Yukimasa Mitsuhashi

Sensitive spectrophotometric method for the determination of ethylenediaminetetraacetic acid in foods

A sensitive spectrophotometric method for the determination of ethylenediaminetetraacetic acid (EDTA) in foods is described. The method involves the reaction of EDTA with Fe3+ to produce the EDTA-Fe chelate, followed by the removal of excess of Fe3+ by a chelate extraction technique using chloroform and N-benzoyl-N-phenylhydroxylamine and the formation of a chromophore with 4,7-diphenyl-1,10-phenanthroline-disulfonic acid. The calibration graph was linear in the range 0.5-40.0 micrograms cm-3 of EDTA with a slope of 21.1. The relative standard deviation at 10 micrograms cm-3 of EDTA was 1.6% (n = 10). There was no interference from most of the common ingredients of commercial foods. More than 90% of EDTA added at two levels was recovered from real samples. The method was applied to the determination of EDTA in various foods, and the results obtained were compared with those given by high-performance liquid chromatography.

Application of gas chromatography for the separate determination of free and combined sulphites in foods. I.

ZusammenfassungSchweflige Säure in Lebensmitteln — sowohl freie als auch gebundene läßt sich gaschromatographisch bestimmen.Dazu wird die freie schweflige Säure mit 0,1 m-Weinsäure, die gesamte schweflige Säure mit einem alkalischen Extraktionsmittel, das Seignettesalz und Eisen(II)-sulfat enthält, extrahiert und das SO2 aus dem Extrakt mittels Phosphorsäure freigesetzt. Das Dampfraum-Gas wird in einem Gaschromatographen mit flammenphotometrischem Detektor analysiert.Die Wiederfindungsrate von Sulfit, das getrockneter Ananas, getrockneten Aprikosen, Weiß- und Rotwein zugesetzt wurde, betrug beim freien SO2 zwischen 92,5 und 104,0%, beim gebundenen SO2 zwischen 93,5 und 98% bei einer unteren Nachweisgrenze von 0,5 ppm.SummaryA combination of head-space technique and FPD gas chromatography was applied to the separate determination of free and combined sulphite in foods.0.1 M-Tartaric acid was chosen as an excellent extractant for the selective extraction of free sulphite in the presence of combined sulphite, whilst (N) alkaline extractant containing potassium-sodium tartarate and ferrous sulphite (deoxidant) liberated free and combined sulphite completely.Sulphite was released from each solution in the following way. To 1 ml of filtered solution, 5 ml of 10% phosphoric acid was added, the mixture was shaken vigorously for 10 s kept for 10 min at 0 °C, then again shaken vigorously for 10 s. An aliquot of the head-space gas thus obtained was immediately injected into a FPD gas chromatograph.Recoveries of 10–20 ppm of free sulphite and 100–200 ppm of combined sulphite from dried pineapple, dried apricot, white and red wines were 92.5–104.0 and 93.5–98.0%, respectively, the detection limit being 0.5 ppm.

Enzymic method for the spectrophotometric determination of benzoic acid in soy sauce and pickles

A simple spectrophotometric method for the determination of benzoic acid is described. Benzoic acid is measured enzymically through its reaction with benzoate 4-hydroxylase coupled with NADPH and O2. The entire enzymic procedure required 20 min to complete. The method greatly simplifies the procedure for benzoic acid determination and permits the routine inspection of a number of samples with very little laboratory equipment. The method was compared with HPLC and satisfactory agreement was achieved.

Establishment of a modified rankine method for the separate determination of free and combined sulphites in foods. III

