Waste Frying Oils as Substrate for Enzymatic Lipolysis: Optimization of Reaction Conditions in O/W Emulsion

Waste frying oils (WFO) can be both environmental pollutants and a source of valuable products. In this work we explore the conversion of WFO into surface-active substances, such as FFA and partial glycerides, through enzymatic hydrolysis in O/W emulsion. Two different WFO and three lipases of different origin were tested. In addition, we optimized the conditions for the production of O/W emulsions to be used as reaction medium as well as several reaction parameters, such as the type of enzyme and its concentration, the pH, and the presence of Ca2+ ions. Gum arabic-stabilized emulsions with an oil fraction of 0.15 proved to be the most adequate owing to their high interfacial area and short-term stability. The physicochemical characterization of both WFO revealed the presence of an increased amount of surface-active matter relative to food-grade vegetable oils. These substances, mainly FFA, can interfere with lipase action and reduce the reaction rate. However, the extent of hydrolysis was only slightly affected by them, and remained fairly similar to that achieved with a control mixture of food-grade vegetable oils. The product distribution depended on the enzyme used. Pseudomonas fluorescens lipase was found to be particularly suitable for the production of partial glycerides (mono- and diacylglycerols), which are in great demand by the food industry. In any case our results demonstrate that WFO are a good substrate for enzymatic hydrolysis, comparable to food-grade vegetable oils, providing an alternative route for the valorization of this waste.