Effect of Gamma Irradiation on Some Nutritional Factors of rice. - 1
2.5 EFFECT OF GAW1A IRRADIATION CN SOME NUTRITIONAL FACTORS OF RICE
Mohd. Khan bin Ayob Osman Hassan UKM
INTRODUCTION
When rice is treated with garrma irradiation, for insect and microbial disinfestation, several nutritional factors have to be evaluated to ensure whether or not the technique produces any adverse effect. For instance, it is important to investigate the effect of irradiation on the Theological properties of carbohydrate such as solubility, hygroscopy, viscosity, etc. that affect texture and acceptance of processed product. Sreenivasan (1973) stated that in gamma-irradiation of wheat produced molecular degradation in the starch and the protein components.
Type of packaging material used is another critical factor and should be chosen carefully, though the factor is more important in terms of protection against insects and microbial reinfestation after processing procedures.
Thus, in this work the effect of gamma irradiation at 0 (control), 0.2, 0.4, 0.6, 0.8, 1.0 and types of packaging material used, namely, gunny sack (G), Heavy duty Polyethylene (HD/PE), Woven Non-Laminated (WNL) and Woven Laminated (WL) bags, on moisture content, gel viscosity and reducing sugar of rice was observed.
MATERIALS AND METHODS
Samples were taken to determine their moisture content, gel viscosity and reducing sugar content. Before the determination the samples were ground into rice flour. Data obtained in the first analysis was considered at 0 time (mcnth). Further sanpling, grinding and analysis were repeated every 3 rrcnths.
Moisture content Moisture content of the flour was determined by drying method using infra-red balance.
Gel viscosity The viscosity was determined by using Brookfield Visccmster Model RV-4 using spindel no. 1. Gel was made by heating a colloidal solution of 7.5% rice flour until it is boiling for 2 to 3 min with continuous stirring (20 rpm). The viscosity was determined at temperature 95 *_ 2°C and 80 _+ 2°C, in centipoise (cps).
Reducing sugar Sugar was extracted from 2 g sample of rice flour by using 250 ml warm water at 40 C. 5 ml of the filtrate was used for the determination of reducing sugar content using Nelson method (Pearson, 1976). The content was recorded as % (W/W) of rice flour.
RESULTS M) DISCUSSION
Moisture content Table 2.5.1 indicates the moisture content of samples in various packaging materials during storage. The results show that irradiation doses and packaging material did not significantly (P<0.05) affect the moisture content. The content through-out storage time varied from 9.2 to 12.5% with an average of 11.1%. The average of moisture content in bag G, HD, WNL and WL was 11.3%, 11.2%, 10.9% and 11.9% respectively.
Gel viscosity Figure 2.5.1 indicates gel viscosity of samples in various packaging materials as measured at 95 + 2 C and Figure 2.5.2 the viscosity as measured at 80 _+ 2 C. Results show that packaging materials used dis not affect the gel viscosity. However, it was greatly influenced by irradiation doses and storage time. It was found that increasing the doses markedly reduced the gel viscosity (Figures 2.5-1 and 2.5.2). When the rice was stored for several months, its gel viscosity progressive- ly reduced for the first 3 months of storage. The reduction was relatively slow after 6 months. In a separate study conducted an a pure rice variety (MR 77) a similar trend was observed. As mentioned by Desrosier (1979) irradiation produced molecular changes in starch. Depolyrrerization and degradation occurred with the production of maltotetrose fragments. High dosage of irradiation ultimately yielded hexose units. However, in this study, reduction in visco- sities was not followed by any significant increase in reducing sugar content (Figure 2.5.3). Hence, it is possible that in this case, the degradation of polysaccharide did not proceed beyond the maltotetrose stage.
Reducing sugar
Figure 2.5.3 indicates the content of reducing sugar of samples in various packaging materials. Results showed that the irradiation doses applied and the storage period up to 9 months did not significantly (P<0.05) affect the content. The average contents of reducing sugar of rice packed in bag G, KD, WNL and WL were 0.64%, 0.62%, 0.59% and 0.55%., respectively.
