world of flours and flour milling

Traits included in the SWQL evaluation of breeding samples, the method used, the purpose of the measurement and measurement units are summarized in Table 28. SWQL methods are described in detail below.

Table 3 . Traits measured at SWQL: methods, purpose and units

Whole Grain Moisture, Hardness, and Protein

Whole grain moisture, hardness and protein are measured using the NIR DA7200 Analyzer (Perten Instruments). Adjustment of calibrations was performed in Wooster, Ohio, for hardness, whole grain moisture and protein using values produced on the Single Kernel Characterization System (Perten Instruments), oven moistures (AACC Method 44-01.01) and nitrogen combustion analysis Rapid NIII Nitrogen Analyzer (Elementar), respectively.

Flour Yield

Flour yield is calculated as the percent total flour weight (break flour + mids) of the sample grain weight from a single pass through the Quadrumat break roll unit. For calculation of flour yield, the difference between the grain weight and the bran weight (over 40) is used.

FY = ((GW-Bran)/GW) x 100

The formula is equivalent to:

(Total Flour/GW) x 100

Softness Equivalence

Softness Equivalence (SE) is the percentage break flour (through 94-mesh screen) of the total flour weight (break flour plus mids). SE approximates grain softness and particle size of flour produced from a single pass through the Quadrumat break roll unit (C.W. Brabender Instruments, Inc.) and is analogous to break flour in a large-scale mill (Finney, 1986). Total flour weight is calculated by subtracting bran weight (remaining over the 40-mesh screen) from initial grain weight. Subtracting the weight of the mids (remaining over the 94-mesh screen) from the total flour gives the weight for break flour.

SE = (GW - Bran - Mids)/(GW - Bran) x 100

This formula is equivalent to:

(BkFl/Total flour) x 100

Flour Moisture and Protein

Flour moisture and protein are estimated using the SpectraStar NIR analyzer (Unity Scientific), calibrated yearly for protein by nitrogen combustion analysis using the Rapid NIII Nitrogen Analyzer (Elementar) and for moisture by the oven drying method (AACC method 44-01.01).  Units are recorded in percent moisture or protein converted from nitrogen x 5.7 and expressed on a 14% moisture basis.

Flour protein of 8% to 9% is representative for breeder's samples and SWQL grow-out cultivars.  As flour protein increases, the expansive capability of the cookie during the baking process tends to decrease.  Flour protein is controlled more by climatic conditions and cultural practices, and less by genetic variation.

Protein quality is an evaluation of gluten strength and is not the same as protein quantity.  A cultivar low in protein quantity potential of grain could still exhibit strong gluten strength.  Soft wheat of relatively strong protein is desirable for cracker production.  Gluten strength is estimated using a mixograph and graded on a scale of 1 to 8, weakest to strongest gluten.  Evaluation of gluten strength using the mixograph or farinograph is difficult for soft wheat flours that are 8.5% protein and lower. Lactic acid SRC does not require dough mixing for assessment of gluten strength and tends to be a better measurement of protein quality when evaluating soft wheats.

Solvent Retention Capacity

Solvent Retention Capacity (SRC) assays are performed as described in AACC Method 56-11.02, Solvent Retention Capacity Profile. The profile of SRCs in the four solvents (sucrose, lactic acid, sodium carbonate and water) is used to predict milling and baking quality. In general, lower SRCs are preferred for water, sodium carbonate and sucrose solvents (Kweon, Slade, & Levine, 2011)

Breeder samples processed by intermediate and advanced group testing use straight grade flour (blend of break and reduction flours) for SRC tests.

With the exception of sucrose, SRCs are performed using 1 gram of flour in glass test tubes with rubber stoppers. Sucrose SRCs are performed with 5 grams of flour in 50 mL disposable screw top centrifuge tubes, because the highly viscous sucrose solution impedes even distribution of solution in 1 gram flour tests, reducing the reliability of the small scale test.

SRC Biochemistry and Correlations to Traits

The following descriptions of the biochemistry and correlations of SRCs with milling and baking traits were published in the Soft Wheat Quality Laboratory Annual Report 2011 (Souza, Kweon, & Sturbaum, 2011).

