relative crystallinity of gamma irradiated and un-irradiated rice samples were determined on their flours using X-ray diffraction (XRD) (PANanalytical Empyrean diffractometer) (Eindhoven, the Netherlands). The powdered rice samples were equilibrated at 95% relative humidity (using a 22% glycerol solution) (Darfour et al., 2012) for 5 days at about 25 °C. The XRD operating conditions were: 45 kV, 40 mA and Cu Kα1 (0.154 nm). Samples were scanned from 5° to 40° (2θ) with a step size of 0.20° and a step time of 10 s. The relative intensity peaks were then plotted against 2θ peaks. Relative crystallinity of the flour samples was calculated as percent integrated area of crystalline peaks to the total integrated area above a straight baseline (Cheetham and Tao, 1998). 2.2.8. Pasting properties Pasting properties of gamma irradiated and un-irradiated rice samples were determined on their flours using a Rapid Visco Analyser (RVA Model 3D) (Newport Scientific, Warriewood, Australia). The method described by D'Silva et al. (2011) was used. Briefly, 3 g (db) of rice flour was suspended in distilled water and the weight adjusted with water to 28 g. The flour suspension was initially stirred with a speed of 960 rpm at 50 °C for 30 s and then stirred at 160 rpm for the entire period thereafter. The temperature was increased at a rate of 5.5 °C/min to 91 °C (since water boils at 95 °C in Pretoria, South Africa) and held at this temperature for 5 min. The paste was then cooled to 50 °C at a rate of 5.5 °C/min. The viscosity values were recorded in rapid visco units (RVU). The parameters evaluated from the curve were: peak viscosity (PV), trough/ hot paste viscosity (HPV), final viscosity (FV), setback viscosity (SBV), breakdown viscosity (BDV) and Peak time (time required to reach peak viscosity, PTime). 2.2.9. Statistical analysis Apart from pasting properties which were determined in duplicates, all other analyses were done in triplicates. A multifactor analysis of variance (ANOVA) was used to determine the effects of rice variety and irradiation dose on dependent variables. Fisher's least significant difference (LSD at Po0.05) was used for mean separation, to ascertain where differences existed. MINITAB statistical software (Minitabs Release 14.13, Minitab Inc., USA) was used for the statistical analysis.
3. Results and discussions 3.1. Physicochemical properties The moisture contents for gamma irradiated and un-irradiated JAS rice were significantly (P o0.05) lower than the local cultivars (BAL, VNT, VNS and VWR) (Table 1). Gamma irradiation did not significantly influence the moisture contents of the rice cultivars. Moisture content values for all the rice samples were low, indicating better storage stability of rice as well as its starch keeping quality (Maeda et al., 2004).
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Table 3 Effect of gamma irradiation on RVA pasting properties of rice cultivars.† Cultivar/Type
Dose (kGy)
PTime (min)
PV (RVU)
HPV (RVU)
BDV (RVU)
FV (RVU)
SBV (RVU)
BAL
0 0.25 0.50 0.75 1.0 1.5
12.2fgh 7 0.1 11.9def 7 0.1 13.0k 7 0.0 12.8ijk 7 0.1 12.3gh 70.4 10.9a 7 0.1
318.5mn 7 2.3 283.5k 7 0.8 263.8ij 715.1 295.5kl 7 7.1 249.4ghi 7 0.3 243.3gh 715.0
