Stereoisomeric flavour compounds XXXVIII: Direct chirospecific analysis of γ-lactones using on-line coupled LC-GC with a chiral separation column

Summary Chiral -lactones from the raw flavour extract of strawberries and commercially available fruit-containing products are stereoanalyzed directly by on-line coupling of liquid chromatography (LC) to gas chromatography (GC) and enantiomer separation with 2,6-di-O-pentyl-3-O-acetyl--cyclodextrin as the chiral stationary phase.     

Optimization of a single-drop microextraction procedure for the determination of organophosphorus pesticides in water and fruit juice with gas chromatography-flame photometric detection

A single-drop microextraction (SDME) procedure was developed for the analysis of organophosphorus pesticides (OPPs) in water and fruit juice by gas chromatography (GC) with flame photometric detection (GC-FPD). The significant parameters affecting the SDME performance such as selection of microextraction solvent, solvent volume, extraction time, stirring rate, sample pH and temperature, and ionic strength were studied and optimized. Two types of SDME mode, static and cycle-flow SDME, were evaluated. The static SDME procedure provided more sensitive analysis of the target analytes. Therefore, static SDME with tributyl phosphate (TBP) as internal standard was selected for the real sample analysis. The limits of detection (LODs) in water for the six studied compounds were between 0.21 and 0.56 ng/mL with the relative standard deviations ranging from 1.7 to 10.0%. Linear response data was obtained in the concentration range of 0.5-50 ng/mL (except for dichlorvos 1.0-50 ng/mL) with correlation coefficients from 0.9995 to 0.9999. Environmental water sample collected from East Lake and fruit juice samples were successfully analyzed using the proposed method, but none of the analytes in both lake water and fruit juice were detected. The recoveries for the spiked water and juice samples were from 77.7 to 113.6%. Compared with the conventional methods, the proposed method enabled a rapid and simple determination of organophosphorus pesticides in water and fruit juice with minimal solvent consumption and a higher concentration capability.     

随机森林算法的水果糖分近红外光谱测量

近年来,有关水果糖分等内部品质的近红外光谱测量方法研究很多,并有部分商业化仪器问世。但由于近红外光谱复杂多变,模型的传递性较差,往往所建模型只能针对特定品种甚至特定产地的水果。随机森林(RF)是一种基于决策树的集成算法,通过对分类回归树(CART)模型的集成来提高预测精度。相对于偏最小二乘法(PLS),多元线型回归法(MLR)等方法,随机森林回归方法对非线性数据的解析能力较强。考虑到RF模型的随机性, 通过调试决策树数量(ntree)和分裂变量数目(mtry)等变量来进行模型优选。尝试使用随机森林对不同种类的水果(苹果、梨)糖分进行预测。实验表明,对于同一种类的水果,随机森林和PLS的建模和预测结果均较好。但对于不同种类的水果,随机森林明显增加了模型的预测能力,将建模R2由PLS的0.878提高到了0.999,将建模的RMSEC由0.453降低到了0.015。经过独立的预测集样品对最优RF模型进行检验,预测R2由PLS的0.731提高到为0.888,预测RMSEP由1.148降低到0.334。随机森林在对多种水果糖分预测时,具有明显的优势。这一研究证明了随机森林有望应用于多种水果糖分的近红外光谱测定,进而解决模型的普适性和传递性问题。     

Halloysite nanotubes-titanium dioxide as a solid-phase microextraction coating combined with negative corona discharge-ion mobility spectrometry for the determination of parathion

Halloysite nanotubes-titanium dioxide (HNTs-TiO₂) as a biocompatible environmentally friendly solid-phase microextraction (SPME) fiber coating was prepared. HNTs-TiO₂ was chemically coated on the surface of a fused-silica fiber using a sol–gel process. Parathion as an organophosphorus pesticide was selected as a model compound to investigate the extraction efficiency of the fiber. The extracted analyte was detected by negative corona discharge-ion mobility spectrometer (NCD-IMS). The effective parameters on the extraction efficiency, such as salt effect, extraction temperature and extraction time were investigated and optimized. The extraction efficiency of HNTs-TiO₂ fiber was compared with bare-silica (sol–gel based coating without HNTs-TiO₂), HNTs, carbon nanotubes and commercial SPME fibers (PA, PDMS, and PDMS–DVB). The HNTs-TiO₂ fiber showed highest extraction efficiency among the studied fibers. The intra- and inter-day relative standard deviations were found to be 4.3 and 6.3%, respectively. The limit of detection and limit of quantification values were 0.03 and 0.1 μg L⁻¹, respectively. The dynamic range of the method was in the range of 0.1–25 μg L⁻¹. The spiking recoveries were between 85 (±9) and 97 (±6). The SPME–HNTs-TiO₂ combined with NCD–IMS was successfully applied for the determination of parathion in apple, strawberry, celery and water samples.     

