Ivonne Delgadillo

Application of chemometrics to the 1H NMR spectra of apple juices : discrimination between apple varieties

Discrimination between apple juices produced from different varieties (Spartan, Bramley, Russet) has been achieved by applying principal components analysis (PCA) and linear discriminant analysis to 1H NMR spectra of the juices. The use of covariance and correlation matrix PCA methods was investigated and different regions of the spectrum were analysed in view of the large range of signal intensities. All the methods gave a high success rate of classification, with at least 24 out of 26 samples being correctly assigned when five principal components were used. Under optimum conditions a 100% success rate was achieved. Examination of the principal component loadings showed that the levels of malic acid and sucrose were two important chemical variables, but variations in the composition of the minor constituents were also found to make a significant contribution to the discrimination.

FTIR SPECTROSCOPY AS A TOOL FOR THE ANALYSIS OF OLIVE PULP CELL-WALL POLYSACCHARIDE EXTRACTS

Abstract The sequential extraction of olive pulp cell-wall material (CWM) and its subsequent fractionation by ethanol precipitation and anion-exchange chromatography gave a wide range of cell-wall polysaccharide fractions, characterised by sugar analysis. Several multivariate procedures, such as principal component analysis (PCA), trimmed object projections (TOP), canonical correlation analysis (CCA), and partial least squares regression (PLS), were applied to their FTIR spectra, in the region between 1200 and 850 cm−1. The combination of these chemometric techniques along with the chemical information allowed the type of polymers present to be distinguished: pectic polysaccharides rich in uronic acid, pectic polysaccharides rich in arabinose, arabinose-rich glycoproteins, xyloglucans, and glucuronoxylans. It was also possible to highlight the most important and characteristic wavenumbers for each type of polymer present. A calibration model for the quantification of xylose residues of the hemicellulosic polysaccharides was proposed. The high diversity of samples used and their characteristic features allowed models to be obtained, using a very expeditious methodology, that represent a realistic description of the olive pulp cell-wall polymers.

Isolation and Analysis of Cell Wall Polymers from Olive Pulp

The olive tree (Olea europaeia) is native to countries having a Mediterranean climate (Fernandez-Diez 1971, 1983). Olive fruit is a drupe, i.e. a meaty stone fruit (Rommani and Jennings 1971), and is usually an elongated spheroid. Depending on the variety, the weight of the fruit may vary from 3 to 10 g. During ripening, the colour changes from green to purple or black. The pulp is very bitter, especially during maturation, and comprises between 70 to 90% of the fruit, the bitter taste is due to the presence of a substantial quantity of phenolic compounds (Amiot et al. 1986; Vlahov 1992). The mature seed is very tough and elongated. The olive fruit is rich in oil which originates from the pulp; most cultivated olives have an oil content of 22% by fresh weight (Kiritsakis and Markakis 1987). The fruit is the raw material for a variety of products including olive oil and table olives. The preparation of table olives is a complex industrial process which involves fermentation and/or alkali treatment (Fernandez-Diez et al. 1985). The pulp of the olive fruit is composed of different tissue types (Fig. 1) and there is a paucity of information on the cell walls of these tissues. A knowledge of the structure and chemical composition of olive cell walls is crucial for a better understanding of the biochemical changes that occur in olives during growth, maturation and processing. This chapter describes methods that can be used for the isolation of relatively pure cell walls from olive pulp and the extraction of cell wall polysaccharides by methods that cause minimum degradation. For detailed structural studies, cell wall material virtually free of intracellular compounds is required. However, for certain practical purposes, an alcohol-insoluble residue (AIR) may suffice, provided the limitations of the preparation are borne in mind. The methods used for the separation and characterization of the polymers are described briefly, with particular reference to some of the more recent developments. The experimental details described below are mainly based on our work on the isolation analysis of cell walls of olive pulp (Coimbra 1993; Coimbra et al. 1994).

13C solid-state nuclear magnetic resonance and Fourier transform infrared studies of the thermal decomposition of cork

The thermal decomposition of cork has been studied by Fourier transform infrared (FTIR) spectroscopy and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy with cross-polarization and magic-angle spinning (CP-MAS), high-power 1H decoupling (HPDEC) and cross-polarization depolarization-polarization (CPDP). Waxes and other soluble components of cork begin to decompose at ca. 150 degrees C. This is accompanied by partial decomposition of suberin, probably initiated at the points of attachment to the cell wall. The carbohydrates begin to decompose at ca. 200 degrees C. The decomposition of lignin begins at 250-300 degrees C, while suberin undergoes further degradation. Significant amounts of coke are formed in the process. At 400 degrees C cork has been transformed into coke with traces of partially decomposed suberin. The thermal decomposition of cork is dependent on the calcination time, particularly in the 200-350 degrees C range.

