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Physicochemical properties and silicon content in wheat flour treated with diatomaceous earth and conventionally stored
Journal of Stored Products Research 47 (2011) 316e320
Contents lists available at ScienceDirect
Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr
Physicochemical properties and silicon content in wheat flour treated with diatomaceous earth and conventionally stored Janete Deliberali Freo a, Neiva Deliberali Rosso b, *, Lidiane Borges Dias de Moraes a, Álvaro Renato Guerra Dias a, Moacir Cardoso Elias a, Luiz Carlos Gutkoski c a b c
Post-Graduate Program in Agroindustrial Science and Technology, Federal University of Pelotas (UFPel), Capão do Leão, RS, Brazil Department of Chemistry, State University of Ponta Grossa (UEPG), 84030-900 Ponta Grossa, PR, Brazil Food Research Center, University of Passo Fundo (UPF), Passo Fundo, RS, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Accepted 4 May 2011
This study was done to evaluate the physicochemical properties and to quantify the residual silicon in flour from wheat grains treated with different dosages of DE and stored in a conventional system for 180 days. Samples containing 10.0 kg of wheat grain were treated with 0.00, 2.00 and 4.00 g kg1 of DE and then homogenized and stored in cotton bags at 22 C and 70 5 g 100 g1 relative humidity. Physicochemical analyses were carried out at 0, 60, 120 and 180 days of storage. The experiment was conducted in a randomized design with a factorial 3 4 arrangement (three doses of DE four storage periods), totaling 12 treatments, with three replicates for each treatment. The wheat flour samples were digested and the silicon residue quantification was conducted through colorimetry. The wheat treated with DE presented a lower test weight compared with control, þb* chromaticity coordinate for color and increased ash content and L*. The physicochemical changes in the grain and wheat flour were proportional to the amount of DE applied. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Triticum aestivum Storage Industrial quality Colorimetric method
1. Introduction Diatomaceous earth DE is an inert dust, derived from amorphous sediment originating from the carapaces of vegetal unicellular organisms such as aquatic, lacustrine and marine algae. It is a light material with low density and a color ranging from white to dark grey. It consists of approximately 80e93 g silicon dioxide in 100 g and the remaining content is composed by clay minerals, organic matter, hydroxide, quartz, calcium and magnesium carbonate (Stathers et al., 2004; Korunic et al., 1998). Diatomaceous earth can be used for pest control in grain storage (Quarles, 1992). It is both abrasive and slightly sorptive, and dust particles adhere to the insect exoskeleton and remove lipids from the cuticle, causing dessication (Ebeling, 1971; Korunic, 1998). Inert dusts such as DE are most effective when applied as dusts but some retain activity even when applied as a water-based slurry (Golob, 1997). Diatomaceous earth can cause changes to the physical and mechanical properties of grains, increasing the required grinding time for processing and resulting in abrasion of equipment (Miranda et al., 1999). The classic method for determining the silicon (Si) content in materials is the conversion of insoluble silicate into soluble sodium * Corresponding author. Tel.: þ55 42 32203063. E-mail address: [email protected] (N.D. Rosso). 0022-474X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jspr.2011.05.001
silicate by fusion of the material under analysis with sodium hydroxide at high temperatures. Silicon content can be determined by colorimetry, gravimetric emission spectrometry and atomic absorption (Sripanyakorn et al., 2005). Colorimetry, based on the formation of a reduced molybdenum-silicon complex or molybdenum blue, is the most commonly used method to determine silicon content. However, the successful use of this method depends on the dissolution of the silicon present in the materials. Several other techniques to measure silicon content exist, including ones in which the sample is fused with alkaline substances such as sodium carbonate and sodium hydroxide, and methods based on fluorization in the presence of excess of boric acid (Elliott and Snyder, 1991; Rodrigues and Santana, 2005). In the colorimetric method, the reaction product is a blue compound obtained from the heteropolyacid reduction that occurs in two phases: the formation of silicomolybdic acid and reduction by organic or inorganic agents. The method depends on environmental acidity, which can minimize the influence of interfering agents. When the interference is due to phosphates, oxalic acid is often used as a reducing agent (Ferreira et al., 1987; Snyder, 2001). Although some studies have examined the use of DE in wheat, the literature does not contain information on the amount of residue remaining in the flour after the wheat is ground (Atui et al., 2003). Studies that quantify residual DE in wheat flour are of
J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
interest to the industry and to official food analysis laboratories because of the potential impact on industrial quality. The objective of this study was to evaluate the physicochemical properties and quantify the residual silicon in flour made from wheat grain treated with different doses of DE and stored in a conventional system for 180 days. 2. Material and methods The wheat (Triticum aestivum L) used in the study was from the 2008/2009 harvest of the cultivar Abalone, produced in an experimental field at Biotrigo Genética Ltd., which is located in Passo Fundo City, Rio Grande do Sul State. The wheat grains were harvested with a thrasher combine, pre-cleaned in an air machine and sieves and dried in a stationary dryer until it reached 13 g 100 g1 humidity. The DE used was KeepDryÒ, Brazil, with about 93 g 100 g1 amorphous silicon dioxide (SiO2), an average granulometry of 15 mm, a bulk density of 200 g L1 b, a light color, insolubility in water and a dry powder aspect. Water was deionized and all reagents used were analytical quality (Sigma, Aldrich, Carlo Erba and Merck). The study design was a completely randomized 3 4 factorial arrangement (three DE parts four storage periods) totaling 12 treatments, with three replicates for each treatment. Diatomaceous earth was added to 10.0 kg wheat grain samples in 0.00, 2.00 and 4.00 g kg1 dosages. Samples were homogenized in a Hypo planetary mixer (Model HB 25) and stored in cotton bags at 22 C and 70 5 g 100 g1 relative humidity. Physicochemical analyses were conducted at 0, 60, 120 and 180 days of storage. The wheat