Flour aging is thought to occur naturally during storage of wheat flour. In soft-wheat it is hypothesized that aging may increase water absorption properties of the flour. The aim of this study was to determine if the absorption capacity of flour changes as a response to flour aging. Absorption was monitored by Solvent Retention Capacity (SRC). SRC consists of four tests, each using a different solvent: water, and aqueous solutions of 5% (w/w) sodium carbonate, 50% (w/w) sucrose, and 5% (w/w) lactic acid. Each solvent emphasizes specific polymeric components of flour, respectively: all components; damaged starch; arabinoxylan (fiber) and gliadin; and glutenin. Grain from 4 soft-wheat varieties was milled into flour 0, 3, 6, 12, and 24 weeks after harvest. At each milling date SRC was performed on the stored flour on specified days over a 2 month period. The major differences observed were between varieties. Except for lactic acid SRC, SRC values for 2 of the 4 wheat varieties, Tubbs and Goetze were significantly higher (p ≤ 0.05) than SRC values for the other 2 varieties, Skiles and Bobtail. These differences were greater in magnitude than differences associated with storage and aging and were generally consistent across all weeks after harvest and days after milling. Water and sucrose SRCs showed small but significant increases (p ≤ 0.05) across the storage period. Mean water SRC across all 4 varieties increased from a minimum of 52.5% to a final value at 6 months of 53.3%. Mean sucrose SRC across all 4 varieties increased from a minimum of 72.1% to a final value at 6 months of 73.1%. This supported the original hypothesis of increased absorption during aging. Sodium carbonate and lactic acid SRCs showed small but significant decreases (p ≤ 0.05) across the storage period, partially refuting the original hypothesis. Sodium carbonate SRC was significantly higher at Week 0 Day 0 (p ≤ 0.01) compared to all other days. Mean lactic acid
SRC across all varieties decreased from a maximum of 110.5% to a final value at 6 months of 107.5%. These data indicate that except for carbonate SRC at Week 0 Day 0, SRC analyses could be performed immediately after milling on freshly harvested grain and provide valid comparisons among wheat genotypes. However, the modulating effect of storage and aging is important to note, especially the small increases in water and sucrose SRCs, the decline in carbonate SRC after grain storage and flour aging, and the overall decline in lactic acid SRC that may indicate a decline in gluten performance. Knowledge of the impact of aging on flour functionality predictions is vital in a wheat breeding program, where high throughput in short timeframes is an unavoidable operational demand. This means that testing freshly milled flour from freshly harvested grain is often a necessity. These data suggest that this is valid at least for water and sucrose SRCs in soft white wheat. Sequencing the testing so that carbonate SRC was done last may be an operational strategy to compensate for the observed overestimation of this parameter when testing flour freshly milled from freshly harvested grain.
Funding Statement (additional comments about funding)
The Multicultural Scholars Program (MSP); National Institute of Food and Agriculture (NIFA); US Department of Agriculture (USDA); College of Agricultural Sciences, ER Jackman Internship Support Program; College of Agriculture Sciences, Calvin & Merle Smith Wheat Research Endowment Fund