Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Quinoa as source of type 1 ribosome inactivating proteins: A novel knowledge for a revision of its consumption Nicola Landi a , Maria Rosaria Ruocco b , Sara Ragucci a , Federica Aliotta b , Rosarita Nasso c , Paolo V. Pedone a , Antimo Di Maro a, ⁎ a Department of Environmental, Biological and Pharmaceutical Sciences and Technologies (DiSTABiF), University of Campania ‘Luigi Vanvitelli’, Via Vivaldi 43, 81100 Caserta, Italy b Department of Molecular Medicine and Medical Biotechnology, University of Naples ‘Federico II’, Via S. Pansini 5, 80131 Naples, Italy c Department of Movement Sciences and Wellness, University of Naples ‘Parthenope’, Via F. Acton 38, 80133 Naples, Italy ARTICLE INFO Keywords: ATP assay Chenopodium quinoa Willd. Ribosome inactivating proteins rRNA N-glycosylase Protein purifcation ABSTRACT This study investigates on the presence of toxic proteins in quinoa seeds. To this aim, a plethora of biochemical approaches were adopted for the purifcation and characterization of quinoin, a type 1 ribosome-inactivating protein (RIP) contained in quinoa seeds. We determined its melting temperature (68.2 ± 0.6 °C) and ther- mostability (loss of activity after 10-min incubation at 70 °C). Considering that quinoa seeds are used as a food, we found that quinoin is cytotoxic against BJ-5ta (human fbroblasts) and HaCaT (human keratinocytes) in a dose- and time-dependent manner. Moreover, in an in vitro digestive pepsin-trypsin treatment, 30% of quinoin is resistant to enzymatic cleavage. This toxin was found in seeds (0.23 mg/g of seeds) and in sprouted seeds obtained after 24-h (0.12 mg/g of sprout) and 48-h (0.09 mg/g of sprout). We suggest a thermal treatment of quinoa seeds before consumption in order to inactivate the toxin, particularly in sprouts, generally consumed raw. 1. Introduction Chenopodium quinoa Willd. is an herbaceous annual plant, which has become in recent years a primary crop for its edible seeds. In particular, the growing popularity of quinoa seeds is due to the rich content of proteins, dietary fbers, B vitamins, and dietary minerals as well as for being a gluten-free food (Ceyhun Sezgin & Sanlier, 2019; FAO, 2011). In addition, quinoa seeds are known as functional food considering the beneft action on several human diseases (e.g. diabetes, dyslipidaemia, obesity and celiac disease) (Navruz-Varli & Sanlier, 2016). Conse- quently, in the last decades, the production of quinoa seeds and its derivatives (such as bread, pasta, sponge cakes or biscuits) had a con- tinuous positive trend (Angeli et al., 2020). On the other hand, quinoa seeds are not the elixir (panacea) or the ‘golden grain’ for human nutrition because of the high content of sa- ponins, conferring a bitter taste and toxicity when present at high concentration; indeed, the elimination of saponins is strongly re- commended. In addition, quinoa seeds are rich of phytic acid, tannins, oxalates and trypsin inhibitors, known as anti-nutritional factors (Filho, Pirozi, Borges, Pinheiro Sant'Ana, Chaves, & Coimbra, 2017). Hence, several methods (heat treatment, extrusion, roasting, or mechanical abrasion) are used to remove the excess of saponins and some anti- nutritional factors (El Hazzam et al., 2020). Furthermore, C. quinoa belongs to Caryophyllales (Ceyhun Sezgin et al., 2019), a plant order known as a source of ribosome inactivating proteins (RIPs), toxins essentially produced by plants (Di Maro, Citores, Russo, Iglesias, & Ferreras, 2014; Stirpe & Gilabert-Oriol, 2017). RIPs are enzymes (EC: 3.2.2.22) that damage ribosomes in an irre- versible manner, leading to the arrest of protein synthesis (Stirpe & Gilabert-Oriol, 2017). In particular, RIPs are rRNA N-glycosylase, which remove a specifc adenine (A 4324 in rat) of the Sarcin Ricin Loop (known as SRL) in the 28S ribosomal RNA, involved in the interaction of the ribosome with the eukaryotic elongation factor 2 (EF-2) or the prokaryotic elongation factor G (EF-G), thus blocking translocation during the protein synthesis (Shi, Khade, Sanbonmatsu, & Joseph, 2012). The damage of the protein synthesis machinery is related to RIPs cytotoxicity, in turn triggering apoptosis pathway (Zeng, Zheng, Lu, Wang, Jiang, & Sha, 2015). Furthermore, it has been reported that some RIPs possess additional enzymatic activities on diferent substrates, including polynucleotide:adenosine glycosylase [PNAG (Barbieri, Valbonesi, Bonora, Gorini, Bolognesi, & Stirpe, 1997)], phosphatase activity on lipids, as well as DNase (Aceto et al., 2005), chitinase and https://doi.org/10.1016/j.foodchem.2020.128337 Received 20 August 2020; Received in revised form 5 October 2020; Accepted 6 October 2020 ⁎ Corresponding author. E-mail address: antimo.dimaro@unicampania.it (A. Di Maro). Food Chemistry xxx (xxxx) xxxx 0308-8146/ © 2020 Elsevier Ltd. All rights reserved. Please cite this article as: Nicola Landi, et al., Food Chemistry, https://doi.org/10.1016/j.foodchem.2020.128337