Metabolic discrimination of mango juice from various cultivars by band-selective NMR spectroscopy

NMR-based metabolic analysis of foods has been widely applied in food science. In this study, we performed discrimination of five different mango cultivars, Awin, Carabao, Keitt, Kent, and Nam Dok Mai, using metabolic analysis with band-selective excitation NMR spectra. A combination of unsupervised principal component analysis (PCA) with low-field region (1)H NMR spectra obtained by band-selective excitation provided a good discriminant model of the five mango cultivars. Using F(2)-selective 2D NMR spectra, we also identified various minor components in the mango juice. Signal assignment of the minor components facilitated the interpretation of the loading plot, and it was found that arginine, histidine, phenylalanine, glutamine, shikimic acid, and trigonelline were important for classification of the five mango cultivars.     

Study of the compositional changes of mango during ripening by use of nuclear magnetic resonance spectroscopy

Liquid-state NMR spectroscopy was used to follow the compositional changes in mango juice during ripening, whereas MAS and HR-MAS techniques enabled resolved (13)C and (1)H NMR spectra of mango pulps to be recorded. Spectral assignment enabled the identification of several organic acids, amino acids, and other minor components, and the compositional changes upon ripening were followed through the changes in the spectra. In pulps, sucrose was found to predominate over fructose and glucose at most ripening stages, and citric acid content decreased markedly after the initial ripening stages while alanine increased significantly. Other spectral changes reflect the complex biochemistry of mango ripening and enabled the role played by some compounds to be discussed. Some differences observed between the composition of juices and pulps are discussed. This work shows that NMR spectroscopy enables the direct characterization of intact mango pulps, thus allowing the noninvasive study of the overall biochemistry in the whole fruit.     

Rapid quantification of humic components in concentrated humate fertilizer solutions by FTIR spectroscopy

Journal of Soils and Sediments - The use of humic substances is under thorough discussion of state-of-the-art agricultural science. They are marketed mostly as concentrated aqueous solutions of...     

Application of FT-MIR spectroscopy for fast control of red grape phenolic ripening

The content of phenolic compounds determines the state of phenolic ripening of red grapes and is a key criterion in setting the harvest date to produce quality red wines. In this study, the feasibility of Fourier transform mid-infrared (FT-MIR) spectroscopy combined with partial least-squares (PLS) regression to quantify phenolic compounds is reported. The reference methods used for quantifying these compounds (which were evaluated as total phenolic compounds, total anthocyanins, and condensed tannins) were the usual ones used in cellars that employed UV-vis spectroscopy. To take into account the high natural variability of grapes when building the calibration models, fresh grapes from six varieties, at different phenolic ripening states were harvested during three vintages. Destemmed and crushed grapes were subjected to an accelerated extraction process and used as calibration standards. A total of 192 extracts (objects) were obtained, and these were divided into a training set (106 objects) and a test set (86 objects) to evaluate the predictive ability of the models. Among the different MIR regions of the extract raw spectra, those that provided the highest variability on the absorption were selected. The results showed that the best PLS regression model was the one obtained when working in the region of 1168-1457 cm(-1) because it gave the most accurate and robust prediction for total phenolic compounds (RMSEP%=4.3 and RPD=4.5), total anthocyanins (RMSEP%=5.9 and RPD=3.5), and condensed tannins (RMSEP%=5.8 and RPD=3.8). Therefore, it can be concluded that FT-MIR spectroscopy can be a fast and reliable technique for monitoring the phenolic ripening in red grapes during the harvest period.     

FTIR spectroscopy can be used as a screening tool for organic matter quality in regenerating cutover peatlands

Vegetational changes during the restoration of cutover peatlands leave a legacy in terms of the organic matter quality of the newly formed peat. Current efforts to restore peatlands at a large scale therefore require low cost and high throughput techniques to monitor the evolution of organic matter. In this study, we assessed the merits of using Fourier transform infrared (FTIR) spectra to predict the organic matter composition in peat samples at various stages of peatland regeneration from five European countries. Using predictive partial least squares (PLS) analyses, we were able to reconstruct peat C:N ratio and carbohydrate signatures with reasonable accuracy, but not the micromorphological composition of vegetation remains. Despite utilising different size fractions, both carbohydrate (<200 μm fraction) and FTIR (bulk soil) analyses report on the composition of plant cell wall constituents in the peat and therefore essentially reveal the composition of the parent vegetational material. The accuracy of the FTIR-based PLS models for C:N ratios and carbohydrate signatures was adequate to allow for their use as initial screening tools in the evaluation of the present and future organic matter composition of peat during monitoring of restoration efforts.     

