INFLUENCE OF GAMMA RADIATION ON RHEOLOGICAL PROPERTIES OF WHEAT FLOUR

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1 Eurotherm Seminar 77 Heat and Mass Transfer in Food Processing June 20-22, 2005 Parma, Italy INFLUENCE OF GAMMA RADIATION ON RHEOLOGICAL PROPERTIES OF WHEAT FLOUR Kanemaru, J. *, Tavares, D. T. *, Singer, C. S. *, Hilsenrath, F. C. *, Sabato, S. F., Tadini, C. C. * * Food Eng. Lab. Chemical Eng. Dept., Escola Politécnica, São Paulo University, Brazil, P. O. Box 61548, , SP, Brazil, Phone: , Fax: , catadini@usp.br IPEN-CNEN/SP, Radiation Technology Center, São Paulo, Brazil. Av. Lineu Prestes, 2242, , SP, Brazil, Phone: ext270, Fax: , sfsabato@ipen.br. ABSTRACT Influence of gamma radiation (0.0, 0.5, 1.0 and 2.0 kgy) on rheological properties produced from irradiated wheat before and after milling was investigated. Wheat flour from irradiated grains and irradiated wheat flour were submitted to physicochemical and rheological analyses. Water content was 15.6 ± 0.6 % and 15.5 ± 0.5 % for and flour, respectively. ANOVA indicated that different doses of irradiation did not influence protein content of the flours. In grains irradiation caused a decrease of Falling Number, whereas an increase in flour when submitted to irradiation up to 1.0 kgy. Water absorption was increased by the irradiation, whereas this effect did not influence this property of the irradiated. The stability values suggest weaker dough from flour produced from irradiated grains. However this property was not influenced by irradiation in flour. This observation can be confirmed in the low MTI values. Irradiation applied on increased ratio number indicating stronger dough. Irradiation in studied doses has affected the dough development measured by rheofermentometer in a different manner showing a decreasing tendency. Conversely, irradiation has increased the retention coefficient (%) of the dough. INTRODUCTION Cereal grains are susceptible to attack by a variety of insects and microorganisms during post-harvest storage. Research in many countries has shown the technological feasibility of using gamma irradiation to preserve cereal grains and reduce post-harvest losses caused by insects and microorganisms [1]. Irradiation has also been used as an alternative to fumigation with methyl bromide once it will be banished in 2005 due to its contribution to the ozone layer deterioration [2]. The most important parameter of irradiation process is the energy absorbed by material known as absorbed dose. Doses are established according to insects and stages present in material and the objective of treatment. It is important that food receives a minimum required dose to achieve the desired objective and the uniformity must be maintained in a reasonable level [3]. An extensive research realized in Bhabha Atomic Research Centre situated in India showed effective use of low dose of gamma radiation (bellow 1 kgy) to disinfect insects in [4]. Rao et al. (1975) [5] discussed in their paper about different researches with gamma irradiation in wheat. In general, doses above 5 kgy have had bad influence on bread quality. Studies in irradiated characteristics have concluded that 3 kgy did not alter too much and it could be classified as good to make bread. Doses of 4.5 kgy and 6 kgy have significantly changed studied characteristics, at 5% confidence level [6]. The objective of this work was to study the influence of gamma radiation on rheological properties produced from irradiated wheat before and after milling. For this purpose, from irradiated grains and irradiated were submitted to physicochemical and rheological analyses. MATERIALS AND METHODS Wheat grains from the same batch (60 kg) from Argentina, were divided into two parts. The first one (30 kg) was portioned into 0.5 kg bags and irradiated, in normal atmosphere and at room temperature, in a 60 Co Gamma cell 220 (AECL), with doses of 0.0, 0.5, 1.0 and 2.0 kgy. After that, were milled on a Brabender Quadrumat to. Wheat flour from irradiated grains was submitted to physicochemical and rheological analyses. The other part (30 kg) was milled and portioned into 0.5 kg bags, and irradiated at same doses than. Irradiated wheat flour was submitted to same laboratory analyses. Physicochemical analyses Flour color was analyzed using a Minolta colorimeter (Color Quest II, Hunterlab, Reston, VA, USA). Three dimensions L, a and b were acquired from each flour, in triplicate. The L values give a measure of the lightness of the product color from 100 for perfect white to zero for black, as the eye would evaluate it. The redness/greenness and yellowness/blueness are denoted by a and b values, respectively. Crude protein content was determined according to AACC 46-11A method [7], in triplicate. A factor of 5.7 was used to calculate crude protein content. Water content was determined according to AACC 44-15A method [7], in triplicate.

