红外与拉曼光谱技术对食用油掺伪检测研究进展

食用油是人们日常饮食中的必需品,因种类、产地和营养成分等因素不同而价格差异悬殊。不法商家为追求经济利益,将廉价食用油以次充好掺入优质食用油中,损害了消费者合法权益,因此研究食用油掺伪的快速检测方法至关重要。近些年,光谱技术以其简便、快速、无损、低成本等优点成为食用油掺伪的重要检测技术。文章基于近红外、中红外光谱法和拉曼光谱法的基本原理、优缺点以及互补关系,综述了近年来红外和拉曼光谱技术在橄榄油、山茶油等食用油掺伪检测中的研究进展,总结了几种光谱技术在食用油掺伪检测方面存在的问题,并对未来的检测发展方向进行了展望。     

Proteolysis in model Portuguese cheeses: Effects of rennet and starter culture

To shed further light onto the mechanisms of proteolysis that prevail throughout ripening of Portuguese cheeses, model cheeses were manufactured from bovine milk, following as much as possible traditional manufacture practices – using either animal or plant rennet. The individual role upon proteolysis of two (wild) strains of lactic acid bacteria – viz. Lactococcus lactis and Lactobacillus brevis, which are normally found to high viable numbers in said cheeses, was also considered, either as single or mixed cultures. Our experimental results confirmed the influence of rennet on the proteolysis extent, but not on proteolysis depth. On the other hand, the aforementioned strains clearly improved release of medium- and small-sized peptides, and contributed as well to the free amino acid pool in cheese.     

Application of Near and Mid-Infrared Spectroscopy to Determine Cheese Quality and Authenticity

This paper reviews the current state of development of both near-infrared (NIR) and mid-infrared (MIR) spectroscopic techniques for process monitoring, quality control, and authenticity determination in cheese processing. Infrared spectroscopy has been identified as an ideal process analytical technology tool, and recent publications have demonstrated the potential of both NIR and MIR spectroscopy, coupled with chemometric techniques, for monitoring coagulation, syneresis, and ripening as well as determination of authenticity, composition, sensory, and rheological parameters. Recent research is reviewed and compared on the basis of experimental design, spectroscopic and chemometric methods employed to assess the potential of infrared spectroscopy as a technology for improving process control and quality in cheese manufacture. Emerging research areas for these technologies, such as cheese authenticity and food chain traceability, are also discussed.     

大豆、牛奶纤维定性定量方法探讨

通过显微镜法、燃烧法以及化学溶解法,对大豆、牛奶纤维的鉴别进行了研究,并且对大豆、牛奶纤维与其他纤维混纺的织物进行了含量分析。     

Secondary structural studies of bovine caseins: temperature dependence of β-casein structure as analyzed by circular dichroism and FTIR spectroscopy and correlation with micellization

To obtain a molecular basis for the similarities and dissimilarities in the functional, chemical, and biochemical properties between β-casein and the other caseins, three-dimensional models have been presented. Secondary structural prediction algorithms and molecular modeling techniques were used to predict β-casein structure. The secondary structure of bovine β-casein was re-examined using Fourier transform infrared and circular dichroism spectroscopies to test these predictions. Both methods predict a range of secondary structures for β-casein (28–32% turns, 32–34% extended) at 25°C. These elements were highly stable from 5 to 70°C as viewed by circular dichroism. More flexible conformational elements, tentatively identified as loops, helix and short segments of polyproline II, were influenced by temperature, increasing with elevated temperatures. Another view is that as temperature decreases, these elements are lost (cold denaturation). Several distinct transitions were observed by circular dichroism at 10, 33 and 41°C, and another transition, extrapolated to occur at 78°C. Calculations from analytical ultracentrifugation indicate that the 10, 33 and 41°C transitions occur primarily in the monomeric form of the protein. As β-casein polymers are formed, and increase in size, the transitions at higher temperature may reflect changes in the more flexible conformational elements as they adjust to changes in surface charge during polymer formation. The transition at 10°C may represent an actual general conformational change or cold denaturation. Over the range of temperatures studied, the sheet and turn areas remain relatively constant, perhaps forming a supporting hydrophobic core for the monomers within the micelle-like polymer. This interpretation is in accord with the known properties of β-casein, and those predicted from molecular modeling.     

