Pineapple peel as a source of bioactive compounds with health benefits and potential application in the food industry

Ananas comosus [L.] Merr popularly known as pineapple is one of the world's most consumed tropical fruits after bananas and citrus [1]. The fruity and exotic flavour of this fruit is one of the most appreciated characteristics and the bioactive properties with beneficial impact on health have aroused interest [2]. However, since only the pulp of this fruit is consumed, tons of by-products is produced annually, generating economic losses for the agri-food sector and negative impact on the environment [3]. In this perspective, the present work aimed to characterize the phenolic profile of the pineapple peel, as well as to evaluate its bioactive properties in order to evaluate its potential application as a natural ingredient in the food industry. The extract was obtained through heat-assisted hydroethanolic (EtOH/H2O - 80:20, v/v) extraction. The phenolic compounds were identified and quantified by high-performance liquid chromatography coupled to a diode array detector and electrospray ionization mass spectrometry (HPLC-DAD-ESI/MS). Thirteen phenolic compounds were identified in the pineapple peel extract and classified as a phenolic acids and flavonoids. Flavan-3-ols, such as (epi)gallocatechin, and the flavone apigenin-6,8-C-diglucoside were the major compounds. The antioxidant activity of the extract was evaluated through two in vitro assays: the lipid peroxidation inhibition assay (TBARS) and the oxidative haemolysis inhibition assay (OxHLIA). The cytotoxic activity was evaluated in tumour (MCF-7, NCI-H460, AGS and CaCo-2) and non-tumour (VERO) cell lines using the sulforhodamine B method, and the anti-inflammatory activity in lipopolysaccharide-activated RAW 264.7 macrophages by the ability to inhibit NO production. The antimicrobial activity was evaluated against six strains of bacteria, including three Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus and Listeria monocytogenes) and three Gram-negative bacteria (Escherichia coli, Salmonella Typhimurium and Enterobacter cloacae). The antifungal activity of the extracts was tested against a panel of six fungi (Aspergillus fumigatus, Aspergillus niger, Aspergillus versicolor, Penicillium funiculosum, Penicillium aurantiogriseum and Trichoderma viride). The results showed that the extract has a good of antioxidant activity performance, highlighted by the lower IC50 values and consequently greater activity. The same trend was observed for the cytotoxic activity, and the absence of toxicity for the non-tumour cell line was confirmed up to the maximum concentration tested (GI50 > 400 μg/mL). Finally, the extract also showed excellent antibacterial and antifungal activity against the strains tested. This research confirmed the potential application of this pineapple peel as a source of bioactive compounds, which can be used by the food industry as a natural ingredient, thus contributing to a positive economic and environmental impact.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support through national funds FCT/MCTES to CIMO (UIDB/00690/2020); national funding by FCT, P.I., through the institutional and individual scientific employment program-contract for L. Barros, R.C. Calhelha, J. Pinela (CEECIND/01011/2018) and M. Carocho (CEECIND/00831/2018) contracts; to the research contract of C. Caleja (Project HealthyPETFOOD, POCI-01-0247-FEDER-047073) and E. Pereira (Mobilizador Norte-01-0247-FEDER-024479: ValorNatural®); to FEDER-Interreg España-Portugal program for financial support through the project TRANSCoLAB 0612_TRANS_CO_LAB_2_P, to FEDER through the Regional Operational Program North 2020, under the Project GreenHealth (Norte-01-0145-FEDER-000042); and through the Incentive System to Research and Technological development, within the Portugal2020 Competitiveness and Internationalization Operational Program, under the Project BIOMA (POCI-01-0247-FEDER-046112). This work has been supported by the Ministry of Education, Science and Technological Development of Republic of Serbia (451-03-9/2021-14/200007).