Determination of Protein Content of Raw Fresh Cow’s Milk Using Dielectric Spectroscopy Combined with Chemometric Methods

To investigate the feasibility of dielectric spectroscopy in determining the protein content of raw fresh milk, the dielectric spectra of dielectric constant and loss factor were obtained on 145 raw cow’s milk samples at 201 discrete frequencies from 20 to 4500 MHz using a network analyzer and an open-ended coaxial-line probe. It was found that in below 1000 MHz, there was positive linear relationship between the loss factor and the protein content with a coefficient of determination (R ²) greater than 0.66. In order to identify the most accurate method for determining the protein content, 97 milk samples were selected for calibration set, and the other 48 samples were used as prediction set by using joint x–y distance sample set partitioning method. The standard normal variate method was used to preprocess spectra. Ten, 152, and 7 variables were extracted as characteristic variables using successive projection algorithm (SPA), uninformative variable elimination (UVE) method based on partial least squares, and SPA after UVE (UVE-SPA) methods, respectively. The results showed that applying SPA after UVE was helpful to extract indispensible characteristic variables from full dielectric spectra. The models based on the least squares supporting vector machine (LSSVM) offered the best performance at the same characteristic variable extraction method when compared with those established by partial least squares regression and extreme learning machine. The best model for determining the protein content of milk was LSSVM-UVE-SPA with \( {R}_p^2 \) of 0.865, root-mean-square error of prediction set (RMSEP) of 0.094, and residual predictive deviation (RPD) of 2.604. The results indicate that the protein content of milk could be determined precisely by using dielectric spectroscopy combined with chemometric methods. The study is helpful to explore a new milk protein sensor which could be used in situ or online measurement.     

Determination of Melatonin in Cow’s Milk by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

The aim of the present study is the development of a rapid and accurate analytical method to determine melatonin in milk. In this method, melatonin extracted from milk with ethyl acetate, after application of reversed phase liquid chromatographic separation melatonin, was detected and quantified with tandem mass spectrometry. Performance of method was tested by conducting method validation study wherein limit of detection, limit of quantification, linearity recovery, and precision parameters were determined. Limit of detection and limit of quantification were calculated as 0.016 and 0.054 μg/kg, respectively. Recovery of the method was checked at two different concentration namely 0.5 and 2.5 μg/kg and determined as 106 and 100%, respectively. Precision of the method was determined as interday and intraday precision. Intraday precision calculated as 3.92 and 2.15% for 0.5 and 2.5 μg/kg spike levels. In this study, we describe an analytical method for determination of melatonin in milk with LC-MS/MS. This method offers an efficient, rapid, and easy sample preparation procedure with high selectivity and good sensitivity for the determination of melatonin in milk.     

Temperature-Dependent Dielectric Properties of Raw Cow’s and Goat’s Milk from 10 to 4,500 MHz Relevant to Radio-frequency and Microwave Pasteurization Process

To offer useful information for milk pasteurization with radio-frequency or microwave heating, the dielectric properties (dielectric constant and dielectric loss factor) of raw cow’s milk and goat’s milk were determined over the frequency range of 10–4,500 MHz and temperature range of 25–75 °C by a vector network analyzer and an open-ended coaxial-line probe. The mathematical models describing the relationship between permittivities and temperature were built, and the power penetration depth was investigated. The results showed that both for cow’s milk and goat’s milk, the dielectric constants decreased with an increase of frequency, and the dielectric loss factor decreased with increasing frequency below 1,000 MHz and increased after that. The dielectric constants decreased with increasing temperature at a given frequency. For raw cow’s milk, the dielectric loss factor almost increased with temperature below about 800 MHz, and decreased with temperature above that. For raw goat’s milk, the loss factor decreased with temperature in whole investigated frequency range. Quadratic equations could be used to describe the relationship between permittivities and temperature at interested frequencies with coefficient of determination higher than 0.96. The penetration depth decreased with increasing frequency. Contrasted to frequency, temperature had less effect on penetration depth. Microwave heating at 915 MHz has great potential for raw cow’s milk pasteurization, while radio-frequency heating at 27.12 and 40.68 MHz and microwave heating at 915 MHz can be used for goat’s milk pasteurization.     

