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

Summary Considerable 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.

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Verwendung der modifizierten Rankine-Methode zur getrennten Bestimmung von Sulfiten in Lebensmitteln. III

Zusammenfassung Die 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.

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Studies on the Analyses of Sulphites in Foods (III)     

Determination of sulfite residues in foods by using the modified rankine apparatus and HPLC]

A method for measuring sulfite residues in foods by using the modified Rankine apparatus and HPLC was developed. Sulfites released from foods by bubbling of nitrogen gas and heating for 15 minutes with an electric burner weRe absorbed in 1% triethanolamine solution and detected as sulfite ion by HPLC with a UV detector at 240 nm, using an anion exchange column, IonPac AS9-SC, with 1.8 mmol/L sodium carbonate-1.7 mmol/L sodium hydrogen carbonate solution as the mobile phase. The recoveries of sulfites added to 3 kinds of foods were 98-102%, and the determination limit was 0.001 g/kg. The sulfite values in various kinds of foods determined by the proposed HPLC method were consistent with those obtained by the alkaline titration method and the colorimetric method.     

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

Summary Application 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.

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Vergleichende Bestimmungen der freien und gebundenen Sulphite in Lebensmitteln mittels der modifizierten Rankinemethode und der Gaschromatographie mit Flammenphotometer-Detektor. V.

Zusammenfassung Es 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.

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Studies on the Analyses of Sulphites in Foods (V).     

Survey of sulphites determined in a variety of foods by the optimized Monier-Williams method.

A survey of sulphite levels in a variety of foods including dried fruit, dried mashed potatoes, shrimp, canned mushrooms and fruit juices has been conducted. The levels found ranged from 0 ppm in orange juice to 3722 ppm as sulphur dioxide in dried fruit. The foods were analysed by the optimized Monier-Williams procedure.     

The chemistry of non-enzymic browning in foods and its control by sulphites

Non-enzymic browning involves a complex of chemical reactions with few identifying common features other than the involvement of carbonylic intermediates, the production of brown pigments (melanoidins) and the effect of sulphites in either inhibiting or retarding the development of the melanoidins. In general, amine compounds (amines, amino acids, peptides, proteins) are important in reactions, usually with carbohydrates, which (a) produce highly reactive carbonylic intermediates and (b) involve condensation with these intermediates to produce highly coloured pigments. These reactions occur in many foods and, where they are undesirable, may usually be controlled more or less successfully by the addition of sulphites. This effectiveness of a single additive in controlling a variety of chemical pathways is probably due to the number of different reactions which sulphite can enter into with, for example, reducing sugars, simple carbonyls, αβ-dicarbonyls, β-hydroxycarbonyls, αβ-unsaturated carbonyls and with the melanoidins. It is known that in exerting its anti-browning effect in food, the amount of measurable sulphite decreases and there is some evidence that amongst the products derived from sulphite in a rat diet there is at least one toxic factor. Information is only recently available about the nature of some of the more stable products (e.g. sulphonated deoxyosuloses) arising from sulphite-loss and further investigation of the biological properties of these products seems necessary. With increasing concern about the total dietary intake of sulphite it is becoming more necessary to identify the uses of this additive where there is no adequate alternative and the most effective ways of employing it where it is essential in food processing; further advances in the chemistry of sulphites in relation to food will be important in achieving this.     

Determination of free,bound and total sulphites in foods by indirect photometry-HPLC

Sulphur dioxide and sodium, potassium, calcium salts of hydrogen-sulphite, disulphite and sulphite ions are extensively used as food additives for their technological efficacy and versatility. They are active as antimicrobial agents, enzyme inhibitors, antioxidants, structure modifiers, in the control of enzymatic and nonenzymatic browning reactions with stabilising and conditioning functions. In this study a modified Monier-Williams method has been utilised as a preparative procedure to obtain both the free and bound sulphite fractions. The two fractions have been analysed by HPLC with indirect photometric detection using a 250 × 4.6 mm LC-SAX column eluted with a solution of potassium hydrogen phthalate. Levels of 5–10 ppm of SO₂ in foods, corresponding to 30–60 ng injected are reliably detected by this method. The results confirm that the chromatographic method, unlike the Monier-Williams method, is able to avoid the potential interference of volatile substances derived from matrices or utilised chemicals.     

A review of sulphites in foods: analytical methodology and reported findings

Sulphites in various forms have been added to foods for centuries. Their use became an issue of concern when certain sensitive individuals exhibited adverse reactions to sulphite residues in foods. Analytical methods were developed to monitor these compounds at the regulatory limit of 10 ppm. In this report, analytical methods for determining sulphites in foods are reviewed, along with a critique of their chemistry and procedural schemes. An assessment of the key features of each method category is presented together with some comparative data. The classification scheme used is based upon the fact that determination of the sulphite content of a food is influenced more by the treatment and cleanup of the test solution than by the final determinative step. Based on a 60-year database, the Monier-Williams procedure still remains the method of choice.     

