There are concerns about using synthetic phenolic antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) as food additives because of the reported negative effects on human health. Thus, a replacement of these synthetics by antioxidant extractions from various foods has been proposed. More than 8000 different phenolic compounds have been characterized; fruits and vegetables are the prime sources of natural antioxidants. In order to extract, measure, and identify bioactive compounds from a wide variety of fruits and vegetables, researchers use multiple techniques and methods. This review includes a brief description of a wide range of different assays. The antioxidant, antimicrobial, and anticancer properties of phenolic natural products from fruits and vegetables are also discussed.

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Phytochemicals: Extraction, Isolation, and Identification of Bioactive Compounds from Plant Extracts

Lactobacillus reuteri converts glycerol into a potent cell growth inhibitor. This substance, termed reuterin, inhibits the growth of gram-positive and gram-negative bacteria as well as yeasts, fungi, and protozoa. Semipreparative chromatography was used to purify reuterin, and Fourier transform infrared spectroscopy and liquid chromatography-mass spectrometry were used to establish the molecular weight as well as the molecular functionality of the reuterin molecule. Nuclear magnetic resonance studies of purified reuterin carried out with deuterium oxide confirmed the presence of two three-carbon compounds, beta-hydroxypropionaldehyde and the corresponding hydrated acetal, and a six-carbon cyclic dimer of the aldehyde. Further nuclear magnetic resonance studies with deuterated methanol revealed that in this solvent the compound existed as a three-carbon compound in a methoxy form. Trimethylsilyl derivatives of reuterin were analyzed by gas chromatography-mass spectrometry, and a molecule was identified which had a molecular weight corresponding to a disilylated dimeric structure. On the basis of the above information, reuterin was determined to be an equilibrium mixture of monomeric, hydrated monomeric, and cyclic dimeric forms of beta-hydroxypropionaldehyde. This was subsequently confirmed by chemical synthesis.

Chemical characterization of an antimicrobial substance produced by Lactobacillus reuteri.

We have used 13C-labeled sugars and nuclear magnetic resonance (NMR) spectrometry to study the metabolic pathway of starch biosynthesis in developing wheat grain (Triticum aestivum cv Mardler). Our aim was to examine the extent of redistribution of 13C between carbons atoms 1 and 6 of [1-13C] or [6-13C]glucose (or fructose) incorporated into starch, and hence provide evidence for or against the involvement of triose phosphates in the metabolic pathway. Starch synthesis in the endosperm tissue was studied in two experimental systems. First, the 13C sugars were supplied to isolated endosperm tissue incubated in vitro, and second the 13C sugars were supplied in vivo to the intact plant. The 13C starch produced by the endosperm tissue of the grain was isolated and enzymically degraded to glucose using amyloglucosidase, and the distribution of 13C in all glucosyl carbons was quantified by 13C-NMR spectrometry. In all of the experiments, irrespective of the incubation time or incubation conditions, there was a similar pattern of partial (between 15 and 20%) redistribution of label between carbons 1 and 6 of glucose recovered from starch. There was no detectable increase over background 13C incidence in carbons 2 to 5. Within each experiment, the same pattern of partial redistribution of label was found in the glucosyl and fructosyl moieties of sucrose extracted from the tissue. Since it is unlikely that sucrose is present in the amyloplast, we suggest that the observed redistribution of label occurred in the cytosolic compartment of the endosperm cells and that both sucrose and starch are synthesized from a common pool of intermediates, such as hexose phosphate. We suggest that redistribution of label occurs via a cytosolic pathway cycle involving conversion of hexose phosphate to triose phosphate, interconversion of triose phosphate by triose phosphate isomerase, and resynthesis of hexose phosphate in the cytosol. A further round of triose phosphate interconversion in the amyloplast could not be detected. These data seriously weaken the argument for the selective uptake of triose phosphates by the amyloplast as part of the pathway of starch biosynthesis from sucrose in plant storage tissues. Instead, we suggest that a hexose phosphate such as glucose 1-phosphate, glucose 6-phosphate, or fructose 6-phosphate is the most likely candidate for entry into the amyloplast. A pathway of starch biosynthesis is presented, which is consistent with our data and with the current information on the intracellular distribution of enzymes in plant storage tissues.

Starch Biosynthesis in Developing Wheat Grain Evidence against the Direct Involvement of Triose Phosphates in the Metabolic Pathway

This paper reviews analytical methods that have been developed for characterizing complex liquid mixtures derived from fossil fuels. The analysis of fractions with masses up to ∼400−450 u normally involves gas and liquid chromatography, coupled with mass spectrometry (GC−MS and LC−MS, respectively). However, these techniques cannot readily be adapted to examine samples that contain higher-molecular-mass materials. Chromatographic and mass spectrometric methods are often limited by the volatility of the samples, while liquid chromatographic methods may be limited by solubility in the solvents used. Materials of higher mass are characterized using methods that have been developed to overcome the limitations imposed by volatility and solubility in common solvents. As outlined in the text, they have been the subject of some debate. Much of the work that indicates upper mass limits of ∼1000−1500 u for coal tars, pitches, and petroleum asphaltenes can be explained in terms of limitations of the particular analy...

Characterization of Heavy Hydrocarbons by Chromatographic and Mass Spectrometric Methods: An Overview

Impaired tricarboxylic acid cycle activity in mouse livers lacking cytosolic phosphoenolpyruvate carboxykinase.

The chemical shift range of carbon-13 resonances is so wide (more than 200 ppm for simple functional classes) that most compounds show a separate signal for each different carbon environment in the molecule; this is dramatically illustrated in the spectrum for vitamin B12 at the head of the chapter, and more modestly in the menthol spectrum in figure 5.2.

William Kemp

Papers

Carbon-13 NMR Spectra

Characterization of petroleum feedstocks for coal−oil co-processing

Pyrolysis of SCG extract coal asphaltenes: Gas chromatographic-mass spectroscopic study of the n-pentane soluble fraction

Donor solvent interactions during coal liquefaction

Coal conversion in co-processing with heavy petroleum residues