was ground in a Chopin pilot mill (Model CD1, France) according to the n. 26-10 AACC method (2000). The analyses were performed for 0.100 g samples, with two replications. The test weight was determined according to the Seed Analysis Regulation (Brazil, 1992), and results were presented in kg hL1. The ash content of the wheat grains was determined in accordance with the n. 08-01 AACC method (2000). Analyses were carried out in duplicate and results were presented in g 100 g1. The color of the wheat flour samples was determined in triplicate using a HunterLabÒ spectrophotometer (ColorQuest II, England) with a spherical geometrical optical sensor according to the n. 14-22 AACC model (2000). The intensity values of the L* component (brightness) and chromaticity coordinate þb* (yellowness) were also determined. The wheat flour samples were digested according to the procedure proposed by Elliott and Snyder (1991), with changes in time and incineration temperature and in the amount of NaOH solution. The samples were weighed, transferred to nickel crucibles and heated at 650 C for 4 h. The residue was cooled, and then 3.7 mL of 12.50 M NaOH solution was added. The crucibles were heated slowly to allow the solvent to evaporate. The solids were redissolved in 35 mL deionized water, and the resulting solution was left to sit for 24 h. The crucibles were then washed with 15.0 mL of 0.100 M NaOH solution, transferred to a polyethylene bottle and the volume completed to 50 mL with deionized water. To assess the applicability of this method, known amounts of DE were added to 0.00e0.100 g samples of wheat flour, which were digested as previously described. Additionally, 0.100 g DE samples, wheat flour free, were similarly digested and used to obtain the analytical curve. The experiments were performed with two replications. Silicon determination was conducted with a Shimadzu UVeVis spectrophotometer, (Model 1800, Japan), which operates at wavelengths from 200 to 1100 nm. Silicon content was determined according to the method described by Furlani and Gallo (1978), with changes in the proportion of the reagents used. The spectrophotometer was calibrated with deionized water containing all the reagents except for the sample. For the analyses, 5.0 mL volumetric
317
balloons with 10 mL of the digested sample and 10 mL of 2.50 M sulfuric acid solution, which was enough to stabilize the pH between 4.5 and 5.0, were used. Two hundred microliters of 0.043 M ammonium molybdate were added to the volumetric balloon, and the solution was shaken and allowed to sit for 5 min. Next, a newly prepared solution containing 100 mL of 1.10 M oxalic acid, 30 mL of 2.50 M sulfuric acid and 100 mL of 0.110 mol M ascorbic acid was added. The volume was completed with deionized water and the solution was homogenized and allowed to sit for 15 min. The absorbance reading was conducted at a wavelength of 815 nm. For the silicon content analysis, 1000 mL samples were used, and the remaining reagents were present in proportional amounts. The standard curve for silicon determination was built with the DE solution, treated as previously described, in a concentration range of 0.0 to 7.37 105 M. ANOVA was performed on all physicochemical determinations results using a statistical program SisvarÒ Versão 5.3, Build 75 (Ferreira et al., 2010). Analyses and regression equation graphs were elaborated with the support of the Origin 5.0 program. 3. Results and discussion The variance analysis mean squares for storage time, DE dosages and interaction time dosage were significant (P 0.05) for the L* component of intensity (brightness); the þb* component of color chromaticity (yellow); and for the ash content and test weight of wheat grains treated with DE and stored for 180 days (Table 1). The variation coefficients revealed values with reduced magnitude, reflecting suitable control of these techniques during the experiment as well as the accuracy and reliability of the study outcomes. The flour color was evaluated by measuring brightness and yellowness. Brightness is affected by the presence of meal or foreign material, whereas yellowness is related to the number of pigments present. The flour’s color is defined with the tridimensional color scale, which describes the different color components. Reflected light is provided by a dark or bright component in addition to a red or green and a blue or yellow component, as determined by calorimeters or spectrophotometers (Peterson et al., 2001). After storage for 180 days, the wheat flour became lighter and the L* (brightness) component increased significantly; the regression equations DE0, DE20 and DE40 presented determination coefficients between 0.89 and 0.97 (Fig. 1A). The DE0 samples presented higher L* (brightness) color component intensities at the beginning and maintained the highest brightness levels throughout the entire storage period compared with the other samples. On the other hand, the wheat flour treated with 4.00 g kg1 of DE presented lower values of L*.
Table 1 The variance analysis results for L* components (brightness), flour color þb* (yellow) and the ash content and test weight (TW) of wheat grains treated with DE and stored for 180 days. Variationa
Mean squares
Source
DF
Time (days) Dosage (g) Time dosage Total VC
3 2 6
L*
þb* a
Ash
2.32 9.36a 0.09a
1.62a 6.43a 0.019a
0.016a 0.139a 0.001a
35 0.0006
35 0.0041
23 0.0087
DF e Degrees of freedom; VC e Variation coefficient. a Significant at the level of 0.05 probability (P 0.05).
TW 4.05a 150.22a 0.32a 35 0.0026
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J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
A
93
92
1,8
91
90 -1
DE0 0.00 g kg -1 DE20 2.00 g kg -1 DE40 4.00 g kg
89 0
60
120
1,7 1,6 DEO y= 1,41 + 0,0610X R = 0,96 DE20 y= 1,65 + 0,0250X R = 0,98 DE40 y= 1,74 + 0,0355X R = 0,97
1,5 1,4
180
0
Storage Time (Days)
B
2
DE0 y= 11,06 - 0,1856X R = 0,95 2 DE20 y= 10,01 - 0,1103X R = 0,99 2 DE40 y= 9,390 - 0,0993X R = 0,99
11,0
0
60
DE0 y= 79,83 - 0,4366X R = 0,99 DE20 y= 73,98 - 0,4400X R = 0,98 DE40 y= 73,75 - 0,5500X R = 0,85
76 75 74 73 72
-1
DE0 0.00 g kg -1 DE20 2.00 g kg -1 DE40 4.00 g kg
9,0
180
78
TW (kg/hL)
9,5
120
79 77
10,0
60
Storage Time (Days)
B 80
10,5
+b* (Yellow)
DE0 0.00 g kg DE20 2.00 g kg DE40 4.00 g kg
1,9
Ash (g/100 g)
L* (Brightness)
A
2
DE0 y= 90,94 + 0,3230X R = 0,92 2 DE20 y= 90,49 + 0,2076X R = 0,97 2 DE40 y= 88,93 + 0,4243X R = 0,89
DE0 0.00 g kg DE20 2.00 g kg DE40 4.00 g kg
71 70
120
180
Storage Time (Days)
69 0
60
120
180
Storage Time (Days)
Fig. 1. L* intensity (A) and þb* color chromaticity coordinate (B) of wheat flour ample free of DE (DE0) and the treated with 2.00 and 4.00 g kg1 (DE20 and DE40) DE for 180 days.
