Title: Management of Pre-harvest Sprout Damage in Wheat and Improvement of Soft Wheat Quality in US Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 15, 2010
Publication Date: N/A
Technical Abstract: The United State Department of Agriculture (USDA) estimated world wheat production at 641MMT and US wheat production at 60.5 MMT in 2010/11. About 82% of the world wheat demand is for food and seed use, and about 18% for feed and residual use. Although pre-harvest sprouting occurs for all cereals, most of the damage occurs in wheat because wheat is the most widely grown cereal in the world. Pre-harvest sprouting in wheat occurs in 3-4 years out of 10 in major wheat-producing areas throughout the world including the Unites States. The areas in the US commonly affected by sprout damage are portions of the Pacific Northwest, the upper Midwest and the Northeast. Before wheat is harvested, kernels can start to germinate in the field when wet condition persists due to prolonged and repeated rain, and sprout damage may continue to occur during storage and shipment, resulting in significant economic losses through lower yield, decreased test weight, and activated enzyme complex in the seed. Pre-harvest sprout damage in US wheat ranges from very minor to very severe, and damage occurs mostly in narrow defined areas. The incidence and severity of pre-harvest sprout damage is quite unpredictable because of the variability of inopportune rains and undocumented differences in the susceptibility of prevalent varieties to pre-harvest sprouting. Naturally, not all varieties of wheat have an equal amount of pre-harvest sprouting tolerance. When wet weather continues for a prolonged period, even the most pre-harvest sprouting tolerant wheat varieties will eventually sprout. For example, the weather in Kansas State is usually hot with dry conditions following ripening of hard red wheat, which does not normally favor sprouting. But unexpected damage occurred in parts of the state during 1979, 1989, 1993, 1999, and 2004 when weather conditions were particularly favorable. Since the early 1970s, there have been numerous efforts in the world to improve the resistance to pre-harvest sprouting through wheat breeding programs and research on the genetics and physiology of seed development, dormancy and germination. However, the pre-harvest sprouting problem remains unsolved because of its sporadic occurrence and complex biology. Only a few wheat cultivars resistant to pre-harvest sprouting such as Clark’s Cream, Rio Blanco, Cayuga, and Jensen have been released, and Jensen is among the few resistant varieties still in commercial use. Most wheat cultivars planted currently in the US are susceptible to pre-harvest sprouting. As the severity of sprouting increases, acceptable food uses for wheat are limited. When sprouting in wheat is too severe to use for food, the wheat is pushed to sell as animal feed. To mitigate the economic losses of sprout damage, the wheat industry employs common practices. Early harvesting as soon as grains mature physically is generally recommended to farmers to avoid a risk of pre-harvest sprouting. When prolonged wet weather conditions are forecasted or expected in certain regions, batches of wheat received are subjected to testing to guarantee sound wheat. Depending on sprout severity, sprouteded wheat can be blended with sound wheat, but reducing the proportion of sprouted wheat requires progressively greater expenses because the starch hydrolyzing amylase activity in sprouted wheat increases exponentially as the sprout severity increases. As a result, blending severely sprouted wheat with sound wheat is a difficult and expensive remedy to improve end-use quality. Traditionally visual scoring is used for sprout count, but recently the secondary falling number test has been implemented at grain elevators for testing sprouted wheat. There is still a major problem with the reliability of falling number because many factors affect the result. To manage the sprouted wheat problem, the milling industry has often contracted with grain elevators for purchasing sound wheat, building good relationships with them for trust and cooperation, and blending wheat before milling, minimizing sprout damage without deteriorating flour quality. Baking industry controls and monitors receiving sprouted wheat flour based on flour specifications which include falling number (>300 or >350, depending on the products) or a-amylase activity. If only sprouted wheat flour is available in the market for bakeries, adjustment in formulas (water and sugar levels, leavening system, and enzyme levels) and procedures (mixing time, oven temperature, and baking time) for baked products are necessary. Generally, the bakeries manufacturing fermented products, like bread or saltine type crackers, have better guidelines than the unfermented products bakers for handling the sprouted wheat problems. Wheat is classified into hard and soft by distinct categories of endosperm hardness. Soft wheat is mainly used for cookies, crackers, cakes and pancakes in the US. The Soft Wheat Quality Laboratory (SWQL) located in Wooster, Ohio, is part of the Agriculture Research Service of the USDA and works with breeders, millers, and bakers to improve wheat quality for the domestic and international grain trade. Since the 1930’s, the SWQL has supported breeders in the Eastern US assisting in selection of new soft wheat cultivars and applications of soft wheat flour. The research unit has two missions: one is to evaluate the quality of soft wheat breeding lines and cultivars from the Eastern United States to ensure maintenance and/or improvement of milling and baking quality, and the other is to conduct research in the physics and chemistry of wheat and flour, with particular reference to quality and development of new and improved tests for measuring and predicting quality. Every year the SWQL evaluates milling and baking qualities of about 6000 -7000 wheat breeding lines, mostly soft red and white winter wheat. The laboratory provides interpretation and consultation on the use of the quality data for breeding. Two scientists, one supporting scientist, and eight technicians in the lab conduct service work and research in the area of wheat quality, food formulation, and wheat genetics. Over the years, the SWQL has distributed reports for the US Wheat Associates Overseas Varietal Analysis and the Wheat Quality Council. The reports include soft wheat quality targets as guidelines for quality interpretation. Quality targets include information on test weight/grain condition, field sprouting, kernel texture, milling qualities, protein content, protein strength, solvent retention capacity, and baking qualities for pastry flour and cracker flour. Most of the parameters for the two categories of flour are similar except the gluten strength measurement (lactic acid solvent retention), for which cracker flour requires a higher value. The soft wheat breeding program prioritizes high yield to benefit farmers, followed by disease resistance, and finally quality. For support in screening breeding lines, the SWQL provides milling, baking, and softness scores including test weight, grain protein and hardness, flour yield, softness equivalent, flour protein, four solvent retention capacity values, cookie diameter and top grains. In addition, developing new and improved tests such as a chemically leavened cracker baking method, a pancake method, and a whole grain application of NIR, will be available for predicting milling and baking qualities for breeders, millers and bakers in the future.