Makoto Shimoyamada

Analysis of vitamin E and its oxidation products by HPLC with electrochemical detection.

A sensitive HPLC procedure with postcolumn reduction and electrochemical detection was developed for the analysis of vitamin E and its oxidation products, α-tocopherylquinone, epoxy-α-tocopherylquinones, and 8a-(lipid-dioxy)-α-tocopherones. After the separation on a reversed-phase column, on-line zinc-catalyzed reduction allowed the detection of α-tocopherylquinone and epoxy-α-tocopheryl-quinones, whereas platinum-catalyzed reduction allowed the detection of 8a-(lipid-dioxy)-α-tocopherones. The lowest detectable level of each compound was about 0.2 pmol at the signal-to-noise ratio of 3. This method was applied to the detection of α-tocopherol products in peroxidized human plasma. When the plasma was peroxidized by the addition of a free radical initiator, peaks corresponding to α-tocopherylquinone, epoxy-α-tocopherylquinones, and the addition products of α-tocopherol with peroxyl radicals derived from cholesteryl ester hydroperoxides and PC hydroperoxides were observed. The amount of these oxidation products in the plasma increased with the depletion of endogenous α-tocopherol. The results indicate that the method is useful to detect the oxidation products formed by the peroxyl radical-trapping reactions of α-tocopherol in biological systems.

An antifungal saponin from white asparagus (Asparagus officinalis L) bottoms

An antifungal saponin was isolated from the bottom cut of white asparagus (Asparagus officinalis L), which is unusable in food processing. The structure of the saponin was identified as 3-O-[{α-L-rhamnopyranosyl (1 → 2)} {α-L-rhamnopyranosyl (1→4)}-β-D-glucopyranosyl] (25S) spirost-5-ene-3β-ol from chemical and spectral data. This saponin was shown to be identical with collettinside III from Dioscorea collettii, and to inhibit the growth of some kinds of fungi at μg ml -1 levels.

Amino Acid Sequence of a-Subunit in Hen Egg White Ovomucin Deduced from Cloned cDNA

The primary amino acid sequence of α-subunit in ovomucin (OVM) from hen thick egg white was determined. The 2087 amino acid residues with a relative molecular mass of 230.9 kDa along the full length of the α-subunit were represented. The α-subunit contains domains, arranged from the N- to C-terminals in the following order: D1-D2-D′-D3-R (central region)-D4-C1-CK (Cystine-knot), in a manner similar to the arrangement of D, C and CK domains in human pre-pro-von Willebrand factor (hpp-vWF) and hMUC2. The α-subunit showed identities on amino acid sequences with hpp-vWF and hMUC2 at 33 and 41% in the N-terminal region and 30 and 38% in the C-terminal region, respectively. The numbers and positions of cysteine residues were highly conserved among α-subunit, hpp-vWF and hMUC2. However, R showed no virtual sequence homology with the corresponding regions in two proteins. It was estimated that α-subunit was not part of a large peptide of OVM, but was independently synthesized from β-subunit.

Insolubilisation and gelation of heat-frozen soymilk

Soymilk prepared from soybean seed was heated and frozen. After thawing, precipitation was shown to occur in soymilk. Precipitation from heated and frozen soymilk increased with increase in heating time. Precooling treatment (−5°C) before freeze-storage of heated soymilk resulted in gel-like solidification of soymilk. The gel strength of the freeze-gel formed from soymilk was related to the heating time and the viscosity of the soymilk before freezing. © 1999 Society of Chemical Industry

Iron-catalyzed reaction products of α-tocopherol with 1-palmitoyl-2-linoleoyl-3-sn-phosphatidylcholine (13S)-hydroperoxide

Alpha-tocopherol was reacted with 1-palmitoyl-2-[(9Z,11E)-(S)-13-hydroperoxy-9,11-octadecadienoyl]-3-sn-phosphatidylcholine (13-PLPC-OOH) in the presence of a lipid-soluble iron chelate, Fe(III) acetylacetonate, in methanol at 37 degrees C. The reaction product was isolated and identified as a mixture of 1-palmitoyl-2-[(10E)-(12S,13S)-9-(8a-dioxy-alpha-tocopherone)-12,13-epoxy-10-octadecenoyl]-3-sn-phosphatidylcholine and 1-palmitoyl-2-[(9Z)-(12S,13S)-11-(8a-dioxy-alpha-tocopherone)-12,13-epoxy-9-octadecenoyl]-3-sn-phosphatidylcholine (TOO-epoxyPLPC), in which the 12,13-epoxyperoxyl radicals derived from 13-PLPC-OOH attacked the 8a-position of the alpha-tocopheroxyl radical. The iron and ascorbate-catalyzed reaction of 13-PLPC-OOH with alpha-tocopherol in phosphatidylcholine (PC) liposomes was assessed by measuring the reaction products of alpha-tocopherol. When 13-PLPC-OOH and alpha-tocopherol were added in saturated dimyristoyl-PC liposomes, the products were TOO-epoxyPLPC, alpha-tocopherylquinone, and epoxy-alpha-tocopherylquinones. In 1-palmitoyl-2-linoleoyl-PC (PLPC) liposomes, alpha-tocopherol could react with both the 13-PLPC-OOH derived 12,13-epoxyperoxyl radicals and the PLPC-derived peroxyl radicals and formed the addition products together with alpha-tocopherylquinone and epoxy-alpha-tocopherylquinones. Therefore, the iron-catalyzed decomposition of phospholipid hydroperoxides primarily produces epoxyperoxyl radicals, which react with the 8a-carbon centered radical of alpha-tocopherol in liposomal systems.

Preparation of the addition products of α-tocopherol with cholesteryl linoleate-peroxyl radicals

α-Tocopherol was reacted with cholesteryl linoleate hydroperoxides (Ch18:2-OOH) in the presence of an iron-chelate, Fe(III) acetylacetonate, at 37°C in benzene. The reaction products were isolated and identified as four positional isomers of cholesteryl (8a-dioxy-α-tocopherone)-epoxyoctadecenoates and two positional isomers of cholesteryl (8a-dioxy-α-tocopherone)- octadecadienoates. The result indicates that the peroxyl radicals from Ch18:2-OOH react with the 8a-carbon radical of α-tocopherol to form the addition products.

Studies on the Freeze Concentration of Foods.—Determination of Eutectic Temperatures of Amino Acids in Aqueous Ethanol Solution —

In order to apply a freeze concentration to food constituents, freezing points, solubilities and eutectic temperatures were estimated for an aqueous solution of amino acid (glycine and sodium glutamate) containing various concentrations of ethanol. The eutectic temperatures of each amino acid lowered with the increase in ethanol concentration, but the concentrations at the starting point of precipitation were also decreased. Ethanol addition was effectiveto precipitate glycine and sodium glutamate at their lower concentrations.