Fig. 2. Ash content (g 100 g1) (A) and test weight (kg hL1) (B) in wheat grains treated with DE and stored for 180 days.
The chromaticity coordinate þb* (yellowness) decreased with increased storage time. Every 60 days an average decrease of 0.106 units was observed, with coefficients between 0.95 and 0.99. The decrease was significant in all regression models studied (Fig. 1B). Such alterations were due to the natural wheat grain ripening process. The lowest values of chromaticity þb* were observed with the highest DE dosage. After storage for 180 days, increases in L* values and decreases in þb* values were verified; however, such color alterations were significantly reduced for treatments DE20 and DE40. The slopes for the L* and þb* color compounds determined by regression equations during the storage period were similar for the different DE dosages. Color alterations result from natural pigment oxidation that occurs during storage, and the values vary with the bleaching extension and the wheat flour’s aging (Gutkoski et al., 2008; Ortolan et al., 2010). The ash content in wheat grains varies according to the cultivar, plantation conditions and use of soil fertilizers (Ryan et al., 2004). Statistical analysis revealed significant differences (P < 0.05) in ash levels among all DE dosages studied (Fig. 2A). Regression equations were significant and were used to adjust quadratic terms, with determination coefficients varying between 0.96 and 0.98. The ash content in all samples increased with storage, and higher ash values were found in the samples treated with 2.00 and 4.00 g kg1 DE. Such increases are related to the amount of DE, which contained
93 g of amorphous silicon dioxide, added to the wheat grains, and to the organic fraction degradation that occurred during storage. Korunic et al. (1996) did not find any increases in ash content in wheat grains treated with 0.05e0.3 of DE per kg of wheat. However, when 0.3 g per kg of DE was added, directly into the flour, it was observed that the ash content increased. Such data is in agreement with that reported in this paper. Among the components of wheat, ash presents the lowest variation in total content during storage due to organic fraction degradation. The metabolic activity of the grains and associated microorganisms consumes organic matter, producing carbonic gas, water, heat and other products, any of which can alter the ash proportion in the wheat grains. Thus, the ash content increases proportionally with the amount of organic matter consumed (Bhattacharya and Raha, 2002). Such results are in agreement with the present study. Test weight (TW) is a quality indicator that is positively correlated with flour extraction. TW decreases with increased storage time due to the grain’s organic component consumption (FleuratLessard, 2002). TW values reflect total quantitative losses resulting from grain deterioration processes including intrinsic metabolism, microbial activity and consumption by pests (Park et al., 2008). Figure 2B presents the DE dosage’s effect on the TW of stored wheat grains. Statistical analyses of the results showed significant differences (P < 0.05) based on the storage period and the DE
J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
1,6
Table 2 Wheat flour mass (WF), DE mass, molar quantity (mols), Si theoretical molarity (MT) and experimental molarity (ME) in wheat flour.
1,4
Absorbance (u.a.)
1,2 1,0 0,8 0,6 0,4 Y = 0,05268 + 18143,58762.X r= 0,994
0,2 0,0 0,0
-5
-5
-5
-5
-5
-5
-5
-5
1,0x10 2,0x10 3,0x10 4,0x10 5,0x10 6,0x10 7,0x10 8,0x10 -1
Molarity (mol L ) Fig. 3. Si analytical curve, concentrations from 0.00 to 7.37 105 M DE.
dosage applied to the grains. Regression equations were significant; quadratic terms were used in the adjustment, with determination coefficients above 0.80. The highest variations in TW were observed in DE40 samples. These results are similar to those obtained by Korunic et al. (1998) and Miranda et al. (1999), in which TW reductions were observed in wheat grains treated with DE. For Si residue determination in wheat flour an analytical curve (Fig. 3) was built from the absorbance data for different silicon concentrations in the solutions. Maximum absorbance was observed at a wavelength of 815 nm and decreased proportionally with reductions in Si concentration in the solution. A linearity consistent with the BeereLambert law emerged at 815 nm, with increases in absorbance according to the silicon concentrations in the sample; the correlation coefficient was 0.994. The analytical curve’s high r value indicated the accuracy of the colorimetric method for determining Si levels in DE. Figure 4 presents the spectra obtained from the Si analyses of wheat flour with known amounts of DE. Sample A, which contained no DE, contained no Si; in Samples B, C and D, the absorbance increased proportionally with the amount of DE added to the wheat flour. The absorbance readings from the samples with known amounts of D allowed us to calculate the molarity of each solution
Sample
WF (g)
DE (g)
mols 103
MT (mM)
ME (mM)
A B C D
0.1000 0.0766 0.0471 0.0245
0.00 0.0245 0.0471 0.0766
0.00 0.408 0.783 1.275
0.00 8.26 0.09 15.72 0.06 25.57 0.06
0.00 8.13 0.08 14.77 0.08 25.37 0.26
by employing the analytical curve, where y was the DE samples’ absorbance and x was the Si concentrations in the solutions. Table 2 presents the theoretical molarity calculated from the known amount of DE added to the wheat flour and the experimental molarity. There was total recovery of the DE added to the wheat flour with agreement between the values calculated and those determined by the experiment. This confirms that the sample treatment and the colorimetric method employed to quantify Si were suitable and can be used to determine the residue of DE in the wheat flour on the market. Figure 5 presents the spectra for wheat flour sample obtained after storage and treatment with 0.00, 2.00 and 4.00 g kg1 DE. The absorbance of the wheat flour sample free of DE (DE0) was close to zero, while in samples treated with 2.00 and 4.00 g kg1 (DE20 and DE40), the absorbance increased proportionally. Each solution molarity was calculated from the analytical curve, and the absorbance readings were conducted for wheat flour samples treated with 0.00, 2.00 and 4.00 g kg1 DE. Table 3 presents the theoretical molarities and experimental molarities of wheat flour samples treated with DE. In Samples DE20 and DE40, Si was precisely quantified, and the experimental molarity in both treatments was inferior to the calculated molarity. This difference was due to the treatment of the wheat grains, including storage, pre-grinding and grinding. During the grinding process, part of the DE probably remained in the meal and in the mill brushes, rolls and sieves, which explains why the experimental molarity of the samples was lower than the theoretical molarity. Elliott and Snyder (1991) found greater difficulties in sample solubilization in their attempts to use colorimetry to determine the Si content of rice straw. Rodrigues and Santana (2005) determined the Si content of lignocellulosic materials through colorimetry using a UVeVis spectrophotometer with reproducible results. However, no studies of Si determination in wheat flour were found in the literature.