2 Falling Number was determined, in duplicate, by using a Brabender apparatus (Falling number 1800, Perten Instruments, Huddinge, Sweden) according to AACC 56-81B method [7]. Rheological analyses Measurements of water absorption, dough development time DDT, dough stability and mixing tolerance index MTI were determined by using a farinograph (Brabender OHG, Duisburg, Germany) according to AACC method, constant flour weight procedure [7]. Dough extensibility and maximum resistance to an extension were determined using an extensograph (Brabender OHG, Duisburg, Germany) according to AACC method [7]. Dough development and gaseous release characteristics The rheofermentometer (CHOPIN, Tripette & Renaud, France) was used to study the dough development and gas release of dough prepared from from irradiated grains and from irradiated, according to CHOPIN protocol as follows: test temperature: 28.5ºC; dough contents: 250g flour, 3g instant dry yeast, 5g salt, hydratation according to farinographic results; test duration: 180 min. Measurements of rheofermentometer parameters included: H m = height (mm) of the dough at maximum gas formation time; T 1 = time in h or min of H m ; h = height at end of test; T x = time of gas release; V T = area below the higher curve, total gas production; V R = area below the lower curve, total gas retention; V L = area between the two curves, as shown in Figure 1. Figure 1: Parameters obtained from development and gas release curves. From rheofermentometer parameters it is possible to calculate two others ones, as follows: Weakening coefficient of the dough can be calculated from parameters obtained from dough development curve as in equation 1: H m h WC = 100 (1) Hm Retention coefficient of the dough can be calculated from parameters obtained from gas release curve as in equation 2: V R RC = 100 (2) VT Statistical analysis ANOVA was performed in all results using the statistical program Statgraphics for Windows v4.0 (Manugistics), at a confidence interval of 95%. RESULTS AND DISCUSSION Physicochemical analyses Color, crude protein and water contents, and Falling Number results of from irradiated grains and from irradiated are summarized in Table 1. Water content (%) was 15.6 ± 0.6 % and 15.5 ± 0.5 % for wheat grains and flour, respectively. These results are similar to those obtained by Silva (2003) [8], which showed that the water content did not change significantly with any of the irradiation doses applied on (3.0, 4.5 and 6.0 kgy). ANOVA indicated that different doses of irradiation did not influence the protein content of the flours produced with Brabender Quadrumat Mill, which were ± 0.41 % and ± 0.40 %, for flour produced from irradiated grains and from irradiated flour, respectively. So, results show that the irradiation did not alter the milling efficiency, giving similar rate of extraction. Falling Number is an indication of α-amylase activity in flour. In grains, irradiation caused a decrease of Falling Number, whereas a slight increase was observed in flour when submitted to irradiation up to 1.0 kgy (not statistically significant), followed by a decrease for 2 kgy irradiation dose (Figure 2). Probably, irradiation dose higher than 1.0 kgy changed the enzyme structure, which caused a decrease in its activity. Silva et al. (2002) [6] also observed a decrease on Falling Number with the increase of irradiation dose. For doses up to 4.5 kgy the Falling Number values where still within the range considered ideal for bread making. ANOVA indicated that different doses of irradiation slightly influenced the L color dimension, however no tendency was found. According to Marathe et al. (2002) [4], all color parameters of irradiated with doses between 0.25 and 1.0 kgy did not show statistically significant differences. However, Silva (2003) [8] noticed slight changes in color: irradiated flour became darker with

