Tomato processing by-products valorisation through ohmic heating approach

Abstract

Tomato by-products from processing industries have a higher potential to be reused as a source of bioactive compounds. Reliable national data on tomato by-products and physicochemical characterisation that will inform and find effective planning on tomato waste management in Portugal is absent. To help obtain this knowledge, selected Portugal companies were recruited to obtain representative samples of by-products generation, and physicochemical composition was evaluated. Furthermore, an environmental-friendly method (the ohmic heating (OH) method, which allows the recovery of bioactive compounds in absence of hazardous reagents) was also used and compared with conventional methods to explore new safe value-added ingredients. Total antioxidant capacity and total and individual phenolic compounds were also evaluated by spectrophotometric and high-performance liquid chromatography (HPLC), respectively. Tomato processing by-products have revealed a higher potential since both collected samples from companies were rich in protein (between 16.3 to 19.4 g/100 g DW, with fibre content ranging from 57.8 to 59.0 g/100 g DW). In addition, these samples contain 17.0 g/100 g of fatty acids (mainly polyunsaturated, monounsaturated and saturated, such as linoleic, oleic, and palmitic acid, respectively). Also, they present mainly chlorogenic acid and rutin as phenolic compounds. After understanding its composition, the OH was applied to determine added-value solutions to tomato by-products. With extractions, two types of fractions were obtained, namely liquid fraction rich in phenols, free sugars, and carotenoids and a solid fraction rich in fibre bound to phenols and carotenoids. This treatment has been shown to have the ability to preserve carotenoids, such as lycopene relative to conventional methods. Nevertheless, new molecules were identified by LC-ESI-UHR-OqTOF-MS analysis, such as phene-di-hexane and N-acethyl-D-tryptophan. According to the results, the OH boosts the potential of tomato by-products and can be directly introduced into the process, contributing to the circular economy and zero by-products.