Abstract
The production of bio-based ethanol has been one of the fastest growing industries in the United States during the past decade. Thus, wider exploration of ethanol coproduct uses is necessary in the ethanol plant. Currently, process steams such as whole stillage, thin stillage, and syrup are processed into distiller dried grains with solubles and fed to livestock. The storability of whole stillage, thin stillage, and syrup influences the economic and energetic balances of fuel ethanol production. However, there are few investigations of the shelf life for these products or how to measure these quantities. The objectives of this research were to test physical and biological properties of whole stillage, thin stillage, and syrup and determine storability and allowable shelf life for these materials as influenced by storage temperature levels. Using standard laboratory methods, several properties were determined, including moisture content, water activity, thermal properties (conductivity, resistivity, volumetric heat capacity, and diffusivity), color, mold development, and CO2 production. Also, the separation processes due to settling were observed over 72 h. The thin stillage and whole stillage had relative high average moisture contents of 92% (w.b.) and 87% (w.b.), respectively, and a mean water activity of 0.99; the high water content marked samples easily susceptible to rapid spoilage. Time had a significant effect (p < 0.05) on properties of coproducts. Both thin stillage and whole stillage samples got mold growth after 5 days incubation at 32°C. Thin stillage had the greatest separation rate in the settling experiment. However, syrup had a relative low average moisture content of 62% and an average water activity of 0.92. No mold growth and settling separation happened in syrup samples. There was no evidence showing that a linear relationship exists between Hunter L*, a* and b*, and mold growth. The Solvita® test showed that high-temperature treatment caused high CO2 production in all samples. The exponential models described the relationship between storage time (from 0 to 5 days at 25 and 35°C) and CO2 concentration for the three coproducts. This study is a first step to explore opportunities for utilizing valuable components from these coproducts. Follow-up study should work on separation processes to concentrate the valuable components of these coproducts. Exploring the potential value of ethanol coproducts could maintain and improve the profitability of the ethanol industry.
Highlights
The corn ethanol industry has evolved into an invaluable economic engine for communities across the nation
Initial properties of whole stillage, thin stillage, and syrup results are summarized in Table 2, which provides replications; minimum, FIGURE 6 | (A) Mold development in whole stillage
According to the dried grains with solubles (DDGSs) values from a published study (Rosentrater, 2006), L* ranged from 43.48 to 48.8, a* was from 8.3 to 9.7, and b* ranged from 19.4 to 23.0. These results indicated that whole stillage, thin stillage, and syrup in this study were initially bright, greener, and more yellow, respectively, compared to the DDGS from the previous study
Summary
The corn ethanol industry has evolved into an invaluable economic engine for communities across the nation. In 2014, the fuel ethanol production in the United States (U.S.) was 54,131 m3, which supported 83,949 direct jobs in the agricultural sector and 295,265 indirect jobs across all sectors of the economy (RFA, 2015). The ethanol industry makes an enormous and overlooked contribution to the production animal feed supply. The starch portion of the grain is used to produce ethanol; the remaining protein, fat, and fiber pass through the process. These nutrient-dense coproducts are primarily fed to livestock, including beef cattle, dairy cows, swine, poultry, and fish in nations around the world. In 2014, the ethanol industry produced as estimated 39 billion kilograms of feed, making the renewable fuel sector become the largest animal feed processing segment in the United States (RFA, 2015)
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