Beta-lactoglobulin and its nanocomplexes with pectin as vehicles for ω-3 polyunsaturated fatty acids

The reduction of fat consumption calls for enrichment of non-fat foods and beverages with essential oil-soluble nutraceuticals, including ω-3 fatty acids. However, the low water-solubility and sensitivity to oxidation require new ways to solubilize and protect such sensitive compounds without compromising the desired sensory attributes of the enriched product. Beta-lactoglobulin (β-Lg), the major whey protein of cow milk, is a natural molecular nano-carrier for hydrophobic molecules. The present work provides apparently first evidence for the spontaneous binding (K_b = (6.75 ± 1.38) × 10⁵ M⁻¹) of docosahexaenoic acid (DHA) to β-Lg. Based on a recent study from our group [Ron, N. (2007). β-Lactoglobulin as a nano-capsular vehicle for hydrophobic nutraceuticals. M.Sc. thesis, Advisor: Dr. Yoav D. Livney, The Technion, Israel Institute of Technology, Haifa, Israel], we herein show the formation of colloidally stable nanocomplexes of DHA-loaded β-Lg and low methoxyl pectin below the isoelectric point of β-Lg (5.2), at pH = 4.5. By adding excess of pectin, negatively charged particles were formed containing ∼166 times higher DHA concentration than the surrounding serum. This enabled the formation of dilutable nanoparticle dispersions, which formed transparent solutions containing 0.05% β-Lg and DHA at a 1:2 (β-Lg:DHA) molar ratio, with a very good colloidal stability and average particle size of ∼100 nm. The entrapment by β-Lg, and moreover, the formation of nanocomplexes with the pectin provided good protection against degradation of DHA during an accelerated shelf-life stress test: only about 5–10% lost during 100 h at 40 °C, compared to about 80% lost when the unprotected DHA was monitored. This study presents a new way to nanoencapsulate long chain polyunsaturated fatty acids like DHA, useful for enrichment of clear acid drinks.