Determination of Pb(II) Ions Using Novel Ion-Imprinted Polymer Magnetic Nanoparticles: Investigation of the Relation Between Pb(II) Ions in Cow’s Milk and Their Nutrition

The application of novel Pb(II) ion-imprinted polymer coated on magnetic mesoporous silica was investigated in preconcentration and determination of low level of Pb(II) ions. The job proposed a new method for preconcentration and determination of Pb(II) ions. This novel sorbent was characterized by scanning electron microscopy, thermal gravimetric/differential thermal analysis, elemental analysis, and low-angle X-ray powder diffraction. Effects of various factors such as the effects of the pH of sample solution, eluent (include type, concentration and volume), adsorption and desorption time which are effective in method efficiency, were appraised through this study. In order to investigate the selectivity of this sorbent toward Pb(II) ion, the effects of variety of foreign ions interfering on preconcentration and recovery of Pb(II) ions were also investigated. The limit of detection (LOD) was found to be 0.7 μg L^?1 and the recovery and relative standard deviation of the method were 96.6–102.4 % and 1.3–3.3 %, respectively. Validation of the outlined method was performed by analyzing several standard reference materials with certified Pb(II) concentrations. Finally, this sorbent was applied for separation and determination of Pb(II) ion in grass and cow’s milk, which showed their lead concentration to be below the detection limit of flame atomic adsorption spectroscopy.     

Front-Face Fluorescence Spectroscopy as a Rapid and Non-Destructive Tool for Differentiating Between Sicilo–Sarde and Comisana Ewe’s Milk During Lactation Period: A Preliminary Study

The objective of this study was to assess the potential of front-face fluorescence spectroscopy for differentiating between two genotypes (Comisana and Sicilo–Sarde) of ewe’s milk collected during lactation period. Physico-chemical analyses and fluorescence spectra were performed on milk samples during the first 15 weeks of lactation period. Regarding fluorescence spectra, aromatic amino acids and nucleic acids (AAA+NA), tryptophan, and vitamin A were recorded on milk samples after excitation set at 250, 290, and 322 nm, respectively. Emission spectra of vitamin A were scanned after emission set at 410 nm. Among the investigated intrinsic probes, only the principal component analysis (PCA) performed on AAA+NA allowed a good discrimination between milks produced from Comisana and those collected from Sicilo–Sarde ewes. Also, the PCA carried out on the physico-chemical parameters did not allow any discrimination between milk samples according to their genotypes. It can be concluded that emission spectra of AAA+NA could be considered as fingerprints allowing a good identification of milk samples according to ewe’s genotypes.     

Mechanism of Prevention of Aggregation of Proteins: A Case Study of Aggregation of α-Globulin in Glycerol

The precipitation of proteins due to the changes in pH has been a major limiting factor in their utility especially when the precipitation is concurrent with irreversible aggregation. In the present study, an attempt is made to see the effect of glycerol on the pH-induced aggregation of α- globulin which is the major protein fraction (11S) from Sesame (Sesamum indicum L.) seeds. A second order polynomial relation existed between the cosolvent concentration and precipitation which was prevented in presence of the cosolvent. Similarly, there was a second order polynomial relation between 8-anilino 1-naphthalene sulfonic acid (ANS) binding of the protein (as indicated by fluorescence emission at 466 nm) and the cosolvent concentration. The relative precipitation in presence of glycerol is however linearly proportional to the changes in surface hydrophobicity as seen by behavior of ANS with the protein in presence of the cosolvent. A possible role of the cosolvents in prevention of aggregation due to hydrophobicity of the protein is envisaged and the relation between the different parameters is discussed.     

