Mapping of ice cream formulation using front-face fluorescence spectroscopy

Competitive displacement of sodium caseinate by low-molecular-weight emulsifiers and the effects on emulsion texture and rheology

Low-molecular-weight (LMW) emulsifiers are used to promote controlled destabilization in many dairy-type emulsions in order to obtain stable foams in whippable products. The relation between fat globule aggregation induced by three LMW emulsifiers, lactic acid ester of monoglyceride (LACTEM), saturated monoglyceride (GMS), and unsaturated monoglyceride (GMU) and their effect on interfacial protein displacement was investigated. It was found that protein displacement by LMW emulsifiers was not necessary for fat globule aggregation in emulsions, and conversely fat globule aggregation was not necessarily accompanied by protein displacement. The three LMW emulsifiers had very different effects on emulsions. LACTEM induced shear instability of emulsions, which was accompanied by protein displacement. High stability was characteristic for emulsions with GMS where protein was displaced from the interface. Emulsions containing GMU were semisolid, but only low concentrations of protein were detected in the separated serum phase. The effects of LACTEM, GMS, and GMU may be explained by three different mechanisms involving formation of interfacial α-gel, pickering stabilization and increased exposure of bound casein to the water phase. The latter may facilitate partial coalescence. Stabilizing hydrocolloids did not have any effect on the LMW emulsifiers' ability to induce protein displacement.

Structural changes of soy proteins at the oil-water interface studied by fluorescence spectroscopy

Fluorescence spectroscopy was used to acquire information on the structural changes of proteins at the oil/water interface in emulsions prepared by using soy protein isolate, glycinin, and β-conglycinin rich fractions. Spectral changes occurring from differences in the exposure of tryptophan residues to the solvent were evaluated with respect to spectra of native, urea-denatured, and heat treated proteins. The fluorescence emission maxima of the emulsions showed a red shift with respect to those of native proteins, indicating that the tryptophan residues moved toward a more hydrophilic environment after adsorption at the interface. The heat-induced irreversible transitions were investigated using microcalorimetry. Fluorescence spectroscopy studies indicated that while the protein in solution underwent irreversible structural changes with heating at 75 and 95°C for 15 min, the interface-adsorbed proteins showed very little temperature-induced rearrangements. The smallest structural changes were observed in soy protein isolate, probably because of the higher extent of protein-protein interactions in this material, as compared to the β-conglycinin and to the glycinin fractions. This work brings new evidence of structural changes of soy proteins upon adsorption at the oil water interface, and provides some insights on the possible protein exchange events that may occur between adsorbed and unadsorbed proteins in the presence of oil droplets.

Classification of Sherry vinegars by combining multidimensional fluorescence, parafac and different classification approaches

Sherry vinegar is a much appreciated product from Jerez-Xérès-Sherry, Manzanilla de Sanlúcar and Vinagre de Jerez Protected Designation in southwestern Spain. Its complexity and the extraordinary organoleptic properties are acquired thanks to the method of production followed, the so-called "criaderas y solera" ageing system. Three qualities for Sherry vinegar are considered according to ageing time in oak barrels: "Vinagre de Jerez" (minimum of 6 months), "Reserva" (at least 2 years) and "Gran Reserva" (at least 10 years). In the last few years, there has been an increasing need to develop rapid, inexpensive and effective analytical methods, as well as requiring low sample manipulation for the analysis and characterization of Sherry vinegar. Fluorescence spectroscopy is emerging as a competitive technique for this purpose, since provides in a few seconds an excitation-emission landscape that may be used as a fingerprint of the vinegar. Multi-way analysis, specifically Parallel Factor Analysis (PARAFAC), is a powerful tool for simultaneous determination of fluorescent components, because they extract the most relevant information from the data and allow building robust models. Moreover, the information obtained by PARAFAC can be used to build robust and reliable classification and discrimination models (e.g. by using Support Vector Machines and Partial Least Squares-Discriminant Analysis models). In this context, the aim of this work was to study the possibilities of multi-way fluorescence linked to PARAFAC and to classify the different Sherry vinegars accordingly to their ageing. The results demonstrated that the use of the proposed analytical and chemometric tools are a perfect combination to extract relevant chemical information about the vinegars as well as to classify and discriminate them considering the different ageing.

Front face fluorescence spectroscopy and visible spectroscopy coupled with chemometrics have the potential to characterise ripening of Cabernet Franc grapes

The potential of front-face spectroscopy for grape ripening dates discrimination was investigated on Cabernet Franc grapes from three parcels located on the Loire Valley and for six ripening dates. The 18 batches were analysed by front-face fluorescence spectroscopy and visible spectroscopy. The excitation spectra (250-310nm, emission wavelength=350nm) were characterised by a shoulder at 280nm. Grapes spectra were classified by factorial discriminant analysis (FDA). Ripening dates were well predicted by fluorescence spectra: grapes before veraison were separated from grapes after veraison and almost every ripening date was identified. The common spectroscopic space obtained by CCSWA showed that wavelengths corresponding to anthocyanin absorption in the visible were correlated to fluorescence wavelengths around the starting and ending points of the shoulder (263 and at 292nm). Then, regression models were investigated to predict total soluble solids (TSS), total acidity, malvidin-3G, total anthocyanins and total phenolics content from visible and fluorescence spectra. To predict technological indicators (TSS and total acidity), the PLS model with visible spectra (RMSECV=0.82 degrees Brix or 0.96gL(-1) H(2)SO(4)) was better than those with fluorescence one (RMSECV=1.39 degrees Brix or 2.06gL(-1) H(2)SO(4)). For malvidin-3G and total anthocyanins, all R(c)(2) and R(cv)(2) were superior to 0.90 and RMSECV were low. Visible and fluorescence spectroscopies succeeded in predicting anthocyanin content. Concerning total phenolic, the best prediction was provided by fluorescence spectroscopy.

Interactions between bovine beta-lactoglobulin A and various bioactive peptides as studied by front-face fluorescence spectroscopy

Front-face fluorescence spectroscopy was used for the first time to study the interactions between bovine beta-lactoglobulin variant A (beta-Lg A) and various beta-Lg-derived bioactive peptides. Fluorescence spectra were recorded for beta-Lg A-peptide mixtures at 25 degrees C and pH 6.8 with an excitation wavelength of 290 nm to characterize the molecular environment of tryptophan (Trp) residues present in the protein but absent in the peptides. Spectra remained unchanged following addition of peptides beta-Lg f92-100 and beta-Lg f125-135, while Phe-Phe interaction between beta-Lg f69-83 molecules interfered with analysis. Addition of beta-Lg f102-105 produced a blue shift (3 nm) and a significant increase in fluorescence intensity, while addition of beta-Lg f142-148 also caused a significant increase in fluorescence intensity but accompanied by a red shift (3 nm). These results indicate that the polarity of the Trp environment in the beta-Lg A structure may be modified differently depending on the peptide added.