HPLC–ICP–MS determination of selenium distribution and speciation in different types of nut

Abstract

In addition to determination of total selenium in nuts, the element distribution among different fractions (lipid extract, low molecular weight, and protein fractions), and speciation analysis were studied. Improved precision for total selenium determination was observed after elimination of lipids. Because selenium was not detected in any of the lipid extracts obtained from the different types of nuts (ICP-MS), in each determination and/or speciation procedure used in this work lipids were extracted (chloroform-methanol, 2:1) and discarded before analysis. In agreement with previously reported data, high selenium levels were found in Brazil nuts (those purchased without shells contained approximately a quarter the content than those purchased with shells) and significantly lower levels in walnuts, cashews, and pecans nuts. Low-molecular-weight compounds were extracted with perchloric acid (0.4 mol L(-1)) to furnish a fraction containing 3 to 15% of the total selenium in different types of nuts. The proteins were isolated from nut samples by dissolution in 0.1 mol L(-1) sodium hydroxide and subsequent precipitation with acetone. They were then dissolved in phosphate buffer pH 7.5. Analysis of protein fractions focused on selenium in two possible states - weakly and firmly bound to proteins. Results obtained for Brazil nuts by size-exclusion chromatography with on-line ICP-MS detection, in the absence and in the presence of beta-mercaptoethanol, showed that approximately 12% of total selenium was weakly bound to proteins. To obtain information about firmly bound selenium, the protein extracts were hydrolyzed enzymatically with proteinase K. Speciation was performed by means of ion-pairing HPLC-ICP-MS. The primary species found in all types of nuts was Se-methionine (19-25% of total selenium for different types of nuts).

Determination and fractionation of barium in Brazil nuts

“…On the other hand, selenium was not detected in the lipids fraction as previously pointed out. 7 The concentrations of sulfur and selenium in the protein fraction are similar to those determined in the water soluble fraction. Methionine is apolar and presents low solubility in water.…”

“…Brazil nuts are a rich source of nutrients, vitamins, minerals and fibers. 7 It is a native plant of the Amazon region. The tree produces tasty and highly nourishing almonds and their wood is also valuable.…”

“…11 This effect seems to be related to the high contents of selenium, mainly present in the form of Se-methionine and also associated with compounds of low molecular weight. 7 Brazil nuts are one of the richest foods in proteins and amino acids containing sulfur, particularly methionine and cysteine (380 and 130 mg g -1 , corresponding to 18 and 8%, respectively), contributing for their high nutritional value. [12][13][14] Brazil nuts usually contain high levels of selenium and there is a vast literature about this element.…”

Cu, Fe, Mn and Zn distribution in protein fractions of Brazil-nut, cupuassu seed and coconut pulp by solid-liquid extraction and electrothermal atomic absorption spectrometry

“…Caruso and co-workers 18 studied the distribution of various elements of nutritional and toxicological interest in different molecular weight fractions, ranging from 0.18 to 14 kDa. Chemical speciation has been accomplished for As and Se in Brazilnut [20][21][22] and Ni, Cu, Zn and Mn in different edible nuts. 19,23 Cupuassu (Theobroma grandiflorum) has a whiteyellow pulp with pleasant acidic taste and a strong fragrance, which is widely consumed as juice, ice cream and jam.…”

Avaliação da distribuição de cobre associado a compostos de diferentes massas moleculares na polpa de açaí

“…Técnicas seletivas e com adequada sensibilidade têm sido usadas para detecção de elementos em estudos de fracionamento, distribuição e especiação química (Gonçalves et al 2009; Naozuka e Oliveira 2007; Kannamkumarath et al 2002). A espectrometria de absorção atômica em forno de grafite (GF AAS) é uma técnica analítica bem estabelecida e suficientemente robusta para ser implantada em laboratórios envolvidos com rotina em larga escala (Welz 1999).…”