0,4
1,0
Absorbance (u.a.)
A B C D
0,8
Absorbance (u.a.)
319
0,6 0,4
-1
DE0 0.00 g kg -1 DE20 2.00 g kg -1 DE40 4.00 g kg
0,3
0,2
0,1
0,2 0,0 400
500
600
700
800
900
1000
Wavelength (nm) Fig. 4. Si absorbance spectra in wheat flour samples with DE.
1100
0,0 400
500
600
700
800
900
1000
1100
Wavelength (nm) Fig. 5. Si absorbance spectra in wheat flour samples treated with 0.00, 2.00 and 4.00 g kg1 DE.
320
J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
Table 3 Sample mass (SM), molar quantity (mols), theoretical molarity (MT) and experimental molarity (ME) of wheat flour samples treated with 0.00, 2.00 and 4.00 g kg1 DE. Sample
SM (g)
mols 103
MT (mM)
ME (mM)
DE0 DE20 DE40
0.00 0.1066 0.1069
0.00 0.3875 1.1679
0.00 70.22 0.73 138.19 2.06
0.00 40.59 0.55 92.95 0.55
4. Conclusions Wheat treated with 0.00, 2.00 and 4.00 g kg1 of DE and stored for 180 days presented reductions in test weight, a color chromaticity coordinate of þb* (yellow) and increases in ash content and the L* (brightness) component. Physicochemical alterations in grain and wheat flour were proportional to the amount of DE used, thus the content of silicon affected the quality of the wheat flour. The sample digestion and colorimetric method used to quantify silicon levels in this study are appropriate and can be used to determine the DE residue in wheat flour. The method used, with appropriate modifications, can be recommended to food analysis laboratories to assess the industrial quality of the wheat flour on the market. Acknowledgments Authors are thankful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the productivity grant and financial support to the research. References AACC, 2000. Approved Methods of the AACC, 10th ed. American Association of Cereal Chemists, Saint Paul, MN. Atui, M.B., Lazzari, F.A., Lazzari, S.M.N., 2003. Evaluation of methodology for detection of residues of DE in wheat grain and flour. Journal Institute Adolfo Lutz 62, 11e16. Bhattacharya, K., Raha, S., 2002. Deteriorative changes of maize, groundnut and soybean seeds by fungi in storage. Mycopathologia 155, 135e141. Brazil, 1992. Ministry of Agriculture, Supply and Agrarian Reform. National Secretariat of Agricultural Protection. Rules for seedtesting, Brasilia. Ebeling, W., 1971. Sorptive dusts for pest control. Annual Reviews of Entomology 16, 123e158.
Elliott, C.L., Snyder, G.H., 1991. Autoclave-induced digestion for the colorimetric determination of silicon in rice straw. Journal of Agricultural and Food Chemistry 39, 1118e1119. Ferreira, D.F., Sisvar 5.3, Build 75, 2010. Available at: (accessed 13.04.10). Ferreira, J.R., Kronka, E.A.M., Jacintho, A.O., 1987. Determination of silicon in natural waters by the molybdenum blue method by computer analysis by flow injection. Journal of New Chemical 10, 270e273. Fleurat-Lessard, F., 2002. Qualitative reasoning and integrated management of the quality of stored grain: a promising new approach. Journal of Stored Products Research 38, 191e218. Furlani, P.R., Gallo, J.R., 1978. Determination of silicon in plant material by the colorimetric method of “blue-on-moly”. Journal of Agronomic Science 2, 5e11. Golob, P., 1997. Current status and future perspectives for inert dusts for control of stored product insects. Journal of Stored Products Research 33, 69e79. Gutkoski, L.C., Durigon, A., Mazzutti, S., Silva, A.C.T., Elias, M.C., 2008. Effect of ripening grain in the physical and rheological properties of wheat. Food Science and Technology 28, 888e894. Korunic, Z., 1998. Diatomaceous earths, a group of natural insecticides. Journal of Stored Products Research 34, 87e97. Korunic, Z., Fields, P.G., Kovacs, M.I.P., Noll, J.S., Lukow, O.M., Demianyk, C.J., Shibley, K.J., 1996. The effect of DE on grain quality. Postharvest Biology and Technology 9, 373e387. Korunic, Z., Cenkowski, S., Fields, P., 1998. Grain bulk density as affected by DE and application method. Postharvest Biology and Technology 13, 81e89. Miranda, M.Z., Lorini, I., Guarienti, E.M., 1999. Effect of inert dust used to control insects on stored grain quality characteristics of wheat. In: XVIII Meeting of National Wheat Research, vol. 1. Embrapa, pp. 406e411. Ortolan, F., Hecktheuer, L.H., De Miranda, M.Z., 2010. Effect of storage at low temperature (4 degrees C) in color and acidity of wheat flour. Food Science and Technology 30, 55e59. Park, S.H., Arthur, H.F., Bean, S.R., Schober, T.J., 2008. Impact of differing population levels of Rhyzopertha dominica (F.) on milling and physicochemical properties of sorghum kernel and flour. Journal of Stored Products Research 44, 322e327. Peterson, C.J., Shelton, D.R., Martin, T.J., Sears, R.G., Williams, E., Graybosch, R.A., 2001. Grain color stability and classification of hard white wheat in the US. Euphytic 119, 101e106. Quarles, W., 1992. Diatomaceous earth for pest control. IPM Practitioner 14, 1e11. Rodrigues, L.C., Santana, M.A.E., 2005. Methodology for determination of silica content in lignocellulosic materials via the ultravioletevisible spectrometry. Forest and Environment 12, 57e62. Ryan, M.H., Derrick, J.W., Dann, P.R., 2004. Grain mineral concentrations and yield of wheat grown under organic and conventional management. Journal of the Science of Food and Agriculture 84, 207e216. Snyder, G.H., 2001. Methods for silicon analysis in plants, soils, and fertilizer. In: Datnoff, L.E., Snyder, G.H., Korndörfer, G.H. (Eds.), Silicon in Agriculture. Elsevier Science B.V., pp. 185e207. Sripanyakorn, S., Jugdaohsingh, R., Thompson, R.P.H., Powell, J.J., 2005. Dietary silicon and bone health. Nutrition Bulletin 30, 222e230. Stathers, T.E., Denniff, M., Golob, P., 2004. The efficacy and persistence of DE admixed with commodity against four tropical stored product beetle pests. Journal of Stored Products Research 40, 113e123.
