Extraction of Phenolic Compounds from Raspberry Press Cake

More documents

Recommendations

Info

Although, the highest extract yields were received at 50 °C using water as a solvent,the dry aqueous extracts had the lowest contents of phenolic compounds; the averagevalue of the extracts obtained during three extraction steps was only 30.19 mg g -1 .The data indicates that pure water is not an efficient solvent for phenolic compoundsextraction from raspberry press cake, because it yields the extracts of a low purity.It should be noted that, although the extract yields reduced with each repeated stepof extraction (for all the solvent and extraction regimes used) the dry extract qualityregarding the total phenolics content per one gram basis, remained approximately thesame for all three extraction steps.Investigated dry ethanolic extracts of raspberry press cake had higher amountsof total phenolics in comparison with data reported by Peschel et al. (2006) for thedry methanolic extracts of apple, strawberry and pear wastes (52.2, 59.8 and 18.4 mgin g, respectively).Only small quantities of raspberry pulp (where all anthocyanin pigments areconcentrated) stays in raspberry press-cake after juice pressing, therefore anthocyaninfraction comprised a very small part of the total phenolics content found in dry raspberrypress cake extracts. Naturally, the highest amounts of anthocyanins were extractedduring the thirst extraction step (Fig. 7). The highest percentage of anthocyanins of thetotal amount of phenolic compounds was found in the dry aqueous extracts obtainedat 50 °C (I-st stage 9.44 %, II-nd stage 6.96 % and III-rd stage 5.88 %). Howeveras expressed per one gram basis of the dry extract, higher amounts of anthocyaninswere found in the ethanolic extracts extracted at 50 °C and at ambient temperature(see Fig. 7).Fig. 7. Total anthocyanins content in the extracts7 pav. Bendras antocianinų kiekis ekstraktuose26
Comparing to the total ellagic acid content (the sum of free ellagic acid and ellagicacid released after hydrolysis), relatively low levels of free ellagic acid were presentin the dry extracts of raspberry press cake (see Figs. 8 and 9). This indicates that ellagitanninswere the major source of ellagic acid following the hydrolysis.In the investigated dry extracts free ellagic acid comprised from 6.01 to 18.15 %of the ellagic acid content released after acid hydrolysis. The lowest concentrations offree ellagic acid were found in the dried aqueous extracts extracted at 50 °C (Fig. 8).This could be explained by low solubility of ellagic acid in water.Fig. 8. Free ellagic acid content in the extracts8 pav. Laisvos elago rūgšties kiekis ekstraktuoseSolubility of ellagic acid increases in organic solvents such as ethanol or methanol.Ellagitannins are more water-soluble as compared to ellagic acid however dry aqueousextracts also had the lowest total ellagic acid contents (Fig. 9). Regarding total ellagicacid content dried ethanolic extracts obtained during I-st, II-nd and III-rd extractionsteps remained of approximately the same quality. The total ellagic acid content in dryaqueous extract obtained during III-rd extraction step was more than two times higheras compared to the extract obtained during I-st extraction step (Fig. 9).The dry extracts obtained with 80 % ethanol at 50 °C, where 20 min pre-extractionwith hot water was applied, had the highest radical scavenging activity – on average55.5 % (Fig. 10). However using this type of extraction, the lowest extraction yieldswere received, because in this study the pre-extraction water with part of the extractivecompounds was not concentrated and further evaluated. Anyway evaluating per onegram basis of the dry extract pre-extraction with hot water yielded extracts of higherpurity in terms of phenolics content and as a consequence with higher antiradicalactivity (Figs. 6 and 10). The dry aqueous extracts (50 °C) were found to have thelowest radical scavenging activity – on average 16.8 % (Fig. 10).27
Page 1: SCIENTIFIC WORKS OF THE INSTITUTE O
Page 6 and 7: Fig. 3. Sorbtion of the dry extract
Page 10 and 11: Fig. 9. Total ellagic acid content
Page 12 and 13: 10. Jakobek L., Seruga M., Novok I.

Extraction of Phenolic Compounds from Raspberry Press Cake

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?