Florian C. Stintzing

By-products of plant food processing as a source of functional compounds — recent developments

There is a rapidly growing body of literature covering the role of plant secondary metabolites in food and their potential effects on human health. Furthermore, consumers are increasingly aware of diet related health problems, therefore demanding natural ingredients which are expected to be safe and health-promoting. By-products of plant food processing represent a major disposal problem for the industry concerned, but they are also promising sources of compounds which may be used because of their favourable technological or nutritional properties. The purpose of this review is to highlight the potential of selected by-products as a source of functional compounds.

Stability of Essential Oils: A Review

Abstract In recent years, consumers have developed an ever-increasing interest in natural products as alternatives for artificial additives or pharmacologically relevant agents. Among them, essential oils have gained great popularity in the food, cosmetic, as well as the pharmaceutical industries. Constituting an array of many lipophilic and highly volatile components derived from a great range of different chemical classes, essential oils are known to be susceptible to conversion and degradation reactions. Oxidative and polymerization processes may result in a loss of quality and pharmacological properties. Despite their relevance for consumers, there is a paucity of information available addressing this issue. Therefore, the present review provides a comprehensive summary on possible changes in essential oils and factors affecting their stability. Focusing on individual essential oils, the various paths of degradation upon exposure to extrinsic parameters are outlined. Especially temperature, light, and oxygen availability are recognized to have a crucial impact on essential oil integrity. Finally, analytical methods to assess both genuine as well as altered essential oil profiles are evaluated with respect to their suitability to track chemical alterations. It is believed that only a careful inspection of essential oils by a set of convenient methods allows profound quality assessment that is relevant to producers and consumers alike.

Betacyanins in fruits from red-purple pitaya, Hylocereus polyrhizus (Weber) Britton & Rose

Abstract The betalain pattern of Hylocereus polyrhizus (Weber) Britton & Rose is reported for the first time and a highly practicable technique is described for the simultaneous isolation of pigment and mucilage from the mesocarp by extraction with water. Whereas betaxanthins were totally absent, 10 betacyanins could be separated by HPLC-PDA. For eight betacyanins the respective molecular masses could be obtained by positive ion electrospray mass spectrometry. Five of them were unequivocally assigned to bougainvillein-r-I, betanin, isobetanin, phyllocactin, and iso-phyllocactin. The remaining betacyanins were tentatively identified as (6′-O-3-hydroxy-3-methyl-glutaryl)-betanin, its C15-stereoisomer, and (6′-O-3-hydroxy-3–butyryl)-betanin, respectively. Using the β-glucosidase assay, acylated structures could be distinguished from non-acylated betacyanins. Contrary to white-fleshed Hylocereus undatus (Haworth) Britton & Rose with a slightly pink mesocarp, H. polyrhizus most likely possesses the same set of betalain forming enzymes in both pulp and mesocarp as the betacyanin pattern was found to be similar.

Betacyanins and phenolic compounds from Amaranthus spinosus L. and Boerhavia erecta L.

Stem bark extracts of Boerhavia erecta L. (erect spiderling) and Amaranthus spinosus L. (spiny amaranth), two wild growing weed plants used in traditional African medicine, were characterized with respect to their phenolic profile including the betalains. While the main betalains in A. spinosus were identified as amaranthine and isoamaranthine, the major betacyanins in B. erecta were betanin, isobetanin together with neobetanin. The latter showed higher betalain concentrations amounting to 186 mg/100 g, while the former contained 24 mg betacyanins in 100 g of the ground plant material. Extracts of A. spinosus were found to contain hydroxycinnamates, quercetin and kaempferol glycosides, whereas catechins, procyanidins and quercetin, kaempferol and isorhamnetin glycosides were detected in B. erecta. The amounts of these compounds ranged from 305 mg/100 g for A. spinosus to 329 mg/100 g for B. erecta.

