Sibel Karakaya

A standardised static in vitro digestion method suitable for food-an international consensus

Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

Olive tree (Olea europaea) leaves: potential beneficial effects on human health

Olive tree (Olea europaea L.) leaves have been widely used in traditional remedies in European and Mediterranean countries such as Greece, Spain, Italy, France, Turkey, Israel, Morocco, and Tunisia. They have been used in the human diet as an extract, an herbal tea, and a powder, and they contain many potentially bioactive compounds that may have antioxidant, antihypertensive, antiatherogenic, anti-inflammatory, hypoglycemic, and hypocholesterolemic properties. One of these potentially bioactive compounds is the secoiridoid oleuropein, which can constitute up to 6-9% of dry matter in the leaves. Other bioactive components found in olive leaves include related secoiridoids, flavonoids, and triterpenes. The evidence supporting the potentially beneficial effects of olive leaves on human health are presented in this brief review.

Bioavailability of phenolic compounds.

Phenolic compounds in foods originate from one of the main classes of secondary metabolites in plants. They are essential for the growth and reproduction of plants, and are produced as a response for defending injured plants against pathogens. In recent years, there is a growing interest in phenolic compounds and their presumed role in the prevention of various degenerative diseases, such as cancer and cardiovascular diseases. The importance of antioxidant activities of phenolic compounds and their possible usage in processed foods as a natural antioxidant have reached a new high in recent years. The absorption and bioavailability of phenolics in humans are also controversial. Data on these aspects of phenolics are scarce and merely highlight the need for extensive investigations of the handling of phenolics by the gastrointestinal tract and their subsequent absorption and metabolism. In this article, absorption, metabolism, and the bioavailability of phenolic compounds are reviewed.

Antioxidant activity of some foods containing phenolic compounds

This study was designed to determine the total phenols (TP) and total antioxidant activity (TAA) of some liquid and solid plant foods that are commonly consumed in Turkey. Total phenols were analysed according to the Folin-Ciocalteu method and antioxidant activities of these compounds in aqueous phase were assessed by measuring their direct ABTS.- radical scavenging abilities. Total phenols varied from 68 to 4162 mg/l for liquid foods and from 735 to 3994 mg/kg for solid foods. TAA of liquid and solid foods ranged between 0.61-6.78 mM and 0.63-8.62 mM, respectively. Total antioxidant activities of foods were well correlated with total phenols (r2 = 0.95). According to content of total phenols per serving, liquid foods were in the order of black tea > instant coffee > coke > red wine > violet carrot juice > apricot nectar > Turkish coffee > grape molasses > sage > white wine > linden flower, and solid foods were in the order of red grape > raisins > tarhana > dried black plum > dried apricot > grape > fresh paprika > fresh black plum > Urtica sp. > cherry > fresh apricot > paprika pickle > paprika paste.This study was designed to determine the total phenols (TP) and total antioxidant activity (TAA) of some liquid and solid plant foods that are commonly consumed in Turkey. Total phenols were analysed according to the Folin-Ciocalteu method and antioxidant activities of these compounds in aqueous phase were assessed by measuring their direct ABTS .– radical scavenging abilities. Total phenols varied from 68 to 4162 mg/l for liquid foods and from 735 to 3994 mg/kg for solid foods. TAA of liquid and solid foods ranged between 0.61-6.78 mM and 0.63-8.62 mM, respectively. Total antioxidant activities of foods were well correlated with total phenols (r 2 = 0.95). According to content of total phenols per serving, liquid foods were in the order of black tea > instant coffee > coke > red wine > violet carrot juice > apricot nectar > Turkish coffee > grape molasses > sage > white wine > linden flower, and solid foods were in the order of red grape > raisins > tarhana > dried black plum > dried apricot > grape > fresh paprika > fresh black plum > Urtica sp. > cherry > fresh apricot > paprika pickle > paprika paste.

Radical scavenging and iron-chelating activities of some greens used as traditional dishes in Mediterranean diet

This study aimed at evaluating the antioxidative activity of nine different families of greens. Raphanus raphanistrum (wild radish), Anchusa azurea (bugloss), Daucus carota (wild carrot), Sonchus oleraceus (sowthistle), Papaver rhoeas (corn poppy), Malva sylvestris (blue mallow), Foeniculum vulgare (fennel), Cichorium intybus (chicory) and Salicornia europaea (jointed glasswort) are native to the Mediterranean and are commonly consumed as a salad or an ingredient in some recipes. The antioxidative activities, including the radical scavenging effects, inhibition of hydrogen peroxide (H2O2), and Fe2+-chelating activity, were studied. All samples showed antioxidant activity as a radical scavenger in the experiment using the DPPH• radical. The ratio between the slopes of the kinetic model was used to compare antioxidant efficiency of different greens. Greens also possessed antioxidative activity toward H2O2. Especially, greens exhibited a marked scavenging effect on H2O2 at 0.2 g/ml concentration. The Fe2+ ion-chelating activities of the samples except jointed glasswort were greater than 70%. The antioxidant activity of samples with different methods based on the inhibition of different reactions could not be compared. The current dietary guidelines include recommendations for an increase in the consumption of plant foods. Greens should provide an optimal supply of antioxidant substances in the diet.

In Vitro Models for Studying Secondary Plant Metabolite Digestion and Bioaccessibility

There is an increased interest in secondary plant metabolites, such as polyphenols and carotenoids, due to their proposed health benefits. Much attention has focused on their bioavailability, a prerequisite for further physiological functions. As human studies are time consuming, costly, and restricted by ethical concerns, in vitro models for investigating the effects of digestion on these compounds have been developed and employed to predict their release from the food matrix, bioaccessibility, and assess changes in their profiles prior to absorption. Most typically, models simulate digestion in the oral cavity, the stomach, the small intestine, and, occasionally, the large intestine. A plethora of models have been reported, the choice mostly driven by the type of phytochemical studied, whether the purpose is screening or studying under close physiological conditions, and the availability of the model systems. Unfortunately, the diversity of model conditions has hampered the ability to compare results across different studies. For example, there is substantial variability in the time of digestion, concentrations of salts, enzymes, and bile acids used, pH, the inclusion of various digestion stages; and whether chosen conditions are static (with fixed concentrations of enzymes, bile salts, digesta, and so on) or dynamic (varying concentrations of these constituents). This review presents an overview of models that have been employed to study the digestion of both lipophilic and hydrophilic phytochemicals, comparing digestive conditions in vitro and in vivo and, finally, suggests a set of parameters for static models that resemble physiological conditions.

Mind the gap—deficits in our knowledge of aspects impacting the bioavailability of phytochemicals and their metabolites—a position paper focusing on carotenoids and polyphenols

Various secondary plant metabolites or phytochemicals, including polyphenols and carotenoids, have been associated with a variety of health benefits, such as reduced incidence of type 2 diabetes, cardiovascular diseases, and several types of cancer, most likely due to their involvement in ameliorating inflammation and oxidative stress. However, discrepancies exist between their putative effects when comparing observational and intervention studies, especially when using pure compounds. These discrepancies may in part be explained by differences in intake levels and their bioavailability. Prior to exerting their bioactivity, these compounds must be made bioavailable, and considerable differences may arise due to their matrix release, changes during digestion, uptake, metabolism, and biodistribution, even before considering dose‐ and host‐related factors. Though many insights have been gained on factors affecting secondary plant metabolite bioavailability, many gaps still exist in our knowledge. In this position paper, we highlight several major gaps in our understanding of phytochemical bioavailability, including effects of food processing, changes during digestion, involvement of cellular transporters in influx/efflux through the gastrointestinal epithelium, changes during colonic fermentation, and their phase I and phase II metabolism following absorption.

Quercetin, luteolin, apigenin and kaempferol contents of some foods

Quercetin, luteolin, apigenin and kaempferol contents of Urtica sp., Rosa cannina (rosehip), Salvia officinalis (sage), Tilia platyphyllos (linden flower), black tea, Daucus carota L. spp sativus (violet carrot juice), grape molasses, honey and tarhana were determined by HPLC with UV detection. Consumption of the samples was assessed using a food frequency questionnaire method. One hundred healthy volunteers were asked to state the number of times on average per day, week or month they consumed each item over the last 6 months. Quercetin was determined in all samples except honey, whereas luteolin was determined only in sage. Kaempferol was determined in black tea, linden flower and honey samples, and apigenin was determined in honey and Urtica sp. Quercetin intake by the consumption of tea, linden flower, sage rosehip, violet carrot juice, grape molasses, tarhana and juice of Urtica sp. were estimated as 4.2–25, 2.6, 3.3, and 2.0 μg/day, 1.67 mg/day, 1.70 mg/day, 1.78 mg/month and 21.75–65.25 μg/month, respectively. Luteolin intake by the consumption of sage was estimated as 1.32 μg/day. Apigenin intakes by the consumption of honey and juice of Urtica sp. were estimated as 2.34 mg/day and 3.58–10.73 mg/month, respectively. Kaempferol intakes of the participants from tea, linden flower and honey were estimated as 13.2–79.2, 13.56 and 190 μg/day respectively. ©

Antimutagenic activities of some foods

There has been a recent increase in research into the possible ways of protecting individuals from cancer by making changes in dietary habits. In this study raw and boiled juice and leaf and dried seeds of Urtica sp, Stachys annula, sage, rosehip, grape molasses and tarhana were not found mutagenic in S typhimurium TA 100. All of the foods decreased sodium azide mutagenicity in S typhimurium TA 100. Among the foods tested, raw Urtica sp (46.32%) and rosehip (44.03%) showed the highest antimutagenic effect followed by leaf of Urtica sp (41.25%), boiled juice of Urtica sp (37.22%), Stachys annula (36.42%), grape molasses (33.03%) and tarhana (28.60%), respectively. The antimutagenic activities of Urtica sp and rosehip were found to be significantly higher than the antimutagenic activity of tarhana (p<0.01). © 1999 Society of Chemical Industry

Vegetable and fermented vegetable juices containing germinated seeds and sprouts of lentil and cowpea

Health-promoting effects of vegetable juice (VJ) and fermented vegetable juice (FVJ) were determined. Both juices displayed antioxidant activity against DPPH radical, and ORAC values obtained for both juices were not statistically different. The α-glucosidase inhibitory activities of the VJ and FVJ were not different. However, α-amylase inhibitory effect of the VJ (IC50: 41μM) was higher than that of FVJ (IC50: 149μM) (p<0.05). In vitro bile acid-binding capacity of FVJ was about 4.30times higher than that of VJ (p<0.05). Although in vitro ACE inhibitory activity of VJ was below 50%, FVJ displayed ACE inhibition (80.2%) with an IC50 value of 50μgprotein/ml. Even though ACE inhibitory activities of digested and undigested FVJ were similar, there was a 42-fold decrease in the IC50 value of FVJ after small intestinal digestion (p<0.05). FVJ, diluted by one half, displayed hemagglutinating activity whilst VJ did not display any hemagglutinating activity.