Phenolic acid concentration

Caccetta, R.A., Croft, K.D., Beilin, L.J., and Puddey, I.B., Ingestion of red wine significantly increases plasma phenolic acid concentrations but does not acutely affect ex vivo lipoprotein oxidizability, Am. J. Clin. Nutr., 71, 67, 2000. 

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. 

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]. 

Complete solution changes for multiple phenolic acid treatments were used because phenolic acids supplied to seedlings in the nutrient culture system disappeared from the nutrient solution within 24-48 h (Blum and Dalton 1985 Blum and Gerig 2005). This was due to microbial metabolism, physical breakdown, and/or root uptake. Since we did not want to confound nutrient and phenolic acid effects, complete solution changes were made. An additional benefit of this approach was to reset phenolic acid concentrations to the initial treatment levels for each solution change. This was important since recovery of seedling processes occurred rapidly after phenolic acid depletion (Blum and Dalton 1985 Blum and Rebbeck 1989 Blum and Gerig 2005). 

Multiple additions of phenolic acids were used because phenolic acid concentrations in soil decline rapidly after each addition of phenolic acids (Blum et al. 1987 Blum and Gerig 2006). This was due to microbial metabolism, physical breakdown, root uptake, and/or soil particle sorption. Recovery of seedling processes, although considerably slower than in nutrient culture, also occurred in seedling-soil systems (Blum et al. 1987 Blum and Gerig 2006). To maintain inhibition for extended time periods multiple additions of phenolic acids were required. 

In addition to type of phenolic acid, phenolic acid concentration, and solution pH there are other factors that influence cucumber seedling responses to phenolic acids. For example ... 

Effects of Seedlings, Mixtures of Phenolic Acids, and Microbes on Phenolic Acid Concentrations in Nutrient Culture... 

Cucumber seeds and seedlings have associated with them substantial microbial populations that are difficult to eliminate because microbes are not only found on and in the cutinized surface of the seed coat but can also be found internally within the seed (Leben 1961 Mundt and Hinkle 1976). Depletion of phenolic acids from nutrient solutions thus represent uptake by roots and microbial utilization. By replacing the nutrient solution (control) and nutrient-phenolic acid solutions (treatments) every other day, microbial populations were kept in check and phenolic acid concentrations were brought back to the original treatment concentrations. However, since phenolic acid treatments changed microbial populations on the rhizoplane (Fig. 2.9)... 

When phenolic acids enter the soil environment they are reversibly and irreversibly sorbed to soil particles, polymerized, oxidized, reduced, leached, utilized by microbes, and taken up by roots. Rates for these various processes are highly variable and depend on soil type, biotic and physicochemical soil environmenL types and mixtures of phenohc acids in or added to soils, and time, among others. To eliminate the effects of soil microbes, soils may be autoclaved. Concentrations of individual available phenolic acids in soils at a given point in time may be estimated by extracting soils with appropriate extractants and HPLC analysis. Based on our soils, we recommend water for estimating soil solution concentrations and neutral EDTA for soil solution and reversibly sorbed phenolic acid concentrations. However, the effectiveness of neutral EDTA in recovering available phenolic acids in all other soils should not be assumed. Reversibly sorbed phenolic acids increased or decreased as soil solution concentrations and multivalent cations increased or decreased, respectively. 

There is, however, a caveat for estimating available total phenolic acid concentrations. The estimates of the total available fraction of phenolic acids in soil extracts represent a crude estimate of what actually occurs in soil, not only because of the range of efficiencies of extraction procedures but also because different phenolic acids at the same concentration generate different absorbances with Folin Ciocalteu s phenol reagent (Fig. 3.7 Blum et al. 1991). In addition soil extracts also contain compounds, other than phenolic acids, that react with (i.e., reduce) the Folin Ciocalteu s phenol reagent (McAllister 1969 Box 1983). The assumption, therefore, was that available total phenolic acid values based on the Folin Ciocalteu s phenol reagent expressed as ferulic acid equivalence were relative values that were consistently related to the acmal total available phenolic acids (hereafter just called total phenolic acid) present in soil extracts. The extraction and quantification by HPLC analysis of available individual phenolic acids in soil do not have these particular problems. 

However, there is one more caveat for both total and individual phenolic acids. Soil extractions recover residual or net concentration, i.e., input - losses, for a point or various points in time. Since both input and losses are unknown between points of time the actual available total or individual phenolic acid concentrations in soil over time are also unknown. The concentrations of available phenolic acids interacting with roots could thus be greater, at times much greater, or lower, at times much lower, than the net concentrations determined from soil extracts. 

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