(732b) Subcritical Water Extraction of Protein From Sunn Hemp

                                            2013 American Institute of Chemical Engineers Annual Meeting

San Francisco, CA

November 3-8, 2013

Subcritical Water Extraction of Protein from Sunn

  Emmanuel Nyankson*, Hema Ramsurn*, Alex Roman*, Ram B. Gupta*  and Jorge Mosjidis⁺

        *Department of Chemical Engineering, Auburn University, Auburn, AL 36849            

⁺Department of Agronomy and Soils, Auburn University, Auburn, AL 36849-5127

Sunn Hemp, which originated in India, is a tropical or sub- tropical plant that when grown in the continental United States performs like a summer annual. This tropical plant is reported to have added 134 to 147 pounds of nitrogen per acre after 60 days of growth. Studies have shown that Sunn Hemp contains between 20-30 wt% crude protein.  This high protein content has made Sunn Hemp a good source of animal feed. The protein present in Sunn Hemp can also be extracted and used as a nutritional source for humans. Traditionally in an industrial set-up, organic solvents are commonly used for the extraction of food components. The choice of organic solvent is dictated by the polarity, solubility and mass transfer characteristics of the compounds to be extracted. However, long extraction time and toxic waste generation has resulted in the quest for new extraction methods.

Water as reaction medium is safe, non-toxic, inexpensive and readily available.  Subcritical water is liquid under pressure at temperatures between 100^oC and 374^oC, the critical temperature of water. The unique properties of subcritical water such as low dielectric constant and polarity make it a better replacement for organic solvents. Water can act as an acid/base catalyst precursor below the critical point and at high pressures since the ionic product is up to three orders of magnitude higher than under ambient conditions.  In the subcritical region, the relatively low dielectric constant enhances ionic reactions which promote reactions like hydrolysis.  Furthermore, subcritical water enhances the solubility of the organic compounds, hence improving extraction.

In this study, subcritical water will be used to extract protein from a particular species of Sunn Hemp, developed in the Department of Agronomy and Soils at Auburn University. The effects of temperature (160-240 °C), reaction time (30 mins and 60 mins), different biomass feeding methods (dry powder versus slurry feeding), different catalysts (NaOH and Na₂CO₃) and different catalyst amount (2.5-28 wt %) on the protein yield were investigated.  The maximum protein extraction yield of 74% was obtained at 240^oC with 28 wt% of Na₂CO₃. Reaction time does not have major effect on the protein yield: protein yields of 69 and 66% were obtained at 220 °C with 15 wt% Na₂CO₃ using 30 and 60 minutes reaction time, respectively. The use of 6 wt% of NaOH at 220^oC for reaction time of 30 minutes resulted in a protein yield of 60% compared to 48% obtained when using the same amount of Na₂CO₃. A comparison between the Lowry and Bradford assay in the protein quantification was performed.  Protein yields obtained using the Bradford assay were about 12 to 20% below those obtained by the Lowry assay, indicating detection limitations of the assays with respect to the type of amino acids in the peptide sequence. Amino acid analysis of the extract showed the presence of mainly polar amino acids.