ARS | Publication request: Effects of cooking and screw-pressing on functional properties of protein in milkweed (Asclepias spp.) seed meals and press cakes

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2008
Publication Date: February 20, 2009
Citation: Hojillaevangelist, M.P., Evangelista, R.L. 2009. Effects of cooking and screw-pressing on functional properties of protein in milkweed (Asclepias spp.) seed meals and press cakes. Industrial Crops and Products. 29(1)615-621.

Interpretive Summary: Milkweed (Asclepias spp.), a perennial weed known to the general public as the food source for monarch butterflies, is an industrial crop grown for its seed pods. The seed pods provide the floss that is used in the commercial production of hypoallergenic fillers in comforters and pillows. The seeds are by-products of floss production and contain notable amounts of protein (32%) and oil (21%). Milkweed seed oil has been studied and found to be comparable in quality to soybean oil. In contrast, there is no information on the properties of milkweed seed protein. Chemical and functional properties are important for identifying possible value-added uses of the seed protein. Our study used three cooking conditions for the flaked milkweed seeds, extracted the oil by screw-pressing, and then determined the effects of oil processing conditions on functional properties of milkweed seed proteins. We found that milkweed seed protein was most soluble at the pH range of 7 (neutral) to 10 (alkaline), had excellent emulsifying properties, and produced substantial but easily collapsible foams. We noted that the heat applied during seed cooking and screw-pressing did not reduce protein solubility and improved emulsifying, foaming, and water-holding capacities. Our findings showed definitively that the proteins in milkweed seed press cake from oil processing are still functional and have useful properties that could be utilized in applications such as thickener, paint emulsifier and adhesive extender. Our pioneering study on the functional properties of milkweed seed protein provides fundamental data that could be used by other researchers from universities and industry to define the optimal conditions for extraction and recovery of milkweed seed proteins. Our results can also be used to identify and develop novel uses for seed proteins, thus enhancing the value of the milkweed crop.

Technical Abstract: This study determined the effects of oil processing conditions on functional properties of milkweed seed proteins to evaluate their potential for value-added uses. Flaked milkweed seeds were cooked at 82 degrees C (180 degrees F) for 30, 60 or 90 min in the seed conditioner, and then screw-pressed to extract the oil. Proximate composition and protein functional properties of cooked flakes and press cakes were determined and compared with those of unprocessed ground, defatted milkweed seeds. Milkweed seed protein was most soluble at the pH range of 7-10, had excellent emulsifying properties, and produced substantial but highly unstable foams. Heat applied during seed cooking and screw-pressing did not reduce protein solubility and improved emulsifying, foaming, and water-holding capacities. Emulsifying capacity was much higher at pH 10 than at pH 7. These results showed that the protein in both the milkweed seed and its press cake from oil processing has useful functional properties that could be utilized in applications such as paint emulsifier and adhesive extender.