Research On The Preparation And Digestion Properties Of β-carotene Nanoemulsions

As a widely used and natural antioxidant, β-carotene has the ability in protecting cells and organs from free radicals, and preventing human from cancers. However, due to the poly-unsaturated structure, β-carotene is undissolvable in the aqueous phase, and low soluble in vegetable oils. What’s more, β-carotene can be easily oxidized, decomposed, and isomerized under light, oxygen, and high temperature atmosphere(>50 oC), which restrictly inhibited the application in food industry. As a delivery system, particle size ranging from 10~200 nm, nanoemulsion can significantly improve the aqueous phase solubility and physicochemical stability of those encapsulated lipophilic functional molecules. Meanwhile, with the increase of focuses on the in vivo bioavailability of bioactive compounds, in vitro simulated digestion system is widely used in analyzing the bioaccessiblity and bioavailability of fortified bioactive materials in encapsulation systems for the simple, low-cost, and high-effective features.β-carotene nanoemulsions based on different modified starches(OSA) were prepared under varying homogenization conditions. The results showed that the mean particle diameters were smallest and the relative β-carotene retentions were the highest when homogenized at 100 MPa for 5 times with 30%( w/w) modified starches. And the mean particle sizes were 110±1.8 nm, 91±0.8 nm, and 79±1.2 nm, with OSA1, OSA2, and OSA3, respectively, at the corresponding homogenization conditions. The emulsifying productivity rates were 84.51±0.79 %,85.42±0.23 %,and 90.29±1.86 %, with OSA1, OSA2, and OSA3, respectively. Nanoemulsions storage experiments were done during 30 days at room temperature and the results illustrated that all particle sizes showed a little bit increase but lower than 200 nm, indicating nanoemulsion s were relatively stable. Degradation rates of β-carotene blank(control) were higher than three nanoemulsions, indicating nanoemulsions stabilized with modified starches appreciably improved the chemical stability of β-carotene. The β-carotene retention rate within three modified starches encapsulated nanoemulsions were in the following order: OSA3>OSA2>OSA1. Results suggested that β-carotene retention rates are positively correlated with emulsifying activities and emulsifiying stabilities of modified starches.Besides, the nanoemulsions digestion characteristics and β-carotene bioaccessibilities in vitro simulated digestion models were further evaluated. Compared to the 1.4±0.01 % β-carotene(control) bioaccessibility, the bioaccessibilities of β-carotene in three nanoemulsions were significantly higher than control and were 10.32±1.00%,28.88±3.32%,and 23.43±2.23%, respectivley. The results indicated that nano-encapsulation can appreciably improve the bioaccessibility. During digestion, the results of the molecular weight distribution, the microstructure of the droplets, and particle size changes showed that at mouth and stomach stage, all three nanoemulsions kept relative stable. At intestinal stage, modified starches were rapidly hydrolyzed and oil droplets were fastly digested. β-carotene was released from oil droplets; β-carotene was incorporated into bile salts, and phospholipid; and micelles were formed. Due to the main absorption site of β-carotene was intestine, modified starches as emulsifiers can effectively protect β-carotene from acidic atmosphere and β-carotene can be exactly released at intestine. The β-carotene bioaccessibility was positively correlated with digestion rate of modified starches and release rates of FFA.The effects of the three main factors(emulsifier, oils, and bile salts) on nanoemulsions digestion characteristics and β-carotene bioaccessibility in vitro simulated digestion systems were studied. Without starch enzymes, the β-carotene bioaccessibilities were 4.8±0.6 %, 16.2±1.9 %, and 18±2.2 %, for OSA1, OSA2, and OSA3, respectively, which were lower than the results of starch enzymes added. The results above suggested that the digestion of emulsifier also promote the release of β-carotene. Without oil digestion, β-carotene cannot be released, and no FFAs were released to form micelles, resulting in extremely low β-carotene bioaccessibility. The results showed that the digestion of oils accelerate the release of encapsulated nutrients and the micelles formation. Without bile salts, oils can be digested but no micelles were formed, which resulted in extremely lower bioaccessibility. In conclusion, the order of the effects of three factors on β-carotene bioaccessibility is followed: oil digestion>micellization>emulsifiers digestion. Thus, due to the out of control of lipases and bile salts in real digestion systems, emulsifiers digestion characteristics are the most important factors in modulating the bioavailability of bioactive compounds in delivery systems.In order to further verify the obtained results, another kinds of biomacromolecules, proteins was used to stabilize nanoemulsions and the digestion properties were also studied. The results showed that the extents of protein hydrolyzation were inversely correlated with β-carotene bioaccessibility. And protein digestion, oil digestion, and micellization showed the same impacts on β-carotene bioaccessibility in nanoemulsions stabilized with whey protein isolate, compared with OSA modified starches.