Multivariate optimization by exploratory analysis applied to the determination of microelements in fruit juice by inductively coupled plasma optical emission spectrometry

A method for the direct determination (without sample pre-digestion) of microelements in fruit juice by inductively coupled plasma optical emission spectrometry has been developed. The method has been optimized by a 2³ factorial design, which evaluated the plasma conditions (nebulization gas flow rate, applied power, and sample flow rate). A 1:1 diluted juice sample with 2% HNO₃ (Tetra Packed, peach flavor) and spiked with 0.5 mg L^− 1 of Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sn, and Zn was employed in the optimization. The results of the factorial design were evaluated by exploratory analysis (Hierarchical Cluster Analysis, HCA, and Principal Component Analysis, PCA) to determine the optimum analytical conditions for all elements. Central point condition differentiation (0.75 L min^− 1, 1.3 kW, and 1.25 mL min^− 1) was observed for both methods, Principal Component Analysis and Hierarchical Cluster Analysis, with higher analytical signal values, suggesting that these are the optimal analytical conditions. F and t-student tests were used to compare the slopes of the calibration curves for aqueous and matrix-matched standards. No significant differences were observed at 95% confidence level. The correlation coefficient was higher than 0.99 for all the elements evaluated. The limits of quantification were: Al 253, Cu 3.6, Fe 84, Mn 0.4, Zn 71, Ni 67, Cd 69, Pb 129, Sn 206, Cr 79, Co 24, and Ba 2.1 µg L^− 1. The spiking experiments with fruit juice samples resulted in recoveries between 80 and 120%, except for Co and Sn. Al, Cd, Pb, Sn and Cr could not be quantified in any of the samples investigated. The method was applied to the determination of several elements in fruit juice samples commercialized in Brazil.     

Analysis of Fruit Juices by Inductively Coupled Plasma-Maas Spectroscopy: Determination of Iron,Tin and Lead by Direct Aspiration

Abstract

A method has been developed for the determination of iron, tin and lead in fruit juices using inductively coupled plasma mass spectroscopy. These metals can be determined by direct aspiration of the sample after suitable dilution with water. It is not necessary to treat the sample prior to analysis.     

小型西瓜果实成熟度的无损定性判别

将与西瓜成熟度相关的10项指标,经聚类分析分为完全成熟和不完全成熟两大类,利用PCADA和PLSDA两种建模方法,通过近红外光谱分析,针对小型西瓜京秀果实成熟度进行了定性判定。其中PCADA模型的效果最好。赤道部位建模的效果优于瓜顶部位。两个模型中均有误判,且存在着共同被误判的样品,果实样品理化成分和结构的不同都会对光谱信息产生影响,从而导致误判。漫透射近红外技术在小型西瓜成熟度检测方面可以获得较好的效果。但是建立预测模型时应选择合适的光谱采集部位和建模方法。     

Use of ion chromatography for monitoring microbial spoilage in the fruit juice industry

Fruit juices and purees are defined as fermentable, but unfermented, products obtained by mechanical processing of fresh fruits. The presence of undesired metabolites derived from microbial growth can arise from the use of unsuitable fruit or from defects in the production line or subsequent contamination. This involves a loss in the overall quality that cannot be resolved by thermal treatment following the start of fermentation. With these considerations, together with microbiological control, the analysis of different metabolites, which can be considered as microbial growth markers, such as alcohols (i.e. ethanol, etc.), acids (i.e. acetic, fumaric, lactic, etc.). is fundamental in order to achieve a better evaluation of product quality. Enzymatic determination and other single-component analytical techniques are often used for the determination of these metabolites. When the microbial spoilage is not well known, this results in a long and cumbersome procedure. A versatile technique that is capable of determining many metabolites in one analysis could be helpful in improving routine quality control. For this purpose, an ion chromatographic technique, such as ion exclusion, for separation, and diode array spectrophotometry and conductivity, for detection, were evaluated. Both different industrial samples and inoculated samples were analyzed.     

A new multi-residue method for analysis of pesticide residues in fruit and vegetables using liquid chromatography with tandem mass spectrometric detection

A new multi-residue method for determination of pesticide residues in a wide variety of fruit and vegetables, using the National Food Administration (NFA) ethyl acetate extraction and determination by means of LC-MS/MS, is presented. The method includes pesticides normally detected by LC-UV or LC-fluorescence such as benzimidazoles, carbamates, N-methylcarbamates and organophosphorus compounds with an oxidisable sulphide group as well. After extraction with ethyl acetate, the extract is concentrated and an aliquot of the extract is evaporated to dryness and redissolved in methanol before injection on LC-MS/MS. The method has been validated for 57 different pesticides and metabolites. Representative species from different commodity groups were chosen as matrices in order to study the influence from different matrices on recoveries. The fortification levels studied were 0.01-0.5 mg kg(-1). Matrix effects were tested for all matrices by means of standard addition to blank extracts. The matrix effect, expressed as signal in solvent compared to signal in matrix, was in general found to be small. The obtained recoveries are, with a few exceptions, in the range 70-100%. The proposed method is quick and straightforward and no additional clean-up steps are needed. The method can be used for the analysis of all 57 pesticides in one single determination step at 0.01 mg kg(-1).     

Citric Acid Determination by Dual Wavelength Spectrophotometry

In this study, a dual wavelength spectrophotometric method was presented on the basis of Cu²⁺‐NH₃ complex decomposition by the citrate ion and the formation of Cu²⁺‐citrate complex. Sum of the absorbance decreasing at 600 nm (λ_max for Cu²⁺‐NH₃ complex) and the absorbance increasing at 750 nm (λ_max for Cu²⁺‐citrate complex) was used in quantification. This method is very selective, fast and inexpensive but relatively less sensitive. The calibration curve is linear in the range of 0.4–8 mmol/L with a detection limit of 0.13 mmol/L. The relative standard deviation (RSD%) for the six repeated determinations (2 mmol/L) is 1.75%. Interference studies of more than twenty common compounds, which are present in the studied samples, were carried out. Only oxalic and ascorbic acids are serious interferes and which interferences were eliminated by simple procedures. Finally, the proposed method was successfully applied in the determination of citric acid content in ORS powder and some fruit juices.     

Sequential fluorometric quantification of malic acid enantiomers by a single line flow-injection system using immobilized-enzyme reactors

A method for the sequential enantiomeric quantification of d-malate and l-malate by a single line flow-injection analysis was developed using immobilized-enzyme reactors and fluorescence detection. An immobilized d-malate dehydrogenase (d-MDH) reactor and an immobilized l-malate dehydrogenase (l-MDH) reactor were introduced into the flow line in series. Sample and coenzyme (NAD⁺ or NADP⁺) were injected into the flow line by an open sandwich method. d-Malate was selectively oxidized by d-MDH when NAD⁺ was injected with a sample. When NADP⁺ was injected with a sample, l-malate was oxidized only by l-MDH. NADH or NADPH produced by the immobilized-enzyme reactors was monitored fluorometrically at 455 nm (excitation at 340 nm). Linear relationships between the responses and concentrations of d-malate and l-malate were observed in the ranges of 1 × 10⁻⁶-1 × 10⁻⁴ M and 1 × 10⁻⁶-2 × 10⁻⁴ M, respectively. The relative standard deviations for ten successive injections were less than 2% at the 0.1 mM level. This analytical method was applied to the sequential quantification of d-malate and l-malate in fruit juices and soft drinks, and the results showed good agreement with those obtained using conventional method (F-kit method).