Anthocyanins, Colour and Antioxidant Properties of Eggplant (Solanum melongena L.) and Violet Pepper (Capsicum annuum L.) Peel Extracts

Acetone extracts from eggplant (Solanum melongena L.) and violet pepper (Capsicum annuum L.) peels both belonging to the Solanaceae plant family were characterized with respect to their anthocyanin profiles, colour qualities and antioxidant capacities. According to HPLC-DAD-MS3 analyses the major anthocyanin in eggplant was delphinidin-3-rutinoside, while the predominant pigment in violet pepper was assigned to delphinidin-3-transcoumaroylrutinoside- 5-glucoside. Since virtually all anthocyanins were delphinidin-based, the effect of acylation and glycosylation patterns on colour stability and antioxidant capacity could be assessed. Application of two in vitro-assays for antioxidant capacity assessment revealed that eggplant generally exhibited higher values compared to violet pepper which was ascribed to 3,5-diglycosylated structures predominating in the latter. The higher extent of acylation in violet pepper was reflected by a more purplish colour shade of the extracts, but did not translate into a higher stability against fading which again was attributed to additional glycosyl substitution at C5. These findings support the relevance of structurerelated activities of anthocyanins both for understanding food colour and their particular nutritional value.

Apolar Laurus nobilis leaf extracts induce cytotoxicity and apoptosis towards three nervous system cell lines.

In the course of a bioactivity screening of Mediterranean plants, the assessment of neuroprotective properties of Laurus nobilis L. was of interest. Dried leaves were extracted by sonication using CHCl3 as solvent. The CHCl3 parental extract (CHCl3-pe) was fractionated to yield CHCl3 (LnC-1), EtOAc (LnC-2), MeOH (LnC-3) fractions. Each fraction underwent an extensive screening towards human neuroblastoma (SK-N-BE(2)-C, and SH-SY5Y) and rat glioma (C6) cell lines. MTT and SRB cytotoxicity tests were performed. The effect on the plasma membrane integrity was evaluated by assessment of LDH release. The caspase-3 activation enzyme and DNA fragmentation were also evaluated. The oxidant/antioxidant ability of all the extracts were evaluated using different methods. Furthermore, a metabolite profiling of the investigated extracts was carried out by GC-EI-MS. CHCl3-pe contained terpenes, allylphenols, and α-tocopherol. Dehydrocostus lactone was the main constituent. As result of the fractionation technique, the LnC-1 extract was mainly composed of α-tocopherol, whereas the LnC-2 fraction was enriched in guaiane and eudesmane terpenes. The most cytotoxic LnC-2 fraction induced apoptosis; it was ineffective in preventing in vitro free radicals production. Overall, the experimental results support a possible role of LnC-2 preparation as a chemopreventive agent for neuronal cells or other cells of the CNS.

Antioxidant properties and cytotoxic effects on human cancer cell lines of aqueous fermented and lipophilic quince (Cydonia oblonga Mill.) preparations.

In the course of a screening program on quince phytochemicals, two complex preparations were in the focus of the present study, i.e., a lipophilic quince wax extract (QWE) and an aqueous fermented one (QAFE). While the phytochemical composition has been described earlier, the intention of the current investigation was to complement these data with an extensive antioxidant screening of these preparations including their radical scavenging and reductive power as well as their antilipoperoxidative properties. The Quince Aqueous Fermented Extract (QAFE) effectively scavenged the radical target species exhibiting ID(50) values equal to 68.8 μg/mL towards DPPH· and 73.7 μg/mL towards the anion superoxide radical. Quince wax extract (QWE) was more effective at preventing the formation of thiobarbituric reactive species than QAFE exhibiting an ID(50) value equal to 48.9 μg/mL. Moreover the cytotoxic effects towards human HepG2, A549, and HeLa cell lines were evaluated. The two preparations exerted a different effect on the proliferation of the three tested cell lines. Noteworthy, QAFE was almost always more active than QWE but, sometimes, its effects seemed to be strongly dependent on exposure time. Data obtained demonstrate clearly that both hydrophilic and lipophilic quince preparations are non-toxic and exert health-promoting properties.