REFERENCES
Desrosier, N.D. (1979). The Technology of Food Preservation. AVI. Publ. Westport Conn. V. 448 Pearson, D. (1976). Chemical Analysis of Food. Churchil Livingstone Press, London. Sreenivasan, A. (1973). Compositional and Quality Changes in Some Irradiated Foods. In Improvement of Food Quality by Irradia- tion (Proc. Panel, Vienna, 1973) FAD/IAEA. 129-155. - 4
Table 2.5.1: Effect of Storage Tiiie and Packaging Materials en Moisture Content (%) of Control and Irradiated Rice
Storage ** Dose (kGy) Packaging Materials (month) D 0.2 0.4 0.6 0.8 1.0 2.0
G 12.5 12.0 11.5 11.2 11.5 11.5 11..7 HD 11.6 10,.4 11.6 10.4 10.4 15-4 11..5 0 WNL 12.6 11.6 11.6 11.8 11.4 11.7 11..8 WL 12..9 11..4 11.0 11.7 11.3 11.2 11..0
G 12..5 10..8 11.0 11..0 11.0 11.8 11..5 HD 11..1 11.,1 11.2 11..2 11.2 12.0 11..2 3 WNL 11..6 11..6 11.4 11.A 11.4 11.4 11.A WL 11..8 11..8 11..5 11..6 11..4 11.2 11.A
G 12..0 10.0 11.0 12..0 12,.0 10.0 10..0 HD 11..5 11.5 11..0 10..0 11..5 10.5 12..5 6 WML 12..0 11.5 11..0 11.5 11..0 11.5 11.5 WL 12.,0 12.0 11..5 11..5 11..5 11.5 11.5
G 10..8 11.8 10.8 11..0 11..6 "11.6 11.0 HD 9..8 10.5 10..0 11.8 10..6 10.2 10.6 9 WNL 9.8 10.6 11..2 9-c 11..4 10.4 9.2 WL 11.4 10.2 10..6 11.8 11..0 10.2 11.0
G 11.0 11.5 11..0 11.0 10.,8 11.2 10.9 HD 11.0 11.0 11.5 10.4 11.,6 11.2 11.2 24 WNL 11.5 11.2 11.3 10.6 11.0 10.4 10.6 WL 10.2 10.6 10.1 11.7 10.2 10.6 10.0
G = Gunny, HD = Heavy Duty Polyethylene WNL = Woven ncn laminated polypropylene, WL = Woven laminated polypropylene O--
^ 2~T
PE (HD)
77 24 VISCOSITY 1 MUM 3 24 WL 4- Fig. 2.5.1. Effect of Storage Time on the Viscosity (at 95°C) of Rice Gel After Irradiation at Different Dose. •a 0 JcGy t —' ; 0.4 kGy x , 0.8 JcGy ^ ; 2.0 leGy n PE (HD) —o-- VISCOSITY (cp.) AT 80 C WNL D- 2 ••n—.. 1 Mi •WL •>^.. 1 nnn I HE '-MONTHS Fig. 2.5.2: Effect of Storage Time on the Viscosity (at 80 C) of Rice Gel After Irradiation at Different Dose Q. •. 0 JcGy 4-—• 0.4 x -. 0.8 kOy A A 2.0 JcGy WNL 0. 70 3- — Vjl . (£.1.1 ©. 50 -•K— — 0. 4U 0. 30 6. 20 0 • 1 0 8 1 0 . 90 0 . 80 WL 0. 70 0. 6-0 0. 50 0. 40 0 . 30 0. 20 0. 10 -*-£ TIME •:• MONTH g. 2.5.3: The Effect of Storage Time on the Reducing Sugar Content of Rice Gel Affter Irradiation at Different Dose 0 kGy 0.4 JcGy 0.8 JcGy 2.0 W3y