3 the increase of irradiation dose, there was an increase on the L parameter values. FN (s) Figure 2: Falling number variation with irradiation dose. Rheological analyses "Falling Number" 250 Results of rheological measurements obtained from farinograph and extensograph are summarized in Table 2. Water absorption is the amount of water that flour can absorb until the dough consistency reaches 500 BU (Brabender Units). Water absorption was increased by the irradiation, whereas this effect did not influence this property of the irradiated. Dough stability is the time needed before dough consistency starts to decline from 500 BU line. The stability values suggest weaker doughs from flour produced from irradiated grains. However, this property was not influenced by irradiation in flour. This observation can be confirmed in the low MTI values. Köksel et al. (1998) [1] showed that gamma-irradiation of wheat results in a weakening effect on dough mixing properties, which tends to be more pronounced at the 10 kgy level or higher. According to this study, it is highly likely that the direct effect of irradiation is on glutenin, which results in a deterioration of rheological properties and functional quality. Extensograph gives information about the viscoelasticity of dough. A combination of good resistance and good extensibility results in desirable dough properties. Extensibility of the dough is a measure of its elasticity and the maximum force reached, as the dough is known as the dough resistance. Irradiation applied on increased ratio number indicating stronger doughs. Dough development and gaseous release characteristics Rheofermentometer parameters of from irradiated grains and from irradiated are summarized in Table 3. The height of maximum dough development under constraint, H m, is related to the bread volume. This parameter decreased with irradiation dose on and on, although the time of maximum dough development, T 1 was not significantly influenced. This result suggests that bread made from irradiated or irradiated flour have smaller volume. However, Urbain (1986) [9] reported that bread made from flour irradiated on moderate doses (up to 2.0 kgy) might show an increase in volume, although higher doses cause a volume decrease. The height of the dough at the end of the test, h, decreased with irradiation dose higher than 0.5 kgy, in both and. However, the calculated values for weakening coefficient, WC, did not show significant statistical differences, which means that bread made from irradiated and non-irradiated wheat had proportionally the same amount of volume loss during fermentation (Figure 3). All the parameters obtained from the gas release curve were influenced by irradiation in both and flour. The apparent time of dough s porosity, T X, was increased by irradiation dose. The same occurred to the total volume of gas production, V T, and gas volume retained by dough at the end of the test, V R. In consequence of this, the volume of CO 2 released by dough during its fermentation, V L, decreased with irradiation dose. Thus, irradiation in and flour caused an increase in the retention coefficient, RC, which represents the amount of gas retained by dough at the end of fermentation (Figure 4). This parameter is strongly related to the quality of dough. These results suggest that irradiation improves the resistance of the gluten network. Table 1: Physicochemical results of from irradiated grains and from irradiated. Color L 91.5 a 91.7 b 91.7 b 91.5 a 91.5 a,b 91.6 a,b 91.6 b 91.4 a a 0.4 a 0.4 a 0.4 a 0.4 a 0.4 a 0.4 a 0.4 a 0.5 a b 10.4 a 10.5 a 10.7 b 10.9 c 10.4 a 10.4 a 10.2 a 10.4 a Protein content (%) 10.3 a 10.7 a 10.3 a 10.2 a 10.3 a 10.9 a 10.6 a 10.4 a Water content (%) 16.2 a 16.0 a 15.2 a 15.0 a 16.2 a 15.2 a 15.6 a 15.1 a FN (s) b b b a a,b a,b b a FN: Falling Number

