Sinapic acid comparison

Except perhaps for caffeic acid (H.86), these acids were mainly identified after hydrolysis of extracts, which means after degradation of the chlorogenic acids, CGA (See Section 2.1.4). In commercial roasted coffee, Hughes and Thorpe (1987) identified, by comparison with standard compounds, coumaric acid (without specification, probably p-), isoferulic acid (H.88) but surprisingly not ferulic acid (H.87), caffeic acid (H.86) and its dimethyl ether (H.89) as well as sinapic acid (H.90). They used capillary GC for the separation and identification of these phenolic acids and other carboxylic acids. The cinnamic acids are generally linked to quinic acid, but in robusta coffee caffeic and /j-coumaric (H.84) acids have also been identified as derivatives of tryptophan (see Section 2.1.2) (Morishita et al., 1987 Murata et ah, 1995) and... 

Fig. 3.8 Phenolic acids extracted from wheat stubble, wheat straw from half buried litter bags, and wheat stubble/soybean (no-till) soil. Phenolic acids isolated and quantified were caffeic acid (CAF), ferulic acid (FER), p-coumaric acid (PCO), p-hydroxybenzoic acid (POH), sinapic acid (SIN), syringic acid (SYR), and vanillic acid (VAN). Becausep-coumaric acid was so high in comparison to other phenolic acids in wheat residues, data are presented twice, once with p-coumaric acid (a) and once without p-coumaric acid (b). Because phenolic acids were so low in the soil they are also presented in (c). The absence of standard error bars for wheat straw and soil indicates that the error bars are too small to be visible. Figures based on data from Blum et al. (1991, 1992). Plenum Publishing Corporation, data used with permission of Springer Science and Business Media...

Lacki K, Duvnjak Z. 1996. Comparison of 3 methods for the determination of sinapic acid ester content in enzymatically treated canola meals. Applied Microbiology and Biotechnology, 45(4) 530-537. 

These results concurred with the findings of Thiyam et al. (2006a) that rapeseed meal extracts contained free sinapic acid, which was equivalent to just one-tenth of the content of sinapine. This was further illustrated by the Iree-phenolic fractions of the meal extracts that could recover the free sinapic acid safisfactorily. Usually in analysis, the phenofic extracts are hydrolysed with NaOH and the released-phenolics are extracted with diethyl ether, ethyl acetate or both. Comparisons between the aqueous fraction (rich in sinapine) before and after hydrolysis producing the released fraction (rich in sinapic acid) showed reasonable results with minimum hydrolysis losses affecting the accuracy of the process. Additionally, fiactionation of the 70% methanolic extract showed comparable extraction efficiency to the original extract before fractionation. 

---