BACKGROUND: The natural gamma-decalactone (GDL) produced by microbial fermentation is an essential lactone compound as a generally recognized as safe food additive. Effective control of the substrate ricinoleic acid (RA) concentration in the biotransformation medium is a bottleneck for the industrial manufacture of GDL. In this study, porous starch (P-S) was utilized as a carrier of RA to control its distribution in the medium. The effect of P-S on the biotransformation was evaluated and the mechanism was revealed. RESULTS: Scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis indicated that the RA layer was formed on the surface of P-S, which increased the opportunity for interaction between microorganisms and the substrate. With P-S-embedded RA as a substrate, the yield of GDL increased to 3.36 g L-1 which was 17.5% higher than in the control. In addition, the presence of P-S in this system had no negative effect on the viability of the microorganism. CONCLUSION: This study is a new attempt to apply P-S as a delivery system in the biotransformation of GDL to increase its yield which indicates that the P-S-controlled release is a potential method of improving natural GDL production in industrial scale. (C) 2017 Society of Chemical Industry