Contents lists available at ScienceDirect
Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr
Physicochemical properties and silicon content in wheat flour treated with diatomaceous earth and conventionally stored Janete Deliberali Freo a, Neiva Deliberali Rosso b, *, Lidiane Borges Dias de Moraes a, Álvaro Renato Guerra Dias a, Moacir Cardoso Elias a, Luiz Carlos Gutkoski c a b c
Post-Graduate Program in Agroindustrial Science and Technology, Federal University of Pelotas (UFPel), Capão do Leão, RS, Brazil Department of Chemistry, State University of Ponta Grossa (UEPG), 84030-900 Ponta Grossa, PR, Brazil Food Research Center, University of Passo Fundo (UPF), Passo Fundo, RS, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Accepted 4 May 2011
This study was done to evaluate the physicochemical properties and to quantify the residual silicon in flour from wheat grains treated with different dosages of DE and stored in a conventional system for 180 days. Samples containing 10.0 kg of wheat grain were treated with 0.00, 2.00 and 4.00 g kg1 of DE and then homogenized and stored in cotton bags at 22 C and 70 5 g 100 g1 relative humidity. Physicochemical analyses were carried out at 0, 60, 120 and 180 days of storage. The experiment was conducted in a randomized design with a factorial 3 4 arrangement (three doses of DE four storage periods), totaling 12 treatments, with three replicates for each treatment. The wheat flour samples were digested and the silicon residue quantification was conducted through colorimetry. The wheat treated with DE presented a lower test weight compared with control, þb* chromaticity coordinate for color and increased ash content and L*. The physicochemical changes in the grain and wheat flour were proportional to the amount of DE applied. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Triticum aestivum Storage Industrial quality Colorimetric method
1. Introduction Diatomaceous earth DE is an inert dust, derived from amorphous sediment originating from the carapaces of vegetal unicellular organisms such as aquatic, lacustrine and marine algae. It is a light material with low density and a color ranging from white to dark grey. It consists of approximately 80e93 g silicon dioxide in 100 g and the remaining content is composed by clay minerals, organic matter, hydroxide, quartz, calcium and magnesium carbonate (Stathers et al., 2004; Korunic et al., 1998). Diatomaceous earth can be used for pest control in grain storage (Quarles, 1992). It is both abrasive and slightly sorptive, and dust particles adhere to the insect exoskeleton and remove lipids from the cuticle, causing dessication (Ebeling, 1971; Korunic, 1998). Inert dusts such as DE are most effective when applied as dusts but some retain activity even when applied as a water-based slurry (Golob, 1997). Diatomaceous earth can cause changes to the physical and mechanical properties of grains, increasing the required grinding time for processing and resulting in abrasion of equipment (Miranda et al., 1999). The classic method for determining the silicon (Si) content in materials is the conversion of insoluble silicate into soluble sodium * Corresponding author. Tel.: þ55 42 32203063. E-mail address: [email protected] (N.D. Rosso). 0022-474X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jspr.2011.05.001
silicate by fusion of the material under analysis with sodium hydroxide at high temperatures. Silicon content can be determined by colorimetry, gravimetric emission spectrometry and atomic absorption (Sripanyakorn et al., 2005). Colorimetry, based on the formation of a reduced molybdenum-silicon complex or molybdenum blue, is the most commonly used method to determine silicon content. However, the successful use of this method depends on the dissolution of the silicon present in the materials. Several other techniques to measure silicon content exist, including ones in which the sample is fused with alkaline substances such as sodium carbonate and sodium hydroxide, and methods based on fluorization in the presence of excess of boric acid (Elliott and Snyder, 1991; Rodrigues and Santana, 2005). In the colorimetric method, the reaction product is a blue compound obtained from the heteropolyacid reduction that occurs in two phases: the formation of silicomolybdic acid and reduction by organic or inorganic agents. The method depends on environmental acidity, which can minimize the influence of interfering agents. When the interference is due to phosphates, oxalic acid is often used as a reducing agent (Ferreira et al., 1987; Snyder, 2001). Although some studies have examined the use of DE in wheat, the literature does not contain information on the amount of residue remaining in the flour after the wheat is ground (Atui et al., 2003). Studies that quantify residual DE in wheat flour are of
J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