Microorganisms under high pressure — Adaptation, growth and biotechnological potential

Hydrostatic pressure is a well-known physical parameter which is now considered an important variable of life, since organisms have the ability to adapt to pressure changes, by the development of resistance against this variable. In the past decades a huge interest in high hydrostatic pressure (HHP) technology is increasingly emerging among food and biosciences researchers. Microbial specific stress responses to HHP are currently being investigated, through the evaluation of pressure effects on biomolecules, cell structure, metabolic behavior, growth and viability. The knowledge development in this field allows a better comprehension of pressure resistance mechanisms acquired at sub-lethal pressures. In addition, new applications of HHP could arise from these studies, particularly in what concerns to biotechnology. For instance, the modulation of microbial metabolic pathways, as a response to different pressure conditions, may lead to the production of novel compounds with potential biotechnological and industrial applications. Considering pressure as an extreme life condition, this review intends to present the main findings so far reported in the scientific literature, focusing on microorganisms with the ability to withstand and to grow in high pressure conditions, whether they have innated or acquired resistance, and show the potential of the application of HHP technology for microbial biotechnology.

Study of the influence of micro-oxygenation and oak chip maceration on wine composition using an electronic tongue and chemical analysis

The influence of micro-oxygenation (MOX) and maceration with oak chips treatments on wine was studied on wine samples from three vintages produced in the Yarra Valley, Australia. A full factorial design was employed where two factors (MOX and oak chips treatments) had two levels and one factor (vintage) had three levels. Three replicated treatments were run for each factors setting. Wine samples were analysed using conventional laboratory methods with respect to the phenolic wine compounds and colour attributes since the phenolic fraction of wine is most affected by both MOX and oak maceration treatments. The same wine samples were measured with an electronic tongue based on potentiometric chemical sensors. The significance of treatments and vintage effects on wine phenolic compounds was assessed using ANOVA and ANOVA-Simultaneous Component Analysis (ASCA). Cross-validation was used for the ASCA sub-model optimisations and permutation test for evaluations of the significance of the factors. Main effects of vintage and maceration with oak chips were found to be significant for both physicochemical and the ET data. Main effect of MOX treatment was also found significant for the physicochemical parameters. The largest effect on the phenolic composition of wine was due to its vintage, which accounted for 70% and 33% of total variance in the physicochemical and ET data respectively. The ET was calibrated with respect to the total phenolic content, colour density and hue and chemical ages 1 and 2 and could predict these parameters of wine with good precision.

Use of FT-IR spectroscopy to follow the effect of processing in cell wall polysaccharide extracts of a sun-dried pear

The sun-dried pear is a traditional Portuguese food product with unique organoleptic characteristics. In order to understand the modifications that occur during the drying process, cell wall extracts were prepared from dried and fresh tissues. Cell wall polymers were solubilised from the CWM by sequential extraction with aqueous solutions of CDTA, Na 2 CO 3 . and KOH, with increasing strengths, to leave the cellulosic residue. The polysaccharides present in the different extracts were characterised by sugar analysis and by FT-IR spectroscopy in the region between 1200 and 850 cm -1 . The spectra analysis followed by chemometrics allowed us to distinguish the fresh from the sun-dried pear extracts in CDTA, Na 2 CO 3 , and KOH precipitates. These extracts contain pectic polysaccharides rich in GalA and Xyl-rich hemicellulosic polysaccharides (xylans). The selection of the most important wavenumbers allowed us to identify the spectral region related to GalA in pectic polysaccharide extracts in the range between 1120 and 990 cm -1 . This study shows the potential of the FT-IR spectroscopy and multivariate information in the discrimination of cell wall extracts from dried and fresh pears.

Evidence of ferroelectricity and phase transition in pressed diphenylalanine peptide nanotubes

Self-assembled peptide nanotubes (PNT) are unique nanoscale objects having a great potential for a multitude of applications. Strong piezoactivity and polar properties in aromatic dipeptides were recently observed in stand-alone nanotubes using piezoresponse force microscopy and 2nd harmonic generation. In this work, we report macroscopic dielectric and polarization vs. field measurements on pressed PNTs before and after annealing at 150 °C. The results corroborate nanoscale study and present a clear evidence of ferroelectric-like behaviour and phase transition in this technologically important material. The dielectric constant of PNT pellets obeys apparent Curie-Weiss (CW) law with the CW constant C ≈ 230 °C and transition temperature at T ≈ 142 °C.

HIGH-FIELD PROTON NMR STUDIES OF APPLE JUICES

High‐field (11.7 and 14 T) proton high‐resolution NMR spectra of apple juices obtained from a variety of cultivars are reported and partial spectral assignments are made. There are significant spectral differences between cultivars, which may be of value in identifying the origins of apple juices. The results also indicate that the method is likely to be of value in the authentication of fruit juices. Careful spectral analysis shows that some differences arise simply as a result of the differences in the pH of the juices and that microbiological and oxidative effects must be taken into account. Care must therefore be exercised in the application of multivariate methods to the data as spurious or trivial correlations may be obtained. It is concluded that the richness of the spectra and the ease with which they may be obtained indicate that high‐field proton NMR will prove valuable not only in speciation and authentication studies, but also in the analysis of biochemical changes occurring in fruits and their juices.

Characterization of kafirin and zein oligomers by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Quantitative and qualitative analysis of uncooked zein and kafirin fractions were performed through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and electrophoretic profiles. Kafirins and zeins present the same oligomer and monomer compositions with the exception of a 66 kDa oligomer that is only present in kafirins. The quantitative analysis showed differences between zein and kafirin. The composition of each oligomer was established via preparative SDS-PAGE. Part of the cooked oligomers resists reduction; the presence of those oligomers could be related to the decrease on protein digestibility with the cooking process.