4 Table 2: Results of from irradiated grains and from irradiated obtained from farinograph and extensograph Water abs. (%) 54.8 a 55.2 a 57.3 b 57.5 b 54.8 a 55.5 a 55.8 a 55.7 a DDT (min) 11.8 b 10.8 a,b 11.0 b 9.0 a 11.8 a 11.9 a 12.0 a 11.8 a Stability (min) 17.6 a 17.2 a 16.3 a 14.0 a 17.6 a 17.7 a 17.7 a 17.8 a MTI (BU) 10 a 15 a 23 a 28 a 10 a 10 a 15 b 10 a Extensibility (mm) 150 a 152 a 154 a 155 a 150 b 151 b 135 a 129 a Max. resistance (BU) 668 a,b 710 a 600 a 600 a 668 a 705 a 709 a 849 a Ratio number 2.9 a 2.9 a 2.5 a 2.4 a 2.9 a 3.0 a 3.6 a,b 4.5 b Water abs. : Water absorption (%) DDT: Time required for the dough development or time necessary to reach 500 BU of dough consistency Stability: time during dough consistency at 500 BU MTI: Mixing tolerance index (consistency difference between height at peak and to that 5 min later) Table 3: Results of from irradiated grains and from irradiated obtained from rheofermentometer curves. Dough development curve H m (mm) 19.1 c 19.3 c 10.0 a 14.2 b 19.1 c 15.1 bc 8.1 a 9.7 ab T 1 (min) a a a a a a a a h (mm) 12.4 bc 14.0 c 7.5 a 9.9 ab 11.9 b 11.4 b 3.9 a 6.6 a Gas release curve T X (min) 79.5 a a,b b a,b 79.5 a b b b V T (ml) 1304 a 1363 a,b 1471 b 1481 b 1304 a 1405 b 1408 b 1385 a,b V R (ml) 1190 a 1280 a,b 1427 b 1423 b 1190 a 1362 b 1357 b 1332 b V L (ml) 113 b 83 ab 44 a 58 a 113 b 43 a 51 a 54 a Calculated parameters WC (%) 35.2 a 27.5 a 25.2 a 30.1 a 37.4 a 24.5 a 51.9 a 32.3 a RC (%) 91.3 a 94.0 a,b 97.0 b 96.2 b 91.3 a 96.9 b 96.4 b 96.1 b H m : maximum height (mm) T 1 : time (min) at Hm. h: height at end of test (mm) T X : time (min) of gas release V T : total volume of CO 2 (ml) V R : retention volume of CO 2 (ml) V L : lost volume of CO 2 (ml) WC: weakening coefficient of dough (%) RC: retention coefficient of dough (%)

5 weakwning coefficient (%) Weakening Coefficient 0 Figure 3: Weakening coefficient variation with irradiation dose on flour from irradiated and irradiated retention coefficient (%) Retention Coefficient 89 Figure 4: Retention coefficient variation with irradiation dose on flour from irradiated and irradiated CONCLUSION The present study shows that gamma-irradiation has more influence on physicochemical and rheological properties of flour made by irradiated than by irradiated, same can be observed on the development of dough made from this flour. Resistance of dough made with irradiated seems to be increased with irradiation dose. There were some parameters that did not show significant differences, such as protein and water content, stability and weakening coefficient. For rheological properties, the influence of irradiation on and on were cleared observed and in general showed same tendencies, but for some properties (as weakening coefficients) it has showed different results. ACKNOWLEDGEMENT To CNPQ (National Council for Scientific and Technological Development) and CAPES (National Agency for Graduate Human Resources) for research grants. To Moinho Pacífico and Cereal Laboratory of State University of Campinas for technical support. REFERENCES [1] H. Köksel, H.D. Sapirstein, S. Celik and W. Bushuk, Effects of Gamma-Irradiation of Wheat on Gluten Proteins, Journal of Cereal Science, vol. 28, pp , [2] P.G. Fields and N.D.G. White, Alternatives to methyl bromide treatments for stored-product and quarantine insects. Annual Review of Entomology, vol. 47, pp , [3] ICGFI - International Consultative Group on Food Irradiation. Training Manual on Operation of Food Irradiation Facilities. Viena, (ICGFI document nº 14). [4] S.A. Marathe, J.P. Machaiah, B.Y.K. Rao, M.D. Pednekar and V. Sudha Rao, Extension of shelf-life of whole- by gamma radiation. International Journal of Food Science and Technology, vol. 37, pp , [5] S.R. Rao, R.C. Hoseney, K.F. Finney and M.D. Shogren, Effect of gamma irradiation of wheat on bread making properties. Cereal Chemistry, vol. 52, pp , [6] R.C. Silva, M.A.B. Regitano-D Arce and M.F. Spoto, Avaliação dos parâmetros tecnológicos e sensoriais da farinha de trigo irradiada com diferentes doses. In: XVIII Congresso Brasileiro de Ciência e Tecnologia de Alimentos, Porto Alegre, CBCTA Proceedings, pp , 2002 [7] AACC Approved Methods of the American Association of Cereal Chemists. Methods 44-15A,46-11A, 54-10, 54-21, 56-81B, 9 th ed. Minnesota, USA, [8] R.C. Silva, Qualidade Tecnológica e Estabilidade Oxidativa de Farinha de Trigo e Fubá Irradiados. M.Sc. thesis, University of São Paulo, Piracicaba, SP, [9] W.M. Urbain, Food Irradiation, Academic Press Inc., Orlando, 1986