WaterSRC is a global measure of the water affinity of the macro-polymers (starch, arabinoxylans, gluten, and gliadins). Lower water values are desired for cookies, cakes, and crackers, with target values below 51% on small experimental mills and 54% on commercial or long-flow experimental mills.

Sucrose SRC values are related to content of arabinoxylans (also known as pentosans), which can strongly affect water absorption in baked products. Sucrose SRC is a good predictor of cookie quality and shows a negative correlation with wire-cut cookie diameter (r = -0.66, p<0.0001). The cross hydration of gliadins by sucrose also causes sucrose SRC values to be correlated to flour protein (r = 0.52) and lactic acid SRC (r = 0.62). The 95% target value can be exceeded in flour of high lactic acid SRC.

Sodium carbonate SRC takes advantage of the very alkaline solution to ionize the ends of starch polymers increasing the water binding capacity of the molecule. Sodium carbonate SRC increases as starch damage due to milling increases.

Lactic acid SRC predicts gluten strength of flour. Typical values are below 85% for "weak" protein soft wheat varieties and above 110% for "strong" protein soft wheat varieties. Lactic acid SRC results correlate to the SDS-sedimentation test. The lactic acid SRC is also correlated to flour protein concentration and dependent on genotypes and growing conditions.

Cookie Bakes (sugar snap cookies)

Two sugar snap cookies are baked in the SWQL bake laboratory for each sample as described in AACC Method 10-52, Baking Quality of Cookie Flour. Cookies are baked exclusively for advanced group samples using straight grade flour (blend of break and reduction flours). Diameter of the two cookies is measured and recorded electronically using a Mitutoyo Absolute Digimatic Caliper. Cookies are graded visually for surface appearance and color, from worst to best on a scale of 1 to10.

Falling Number

The falling number test (AACC Method 56-81B) measures the travel time of the plunger in seconds (falling number) from the top to the bottom position in a glass tube filled with a suspension of whole grain meal or milled flour, immediately after being cooked in a boiling water jacket to produce gelatinized starch. The higher the viscosity of whole grain meal or flour paste in the glass tube, the longer the travel time of the plunger. The enzyme a-amylase, produced when grain sprouts, hydrolyzes starch molecules and lowers viscosity of gelatinized starch, resulting in a decreased travel time of the plunger (falling number). The test is performed using the Perten Falling Number Instrument. Alpha-amylase can be measured directly using a kit from Megazyme, International (AACC Method 22-02-01, Measurement of alpha-Amylase in Plant and Microbial Materials Using the Ceralpha Method). The SWQL uses a modified micro method of the Megazyme assay.

Flour Ash

Flour Ash is measured according to the AACC method 08-01 and detects residual inorganic materials after combustion. Since inorganic materials are higher in bran than in endosperm, flour ash is an indirect indicator of residual bran in the flour.

Quality Materials and Methods References

Finney, P. A. (1986). Revised Microtesting for Soft wheat Quality Evaluation. Cereal Chemistry , 177-182.

Gaines, C. F. (2000). Developing agreement Between Very Short Flow and Longer Flow Test Wheat Mills. Cereal Chemistry , 187-192.

Kweon, M., Slade, L., & Levine, H. (2011). Solvent Retention Capacity (SRC) Testing of Wheat Flour: Principles and Value in Predicting Flour Functionality in Different Wheat-Based Food Processes and in Wheat Breeding-A Review. Cereal Chemistry, 88, 537-552.

Souza, E., Kweon, M., & Sturbaum, A. (2011). Research Review. USDA-ARS Soft Wheat Quality Laboratory.

Genotyping

DNA markers applied in marker assisted selection and genotyping are included below. The SWQL sends samples to the Eastern Regional Small Grains Genotyping Laboratory for SNP genotyping.

