Solid-state fermentation for enhanced extractability of nutraceutical compounds of tomato by-products

Abstract

Tomato pomace is a food industry by-product produced in significant quantities, mainly composed of the tomato seeds and peel, and pulp residues. This organic by-product is both rich in functional nutraceutical compounds like carotenes and phenolic compounds, which have proven to offer antioxidant, anti-inflammatory and anti-carcinogenic properties. Nutraceutical compounds can be extracted by a wide variety of techniques, like with the use of organic solvents, enzymatic hydrolysis, supercritical fluid extraction, or ultrasound- assisted extraction. Solid-state fermentation (SSF) is a bioprocessing technique that has previously been used to generate compounds of interest. However, it has not been used as a specialized pretreatment for extracting nutraceutical compounds already present in the substrate. Based on that, this study aimed to evaluate the potential effectiveness of an SSF as part of pretreatment to increase the extraction of nutraceutical compounds like lycopene and phenolic compounds. The extractions of SSF were directly compared with other pretreatments, including industrial-grade enzymes and enzymatic cocktails from fungi. Two fungal strains, Aspergillus niger ATCC 6275 and Rhizopus oryzae BIOTEC00X (isolated from agave pomace and identified by MALDI-TOF mass spectrometry), were used for the fermentation of tomato pomace for three 3 days at 30 °C and 80% humidity. Then, the tomato pomace was dried until constant weight and was subsequently subjected to an extraction using hexane for total carotenes and methanol for total phenolic compounds. Spectrophotometric measurements were used as a quick screening method to determine the best extraction performance. Results showed that SSF as a pretreatment helped to obtain between 50-60% more carotenes than the control, while commercial enzymes offered an increase of 107%. The best treatment for phenolics was obtained with an enzyme-rich broth, with an increase of 90-97% in extracted total phenolics, followed by the SSF with an increase of a 24-38% over the controls. Individual phenolic compounds were identified and quantified by the application of ultra-high-performance liquid chromatography (UHPLC). This technique allowed the tentative identification of 15 compounds, from which naringenin derivative III, protocatechuic acid and feruloylquinic acid were the most susceptible to variate depending on the pretreatment applied to the tomato pomace. It is concluded that SSF increases the extraction of nutraceutical compounds present in tomato by-products and could become an alternative method of extraction at an industrial scale, given that it is an innovative and green technology.