近红外光谱分析技术在水果品质无损检测上的应用

近红外光谱分析技术具有快速、非破坏性、低成本及同时测定多种成分等特点,在很多领域得到广泛应用。本文简介了近红外光谱技术的检测原理,指出其检测优点和不足。综述了国内外将近红外光谱技术应用于水果品质无损检测方面的研究进展,并对利用近红外光谱技术进行水果品质无损检测的研究前景进行了展望。     

果皮厚度对水果组织中光传输特性的影响

水果产品品质检测技术在水果的生产和消费中起着十分重要的作用。利用水果产品的光学特性进行无损检测是水果品质无损检测与分级技术中最实用的和最成功的技术之一。深入研究光在水果组织中的输运规律,对于水果产品品质的光学检测有着十分重要的意义。本文以仁果类薄皮水果苹果和厚皮水果柑橘为例,建立果皮和果肉两层组织模型,利用蒙特卡罗法模拟了808 nm的波长下高斯光束在水果组织中传输的光学特性,揭示了水果果皮厚度对光在组织中的传输特性如漫反射率、透射率、内部吸收率和穿透深度等特性的影响,分析了果肉组织的检测效率。研究结果表明,果皮越厚,透射率和穿透深度越小,果皮比果肉的光吸收能量密度在径向距离上的分布范围更广,随着水果组织内部深度的增加,光吸收能量密度逐渐减小,径向方向减弱的更快。而对于漫反射率,在径向距离0.2～1.2 cm之间,果皮越薄漫反射率越小,在1.2～4.0 cm之间,果皮越厚漫反射率越小。此研究结果表明在用光学检测方法对水果进行无损检测和分级时,无论是透射或反射测量,果皮厚度和光束的相互作用都不应忽视,也为不同类型的水果产品设计更为有效的光学检测装置(如光源的强度、检测器的大小以及位置等)提供了理论基础,对于水果产品品质的光学检测有着十分重要的意义。     

烟用香料无花果提取物的热裂解产物研究

为了评价无花果提取物在卷烟加料中的使用效果,采用热裂解-气相色谱-质谱联用(PY-GC-MS)方法对无花果提取物的热裂解产物进行剖析.结果表明无花果提取物热裂解后产生大量醛类、酮类和呋喃类物质,这些物质是构成卷烟香味的重要成分,能有效改善卷烟吸味.     

Analysis of pesticide residues in fruit and vegetables by matrix solid phase dispersion (MSPD) and different gas chromatography element-selective detectors

Summary A comparison between different element selective detectors for the determination of organophosphorus and organochlorine pesticide residues, from fruit and vegetables, was performed by capillary GC with electron capture detector (ECD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD) in the sulphur and phosphorus modes, and mass spectrometry detector (MSD) in selected ion monitoring (SIM) mode. Pesticides were extracted from the different foodstuffs by Matrix Solid Phase Dispersion (MSPD). Recoveries of 41–108 % with relative standard deviation of 2–14 % in the concentration range 0.5–10 μg L⁻¹ were obtained in oranges, lemons, grapefruit, pears, plums, lettuces and tomatoes. The results demonstrated that the extracts of all the samples can be analyzed by the detectors used since no interfering co-extracted compounds were detected.     

Fluorimetric kinetic method for the determination of total ascorbic acid with o-phenylenediamine

A fluorimetric reaction-rate method for the determination of L-ascorbic acid (AA) in aqueous solution is presented. The technique is based on the rapid oxidation of AA by mercury(II) chloride to dehydro-L-ascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The formation of the product is monitored fluorimetrically with a data acquisition system based on a microcomputer, a voltage-to-frequency converter and a timer-counter board. The initial rate is estimated with a fixed-time computational method. With a 20-s measurement time (after a 5-s delay from initiation of the reaction), the detection limit for AA is 0.02 μg ml^?1 with a linear dynamic range extending to 10 μg ml^?. The procedure is applied to the determination of the AA in vitamin pills and juice. The relative standard deviation is 1.9% or better.     

Functional poly(carboxybetaine methacrylate)coated paper sensor for high efficient and multiple detection of nutrients in fruit