ZusammenfassungDie Rankine-Methode wurde bedeutend verbessert. Ein Umtausch der Aspiration mit Blasensystem trug beträchtlich zur Vereinfachung des Bestimmungsverfahrens bei, und die Reproduzierbarkeit wurde verbessert. Luft (Fließrate 1,01/min) wurde als Blasengas benutzt, da der Gebrauch von Inertgas für die Wiederfindungsrate unbedeutend ist.Natriumhydrogensulfit (freies Sulfit) und drei Arten gebundener Sulfite (Acetaldehydhydrogensulfit, Pyruvathydrogensulfit undd-Mannosehydrogensulfit) dienten dazu, die geeignetsten Bedingungen für die getrennte Bestimmung der freien und gebundenen Sulfite zu ermitteln.Freies Sulfit wurde bei 0 °C durch 30 min Durchblasen vertrieben. Hierbei ging kein gebundenes Sulîit verloren. Die Phosphorsäurekonzentration war wichtig für die Freisetzung des Sulfites. Wenn man 25%ige Phosphorsäure verwendet, werden > 99% freien Sulfites beim Durchblasen in der Kälte vertrieben, während > 99% gebundenen Sulfites durch nachheriges 10 min langes Erhitzen wiedergewonnen werden.Die modifizierte Rankine-Methode wurde weiterhin für konzentrierte Säfte verwendet.SummaryConsiderable improvements were made to the original Rankine method. Replacement of aspiration with an injection system contributed a great deal to the simplification of procedure, being accompanied with an increase in reproducibility. Air (flow rate 1.01/min) was used for injection because the use of inert gas gave little increase in recovery rate.Sodium bisulphite (free sulphite) and three kinds of combined sulphite compound (bisulphite adducts of acetaldehyde, pyruvic acid and D-mannose) were used to find the most suitable conditions for the separate determination of free and combine sulphites.Free sulphite was expelled from the sample by bubbling at 0 °C for 30 min. It was confirmed that no combined sulphite was dissociated under these conditions. The phosphoric acid concentration had an important role in the liberation of sulphite. When 25% phosphoric acid was used, more than 99% of free sulphite was expelled by cold bubbling and more than 99% of combined sulphite was recovered by heating afterwards for 10 min.The scope of the modified Rankine method was also extended to the determination of sulphite in concentrated orange juice.

Enzymic method for the determination of nitrite in meat and fish products

A simple spectrophotometric method for the determination of nitrite is described. Nitrite is measured enzymically through its reaction with nitrite reductase coupled with NADH. The entire enzymic procedure required 15 min to complete. The calibration curve was linear in the range 0.1-10 micrograms cm-3 nitrite with a slope of 6.25. The relative standard deviation at 5 microgram g-1 was 1.7% (n = 5). The method greatly simplifies the procedure of nitrite determination and enables the routine inspection of a number of samples with very little laboratory equipment. A comparison study showed that the method was superior to the GC method for samples containing large amounts of reducing substances while good agreement was achieved between both methods for other foods.

Enzymic method for the spectrophotometric determination of aspartame in beverages

A sensitive spectrophotometric method for the determination of aspartame in beverages is described. The method involves the enzymic conversion of aspartame into formaldehyde by the alpha-chymotrypsin-alcohol oxidase system, followed by the formation of a chromophore with 4-aminopent-3-en-2-one. The calibration graph was linear in the range 2.0-30.0 micrograms ml-1 of aspartame. Many common ingredients of beverages do not interfere with the proposed method. The method was applied to the determination of the aspartame content of various real samples, and the results obtained were compared with those given by high-performance liquid chromatography.

Determination of glycerol in foods by high-performance liquid chromatography with fluorescence detection

Abstract A high-performance liquid chromatographic method for the determination of glycerol in foods is described. The method involves the conversion of glycerol into formaldehyde by sequential enzymatic reactions (glycerokinase, glycerol-3-phosphate oxidase, catalase), followed by the derivatization of formaldehyde with 4-amino-3-penten-2-one. The calibration graph was linear in the range. 0.1-4.0 μg/ml of glycerol. Many common ingredients of foods did not interfere. More than 90% of glycerol added at three levels was recovered from several foods. The method is simple and accurate. The detection limit was 1.0 μg/g when 5 g of sample were assayed.

Determination of hydrogen peroxide in beverages by high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic method is described for the determination of hydrogen peroxide in beverages. The method involves the enzymatic conversion of hydrogen peroxide into formaldehyde by catalase-methanol, followed by the derivatization of formaldehyde with 4-amino-3-penten-2-one. The reaction was carried out under the flow of nitrogen, which allows the detection of hydrogen peroxide without interference from reducing substances such as ascorbic acid. More than 90% of hydrogen peroxide spiked at the 2 ppm level was recovered from several beverages. The method exhibits good linearity, accuracy and precision, and the minimum detectable level was 0.05 ppm.