Detection of adulteration of extra-virgin olive oil by chemometric analysis of mid-infrared spectral data

This study focuses on the detection and quantification of extra-virgin olive oil adulteration with different edible oils using mid-infrared (IR) spectroscopy with chemometrics. Mid-IR spectra were manipulated with wavelet compression previous to principal component analysis (PCA). Detection limit of adulteration was determined as 5% for corn–sunflower binary mixture, cottonseed and rapeseed oils. For quantification of adulteration, mid-IR spectral data were manipulated with orthogonal signal correction (OSC) and wavelet compression before partial least square (PLS) analysis. The results revealed that models predict the adulterants, corn–sunflower binary mixture, cottonseed and rapeseed oils, in olive oil with error limits of 1.04, 1.4 and 1.32, respectively. Furthermore, the data were analysed with a general PCA model and PLS discriminant analysis (PLS-DA) to observe the efficiency of the model to detect adulteration regardless of the type of adulterant oil. In this case, detection limit for adulteration is determined as 10%.     

Preliminary investigations on the effects of ageing and cooking on the Raman spectra of porcine longissimus dorsi

The influence of ageing and cooking on the Raman spectrum of porcine longissimus dorsi was investigated. The rich information contained in the Raman spectrum was highlighted, with numerous changes attributed to changes in the environment and conformations of the myofibrillar proteins.Predictions equations for shear force and cooking loss were developed from the Raman spectra of both raw and cooked pork. Good correlations and standard errors of prediction were obtained for both WB shear force and cooking loss, with the raw and the cooked samples showing almost identical results R² = 0.77, root mean standard error of prediction (RMSEP)% of mean = 12% for shear force; R² = 0.71, RMSEP% of mean = 10% for cooking loss. The Raman spectra were also able to predict the extent of cooking that occurred within the pork (R²_val = 0.94, RMSEP% of range = 5.5%).Raman spectroscopy has considerable potential as a method for non-destructive and rapid determination of pork quality parameters such as tenderness. Raman spectroscopy may provide a means of determining changes during cooking and the extent to which foods have been cooked.     

Application of temperature-controlled attenuated total reflectance-mid-infrared (ATR-MIR) spectroscopy for rapid estimation of butter adulteration

There is a continual need for development of rapid methods that meet or exceed the detection levels of currently available analytical methods for authentication of food products. The objective of this study was to evaluate temperature-controlled attenuated total reflectance-mid-infrared (ATR-MIR) spectroscopy combined with multivariate analysis as a simple and rapid method for the determination of butter adulteration as a dairy food system. Commercial samples of butter fat were adulterated with margarine fat at levels ranging from 0% to 100% (v/v). Partial least square regression (PLSR) models gave standard error of cross-validation (SECV) of <1.2% (v/v) and correlation coefficients (r) > 0.99. Excellent predicting capabilities were obtained using an external validation set consisting of butter adulterated with margarines at ratios of 2.5%, 13%, and 45%. We have demonstrated the feasibility of a temperature-controlled ATR-MIR spectroscopy technique that would allow for rapid analysis of dairy products.     

Cluster formation and phase separation in mixtures of sodium κ-carrageenan and sodium caseinate

Mixtures of the polysaccharide κ-carrageenan (KC) and caseinate proteins (SC) from milk were investigated at pH 7 in aqueous solution using confocal scanning laser microscopy and light scattering. Phase separation was observed at higher concentrations and the phase diagram was established. In the mixtures SC was observed to form large aggregates mediated by a relatively small amount of KC. At small KC concentrations the aggregates were initially relatively small and could be characterized by light scattering. At higher KC concentrations or on longer storage at 20 °C, dense clusters with a radius of a few microns were formed that slowly precipitated. The fraction of precipitated protein increased linearly with increasing KC concentration, but was independent of the protein concentration. It increased with decreasing pH from about 20% at pH 8 to 100% at pH 5.     

