Second order derivative spectrophotometric method for determination of vitamin C content in fruits,vegetables and fruit juices

A second-order derivative UV spectrophotometric method for determination of vitamin C [ascorbic acid (AA)] content in a variety of natural samples is described. The method is based on the measurement of a peak–baseline amplitude in the second derivative of the AA spectrum at 267.5 nm. The following corresponding regression equation was obtained within the concentration range 2×10^-5 to 1×10^-4 M AA (3.5–17.6 g/cm³ AA) in 1.0 M HCl solution: ²D_267.5=2.420×10⁴ c+0.025; the correlation coefficient was 0.9993 and the detection limit 4.2×10^-6 M. The results obtained by analysing 21 different species of fruits, vegetables and juices indicated a possibility for a more extensive application of the proposed method. This method is rapid, simple and requires no pretreatment of the analysed material, which makes it suitable for routine analyses. The reliability of the method was confirmed by comparative determinations with the generally accepted 2,6-dichloroindophenol method.     

Validation of a HPLC method for simultaneous determination of main organic acids in fruits and juices

A liquid chromatographic method for fast and simultaneous determination of tartaric, malic, ascorbic and citric acids was validated for further application to fruits and juices. Moreover, the organic acids content of commercial samples of fruits and juices were evaluated, as well as the ascorbic acid stability during the storage. Determination of organic acids was carried out using a liquid chromatograph coupled to a diode array detector, with reversed phase (C₁₈ column) and isocratic elution with 0.01 mol L⁻¹ KH₂PO₄ (pH = 2.60) mobile phase. The validation parameters showed efficiency, adequate linearity, relative standard deviation values between 0.4% and 2.3% (n = 10) for repeatability and from 1.2% to 5.0% (n = 18) for reproducibility, limits of detection (LD) were between 0.03 and 3.31 μg mL⁻¹ and quantification (LQ) were between 0.10 and 11.03 μg mL⁻¹, recovery rates were between 82% and 110%, for two levels. In addition, the method is fast (10 min) and generates low and non-toxic residues. The values found for vitamin C were about 10 times above the values declared at the package. Ready to drink juices have a composition similar to the fruit, concerning to organic acids, except for the powder juice, in which only ascorbic and citric acids were found, for all tastes. After opening the package, a decrease of 14.0% and 27.0% in ascorbic acid content was observed for orange powder and ready to drink juices, respectively.     

Bergamot: A source of natural antioxidants for functionalized fruit juices

Bergamot is a common Italian citrus fruit, cultivated almost exclusively to produce essential oils; the juice is considered a waste product, which represents a serious environmental and economic problem for the industries. The aim of this study was to re-evaluate bergamot juice through its chemical characterization and its use to enrich and fortify fruit juices. To investigate this, apples and apricots were used for the laboratory-scale production of fruit juice, following both the traditional industrial recipe and those with the addition of bergamot juice at 10% or 20%, together with or in order to replace the synthetic additives normally used in the industrial process (ascorbic acid and citric acid). The ascorbic acid content and the antioxidant activity were measured during the different steps of juice production and after storage at 37 °C for 15 days to evaluate juice shelf-life. Apricot and apple juices fortified with bergamot juice showed a significant increase in their antioxidant properties and a decreased reduction in ascorbic acid content after the typical production steps. All of the results obtained support the hypothesis that the addition of bergamot juice to juices preserves their ascorbic acid content from thermal degradation and contributes to enhance the antioxidant activity, ensuring a product much richer in antioxidants and ascorbic acid. A preliminary consumer test encouraged the production of bergamot fortified fruit juices. Finally, this is the first time that isorhoifolin and rutin have been detected in bergamot juice.     

Improved method for the determination of benzene in soft drinks at sub-ppb levels

An automated, simple, and reproducible method based on isotope dilution headspace gas chromatography/mass spectrometry developed previously for the determination of benzene in soft drinks was further improved by adding sodium sulfate to samples, lowering the gas chromatography oven starting temperature to narrow benzene peak width, and increasing sample injection volume. This improved method had a lower detection limit (0.016 µg l^?1) and good repeatability, and was used in a follow-up survey to assess benzene levels in 139 samples of soft drink products. Benzene was detected in 67% of the 139 products tested. Compared with the previous survey, the average benzene concentrations in most products from this survey were lower, and only a few products had benzene at elevated levels.     