289.6no 7 1.0 256.1ijk 7 0.5 246.0hij 714.2 273.0lmn 77.7 230.7fgh 7 2.1 216.8ef 7 12.2
28.9hi 7 1.3 27.4ghi 7 0.3 17.7cde 70.9 22.5efg 7 0.6 18.7cde 71.8 26.5ghi 7 2.8
414.5no 71.9 359.2lm 7 4.3 330.3ijk 7 17.0 372.0m 7 4.7 329.3ijk 7 0.1 312.2hi 7 15.0
124.9n 7 0.9 103.1kl 7 4.8 84.2def 7 2.8 99.0ijk 7 3.1 98.5ijk 7 2.2 95.4hij 72.8
VNT
0 0.25 0.50 0.75 1.0 1.5
12.8ijk 7 0.3 13.0k 7 0.0 12.6hij 7 0.3 13.0k 7 0.0 12.8ijk 7 0.1 12.5hi 70.1
295.4kl 7 6.2 294.0kl 7 3.8 282.6k 7 1.4 222.0ef 7 3.2 231.0fg 710.0 193.3d 7 2.6
272.6klm 7 6.4 273.8lmn 71.5 257.9jkl 77.9 210.5e 7 3.0 218.7ef 7 10.4 183.2d 7 2.2
22.8efg 7 0.1 20.2def 7 2.3 24.7fgh 7 6.5 11.5ab 7 0.2 12.3ab 7 0.5 10.2a 7 0.4
365.4m 7 8.0 363.9lm 78.8 339.1jk 7 8.5 291.9fg 7 1.6 301.5gh 710.5 256.7e 7 2.0
92.8ghi 7 1.6 90.2fgh 7 7.3 81.2d 70.6 81.4d 71.4 82.8de 7 0.1 73.5c 7 0.2
VNS
0 0.25 0.50 0.75 1.0 1.5
13.0k 7 0.0 13.0k 7 0.0 13.0k 7 0.0 12.9jk 7 0.1 13.0k 7 0.0 13.0k 7 0.0
204.5de 7 18.0 167.7c 7 4.7 147.7b 73.6 167.5c 7 21.4 169.6c 7 6.4 121.6a 71.5
184.3d 7 15.8 148.8c 72.8 131.5b 7 2.5 149.8c 722.6 146.7bc 71.0 109.8a 7 1.6
20.1def 7 2.2 18.9cde 71.8 16.2bcd 7 1.1 17.7cde 71.2 22.9efg 7 5.4 11.9ab 7 0.2
211.1d 7 21.4 171.4bc 74.6 152.2b 71.9 177.0c 7 24.9 174.2c 7 1.4 131.3a 7 1.5
26.8ab 7 5.7 22.6ab 7 1.8 20.7a 7 0.5 27.2b 7 2.4 27.5b 7 0.4 21.6ab 70.1
VWR
0 0.25 0.50 0.75 1.0 1.5
11.0a 70.2 11.1ab 7 0.2 11.4bc 7 0.0 11.1ab 7 0.2 10.9a 7 0.2 11.2abc 7 0.2
352.8p 7 15.8 339.9op 74.4 319.1mn 7 14.7 285.3k 7 8.6 294.3kl 7 7.4 252.8hi 7 3.9
297.3o 7 9.9 291.0o 75.1 280.8mno 7 12.7 245.2hij 75.4 244.1hij 77.1 221.9ef 7 3.1
55.6n 7 5.9 49.0m 7 0.8 38.3kl 7 2.1 40.0l 7 3.2 50.3m 7 0.4 31.0ij 7 0.8
447.3p 7 14.5 424.5o 72.4 397.7n 7 14.8 367.0m 7 8.1 364.1lm 7 2.9 326.0ijk 7 8.0
150.1p 7 4.6 133.5o 7 2.8 116.9m 7 2.1 122.7mn 7 2.8 120.0mn 7 4.2 103.9kl 7 4.8
JAS
0 0.25 0.50 0.75 1.0 1.5
11.5c 7 0.1 11.5cd 7 0.2 11.6cde 7 0.0 12.2fgh 7 0.3 11.9ef 7 0.0 12.0efg 70.4
329.4no 73.1 308.3lm 7 5.7 279.5jk 7 0.6 257.6hi 7 8.4 242.9gh 70.6 204.8de 7 13.6
293.3o 7 0.0 274.0lmn 70.5 251.8ij 7 0.1 239.4ghi 76.2 224.6efg 7 1.0 190.1d 7 14.1
36.0jkl 7 3.1 34.3jk 7 5.1 27.7ghi 7 0.6 18.2cde 72.2 18.3cde 71.6 14.7abc 7 0.5
419.4o 71.1 395.0n 72.4 369.3m 7 0.4 345.2kl 710.1 324.3ij 73.1 277.9f 7 13.1
126.1n 7 1.1 121.0mn 7 2.9 117.5m 7 0.4 105.8l 73.8 99.7jkl 7 4.1 87.8efg 7 0.9
PTime ¼Peak Time; PV ¼Peak viscosity; HPV¼ Hot paste viscosity; BDV ¼ Breakdown viscosity; FV ¼Final viscosity; SBV ¼ Setback viscosity; PS ¼Paste stability. †
Each value represents the mean of two experiments 7standard deviation. Values with different letters in a column are significantly different at p o0.05.
parameter for determining packaging requirement and material handling in the food industry (Falade et al., 2014). Gamma irradiation significantly (P o0.05) decreased water absorption capacity and swelling power as well as increased the oil absorption capacity and solubility of the rice cultivars (Table 1). The above changes due to gamma irradiation have been attributed to depolymerisation of amylopectin chains in the starch molecules (El Saadany et al., 1979; Liu et al., 2012). 3.3. X-ray diffraction (XRD)
Fig. 2. A representative RVA pasting curve of flour from local rice cultivars compared with imported (commercial) type.
