A simple, rapid and sensitive method for monitoring contamination of aseptically processed tomato paste

A simple, rapid and sensitive method for the detection of microbial contamination of the system of aseptically processing tomato paste has been developed. The method involves the rapid growth of any lactobacilli present in the product and detection of metabolites produced by these micro-organisms. The metabolites used are acetoin, diacetyl, carbon dioxide and lactic acid. It was found that with this method it is possible to detect the presence of both homofermentative and heterofermentative lactobacilli within 10–25 hr, depending on the level of contamination.     

A rapid,simple and sensitive fluorescence method for the assay of angiotensin-I converting enzyme

A fluorescent assay for angiotensin-I converting enzyme (ACE; EC 3.4.15.1) is described. It is based in the hydrolysis of the internally quenched fluorescent substrate o-aminobenzoylglycyl-p-nitrophenylalanylproline by the action of ACE. The fluorescence generated by the liberation of the product (the o-aminobenzoylglycine group) is read in a microtiter-plate multiscan fluorometer. The different conditions for the assay have been optimised for linearity, sensitivity and precision. Maximal enzyme activity was reached in the pH range 8.0–8.5 and 0.5–0.75 M NaCl concentration in the assay mixture. Kinetics of the enzyme reaction displayed a K_m = 109 μM, obtaining an optimal substrate concentration of 0.3 mM in the assay mixture. The assay was adequate for the study of ACE inhibition by captopril and several peptides and it also showed a very good correlation with a well-established method [Biochemical Pharmacology, 20(7) (1971) 1637]. The method has important advantages, being the availability of reagents, its simplicity and the capacity to process a high number of samples in a short time, most outstanding.     

A novel volumetric method for quantitation of titanium dioxide in cosmetics

Nowadays there are many sun‐protection cosmetics incorporating organic or inorganic UV filters as active ingredients. Chemically stable inorganic sunscreen agents, usually metal oxides, are widely employed in high‐SPF (sun protection factor) products. Titanium dioxide is one of the most frequently used inorganic UV filters. It has been used as a pigment for a long period of cosmetic history. With the development of micronization techniques, it has become possible to incorporate titanium dioxide in sunscreen formulations without the previous whitening effect, and hence its use in cosmetics has become an important research topic. However, there are very few works related to quantitation of titanium dioxide in sunscreen products. In this research, we analysed the amounts of titanium dioxide in sunscreen cosmetics by adapting redox titration, reduction of Ti(IV) to Ti(III), and reoxidation to Ti(IV). After calcification of other organic ingredients of cosmetics, titanium dioxide is dissolved by hot sulfuric acid. The dissolved Ti(IV) is reduced to Ti(III) by adding metallic aluminum. The reduced Ti(III) is titrated against a standard oxidizing agent, Fe(III) (ammonium iron(III) sulfate), with potassium thiocyanate as an indicator. In order to test the accuracy and applicability of the proposed method, we analysed the amounts of titanium dioxide in four types of sunscreen cosmetics, namely cream, make‐up base, foundation, and powder, after adding known amounts of titanium dioxide (1 ~ 25 w/w%). The percentages of titanium dioxide recovered in the four types of formulations were in the range between 96% and 105%. We also analysed seven commercial cosmetic products labelled with titanium dioxide as an ingredient and compared the results with those obtained from ICP‐AES (inductively coupled plasma‐atomic emission spectrometry), one of the most powerful atomic analysis techniques. The results showed that the titrated amounts were well in accord with the analyzed amounts of titanium dioxide by ICP‐AES. Although instrument‐based analytical methods, namely ICP‐MS (inductively coupled plasma–mass spectrometry) and ICP‐AES, are best for the analysis of titanium, it is difficult for small cosmetic companies to install such instruments because of their high cost. It was found that the volumetric method presented here gives quantitatively accurate and reliable results with routine lab‐ware and chemicals.     