Improved method for the determination of benzene in soft drinks at sub-ppb levels

An automated, simple, and reproducible method based on isotope dilution headspace gas chromatography/mass spectrometry developed previously for the determination of benzene in soft drinks was further improved by adding sodium sulfate to samples, lowering the gas chromatography oven starting temperature to narrow benzene peak width, and increasing sample injection volume. This improved method had a lower detection limit (0.016 µg l^-1) and good repeatability, and was used in a follow-up survey to assess benzene levels in 139 samples of soft drink products. Benzene was detected in 67% of the 139 products tested. Compared with the previous survey, the average benzene concentrations in most products from this survey were lower, and only a few products had benzene at elevated levels.     

Corrosion of aluminium in soft drinks

The corrosion of aluminium (A1) in several brands of soft drinks (cola- and citrate-based drinks) has been studied, using an electrochemical method, namely potentiodynamic polarization. The results show that the corrosion of A1 in soft drinks is a very slow, time-dependent and complex process, strongly influenced by the passivation, complexation and adsorption processes. The corrosion of A1 in these drinks occurs principally due to the presence of acids: citric acid in citrate-based drinks and orthophosphoric acid in cola-based drinks. The corrosion rate of A1 rose with an increase in the acidity of soft drinks, i.e. with increase of the content of total acids. The corrosion rates are much higher in the cola-based drinks than those in citrate-based drinks, due to the facts that: (1) orthophosphoric acid is more corrosive to A1 than is citric acid, (2) a quite different passive oxide layer (with different properties) is formed on A1, depending on whether the drink is cola or citrate based. The method of potentiodynamic polarization was shown as being very suitable for the study of corrosion of A1 in soft drinks, especially if it is combined with some non-electrochemical method, e.g. graphite furnace atomic absorption spectrometry (GFAAS).     

High performance liquid chromatographic determination of soluble carbohydrates in commercial drinks

High performance liquid chromatography was carried out to determine the soluble sugar content in canned soft drinks and commercial fruit juices stored in different types of containers. The total amount of sugars ranged from 9.2 to 13.5 g 100 ml^?1 for the soft drinks, 10 to 14 g 100 ml^?1 in fruit nectars and 3 g 100 ml^?1 in tomato juice. The individual sugar content of soft drinks varied between different batches, although the total amount remained fairly constant for each kind of drink or juice. Only in tomato juice where sucrose was not present, did the values for glucose and fructose remain constant.     

乳酸菌发酵果蔬汁的风味研究进展

风味是人的感官受食物刺激后各种感觉的综合,是消费者判断果蔬汁品质的重要指标。果蔬汁通过乳酸菌发酵可改善原有风味与品质,但存在加工工艺不成熟、风味形成机制尚不明确等问题。文章从乳酸菌发酵对果蔬汁风味的影响以及工艺优化措施等方面进行系统梳理,并对益生菌发酵果蔬饮料的发展趋势与面临的挑战提出了展望,以期为果蔬汁的深度开发、风味调控等方面提供借鉴。     

Stability of black carrot anthocyanins in various fruit juices and nectars

Fruit juices (apple, grape, orange, grapefruit, tangerine and lemon) and nectars (apricot, peach and pineapple) were coloured with black carrot juice concentrate and stability of black carrot anthocyanins in these matrices was studied during heating at 70–90 °C and storage at 4–37 °C. Anthocyanin degradation, in all coloured juices and nectars, followed first-order reaction kinetics. During heating, black carrot anthocyanins in apple and grape juices showed higher stability than those in citrus juices at 70 and 80 °C. High stability was also obtained for the anthocyanins in peach and apricot nectars at these temperatures. Black carrot anthocyanins were the least stable in orange juice during both heating and storage. During storage, degradation of anthocyanins was very fast at 37 °C, especially in pineapple nectar. Refrigerated storage (4 °C) markedly increased the stability in all samples. Activation energies for the degradation of black carrot anthocyanins in coloured juices and nectars ranged from 42.1 to 75.8 kJ mol⁻¹ at 70–90 °C and 65.9–94.7 kJ mol⁻¹ at 4–37 °C.     