Midinfrared spectroscopy for juice authentication-rapid differentiation of commercial juices

The determination of food authenticity is a crucial issue for food quality and safety. Midinfrared spectroscopy provides rapid chemical profiling of agricultural products and could become an effective tool for authentication when coupled to chemometrics. This study developed a simple protocol for classifying commercial juices using attenuated total reflectance infrared spectroscopy. Spectra from a total of 52 juices together with their extracted sugar-rich and phenol-rich fractions were obtained to construct multivariate models [hierarchical cluster analysis (HCA) and soft independent modeling of class analogy (SIMCA)] for pattern recognition analysis and prediction. Spectra of the sugar-rich fraction, comprised primarily of sugars and simple acids, almost superimposed the whole juice spectra. Solid-phase extraction enriched phenol compounds and provided signature-like spectral information that substantially improved the SIMCA modeling power over the whole juice or sugar-rich fraction models and allowed for the differentiation of juices with different origins. Zero percent misclassification was achieved by the phenol-rich fraction model. HCA successfully recognized the natural grouping of juices based on ingredients similarity. The infrared technique assisted by a simple fractionation and chemometrics provided a promising analytical method for the assurance of juice quality and authenticity.     

Impact of the stage of ripening and dietary fat on in vitro bioaccessibility of beta-carotene in 'Ataulfo' mango

Pulp from "slightly ripe", "moderately ripe", or "fully ripe" mangoes was digested in vitro in the absence and presence of processed chicken as a source of exogenous fat and protein to examine the impact of stage of ripening of mango on micellarization during digestion and intestinal cell uptake (i.e., bioaccessibility) of beta-carotene. The quantity of beta-carotene transferred to the micelle fraction during simulated digestion significantly increased as the fruit ripened and when chicken was mixed with mango before digestion. Qualitative and quantitative changes that occur in pectin from mango pulp during the ripening process influenced the efficiency of micellarization of beta-carotene. Finally, the uptake of beta-carotene in micelles generated during simulated digestion by Caco-2 human intestinal cells confirmed the bioaccessibility of the provitamin A carotenoid in mango.     

Development of a rapid method for the sequential extraction and subsequent quantification of fatty acids and sugars from avocado mesocarp tissue

Methods devised for oil extraction from avocado (Persea americana Mill.) mesocarp (e.g., Soxhlet) are usually lengthy and require operation at high temperature. Moreover, methods for extracting sugars from avocado tissue (e.g., 80% ethanol, v/v) do not allow for lipids to be easily measured from the same sample. This study describes a new simple method that enabled sequential extraction and subsequent quantification of both fatty acids and sugars from the same avocado mesocarp tissue sample. Freeze-dried mesocarp samples of avocado cv. Hass fruit of different ripening stages were extracted by homogenization with hexane and the oil extracts quantified for fatty acid composition by GC. The resulting filter residues were readily usable for sugar extraction with methanol (62.5%, v/v). For comparison, oil was also extracted using the standard Soxhlet technique and the resulting thimble residue extracted for sugars as before. An additional experiment was carried out whereby filter residues were also extracted using ethanol. Average oil yield using the Soxhlet technique was significantly (P < 0.05) higher than that obtained by homogenization with hexane, although the difference remained very slight, and fatty acid profiles of the oil extracts following both methods were very similar. Oil recovery improved with increasing ripeness of the fruit with minor differences observed in the fatty acid composition during postharvest ripening. After lipid removal, methanolic extraction was superior in recovering sucrose and perseitol as compared to 80% ethanol (v/v), whereas mannoheptulose recovery was not affected by solvent used. The method presented has the benefits of shorter extraction time, lower extraction temperature, and reduced amount of solvent and can be used for sequential extraction of fatty acids and sugars from the same sample.     