/Main/docs.htm?docid=19522

Molecular markers and protocols are available at the University of California Davis website:

http://maswheat.ucdavis.edu/

Quality Genotyping - Primer Sequences, amplification conditions and references

The molecular markers described below are the most commonly used markers at the SWQL. These are reliable and robust reactions that have been useful in assessing wheat quality. Primer sequences are 5' to 3'.

High Molecular Weight Glutenins and ?-gliadin

GluA1

Amplifies at 58? C, 1,200 bp product, present or absent using single forward primer, alternate (Ma et al., 2003), (Liu et al., 2008)

GluD1

Amplifies 664 bp product, present or absent using single forward primer, alternate reverse primers, touch down amplification.
(Wan et al., 2005)

GluB1

Amplifies at 64? C a 404 bp for wild-type or 447 bp product for over-expressing Bx7.
(Lei et al., 2006)

?-gliadin

Amplifies at 56? C, a 264 bp product for gliadin 1.1 or or 270 bp product for gliadin 1.2, using single forward primer, alternate reverse primers.
(Zhang et al., 2003)

Translocations and Disease Resistance

1B/1R and 1A/1R - Chromosome 1B or 1A substituted with rye secalin

Tailed Reaction

Amplifies using a tailed reaction, 207 bp for 1B/1R or or 203 bp for 1A/1R.
(De Froidmont)

2B translocation - Sr36 stem rust resistance

Amplifies with 62/55? C touchdown program producing a 162 fragment indicative of the 2B translocation carrying Sr36 or 192 bp for wild type 2B.
(Tsilo et al., 2008)

Sucrose Synthase type 2 Sus2

Amplifies each of the primer pairs independently at 52? C to produce a 423 (HapH) or 381 bp (HapL) fragment. Haplotypes indicate high or low grain weight, respectively.
(Jiang et al., 2011)

Pre-harvest sprouting

Amplifies at 62? C a 569 or 845 bp fragment for reported tolerance to preharvest sprouting.
(Yang et al., 2007)

Genotyping Materials and Methods References

De Froidmont, D. (1998). A Co-dominant Marker for the 1BL/1RS Wheat-rye Translocation via Multiplex PCR. J. Cereal Sci. 27, 229-232.

Jiang, Q., Hou, J., Hao, C., Wang, L., Ge, H., Dong, Y., and Zhang, X. (2011). The wheat (T. aestivum) sucrose synthase 2 gene (TaSus2) active in endosperm development is associated with yield traits. Funct. Integr. Genomics 11, 49-61.

Lei, Z.S., Gale, K.R., He, Z.H., Gianibelli, C., Larroque, O., Xia, X.C., Butow, B.J., and Ma, W. (2006). Y-type gene specific markers for enhanced discrimination of high-molecular weight glutenin alleles at the Glu-B1 locus in hexaploid wheat. J. Cereal Sci. 43, 94-101.

Ma, W., Zhang, W., and Gale, K.R. (2003). Multiplex-PCR typing of high molecular weight glutenin alleles in wheat. Euphytica 134, 51-60.

Tsilo, T.J., Jin, Y., and Anderson, J.A. (2008). Diagnostic Microsatellite Markers for the Detection of Stem Rust Resistance Gene in Diverse Genetic Backgrounds of Wheat. Crop Sci. 48, 253.

Wan, Y., Yan, Z., Liu, K., Zheng, Y., D'Ovidio, R., Shewry, P.R., Halford, N.G., and Wang, D. (2005). Comparative analysis of the D genome-encoded high-molecular weight subunits of glutenin. Theor. Appl. Genet. 111, 1183-1190.

Yang, Y., Zhao, X.L., Xia, L.Q., Chen, X.M., Xia, X.C., Yu, Z., He, Z.H., and R?der, M. (2007). Development and validation of a Viviparous-1 STS marker for pre-harvest sprouting tolerance in Chinese wheats. Theor. Appl. Genet. 115, 971-980.

Zhang, W., Gianibelli, M.C., Ma, W., Rampling, L., and Gale, K.R. (2003). Identification of SNPs and development of allele-specific PCR markers for ?-gliadin alleles in Triticum aestivum. Theor. Appl. Genet. 107, 130-138.