interest to the industry and to official food analysis laboratories because of the potential impact on industrial quality. The objective of this study was to evaluate the physicochemical properties and quantify the residual silicon in flour made from wheat grain treated with different doses of DE and stored in a conventional system for 180 days. 2. Material and methods The wheat (Triticum aestivum L) used in the study was from the 2008/2009 harvest of the cultivar Abalone, produced in an experimental field at Biotrigo Genética Ltd., which is located in Passo Fundo City, Rio Grande do Sul State. The wheat grains were harvested with a thrasher combine, pre-cleaned in an air machine and sieves and dried in a stationary dryer until it reached 13 g 100 g1 humidity. The DE used was KeepDryÒ, Brazil, with about 93 g 100 g1 amorphous silicon dioxide (SiO2), an average granulometry of 15 mm, a bulk density of 200 g L1 b, a light color, insolubility in water and a dry powder aspect. Water was deionized and all reagents used were analytical quality (Sigma, Aldrich, Carlo Erba and Merck). The study design was a completely randomized 3 4 factorial arrangement (three DE parts four storage periods) totaling 12 treatments, with three replicates for each treatment. Diatomaceous earth was added to 10.0 kg wheat grain samples in 0.00, 2.00 and 4.00 g kg1 dosages. Samples were homogenized in a Hypo planetary mixer (Model HB 25) and stored in cotton bags at 22 C and 70 5 g 100 g1 relative humidity. Physicochemical analyses were conducted at 0, 60, 120 and 180 days of storage. The wheat was ground in a Chopin pilot mill (Model CD1, France) according to the n. 26-10 AACC method (2000). The analyses were performed for 0.100 g samples, with two replications. The test weight was determined according to the Seed Analysis Regulation (Brazil, 1992), and results were presented in kg hL1. The ash content of the wheat grains was determined in accordance with the n. 08-01 AACC method (2000). Analyses were carried out in duplicate and results were presented in g 100 g1. The color of the wheat flour samples was determined in triplicate using a HunterLabÒ spectrophotometer (ColorQuest II, England) with a spherical geometrical optical sensor according to the n. 14-22 AACC model (2000). The intensity values of the L* component (brightness) and chromaticity coordinate þb* (yellowness) were also determined. The wheat flour samples were digested according to the procedure proposed by Elliott and Snyder (1991), with changes in time and incineration temperature and in the amount of NaOH solution. The samples were weighed, transferred to nickel crucibles and heated at 650 C for 4 h. The residue was cooled, and then 3.7 mL of 12.50 M NaOH solution was added. The crucibles were heated slowly to allow the solvent to evaporate. The solids were redissolved in 35 mL deionized water, and the resulting solution was left to sit for 24 h. The crucibles were then washed with 15.0 mL of 0.100 M NaOH solution, transferred to a polyethylene bottle and the volume completed to 50 mL with deionized water. To assess the applicability of this method, known amounts of DE were added to 0.00e0.100 g samples of wheat flour, which were digested as previously described. Additionally, 0.100 g DE samples, wheat flour free, were similarly digested and used to obtain the analytical curve. The experiments were performed with two replications. Silicon determination was conducted with a Shimadzu UVeVis spectrophotometer, (Model 1800, Japan), which operates at wavelengths from 200 to 1100 nm. Silicon content was determined according to the method described by Furlani and Gallo (1978), with changes in the proportion of the reagents used. The spectrophotometer was calibrated with deionized water containing all the reagents except for the sample. For the analyses, 5.0 mL volumetric
317
balloons with 10 mL of the digested sample and 10 mL of 2.50 M sulfuric acid solution, which was enough to stabilize the pH between 4.5 and 5.0, were used. Two hundred microliters of 0.043 M ammonium molybdate were added to the volumetric balloon, and the solution was shaken and allowed to sit for 5 min. Next, a newly prepared solution containing 100 mL of 1.10 M oxalic acid, 30 mL of 2.50 M sulfuric acid and 100 mL of 0.110 mol M ascorbic acid was added. The volume was completed with deionized water and the solution was homogenized and allowed to sit for 15 min. The absorbance reading was conducted at a wavelength of 815 nm. For the silicon content analysis, 1000 mL samples were used, and the remaining reagents were present in proportional amounts. The standard curve for silicon determination was built with the DE solution, treated as previously described, in a concentration range of 0.0 to 7.37 105 M. ANOVA was performed on all physicochemical determinations results using a statistical program SisvarÒ Versão 5.3, Build 75 (Ferreira et al., 2010). Analyses and regression equation graphs were elaborated with the support of the Origin 5.0 program. 3. Results and discussion The variance analysis mean squares for storage time, DE dosages and interaction time dosage were significant (P 0.05) for the L* component of intensity (brightness); the þb* component of color chromaticity (yellow); and for the ash content and test weight of wheat grains treated with DE and stored for 180 days (Table 1). The variation coefficients revealed values with reduced magnitude, reflecting suitable control of these techniques during the experiment as well as the accuracy and reliability of the study outcomes. The flour color was evaluated by measuring brightness and yellowness. Brightness is affected by the presence of meal or foreign material, whereas yellowness is related to the number of pigments present. The flour’s color is defined with the tridimensional color scale, which describes the different color components. Reflected light is provided by a dark or bright component in addition to a red or green and a blue or yellow component, as determined by calorimeters or spectrophotometers (Peterson et al., 2001). After storage for 180 days, the wheat flour became lighter and the L* (brightness) component increased significantly; the regression equations DE0, DE20 and DE40 presented determination coefficients between 0.89 and 0.97 (Fig. 1A). The DE0 samples presented higher L* (brightness) color component intensities at the beginning and maintained the highest brightness levels throughout the entire storage period compared with the other samples. On the other hand, the wheat flour treated with 4.00 g kg1 of DE presented lower values of L*.
