Comprehensive Characterization and Quantification of Antioxidant Compounds in Finger Lime (Citrus australasica L.) by HPLC-QTof-MS and UPLC-MS/MS

Ramón Aznar,Celia Rodríguez-Pérez,Dilip K Rai

doi:10.3390/app12031712

Abstract

Australian finger limes (Citrus australasica L.), an unusual citrus due to its unique pulp with a caviar-like appearance, has reached the global market as a promising source of bioactive compounds that promote health. This research was, therefore, performed to shed light on the bioactivity and composition of different parts of Citrus australasica L. (peel and pulp). Initial ultrasound-assisted extraction using MeOH:H2O (80:20, v/v) was carried out. After that, four fractions (hexane, ethyl acetate, butanol and water) were generated through liquid–liquid partitioning, and the total phenolic content (TPC) and antioxidant activity were evaluated using the Folin–Ciocalteu and the ferric reducing antioxidant power (FRAP) assays, respectively. The ethyl acetate fraction in the peel, which presented the highest values of TPC and antioxidant activity, was characterized using high-performance liquid chromatography coupled to quadrupole time-of-flight (HPLC-QTof) mass spectrometry. Fifteen compounds were identified, of which seven were characterized for the first time in this matrix. Moreover, ten phenolic compounds were quantified using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The major compounds in the sample were citric acid, pyrogallol, caffeic acid, coumarin, rutin, naringin, 2-coumaric acid, didymin, naringenin and isorhamnetin, which were found in a range from 2.7 to 8106.7 µg/g sample dry weight. Finally, the results presented in this novel work confirmed that the peel by-product of C. australasica L. is a potential source of bioactive compounds and could result in a positive outcome for the food, cosmetics and pharmaceutical industries.

Highlights

IntroductionCitrus is one of the most widely cultivated, processed and consumed fruits throughout the world [1], with an estimated production of 98 million metric tons in 2020–2021 [2]
Citrus is one of the most widely cultivated, processed and consumed fruits throughout the world [1], with an estimated production of 98 million metric tons in 2020–2021 [2].It produces a large number of by-products that can cause, on one hand, severe environmental pollution [1] and, on the other hand, the loss of bioactive compounds that could be key components for developing nutraceuticals and functional foods
Due to the novelty of the matrix and its potential interest as a source of bioactive compounds, the aims of this work were: (1) to assess the antioxidant activity and the total phenolic content (TPC) of different fractions of C. australasica L. in peel and pulp, (2) to characterize for the first time the phenolic content of the most active fraction using high-performance liquid chromatography coupled to quadrupole time-offlight (HPLC-QTof) mass spectrometry, and (3) to quantify the most relevant phenols using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS)

Summary

Introduction

Citrus is one of the most widely cultivated, processed and consumed fruits throughout the world [1], with an estimated production of 98 million metric tons in 2020–2021 [2]. It produces a large number of by-products (e.g., peels or seeds) that can cause, on one hand, severe environmental pollution [1] and, on the other hand, the loss of bioactive compounds that could be key components for developing nutraceuticals and functional foods.

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