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a Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506
b Dep. of Grain Science, Kansas State Univ., Manhattan, KS 66506
* Corresponding author (wts{at}ksu.edu)
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Abbreviations: AOAC, Association of Official Analytical Chemists • ASTM, American Society of Testing and Materials • ßc, ß-conglycinin • G, glycinin • NASS, National Agricultural Statistics Service • PC, polycarbonate • PPCO, polypropylene copolymer • REML, restricted maximum likelihood estimation • USDA, United States Department of Agriculture
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Current bio-based research is focusing on developing new safe, renewable alternatives to synthetic wood adhesives. The abundance of soybean grown throughout the world creates the potential for soy-based resins and adhesives to be produced at high volumes and low cost. In 1998, an estimated 1.37 million metric tons of wood adhesives and resins were used in the USA (Sellers, 2001). One kilogram of soy flour can make approximately 2 to 3 kg of plywood adhesive (X.S. Sun, personal communication, 2004). Soybean seed is composed of approximately 80% soy flour; thus it would take 570 000 to 850 000 metric tons of soybean seed to fill this adhesive demand. In 2003, the USA produced more than 65 million metric tons of soybean, which can readily meet this demand (National Agricultural Statistics Service, 2004).
The quality of natural-based wood adhesives has improved. Modifications to soy proteins have allowed adhesives to be developed that possess improved shear strength and water resistance. Soy proteins modified under alkali conditions or with trypsin exhibit greater shear strength and enhanced water resistance (Hettiarachchy et al., 1995). Huang and Sun (2000a, 2000b) also found superior shear strength and water resistance in adhesives made from soy proteins modified by sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, urea, or guanidine hydrochloride. None of these studies, however, examined how proteins acquired from different genotypes or environments affected soybean adhesive quality.
To develop the most superior soybean adhesives, it is desirable to know which genotypes are the most suitable for adhesive development. Studies have shown that genotype x environment interactions can affect end-use quality characteristics of some products. Bassett et al. (1989) studied the effects of genotype and environment on the quality of flour made from soft white winter wheat seed. It was found that genotype, environment, and genotype x environment effects significantly affected end-use quality characteristics, such as flour protein, in soft white winter wheat. Genotype, environment, and their interaction also significantly affect hard red winter wheat end-use quality characteristics, including flour protein (Peterson et al., 1992).
In soybean, genotype and environment are known to affect end-use quality characteristics, particularly in the food industry. Natto, a soybean food product consumed primarily in Japan, has been evaluated for genotype and environment influences (Cober et al., 1997). Aziadekey et al. (2002) showed that genotype and environment also affect soymilk and tofu quality, with genotype being a primary source of variation.
Research by Fehr et al. (2003) has noted significant differences in the protein components ß-conglycinin (ßc) and glycinin (G) and their subunits among genotypes and environments. The ßc subunits studied were 
, ', and ß peptides. G subunits studied included A3; total A1a, A1b, A2, and A4; and total basic peptides. The ßc, G, and the G/ßc ratio showed significant differences among the 24 environments studied. Significant differences were noted among genotypes for all components and subunits except the A3 subunit of G. The genotype x environment interaction was not significant for any of the protein components studied. Yaklich (2001) found that subunit amounts varied among soybean genotypes and that high-protein genotypes contained more ßc and G than did genotypes with average protein contents.
Khatib et al. (2002) found that soybean genotypes with different protein components had unique functional properties for soy food applications. Protein solubility in water, foaming properties, emulsifying properties, water-holding capacity, surface tension, and gel rheology were all significantly affected by genotypes with differing ßc and G fractions. Genotype and environment effects on protein components affect end-use quality characteristics. Zutara and Sun indicated that adhesive shear strength was affected by protein components (unpublished data, 2004). Therefore, the end-use quality characteristic, adhesive shear strength, may also be affected by the genotype and environment influences on protein components. The objective of this study was to determine if genotype and environment influence the shear strength of soybean-based adhesives.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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In 2003, entries were grown at three locations. Environment 4 was irrigated on a Eudora silt loam (coarse-silty, mixed, superactive, mesic Fluventic Hapludolls) field at the Ashland Bottoms Agronomy Farm. Environment 5 was at the Agronomy North Farm in Manhattan, KS was a dryland site on a Kahola silt loam (fine-silty, mixed, superactive, mesic Cumulic Hapludolls). Environment 6 was a dryland, Woodson silt loam at the East Central Kansas Experiment Field.
