Extraction of Phenolic Compounds from Tucuma (<i>Astrocaryum vulgare</i> Mat.) Postprocessing Cake Mediated by Rhamnolipids: Evaluation of Its Antifungal Potential against Common Fruit Pathogens

Tucuma is a native Amazon palm strategic to the local economy due to its pulp and kernel oil utilization and its possibility to be used in the recovery of degraded areas. The oil extraction generates a postpressing cake with potential industrial utilization. The utilization of this residue to generate new products is an opportunity to expand the market of the fruit, aiming at an almost zero waste industrial plant; moreover, it also helps to boost the local bioeconomy. The present work aims to evaluate the hydroethanolic extraction of phenolic compounds, with and without surfactant addition, from the tucuma pulp postpressing cake. For this, the hydroethanolic extraction was carried out at 62 °C, a solid:liquid ratio of 1:13, and an ethanol concentration equal to 54%; at this condition two rhamnolipid (RML) type surfactants, one with a majority of mono-RML and the other with a majority of di-RML, was added. The hydroethanolic extraction without RML presented catechin, epicatechin, and epigallocatechin. The addition of the RMLs in the extraction media modulates the phenolic compounds extracted and their quantities due to the relationship between the polarity of the phenolic compound (Log P) and the hydrophilic–lipophilic balance (HLB) of RMLs. The addition of mono-RML (HLB = 7.0) shifts the polarity of the system and enables the extraction of more hydrophobic compounds (epigallocatechin gallate, p-hydroxybenzoic acid, and 3,4-dihydroxybenzoic acid) and catechin. The di-RML hydroethanolic extract (HLB = 9.0) was the one with the highest number of compounds (catechin, epigallocatechin gallate, epicatechin, epigallocatechin, and p-hydroxybenzoic acid). This is probably due to the higher surfactant HLB and the proportion of mono/di-RML. The antifungal capacity of the extracts against fungi that cause postharvest rot in oranges and strawberries was also evaluated. Both mono-RML and di-RML hydroethanolic extracts presented higher inhibitory activity than the sole hydroethanolic extract or the sole RML, when evaluated against rot fungi. The RML extracts antifungal activity is probably due to the synergism between the phenolic compounds and RML. This is the first time that different RML congeners have been evaluated to extract different categories of phenolic compounds with different fungicidal actions.