Concentrations of phenolic acids

The concentration of phenolic acids can vary from 0.01 to 10 ppm (Anklam, 1998). The dominant acids are gallic acid and p-coumaric acid, followed by the caffeic, ferulic, ellagic, chlorogenic, syringic, vanillic, cinnamic, and p-hydroxybenzoic acids (Baltrusaityte et al., 2007 Bertoncelj et al., 2007 Estevinho et al., 2008). The high concentrations of benzoic, phenylacetic, mandelic, and (S-fenil lactic acids (Anklam, 1998) can be used in the identification of heather honey. 

Because phenolic acid concentrations in soil solutions are determined not only by input processes (e.g., leaching, exudation, release of bound forms) but also by output processes (e.g., sorption, polymerization, utilization by microorganisms), simply determining soil solution concentrations over time cannot provide information on how any one of these processes may actually influence the soil solution concentrations of phenolic acids. The effects of each process must be characterized separately. The impact of soil or rhizosphere microorganisms, for example, could be estimated by coupling changes in soil solution concentrations of phenolic acids with the activity of soil or rhizosphere microorganisms that can utilize phenolic acids as a carbon source. This approach, however, assumes that all the other output process rates remain constant. 

Highest and lowest concentrations of phenolic acids in 17-day old wheat root... 

The vinyl-phenol content of a white wine depends on the concentration of phenol acid precnrsors in the must, on the one hand, and the CD activity of the yeast strain responsible for alcoholic fermentation, on the other hand. 

Five soluble phenolic acids (free and esterifled), one of which is a hydroxylated derivative of benzoic acid (gallic acid) and four are cinnamic acid derivatives (caffeic, p-coumaric, ferulic, and sinapic acids), have been studied and tentatively identified in ethanolic extracts of hazelnut kernel and hazelnut by-products (Table 13.2) [31]. The order of total phenolic acid concentration was as follows hazelnut hard shell > hazelnut green leafy cover > hazelnut tree leaf > hazelnut skin > hazelnut kernel. Different phenolic acids predominate in each plant part examined. Among the identified phenolic acids, p-conmaric acid was most abundant in hazelnut kernel, hazelnut green leafy cover, and hazelnut tree leaf, whereas gallic acid was most abundant in hazelnut skin and hazelnut hard shell, possibly implying the presence and perhaps the dominance of tannins in the latter samples (Table 13.2). The same number, but different concentration, of phenolic acids have also been reported in hazelnnt kernel and hazelnut green leafy cover [30]. 

For the soil columns (Fig. 2.2), water, nutrient solution, or various concentrations of phenolic acid in water or nutrient solution was supplied to the top of each column at 2-3.5 ml/h with a cassette pump (Blum et al. 1999a). Solutions were collected from the bottom of the column for 30 min at 12-h intervals during phenolic acid treatment to estimate the amount of phenolic acid lost (leached) from the systems. 

In addition, depletion rates also varied with the type of phenolic acid present, the number of phenolic acids tfeatments received by seedlings, the number and concentrations of phenolic acids present in a solution, and the level of aeration of the nutrient solution (Blum and Dalton 1985 Blum et al. 1985a Shann and Blum 1987a Lyu et al. 1990 Lyu and Blum 1990 Lehman and Blum 1999b Blum and Gerig 2005). For example ... 

In summary, observed effects of individual phenolic acids or phenolic acid mixtures were similar to what had been observed in nutrient culture but the response times and the magnitude of effects (see Section 2.4.8 for direct comparison) were slower and lower, respectively. Relative potencies of phenolic acids were lower when compared to nutrient culture. Increasing the number of phenolic acids in a mixture of phenolic acids reduced the concentrations of the individual phenolic acids required for a given percent inhibition. The presence of other readily available organic compounds (inhibitory or non-inhibitory) also reduced the concentration of phenolic acids required for a given percent inhibition. The addition of nitrate or nutrient solution reduced the inhibitory activity of phenolic acids. The inhibition of methionine, an amino acid, on the other hand was enhanced by the addition of nitrate. Finally phenolic acid effects were greater under acidic than under neutral conditions. 

Effects of Seedling-Microbe-Soil Systems on the Available Concentrations of Phenolic Acids in Soil Solutions... 

The higher concentrations of phenolic acids required for a given percent inhibition between the two systems stem from the fact that nutrient cultures have a much more consistent environment than soil culture systems in that water, nutrients, and phenolic acids are evenly distributed in the treatment container and thus are readily available to interact with root surfaces. Soil systems, on the other hand, are much more complex heterogeneous environments in which roots must compete with a variety of soil sinks (e.g., clays, organic matter, and microbes) for water, nutrients, and phenolic acids. There is also mechanical resistance to the movement of water, nutrients, and phenolic acids and the growth of roots in soils. The slower development of inhibition after treatment and the slower recovery after phenolic acid depletion in soil systems is very likely related to the slower growth of seedlings in soil culture. 

So what were the concentrations of phenolic acids in the Cecil A soil wheat stubble (Triticum aestivum L. Coker 916 )/soybean (Glycine maxL. Deltapine417 ) systems Subsamples taken from wheat stubble/soybean (no-till), wheat stubble tilled under/soybean (conventional-till), and fallow/soybean soil (conventional-till) cores were extracted by the water-autoclave procedure and analyzed for 7 common phenolic acids (ferulic, caffeic, p-coumaric, p-hydroxybenzoic, sinapic, syringinc, and vanillic) and total phenolic acid (Blum et al. 1991). With minor exception, individual phenolic acids were correlated with each other, with the sum of the 7 phenolic acids identified by HPLC analysis, and total phenolic acid as determined by the Folin Ciocalteu s phenol reagent method. 

Pro 2 Selection and induction of phenolic acid-utilizing microbes are not evident unless high concentrations of phenolic acids are supplied to soil systems over time and environmental conditions are appropriate. However, what is really more important here is the activity of these microbes, i.e., utilization rates for phenolic acid (see 3). 

Pro 4 Very rapid irreversible sorption occurs on initial addition of high concentrations of phenolic acids to soil subsequently, however, sorption is very slow for cinnamic acid derivatives and almost non-existent for benzoic acid derivatives. For soil systems with continuous production of phenolic acids a semi-steady state will occur and irreversible sorption will thus be very small. That phenolic acids and soils can potentially reach a steady state has been demonstrated in the continuous-flow system. 

The solvent extraction is the most used method for phenolic compoimds obtainment from plant tissue. The main factor is the phenolics solubility, which depends on its chemical structure. Plant materials may contain different concentrations of phenolic acids, phenylpropanoids, anthocyanins and tannins. It is possible to occur interactions between phenolics and other plant components, such as carbohydrates and proteins which form complexes responsible for insolubility. Besides that, the polarity of solvent affects the solubility and therefore, it is eonsidered difficult to develop a extraction method suitable for all plant phenolics [18]. 

In white grapes, the concentrations of phenolic acids esterified by tartaric add, flavan-3-ols and oligomeric procyanidins are high at the beginning of development They then diminish to minimal concentrations at maturity. 

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