Table 1 The variance analysis results for L* components (brightness), flour color þb* (yellow) and the ash content and test weight (TW) of wheat grains treated with DE and stored for 180 days. Variationa
Mean squares
Source
DF
Time (days) Dosage (g) Time dosage Total VC
3 2 6
L*
þb* a
Ash
2.32 9.36a 0.09a
1.62a 6.43a 0.019a
0.016a 0.139a 0.001a
35 0.0006
35 0.0041
23 0.0087
DF e Degrees of freedom; VC e Variation coefficient. a Significant at the level of 0.05 probability (P 0.05).
TW 4.05a 150.22a 0.32a 35 0.0026
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A
93
92
1,8
91
90 -1
DE0 0.00 g kg -1 DE20 2.00 g kg -1 DE40 4.00 g kg
89 0
60
120
1,7 1,6 DEO y= 1,41 + 0,0610X R = 0,96 DE20 y= 1,65 + 0,0250X R = 0,98 DE40 y= 1,74 + 0,0355X R = 0,97
1,5 1,4
180
0
Storage Time (Days)
B
2
DE0 y= 11,06 - 0,1856X R = 0,95 2 DE20 y= 10,01 - 0,1103X R = 0,99 2 DE40 y= 9,390 - 0,0993X R = 0,99
11,0
0
60
DE0 y= 79,83 - 0,4366X R = 0,99 DE20 y= 73,98 - 0,4400X R = 0,98 DE40 y= 73,75 - 0,5500X R = 0,85
76 75 74 73 72
-1
DE0 0.00 g kg -1 DE20 2.00 g kg -1 DE40 4.00 g kg
9,0
180
78
TW (kg/hL)
9,5
120
79 77
10,0
60
Storage Time (Days)
B 80
10,5
+b* (Yellow)
DE0 0.00 g kg DE20 2.00 g kg DE40 4.00 g kg
1,9
Ash (g/100 g)
L* (Brightness)
A
2
DE0 y= 90,94 + 0,3230X R = 0,92 2 DE20 y= 90,49 + 0,2076X R = 0,97 2 DE40 y= 88,93 + 0,4243X R = 0,89
DE0 0.00 g kg DE20 2.00 g kg DE40 4.00 g kg
71 70
120
180
Storage Time (Days)
69 0
60
120
180
Storage Time (Days)
Fig. 1. L* intensity (A) and þb* color chromaticity coordinate (B) of wheat flour ample free of DE (DE0) and the treated with 2.00 and 4.00 g kg1 (DE20 and DE40) DE for 180 days.
Fig. 2. Ash content (g 100 g1) (A) and test weight (kg hL1) (B) in wheat grains treated with DE and stored for 180 days.
The chromaticity coordinate þb* (yellowness) decreased with increased storage time. Every 60 days an average decrease of 0.106 units was observed, with coefficients between 0.95 and 0.99. The decrease was significant in all regression models studied (Fig. 1B). Such alterations were due to the natural wheat grain ripening process. The lowest values of chromaticity þb* were observed with the highest DE dosage. After storage for 180 days, increases in L* values and decreases in þb* values were verified; however, such color alterations were significantly reduced for treatments DE20 and DE40. The slopes for the L* and þb* color compounds determined by regression equations during the storage period were similar for the different DE dosages. Color alterations result from natural pigment oxidation that occurs during storage, and the values vary with the bleaching extension and the wheat flour’s aging (Gutkoski et al., 2008; Ortolan et al., 2010). The ash content in wheat grains varies according to the cultivar, plantation conditions and use of soil fertilizers (Ryan et al., 2004). Statistical analysis revealed significant differences (P < 0.05) in ash levels among all DE dosages studied (Fig. 2A). Regression equations were significant and were used to adjust quadratic terms, with determination coefficients varying between 0.96 and 0.98. The ash content in all samples increased with storage, and higher ash values were found in the samples treated with 2.00 and 4.00 g kg1 DE. Such increases are related to the amount of DE, which contained
93 g of amorphous silicon dioxide, added to the wheat grains, and to the organic fraction degradation that occurred during storage. Korunic et al. (1996) did not find any increases in ash content in wheat grains treated with 0.05e0.3 of DE per kg of wheat. However, when 0.3 g per kg of DE was added, directly into the flour, it was observed that the ash content increased. Such data is in agreement with that reported in this paper. Among the components of wheat, ash presents the lowest variation in total content during storage due to organic fraction degradation. The metabolic activity of the grains and associated microorganisms consumes organic matter, producing carbonic gas, water, heat and other products, any of which can alter the ash proportion in the wheat grains. Thus, the ash content increases proportionally with the amount of organic matter consumed (Bhattacharya and Raha, 2002). Such results are in agreement with the present study. Test weight (TW) is a quality indicator that is positively correlated with flour extraction. TW decreases with increased storage time due to the grain’s organic component consumption (FleuratLessard, 2002). TW values reflect total quantitative losses resulting from grain deterioration processes including intrinsic metabolism, microbial activity and consumption by pests (Park et al., 2008). Figure 2B presents the DE dosage’s effect on the TW of stored wheat grains. Statistical analyses of the results showed significant differences (P < 0.05) based on the storage period and the DE
J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
1,6
Table 2 Wheat flour mass (WF), DE mass, molar quantity (mols), Si theoretical molarity (MT) and experimental molarity (ME) in wheat flour.
1,4
Absorbance (u.a.)