Use of phytate determination for estimation of soya proteins in meat products

Phytates present in vegetable protein preparations were used to measure the degree of substitution of meat proteins by vegetable proteins. In two series of beef blends with soybean protein preparations 6–30% of meat proteins was substituted by soybean proteins. To some blends pickling solutions containing i.a. Na₄P₂O₇ were added. Phytic phosphorus was determined colorimetrically, after extraction with HCl, in raw, pasteurized, and sterilized blends both with and without addition of inorganic phosphate. In blends with no pickling solution the contents of phytic P increased linearly with increasing contents of soybean proteins and the linearity was not influenced by the heat treatment. In blends containing the pickling solution the amount of phytic P increased with increasing heat treatment conditions and with increasing amount of inorganic phosphate added. These relationships reduce the applicability of the method for practical estimation of substitution degree of meat by vegetable proteins.     

Nutritional evaluation of meat–soya bean protein product blends

The nutritive value of protein of blends consisting of meat and soya bean protein products, which replaced either 20 or 40 % of protein of meat, were determined in rat feeding experiments. Protein efficiency ratio (PER) and net protein utilisation (NPU) were significantly lower (P<0.05) in blends containing either 20% protein from soya isolate or 40% protein from soya concentrate or soya flakes than blends containing sirloin only. However, there were no significant differences in PER and NPU when model meat (consisting of 70 and 30% protein from sirloin and connective tissue, respectively) was replaced by up to 20% protein from soya isolate or up to 40% protein from soya concentrate.     

A new enzymatic method for determination of sulphite in food

A novel enzymatic method for determining sulphite is described. Using the enzyme sulphite oxidase (EC 1.8.3.1) isolated from chicken liver, sulphite is oxidised to sulphate and hydrogen peroxide is formed. This is allowed to react with reduced nicotinamide-adenine dinucleotide (NADH) in the presence of NADH-peroxidase from microorganisms (EC 1.11.1.1). The decrease of NADH, which is proportional to the concentration of sulphite, is measured photometrically.In spite of doubts about determining sulphite quantitatively according to this principle, the reaction conditions could be optimised: sulphite is oxidised in triethanolamine buffer (TEA) at pH8·0 with 40 mU/ml sulphite oxidase and 47 mU/ml NADH-peroxidase quantitatively within a period of 20 min. The precision of measurement is very high in the range 13–205 μmol sulphite/litre test solution. The coefficient of variation is found to be CV = 0·67% in a solution of 67 μmol SO₂/litre.The accuracy of the enzymatic measurements in pure aqueous sulphite solutions is confirmed by comparison with chemical determination. The correlation with the iodimetric method is R = 0.995.High specificity for sulphite is found when applying the enzymatic test described here. Carbonyl/sulphite addition compounds (e.g. those occurring in wine) are converted to sulphate and the free carbonyl compound. The majority of sulphur-containing compounds do not react in the test. Only glycosides of isothiocyanates (e.g. in mustard) are oxidised like sulphite, though more slowly.The majority of substances occurring in food do not interfere significantly with the test. Ascorbic acid influences the determination if it is present in high concentrations. Therefore, it should be removed from the sample before measuring sulphite.The method has been proven in use for a large number of foodstuffs. By using the method described here, sulphite can be determined in food rapidly and with high reliability.     

还原型谷胱甘肽简便测定法

对测定还原型谷胱甘肽-四氧嘧啶305法的改进。适合于GSH浓度介于0.02￣0.10mg/mL的样品分析,回归方程为:y=5.77x,R2=0.9970,最大误差不超过4%。该法可用于发酵液中GSH的直接测定,结果满意。     

A novel approach to the determination of soya proteins in meat products using peptide analysis

Analysis of trypsin-treated extracts from cooked meat products can be used to assess their soya protein content. The technique is based on fractionation of positively charged peptides using an automatic cation exchange amino acid analyser system. A peptide, unique to digests of soya protein, is used for quantitation purposes. Assessment of the quantitative performance is not yet complete, but results so far indicate that the lower limit of detection will be 5–10 g soya protein per 100 g total protein. The accuracy is expected to be ±5%.     

