Development of new metal chelates for animal nutrition and of analytical methods for their quantitative determination and quality control

Abstract

The growing interest for mineral integration to increase mineral bioavalability brought researchers to re-examine accurately the impact that complexes and chelates can have for food industry. In fact, the so-called organic or chelate mineral forms, in particular those associated with amino acids, peptides or other organic molecules, afforded encouraging results in different in vivo tests on animals of economic interest fed with fodder containing minerals in the form of chelates. Moreover, it is possible to underline that the greatest interest of the feedstuff production industry, driven by the immediate possibility to put new products on the market, is addressed mainly to chelating species normally in the feedstuff for other functions and to those metals that can more easily induce deficiency stages in animals. This is the case of 2-hydroxy-4-methylthiobutanoic acid (MHA the so-called methionine hydroxy-analogue), that is an alpha-hydroxyacid largely used in animal nutrition as a source of methionine, and of glycine, also corrently used in the diet. On the other hand, concerning the metals, the attention is addressed to the Zinc (Zn), copper (Cu) and Iron (Fe) for the physiological roles they play in animals and to a lesser extent also to Calcium (Ca), Magnesium (Mg), Manganese (Mn) and Cobalt (Co). Therefore, the aim of this work, was to complete the physico-chemical characterization of metal chelates of MHA, whose properties were till now not fully investigated. A prominent feature of MHA is the better stability of its metal chelates in acidic medium with respect to the corresponding chelates of other ligands, in particular aminoacids. In this contest, an important goal of this investigations was to estabilish the effective chelation of MHA towards metal cations, both in solution and in the solid state. In addition, this work deal with the attempts to develope reliable analytical methods in order to recognize and determine MHA metal chelates in commercial samples. From the analytical point of view two different approaches were followed: the first one based on the solid-liquid extraction of the metal chelate from the matrix and HPLC analysis, the second based on the direct characterization of the target analyte by infrared spectrophotometry. The present work has allowed to reach the following goals: 1. The effective chelation of MHA toward transition metal cations has been demonstrated in the solid state by solving the crystal structure of the zinc derivative; 2. The presence of metal chelates in solution has been demonstrated by electrochemical and NMR spectroscopic methods; 3. The limit of determination by MS spectrometric methods in water solution have been defined and a relevant analytical procedure has been set up. 4. IR spectrometric methods both in the MIR and in the NIR region have been set up and can be conveniently proposed for the determination of MHA chelates in solid commercial samples. 5. Rapid procedures for the evaluation of the chelating strenght of commercial misture have been develop for practical purpose.