Essential and non-essential elements in white lupin (Lupinus albus L.) cultivated in Southern Italy

Abstract We assessed the presence of V, Cr, Ni, Cu, Zn, As, Se, Sb, Cd, and Pb in white lupin samples cultivated in Southern Italy by the validation of an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) method. The ICP-MS method validation showed satisfactory values of linearity (r2 > 0.999), recovery (87.4–100.7%), repeatability, and reproducibility values. Zinc was the most abundant element; showing mean concentrations of 0.778 ± 0.09 mg/Kg wet weight (w.w.) and a maximum of 1.013 mg/Kg w.w., followed by copper (0.191 ± 0.05 mg/Kg w.w.). Among the non-essential elements, important levels of cadmium were found (0.017 ± 0.004 mg/Kg w.w.), with 28% exceeding the limits set by the EU Regulation. The results of this work confirm the role of white lupins and other legumes in reducing the pH of the soil, increasing the exchangeable forms of Cd. This work also provides the first data on the nutritional and antinutritional properties of white lupins cultivated in Italy. Graphical Abstract


Introduction
Lupins are the seeds of the Lupinus plant, a legume belonging to the Fabaceae family.White lupin (Lupinus albus) is one of the four lupin species (L.angustifolius, L. luteu, L. mutablis) most consumed and produced in the world, especially in Australia and Europe (Huyghe 1997).They are a good dietary source of proteins with an average content of up to 36% (Sujak et al. 2006), constituting a valid protein alternative for vegans or ovo-lacto vegetarians.White lupins are also a valuable source of dietary fiber, even higher than the most known soybean seeds (P ısa r ıkov a and Zral y 2010; Amen et al. 2015).Furthermore, the consumption of white lupins provides numerous health benefits counteracting diseases connected with high blood pressure, insulin resistance, and high cholesterol levels (Prusinski 2017).For these reasons, the interest in lupin production is increasing, especially in Eastern Europe countries and Southern Italy, where it was previously used in crop rotation during intensive grain production due to its high capability of nitrogen fixation and organic phosphorus release (Fan et al. 2002).However, despite the broad literature on the nutritional properties of white lupins, there are few data on the levels of essential and non-essential elements of this type of product (Zelalem and Chandravanshi 2014).Furthermore, there is no literature on the element's contents of white lupins cultivated and processed in Italy.Given that the chemical composition of legumes and other vegetables may vary based on the cultivar, geographical belonging, and growth conditions (Zelalem and Chandravanshi 2014;Pantano et al. 2016) this work aimed at evaluating the concentration of 10 essential and non-essential elements (V, Cr, Ni, Cu, Zn, As, Se, Sb, Cd and Pb) in white lupins cultivated and commercialised in Italy by the implementation of a reliable ICP-MS method to deepen their nutritional values and highlight possible risks due to the presence of toxic metals.

Results and discussion
The linearity test of the ICP-MS method for V, Cr, Ni, Cu, Zn, As, Se, Sb, Cd, and Pb analysis gave satisfactory results (r 2 > 0.999).The LOD and LOQ values obtained were in accordance with the regulation (EC) n. 333/2007.Recoveries studies showed values between 87.4% and 100.7%.All the results were satisfactory for the limit of repeatability (metrological approach).All concentration levels showed Horrat values of repeatability and reproducibility lower than two as specified by the Commission Regulation n 836/2011.
The mean contents for essential and non-essential elements are shown in Table 1.All the samples analysed showed V, Cr, Ni, Cu, Zn, As, Se, Sb, and Pb values above the limits of the quantification of the method.Only 3 (12%) pools showed Cd values below the LOQ.The mean contents of trace elements followed the order Zn > Cu > Cd > Pb > Sb > As > V>Cr > Se > Ni.Zinc was the most abundant element, showing a mean of 0.778 ± 0.09 mg/Kg and a maximum of 1.013 mg/Kg, followed by copper (0.191 ± 0.05 mg/Kg).Conversely, Se, Cr, and Ni were the less abundant elements, with mean values of 0.009 ± 0.0003 mg/Kg, 0.011 ± 0.001 mg/Kg, and 0.007 ± 0.004 mg/Kg, respectively.Among the non-essential elements, very high cadmium contents were found, with 7 pools (28%) that reached levels above the EU Regulation 2021/1323.Legumes are well known to reduce pH values because these plants exude large quantities of H þ during the process of nitrogen fixation.
Consequently, the co-cultivation with legumes reduced soil pH, which somewhat increased the exchangeable forms of Cd (Liu et al. 2012).Furthermore, legumes may increase the total Cd uptake of neighbouring crops through root interaction.Conversely, no hazardous Pb contents were found in all the samples examined, with levels below the EU Regulation 2006/1881 for legumes.
The Cd contents found in this work were significantly higher than those found by Ka and Chandravanshi (2014) in processed white lupins (L.albus L.) from Ethiopia, which did not detect concentrations that could be determined by their method.However, it should be considered that the Flame Atomic Absorption Spectroscopy method proposed by Ka and Chandravanshi is less sensible than the method proposed in this study.The high Zn concentration found in this work could be due to the fact that this ion is readily from the soil to the plants, leading to its accumulation in the plant (Wood 1985).Conversely, the lower Cu contents could be due to the low intake of this element by the plant or its bioavailability in the plant is very small.The trace elements pattern obtained could be related to the physical and chemical properties of the soil, leading to the fact that the presence of trace elements is influenced by the environmental and geological conditions of the cultivation area.Furthermore, the processing by soaking could decrease the nutritive value as a result of removing soluble elements, because all the water-soluble elements are often lost with the steeping medium and rinsing procedure (Zelalem and Chandravanshi 2014).However, this type of processing seems to be important to avoid the presence of antinutritional substances such as alkaloids of the quinolizidine group that make the lupins unpalatable and sometimes toxic (Sujak et al. 2006).As far as we know, this is the first report on the detection of V, As, Se and Sb in white lupin, suggesting that further studies are needed to have a comprehensive evaluation on the essential and non-essential elements presence in this type of products.Very alarming cadmium levels have been found, in contrast to other studies reported in the literature (Zelalem and Chandravanshi 2014), with mean values very close to the limits set by the EU Reg.2021/1323.The European Food Safety Authority has stated that the average exposure to cadmium in adults in the European Union is close to or slightly above the tolerable weekly dose.EFSA also concluded that in sub-groups such as vegetarians, children, and people residing in highly contaminated areas, a weekly dose might be encountered which is about double that tolerable.The EFSA's CONTAM panel concluded that the current exposure to cadmium levels must be reduced.Considering this, the present work provides the first data for lupins produced in Italy to encourage future studies on the risk assessment of exposure to cadmium.The interesting Zn and Cu values obtained also suggest this type of product as a valuable source of essential elements.

Experimental
See the supplementary material for the experimental section.

Table 1 .
Essential and non-essential elements contents of the white lupin samples analysed (mg/Kg).