Detoxification of alperujo using solid-state fermentation: statistic optimization of the process

Abstract

The alperujo (AL) is the waste produced by the process of olive oil extraction using two phase systems. The AL is a very contaminant residue and its direct disposal is not allowed in Argentine. Moreover, seasonality of the production motivates the accumulation of great amounts of AL, to be handled in short time. The organic fraction of AL includes polyphenolic compounds, reported as responsible for its antibiosis and phytotoxicity. The use of biotechnological processes, alone or combined with physic-chemical procedures, has been recommended for the treatment of the AL. However, there are not yet processes that solve environmental and economic drawbacks, in a satisfactory way. The solid-state fermentations (SSF), including composting, are biotechnological treatments proper to be applied to the AL, with the aim of detoxifying and reducing its mass, to allow its reuse and/or final disposal. The objective of the present work is to assess the optimal conditions for the relevant variables for the AL detoxification by SSF. Twelve lab-scale SSF experiences were done for the selection of the relevant variables using the Plackett-Burman design. The variables taken into account were: inoculums, oil-extraction, time, initial humidity (H), initial pH, temperature, sterility, structural support (SS), PO4(NH4)2, and SO4Cu. As response, the polyphenol loss was evaluated (PPL). The variables SO4Cu, H and SS were found as the most relevant, and these were optimized by the Box-Behnken method (15 new experiments were carried out). The optimal values determined were H: 47.9%, SO4Cu: 4.66%, SS: 36.29%; whereas at 14 days, the maximum PPL achieved was 9.8 mg/g of dried matter, which represents more than 94% of original polyphenolic content. Results are encouraging and bench-scale SSF experiences studying aeration and mixing will be soon reported.