Abstract
Poor water solubility and low bioavailability of hydrophobic flavonoids such as rutin remain as substantial challenges to their oral delivery via functional foods. In this study, the effect of pH and the addition of a protein (sodium caseinate; NaCas) on the aqueous solubility and stability of rutin was studied, from which an efficient delivery system for the incorporation of rutin into functional food products was developed. The aqueous solubility, chemical stability, crystallinity, and morphology of rutin (0.1–5% w/v) under various pH (1–11) and protein concentrations (0.2–8% w/v) were studied. To manufacture the concentrated colloidally stable rutin–NaCas particles, rutin was dissolved and deprotonated in a NaCas solution at alkaline pH before its subsequent neutralisation at pH 7. The excess water was removed using ultrafiltration to improve the loading capacity. Rutin showed the highest solubility at pH 11, while the addition of NaCas resulted in the improvement of both solubility and chemical stability. Critically, to achieve particles with colloidal stability, the NaCas:rutin ratio (w/w) had to be greater than 2.5 and 40 respectively for the lowest (0.2% w/v) and highest (4 to 8% w/v) concentrations of NaCas. The rutin–NaCas particles in the concentrated formulations were physically stable, with a size in the range of 185 to 230 nm and zeta potential of −36.8 to −38.1 mV, depending on the NaCas:rutin ratio. Encapsulation efficiency and loading capacity of rutin in different systems were 76% to 83% and 2% to 22%, respectively. The concentrated formulation containing 5% w/v NaCas and 2% w/v rutin was chosen as the most efficient delivery system due to the ideal protein:flavonoid ratio (2.5:1), which resulted in the highest loading capacity (22%). Taken together, the findings show that the delivery system developed in this study can be a promising method for the incorporation of a high concentration of hydrophobic flavonoids such as rutin into functional foods.
Highlights
The findings show that the delivery system developed in this study can be a promising method for the incorporation of a high concentration of hydrophobic flavonoids such as rutin into functional foods
At a low concentration (0.01% w/v), most of the rutin was soluble in water regardless of the pH, which corresponds with the results of our previous study where the aqueous solubility of the same rutin product was evaluated [17], as well as the results of other studies [1,39]
In the case of the dispersion containing 5% rutin, most of the rutin was soluble at pH 9, but the solubility started to decrease below this pH (Figure 1). This was expected, as a pH below 9.0 is outside the major pKa s of rutin [40,41]. This is in agreement with the results of another published report [42], where a slight degradation of rutin was found at pH 11.0 at 21 ◦ C, over a 30 min time period, which could be attributed to the decomposition of this flavonoid into phenolic acids under an alkaline environment
Summary
The beneficial health effects of rutin supplementation in patients with diabetes mellitus through clinical trials have already been established [1,2,3,4] This flavonoid has been suggested for treating some complicated health problems such as cerebral ischemia, owing to its antioxidant properties [5,6]. Both pharmaceutical and nutraceutical applications of rutin are limited because of its poor aqueous solubility, which in turn, results in a low bioavailability [7,8]. Flavonoids such as rutin (with logP of 0.15—logP is defined as the logarithm of the ratio of the concentrations of the un-ionized solute in the solvents) undergo both chemical and enzymatic degradation once exposed to either the environment (e.g., within the structure of the food or during its processing) or the gastrointestinal tract (GIT) [9,10,11]
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