pH values for JAS were significantly (Po0.05) lower than the local cultivars (BAL, VNT, VNS and VWR) (Table 1). pH values decreased with increase in gamma irradiation dose. The decreases in pH, due to gamma irradiation were not in dose-dependent manner. The non-dose dependence effect observed could be due to the low doses used in the present study. The decreases in pH observed could be attributed to partial break down of starch molecules by the gamma rays, causing the formation of carboxylic acid (COOH) (Sokhey and Chinnaswamy, 1993). 3.2. Functional properties There were generally, varietal differences in the functional properties of the rice samples (Table 1). Gamma irradiation did not significantly (P 40.05) influence the bulk density values for all the rice cultivars (Table 1). Bulk density, is considered a useful
The X-ray diffractograms and relative crystallinity for gamma irradiated and un-irradiated rice cultivars are shown in Fig. 1a–e and Table 2, respectively. All the rice cultivars (irradiated and unirradiated) had major peak intensities at 2θ E15°, 17°, 18° and 23°. These 2θ peaks have been attributed to the presence of A-type crystal starches. Minor peak intensities were also observed at 2θ E20 and 27°. The peak observed at 2θ E20° indicates the presence of some V-type starch crystals in the rice cultivars. Gamma irradiation did not change the crystal type (XRD pattern) of the rice cultivars (Fig. 1a–e). Bao et al. (2005) reported an A-type X-ray diffraction pattern for flour and starch isolated from irradiated and un-irradiated white rice. Strong reflections at 2θ E15°, 17°, 18°, and 23° have also been reported by Yu et al. (2012). The relative crystallinity values for un-irradiated rice cultivars ranged from 29.0% to 32.5% (Table 2). There were no significant differences (P 40.05) between the relative crystallinity values for all the rice cultivars. Gamma irradiation had no significant (P 40.05) effects on the relative crystallinity of the rice cultivars (Table 2). Bao et al. (2005) reported relative crystallinity value of 31.5% for flour from un-irradiated white rice.
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3.4. Pasting properties
References
The pasting behaviours of the rice cultivars varied (Table 3, Fig. 2). Significant (P o0.05) differences were found in peak time, peak viscosity, trough, breakdown viscosity, set back and final viscosities of the rice cultivars used in the present study. Similar variations have been reported by other authors (Asante et al., 2013). Gamma irradiation of the rice cultivars significantly (P o0.05) decreased peak time for BAL and VNT (Table 3). However, gamma irradiation did not change the peak time for VNS, VWR and JAS. Decreased pasting time has been reported for flours obtained from high proton beam irradiated rice cultivars (Kim and Kim, 2013). The current study indicates that gamma irradiation significantly (P o0.05) decreased the PV, HPV, BDV, FV and SBV for all the cultivars studied (Table 3). However the decreases were not dosedependent in most cases. The non-dose dependence effect observed, as stated earlier could be due to the low doses used in the present study. The decreases in these characteristic features (PTime, PV, HPV, BDV, FV and SBV) of rice flour upon gamma irradiation of the rice seeds could be due to depolymerisation of the rice starch molecules through chain scission. Gamma irradiation (0–3 kGy) of brown rice has been reported to decrease the peak viscosity, hot paste viscosity, final viscosity, breakdown viscosity and setback viscosity (Sabularse et al., 1992). Decreased viscosity has been attributed to degradation and uncoiling of starch chains as well as breakdown of hydrogen bonding within the starch molecules by irradiation (MacArthur and D'Appolonia, 1983). Also, decreased setback viscosity due to irradiation has been attributed to the breakdown of the starch molecules which were not able to produce longer helical structures and association between starch molecules, hence less starch retrogradation (Sabularse et al., 1992). Similar trends have also been reported by Bao et al. (2001) and Kim and Kim (2013) for flours obtained from gamma irradiated (2, 4, 8 and 12 kGy) and proton beam irradiated (0, 300, 500, 800, 1200 Gy) milled rice, respectively. The reductions in viscosities of the rice cultivars due to gamma irradiation suggest that irradiated rice may not be suitable for use as thickeners in foods. However, they can be used in children foods, such as soft porridge. Due to the low viscosity of the flours obtained from gamma irradiated rice, more solids could be added to enhance the production (preparation) of high energy porridges to support the child's nutritional requirements. The flours from gamma irradiated rice could also be used as starch matrix fillers.
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4. Conclusions All the rice cultivars exhibited A-type crystallinity pattern, and varied pasting properties. Gamma irradiation did not change the XRD pattern of the rice cultivars. The pasting properties (viscosity) of the rice cultivars were reduced by gamma irradiation. The study shows that flours from gamma irradiated rice cultivars have potential in food formulations that require low viscosity, such as children foods.
Acknowledgement We are grateful to the Department of Food Science, University of Pretoria, South Africa for allowing us use their RVA. Thanks to Prof. Naushad M. Emmambux for his support. Thanks also go to the technicians and technologists at the XRD laboratory, Department of Physics, University of Ghana for helping us with the XRD analysis.