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United States Department of Agriculture

Agricultural Research Service

Research Project: RELATIONSHIPS BETWEEN SORGHUM GRAIN ATTRIBUTES, MILLING QUALITY AND FLOUR QUALITY/FUNCTIONALITY
2009 Annual Report


1a.Objectives (from AD-416)
The objectives of this research are: (1) Optimize a milling procedure for sorghum to produce high quality flour, (2) characterize milling fractions of sorghum produce by various milling procedures, and (3) relate physical attributes of sorghum grain to milling performance.


1b.Approach (from AD-416)
Optimize milling of sorghum under tightly controlled conditions with different sorghum samples that vary in physical attributes such as hardness and diameter. Different mill streams will be isolated and characterized for their chemical properties and functionality in various food products.


3.Progress Report

While sorghum has traditionally been used in the United States as animal feed, nearly 40% of the global sorghum crop is used for human consumption (Waniska and Rooney 2000). However, the growers in the U.S. are increasing their interest in producing human food products from sorghum due to the development of the aforementioned white sorghum. It has a neutral flavor and color profile, thus allowing it to be more easily incorporated into new food products. Sorghum has potential for use in foods, especially in gluten-free products, whose market is projected to grow to $1.3 billion by 2010 from its $700 million value in 2006.

Dry milling of grain sorghum is a small, but expanding segment of the milling industry. Limited publications exist on sorghum milling techniques, and processes developed for individual sorghum milling operations remain proprietary. However, as research regarding sorghum utilization continues to expand, milling techniques will be developed that take advantage of the unique characteristics of the sorghum kernel.

The objective of any flour milling operation is twofold: the first is to reduce the kernel into finer particles; the second is to achieve an efficient separation of the kernel entities. More specifically, it is desirable to produce the cleanest possible separation of endosperm, germ, and bran, while recovering a maximum yield of endosperm. Depending on the objective, either clean endosperm grits or flour are the desired end-products. For flour production—the focus of this review—there are two general approaches to milling. The first involves the removal of the germ and the kernel’s outer layers (including pericarp, seed coat, aleurone, and nucellus—referred to as “bran”), collectively called “degermination.” This step is followed by subsequent reduction of the remaining endosperm. This method is utilized in maize milling. Alternatively, the kernel can first be broken open, allowing the endosperm to be scraped from the bran layer. This method is primarily utilized for wheat and rye milling. With either method, the endosperm fraction should have as little bran and germ contamination as possible, as these products discolor the flour and affect the shelf-life of the product. Additionally, for both methods, a product composed of overlapping kernel fractions is obtained, designated as “shorts” or “fines.” Included in this fraction are portions of all milling streams, which due to composition, color, or most importantly, particle size, cannot be combined into the flour or bran fractions. To do so would sacrifice product quality.

The report herein is focused on the processing and utilization of sorghum and sorghum products in food applications not yet prevalent in the North American market. These areas include sorghum flour production, treatment, and batter bread and gluten free beer.

Activities of this project are monitored by frequent personal meetings, emails and phone calls, as well as through shared graduate students between the ADODR and PI.


Last Modified: 10/22/2014
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