Sinapine Phenolic compound

A number of spectrophotometric methods for the quantification of phenolic compounds in plant materials have been developed. Based on different principles, these assays are used to determine various structural groups present in phenolic compounds. Spectrophotometric methods may quantify all extractable phenolics as a group (Marshall and others 2008), or they may determine a specific phenolic substance such as sinapine (Ismail and Eskin 1979) or a given class of phenolics such as phenolic acids (Brune and others 1989). 

Sinapic acid, an important hydroxydnnamic acid is the most significant phenolic compound in rapeseed and forms 70.2-85.4% of free phenolic adds in defatted canola meals. Esterified forms of these phenolic acids constitnte abont 99% of total phenolics in rapeseed flour of which the sinapine, the choline ester of sinapic acid, is the main ester. A phenolic glucoside namely glucopyranosyl sinapate is also reported in canola (Amarowicz and Shahidi, 1994). Figure 2.1 shows the structures of sinapic acid, sinapine and glucopyranosyl sinapate. 

Vermorel M, Hocquemiller R, Evrard J. 1987. Valorization of rapeseed meal. 5. Effects of sinapine and other phenolic compounds on food intake and nutrient uttiization in growing rats. Reproduction Nutrition Development, 27(4) 781-790. 

The main phenolic compounds of rapeseed meal are commonly sinapic acid (Figure 15.3a) and its derivatives—sinapine the choline ester of sinapic acid (Figure 15.3b), or as the glucosidic ester, glucopyranosyl sinapate. About 80-90% of all the phe-nolics in the meal are sinapic acid esters (SAEs) as discussed earlier. Thus, 70% methanolic rapeseed meal extracts of the meal have been classified into free-pheno-lics, esterifled phenolics and released-phenolics according to Krygier et al. (1982). Krygier et al. (1982) extracted free and esterified phenolics, which were methanol soluble and demonstrated that only a small fraction of the total phenolic compounds of rapeseed occurs as free sinapic acid (Koski et al., 2002 Vuorela et al., 2003). 

FIGURE 15.7 Total phenolic compounds (750 nm) of 70% methanolic extract of commercial meals expressed as sinapine equivalents (SiE mg/g fat-free meal). Right to left mustard Delhi, mustard Manipur, meals X, Y, A (non-specified), husk meal, second-pressed first-pressed, solvent-extracted and cold-pressed meals. From the same company. Each error bar represents the mean of two measurements p < 0.05). 

While the main phenolic compounds of olive oil, hydroxytyrosol and oleuropein, give the oil its bitter and pungent taste, the major phenolic compounds in canola seeds are esterified phenolic acids. The main component of the latter is sinapine, the choline-ester of sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid) (Krygier et al., 1982). Some free phenolic compounds of about 15% are also present with... 

Sinapine, a choline ester of sinapic acid (Figure 10 was identified in yellow, brown, and oriental mustard Tins compound, 3,5-dimethoxy hydroxy cinnamoy) choline, is common in the Brassica group Researchers have shown that although sinapine is the positive ion to sinalbin, the glucosinolatc and phenolic choline ester contents are not correlated with one another (7). For this reason sinapine is seen in both brown... 

Fig. 2a All seven Semen Sinapis methanol extracts show in VIS 4 -5 dark blue zones with Sinalbin at =0.58 (Tl) partly overlapped with sinigrin which in Sinapis alba is contained only in low concentration. In Sinapis nigra it is reported to be the dominant compound. The blue zone at ] =0.24 might be identical with sinapin the choline derivative of Sinapic acid (see also Fig. 2b). The blue zones in the front zone (I =0.85 - 0.95) might be Sinapic acid and phenol carboxylic acid derivatives.

Sinapoyl esters are considered antinutritional compounds because they have a bitter and astringent taste, thus contributing to the bitter taste of rapeseed meal. The intensity of the bitter taste is comparable to the intensity of the bitter taste of caffeine. In the refining of rapeseed oil, sinapines form complexes with proteins. They show lower antioxidant activity than the corresponding phenolic acids and do not have antimicrobial effects. Sinapines present in the feed of some breeds of laying hens cause an off-flavour and fish-like odour of yolks. 

The theoretical contribution of the phenolic constituents, such as free sinapic acid, sinapoyl glucose and sinapine, to the total radical scavenging activity of the extracts is shown in Figure 15.11. The concentration of the phenolic constituents was recorded by HPLC (330 nm). Calibration curves for the RSA were recorded using standard compounds. 

Results of the present stndy indicate that the bonnd and the non-fractionated extract could inhibit the hydroperoxides, propanal and hexanal in a similar manner to sinapine alone when compared with the control sample withont any added antioxidant. This was in contrast to the resnlts illustrated in the bnik rapeseed oil system, where these extracts and sinapine fnnctioned as a mild pro-oxidative or ineffective antioxidant. The non-fractionated extract and sinapine represented a comparable manner in inhibiting PV increase, whereas the bound fraction was more effective as compared with sinapine and nonfractionated extract. This means that in this case, the unidentified peaks of the hydrophilic compounds contributed to the enhanced activity of the bound-phenolic fraction. It was also observed that sinapic acid and the free-phenolic fraction functioned in a similar manner until the 18th day of incnbation. 

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