Marina Heinonen

Antimicrobial effects of Finnish plant extracts containing flavonoids and other phenolic compounds

Plant phenolics, especially dietary flavonoids, are currently of growing interest owing to their supposed functional properties in promoting human health. Antimicrobial screening of 13 phenolic substances and 29 extracts prepared from Finnish plant materials against selected microbes was conducted in this study. The tests were carried out using diffusion methods with four to nine microbial species (Aspergillus niger, Bacillus subtilis, Candida albicans, Escherichia coli, Micrococcus luteus, Pseudomonas aeruginosa, Saccharomyces cerevisiae, Staphylococcus aureus and Staphylococcus epidermidis). Flavone, quercetin and naringenin were effective in inhibiting the growth of the organisms. The most active plant extracts were purple loosestrife (Lythrum salicaria L.) against Candida albicans, meadowsweet (Filipendula ulmaria (L.) Maxim.), willow herb (Epilobium angustifolium L.), cloudberry (Rubus chamaemorus L.) and raspberry (Rubus idaeus L.) against bacteria, and white birch (Betula pubescens Ehrh.), pine (Pinus sylvestris L.) and potato (Solanum tuberosum. L.) against gram-positive Staphylococcus aureus.

Antimicrobial properties of phenolic compounds from berries.

Aims: To investigate the antimicrobial properties of phenolic compounds present in Finnish berries against probiotic bacteria and other intestinal bacteria, including pathogenic species.

Anti-Inflammatory Effects of Flavonoids: Genistein, Kaempferol, Quercetin, and Daidzein Inhibit STAT-1 and NF-κB Activations, Whereas Flavone, Isorhamnetin, Naringenin, and Pelargonidin Inhibit only NF-κB Activation along with Their Inhibitory Effect on iNOS Expression and NO Production in Activated Macrophages

In inflammation, bacterial products and proinflammatory cytokines induce the formation of large amounts of nitric oxide (NO) by inducible nitric oxide synthase (iNOS), and compounds that inhibit NO production have anti-inflammatory effects. In the present study, we systematically investigated the effects of 36 naturally occurring flavonoids and related compounds on NO production in macrophages exposed to an inflammatory stimulus (lipopolysaccharide, LPS), and evaluated the mechanisms of action of the effective compounds. Flavone, the isoflavones daidzein and genistein, the flavonols isorhamnetin, kaempferol and quercetin, the flavanone naringenin, and the anthocyanin pelargonidin inhibited iNOS protein and mRNA expression and also NO production in a dose-dependent manner. All eight active compounds inhibited the activation of nuclear factor-κB (NF-κB), which is a significant transcription factor for iNOS. Genistein, kaempferol, quercetin, and daidzein also inhibited the activation of the signal transducer and activator of transcription 1 (STAT-1), another important transcription factor for iNOS. The present study characterises the effects and mechanisms of naturally occurring phenolic compounds on iNOS expression and NO production in activated macrophages. The results partially explain the pharmacological efficacy of flavonoids as anti-inflammatory compounds.

Protein oxidation in muscle foods: a review.

Protein oxidation in living tissues is known to play an essential role in the pathogenesis of relevant degenerative diseases, whereas the occurrence and impact of protein oxidation (Pox) in food systems have been ignored for decades. Currently, the increasing interest among food scientists in this topic has led to highlight the influence that Pox may have on meat quality and human nutrition. Recent studies have contributed to solid scientific knowledge regarding basic oxidation mechanisms, and in advanced methodologies to accurately assess Pox in food systems. Some of these studies have provided insight into the reactions involved in the oxidative modifications undergone by muscle proteins. Moreover, a variety of products derived from oxidized muscle proteins, including cross-links and carbonyls, have been identified. The impact of oxidation on protein functionality and on specific meat quality traits has also been addressed. Some other recent studies have shed light on the complex interaction mechanisms between myofibrillar proteins and certain redox-active compounds such as tocopherols and phenolic compounds. This paper is devoted to review the most relevant findings on the occurrence and consequences of Pox in muscle foods. The efficiency of different anti-oxidant strategies against the oxidation of muscle proteins is also reported.

The Biological Relevance of Direct Antioxidant Effects of Polyphenols for Cardiovascular Health in Humans Is Not Established

Human studies provide evidence for beneficial effects of polyphenol-rich foods on cardiovascular health. The antioxidant activity of polyphenols potentially explains these effects, but is the antioxidant activity a reliable predictor for these effects? An International Life Sciences Institute Europe working group addressed this question and explored the potential of antioxidant claims for polyphenols in relation to cardiovascular health by using the so-called Process for the Assessment of Scientific Support for Claims on Foods project criteria. In this process, analytical aspects of polyphenols, their occurrence in foods, dietary intake, and bioavailability were reviewed. Human studies on polyphenols and cardiovascular health were reviewed together with methods for biomarkers of oxidative damage and total antioxidant capacity (TAC). In retrospective studies, F2-isoprostanes and oxidized LDL, the most reliable biomarkers of lipid peroxidation, and measures for TAC showed the expected differences between cardiovascular disease patients and healthy controls, but prospective studies are lacking, and a causal relationship between these biomarkers and cardiovascular health could not be established. Therefore, the physiological relevance of a potential change in these biomarkers is unclear. We found limited evidence that some types of polyphenol-rich products modify these biomarkers in humans. A direct antioxidant effect of polyphenols in vivo is questionable, however, because concentrations in blood are low compared with other antioxidants and extensive metabolism following ingestion lowers their antioxidant activity. Therefore, the biological relevance of direct antioxidant effects of polyphenols for cardiovascular health could not be established. Overall, although some polyphenol-rich foods exert beneficial effects on some biomarkers of cardiovascular health, there is no evidence that this is caused by improvements in antioxidant function biomarkers (oxidative damage or antioxidant capacity).

