Location: Food Components and Health Laboratory2011 Annual Report
1a. Objectives (from AD-416)
Objective 1: Elucidate factors which influence bioavailability, metabolism, and kinetics of dietary phytonutrients, such as anthocyanins, ellagitannins, flavonoids, allylic sulfides, and isoflavones, and define the observed inter-individual variation as well as the genetic basis for the observed variation. Sub-objective 1.A: Characterize effects of postharvest processing on phytonutrient content. Sub-objective 1.B.: Determine the importance of aglycone structure on anthocyanin bioavailability. Sub-objective 1.C.: Determine the importance of acylation on anthocyanin bioavailability. Sub-objective 1.D.: Determine the influence of protein on anthocyanin bioavailability. Sub-objective 1.E.: Identify metabolites of anthocyanins. Sub-objective 1.F.: Develop methods to isotopically label quercetin in leaf lettuce. Sub-objective 1.G.: Identify metabolites of quercetin. Sub-objective 1.H.: Develop methods to isotopically label isoflavones in soy. Objective 2: Determine the ability of plant-based dietary components to influence oxidative stress, inflammation, DNA damage, glucoregulation, and blood pressure, and define the inter-individual variation in these responses as well as the genetic basis for the variation. Sub-objective 2.A.: Determine the effect of pomegranate juice on blood pressure, endothelial function, and inflammation. Sub-objective 2.B.: Discover mechanisms by which garlic phytonutrients affect risk factors for cancer and cardiovascular disease.
1b. Approach (from AD-416)
Epidemiological studies have repeatedly shown that diets high in fruits and vegetables are associated with decreased risk of chronic diseases that ultimately strike most Americans. However, the scientific foundation necessary to translate these epidemiological findings into dietary recommendations is weak. Research is needed to clarify specific health benefits of phytonutrients, to determine their bioavailability, to delineate rates of metabolism and elimination from the body, and to identify genetic differences among individuals that impact phytonutrient action in the body. This plan describes a five-year research project to investigate content, bioavailability, metabolism, and health benefits of selected phytonutrients. Studies will be conducted to determine the effect of postharvest processing on phytonutrient content. The initial focus of the postharvest studies will be leaf lettuce and tomatoes, and these studies will be expanded to include kale, spinach, swiss chard, and strawberries as funding is available. Several studies will be conducted to improve understanding of phytonutrient bioavailability and metabolism. The proposed focus of these studies is anthocyanins, building on previous work in our lab. Methods will be developed to isotopically label quercetin in lettuce and isoflavones in soy. These studies will expand our isotopic labeling program from carotenoids and anthocyanins to other phytonutrients. The influence of phytonutrients on biomarkers of chronic disease will be investigated, with an initial focus on garlic due to its promising role in cancer prevention. Genotyping will be included in clinical studies whenever sufficient scientific justification exists. This research will be conducted through plant growth and postharvest studies, human feeding trials, quantitative and qualitative chemistry, molecular biology, and kinetic mathematical modeling techniques. Information generated from this project can be used to develop recommendations for dietary intakes of phytonutrients that will improve health and reduce risk of chronic disease.
3. Progress Report
This is a project through which investigations into the health benefits of phytonutrients in humans are being conducted. The project has two primary components, one involving feeding agricultural products to humans to assess health impact and one involving investigation of environmental impacts on plant nutrients. Studies conducted under this project address National Program 107 (Human Nutrition), with emphasis on Program Priorities 2A-Identify Roles of Food, Nutrients, Food Components, and Physical Activity in Promoting Health and Preventing Disease and 2B-Improve the Scientific Basis for Updating National Dietary Standards and Guidelines. Progress has been made on several aspects of the human feeding program. A large feeding study was completed to investigate the effects of cranberry juice on markers of cardiovascular disease. For this study, 57 volunteers consumed cranberry juice or a placebo beverage for 8 weeks, then provided blood, urine, and fecal samples for analysis. Sample analysis is underway for blood cholesterol levels, ability to form blood clots, and inflammation. Fecal samples will be analyzed for bacterial content and character. Another large feeding study was completed to determine the influence of blackberry consumption on cancer risk factors. For this study, 52 volunteers consumed blackberries or placebo to determine impact on cancer biomarkers, with the primary focus on damage to DNA. A third study was completed to determine how characteristics of the stomach environment affect the body’s absorption of healthful pigments from berries. The stomach is usually a very acidic compartment, which is thought to promote berry pigment stability. However, when individuals are treated for gastric reflux, the stomach environment becomes much less acidic, potentially allowing destruction of the healthful pigments and rendering them useless by the body. In a feeding study, volunteers consumed berries with or without over-the-counter acid blocking medication (to reduce stomach acid). The volunteers provided blood and urine samples for several hours, and those samples are being analyzed for berry pigment content. Laboratory analysis was conducted on samples collected from a human study conducted the previous year to determine the effects of garlic on pathways of metabolism. Cutting-edge techniques were used to assess how human genes were “turned up” or “turned down” by garlic. Interpretation of the results is underway. In preparation for future research, protocols were written for two new studies: one to investigate pomegranate juice and vascular health and one to investigate metabolites of grape polyphenols. Progress has been made on several aspects of the program to examine environmental changes and plant phytonutrient content. Differential sensitivity to ultraviolet was determined for the induction of flavonoids (quercetin and cyanidin) in lettuce varieties. Increasing antioxidants that provide color, flavor and possibly nutritional value in green leafy vegetables is an important goal, especially under conditions in which these compounds are low (e.g., winter greenhouse production).
1. Structural features of plant pigments affecting bioavailability. The body’s absorption and utilization of plant flavonoid pigments in poorly understood, thus impeding the ability of health professionals to make dietary recommendations. ARS researchers in Beltsville, MD, used mathematical techniques to analyze data from a human feeding trial to determine rates of absorption and elimination of flavonoid pigments called anthocyanins. Special chemical side-chains called acylations were found to severely inhibit the absorption of these healthful pigments, as well as alter the body’s elimination of these compounds. These results add to the body of knowledge regarding how much of these healthful pigments should be consumed daily.
2. Differential sensitivity of flavonoids in leaf lettuce to ultraviolet light. Winter greenhouse production of green leafy vegetables can result in lower flavonoid content due to diminished exposure to light, thus resulting in a crop that is lower in antioxidants, color, flavor, and nutritional value. Using ultraviolet light-emitting diodes (LEDs), ARS researchers at Beltsville, MD, demonstrated that quercetin and cyanidin increased several-fold in one variety of red leaf lettuce (cv ‘Galactic’) at low levels of ultraviolet that had no effect on a second variety (cv. ‘Red Sails’). Using information from these studies (wavelength sensitivity, requirements for daily integral irradiance), an array of LEDs was designed to move cyclically back and forth along a bench and provide intermittent “pulses” of ultraviolet every two minutes. This treatment induced 5-fold increases in flavonoids in the sensitive line under winter greenhouse conditions. The development of the LED system provides a method to improve the quality of leafy vegetables, and the demonstration that lettuce varieties are differentially sensitive to ultraviolet light will allow interventions to be more effectively targeted.
Novotny Dura, J., Harrison, D.J., Pawlosky, R., Flanagan, V.P., Harrison, E.H., Kurilich, A.C. 2010. Beta-Carotene conversion to vitamin A decreases as the dietary dose increases in humans. Journal of Nutrition. 140(5):915-918.