Rapid and simultaneous in situ detection of multi-components is extremely crucial for the real-time monitoring of nutrients in fruits.Herein,a facile and user-friendly poly(carboxybetaine methacrylate)-coated paper-based microfluidic device(pCBMA-μPAD) has been exploited to synchronously identify and semi-quantify vitamin C. glucose,sucro se and fructose in fruits.The pCBMA was successfully grafted from the surface of paper sensor using a co nvenient and robust method,which was confirmed by Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectrometry(XPS).The superior hydrophilicity and ultra-low fouling of pCBMA endowed the pCBMA-μPAD with remarkably rapid response(3 min),high sensitivity,good linear relationship and low detection limit(LOD)(vitamin C:y=33.809+5.175 x,R~2=0.993,LOD=0.179 mmol/L;glucose:y=-0.113+30.0661 g(x),R~2=0.988,LOD=0.095 mmol/L;sucrose:y--5.334+34.858 lg(x),R~2=0.996,LOD=0.097 mmol/L;fructose:y=4.996+23.325 lg(x),R~2=0.994,LOD=0.140 mmol/L).Furthermore,satisfactory results were yielded in the detection of these nutrients in 9 fruits,which were much agreed well with those obtained by spectrophotometry.Such a portable and versatile pCBMA-μPAD will pro foundly shape the future of food analysis,especially for the assessment of food quality and nutrition in the process of agricultural production and marketing.     

Optimization of a new mobile phase to know the complex and real polyphenolic composition: towards a total phenolic index using high-performance liquid chromatography

An HPLC method is reported for the separation and quantification of five major polyphenolic groups found in fruits and related products: single ring phenolic acids (hydroxybenzoic acid and hydroxycinnamic acid derivatives), flavan-3-ols, flavonols, anthocyanins, and dihydrochalcones. A binary mobile phase consisting of 6% acetic acid in 2 mM sodium acetate aqueous solution (v/v, final pH 2.55) (solvent A) and acetonitrile (solvent B) was used. The use of sodium acetate was new and key to the near baseline separation of 25 phenolics commonly found in fruits. A photodiode array detector was used and data were collected at four wavelengths (280, 320, 360, and 520 nm). This method was sensitive and gave good separation of polyphenolics in apple, cherry, strawberry, blackberry, grape, apple juice, and a processing by-product. The improved separation has led to better understanding of the polyphenolic profiles of these fruits. Individual as well as total phenolic content was obtained, and the latter was close to and correlated well with that obtained by the Folin-Ciocalteu method (FC). The HPLC data can be used as a total phenolic index (TPI) for quantification of fruit phenolics, which is advantageous over the FC because it has more information on individual compounds.     

Comparison of indices and multivariate models to non-destructively predict the fruit chlorophyll by means of visible spectrometry in apple fruit

Non-destructive, rapid, instrumental tools in fruit production are required for predicting the optimum harvest window and monitoring fruit quality during shelf life. The degree of chlorophyll degradation is a sensitive indicator for fruit maturation and ageing. Adequate indices for chlorophyll prediction by means of non-destructive spectral analysis have been studied in the fields of photosynthesis research and remote sensing developments. However, an evaluation of these indices and multivariate linear regression models does not exist so far for predicting the fruit chlorophyll content.Spectral transmittance recordings in the visible wavelength range were carried out on apple fruit Malus domestica Borkh. ‘Elstar’ (n=99) and ‘Jonagold’ (n=117). The fruit chlorophyll a content of ‘Elstar’ apples was measured wet-chemically and predicted by means of the specific indices: NDVI, Tr₆₉₈/Tr₇₆₀, red-edge, TrII on Tr′(λ), TrII, and RVSI with the correlation coefficients of determination R²=0.84, 0.81, 0.75, 0.81, 0.15, and 0.67, respectively. Partial least-squares (PLS) calibration models were built using calibrated spectra (630-730 nm), first derivative of spectra and second derivative of spectra yielding multivariate correlation coefficients of determination R²=0.81, 0.86, and 0.92, respectively. Similar results were found for ‘Jonagold’ apple fruit. Linear regression of indices and PLS calibration models were empirically tested on the chlorophyll a content of apple fruit measuring the same cultivars grown in a different seasons and growing locations. In the case of ‘Elstar’ apple fruit, correlation coefficients of fruit chlorophyll a content analysed wet-chemically as well as fruit maturation measured as calendar weeks were similar to those in the calibration experiment. Application of linear regression equations of indices and PLS models on spectra of ‘Jonagold’ apple fruit led to less accurate results for those methods, which use wavelengths above 720 nm as indicative range.     

Divalent pairing ion for ion-interaction chromatography of sulphonates and car☐ylates

An ion-interaction method for the simultaneous separation and UV detection of compounds with weak or strong ionic groups, using a divalent cationic ion pair reagent, namely hexamethonium bromide, has been studied and developed. The analytes considered were tartaric, fumaric, pyruvic, maleic, phthalic, benzoic, sorbic, 4-hydroxybenzoic, benzene and toluene-4-sulphonic acids, and they were chosen for their practical importance. The chromatographic optimization for their separation has been achieved by varying eluent composition (methanol, NaCl and hexamethonium concentrations) and studying the performance of different stationary phases (octyl- and octadecyl-silica based columns). The method developed has been successfully applied to benzoate and sorbate determination in orange juices.