The objective of this study was to determine and compare the total phenolic content and antioxidant capacity in the seeds, skin, and pulp of eight cultivars of Florida-grown muscadine grapes and to identify the phenolic compounds in these respective portions. Total phenolic contents were determined colorimetrically using Folin-Ciocalteu reagent, and antioxidant capacity was determined by oxygen radical absorbance capacity (ORAC). High-performance liquid chromatography equipped with diode array (HPLC-DAD) and electrospray ionization mass spectrometric detection (ESI-MS(n)) was used to identify the phenolic compounds in the seeds, skin, and pulp of muscadine grapes. The total phenolic content and antioxidant capacity, based on fresh weight, were highest in seeds followed by skin and pulp. On average, 87.1, 11.3, and 1.6% of phenolic compounds were present in seeds, skin, and pulp, respectively. A total of 88 phenolic compounds of diverse structures were tentatively identified in muscadines, which included 17 in the pulp, 28 in the skin, and 43 in the seeds. Seventeen compounds were identified for the first time in muscadine grapes. The compounds identified in seeds included hydrolyzable tannins, flavan-3-ols and condensed tannins, ellagic acid derivatives, and quercetin rhamnoside. The skin contained hydrolyzable tannins, flavonoids, including anthocyanin 3,5-diglucosides, quercetin, myricetin, and kaempferol glycosides.

Diet is an essential factor that affects the risk of modern-day metabolic diseases, including cardiovascular disease, diabetes mellitus, obesity, and Alzheimer disease. The potential ability of certain foods and their bioactive compounds to reverse or prevent the progression of the pathogenic processes that underlie these diseases has attracted research attention. Red raspberries (Rubus idaeus L.) are unique berries with a rich history and nutrient and bioactive composition. They possess several essential micronutrients, dietary fibers, and polyphenolic components, especially ellagitannins and anthocyanins, the latter of which give them their distinctive red coloring. In vitro and in vivo studies have revealed various mechanisms through which anthocyanins and ellagitannins (via ellagic acid or their urolithin metabolites) and red raspberry extracts (or the entire fruit) could reduce the risk of or reverse metabolically associated pathophysiologies. To our knowledge, few studies in humans are available for evaluation. We review and summarize the available literature that assesses the health-promoting potential of red raspberries and select components in modulating metabolic disease risk, especially cardiovascular disease, diabetes mellitus, obesity, and Alzheimer disease-all of which share critical metabolic, oxidative, and inflammatory links. The body of research is growing and supports a potential role for red raspberries in reducing the risk of metabolically based chronic diseases.

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Red raspberry (Rubus idaeus L.) contains a variety of polyphenols including anthocyanins and ellagitannins. Red raspberry polyphenols absorbed in different forms (parent compounds, degradants or microbial metabolites) are subject to xenobiotic metabolism in the intestine, liver, and/or kidney, forming methylate, glucuronide, and sulfate conjugated metabolites. Upon acute exposure, (poly)phenol/metabolite presence in the blood depends mainly on intestinal absorption, enterohepatic circulation, and metabolism by resident microbiota. However, chronic exposure to red raspberry polyphenols may alter metabolite patterns depending on adaptions in the xenobiotic machinery and/or microbiota composition. Understanding the metabolic fate of these compounds and their composition in different biological specimens relative to the exposure time/dose will aid in designing future health benefit studies, including the mechanism of action studies. The present exploratory study applied ultra-high performance liquid chromatography (UHPLC) coupled with quadrupole time-of-flight (QTOF) and triple quadrupole (QQQ) mass spectrometries to characterize red raspberry polyphenols in fruit and then their appearance, including metabolites in human biological samples (plasma, urine and breast milk) after the chronic intake of red raspberries. The results suggested that the most abundant polyphenols in red raspberries included cyanidin 3-O-sophoroside, cyanidin 3-O-glucoside, sanguiin H6 and lambertianin C. Sixty-two (poly)phenolic compounds were tentatively identified in the plasma, urine and breast milk samples after the intake of red raspberries. In general, urine contained the highest content of phenolic metabolites; phase II metabolites, particularly sulfated conjugates, were mainly present in urine and breast milk, and breast milk contained fewer parent anthocyanins compared to urine and plasma.