Effect of Drying Conditions and Level of Condensed Distillers Solubles on Protein Quality of Wheat Distillers Dried Grain with Solubles

Abstract

Reduced protein quality is one of the concerns currently confronting the supply and utilization of wheat distillers dried grain with solubles (DDGS) as an animal feed ingredient. This study assessed the protein quality of wheat DDGS, expressed as acid detergent insoluble crude protein (ADICP) and lysine content, by blending wet distillers grain (WDG) with varying condensed distillers solubles (CDS) levels and drying using forced air convection, microwave, and microwave–convection methods. As the CDS level was increased, the protein content of wheat DDGS generated from the three drying methods increased. Interactions of CDS level with drying air temperature, microwave power, and microwave–convection settings had a significant effect (p < 0.05) on average ADICP and lysine contents. Higher ADICP and lower lysine contents were observed in samples dried at higher temperature, microwave power, and microwave convection settings. Further, the CDS level significantly affected the color parameters of microwave- and microwave–convection-dried samples and the drying air temperature–CDS level interaction significantly affected the color of forced air convection–dried samples. Significant lysine content–redness, ADICP–lightness color parameter, and ADICP–total color difference correlations were found in forced air convection–, microwave-, and microwave–convection-dried samples, respectively. Microwave and microwave–convection drying achieved desirable protein quality associated with low-temperature drying at much shorter times.

Keywords:

• ADICP
• Condensed distillers solubles
• Drying
• Lysine
• Microwave
• Protein quality

ACKNOWLEDGMENTS

The authors acknowledge the Feed Opportunities for the Biofuels Industry (FOBI) network and the Agricultural Bioproducts Innovation Program (ABIP) of Agriculture and Agri-Food Canada for the funding support; Irene Northey, Angela Hennings, Zhi Niu, and Darina Kuzma of the University of Saskatchewan Animal and Poultry Science Department and Louis Roth and Bill Crerar of the University of Saskatchewan Chemical and Biological Engineering Department for their technical assistance; and Shivani Trivedi and Edward Robertson, undergraduate research assistants, for their help during sample preparation.

Notes

Tukey's test at 5% significance level for the same CDS level at various drying air temperature (a, b, c), microwave power le (d, e, f, g), and microwave convection setting (h, i, j, k); for the same drying air temperature, microwave power, or microwave convection setting at various CDS level (A, B, C). Means under each drying method followed by same set of letters are not significantly different.

^a Drying rate constant.

^b Page model parameter.

^c Coefficient of determination.

^d Mean square error.

^e P4–420 W; P6–676 W; P8–701 W; P10–805 W.

^f C1–130°C–30% power (303 W); C2–150°C–30% power (316 W); C3–160°C–30% power (327 W); C4–190°C–30% power (332 W).

^a Color parameters L, a, and b represent lightness, redness, and yellowness, respectively.

^b Freeze-dried laboratory-prepared samples.

Tukey's test at 5% significance level for the same CDS level at various drying air temperature (a, b, c), microwave power le (d, e, f, g), and microwave convection setting (h, i, j, k); for the same drying air temperature, microwave power, or microwave convection setting at various CDS level (A, B, C). Means under each drying method followed by same set of letters are not significantly different.

^a N = 2.

^b N = 3.

^c P4–420 W; P6–676 W; P8–701 W; P10–805 W.

^d C1–130°C–30% power (303 W); C2–150°C–30% power (316 W); C3–160°C–30% power (327 W); C4–190°C–30% power (332 W).

^a C2–150°C–30% power (316 W).

^b C4–190°C–30% power (332 W).