Total phenolic acid

MATTILA p and KUMPULAINEN J (2002) Determination of free and total phenolic acids in plant-derived foods by HPLC with diode-array detection, JAgric Food Chem, 50, 3660-67. 

To analyze free-form phenolic acids in fmit or vegetable juice, the sample preparation is straightforward and simple. The juice can be directly injected into an HPLC system after it is filtered to remove any insoluble particles. However, for a sample with a solid fraction containing both free and bound phenolic acids, the sample preparation is not as simple. A mechanical method is needed to physically break down the sample and release the free phenolic acids, which are blocked in the inner core of the sample matrix. Chemical (acid or alkaline) or enzymatic hydrolysis must be applied to break down linkages in the bound phenolic acids to release free phenolic acids. However, the recovery of total phenolic acids is significantly affected by hydrolysis and other extraction conditions. An intensive hydrolysis condition may increase the release rate of bound phenolic acids to free phenolic acids however, it can also cause degradation of some phenolic acids and lower... 

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]. 

Ad/Al ratio The ratio of concentrations of the total phenolic acids relative to the total phenolic aldehydes derived from depolymerization of lignin. Larger Ad/Al ratios are indicative of greater oxidation of the lignin fraction of organic matter in a sediment sample. 

Wanasundara and Shahidi (1994a) reported that the total content of phenolic acids of flaxseed meal was about 220 mg/lOOg, on a dry weight basis. Methanol-ammonia-water/hexane extraction lowered the total phenolic acid content of the meals by approximately 48%. The content of condensed tannins of flaxseed meal was about 136 mg/lOOg, determined as (+)catechin equivalents, and this must have originated from the seed coat. The two-phase solvent extraction system (methanol-ammonia-water/hexane) reduced the content of tannins in the meal by 74% (Wanasundara and Shahidi, 1994a). 

Ahmad J, Langrish TAG (2012) Optimisation of total phenolic acids extraction from mandarin peels using microwave energy The importance of the Maillard reaction. J Food Engin 109(1) 162-174... 

Fig. 2.25 Effects of total phenolic acid composed of a 4-equal-molar mixture of p-coumaric acid, ferulic acid.p-hydroxybenzoic acid, and vanillic acid on absolute rates of leaf expansion (cm /day ...

Thus the summed or average action of extracted available total phenolic acids in soils is just as important as understanding the action of available individual phenolic... 

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. 

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. 

Total phenolic acid content of the cover crops taken at monthly intervals from the field after glyphosate desiccation declined over time. However, the decline of total phenolic acid content for rye and wheat residues was not evident until 2 months after glyphosate desiccation (Lehman 1993). After 4 months the total phenolic acid content of the cover crops had declined by 31, 36, 38, and 56% for wheat, crimson clover, rye, and subterranean clover, respectively (Lehman 1993). Estimates of ferulic acid for sterilized (autoclaved) cover crop residues extracted with 0.25 M... 

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