Investigations into the Phenolic Constituents of Dog's Mercury (Mercurialis perennis L.) by LC-MS/MS and GC-MS analyses

INTRODUCTION Dogs mercury (Mercurialis perennis L.) is a traditional European medicinal plant considered as a rich source of bioactive natural products. Yet phytochemical data of the plant are scant. OBJECTIVE This study aimed to identify the hydrophilic phenolic constituents from M. perennis by aqueous and hydroalcoholic extraction. METHODOLOGY Extracts of herbal parts were investigated in-depth by HPLC(DAD)-MS/MS and GC/MS analyses. In addition, a novel compound was isolated and fully characterised by 1- and 2D-NMR experiments. RESULTS Several conjugates of caffeic, p-coumaric and ferulic acids together with glucaric or 2-hydroxyglutaric acids (depsides) were detected in the aqueous extracts from aerial plant parts by use of LC-MS/MS techniques as well UV-spectral data. By implementation of preparative chromatography on polyamide pretreated with formic acid followed by vacuum liquid chromatography on reversed-phase C(18) -silica, one of the predominant depsides was isolated as a pure compound. The NMR spectra ((1) H and (13) C NMR) together with 2D-hetereonuclear multiple bond correlation NMR experiments (gHMBC and gHSQC) and chiral GC investigation, allowed identification of this compound as (-)-(E)-caffeoyl-2-(R)-oxoglutarate. This structure was additionally supported by GC/MS data after silylation and methylation reactions. The hydroalcoholic extract from aerial parts was separated by solvent partition between ethyl acetate and n-butanol. The latter fraction (n-butanol) yielded a mixture of mono- and oligo-glycosides of kaempferol and quercetin, all of them being assigned by LC-MS/MS. CONCLUSIONS The present investigation constitutes the first comprehensive report on the hydrophilic constituents of the rarely studied plant Mercurialis and thus completes the phytochemical knowledge on M. perennis.

Phenolic Compound Profiles and their Corresponding Antioxidant Capacity of Purple Pitaya (Hylocereus sp.) Genotypes

Folin-Ciocalteu and TEAC (Trolox equivalent antioxidant capacity) assay together with the spectrophotometric determination of betalains were applied to investigate the correlation between phenolics and their contribution to the antioxidant capacity of five different Costa Rican genotypes of purple pitaya (Hylocereus sp.) and of H. polyrhizus fruits. Maximum antioxidant capacity, total phenolic and betalain contents were observed in the genotype ‘Lisa’. While non-betalainic phenolic compounds contributed only to a minor extent, betalains were responsible for the major antioxidant capacity of purple pitaya juices evaluated. The phenolic pattern of each genotype was also thoroughly investigated using liquid chromatography coupled to positive electrospray ionization (ESI) tandem mass spectrometry. In addition to the well known betalains previously reported in Hylocereus fruits, several biosynthetic precursors were detected. Notably, decarboxylated and dehydrogenated betalains were identified as genuine compounds of the juices. Some of these compounds were previously described as artifacts upon heat exposure. Moreover, gallic acid was identified for the first time in pitaya fruits. While the phenolic profiles generally differed between genotypes, phenolic compound composition of ‘Rosa’ resembled that of H. polyrhizus with respect to total contents of betacyanins, betalainic precursors, phyllocactin and cyclo-Dopa malonyl-glucosides.

Studies on Betaxanthin Profiles of Vegetables and Fruits from the Chenopodiaceae and Cactaceae

The present study provides an update on the betaxanthin (bx) compositions of red and yellow beetroots, yellow-coloured Swiss chard petioles, and yellow-orange cactus pear. Applying RP-HPLC coupled with positive ion electrospray mass spectrometry and by comparison with UV-vis and mass spectrometric characteristics as well as retention times of semisynthesized reference compounds, 24 betaxanthins were identified in red and yellow beetroot hypocotyls. Twenty-five and thirteen betaxanthins were present in yellow Swiss chard petioles and the cactus pear cultivar ‘Gialla’, respectively. Ethanolamine-bx and threonine-bx were found to be novel betaxanthins in Chenopodiaceae representatives, which to the best of our knowledge have not been reported as genuine pigments so far. Furthermore, aspartic acidbx (miraxanthin II), lysine-bx, and methionine-bx, hitherto found in other families, were identified in the Chenopodiaceae for the first time. Additionally, tyrosine-bx (portulacaxanthin II) and tryptophan-bx have not been earlier reported to occur in the Cactaceae. These findings provide valuable phytochemical information and may be useful for a better understanding of the functional properties of betaxanthins in plants.