Nadine Schulze-Kaysers

Evidence for the Formation of Benzacridine Derivatives in Alkaline-Treated Sunflower Meal and Model Solutions

Sunflower extraction meal (SEM) is an economically interesting protein source. During alkaline extraction of proteins, the presence of chlorogenic acid (CQA) in the meal gives rise to the formation of o-quinones. Reactions with nucleophiles present in proteins can lead to green discoloration. Although such reactions have been known for a long time, there is a lack of information on the chemical nature of the reaction products. SEM and model systems consisting of amino acids and CQA were subjected to alkaline treatment and, for comparison, to oxidation of CQA by polyphenoloxidase (PPO). Several green trihydroxy benzacridine (TBA) derivatives were tentatively identified in all samples by UHPLC-DAD-MS/MS. Surprisingly, in alkaline-treated samples of particular amino acids as well as in SEM, the same six TBA isomers were detected. In contrast, the enzymatically oxidized samples resulted in only three TBA derivatives. Contrary to previous findings, neither peptide nor amino acid residues were attached to the resultant benzacridine core. The results indicate that the formation of TBA derivatives is caused by the reaction between CQA quinones and free NH2 groups. Further research is necessary to elucidate the structure of the addition products for a comprehensive evaluation of food and feed safety aspects.

Phenolic compounds in edible species of the Anacardiaceae family – a review

The Anacardiaceae is a plant family that includes numerous species of high economic importance, e.g. mango, cashew, pistachio, and pink pepper as well as plants that are of local importance. Members of this family have been known as polyphenol-rich, however, this early view was based mainly on the results obtained using relatively basic analytical methods. During the past decades, tremendous progress has been made in analytical chemistry, which has led to new knowledge about the polyphenol composition of Anacardiaceae species. This review, covering 160 references, summarizes the most important literature on phenolic compounds present in edible species of the Anacardiaceae family. Structures of selected phenolic compounds are presented and chemotaxonomic aspects are discussed.

Characterization of phenolic and other polar compounds in peel and flesh of pink guava (Psidium guajava L. cv. ‘Criolla’) by ultra-high performance liquid chromatography with diode array and mass spectrometric detection

Pink guava (Psidium guajava L.) is a highly consumed fruit in tropical countries. Despite of interesting research on health effects of this fruit, investigations into the profile of secondary plant metabolites are scarce. In this study, the phenolic compounds in the peel and flesh of pink guava were characterized by ultra-high performance liquid chromatography with diode array and mass spectrometric detection. Sixty phenolic compounds were characterized by MS2 and classified as ellagitannins, flavones, flavonols, flavanols, proanthocyanidins, dihydrochalcones, and anthocyanidins, and non-flavonoids such as phenolic acid derivatives, stilbenes, acetophenones, and benzophenones. Forty-two polyphenols are reported for the first time in both peel and flesh, and twenty-four compounds were detected for the first time in P. guajava, e.g., phlorizin, nothofagin, astringin, chrysin-C-glucoside, valoneic acid bilactone, cinnamoyl-glucoside, and two dimethoxycinnamoyl-hexosides.

Separation and isolation of saturated and unsaturated 5-n-alk(en)ylresorcinols from rye bran

Alkylresorcinols (AR) are a class of phenolic lipids which are found in a number of plants and microorganisms and which are associated with various biological activities. In view of the very limited availability of reference compounds, we developed a process for the isolation of AR from rye bran. For this purpose, a crude extract was subjected to deep bed filtration at -80 °C, whereby the crystallized saturated AR were separated from the unsaturated homologues. Highly purified, individual compounds were subsequently isolated by semi-preparative HPLC. In contrast to previously published approaches, the method reported here is relatively easy to perform and allows the recovery of saturated and unsaturated AR of high purity. Furthermore, it is superior to argentation chromatography because it does not necessitate the removal of silver ions for subsequent bioassays.

Growth suppression of Fusarium culmorum, Fusarium poae and Fusarium graminearum by 5-n-alk(en)ylresorcinols from wheat and rye bran

Alk(en)ylresorcinols (AR), a class of phenolic lipids, are regarded as antifungal compounds showing high potential for the use in plant protection, especially against Fusarium head blight (FHB). In view of the very limited knowledge of the activity of single AR against Fusarium species, the antifungal effect of crude extracts, fractions and isolated homologues from wheat and rye bran was determined. It was shown that the saturated AR are the active compounds in the extracts, whereas the presence of unsaturated molecules leads to an antagonistic effect. The activity of single saturated AR is dependent on the chain length, but for highest antifungal efficiency a mixture of saturated homologues is required. Affecting the stage of germination, these molecules reduce, and may even completely prevent, the growth of the tested Fusarium species.

Characterization and Quantification of Polyphenols in Fruits

Polyphenols are a chemically diverse group of secondary metabolites that occur ubiquitously in plants. As a result of their pronounced structural diversity and hence their greatly differing chemical and physical properties, their analysis has proved to be challenging. In fruits and fruit-derived products, phenolic compounds are characterized and quantified for various reasons, for example, to determine the profile of potentially health-promoting bioactive compounds or for authentication purposes. While spectrophotometric methods are fast and inexpensive, they are non-specific and tend to overestimate the polyphenol content. In contrast, chromatographic techniques such as (U)HPLC, especially when combined with diode array and mass spectrometric detection, allow the characterization and quantification of individual compounds and are considered the method of choice nowadays. This contribution summarizes the most important publications including reviews on the analysis of phenolic compounds in fruits.

Effect of selected plant extracts on the inhibition of enzymatic browning in fresh-cut apple

This study describes the evaluation of the antibrowning effect of 36 plant extracts, divided into three groups: (1) fruits, vegetables, and oil seeds, (2) herbs and tea plants, and (3) medicinal plants, on minimally processed fresh apples. The extracts were applied to fresh-cut apple slices as dipping solutions. Development of browning was analyzed by measuring L *, a *, and b * values. The greatest inhibition of browning was caused by extracts from pumpkin seed (group 1), hibiscus flower (group 2), and pelargonium root (group 3). However, the latter caused intense passive staining. The inhibitory potential might be attributable to the antioxidative activity of secondary plant metabolites, especially phenolic compounds. Furthermore, these bioactive substances might influence enzyme activity directly by acting as competitive or non-competitive inhibitors.

Differentiation of Brazilian Peppertree (Schinus terebinthifolius Raddi) and Peruvian Peppertree (Schinus molle L.) Fruits by UHPLC–UV–MS Analysis of Their Anthocyanin and Biflavonoid Profiles

The objectives of this work were to determine the phenolic profile of Schinus terebinthifolius and Schinus molle fruits and to develop a reliable method for the differentiation of these two similar spices both known as pink pepper. Anthocyanins, biflavonoids and gallotannins, some of which are reported for the first time in these species, were identified by UHPLC-UV/vis-MS/MS. Consideration of the relative and absolute amounts of phenolics as well as indicator compounds from 18 samples revealed that the relative amounts of anthocyanins and biflavonoids are the most trustworthy parameters. Principal component analysis and cluster analysis (CA) allowed a grouping of the samples according to their species, showing that the anthocyanins are most important for the identification of species. As a result, authentication of the two Schinus species can be accomplished by UHPLC analysis of the relative amounts of anthocyanins combined with CA.