Determination of patulin in fruit juices using HPLC-DAD and GC-MSD techniques

A high performance liquid chromatography with a diode-array detector (HPLC-DAD) and a gas chromatography with a mass spectrometer (GC-MSD) are described for the determination of patulin (PAT) in apple juice. The limits of detection (DL) and quantification (QL) for the HPLC-DAD and GC-MSD method were found to be (DL = 0.23 μg kg⁻¹ QL = 1.2 μg kg⁻¹) and (DL = 5.8 μg kg⁻¹ and QL = 13.8 μg kg⁻¹), respectively. The recovery factors for HPLC-DAD and GC-MSD were found to be 99.5% (RSD% = 0.73) and 41% (RSD% = 10.03), respectively. The HPLC-DAD method was used to determine the occurrence of PAT in 90 samples of fruit juices.     

Occurrence of caffeine,saccharin, benzoic acid and sorbic acid in soft drinks and nectars in Portugal and subsequent exposure assessment

A reliable method for the determination of benzoic and sorbic acids, caffeine and saccharin in soft drink and nectars using high performance liquid chromatography and UV detection was validated. The chromatographic separation was achieved with a C18 column (250 × 4.6 mm) and one buffered mobile phase, KH₂PO₄ 0.02 M/ACN (90:10)/phosphoric acid at pH 4.2. The effluent was monitored at 220 nm.     

Reduced and total glutathione and cysteine profiles of citrus fruit juices using liquid chromatography

A liquid chromatography assay for the determination of different species of glutathione and cysteine in fruit juices is described. The method is based on derivatization of thiols with 2-chloro-1-methylquinolinium tetrafluoroborate followed by chromatographic separation and UV-absorbance detection and quantitation. The method is linear in wide range of concentrations with a regression coefficient better than 0.99. The detection limits for glutathione and cysteine were 0.1 and 0.05 μmol L⁻¹, respectively. Analytical recovery and the imprecision for both analytes were in the ranges 99.1–101.3% and 2.0–9.0%, respectively. The method was successfully applied to analysis of orange and grapefruit juices for reduced and total glutathione and cysteine.     

Nonenzymatic browning of selected fruit juices affected by D-galacturonic acid

This work studies the effect of d ‐galacturonic acid (AGA) on the non‐enzymatic browning of three types of clarified concentrated fruit juices (apple, pear and peach). It was observed that the presence of AGA increases the browning of juices. This was evaluated by the evolution of the absorbance at 420 nm (A₄₂₀) with the treatment time that these juices show. The evolution at A₄₂₀ over time was fitted to first‐order kinetics and it was observed that the kinetic constant values increased with both the increase in the AGA content and the rise in the treatment. The effect of the temperature treatment on the non‐enzymatic browning of these juices was quantified by fitting the variation of the kinetic constants with the Arrehnius equation, thus obtaining the corresponding activation energies. In the case of apple juice, it was observed that for the increase in AGA content the activation energy increases considerably, while for the pear and peach juices, a slight increase of the activation energy was observed with the increase in AGA.     

Estimated intake of the sweeteners,acesulfame-K and aspartame,from soft drinks,soft drinks based on mineral waters and nectars for a group of Portuguese teenage students

In a survey of levels of acesulfame-K and aspartame in soft drinks and in light nectars, the intake of these intense sweeteners was estimated for a group of teenage students. Acesulfame-K was detected in 72% of the soft drinks, with a mean concentration of 72 mg l^?1 and aspartame was found in 92% of the samples with a mean concentration of 89 mg l^?1. When data on the content of these sweeteners in soft drinks were analysed according to flavour, cola drinks had the highest mean levels for both sweeteners with 98 and 103 mg l^?1 for acesulfame-K and aspartame, respectively. For soft drinks based on mineral water, aspartame was found in 62% of the samples, with a mean concentration of 82 mg l^?1 and acesulfame-K was found in 77%, with a mean level of 48 mg l^?1. All samples of nectars contained acesulfame-K, with a mean concentration of 128 mg l^?1 and aspartame was detected in 80% of the samples with a mean concentration of 73 mg l^?1. A frequency questionnaire, designed to identify adolescents having high consumption of these drinks, was completed by a randomly selected sample of teenagers (n = 65) living in the city of Coimbra, in 2007. The estimated daily intakes (EDI) of acesulfame-K and aspartame for the average consumer were below the acceptable daily intakes (ADIs). For acesulfame-K, the EDI was 0.7 mg kg^?1 bw day^?1 for soft drinks, 0.2 mg kg^?1 bw day^?1 for soft drinks based on mineral waters, and 0.5 mg kg^?1 bw day^?1 for nectars, representing 8.0%, 2.2%, and 5.8% of the ADI, respectively. A similar situation was observed for aspartame. In this way, the EDI for soft drinks was 1.1 mg kg^?1 day^?1, representing only 2.9% of the ADI. In respect of nectars, the EDI was 0.2 mg kg^?1 bw day^?1, representing 0.5% of the ADI. Soft drinks based on mineral waters showed the lowest EDI values of 0.3 mg kg^?1 bw day^?1, accounting for 0.7% of the ADI.     

