Masanori Yamamoto

Reduction of Stale Aldehyde of Beer with Membrane Fraction of Acetic Acid Bacteria

The oxidation of trans-2-nonenal, the main compound causing staleness in beer, with a membrane fraction of acetic acid bacteria was investigated. For use of the fraction, it was necessary to inactivate membrane-bound alcohol dehydrogenase (ADH) first to avoid oxidation of alcohol, while maintaining membrane-bound aldehyde dehydrogenase (ALDH) activity. ADH was completely inactivated by treatment of the membrane fraction at 60°C for 15 min, without any loss of ALDH activity. ALDH activity was not affected by heat treatment even in the presence of 10% alcohol. Results of HPLC showed that a fraction incubated at 60°C for 15 min oxidized 50 ppb trans-2-nonenal added to a commercial beer sample without affecting the alcohol content. Our sensory panel found that the stale odor of trans-2-nonenal disappeared when the membrane fraction was so treated, with the resulting odor better than that of beer with trans-2-nonenal added but not treated with the fraction.

Synergistic Effect of Tocopherol, Citric acid, and Sodium Pentapolyphosphate on the Thermal Oxidation of Edible Fats and Oils

Using tocopherol as a natural antioxidant and citric acid and sodium pentapolyphosphate as synergists, the prevention of heat deterioration of frying oils was investigated. The addition of condensed phosphate, which chelates a trace amount of metal ions, to the refined palm oil containing tocopherol and citric acid caused the oxidative stability of the oil to increase by about twice as much. The synergistic effects o tocopherol, citric acid and sodium pentapolyphosphate in combination were also observed, on other edible fats and oils such as refined hydrogenated rapeseed oil, refined tallow and refined lard. The oxidative stabilities of these oils increased by about 2.0, 3.0, and 1.5 times, respectively, those in the absence of additions.