Methods of Accelerating the Removal of Moisture from Duckweed and their effect on the Crude Protein Content
Date of Award
The two major objectives were to investigate methods for drying duckweed and to determine the effect of the methods on the crude protein content of the plant. The drying methods were oven drying, sun drying, pressing with heat, pressing without heat, pressing combined with oven drying, parboiling combined with oven drying and drying in a spouted bed. A series of drying curves were developed for each drying method. Due to the high moisture content of duckweed (92.9 to 94.0% wet basis), the drying curves exhibited a long constant rate drying period as opposed to grain crops and hay. Equations were developed for each set of curves in the form F = 1-bT Where: F = fraction of water remaining in the sample T = drying time in hours b = drying coefficient In the oven drying, the duckweed was exposed to temperatures of 80, 100, 120 and 140°C. At 120°C and above, the samples exhibited a burned appearance. The samples dried in the sun generally took 11/2 times to 3 times as long to dry as in the oven with the same depth. Parboiling prior to oven drying increased the initial moisture by 0.9% but reduced the drying time. Samples were pressed at 60, 125 and 250 psi and then oven dried. These samples took less time to dry than oven dried samples at the same depth. The samples pressed at higher pressures turned darker green as the pressure was increased. Duckweed was also dried in a spouted bed apparatus at 27 and 50°C. This method took less time to dry the duckweed than any other drying method investigated in this study. The crude protein content of the samples was determined by a standard Kjeldahl analysis. A statistical analysis was then made on the results. Two analyses of variance were made: (1) to compare the oven dried samples to the untreated samples and (2) to compare all other methods to one another. In the second analysis the samples pressed at 780 to 7,810 psi were not included since it was obvious from visual observation that the crude protein contents were significantly decreased by pressing. Pressing at high pressures reduced the crude protein by 66 to 71%.
Lawson, Thomas Booker, "Methods of Accelerating the Removal of Moisture from Duckweed and their effect on the Crude Protein Content" (1973). LSU Historical Dissertations and Theses. 8318.