Consumers’ associations with wellbeing in a food-related context: A cross-cultural study

Consumers’ perception of wellbeing in a food context can affect food choices and might provide a more holistic evaluation of products than overall liking or healthfulness scores. However, considering that wellbeing is a broad concept which lacks of a unique definition, it is necessary to explore how consumers perceive wellbeing in a food-related context. The present work aims at exploring consumers’ associations with wellbeing in a food-related context, taking into account the views of consumers from five countries: Brazil, France, Portugal, Spain and Uruguay. A total of 755 consumers were asked to complete a questionnaire comprising five open-ended questions about foods and wellbeing. The elicited terms were translated into English, coded and grouped into categories. The frequency of mention of the categories was determined and differences among countries were evaluated. In the five countries wellbeing was mainly associated with calmness, health, happiness, food products, positive emotions and satisfaction with specific aspects of life. The effects of foods on wellbeing were strongly related to physical health, pleasure and emotional aspects. Meanwhile, consumers regarded sensory characteristics, manufacturing processes, nutritional composition and context of food consumption as the main factors underlying food-related wellbeing. Vegetables, fruits, fish and seafood, meat products, grains and cereals, and dairy products were the main foods recognized as positive for wellbeing, whereas foods high in fat, salt and sugar, meat products, junk food and fried food were perceived as harmful. Significant differences among countries were identified in the frequency of mention of the categories elicited in the five questions, suggesting that culture affected consumers’ associations with wellbeing.     

Factors determining organic consumers’ knowledge and practices with respect to wild plant foods: A countrywide study in Austria

Organically-certified wild plant foods are rarely addressed in scientific or public discourses on organic food even though 30% of the world’s organically-certified land is dedicated to wild plant gathering. This oversight may leave organic consumers unaware of the market relevance of wild plant foods. The aim of this study was therefore to understand organic consumers’ attitudes, knowledge and purchasing and gathering practices with respect to wild plant foods, and how sociodemographic variables and attitudes can predict knowledge and practices. A purposive sample was drawn from 22 urban and rural food markets across Austria and 497 organic consumers were interviewed using successive freelists and four-point Likert scale questions on attitudes. Data were analysed using exploratory factor analysis and multiple linear regressions. Organic consumers knew a median of nine wild food plants, and reported five as being gathered and one as being purchased. They valued food quality and the responsible harvest of wild food plants, but assigned them a low economic relevance, with some respondents sceptical about their suitability as food. Rural residence, a higher share of organic consumption and a greater emphasis on responsible harvesting predicted knowledge and gathering of a larger number of plant species. These results confirm that organic consumers know, gather and have positive attitudes with respect to wild plant foods, although they are hardly aware about their market relevance. We argue that consumers need to be better informed about the wild origin of food ingredients and the added value of organic certification of wild plant foods.     

Bisphenol A diglycidyl ether (BADGE) migrating from packaging material ‘disappears’ in food: reaction with food components

Bisphenol A diglycidyl ether (BADGE) is widely used as a monomer for coatings and adhesives for food-contact applications. Previous publications indicate that, after migration from packaging into foodstuffs, BADGE undergoes various reactions with unidentified food components. In order to elucidate the fate of BADGE, losses were determined after incubation with different foodstuffs and food components. Food proteins were identified as the main reaction partner with BADGE. Adduct formation was found with nucleophilic side-chains of amino acids. In vitro, cysteine exhibited significant activity. The previously reported occurrence of methylthio-derivatives of BADGE in foodstuffs was shown to originate from the reaction of BADGE with methionine. BADGE-methylthio derivatives can, therefore, be used as marker substances in foodstuffs for protein reactions with BADGE. The reported results offer a new viewpoint on the evaluation of BADGE migration. The hydrolysis and hydrochlorination derivatives subject to European legislation make up only a fraction of the totally migrated BADGE, and a further concern is that the toxic or allergenic potential of the protein adducts are unknown.