-The present study deals with the physicochemical interactions between aroma compounds and various dairy media used as models of complex food matrices, as well as the consequences of the interactions on aroma partitioning between the air and matrix. Five aroma compounds were investigated: amyl and isoamyl acetate, ethyl pentanoate, hexanal and t-2-hexenal. Skim milk, anhydrous milk fat and full-fat cream were chosen as dairy media, while water was used as a reference medium. Apparent partition coefficients of the five aromas were determined between the air and media between 30 and 80 °C by static headspace-gas chromatography. Partition coefficients over full-fat cream were also calculated from partition coefficients over skim milk and anhydrous milk fat. Compared with water, a significant retention of t-2-hexenal was observed in skim milk (nearly 90% whatever the temperature), whereas the retention of the other aromas varied from 6% for isoamyl acetate to 40% for hexanal in skim milk. Hydrophobic interactions were responsible for the retention of esters, whereas covalent binding of t-2-hexenal by dairy proteins was probably involved. The volatility of the 5 aromas was drastically reduced over anhydrous milk fat, because of their hydrophobic nature (log P > 1). There were discrepancies between calculated and measured partition coefficients over full-fat cream, which depended on aroma compounds and temperature. Measured and calculated ethyl pentanoate retentions were similar whatever the temperature. For isoamyl acetate, hexanal and, to a lesser extent, t-2-hexenal, aroma retention was greater than expected. The reverse phenomenon was observed with amyl acetate. The so-called "enthalpy of affinity" was calculated from the variation of the partition coefficient with temperature. This parameter allowed an overview of the relative importance of aroma compounds-matrices interactions. Anhydrous milk fat
Substitution of the chloro ligands of cis‐[Pt(PEt3)2Cl2] by 4‐methylthio‐2‐thioxo‐1,3‐dithiole‐5‐thiolate (L) leads to the thiolato complexes trans‐[Pt(PEt3)2ClL] (2) and trans‐[Pt(PEt3)2L2] (1), which have been characterised by X‐ray crystallography. In the solid state, the square planar arrangement is capped by an endocyclic sulfur atom of L, which gives rise to distorted square‐pyramidal and pseudooctahedral geometries for 2 and 1, respectively. Complex 1 coexists in solution with [Pt(PEt3)(η1‐L)(η2‐L)] (3), which results from the reversible dissociation of one phosphane ligand. The combination of η1‐(thiolato) and η2‐(thiolato/thioether) L in 3 has been established by variable‐temperature 1H NMR spectroscopy and crystal structure determination. The η2‐coordination mode of L is also observed in cis‐[Pt(PEt3)2L]+ (4), which results from the abstraction of the chloro ligand of 2 by excess TlPF6. An S‐demethylation reaction occurs when 1 is heated in acetonitrile to yield the structurally‐characterised dithiolene complex [Pt(PEt3)2(dmit)] (5) (dmit2– = 2‐thioxo‐1,3‐dithiole‐4,5‐dithiolate) and MeL. Treatment of cis‐[Pt(PPh3)2Cl2] with 2 equiv. of L leads to a mixture of [Pt(PPh3)2(dmit)] (6) and [Pt(PPh3)(η1‐L)(η2‐L)] (7). Complex 7 predominates in solution over its parent compound,[Pt(PPh3)2L2]. The identification of CH3Cl by 1H NMR spectroscopy proves that [Pt(PPh3)2ClL] is involved as an intermediate in the demethylation process. The reaction of L with platinum precursors that are blocked in a cis arrangement by chelation of 1,1‐bis(diphenylphosphanyl)methane (dppm) and 1,1‐bis(diphenylphosphanyl)ethane (dppe) leads to the formation of the thiolato complexes cis‐[Pt(η2‐dppm)L2] (8) and cis‐[Pt(η2‐dppe)L2] (9). The solid‐state structure of 8 reveals the occurrence of an additional weak interaction between a thiomethyl group and the platinum centre (Pt–S 3.073 Å).
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