1,2 1,0 0,8 0,6 0,4 Y = 0,05268 + 18143,58762.X r= 0,994
0,2 0,0 0,0
-5
-5
-5
-5
-5
-5
-5
-5
1,0x10 2,0x10 3,0x10 4,0x10 5,0x10 6,0x10 7,0x10 8,0x10 -1
Molarity (mol L ) Fig. 3. Si analytical curve, concentrations from 0.00 to 7.37 105 M DE.
dosage applied to the grains. Regression equations were significant; quadratic terms were used in the adjustment, with determination coefficients above 0.80. The highest variations in TW were observed in DE40 samples. These results are similar to those obtained by Korunic et al. (1998) and Miranda et al. (1999), in which TW reductions were observed in wheat grains treated with DE. For Si residue determination in wheat flour an analytical curve (Fig. 3) was built from the absorbance data for different silicon concentrations in the solutions. Maximum absorbance was observed at a wavelength of 815 nm and decreased proportionally with reductions in Si concentration in the solution. A linearity consistent with the BeereLambert law emerged at 815 nm, with increases in absorbance according to the silicon concentrations in the sample; the correlation coefficient was 0.994. The analytical curve’s high r value indicated the accuracy of the colorimetric method for determining Si levels in DE. Figure 4 presents the spectra obtained from the Si analyses of wheat flour with known amounts of DE. Sample A, which contained no DE, contained no Si; in Samples B, C and D, the absorbance increased proportionally with the amount of DE added to the wheat flour. The absorbance readings from the samples with known amounts of D allowed us to calculate the molarity of each solution
Sample
WF (g)
DE (g)
mols 103
MT (mM)
ME (mM)
A B C D
0.1000 0.0766 0.0471 0.0245
0.00 0.0245 0.0471 0.0766
0.00 0.408 0.783 1.275
0.00 8.26 0.09 15.72 0.06 25.57 0.06
0.00 8.13 0.08 14.77 0.08 25.37 0.26
by employing the analytical curve, where y was the DE samples’ absorbance and x was the Si concentrations in the solutions. Table 2 presents the theoretical molarity calculated from the known amount of DE added to the wheat flour and the experimental molarity. There was total recovery of the DE added to the wheat flour with agreement between the values calculated and those determined by the experiment. This confirms that the sample treatment and the colorimetric method employed to quantify Si were suitable and can be used to determine the residue of DE in the wheat flour on the market. Figure 5 presents the spectra for wheat flour sample obtained after storage and treatment with 0.00, 2.00 and 4.00 g kg1 DE. The absorbance of the wheat flour sample free of DE (DE0) was close to zero, while in samples treated with 2.00 and 4.00 g kg1 (DE20 and DE40), the absorbance increased proportionally. Each solution molarity was calculated from the analytical curve, and the absorbance readings were conducted for wheat flour samples treated with 0.00, 2.00 and 4.00 g kg1 DE. Table 3 presents the theoretical molarities and experimental molarities of wheat flour samples treated with DE. In Samples DE20 and DE40, Si was precisely quantified, and the experimental molarity in both treatments was inferior to the calculated molarity. This difference was due to the treatment of the wheat grains, including storage, pre-grinding and grinding. During the grinding process, part of the DE probably remained in the meal and in the mill brushes, rolls and sieves, which explains why the experimental molarity of the samples was lower than the theoretical molarity. Elliott and Snyder (1991) found greater difficulties in sample solubilization in their attempts to use colorimetry to determine the Si content of rice straw. Rodrigues and Santana (2005) determined the Si content of lignocellulosic materials through colorimetry using a UVeVis spectrophotometer with reproducible results. However, no studies of Si determination in wheat flour were found in the literature.
0,4
1,0
Absorbance (u.a.)
A B C D
0,8
Absorbance (u.a.)
319
0,6 0,4
-1
DE0 0.00 g kg -1 DE20 2.00 g kg -1 DE40 4.00 g kg
0,3
0,2
0,1
0,2 0,0 400
500
600
700
800
900
1000
Wavelength (nm) Fig. 4. Si absorbance spectra in wheat flour samples with DE.
1100
0,0 400
500
600
700
800
900
1000
1100
Wavelength (nm) Fig. 5. Si absorbance spectra in wheat flour samples treated with 0.00, 2.00 and 4.00 g kg1 DE.
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J.D. Freo et al. / Journal of Stored Products Research 47 (2011) 316e320
Table 3 Sample mass (SM), molar quantity (mols), theoretical molarity (MT) and experimental molarity (ME) of wheat flour samples treated with 0.00, 2.00 and 4.00 g kg1 DE. Sample
SM (g)
mols 103
MT (mM)
ME (mM)
DE0 DE20 DE40
0.00 0.1066 0.1069
0.00 0.3875 1.1679
0.00 70.22 0.73 138.19 2.06
0.00 40.59 0.55 92.95 0.55
4. Conclusions Wheat treated with 0.00, 2.00 and 4.00 g kg1 of DE and stored for 180 days presented reductions in test weight, a color chromaticity coordinate of þb* (yellow) and increases in ash content and the L* (brightness) component. Physicochemical alterations in grain and wheat flour were proportional to the amount of DE used, thus the content of silicon affected the quality of the wheat flour. The sample digestion and colorimetric method used to quantify silicon levels in this study are appropriate and can be used to determine the DE residue in wheat flour. The method used, with appropriate modifications, can be recommended to food analysis laboratories to assess the industrial quality of the wheat flour on the market. Acknowledgments Authors are thankful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the productivity grant and financial support to the research. References AACC, 2000. Approved Methods of the AACC, 10th ed. American Association of Cereal Chemists, Saint Paul, MN. Atui, M.B., Lazzari, F.A., Lazzari, S.M.N., 2003. Evaluation of methodology for detection of residues of DE in wheat grain and flour. Journal Institute Adolfo Lutz 62, 11e16. Bhattacharya, K., Raha, S., 2002. Deteriorative changes of maize, groundnut and soybean seeds by fungi in storage. Mycopathologia 155, 135e141. Brazil, 1992. Ministry of Agriculture, Supply and Agrarian Reform. National Secretariat of Agricultural Protection. Rules for seedtesting, Brasilia. Ebeling, W., 1971. Sorptive dusts for pest control. Annual Reviews of Entomology 16, 123e158.
Elliott, C.L., Snyder, G.H., 1991. Autoclave-induced digestion for the colorimetric determination of silicon in rice straw. Journal of Agricultural and Food Chemistry 39, 1118e1119. Ferreira, D.F., Sisvar 5.3, Build 75, 2010. Available at: