Nora M. O’Brien

Dietary flavonols: chemistry, food content, and metabolism.

The flavonols belong to a large group of compounds called flavonoids, which are diverse in their chemical structure and characteristics. Fruits, vegetables, and beverages such as tea and red wine are major sources of flavonols in the human diet. The daily consumption of flavonols is difficult to estimate because values depend on accurate assessment of feeding habits and flavonol content in foods. Food sources, dietary intakes, and bioavailability of flavonols are strongly influenced by variations in plant type and growth, season, light, degree of ripeness, food preparation, and processing, all of which are discussed. In the past few years, a number of studies on the absorption and metabolism of flavonols in humans have been published and the findings from these studies are reviewed. We do not discuss the health effects of flavonols.

Micellarisation of Carotenoids from Raw and Cooked Vegetables

The efficiency of carotenoid micellarisation from plant foods can be used as an effective tool for the initial screening of carotenoid bioavailability. Therefore, the objectives of the present study were to assess the effects of cooking on the micellarisation of β-carotene, lycopene, β-cryptoxanthin and lutein from courgette (zucchini), red pepper and tomato; and, to a minor extent, investigate uptake of lutein by Caco-2 cells from micellar fractions obtained from raw and cooked courgettes. Both raw and cooked vegetables were subjected to an in vitro digestion procedure. β-Carotene levels were significantly decreased in the digesta from each vegetable after boiling, grilling, microwave-cooking, or steaming, however all of the cooking methods enhanced β-carotene transfer to micelles. Carotenoid micellarisation ranged from 1.7% to 100% depending on the food, carotenoid, and the cooking method tested. Grilling and microwave-cooking were generally the most detrimental on the transfer of xanthophyll carotenoids, namely β-cryptoxanthin, to the micelles. Caco-2 cells absorbed greater amounts of lutein from the micelles of microwave-cooked courgettes than those that were raw, boiled, grilled, or steamed. Depending on the cooking methods used, carotenoid retention as well as micellarisation varied for each carotenoid among the different vegetables and different carotenoids present in each particular food.

UV-B-Induced Secondary Plant Metabolites - Potential Benefits for Plant and Human Health

Epidemiological studies have revealed an inverse association between the consumption of fruit, vegetables, and herbs and the risk of both cancer and cardiovascular disease. This protective effect is mostly due to secondary metabolites present in plant tissues. During the last decade, it has become increasingly clear that UV-B radiation is an important regulator of plant secondary metabolism. Low, ecologically-relevant UV-B levels trigger distinct changes in the accumulation of, among others, phenolic compounds, carotenoids and glucosinolates. Fundamental understanding of plant UV-B perception and responses opens up new opportunities for crop manipulation. Thus, targeted low dosage UV-B radiation treatments as emerging technology may be used to generate fruit, vegetables, and herbs enriched with secondary plant metabolites for either fresh consumption or as a source for functional foods and nutraceuticals, resulting in increased ingestion of these health-promoting substances. The UV-B induced accumulation of secondary plant metabolites is likely to have evolved as a plant defense response against harmful UV-B radiation. However, UV-B induced secondary metabolites also alter other trophic interactions, for example by altering plant herbivore resistance. Thus, UV-B driven metabolic changes in the plants secondary metabolism have benefits for both ends of the bio-based food chain, i.e., for plants themselves as well as for humans.

Bioactivities of glycoalkaloids and their aglycones from Solanum species.

Potatoes, tomatoes, and aubergines are all species of the Solanum genus and contain a vast array of secondary metabolites including calystegine alkaloids, phenolic compounds, lectins, and glycoalkaloids. Glycoalkaloids have been the subject of many literature papers, occur widely in the human diet, and are known to induce toxicity. Therefore, from a food safety perspective further information is required regarding their analysis, toxicity, and bioavailability. This is especially important in crop cultivars derived from wild species to prevent glycoalkaloid-induced toxicity. A comprehensive review of the bioactivity of glycoalkaloids and their aglycones of the Solanum species, particularly focused on comparison of their bioactivities including their anticancer, anticholesterol, antimicrobial, anti-inflammatory, antinociceptive, and antipyretic effects, toxicity, and synergism of action of the principal Solanum glycoalkaloids, correlated to differences of their individual molecular structures is presented.

Dietary Antioxidants in Health and Disease

Abstract Cellular systems are subject to constant oxidative stress by reactive oxygen species (ROS). Oxidative stress has been implicated as a factor in the aetiology of a variety of degenerative diseases and in the ageing process. ROS are capable of causing adverse modifications of macromolecules including lipids, DNA and proteins. Cellular systems also possess antioxidant defence systems whose role is to minimise adverse oxidative changes. The balance between prooxidant forces and antioxidant defence systems influences the body’s susceptibility to prooxidant damage. A variety of nutrient and non-nutrient dietary constituents, including vitamins C, E and carotenoids, have been shown to affect this prooxidant/antioxidant balance and consequent risk of certain degenerative diseases. Defining optimal intakes of these nutrients and non-nutrients is a key challenge in nutrition research.

Involvement of oxysterols in age-related diseases and ageing processes.

Ageing is accompanied by increasing vulnerability to major pathologies (atherosclerosis, Alzheimers disease, age-related macular degeneration, cataract, and osteoporosis) which can have similar underlying pathoetiologies. All of these diseases involve oxidative stress, inflammation and/or cell death processes, which are triggered by cholesterol oxide derivatives, also named oxysterols. These oxidized lipids result either from spontaneous and/or enzymatic oxidation of cholesterol on the steroid nucleus or on the side chain. The ability of oxysterols to induce severe dysfunctions in organelles (especially mitochondria) plays key roles in RedOx homeostasis, inflammatory status, lipid metabolism, and in the control of cell death induction, which may at least in part contribute to explain the potential participation of these molecules in ageing processes and in age related diseases. As no efficient treatments are currently available for most of these diseases, which are predicted to become more prevalent due to the increasing life expectancy and average age, a better knowledge of the biological activities of the different oxysterols is of interest, and constitutes an important step toward identification of pharmacological targets for the development of new therapeutic strategies.

The effect of lutein, sesamol, ellagic acid and olive leaf extract on lipid oxidation and oxymyoglobin oxidation in bovine and porcine muscle model systems

The effect of lutein (100, 200, 300μg/ml), sesamol (500, 1000, 2000μg/ml), ellagic acid (300, 600, 900μg/ml) and olive leaf extract (100, 200, 300μg/ml) on oxymyoglobin oxidation and lipid oxidation in bovine and porcine muscle model systems (25% M. longissimus thoracis et lumborum homogenates) was examined. Radical scavenging activity, using the DPPH assay, and iron-chelating activities of lutein, sesamol, ellagic acid and olive leaf extract were assessed at concentrations ranging from 200 to 1000ppm. The radical scavenging activity was of the order: ellagic acid>sesamol>olive leaf extract>lutein. None of the natural antioxidants examined exhibited iron chelating activity. Following induced lipid oxidation (FeCl(3)/sodium ascorbate addition), lipid oxidation and oxymyoglobin oxidation were measured after 24h at 4°C. In bovine and porcine muscle model systems, lipid oxidation decreased (P<0.001) following addition of each of the natural antioxidants relative to the control and antioxidant potency followed the order: sesamol>ellagic acid>olive leaf extract>lutein. Ellagic acid and olive leaf extract decreased oxymyoglobin oxidation (P<0.001) while sesamol increased oxymyoglobin oxidation in both systems. The natural antioxidants examined may have applications in the development of nutritional enhanced meat products with enhanced shelf-life characteristics.

Carotenoid Content of Commonly Consumed Herbs and Assessment of Their Bioaccessibility Using an In Vitro Digestion Model

Herbs are a rich source of bioactive phytochemicals such as carotenoids, which are known to exert various positive biological effects. However, there is very limited information in the literature regarding the content and bioavailability of carotenoids from commonly consumed herbs. Therefore, the objectives of the present study were first, to determine the carotenoid content of eight herbs namely basil (Ocimum basilicum), coriander (Coriandrum sativum), dill (Anethum graveolens), mint (Metha L.), parsley (Petroselinum crispum), rosemary (Rosmarinus officinalis), sage (Salvia officinalis), and tarragon (Artemisia dracunculus L.); and second, to assess carotenoid bioaccessibility from these herbs using a simulated human in vitro digestion model. Carotenoid bioaccessibility is defined as the amount of carotenoids transferred to micelles after digestion when compared with the original amount present in the food. The content of individual carotenoids varied significantly among the herbs tested. Carotenoid bioaccessibility varied from 0 to 42.8%. Basil and coriander, and their respective micelles, contained the highest levels of β-carotene, β-cryptoxanthin, and lutein + zeaxanthin. Our findings show that herbs are rich sources of carotenoids and that these foods can significantly contribute to the intake of bioaccessible carotenoids.

The effect of dietary supplementation with the citrus limonoids, limonin and nomilin on xenobiotic-metabolizing enzymes in the liver and small intestine of the rat

The aim of this study was to assess the effect of the citrus compounds, limonin and nomilin on activities of the phase I cytochrome P450 enzyme system and the phase II enzyme glutathione S-transferase (GST) in the liver and small intestine of the rat. Male Wistar rats were fed an American Institute of Nutrition-76 (AIN-76) diet containing increasing doses of limonin or nomilin (1, 2, 5 and 10 mg/day) for 10 days. A control group received the AIN-76 diet alone. The positive control group was fed the control diet containing 3-methylcholanthrene (3-MC; 15mg/day), a known inducer of cytochrome P450 and GST. No significant (P < 0.05) changes were observed in liver and small intestine cytochrome P450 isoenzyme activities from animals fed diets containing limonin or nomilin. In contrast, GST activity increased in a dose-dependent manner in the liver of rats fed diets containing limonin and nomilin. A significant dose-dependent increase in small intestinal GST activity was also observed in nomilin fed animals. Our results add to the increasing body of evidence that these citrus limonoids are inducers of the detoxifying enzyme GST.

The effects of salinity on the Manila clam (Ruditapes philippinarum) using the neutral red retention assay with adapted physiological saline solutions

This study investigated the internal osmotic regulatory capabilities of the Manila clam (Ruditapes philippinarum) following in vivo exposure to a range of salinities. A second objective was to measure the health status of the Manila clam following exposure to different salinities using the neutral red retention (NRR) assay, and to compare results using a range of physiological saline solutions (PSS). On exposure to seawater of differing salinities, the Manila clam followed a pattern of an osmoconformer, although they seemed to partially regulate their circulatory haemolytic fluids to be hyperosmotic to the surrounding aqueous environment. Significant differences were found when different PSS were used, emphasizing the importance of using a suitable PSS to reduce additional osmotic stress. Using PSS in the NRR assay that do not exert additional damage to lysosomal membrane integrity will help to more accurately quantify the effects of exposure to pollutants on the organism(s) under investigation.