A multi-pumping flow system for chemiluminometric determination of ascorbic acid in powdered materials for preparation of fruit juices

A multi-pumping flow-based procedure with chemiluminescent detection is proposed for the determination of ascorbic acid, AA, in fruit juices (powdered form). The method relies on the inhibitory effect of AA on the oxidation of luminol by hydrogen peroxide in alkaline medium. The system comprises several discretely actuated solenoid pumps as the only active components. It handles 100 samples per hour, and requires 96 μl of sample, 42 μg of luminol and 105 μg of potassium hexacyanoferrate(III) per determination. The analytical curve is linear up to about 11 mmol l^− 1 AA, and detection limit is 0.17 mmol l^− 1 AA. The system yields precise measurements (r.s.d. < 1%; n = 11), and recovery ranges from 94% to 106%. Results are in agreement with the reference method (AOAC) at the 95% confidence level.     

中华猕猴桃果实香气成分的GC-MS分析

采用溶液萃取法，提取“早鲜”猕猴桃果实中的香气成分，经气相色谱－质谱联机分析，鉴定出45个香气组分，占总峰面积的95．9％，其相对含量，以棕榈酸，辛酸，油酸，3－羟基丁酸乙酯，（Z，Z）－9，12－十八二烯酸，1，2，4－三羟基－（对）－萜烷，（E）－2－己烯醛，1，2－苯二甲酸双（2－甲氧基乙基）酯，硬脂酸，2－己烯醛等为主。     

喷洒植物营养素后稻米、蔬菜、水果中几种微量元素的测定

对施用新型“农药”——植物营养素后几种不同农作物的前处理方法进行了研究,提出了操怍简便、精密、准确的测定方法,为在我国建立评价施药后农作物中微量元素变化水平提供了可靠的测试手段。并通过对施药前后,农作物中锌、铜、铁三种微量元素含量的测定和比较,为植物营养素类“农药”的卫生鉴定提供了新的指标。     

基于近红外光谱的果蔬脆片品质评价方法研究

本文选取苹果脆片为研究对象,结合最新果蔬脆片研究成果和支持向量机机器学习方法,以苹果脆片近红外光谱吸收值数据样本为基础,根据不同苹果样本、不同时序的红外光谱吸收值数据特征信息,产生不同的映射关系,将红外光谱吸收值映射到对应样本在对应时刻的各项品质指标(如水分含量),然后利用支持向量机(Support Vector Machine,SVM)方法对近红外光谱吸收值的数据样本进行训练,通过调整模型参数来体现不同苹果个体间的生理差异,以取得更接近于实际情况的品质指标预测效果。模拟仿真实验表明该模型的平均相关系数(R~2)达到93.81%,均方误差(MSE)为0.0057。该研究可为果蔬脆片的评价体系提供新的参考方法。     

High-pressure (vapour + liquid) equilibria for ternary systems composed by {(E)-2-hexenal or hexanal + carbon dioxide + water}: Partition coefficient measurement

A new apparatus based on a static–analytic method assembled in this work was utilised to perform high-pressure (vapour + liquid) equilibria measurements of aqueous ternary systems. This work includes values of isothermal partition coefficients between CO₂ and water of two apple aroma constituents, (E)-2-hexenal and hexanal. Additionally, this work reports new experimental (vapour + liquid) equilibria measurements for the ternary systems (CO₂ + (E)-2-hexenal + water) and (CO₂ + hexanal + water), at fixed liquid phase composition (600 mg · kg⁻¹), at temperatures of (313, 323 and 333) K and at pressures from (8 to 19) MPa. Vapour liquid interphase was checked and monitored visually for all the systems studied in this work. No liquid immiscibility was observed at the composition, temperatures and pressures studied. In order to suggest reasonable operation conditions for fractionation of aromas with dense carbon dioxide, partition coefficients of the aroma compounds between CO₂ and water along with their separation factors from water were calculated. Partition coefficients of (E)-2-hexenal between CO₂ and water were in the range of (6 to 91) and where found to be near six times higher than those of hexanal (9 to 17). Very high separation factors from water were observed (∼10⁴) especially for (E)-2-hexenal. The highest separation factor, for both compounds, was found at a temperature of 313 K and pressures from (12 to 14) MPa.     

高光谱成像技术在果蔬品质与安全无损检测中的原理及应用

水果和蔬菜的品质与安全是消费者最为关心的问题。传统的化学检测方法是一种费时费力的破坏性检测技术。随着成像和光谱技术的快速发展,高光谱成像技术已经广泛应用于农产品品质与安全的快速无损检测中。高光谱成像技术融合了传统的成像和光谱技术的优点,可以同时获取被检测物体的空间信息和光谱信息,因此该技术既可以像检测物体的外部品质,又可以像光谱技术一样检测物体的内部品质和品质安全。目前,已经有大量的基于高光谱成像技术检测水果和蔬菜品质与安全的研究性论文发表,为了深入了解高光谱成像技术的检测原理并跟踪国内外最新的研究进展,综述了高光谱成像技术在水果和蔬菜外部品质、内部品质和品质安全检测中的原理、发展和应用。另外,还简要介绍和讨论了高光谱成像系统的构成、常用的数据分析方法、发展趋势及面临的挑战。