Liquid chromatographic determination of naringin and neohesperidin as a detector of grapefruit juice in orange juice

Naringin/neohesperidin ratios can be used to differentiate orange juice which may contain added grapefruit juice from orange juice which may include juices from other naringin-containing cultivars. The naringin/neohesperidin ratios in juice vary from 14 to 83 in grapefruit (C. grandis) and from 1.3 to 2.5 in sour orange (C. aurantium) cultivars; the ratio is always less than 1 for the K-Early tangelo. Concentrations of both naringin and neohesperidin can be determined in orange juice by using a single liquid chromatographic isocratic reverse-phase system with a C-18 column. The detection limit for both compounds is 1 ppm with a linear working range to 500 ppm. Concentration relative standard deviations range from 0.47 to 1.06% for naringin and from 0.4 to 1.27% for neohesperidin. Naringin and neohesperidin recoveries ranged from 93 to 102% at concentrations of 5 and 50 ppm. Naringin values from blind duplicate samples of orange/grapefruit juice blends could be duplicated to +/- 3%.     

Change in the carotenoid and antioxidant content of spice red pepper (paprika) as a function of ripening and some technological factors

A study was conducted to investigate the change in quality attributes of red pepper (paprika) (Capsicum annuum L. var. Km-622) as a function of ripening and some technological factors. Of quality attributes, carotenoids and bioantioxidants (ascorbic acid and tocopherols) have been studied. It was found that the dynamics of fruit ripening with regard to carotenoids and bioantioxidants was influenced to a considerable extent by weather conditions of the production season. A rainy and cool season yielded fruits with more beta-carotene but less diesters of red xanthophylls as compared to those produced in a relatively dry and warm season. The ripening stage at harvest was found to affect the quality of paprika. Harvest at unripe stages (color break or faint red) resulted in a high accumulation of dehydroascorbic acid in the overripe fruits, whereas de novo biosynthesis of carotenoids and tocopherols was partially retarded. Application of pre-drying centrifugation resulted in a marked loss of ascorbic acid, and as a consequence, carotenoid stability was impaired during the storage of ground paprika. Sugar caramelization caused dry pods and ground paprika to retain more pigments and tocopherol as compared to those from control or centrifuged red pepper samples. During the storage of ground paprika, color stability was improved by grinding the seeds with the pericarp.     

Changes in the contents of sugars and organic acids during the ripening and storage of sufu, a traditional Oriental fermented product of soybean cubes

In the present study, sufu, an oriental fermented product of soybeans, was prepared by ripening the tofu cubes in Aspergillus oryzae fermented rice-soybean koji mash for 16 days at 37 °C. The sufu product was further kept at room temperature for another 30 days. Examining the changes in the sugar content revealed that stachyose, raffinose, and sucrose contents of tofu and rice-soybean koji granules decreased while levels of glucose and fructose increased during the ripening period and after storage. Glucose was the most abundant sugar detected. Four organic acids, including oxalic, lactic, acetic, and citric acid, were detected in the sufu product and koji granules after ripening. Generally, the contents of these organic acid increased as the ripening period was extended. Among them, acetic acid was the most highly detected.     

Multivariate analysis of NMR and FTIR data as a potential tool for the quality control of beer

In this work, principal component analysis (PCA) is applied to the FTIR-ATR and the (1)H NMR spectra of 50 beers differing in label and type (ale, lager, alcohol-free), to identify the spectral parameters that may provide rapid information about factors affecting beer production. PCA of FTIR data resulted in the separation of beers mainly according to their alcoholic content, providing little information on components other than ethanol contributing to the variability within the samples. PCA of (1)H NMR spectra, performed on the region where major beer components resonate (3.0-6.0 ppm), resulted in the separation of samples into four groups: two groups characterized by the predominance of dextrins, one group of alcohol-free beers characterized by the predominance of maltose, and one group where glucose was found to predominate. By performing PCA on aliphatic and aromatic regions, the contribution of minor components was highlighted. In particular, most ales, lagers, and alcohol-free samples could be distinguished based on their aromatic composition, thus reflecting the high sensitivity of the low-field NMR region toward different types of beer fermentation.     

