Masahiro Iwaida

Comparison of Two Methods and Improvements for Colorimetric Determination of Nitrite in Cod Roe

Attempts were made to develop a sensitive and reproducible method to determine nitrite in cod roe. Two diazotation-coupling reaction methods were considered; (a) the method defined by the Ministry of Health and Welfare of Japan (Method 1) and (b) the reference method of ISO (Method 2). Since the nitrite content in cod roe was much less than in meat products, Method 2 was modified to make it suitable for microanalysis at 1 ppm level as NO2. Modifications included reducing volumes of color-development solutions and making changes in the color development process, thus making the color intensity four times as great as before. Carrying out corrections with both reagent and water blanks made the effect of the blank on measured values negligible. Recoveries of nitrite at 20- and 2-ppm levels were 94.7 and 88.1%, respectively, reproducibility being ± 7 .9%, as the coefficient of variation. The obtained values by the modified method were, on the average, higher than those of the original method by 37.1%. Nitrite contents obtained by Method 1 were lower than those by the original Method 2. These low values might be attributed to loss of nitrite during extraction from the sample without pH adjustment, since the measured value showed a remarkable increase by addition of alkaline solution before extraction. Nitrite contents in imported cod roe were within the range 0.16-1.03 ppm expressed as NO2.

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.

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.

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.

Rapid Determination of Ortho- and Polyphosphates in Soft Drinks

Ortho-, poly (pyro- and higher)- and meta-phosphates can be separated from each other with two dimensional thin layer chromatography, the detection level being 1 μg as P2O5. For determination of ortho- and poly (including polymeta-)-phosphates, an ion-exchange column chromatography was used. A single concentration elution with 0.2 M potassium chloride was effective for separating of orthophosphates from polyphosphates, and the residual polyphosphates could be recovered with 6 N hydrochloric acid. This system was used for a survey of polyphosphates in 61 samples of soft drinks sold in Osaka. Results showed that the total phosphate contents within the range of 0 - 0.420 g of P2O5/kg. Only three samples contained polyphosphates. The highest being 0.261 g of polyphosphate/kg in a soft drink containing 20% mango juice.

Colorimetric microdetermination of sulphites in foods by use of the modified rankine apparatus. IV.

ZusammenfassungGeringe Sulfitmengen in Lebensmitteln (geschälte Garnelen, gezuckerte Bohnen) können colorimetrisch bestimmt werden. Die neuentwickelte Methode beruht auf einer Kombination von colorimetrischer Bestimmung mittels p-Rosanilin und der Bestimmungsmethode nach Rankine. Auf diese Weise lassen sich Gehalte von 2 μg noch genau bestimmen. Bei der Farbentwicklung wurde das giftige Quecksilbertetrachlorid durch 0.1 n-NaOH ersetzt, anstelle von Luft Stickstoff als Trägergas verwendet und somit eine Oxydation des Sulfits während der Bestimmung vermieden. Da Nitrit und Aldehyde die Farbentwicklung stören, wurde ihr Einfluß durch Dimedon und Natriumazid ausgeschaltet.SummaryDetection and determination of traces of sulphites in foods was attempted by use of the modified Rankine apparatus and pararosaniline colorimetry. Replacement of alkaline titration reported previously by pararosaniline colorimetry lowered the absolute detection limit from 30 μg (titration method) to 2 μg. In view of clean analysis, in the color developing system, 0.1 N-sodium hydroxide was used in place of mercuric chloride solution commonly used as an absorbant of sulphites. In order to prevent oxidative decomposition of sulphites during operation, nitrogen gas was used as carrier instead of air. Dimedone and sodium azide were used for the elimination of aldehydes and nitrites, respecitvely, in the sample, which will disturb the color development of sulphites with pararosaniline-formaldehyde reagents. With this improved method, it was possible to determine the residual sulphites in frozen peeled shrimps, sugared beans and other foods with low sulphite contents accurately.

Gas-liquid chromatographic determination of butylated hydroxytoluene in modified powdered milk.

A method to determine butylated hydroxytoluene (BHT) in modified powdered milk was established. After solvent extraction of fat from powdered milk, BHT was analyzed by gas chromatography. Recovery of BHT from the sample was 89.2% at 10 ppm of spiking, the detection limit being 0.1 ppm. Then an investigation was carried out on the BHT content of modified powdered milk for infants manufactured in Japan. The products manufactured to the end of 1977 contained 0.25-0.40 ppm of BHT. Throughout 1978, a campaign was carried out to avoid contact with plastics during production and manufacture; results were fruitful and the products in the first half of 1979 were quite free of BHT.

Determination of Dibromochloropropane and Related Fumigants in Citrus Fruit

A simple and systematic procedure for determination of 1,2-dibromo-3-chloropropane (DBCP), 1,3-dichloropropene (DCP), chlorobutol (TCB) and seven related compounds in citrus fruits was established. Since these compounds have extremely high volatility, the distillation apparatus for volatile oil determination was used. These compounds were trapped into cyclohexane (more than 94.2-98.4% at spiking levels of 0.5-50 ppm) by this distillation. The distillate was purified by Florisil column chromatography. All compounds except TCB were eluted with n-hexane:ether(93:7) and TCB was eluted with ether. Each eluate was injected into an ECD-gas chromatograph directly for determination. Their recoveries from lemon, orange and grapefruit were within 91.5-98.6% at the spiking levels of 0.01-1 ppm.

Fluorescence in Candies Caused by Methyl Anthranilate, a Flavoring Agent

A fluorescent substance was found in imported fruit candy. In the elution test of the fluorescent substance, it reacted in the same manner as fluorescent dyes. Further pursuit revealed that the fluorescence was derived from the grape flavor preparation added during manufacture and the fluorescence spectra of the candy and the grape flavor were quite coincident with that of methyl anthranilate. Methyl anthranilate contents in the candy and grape flavor were determined gas chromatographically to be 40.0 and 33,000 ppm, respectively, and it was calculated that the addition level of grape flavor to the candy was about 0.12%.