Interdisciplinary applications for enhancing dietary polyphenol consumption, bioavailability, and health impact

Abstract

Chronic diseases such as cardiovascular disease (CVD) continue to be leading causes of morbidity and mortality worldwide. Consumption of plant foods, rich in phytochemicals such as polyphenols, are associated with reduced CVD risk through improvements in oxidative stress, inflammation, vascular function, and other mechanisms. However, consumption of fruits and vegetables in the United States remains inadequate despite the best efforts of health practitioners, researchers, and policymakers though public health guidelines. Furthermore, polyphenol bioavailability in the gastrointestinal (GI) tract is very low and many polyphenols undergo spontaneous degradation in the upper GI tract, which may limit the bioavailability of polyphenols and their metabolites. Increasing polyphenol concentrations in foods and polyphenol bioavailability may enhance the health-promoting properties of the fruits and vegetables consumed in the standard American diet. This may be accomplished through biofortification of polyphenol-rich foods using modern production practices like controlled environment agriculture (i.e. indoor farming), through the strategic combination of polyphenol-rich foods with other meal components like protein powder to facilitate polyphenol bioavailability, and through the identification and evaluation of novel phytochemical-rich foods for human consumption. The objectives of this dissertation were to 1) assess the feasibility and tolerability of daily 'bull's blood' beet (Beta vulgaris) and red cabbage (Brassica oleracea var capitate) consumption, novel polyphenol-rich foods, in healthy middle-aged and older adults, 2) develop an optimized protocol for producing biofortified red cabbage microgreens using controlled environment agriculture, and 3) examine the impact of co-consumption of protein powder dietary supplements from dairy and plant sources on blueberry polyphenol bioavailability in healthy adults. To achieve our first objective, we performed a randomized crossover clinical trial where participants, healthy adults aged 45-65 years, consumed either two cups of red cabbage microgreens or 'Bull's Blood' red beet microgreens for two weeks in a random order, with two weeks of washout between treatments. Feasibility was determined by participant retention and compliance, which was measured through self-reported dosing logs. GI tolerability was measured through self-reported GI health questionnaires and bowel movement logs. High participant retention (initial n=26, final n=24) and a treatment compliance of 95.6% is indicative of the feasibility of daily microgreens consumption. In some categories, GI symptom severity scores improved with red cabbage microgreens consumption, and no adverse effects were observed, suggestive of GI tolerability of daily microgreen consumption. To achieve our second objective, red cabbage microgreens were grown in environmentally controlled growth chambers using a dynamic temperature protocol. Red cabbage microgreens were germinated at 26°C in the dark for 4 days. Following germination, microgreens were grown at 21°C under 200 µmol·m-2·s-1 (ePPFD, 400-750 nm) with a 16-hour photoperiod and 55%/65% (day/night) relative humidity. On days 8 and 11 of production, trays of microgreens were transferred to 12°C for the remainder of production to induce polyphenol accumulation. Additionally, one group of microgreens was transferred to 4°C on day 11 of production. All microgreens were harvested on day 12 and yield, morphological, and phytochemical data were collected. Microgreens transferred on day 8 to 12°C had increased total polyphenol content, but reduced yield and glucosinolate content. Microgreens transferred on day 11 to 4°C did not show elevations in polyphenol content, but increased glucosinolates were observed and yield was preserved. Future research should identify protocols for simultaneous polyphenol and glucosinolate biofortification. Finally, to achieve our third objective, we performed a randomized, single-blind, crossover clinical trial in healthy adults to evaluate the effect of co-consuming 15 g whey, hemp, or pea protein with 22 g freeze-dried blueberries compared to consuming blueberry only (control) on polyphenol bioavailability. Healthy adults (n=14) consumed four treatments on independent test days in random order with at least one week of washout between test visits. At each test visit, blood pressure, pulse wave analysis, and a blood draw via intravenous catheter were performed at baseline (pre-intervention). Then, participants consumed their treatment beverage and subsequent blood pressure, pulse wave analysis, and blood draws were performed at 1, 2, 4, and 6 hours postprandially. A final blood draw was performed 24 hours postprandially following an overnight fast. There were no major differential responses to consumption of blueberry powder with or without whey, hemp, or pea protein powder on aortic or brachial blood pressure, augmentation index, or plasma nitrate. However, specific plasma polyphenols associated with blueberry health benefits were elevated following consumption of the blueberry-hemp protein shake compared to blueberry alone, including chlorogenic acid, ferulic acid 4-O-sulfate, and 2,5-dihydroxybenzoic acid. Additionally, plasma polyphenols following the consumption of the blueberry-whey protein shake were lower in several instances compared to the blueberries alone. These polyphenols that were reduced included caffeic acid 3-O-sulfate, protocatechuic acid 3-O-sulfate, and 3-feruloylquinic acid. This study suggests that co-ingestion of blueberries with protein powder affects circulating polyphenol metabolite exposure which has implications for their health impacts. Cumulatively, the results of these studies indicate that polyphenol consumption can be increased through use of novel foods and biofortification of polyphenol-rich foods, and bioavailability may be enhanced through protein food matrix interactions.