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Lemon Juice Formulations Modulate In Vitro Digestive Recovery of Spinach Phytochemicals

Valerija Vujčić Bok*orcid tiny, Ivana Šolaorcid tiny and Gordana Rusakorcid tiny

1Department of Biology, Faculty of Science, University of Zagreb, Marulićev trg 9a,10000 Zagreb, Croatia

Article history:

Received: 16 December 2020

Accepted: 28 April 2022

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Spinacia oleracea L.; polyphenols; L-ascorbic acid; nitrate; oxalate; in vitro digestion


Research background. Citrus limon (L.) Burm lemon juice is rich with many important natural chemical components (flavonoids, citric acid, vitamin C) and is used in traditional medicine is well known. Formulations of lemon juice with fruit polyphenols in beverage systems has been investigated, but there is very little information about their ability to modulate polyphenol digestive behavior. The goal of this study was to determine stability and digestive availability of spinach (Spinacia oleracea L.) polyphenols by adding different concentrations of lemon juice (0, 2, 5, 10 and 20 %) during in vitro digestion.

Experimental approach. Content of polyphenols, and other spinach rich compounds including nitrate, oxalic acid, L-ascorbic acid in spinach formulation with various concentrations of lemon juice were measured in predigested and digested samples using in vitro human digestion model. Antioxidant activity and α-amylase inhibitory activity of spinach lemon juice formulation was also measured.

Results and conclusions. Highest increases in total polyphenols, total flavonoids, total phenolic acids, oxalic acid and nitrate content were noted in predigested and almost all digested spinach samples formulated with highest concentration of lemon juice. In the same sample concentration of individual compounds significantly increased after salivary (L-ascorbic acid), initial (p-coumaric acid) and intestinal (quercetin) phase of digestion for each phase individually. High bioaccessibility of polyphenols, nitrate, oxalic and L-ascorbic acid for all phases of digestion were observed in almost all spinach lemon juice formulation with the exception for nitrate (gastric and intestinal phase) and oxalic acid (intestinal phase) which had moderate bioaccessibility.

Novelty and scientific contribution. For the first time stability and digestive availability of spinach polyphenols, oxalic acid, nitrate and L-ascorbic acid were tested with different concentrations of lemon juice. Lemon juice pH and L-ascorbic acid increase stability and availability of polyphenols in spinach lemon juice formulation during in vitro digestion. Antioxidant and α-amylase inhibitory activity increase in dose depending manner after lemon juice addition. Accordingly, spinach formulated with 20 % of lemon juice appears as the best source of dietary polyphenols with antioxidant activity, antidiabetic activity and nitrate that may be used as functional drink.

*Corresponding author: +38514898089

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