双酶水解蛋清蛋白最优工艺的研究

为优化蛋清蛋白质的酶水解条件,实验采用Alcalase~2.4LFG和Flavourzyme~500MG复合酶对蛋清蛋白进行水解,并获得了Alcalase~2.4LFG酶水解的最佳工艺条件是底物浓度(S)4.5%、pH值9.5、加酶量(E/S)5%、温度70℃、水解时间为4h。Flavourzyme~500MG酶水解的最佳工艺条件为pH值7、加酶量2%、温度50℃、时间为3h。     

A novel enzymatic method for the measurement of lactose in lactose-free products

The cover image is based on the Research Article A novel enzymatic method for the measurement of lactose in lactose-free products by David Mangan et al., DOI: 10.1002/jsfa.9317 . This cover was supported by Megazyme.

     

生物酶法制备磷脂酰丝氨酸的研究进展

近年来的研究表明,磷脂酰丝氨酸具有预防老年痴呆症、改善记忆力等功能。但是天然存在的磷脂酰丝氨酸很少,提取工艺繁杂,并且产品安全性受到人们质疑。生物酶法制备磷脂酰丝氨酸具有反应条件温和、环境友好、产品质量好等优点,近年来受到越来越多的关注。从用于生物酶法制备磷脂酰丝氨酸的酶和反应体系等方面综述了国内外生物酶法制备磷脂酰丝氨酸的相关研究进展,并指出开发稳定高效的酶制剂和探寻绿色安全的新工艺等措施有助于促进生物酶法工业化生产磷脂酰丝氨酸。     

一种热敏纸静态发色性能的检测方法

静态发色性能是热敏纸的关键性能指标,国标规定其使用的检测仪器不具备普遍性,由此导致其供应链的不同环节对静态发色性能的检测结果不能达成一致意见,造成对产品质量的投诉增多,有的甚至形成纠纷。本试验室通过大量试验,研究出一种接近标准静态发色仪的发色体系:将铜保温模块放置在普通鼓风干燥箱内,可以使热敏纸稳定饱和发色。该新方法旨在推动热敏纸静态发色性能检测的标准化,避免生产者与用户间的质量纠纷。     

A rapid, sensitive and economic method for the detection, quantification and confirmation of aflatoxins

Summary A rapid, sensitive and economic method for the detection, quantification and confirmation of aflatoxins is described. Aflatoxins B₁, B₂, G₁, and G₂, are extracted by methanol/water (85+15) and partitioned into methylene dichloride. The methylne dichloride solution is cleaned up on a polypropylene column, filled with 0.5 g silica gel 60. The aflatoxins are eluted with cloroform-acetone (90:10) and are detected using bidirectional thin-layer chromatography (TLC) with aluminium silica gel foil. The mean recovery of aflatoxins B₁, B₂, G₁, and G₂, in corn samples was 73, 78, 80, and 64%, respectively; the limit of detection was 0.5 g/kg. The results can also be confirmed by derivative formation using trifluoroacetic acid on the TLC plate. The method has been applied to a wide range of foods with good results.

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Eine schnelle, empfindliche und kostengünstige Methode zum Nachweis, zur Bestimmung und Bestätigung von Aflatoxinen

Zusammenfassung Es wird eine schnelle, empfindliche und kostengünstige Methode zum Nachweis, Bestimmung und Bestätigung von Aflatoxinen beschrieben. Die Aflatoxine B₁, B₂, G₁ und G₂ werden mit Methanol/Wasser (85+15) extrahiert und in Dichlormethan überführt. Der Dichlormethanextrakt wird auf einer mit 0,5 g Kieselgel 60 gefüllten Polypropylensäule gereinigt. Die Aflatoxine werden mit Chloroform/Aceton (90+10) eluiert und mit zweidimensionaler DC auf Kieselgel-Alufolien nachgewiesen. Die mittleren Wiederfmdungsraten für die Aflatoxine B₁, B₂, G₁ und G₂ in Maismehl betragen 73, 78, 80 und 64%, die Nachweisgrenzen liegen durchschnittlich bei 0,5 g/kg. Zur Bestätigung verdächtiger Befunde kann auf der Platte mit Trifluoressigsäure derivatisiert werden. Die Methode ist bisher an einer Vielzahl von verschiedenen Lebensmitteln mit gutem Erfolg getestet worden.

