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Background  Astaxanthin, a naturally occurring carotenoid pigment molecule, displays strong antioxidant, anti-cancer, and immunity-enhancing properties, and is often utilized in food, biomedical, cosmetic, and other industries. Free astaxanthin has better solubility than astaxanthin esters (Ast-E), and is a useful auxiliary ingredient in health foods and medicines. Our goal was to establish an improved enzymatic method for preparation of free astaxanthin from natural sources (e.g., the microalga  Haematococcus pluvialis ), to expand the potential applications of free astaxanthin.    Results  The alkaline lipase gene  proalip  and its propeptide were cloned and successfully fusion-expressed in  Pichia pastoris  X-33. The recombinant lipase was termed Lipase-YH. Through optimization of culture conditions (medium formulation, pH, added methanol concentration), cell growth (OD 600 ) and secreted enzyme activity respectively reached to 280 and 2050 U/mL in a 50-L autofermentor. Activity of Lipase-YH enzyme powder was about 40,000 U/g. Hydrolysis of Ast-E (extracted from  H. pluvialis ) by Lipase-YH occurred in aqueous phase, and reaction conditions were optimized based on emulsification method and enzyme/substrate ratio. The highest enzymatic reaction rate was observed for substrate concentration 200 μg/mL, with maximal free astaxanthin yield (80%) at 1 h, and maximal Ast-E hydrolysis rate 96%, as confirmed by TLC, HPLC, and mass spectroscopy.    Conclusion  A novel, efficient enzymatic process was developed for production of free astaxanthin through hydrolysis of Ast-E. Lipase activity was enhanced, and production cost was greatly reduced. The unique structure of free astaxanthin allows linkage to various functional compounds, which will facilitate development of novel pharmaceutical and food products in future studies.    Electronic supplementary material  The online version of this article (10.1186/s13068-018-1180-2) contains supplementary material, which is available to authorized users.

Efficient heterologous expression of an alkaline lipase and its application in hydrolytic production of free astaxanthin