高压液相色谱法快速测定饮料中的五种食品添加剂

目的 建立一种高压液相色谱方法同时检测饮料制品中3种甜味剂(安赛蜜、糖精钠、阿斯巴甜)和2种防腐剂(苯甲酸、山梨酸)。方法 样品采用起始流动相稀释后直接过膜分析, 色谱分离在极性修饰XAqua C18色谱柱上进行, 流动相采用50 mmol/L pH 4.5 KH2PO4和乙腈, 梯度模式洗脱, 流速2 mL/min, 柱温40 ℃, 6 min内即可完成一次分离分析, 加上4 min梯度平衡时间, 10 min内即可完成平衡及分离。结果 5种食品添加剂在0.5~50 mg/L内线性关系良好, 相关系数r2均大于0.9999。在两种饮料基质中添加50、100、150 mg/kg 3个浓度水平, 方法回收率为96.48%~105.64%, 相对标准偏差为0.21%~5.39%; 以信噪比S/N =3计算, 方法检测限为0.02~0.08 mg/L。结论 建立的分析方法快速、准确, 可满足饮料中甜味剂和防腐剂的同时检测。     

Variations in the phenolic composition of fruit juices with different treatments

 In this work we have determined the variations in the composition of phenolic compounds of natural peach and apple juice with different thermal and enzymatic treatments. The following phenolic compounds were identified and quantified in samples of treated and untreated fruit juices: cinnamic acids (caffeic, p-coumaric and ferulic acids), cinnamic derivatives (chlorogenic and p-coumarylquinic acids and feruloylglucose), flavonols (quercetin glycosides), dihydrochalcones (phloretin glycosides), flavan-3-ols [(+)-catechin and (−)-epicatechin], and procyanidins (dimer B₂, trimer C₁ and tetramer T₄). Furfural derivatives, compounds widely used as indicators of prior thermal treatment, were also studied using these samples. The results indicate that the different processes tested gave rise to a series of changes in composition that may make it possible to identify the type of treatment employed on the basis of the composition of phenolic compounds in the fruit juices. Received: 18 March 1996     

Migration measurement and modelling from poly(ethylene terephthalate) (PET) into soft drinks and fruit juices in comparison with food simulants

Poly(ethylene terephthalate) (PET) bottles are widely used for beverages. Knowledge about the migration of organic compounds from the PET bottle wall into contact media is of interest especially when post-consumer recyclates are introduced into new PET bottles. Using migration theory, the migration of a compound can be calculated if the concentration in the bottle wall is known. On the other hand, for any given specific migration limit or maximum target concentration for organic chemical compounds in the bottled foodstuffs, the maximum allowable concentrations in the polymer C _P,0 can be calculated. Since a food simulant cannot exactly simulate the real migration into the foodstuff or beverages, a worse-case simulation behaviour is the intention. However, if the migration calculation should not be too overestimative, the polymer-specific kinetic parameter for migration modelling, the so-called A _P value, should be established appropriately. One objective of the study was the kinetic determination of the specific migration behaviour of low molecular weight compounds such as solvents with relatively high diffusion rates and, therefore, with high migration potential from the PET bottle wall into food simulants in comparison with real beverages. For this purpose, model contaminants were introduced into the bottle wall during pre-form production. The volatile compounds toluene and chlorobenzene were established at concentrations from about 20–30 mg kg^?1 to 300–350 mg kg^?1. Phenyl cyclohexane was present at concentrations of 35, 262 and 782 mg kg^?1, respectively. The low volatile compounds benzophenone and methyl stearate have bottle wall concentrations of about 100 mg kg^?1 in the low spiking level up to about 1000 mg kg^?1 in the highly spiked test bottle. From these experimental data, the polymer specific parameters (A _P values) from mathematical migration modelling were derived. The experimental determined diffusing coefficients were determined, calculated and compared with literature data and an A _P′ value of 1.0 was derived thereof for non-swelling food simulants like 3% acetic acid, 10% ethanol or iso-octane. For more swelling condition, e.g. 95% ethanol as food simulant, an A _P′ value of 3.1 seems to be suitable for migration calculation. In relation to PET recycling safety aspects, maximum concentrations in the bottle wall were established for migrants/contaminants with different molecular weights, which correspond with a migration limit of 10 μg kg^?1. From the experimental data obtained using food simulants and in comparison with beverages, the most appropriate food simulant for PET packed foods with a sufficient but not too overestimative worse-case character was found to be 50% ethanol. In addition, it can be shown that mass transport from PET is generally controlled by the very low diffusion in the polymer and, as a consequence, partitioning coefficients (K _P/F values) of migrants between the polymer material and the foodstuff do not influence the migration levels significantly. An important consequence is that migration levels from PET food-contact materials are largely independent from the nature of the packed food, which on the other hand simplifies exposure estimations from PET.     