In 2002, Environment 1 had 40 cm of precipitation during the growing season (May to September). This amount is well below the 30-yr average (1970–2000) of 54 cm, but this site was irrigated as needed. Temperatures were near normal, but the July daily high temperature of 36°C, was 3°C above average, with temperatures exceeding 38°C on several days. Environment 2 had growing-season precipitation of 42 cm, compared with a normal 30-yr average of 55 cm. Drought was especially significant during June, with only 2.0 cm of precipitation compared with the June average of 12 cm. In addition to the lack of precipitation, monthly average day time temperatures for June (31°C) and July (34°C) were slightly elevated, compared with the 30-yr average, of 29 and 32°C for June and July, respectively. During the 2002 growing season, Environment 3 was severely drought stressed, receiving 38 cm of total precipitation, which was well below the normal 56 cm. July and August were especially dry, with actual rainfall received being 2.5 and 4.8 cm, respectively, compared with the average precipitation of 9.1 cm for July and 9.4 cm for August. In 2002, near-average temperatures were recorded for Environment 3. In 2003, Environment 4 had near-normal growing season precipitation and temperatures, but, was not significantly affected by precipitation amount because it was irrigated as needed. During 2003, Environment 5 also had near-normal growing season rainfall and temperature, but it was not irrigated. Environment 6 had near-normal growing-season temperatures and precipitation. July had a lower-than-average precipitation of 3.6 cm, whereas August had higher-than-average precipitation of 13 cm. Plants were stressed during July and early August. In 2003, temperatures were slightly above-normal in July and August, which increased plant stress during this time (Kansas State University Research and Extension, 2004). Overall, the 30-yr temperature averages for these environments are similar. Environment 2, however, averaged 1 to 2°C lower in temperatures than the other locations.
In both 2002 and 2003, two replications of each entry were grown per environment in a randomized complete-block design. The entries were planted at 25 seeds m–1 in 4.1-m rows spaced 76 cm apart. Row length was end-trimmed to 3.35 m before harvest. Plots were 2 and 4 rows in 2002 and 2003, respectively. Both rows were harvested from each plot in 2002, and in 2003, the center two rows from each four-row plot were harvested. Protein and oil concentrations of seed from each plot were determined by using near infrared reflectance (Association of Official Analytical Chemists, 1996) on a 30-g sample.
In 2002, Environment 1 was planted on May 21; plots were harvested as they matured from September 25 to October 18. Environment 2 was planted on May 20 and harvested on September 26 and 27 and October 9. Environment 3 was planted on May 22 and harvested on September 16 and 25. In 2003, Environment 4 was planted on May 15; plots were harvested as mature on October 2 and October 21. Environment 5 was planted on May 28 and harvested on October 3 and October 10. Environment 6 was planted on June 10; mature plots were harvested on October 8, with remaining plots harvested on October 22. After harvest, seed was cleaned and stored at room temperature until protein extraction.
Protein Extraction
Protein extraction and adhesive evaluation was performed on seed from each field plot. The protein extraction process was based on the isolation protocol described by Khatib et al. (2002) and modified by Zutara and Sun (personal communication, 2004). Thirty grams of seed from each plot was ground with a kitchen mill (Model 91; K-tec, Inc., Orem, UT) on the finest setting, producing a pastry-flour size particle (50–140 µm.) Ground beans were mixed into a slurry with 0.15% Na2S2O5 at 1:15 (w/v). Slurry pH was adjusted to 8.5 using 2 M NaOH. The mixture was stirred for 1.5 h and then filtered through two sets of two layers of cheesecloth. The slurry, about 200 mL of solution, was centrifuged in 250-mL polycarbonate (PC) centrifuge bottles at 10000 x g at 4°C for 20 min. The resulting supernatant was recovered and filtered through two consecutive funnels plugged with glass wool. The supernatant's pH was then adjusted to 4.2 with 2 M HCl, and the solution was stored overnight at 4°C.
The protein solution (
200 mL) was centrifuged (6500 x g) at 4°C for 20 min in 250-mL PC centrifuge bottles. After decanting the supernatant, the precipitate was cleansed twice by suspension in 100 to 150 mL of water. The solution was centrifuged at 6500 x g at 4°C for 20 min. The supernatant was discarded, and the precipitate was resuspended in approximately 100 mL of distilled water and stirred at 700 rpm for 3 h. The solution was adjusted to pH 7.6 with 2 M, 1 M, or 0.5 M NaOH as needed, then placed in a freezer (–20°C) overnight. The frozen solution was freeze-dried in an 800-mL glass canning jar for 3 d (freeze dryer, Model 6211–0495; The Virtis Co., Inc., Gardiner, NY).
The freeze-dried sample was milled to a powder (particles 
1 mm) with a Cyclone Sample Mill (Model 3010–030; UDY Corp., Fort Collins, CO). The powder, approximately 5 g of isolate, was then mixed with petroleum ether in a 1:5 (w/v) ratio for defatting. The resulting solution (40 mL) was agitated by shaking with a mechanic platform shaker at 250 rpm for 5 min, followed by centrifugation for 10 min (1000 x g at 20°C) in 250-mL PPCO (polypropylene copolymer) centrifuge bottles. Supernatant was decanted, and the defatting procedure was repeated three more times. After the final decanting, the protein precipitate was left overnight in a fume hood for evaporation of remaining solvent. The freeze dryer was used to apply a vacuum for 24 h to the precipitate to remove traces of the solvent. The resulting protein isolate powder was placed in the freezer (–20°C) until adhesive evaluation could be performed.
