Phenolic Constituents in Commercial Aqueous Quillaja (Quillaja saponaria Molina) Wood Extracts

Abstract

Phenolic compounds in aqueous, saponin-rich soapbark tree (Quillaja saponaria Molina) extracts were qualitatively and quantitatively characterized by HPLC-PDA-MS(n) and NMR spectroscopy. (+)-Piscidic acid represented the major constituent (75-87% (w/w) of total phenolics) in all examined extracts (n = 4), ranging from 22.1 ± 0.1 to 34.0 ± 0.2 mg/g of dry matter (DM). Derivatives of p-coumaric acid were present at concentrations from 2.2 to 9.3 mg/g of DM (8.1-20.4% of total phenolics), whereas other phenolic constituents such as glucosyringic acid and vanillic acid derivatives accounted for less than 7% of total phenolics. Generally, all Quillaja extracts showed a highly similar but unique pattern, potentially being useful to authenticate Quillaja extracts in foods, cosmetics, and pharmaceutical formulations. Furthermore, the desired antioxidant activity as well as undesired browning reactions in the final product might also be explained by these phenolic compounds, which were identified for the first time in Q. saponaria extracts.

Cross-linking oppositely charged oil-in-water emulsions to enhance heteroaggregate stability

“…In addition, one of the emulsifiers was required to be naturally accompanied by phenolic compounds, enabling laccase-initiated cross-linking. Therefore, due to their negative charge over a wide pH range [4] and their natural content in phenolic constituents [7,8], Quillaja saponins and sugar beet pectin were selected for the formation of negatively charged emulsion droplets. LAE, fish gelatin, and whey protein isolate were considered to form positively charged emulsion droplets, particularly since they contain numerous nucleophilic groups, potentially allowing cross-linking reactions with the enzymatically formed quinones.…”

“…carbonyl atoms) of glutaraldehyde [25] or the laccase-formed quinones [6]. In Quillaja saponin extracts, unbound phenolic components, such as (+)-piscidic acid and p-coumaric acid derivatives [7] , will be rapidly converted into highly reactive quinones as catalyzed by laccase. Subsequently, they might mediate cross-linking reactions by reacting with nucleophilic side chains of whey protein isolate or fish gelatin membrane proteins.…”

“…This might be due to relatively high glutaraldehyde concentrations (50 and 500 mM), since only ca. 0.5 µM phenolic compounds were present in the heteroaggregation experiment with laccase and Quillaja saponins [7], neglecting phenolic groups (e.g. from tyrosine) of proteins.…”

“…After enzymatic oxidation of the phenolics to reactive quinones, nucleophilic partners such as amine groups of proteins may covalently link to the quinone [6], ultimately yielding polymeric reaction products. High amounts of such oxidizable phenolic compounds were previously identified in the saponins-rich extracts from Quillaja saponaria Molina [7] and sugar beet pectin [8]. Therefore, those two emulsifiers were used in our study to form the negatively charged emulsions.…”

“…They were conducted in duplicate with independently and freshly prepared samples. The values reported represent means of at least Evaluation of the enzyme activities towards p-coumaric acid p-coumaric acid derivatives and the p-hydroxyphenyl phenolic (+)-piscidic acid represent the main phenolic compounds of Quillaja saponaria Molina extracts[7], thus being potentially suitable for enzymatic cross-linking oppositely charged emulsions. Therefore, p-coumaric acid was used for the determination of the enzyme activity.…”