Isomerization of Commercially Important Carotenoids (Lycopene, β‑Carotene, and Astaxanthin) by Natural Catalysts: Isothiocyanates and Polysulfides

Effects of natural catalysts, isothiocyanates and polysulfides, on Z-isomerization and decomposition of (all-E)-carotenoids (lycopene, β-carotene, and astaxanthin) after heat treatment were investigated. When isothiocyanates were added to (all-E)-carotenoid solutions and heated, Z-isomerization and decomposition of carotenoids were enhanced and the degree differed depending on the isothiocyanate type. Interestingly, when polysulfides were applied in the same manner, in addition to promoting the Z-isomerization reaction, they markedly improved the thermal stability of carotenoids. Successively, we investigated the reaction characteristics of allyl isothiocyanate (AITC) and diallyl disulfide (DADS) using (all-E)-lycopene; that is, effects of the amount added, solvent used, and reaction temperature and time, as well as the combination use on Z-isomerization and decomposition of lycopene, were investigated. With increases in the amount added and reaction temperature and time, Z-isomerization of lycopene was promoted for both catalysts. The high-temperature treatment tests clearly showed that AITC induced thermal decomposition of lycopene, whereas DADS improved the lycopene stability. Moreover, the simultaneous use of AITC and DADS resulted in a synergetic effect on the Z-isomerization efficiency

Formation and Characterization of <i>Z</i>‑Isomer-Enriched Carotenoid-Loaded Microparticles with Poly(vinylpyrrolidone) Using a Spray Drying Technique

Carotenoid Z-isomers exhibit higher bioavailability and potentially beneficial biological activities than their all-E-isomers, which predominate in nature. However, they are chemically unstable and poorly soluble in water, which hinder the practical use of Z-isomer-enriched carotenoid materials. Encapsulating carotenoid Z-isomers in water-soluble carriers can overcome these problems. Here, we successfully prepared Z-isomer-enriched carotenoids (lycopene, β-carotene, and astaxanthin)/poly(vinylpyrrolidone) (PVP, a water-soluble polymer) inclusion complexes using a continuous-flow system which is constituted of a heated flow reactor and a spray dryer. Processing in the flow reactor at 200 °C for 15 s prior to spray drying improved the total Z-isomer ratio of the encapsulated carotenoids (>55%) and encapsulation efficiency of carotenoids in PVP. Furthermore, storage tests of the resulting complexes demonstrated that formulating (Z)-carotenoids with PVP stabilized their Z-structures. The results of this study contribute to the realization of industrial applications of Z-isomer-enriched carotenoids with great utility and health benefits

Alternating Current Electrolysis for Individual Synthesis of Methanol and Ethane from Methane in a Thermo-electrochemical Cell

The individual synthesis of methanol and ethane from methane was investigated using a thermo-electrochemical cell in gas flow mode over the temperature range of 150–200 °C. Methane was directly oxidized at an anode consisting of sub-10 nm Pt and Fe particles. In the electrolysis of humidified methane, methanol was produced through the formation of active oxygen intermediates from water vapor. In the electrolysis of unhumidified methane, ethane was produced via the dissociation of C–H bonds, followed by dimerization of the resultant •CH3 radicals. However, the formation rates for the target products decreased with time during electrolysis because of overoxidation of the anode by the direct-current (DC) voltage. The alternating current (AC) electrolysis of methane avoided this problem. Under optimized AC polarization conditions at a square waveform voltage of ±2.5 V with a pulse time of 5 s, this cell generated methanol and ethane at rates of 5.1 × 10–5 mol m–2 s–1 (92 mmol gcat–1 h–1) and 3.8 × 10–5 mol m–2 s–1 (69 mmol gcat–1 h–1), respectively, without a substantial loss of activity during continuous electrolysis

Efficient Hydrogen Production by Direct Electrolysis of Waste Biomass at Intermediate Temperatures

Biomass has been considered as an alternative feedstock for energy and material supply. However, the lack of high-efficiency and low-cost processes for biomass utilization and conversion hinders its large-scale application. This report describes electrochemical hydrogen production from waste biomass that does not require large amounts of energy or high production costs. Hydrogen was produced by the electrolysis of bread residue, cypress sawdust, and rice chaff at an onset cell voltage of ca. 0.3 V, with high current efficiencies of approximately 100% for hydrogen production at the cathode and approximately 90% for carbon dioxide production at the anode. The hydrogen yields per 1 mg of the raw material were 0.1–0.2 mg for all tested fuels. Electrolysis proceeded continuously at plateau voltages that were proportional to the current. These characteristics were attributable to the high catalytic activity of the carbonyl-group functionalized mesoporous carbon for the anode reaction, and that the major components of biomass such as cellulose, starch, lignin, protein, and lipid were effectively utilized as fuels for hydrogen production

Isomerization of <i>Paracoccus carotinifaciens</i>-Derived Carotenoids (Astaxanthin, Adonirubin, and Adonixanthin) under Subcritical Water Conditions

Recent studies have shown that Z-isomers of carotenoids exhibit greater bioavailability and tissue accumulation efficiency than the natural isomer, the all-E-isomers. Here, we attempted to carry out the Z-isomerization of Paracoccus carotinifaciens-derived carotenoids (astaxanthin, adonirubin, and adonixanthin) by subcritical water processing. An aqueous solution dispersed with P. carotinifaciens was treated in a pressure-resistant vessel in the range of 140–240 °C and 4–16 MPa. The processing pressure in the above range did not affect carotenoid isomerization; however, depending on the heating temperature, the total Z-isomer ratio markedly increased, and carotenoid degradation was also accelerated. Moreover, to promote the Z-isomerization efficiency, the effect of adding an entrainer, ethanol, was investigated. The results showed that the addition of ethanol markedly promoted the Z-isomerization efficiency. Finally, we achieved over 50% of the total Z-isomer ratio of P. carotinifaciens-derived carotenoids while inhibiting their degradation by 30 min subcritical water processing