Thermal destruction of soil water repellency and associated changes to soil organic matter as observed by FTIR spectroscopy

The heat generated during wildfires often leads to increases in soil water repellency. Above a critical heating threshold, however, its destruction occurs. Although the temperature thresholds for repellency destruction are relatively well established, little is known about the specific changes in the soil organic matter that are responsible for repellency destruction. Here we report on the analysis of initially water repellent surface soil samples (Dystric Cambisol, 0–5 cm depth) by transmission Fourier Transform Infrared (FTIR) spectroscopy analysis before and after destruction of its water repellency by heating to 225 °C in order to investigate heating-induced changes in soil organic matter (SOM) composition. Although assignment of absorption bands is made difficult by overlapping of some bands, it was possible to distinguish bands relevant for hydrophobicity of SOM in the soil before heat treatment. The most significant decrease in absorbance following water repellency destruction took place in the frequency area corresponding to stretching vibrations of aliphatic structures within SOM. The results suggest that besides a general decrease of SOM content during heating, the loss of soil water repellence is primarily caused by the selective degradation of aliphatic structures.     

Amino sugars as specific indices for fungal and bacterial residues in soil

Amino sugars are important indices for the contribution of soil microorganisms to soil organic matter. Consequently, the past decade has seen a great increase in the number of studies measuring amino sugars. However, some uncertainties remain in the interpretation of amino sugar data. The objective of the current opinion paper is to summarize current knowledge on amino sugars in soils, to give some advice for future research objectives, and to make a plea for the correct use of information. The study gives an overview on the origin of muramic acid (MurN), glucosamine (GlcN), galactosamine (GalN), and mannosamine (ManN). Information is also provided on measuring total amino sugars in soil but also on compound-specific δ¹³C and δ¹⁵N determination. Special attention is given to the turnover of microbial cell-wall residues, to the interpretation of the GlcN/GalN ratio, and to the reasons for converting fungal GlcN and MurN to microbial residue C. There is no evidence to suggest that the turnover of fungal residues generally differs from that of bacterial residues. On average, MurN contributes 7% to total amino sugars in soil, GlcN 60%, GalN 30%, and ManN 4%. MurN is highly specific for bacteria, GlcN for fungi if corrected for the contribution of bacterial GlcN, whereas GalN and ManN are unspecific microbial markers.     

Qualitative and semiquantitative analysis of phenolic compounds in extra virgin olive oils as a function of the ripening degree of olive fruits by different analytical techniques

Capillary electrophoresis (CE) can be effectively used as a fast screening tool to obtain qualitative and semiquantitative information about simple and complex phenolic compounds of extra virgin olive oil. Three simple phenols (tyrosol, hydroxytyrosol, and vanillic acid), a secoiridoid derivative (deacetoxy oleuropein aglycon), and two lignans (pinoresinol and acetoxypinoresinol) were detected as the main compounds in extra virgin olive oils by high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE). Spectrophotometric indices, radical scavenging activity, and oxidative stability of extra virgin olive oil samples obtained from olives hand-picked at different ripening degrees were statistically correlated with the CZE and HPLC quantification. The concentration of phenols in extra virgin olive oil decreased with ripeness of olive fruits. The high correlations found between CZE and the other analytical results indicate that CE can be applied as a rapid and reliable tool to routinely determine phenolic compounds in extra virgin olive oils.     

Use of fourier transform near-infrared reflectance spectroscopy for rapid quantification of castor bean meal in a selection of flour-based products

Methodology was developed and evaluated for the rapid detection of castor bean meal (CBM) containing the toxic protein ricin by using Fourier transform near-infrared (FT-NIR) spectroscopy and multivariate techniques. The method is intended to be a prototype to develop a more general approach to detect food tampering. Measurements were made on an FT-NIR system using a diffuse reflection-integrating sphere. Flours spiked with caffeine, crystalline sugar, and corn meal, 1-20% w/w, were used as test articles to evaluate the methodologies. Food matrices (bleached flour, wheat flour, and blueberry pancake mix) spiked with CBM (0.5-8% w/w) were analyzed. Multiplicative scatter correction transformed partial least-squares regression models, using a specific NIR spectral region, predicted CBM contamination in foods with a standard error of cross-validation of <0.6% and a coefficient of determination (R(2)) of >94%. Models discriminated between flour samples contaminated with CBM and other protein sources (egg white, soybean meal, tofu, and infant formula). CBM had loading spectra with bands characteristic of amide groups (4880 and 4555 cm(-1)) and lipids (5800, 5685, 4340, and 4261 cm(-1)).     

