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Evaluation of drying technologies and physico-chemical characterization of wheat distillers dried grain with solubles (DDGS) (with a case study application in the Philippines)



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Wheat distillers dried grain with solubles (DDGS) is a co-product of ethanol production, primarily utilized as an animal feed ingredient. Reduced protein quality, a highly energy-intensive drying process, and product variability are some of the challenges that currently confront its production in western Canada. The main focus of this research undertaking was to examine, on a laboratory-scale, the effect of condensed distillers solubles (CDS) : wet distillers grain (WDG) blending ratio and drying conditions on the protein quality and physico-chemical characteristics of wheat DDGS. The potential of microwave-based drying methods in minimizing protein damage and energy consumption was investigated. An auxiliary case study was also conducted in the Philippines to apply the knowledge and skills acquired from the PhD research undertaking to a related problem situation in a developing country. It aimed to provide more information about brewers spent grain (BSG) supply and utilization in Misamis Oriental, Philippines and enhanced the efficiency and safety of BSG utilization as an animal feed ingredient. Laboratory-scale investigations used samples produced at three CDS:WDG blending ratios (by mass): 15:85 (15% CDS), 30:70 (30% CDS), and 45:55 (45% CDS) and dried under forced air convection (40-120C), and under microwave (420 – 805 W) and microwave convection (nominal settings of 130C-30% power to 190C-30% power) methods using a domestic microwave oven. Freeze-dried samples were used as standards in evaluating chemical composition and color of wheat DDGS. As CDS level in the blend was increased, protein and ash content of freeze-dried samples increased while fat, acid detergent fiber (ADF) and neutral detergent fiber (NDF) content decreased. These trends were attributed to proximate composition differences between CDS and WDG fractions. The CDS fraction had higher protein and ash and lower fat, ADF, and NDF contents compared to WDG. Variation in the CDS:WDG blending ratio employed in the source ethanol plant could be one of the factors contributing to the observed proximate composition differences between two ethanol plant-sourced wheat DDGS samples. This was verified through proximate analyses of: (i) plant-sourced wheat DDGS samples from two production batches; (ii) CDS and WDG samples obtained on the same production date; and (iii) laboratory-produced wheat DDGS samples at varying CDS:WDG blending ratios. Protein, ash, and NDF contents of forced-air convection-, microwave-, and microwave convection-dried samples also showed strong linear relationships with CDS level. Fat and ADF content, however, did not exhibit similar strong relationships with CDS level, indicating the influence of drying conditions. Maximum lysine and minimum acid detergent insoluble crude protein (ADICP) contents were achieved in blends with the highest CDS level (45% CDS) and dried under lower drying temperature (80C), microwave power (676 W), and microwave convection (150C-30% power) settings. Microwave- and microwave convection drying achieved desirable protein quality associated with lower temperature drying under much shorter times. Laboratory-scale drying of ethanol plant-sourced wet distillers grain with solubles (WDGS) under forced air convection produced DDGS samples with decreased lysine content as drying air temperature was increased. In terms of physical properties, dried samples with higher CDS level were significantly finer, denser, less flowable, less dispersible, have lower thermal diffusivity and higher internal friction coefficients, and produced denser and stronger pellets. Color parameters of freeze-dried samples were significantly affected by CDS level. As CDS level increased, lightness (Hunter L) decreased while redness (Hunter a) increased. The color parameters of forced-air convection-, microwave-, and microwave convection-dried DDGS samples did not, however, exhibit similar linear trends with CDS level as these were also affected by drying conditions, such as drying air temperature and microwave power level. Effective moisture diffusivity values, estimated from the drying data, were also significantly affected by drying conditions (drying air temperature and microwave power levels), CDS level, and interaction between drying air temperature and CDS level. Effective moisture diffusivity decreased as CDS level was increased. Physical properties of two commercial (ethanol plant-sourced) wheat DDGS samples, as affected by moisture content, were also assessed. Techno-economic evaluation results indicated that complete replacement of the conventional hot air drying with microwave drying technology was not yet economically feasible. Although energy consumption during drying was substantially reduced with the use of microwave energy, the cost of electricity to generate microwave energy was high. Incorporating microwave drying toward the end of the hot air drying process was seen as the more economically viable alternative. Drying of BSG was not commonly practiced in Misamis Oriental, Philippines. The material was typically stored in open concrete bins and commonly fed to dairy cattle in its wet form. A prototype batch dryer, powered either by solar or biomass energy, was developed to improve shelf life and safe use of BSG. Initial tests showed that drying spent grain using a biomass furnace was feasible. Operating the dryer using solar energy was not an attractive option because of the long drying time. Basic physical attributes, proximate composition, and moisture sorption characteristics of the dried BSG were also determined. Practical implications of the results of these two studies to their respective local contexts were discussed. Recommendations to further improve understanding of wheat DDGS protein quality and physico-chemical characteristics, BSG dryer performance, backyard farmers’ sustainable access and safe use of BSG were also presented.



DDGS, drying, microwave, physical properties, protein quality, proximate composition, wheat distillers dried grain with solubles



Doctor of Philosophy (Ph.D.)


Chemical and Biological Engineering


Biological Engineering


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