     

Determination of soya proteins in food using an enzyme-linked immunosorbent assay procedure

Classical immunoanalytical techniques are based on native antigens and their precipitation with specific antibodies: they are not very appropriate for the investigation of processed denatured mixtures. This report describes an immunoassay based on the more recent but well-established enzyme-linked immunosorbent assay (ELISA) procedure, which in this case is specific for soya proteins that have been solubilised in urea and then ?renatured’? by removing or diluting the denaturant. Levels of soya protein 100 g^?1 total protein (nominally 100%) were determined with 34 commercial soya products, using a standard reference antigen. Normal expected levels were observed with flours (average 107%) and isolates (108%), while results with concentrates (82%) and texturates (79%) were somewhat lower. Some specialised products gave little or no response, presumably because they are hydrolysed. Meat, milk, egg, wheat and field bean proteins displayed negligible interference. These preliminary results suggest that the ELISA procedure will provide a convenient general method for the qualitative characterisation and quantitative estimation of individual proteins in food products even after severe processing; it seems more attractive than many other methods reported. Immunoassay is capable of large numbers of inexpensive but sophisticated determinations of specific food components. The food analyst should regard ELISA (for the determination in situ of specific antigens in mixtures) as a powerful technique complementary to classical chromatographic and electrophoretic methods which depend on separation before determination.     

Influence of isoelectric precipitation on the solubility of soya bean proteins

The factors controlling the solubility characteristics of soya bean proteins consequent upon acid precipitation were investigated. Two processes of protein insolubilisation, fundamentally different in their effects, were identified. One, termed ?pH sensitivity’?, involved principally haemagglutinin and low molecular weight (2S) proteins, and was affected by exposure to low pH (4.5) in the presence of reducing agents; resolubilisation could be achieved by adjusting the pH to 7.6, but only at low ionic strength. The second process concerned a precipitation-induced aggregation of the globulins which was produced in the absence of, and largely eliminated in the presence of, reducing agent. In this case, complete resolubilisation was afforded by readjustment of the pH to 7.6, either by back titration or dialysis against a phosphate buffer, but was not dependent upon the presence of reducing agent. The mechanisms underlying these insolubilisation processes were concluded to be mainly of an electrostatic nature, rather than ones involving disulphide exchange reactions.     

Fluorometric method for determination of vitamin B6 in soya bean

Summary The simple fluorometric method for determination of added pyridoxine-HCl in enriched food, based on oxidation of pyridoxine to 4-pyridoxic acid by means of KMnO₄, has been modified for determination of total B₆ in soya bean. In comparison to the other fluorometric procedures, the proposed method is the simplest one, rapid and easy to perform, demanding the least time for oxidation and not using hazardous chemicals (KMnO₄ instead of KCN). Good recovery, low relative standard deviation and low total error allow the proposed procedure to be included into the group of excellent methods.

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Die fluorometrische Methode zur Vitamin B₆-Bestimmung in Soja

Zusammenfassung Die einfache fluorometrische Methode zur Bestimmung von zugegebenem Pyridoxin in angereicherten Lebensmitteln basiert auf der Oxidation des Pyridoxins mit Kaliumpermanganat zur 4-Pyridoxinsäure und wurde für die Bestimmung des gesamten Vitamin B₆ in Soja modifiziert. Im Vergleich mit anderen fluorometrischen Methoden ist die vorgeschlagene, einfach, schnell und leicht durchzuführen. Diese Methode braucht nur wenig Zeit für die Oxidation und verwendet ungiftige Chemikalien (KMnO₄ statt KCN). Die gute Wiederfindung, die geringe relative Standardabweichung und der geringe Gesamtfehler reiht das vorgeschlagene Verfahren in die Gruppe der ausgezeichneten Methoden ein.