Identification and quantification of short oligomeric proanthocyanidins and other polyphenols in boysenberry seeds and juice

Proanthocyanidins and other polyphenols in the seeds and juice of boysenberry were quantitatively analyzed. Polyphenolic extracts were prepared from the waste seeds and commercial juice by chromatographic fractionation. Compositional analysis revealed that both extracts contained six polyphenolic classes: flavanol monomers, proanthocyanidins, anthocyanins, ellagic acid, ellagitannins, and flavonol glycosides. Ellagitannins were the most abundant polyphenols in both extracts. Proanthocyanidins were present as short oligomers consisting of dimeric and trimeric procyanidins and propelargonidins, with the most abundant component being procyanidin B4 in both extracts. Quantification by high-performance liquid chromatography-mass spectrometry (HPLC-MS) revealed that the seeds contained a 72-fold higher amount of proanthocyanidins than the juice. These results indicate that boysenberry fruits contain short oligomeric proanthocyanidins along with flavanol monomers and the seeds represent a good source of short oligomeric proanthocyanidins.     

FTIR spectroscopy and multivariate analysis can distinguish the geographic origin of extra virgin olive oils

This work investigates whether Fourier transform infrared spectroscopy (FTIR), in combination with multivariate analysis, can distinguish extra virgin olive oils from different producing countries. Duplicate spectra were collected from 60 oils from four European countries. Two approaches to data analysis were used as follows: first, the "whole spectrum" method of partial least squares (PLS) followed by distance-based linear discriminant analysis (LDA) applied to the PLS scores, and second, a genetic algorithm (GA) for variate selection from the raw data, followed by LDA applied to the selected subset. The PLS-LDA approach produced a cross-validation success rate of 96%, whereas the GA-LDA approach achieved a 100% cross-validation success rate, from subsets comprising only eight variates. Neither the selected variate nor the whole spectrum approach was able to offer insight into the origin of the discrimination in biochemical terms. However, FTIR analysis is rapid, and this work shows that it has the required discriminatory power to potentially offer a "black box" method of screening oils to verify their country of origin.     

Rapid determination of free fatty acids in poultry feed lipid extracts by SB-ATR FTIR spectroscopy

A simple, rapid, and reproducible method has been developed for the quantitative determination of free fatty acid (FFA) content in lipids extracted from poultry feeds by Fourier transform infrared (FTIR) spectroscopy with the use of a single-bounce attenuated total reflectance (SB-ATR) accessory. An FTIR calibration curve was prepared by gravimetrically adding oleic acid (15-37%) to pure refined, bleached, and deodorized (RBD) canola oil and measuring the area of the COOH absorption band at 1710 cm-1. The oil from each of 12 poultry feed formulations was extracted using conventional Soxhlet extraction, and after evaporation of the solvent, the FFA content was determined by the conventional AOCS titrimetric procedure and by the SB-ATR/FTIR method. The SB-ATR/FTIR FFA predictions were related to those determined by the AOCS titrimetric method by linear regression, producing an R value of 0.999 and a SD of +/-0.28% FFA. Time-course spectra collected as lipids extracted into hexane indicated that a 15 min extraction was adequate to obtain a representative sample for FFA determination, with further extraction resulting in little, if any, change in the proportion of FFA in the lipid extract. Only a small volume of the hexane extract ( approximately 20 mL) yielded sufficient material for the SB-ATR/FTIR analysis. Thus, by shortening the extraction time and taking a small sample so as to reduce solvent removal time, the SB-ATR/FTIR procedure provides a very simple and rapid means of determining the FFA content of poultry feed lipids.     

Detection of sugar adulterants in apple juice using fourier transform infrared spectroscopy and chemometrics

Fourier transform infrared spectroscopy and attenuated total reflection sampling have been used to detect adulteration of single strength apple juice samples. The sample set comprised 224 authentic apple juices and 480 adulterated samples. Adulterants used included partially inverted cane syrup (PICS), beet sucrose (BS), high fructose corn syrup (HFCS), and a synthetic solution of fructose, glucose, and sucrose (FGS). Adulteration was carried out on individual apple juice samples at levels of 10, 20, 30, and 40% w/w. Spectral data were compressed by principal component analysis and analyzed using k-nearest neighbors and partial least squares regression techniques. Prediction results for the best classification models achieved an overall (authentic plus adulterated) correct classification rate of 96.5, 93.9, 92.2, and 82.4% for PICS, BS, HFCS, and FGS adulterants, respectively. This method shows promise as a rapid screening technique for the detection of a broad range of potential adulterants in apple juice.