Salting and the role of salt in cheese

Salt levels in cheese range from ∼0.7% (w/w) in Swiss-type to ∼6% (w/w) in Domiati. Salt has three major functions in cheese: it acts as a preservative, contributes directly to flavour, and is a source of dietary sodium. Together with the desired pH, water activity and redox potential, salt assists in cheese preservation by minimizing spoilage and preventing the growth of pathogens. The dietary intake of sodium in the modern western diet is generally excessive, being two to three times the level recommended for desirable physiological function (2.4 g Na, or ∼6 g NaCl per day). However, cheese generally makes a relatively small contribution to dietary sodium intake except if high quantities of high-salt cheeses such as Domiati and feta are consumed. In addition to these functions, salt level has a major effect on cheese composition, microbial growth, enzymatic activities and biochemical changes, such as glycolysis, proteolysis, lipolysis and para -casein hydration, that occur during ripening. Consequently, the salt level markedly influences cheese flavour and aroma, rheology and texture properties, cooking performance and, hence, overall quality. Many factors affect salt uptake and distribution in cheese and precise control of these factors is a vital part of the cheesemaking process to ensure consistent, optimum quality.     

Evaluation of the effect of salts on chemical,structural, textural,sensory and heating properties of cheese: Contribution of conventional methods and spectral ones

ABSTRACT

Chemical composition, sensory characteristics, textural and functional properties are among the most important characteristics, which directly relates to the global quality of cheese and to consumer acceptability. A number of factors including milk composition, processing conditions and salt content, influences these properties. The past decades many investigations were performed on the possibilities to reduce salt content of cheese due to its adverse health effects, the current lifestyle and the awareness of the consumers for nutrition quality products. Due to the multiple potential effects of reducing NaCl (simple reduction or substitution) on cheese attributes, it is of utmost importance to identify and understand those effects in order to control the global quality and safety of the final product.

In the present review a collection of the different results and conclusions drawn after studying the effect of salts by conventional (e.g. wet chemistry) and instrumental (e.g. spectral) methods on chemical, structural, textural, sensory and heating properties of cheese are presented.     

卷烟主流烟气及其气相成分的中红外光谱

搭建了卷烟主流烟气傅里叶变换中红外光谱检测平台,分析了4个牌号卷烟主流烟气及其气相成分的中红外光谱特征和指纹图谱。结果表明：①4个牌号卷烟主流烟气气相成分中红外光谱图的峰型、峰位相似,说明不同牌号卷烟主流烟气气相成分之间化学基团的种类相似。②卷烟主流烟气气相成分中红外光谱图在3 185~2 581 cm^-1（P＜0.05）、1 760~1 650 cm^-1（P＜0.05）和950~900 cm^-1（P＜0.01）区间存在明显差异。③卷烟主流烟气中红外光谱在3 700~3 550 cm^-1（P＜0.01）、3 185~2 581 cm^-1（P＜0.01）、1 460~1 150 cm^-1（P＜0.001）、1 080~1 040 cm^-1（P＜0.001）和950~900 cm^-1（P＜0.01）区间存在差异。④在3 740~3 730、2 387~2 383、2 293~2 280、1 768~1 718和706~694 cm^-1区间内,卷烟主流烟气气相成分的释放量高于卷烟主流烟气的释放量;在3 040~2 830、1 460~1 350、1 300~1 200、1 140~980、940~845和692~648 cm^-1区间内,卷烟主流烟气气相成分释放量低于卷烟主流烟气的释放量。该方法操作简便、重现性好,可为卷烟主流烟气光谱特征分析提供一种快速分析方法。