Characterization and Thermal Isomerization of (all-E)‑Lycopene

• Published in: Journal of agricultural and food chemistry Vol. 62; no. 1; pp. 264 - 269
• Main Authors: Takehara, Munenori, Nishimura, Masatoshi, Kuwa, Takahiro, Inoue, Yoshinori, Kitamura, Chitoshi, Kumagai, Tsutomu, Honda, Masaki
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08.01.2014
• Subjects: absorbance; absorption; acetone; benzene; carbon disulfide; Carotenoids - chemistry; Carotenoids - isolation & purification; differential scanning calorimetry; hexane; Hot Temperature; Isomerism; isomerization; isomers; Kinetics; Lycopersicon esculentum - chemistry; Magnetic Resonance Spectroscopy; melting point; nuclear magnetic resonance spectroscopy; Plant Extracts - chemistry; Plant Extracts - isolation & purification; solvents; tomato paste; Transition Temperature; washing; tomatoes; spectrum analysis; lycopene; thermal isomerization; purification; density functional theory
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf404497k

A large amount of (all-E)-lycopene was successfully purified from tomato paste using an improved method that included a procedure to wash crystalline powder with acetone. The total yield of the pure (all-E) form was at least 30%. The melting point of (all-E)-lycopene was determined to be 176.35 °C by differential scanning calorimetry (DSC) measurements. Bathochromic shifts were observed in the absorption maxima of all solvents tested (at most a 36 nm shift for λ2 in carbon disulfide, as was observed in hexane) and were accompanied by absorbance decreases, namely, a hypochromic effect, showing a higher correlation between the position and the intensity of the main absorption bands. This bathochromic shift was dependent upon the polarizability of the solvent rather than its polarity. The structure of (all-E)-lycopene in CDCl3 and C6D6 was identified on the basis of one- and two-dimensional nuclear magnetic resonance (NMR) spectra, including 1H and 13C NMR, homonuclear correlation spectroscopy (1H–1H COSY), heteronuclear multiple-quantum coherence (HMQC), and heteronuclear multiple-bond connectivity (HMBC). The rate constants of the decrease in (all-E)-lycopene with hexane and benzene were calculated to be 3.19 × 10–5 and 3.55 × 10–5 s–1, respectively. The equilibrium constants between (all-E) and (13Z) isomers were estimated to be 0.29 in hexane and 0.31 in benzene, respectively, from the point at which the amount of (13Z)-lycopene reached its maximum.