In vitro bioaccessibility of citrus pomace compounds possessing health promoting properties with potential to reduce the risk of diabetes

Citrus (mandarin and orange) pomace is an agro-food industrial waste rich in polyphenols and dietary fiber with great potential as a functional ingredient. In this work, the chemical composition and in vitro bioaccessibility of health-promoting compounds present in raw citrus pomaces (Clemenule and Ortanique mandarins and Navel and Valencia oranges) were studied. In addition, the by-products were employed as food ingredients in cookies and the effect of the food matrix on the bioaccessibility of their bioactive compounds was evaluated. Nobiletin, hesperidin/neohesperidin, tangeretin, heptamethoxyflavone, tetramethylscutellarein, and naringin/narirutin were detected in the citrus samples by UHPLC-MS. Citrus pomaces were in vitro digested mimicking the human oral gastrointestinal conditions and the bioactivity of the digests (antioxidant, carbohydrases modulation, and anti-inflammatory effects) was assessed. The bioaccessibility of the antioxidants in the by-products was confirmed by Total Polyphenol Content (TPC) (6.6–11.0 mg GAE/g digest), ABTS (65.5–97.1 µmol TE/g digest), ORAC-FL assays (135.5–214.8 µmol TE/g digest), and inhibition of Reactive Oxygen Species (ROS) formation induced by treatment with tert-butyl hydroperoxide 1 mM in intestinal IEC-6 (19–45%) and CCD-18Co (28–45%) cells pretreated with the digests at concentrations ranging between 5 and 25 µg/mL. Inhibitors of the enzymatic activity of α-glucosidase (IC50 3.97–11.42 mg/mL) and α-amylase (IC50 58.04–105.68 mg/mL) also remained bioaccessible after in vitro digestion of citrus pomaces. In addition, the bioaccessible compounds in orange pomace samples significantly reduced (p < 0.05) the lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 macrophages. The digests of orange pomace cookies with the nutrition claims “no-added sugars” and “source of fiber” presented antioxidant and anti-diabetic properties, and good sensory quality (6.9–6.7 on a scale of 1 to 9). The results obtained support the feasibility of unfractionated orange pomace as a functional ingredient for reducing the risk of diabetes. The health-promoting benefits observed in the present research might be, at least partially, associated with flavonoids.