Colorimetric determination of ethylenediaminetetra-acetic acid in foods

A simple colorimetric method is described for the determination of ethylenediaminetetra-acetic acid (EDTA) in three kinds of foods. The samples were homogenized with 0.1 N-NaOH, then subjected to equilibrium dialysis against 0.02 N-NaOH. EDTA in the dialyzate was converted into a Cu-EDTA complex by the addition of CuSO4. Afterwards, this solution was subjected to the determination of both free and total (free plus complexed) copper ion. EDTA was calculated from the difference between the absorbances (477 nm) obtained with free and total copper ions. Analyses of mayonnaise, dressings and canned mushroom samples with EDTA added at the 1-mM level showed a recovery of greater than 98%.     

The use of non-hypothetical experimental markets for measuring the acceptance of genetically modified foods

The findings from a study measuring consumer acceptance of genetically modified (GM) foods are presented. The empirical data were collected in an experimental market, an approach used extensively in experimental economics for measuring the monetary value of goods. The approach has several advantages over standard approaches used in sensory and marketing research (e.g., surveys and focus groups) because of its non-hypothetical nature and the realism introduced by using real goods, real money, and market discipline. In each of three US locations, we elicited the monetary compensation consumers required to consume a GM food. Providing positive information about the benefits of GM food production, in some cases, reduced the level of monetary compensation demanded to consume the GM food.     

Detection of genetically modified organisms in foods by DNA amplification techniques

In this article, the different DNA amplification techniques that are being used for detecting genetically modified organisms (GMOs) in foods are examined. This study intends to provide an updated overview (including works published till June 2002) on the principal applications of such techniques together with their main advantages and drawbacks in GMO detection in foods. Some relevant facts on sampling, DNA isolation, and DNA amplification methods are discussed. Moreover; these analytical protocols are discuissed from a quantitative point of view, including the newest investigations on multiplex detection of GMOs in foods and validation of methods.     

On the use of the WLF model in polymers and foods.

The validity of the WLF model with fixed "universal" coefficients was tested against that of the model original form with variable coefficients using published coefficients of polymers and amorphous sugars crystallization and viscosity data. The disagreement between the two versions of the model is particularly large at temperature ranges starting about 20 to 30 degrees K above the glass transition or reference temperature, excluding the former from being a model of general applicability. Because the WLF model mathematical structure entails the existence of an almost linear region near the reference temperature, establishment of its validity as a kinetic model and meaningful determination of its constants requires data spread over an extended temperature range, especially when the experimental results have a scatter.     

Collaborative study on the use of motility enrichment on modified semisolid Rappaport-Vassiliadis medium for the detection of Salmonella from foods.

A collaborative study was performed in 15 laboratories to evaluate the use of motility enrichment on modified semisolid Rappaport-Vassiliadis (MSRV) medium for rapid Salmonella detection in a variety of food products. The results of this procedure were compared with those obtained by the cultural procedure using Rappaport-Vassiliadis (RV) broth as selective enrichment and modified brilliant green agar for selective plating. The tests were performed with Salmonella reference samples (SRS) as well as with naturally contaminated food products. When SRS were used without added food the productivity of both MSRV and RV was 96%. When SRS were combined with reference samples containing competitive bacteria the productivity was 98% for MSRV and 95% for RV. In the tests with food samples the productivity of MSRV was 92% with SRS added to food and 96% with naturally contaminated samples, while the productivity of RV was 88% and 90%, respectively. Statistical analysis showed that there was no significant difference between the procedures.     

钼蓝比色法测定保健食品中微量硒

建立了钼蓝比色法测定保健食品中微量硒的新方法。该方法最大吸收波长760nm,在0～100ng/mL浓度范围内浓度与吸光度呈线性关系,回归方程y=-4.142＋133.2x,相关系数r=0.9991,最低检测量1ng/mL,重复性好,RSD=3.17%,回收率95.98%～105.00%。该方法简便、快速、灵敏、准确,适合不同补硒类保健食品中的硒含量测定,该方法的建立有利于这类产品质量控制和提高。     

改性聚葡萄糖在低热量焙烤食品中的应用

介绍了新型原料改性聚葡萄糖在新型低热量焙烤食品中的新应用。     

Electrochemical sensing of total sulphites in beer using non‐modified screen‐printed carbon electrodes

An analytical method that combines gas‐diffusion microextraction with square‐wave voltammetric detection using commercial non‐modified screen‐printed carbon electrodes was employed in the determination of total sulphites in beer. The developed methodology showed low limits of detection (0.050 mg L⁻¹) and quantification (0.17 mg L⁻¹) and an intraday precision of 4.8%. The proposed method was also compared with a reference methodology used in the beer industry (EBC method 9.25.3) showing no significant differences in the obtained results. This is a simple, cheap and notably portable alternative for brewers that wish to quantify sulphites in their products. Copyright © 2017 The Institute of Brewing & Distilling     

A review on the use of cyclodextrins in foods

Cyclodextrins (CDs) are cyclic oligomers widely used in the food industry as food additives, for stabilization of flavours, for elimination of undesired tastes or other undesired compounds such as cholesterol and to avoid microbiological contaminations and browning reactions. In this review the characteristics of the most important CDs at industrial level (α-CD, β-CD and γ-CD) and their main properties from a technological point of view, such as solubility and their capability to form inclusion complexes are described. In addition, the present state-of-the-art on the use of these compounds in the food industry was reviewed.