Berry phenolics selectively inhibit the growth of intestinal pathogens

Aims:  To investigate the effects of berries and berry phenolics on pathogenic intestinal bacteria and to identify single phenolic compounds being responsible for antimicrobial activity.

Berry Phenolics: Antimicrobial Properties and Mechanisms of Action Against Severe Human Pathogens

Abstract: Antimicrobial activity and mechanisms of phenolic extracts of 12 Nordic berries were studied against selected human pathogenic microbes. The most sensitive bacteria on berry phenolics were Helicobacter pylori and Bacillus cereus. Campylobacter jejuni and Candida albicans were inhibited only with phenolic extracts of cloudberry, raspberry, and strawberry, which all were rich in ellagitannins. Cloudberry extract gave strong microbicidic effects on the basis of plate count with all studied strains. However, fluorescence staining of liquid cultures of virulent Salmonella showed viable cells not detectable by plate count adhering to cloudberry extract, whereas Staphylococcus aureus cells adhered to berry extracts were dead on the basis of their fluorescence and plate count. Phenolic extracts of cloudberry and raspberry disintegrated the outer membrane of examined Salmonella strains as indicated by 1-N-phenylnaphthylamine (NPN) uptake increase and analysis of liberation of [14C]galactose- lipopolysaccharide. Gallic acid effectively permeabilized the tested Salmonella strains, and significant increase in the NPN uptake was recorded. The stability of berry phenolics and their antimicrobial activity in berries stored frozen for a year were examined using Escherichia coli and nonvirulent Salmonella enterica sv. Typhimurium. The amount of phenolic compounds decreased in all berries, but their antimicrobial activity was not influenced accordingly. Cloudberry, in particular, showed constantly strong antimicrobial activity during the storage.

Fluorescence spectroscopy as a novel approach for the assessment of myofibrillar protein oxidation in oil-in-water emulsions

The oxidation of oil-in-water emulsions (37°C/10 days) containing increasing levels of myofibrillar proteins (MP) (0.5%, 1% and 2% on the basis of lipid content) was investigated. Protein oxidation was assessed by measuring the loss of natural tryptophan fluorescence and the increase in fluorescent protein oxidation products (FP) using fluorescence spectroscopy. Lipid oxidation was simultaneously analysed by measuring the increase of conjugated dienes (CD) and hexanal. The oxidative degradation of tryptophan residues occurred as an early event in MP oxidation whereas FP formed later as secondary protein oxidation products. The shift of the tryptophan maximum fluorescence emission wavelength during oxidation provided information about the location of oxidising tryptophan residues. Emulsions with higher concentrations of MP displayed higher tryptophan fluorescence and yielded a higher amount of FP. MP acted as inhibitors of lipid oxidation because emulsions with higher MP contents contained lower levels of CD and hexanal. Significant negative correlations were found between tryptophan fluorescence and CD, reflecting the timely interaction between primary lipid oxidation products and protein oxidation. Both spectrophotometric techniques were useful although the loss of tryptophan fluorescence is more reliable since it is a specific measurement which is not affected by the presence of other fluorescent protein oxidation products.

Analysis of protein carbonyls in meat products by using the DNPH-method, fluorescence spectroscopy and liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS).

Liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) was applied as an advanced methodology to study the suitability of using α-aminoadipic semialdehyde (AAS) and γ-glutamic semialdehyde (GGS) as protein oxidation markers in meat products. The results obtained were compared to those obtained by using the DNPH-method and fluorescence spectroscopy for the analysis of protein carbonyls. Lipid oxidation was also investigated in order to elucidate the relationship between lipid and protein oxidation measurements. Both semialdehydes were originally detected in a food system which proves that lysine, arginine and proline are degraded as a result of oxidative reactions to yield AAS and GGS in meat products. A lack of consistency was observed between the MS results for AAS and GGS and the values obtained by the DNPH-method and the fluorescence spectroscopy. Unlike the last two methods, AAS and GGS measurements have proved to be unaffected by the composition or the structure of the food matrix providing precise information about the fate of particular amino acids during processing of muscle foods. These semialdehydes, and particularly GGS, could be used as indicators of protein oxidation in meat products like TBARS numbers are commonly used as lipid oxidation markers. In fact, a significant correlation was found between GGS values and TBARS highlighting the timely interaction between lipid and protein oxidation.

Metabolism of berry anthocyanins to phenolic acids in humans.

We studied the metabolism of berry anthocyanins to phenolic acids in six human subjects by giving them bilberry-lingonberry puree with and without oat cereals. Puree + cereals contained 1435 micromol of anthocyanins and 339 micromol of phenolic acids. The urinary excretion of measured 18 phenolic acids increased 241 micromol during the 48 h follow-up after the puree + cereals supplementation. The excretion peak of dietary phenolic acids was observed at 4-6 h after the puree + cereals supplementation and 2 h earlier after the supplementation of the puree alone. Homovanillic and vanillic acids were the most abundant metabolites, and they were partly produced from anthocyanins. No gallic acid, a fragmentation product of delphinidin glycosides, was detected, and only a very low amount of malvidin glycosides was possibly metabolized to syringic acid. Although anthocyanins were partly fragmented to phenolic acids, still a large part of metabolites remained unknown.