Application of channel flow double electrode to the study on platinum dissolution during potential cycling in sulfuric acid solution

The applicability of a channel flow double electrode (CFDE) as an in situ monitoring method of Pt dissolution during potential cycling in 0.5 M H₂SO₄ solution at 25 °C was investigated. In the CFDE, Pt ions (Ptⁿ⁺) dissolved from a platinum working electrode were detected by reducing them to Pt on a gold collector electrode which was placed at the downstream. The detection of the Pt dissolution by the collector current was confirmed by EPMA analysis of the collector electrode surface. In anodic scan, a rise of the collector current above 1.05 V clearly indicated the platinum dissolution. The collector current showed two different rates of dissolution, i.e. a lower rate from 1.05 to 1.3 V where only one layer of oxide (PtO) is formed and the higher rate from 1.3 to 1.46 V where two layers of oxides (probably PtO/PtO₂) are formed. The collector current, in the cathodic scan, clearly showed two different reduction peaks due to the Pt deposition, which was confirmed by EPMA analysis. On the basis of collector current, the rate and potential range of the Pt dissolution are discussed.     

Isolation and characterization of a high-acetate-producing sake yeast Saccharomyces cerevisiae

The result of sensory evaluation of sake showed that acetic acid imparted desirable acidity when the proportion of acetic acid to lactic acid was about 1/3, even if the concentration of acetic acid was 0.75 g/l. Glycerol balanced the acidity and brought about a harmony between sweetness and acidity in sake. A high-acetate producing sake yeast (MHA-3) was isolated from mutants having low NADH dehydrogenase (NDE) activity. MHA-3 produced 15 times more acetate and 5 times more lactate than the parental strain Kyokai no. 901 (K-901) in a small-scale sake brewing test using 10 kg of rice. In addition, the concentrations of glycerol in sake brewed with MHA-3 were approximately 1.5-fold higher than in that brewed with K-901. The proportion of acetic acid to lactic acid was about 1/3 in sake fermented with MHA-3 and it exhibited a good balance between sweetness and acidity. The activities of glycerol-3-phosphate dehydrogenase (GPD) and aldehyde dehydrogenase (ALD) in MHA-3 were 1.4-fold and 3.1-fold, respectively, higher than those in K-901 while the activity of NDE was 40% that of K-901. MHA-3 accumulated higher amounts of acetate and glycerol than K-901 in static YNB10 medium. The concentrations of acetic acid produced, depending on the quantity of yeast cells added, increased in conjunction with increases in glycerol produced. We suggest that NDE might be linked with GPD and that the nde mutants, which can be used in sake brewing, produced higher amounts of acetate and glycerol.     

Emulsifying and Bactericidal Properties of a Protamine-Galactomannan Conjugate Prepared by Dry Heating

Protamine was conjugated with galactomannan (GM) in a controlled dry state at 60° and 79% relative humidity. The covalent attachment of GM to protamine was confirmed by SDS-PAGE and gel chromatography. The resulting protamine-GM conjugate had excellent emulsifying properties without significant loss in bactericidal activity. The emulsifying activity was six times and the emulsion stability of the conjugate more than 10 times higher than those of protamine. In acidic (pH 3) and salt (0.2M NaCl) systems the conjugate showed much more effective emulsifying properties than commercial emuJsifiers. In addition, the emulsifying properties of the conjugate were retained after preheating at 90°. Protamine-GM conjugate could be used for processed foods as a bifunctional food additive, emulsifier and antibacterial reagent.