Adhesive Evaluation
A modified procedure of Sun and Bian (1999) was followed for adhesive preparation. Adhesive was prepared by diluting 500 mg of protein isolate powder with distilled water in a 12:100 (w/v) ratio and stirring on a stir plate (500 rpm) for 2 h in a glass beaker.
Cherry wood samples measuring 3 x 52 x 126 mm (thickness x width x length) (Veneer One, Oceanside, NY) were preconditioned for 7 d at 23°C and 50% relative humidity. Wood samples were prepared and tested for shear strength according to American Society of Testing and Materials (ASTM) standard method D-2339–94a (ASTM, 1995.) Two wood pieces were prepared by brushing 0.6 mL of the protein slurry on one side of each piece in a 20 x 126 mm area. After 8 min, the glued areas of the two pieces were overlapped and pressed together by hand. The samples were hot-pressed (Model 3890; Auto "M," Carver Inc., Wabash, IN) at 105°C and 20 kg cm–3 for 15 min. Assembled wood samples were then conditioned for 2 d at 23°C and 50% relative humidity. Each sample was cut into five subsamples 20 mm wide. After cutting, the samples were conditioned as previously described for an additional 5 d.
Wood samples were tested by using an Instron test machine (Model 4466; Canton, MA.) The operational crosshead speed was 1.6 mm per min. Shear strength in MPa at maximum load was recorded for each subsample. In 2002, the glue from each plot was used to assemble and test three wood boards. The three samples were each cut into five subsamples, for a total of 15 subsamples per plot. In 2003, two wood samples were tested per plot, for a total of 10 subsamples. Data from subsamples were averaged to obtain mean shear strength for each plot.
Data was evaluated according to the Mixed procedure of SAS (Littell et al., 1996; SAS Institute, 1985). Genotype was considered a fixed effect. Environment and environment x genotype were random effects. The Restricted Maximum Likelihood (REML) estimation method was used to test the effect of genotype on shear strength. The Type 3 estimation method was used to test random effects. Genotype shear strength means were compared by using Tukey's multiple comparison procedure (p 0.05).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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The Tukey's comparison of adhesive shear strength showed a significant separation of entry means at p 0.05 when averaged across environments (Table 1). Shear strength means for genotype ranged from 3.71 to 3.22 MPa. The entry with the highest shear strength mean was PI446893, a Group III maturity line from China. PI437401, a Group III maturity line from Russia, had the lowest shear strength mean. The shear strength of PI437401 was significantly lower than that of the top twelve entries in this test. Two of the top twelve entries were the commercial cultivars IA3010 and Macon. Shear strength means for IA3010 and Macon were 3.61 and 3.59 MPa, respectively. Because IA3010 and Macon have shear strength means comparable with that of the top-ranking genotypes, these cultivars could be used for the development of superior adhesives.
The shear strength differences observed in this study among soybean genotypes were anticipated. Fehr et al. (2003) noted significant genotypic differences in protein components, and research by Zutara and Sun showed that adhesive shear strength was affected by protein components (unpublished data, 2004). Therefore, significant genotypic effects in this study could have been due to genotypic difference for protein components. Protein concentration, which averaged from 385 to 455 g kg–1 across environments for entries, was not related to differences observed in shear strength (Table 1).
Only a small number of genotypes were evaluated for this study. Greater separation of entries may be observed when more extensive screening of soybean genotypes is conducted. Lack of separation among the top entries tested could also have resulted from difficulties in testing. Wood adhesives can be stronger than the test wood fibers when shear strength is tested parallel to the grain, the method used in this experiment (Vick, 1999). As a result, wood failure could occur at high shear strengths. In this study, wood failure occurred sporadically when subsample shear strengths reached values <5.0 MPa. Although wood breakage was minimal in this experiment, wood failure should be a consideration in future screenings if greater shear strengths are observed. One option to counteract these failures is to use a stronger wood than the cherry boards used in this study.
Genotype x environment effects were not significant (p = 0.08), indicating that the relative performance among genotypes across environments was consistent. This interaction, however, was close to significant. The lack of significance may be due, in part, to the modest separation of genotype shear strength means, and could prove to be a factor if greater genotypic effects are observed in future studies. For this study, however, the lack of significance and consistent relative performance of entries indicate that it should be possible for breeders to assess cultivars for adhesive performance in a limited number of environments.
The results of this study suggest that it may be possible to select for superior adhesive shear strength among soybean genotypes. Breeders may be able to select for adhesive shear strength in different environments, without regard for environmental impacts and genotype x environment interactions. The genotypes evaluated in this study represented only a small sample of the soybean genetic base. A more extensive screening for adhesive performance among genotypes is desirable to determine if other genotypes produce adhesives with higher or lower shear strengths.
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ACKNOWLEDGMENTS |
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Received for publication September 29, 2005.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