Comparative determination of free and combined sulphites in foods by the modified rankine method and flame photometric detection gas chromatography. V.

ZusammenfassungEs wurde eine vergleichende Sulfitbestimmung in verschiedenen Lebensmitteln mit Hilfe der modifizierten Rankinemethode (MR), der Gaschromatographie und der Monier-Williams-Methode durchgeführt. Die Ergebnisse stimmen gut überein, wobei die Monier-Williams-Methode geringfügig höhere Werte erbrachte. Diese Methode wird durch schwefelhaltige Lebensmittelinhaltsstoffe empfindlich gestört.Des weiteren wurde in verschiedenen Lebensmitteln die Relation von freiem zu gebundenem Sulfit ermittelt. Dabei stellte sich heraus, daß in den meisten Lebensmitteln 65% des Sulfits in gebundener Form vorliegen. Sowohl MR-Methode als auch Gaschromatographie erlauben eine getrennte Bestimmung von freiem und gebundenem Sulfit. Da beide Methoden einfach und schnell durchzuführen sind, eignen sie sich für die Routinebestimmung.SummaryApplication of the modified Rankine (MR), GLC and present official Monier-Williams methods to the determination of sulphites in a variety of foods was attempted. Generally, sulphite contents determined by these three methods were in good agreement although the values obtained by the modified Monier-Wiliams method were slightly higher than by the other two. A marked interfering effect of other sulphur compounds was observed in the case of determinations by the Monier-Williams method. On the other hand, the determined sulphite values by the MR and GLC methods were independent of the coexisting sulphur compounds. The ratios of free or combined sulphites to total sulphites were compared among the two methods, and in most foods tested the rations of combined to total sulphites were not less than 65%. We conclude that both the MR and GLC methods are valid for the separate determination of free and combined sulphites in most foods, and these two methods will be preferred for routine analysis because of their simplicity and speed.

On the combination of sulphite with food ingredients (aldehydes, ketones and sugars). II.

ZusammenfassungEs wird die Darstellung der Bisulfit-Anlagerungsverbindungen von Acetaldehyd, Brenztraubensäure undd-Mannose beschrieben. Die Reinheit der gen. Verbindungen beträgt 99%.fünfAn Hand dieser Verbindungen wird überprüft, welche von fünf Standardmethoden zur Sulfitbestimmung in Lebensmitteln für die Bestimmung des gebundenen Sulfits geeignet ist. Hierbei ergeben die abgeänderte Monier-Williams-Methode, die Jodometrie und die Wasserdampfdestillation/Colorimetrie befriedigende Ergebnisse, während die Mikrodiffusion und die direkte Colorimetrie ungeeignet erscheinen.Die gen. Anlagerungsverbindungen bilden sich bei Zimmertemperatur im schwach sauren bis schwach alkalischen Milieu innerhalb kurzer Zeit. In einer äquimolaren Lösung aus Acetaldehyd bzw. Brenztraubensäure und Natriumhydrogensulfit liegt nach kurzer Zeit 50% des Sulfits als Anlagerungsverbindung vor.SummaryThree kinds of combined sulphites (bisulphite adducts of acetaldehyde, pyruvic acid and D-mannose), different in combination strength, were prepared to provide a model system for comparative studies on the accuracy of several determination methods for combined sulphites. The purity of the combined sulphites, obtained either as crystals or amorphous powder, was shown to be not less than 99%.Five methods, formerly applied on the determination of residual sulphites in foods, were subjected to the determination of these combined sulphites. A modified Monier-Williams method, iodimetry and distillation-colorimetry were effective for the determination of combined sulphite, whilst a microdiffusion method and direct colorimetry (by use of mercuric chloride) were shown to be inadequate for the determination of combined sulphite.Three combined sulphites were shown to be produced by the reaction between free sulphite and acetaldehyde, pyruvic acid or D-mannose at room temperature within a short time in the weak acid to slightly alkaline pH range. About 50% of combined sulphite were produced by the reaction of equimolar amounts of sodium bisulphite and acetaldehyde or pyruvic acid.