Hiroyuki Horitsu

Cloning and sequencing of two d-xylose reductase genes (xyrA and xyrB) from Candida tropicalis

Abstract Two d -xylose reductase (XR) genes, xyrA and xyrB , of Candida tropicalis IFO 0618 were cloned and sequenced. Each XR gene had an open reading frame consisting of 324 amino acids (972 bp). The deduced amino acid sequences of each XR gene were very similar to each other, except for three amino acids. The molecular weights of the deduced gene products were 36,551 ( xyrA ) and 36,596 ( xyrB ). These genes were 73.0% identical to the Pichia stipitis XR gene.

Optimization of kojic acid production rate using the Box-Wilson method

Abstract In order to increase the rate of kojic production using Aspergillus oryzae , the initial glucose and Polypepton concentrations were optimized by the Box-Wilson method. A kojic acid production rate of 4.44 g/ l ·d was obtained when the initial glucose and Polypepton concentrations were 148.0 g/ l and 4.8 g/ l , respectively, at a K L a value of 164.7 h −1 .

A novel model for continuous fermentation process for Worcestershire sauce production using a trickle bed bioreactor

Abstract The mass balances of sugar and ethanol were computed on the assumption that the trickle bed bioreactor used was a continuous-flow stirred-tank reactor (CSTR), and simulation of the steady ethanol concentration at various dilution rates was performed using a modified Contois equation. The equation proposed here represents the conventional Contois equation as a particular equation of the modified formula ( m =1.0). The stability of the continuous fermentation in the production of Worcestershire sauce was evaluated, and this process was kinetically analyzed using the modified Contois equation. Neither decrease in yeast activity nor clogging with growth yeasts was observed in the trickle bed bioreactor with comb-shaped ceramic carriers during the fermentation period (about 6 months). From the results of the evaluation of mixing conditions this bioreactor can be regarded as a combination of a plug flow reactor (PFR) in the ceramic part, and a CSTR in the retention part. However, the trickle bed bioreactor could function as a CSTR having the same capacity as the actual volume of the retention part for the fermentation contribution rate of each part of the bioreactor. The observed ethanol concentration and productivity at the steady states were almost the same as the values calculated using the material balance equations of the sugar concentration and the ethanol concentration in a CSTR and the modified Contois equation with m =6.0. Thus, the modified Contois equation ( m =6.0) has been proposed as a design equation for a fermentation process for Worcestershire sauce production. When the modified Contois equation was applied to an acetic acid fermentation process and a plant tissue culture the observed product concentrations at each dilution rate were similar to the calculated values. It has been proved that the modified Contois equation is applicable not only to an alcohol fermentation process for Worcestershire sauce production but also to other fermentation processes and growth reactions.

Simultaneous Assay of Eight Food Preservatives in Imported Fruit Vinegars by Solid-Phase Extraction Gas-Liquid Chromatography.

Sorbic acid (SOA), dehydroacetic acid (DA), benzoic acid (BA), and five esters of phydroxybenzoic acid (PHBA) in imported fruit vinegars were first passed through a Sep-Pak C18 cartridge and then analyzed simultaneously by gas-liquid chromatography. In brief, the vinegar samples were further acidified with hydrochloric acid, the test solution was saturated with sodium chloride and stirred vigorously, and the solution was put on the cartridge. Acetone as the solvent gave satisfactory results. A wide-bore capillary column was used for the gas chromatography. An FFAP column was most suitable for analysis of SOA, DA, and BA, and an MS column was most suitable for analysis of the five esters of PHBA in terms of stability, separability and sensitivity. Five fruit vinegars, fortified with 20μg/ml of eight food presertives, gave recovery of 91.6-100.5%, and the coefficient variation was 0.16% to 2.23%. The detection limit was 2μg/ml for each vinegar. This method could be used for various vinegars and was superior to conventional systematic methods for the assay of food preservatives. By this method, analytical results for 20 samples of imported fruit vinegars showed that SOA was present at the concertration of l.0-6.5μg/ml in two red wine vinegars, two sherry vinegars, and a balsamic vinegar. BA was detected at the concentration of 2.8μg/ml in a cider vinegar.

Pentose Metabolism in Clostridium acetobutylicum :Part I. L-Arabinose Ketol Isomerase

L-Arabinose ketol-isomerase (EC 5.3.1.4) was extracted from the L-arabinose-grown cells of Clostridium acetobutylicum and partially purified by ammonium sulfate fractionation, DEAE-cellulose column chromatography and the gel filtration on Sephadex G-200. Optimum pH and temperature for the activity of the enzyme were 7.5 and 37°C, respectively. The enzyme was inhibited by EDTA, Na-pyrophosphate and KCN, and its activity was restored by the addition of divalent metal ions such as Mn2+ and C02+. The Michaelis-Mentens constants for L-arabinose, Mn2+ and Cot2+ were 1.08 x 10-2 M, 0.83 x 10-4 M and 0.38•~10-4M, respectively. The equilibrium constant (K=ribulose/arabinose) was 3.14 (37°C, pH 7.5). The thermodynamic quantities, AH, AG (37°C), AS (37°C) and E were +7354 cal/mole, -710.7 cal/mole, +26.0 cal/(deg. mole) and -+7471 cal/mole, respectively.

Studies on the Sunlight Flavour of Beer:Part VI. Correlation of the Occurrence of the Sunlight Flavour of Beer to Humulone, Lupulone and related Compounds

In order to establish the mechanism of occurrence of sunlight flavour of beer in continuation of the preceding paper, humulone, lupulone, and their analogues and degradation compounds, i.e., cohumulone, adhumulone, 5-acetyl-3-methylfilicinic acid including analogues, tetrahydrohumulone, hexahydrolupulone, humulinic acid and lupuloxinic acid, were tested for the occurrence of sunlight flavour of beer.As a result, among the above-mentioned compounds, humulone, lupulone, cohumulone, adhumulone, tetrahydrohumulone and hexahydrolupulone were found to cause the sunlight flavour, but the other compounds did not cause typical sunlight flavour. This fact shows that some specific structural components seem requisite for the occurrence of sunlight flavour of beer.It was also revealed that isomerization caused by boiling accelerates the occurrence of the sunlight flavour of beer. Finally, the result of the experiment conducted by the gas chromatographic procedure showed that any new component is not detected by the e...