Construction Of Efficient Extraction Process For ε-poly-L-lysine: Solid-liquid Separation And Decoloration

At present, ε-poly-L-lysine has been widely used as a biological food preservative due to its broad antibacterial spectrum, strong stability, good water solubility, safety and non-toxicity,etc. ε-PL has been approved as a new food additive since April 2014 in China, which is helpful for its industrialization in our country. However, the separation and purification of ε-PL from fermentation broth is of great challenge to realize its industrial production. Because it not only directly determines the quality of final product, but also restricts its cost.Based on our previous studies in the laboratory, this dissertation is committed to solve the shortcomings in the developed extraction process, i.e. solid-liquid separation and decoloration issues. Therefore, we have employed flocculation combined with frame filter approach for fermentation broth solid-liquid separation and employed macroporous resin for decoloration. Finally, an efficient process for ε-PL extraction from fermentation broth was re-established in the study. The main results were as follows:1. Bacteria flocculation and plate frame filter approach was developed for ε-PL fermentation broth solid-liquid separation. With filtration rate, ε-PL recovery and deproteinization ratios as indexes, flocculant 2#(molecular weight 10 million) was screened to have the best flocculation effect from 10 typical flocculants. Under the optimal flocculation conditions, i.e. p H 1.5, 800 mg×L-1 of locculant 2#, when 100 m L ε-PL fermentation broth was treated, filtration rate, ε-PL recovery and deproteinization ratios were achieved by 3.70 m L×min-1, 96.68% and 74.05%, respectively. 1 μm membrane was chosen as the filter media on the scale of 3 L plate frame filter. Its average filtration rate was about 35 L·m-2·h-1, ε-PL loss ratio was about 5% and deproteinization ratio was about 72%.2. The method of removing pigments by macroporous adsorption resin was established.SX-8 resin was found to be the best from 6 macroporous resins through static and dynamic adsorption tests. Under the optimized dynamic adsorption conditions, i.e. p H 7.0, 30 oC, 1BV·h-1 uploading rate, 7 g·L-1 ε-PL concentration, SX-8 resin was employed to the treatment of 100 m L(10 BV) ε-PL ion exchange eluate, and the resulting ε-PL recovery and decoloration ratio were 83.9% and 97.3%, respectively. The pigments of absorption wavelength at 300-900 nm were almost removed completely through full wavelength scanning, and appearance of the decolorized solution was nearly colorless. In addition, the regeneration of macroporous adsorption resin SX-8 was easy. It could be used repeatedly and have the potential for industrial application.3. The efficiency of each unit operation on the thermal flocculation and flocculant extraction process was systematically compared and analyzed. Flocculant extraction process was superior to thermal flocculation extraction process by comparing their separation process.In the flocculant extraction process, the total yield of ε-PL was over 70%, the purity of ε-PL was about 90%, protein content was about 6% and ash content was 1 to 3.5%.