Application of a monoclonal-based immunoassay for the determination of imazalil in fruit juices

A monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of imazalil [(RS)-1-(β-allyloxy-2,4-dichlorophenylethyl)imidazole] in apple, tomato and orange juice samples. From an imazalil hapten, which mimics the analyte structure, several monoclonal antibodies were obtained. An ELISA in the conjugate-coated format was developed and optimized using the antibody showing the highest sensitivity. For standards, the detection limit of the ELISA was 0.2 nM (0.06 ng ml^-1), with an I₅₀ value of 1.6 nM (0.5 ng ml^-1). The study of the influence of matrices on assay reliability indicated that the ELISA could determine imazalil in fruit juices at the low ng ml^-1 level simply by diluting the sample, without any clean-up or concentration step. Recovery and precision of the method were evaluated by spiking juice samples with imazalil in the 10-500 ng ml^-1 range. The mean recovery from fruit juices was 97% and the mean coefficient of variation was ∼20%. In addition to being precise and accurate, the method has proved to be simple and sensitive, with a quantification limit well below the maximum residue limits for imazalil in these matrices.     

Development of an improved extraction and HPLC method for the measurement of ascorbic acid in cows' milk from processing plants and retail outlets

An improved extraction (2.5% HPO₃, 5 mm dithiothreitol) and HPLC quantification methodology using a C–18 column at 35 °C and 0.1 m acetic acid (98%) and acetonitrile (2%) mobile phase was developed to quantify total ascorbic acid (AA) in commercial whole/semi‐skim/skim raw/pasteurised/UHT milk packaged in opaque bags, transparent plastic, cardboard and Tetra Brik^?. AA content ranged from 0.21 to 10 and from 3.4 to 16 mg L^?1 in milk from retail outlets and processing plants, respectively, and was higher in organic milk. For same processor/lot samples, pasteurised milk showed higher AA content than UHT milk. This was not true for retail outlets samples. AA content was similar for whole/semi‐skim and semi‐skim/skim milk, but not for whole/skim comparisons. Among UHT samples, the AA content trend was whole<semi‐skim<skim and lower for UHT milk in opaque plastic and Tetra Brik^? container. After 14 days at 4 °C in the dark, AA losses ranged 35–83% depending on milk type and preservation method with a higher AA retention in unopened containers.     

果汁饮料中合成色素检测方法的改进

目的:本实验通过对国标中合成色素检测前处理方法的改进,考察了吸附解吸装置、洗脱剂中氨水比例、聚酰胺粉用量、旋转蒸发温度对实验结果的影响,建立了测定果汁饮料中柠檬黄、日落黄的HPLC检测方法.方法:样品经聚酰胺粉吸附,甲醇—甲酸溶液除去天然色素,乙醇—氨水—水混合溶液(5:4:1)洗脱,70℃旋干溶液,复溶后经C18液相色谱柱分离,甲醇-0.02mol/L乙酸铵溶液(pH=4)梯度洗脱,紫外检测器检测.结果:柠檬黄的检出限为0.2mg/kg,日落黄的检出限为0.3mg/kg.柠檬黄和日落黄的回收率均＞99.0％.结论:该方法稳定性好、回收率高、适用范围广,可用作复杂基质中多种合成色素的同时检测.