| Carotenoids have been claimed to have numerous potential benefits to human health.However,due to the high hydrophobicity of carotenoids preventing them from simple diffusing from the plant tissues to the absorption site at the enterocyte,the bioavailability of carotenoids is extremely low when ingested directly from green leafy vegetables,which highly limited their potential health benefits.In recent years,studies have shown that the excipient emulsion can be designed to enhance the efficacy of nutraceuticals in fruits and vegetables that are co-ingested with it,but the effects depends on the structure and composition of the emulsion.Therefore,in order to design the excipient emulsiosn to effectively enhance the bioavailability of carotenoids in fruits and vegetables,we systematically studied the particle size and composition of the excipient emulsion,and the effect of heat processing on the bioaccessibility of carotenoids in spinach,which is one of the main dietary sources of carotenoids.The research results are of great significance for improving the bioavailability of carotenoids in spinach and giving full play to the potential benefits of carotenoids in fruits and vegetables.The main research contents and results are as follows:(1)The influence of particle size of excipient emulsions on bioaccessibility of carotenoids in spinach.The excipient emulsions with different particle size(200 nm,500 nm and 10 ?m)were mixed with spinach pure,and then passed through a simulated gastrointestinal tract(GIT),and the changes in physical properties(particle size,?-potential),chemical properties(lipid digestion),microstructure and carotenoids bioaccessibility were measured.The results showed that there was no significant difference in physichemical properties,microstructure and bioaccessibility of the sample containing fine(200 nm)and medium emulsion(500 nm)(p>0.05),but significantly different from that of large emulsion(10 ?m)(p<0.05)during the simulated GIT.The bioaccessibility of the carotenoids was significantly higher for emulsions initially containing small droplets(fine and medium emulsions)than those containing large droplets(large emulsion and bulk oil).Compared with the control(no lipids),the bioaccessibility of ?-carotene was increased from 6.84% to 28.78% and 28.65%,respectively.The particle size of the excipient emulsions did not significantly affect the bioaccessibility of lutein(p>0.05).(2)The impact of lipid type in excipient emulsions on bioaccessibility of carotenoids in spinach.The influence of lipid type(chain length and unsaturation degree of the fatty acids,and the lipids digestibility)on the ability of excipient emulsion at enhancing the bioaccessibility of lutein and ?-carotene from spinach was investigated using a simulated GIT.The results showed that the excipient emulsions foremed by the lipids mainly containing medium chain saturated fatty acids(MC-SFA)(MCT oil and coconut oil)had faster initial lipids digestion rate and higher digestibility,formed smaller size of mixed micelles,and showed higher bioaccessibility of lutein than the long chain triacylglycerol(LCT)(corn oil,olive oil and fish oil).Compared with the control(no oil),the bioaccessibility of lutein was increased from 20.88% to 67.18% and 45.50% when co-indegested with the excipient emulsion prepared by MCT oil and coconut oil,respectively.While,those two excipient emulsions did not have a significant effect on the bioaccessibility of ?-carotene(p>0.05).The excipient emulsions rich in long chain monounsaturated fatty acids(LC-MUFA)(corn oil and olive oil),formed larger size of the mixed micelles and were superior to MC-SFA(MCT oil and coconut oil)or the long chain polyunsaturated fatty acids(LC-PUFA)(fish oil)in enhancing the bioaccessibility of ?-carotene.Compared with the control(no oil),the bioaccessibillity of ?-carotene was increased from 6.84% to 28.78% and 22.96%,when co-ingested with the excipient emulsions prepared by corn oil and olive oil.However,those two excipient emulsions did not have a significant effect on the bioaccessibility of ?-carotene(p>0.05).Fish oil,which rich in long-chain polyunsaturated fatty acids,lead to a significantly lower ?-carotene bioacessibility than the control(p<0.05),and there was no significant effect on the bioaccessibility of lutein(p>0.05).The excipient emulsions fabricated by undigestible oil(orange oil)had no significant effect on the bioaccessibility of ?-carotene(p>0.5),but significantly increased the bioavailability of lutein in spinach(p<0.05).(3)The impact of emulsifier type in excipient emulsions on the bioaccessibility of carotenoids in spinach.Tween 20,sodium caseinate,and octenyl succinic acid anhydride(OSA)modified starch were selected as emulsifiers and formed another three emulsions to exam the effects of emulsifier type on the bioaccessibility of carotenoids from spinach.The results showed that the emulsifier type had significant influence on physical properties(particle size,potential),chemical properties(lipid digestion)of the emulsion/spinach mixtures(p<0.05).Emulsifier type had significantly different effects on the bioaccessibility of lutein and ?-carotene(p<0.05).As for ?-carotene,the excipient emulsion stabilized by sodium caseinate(28.78%)showed the highest ability to enhance ?-carotene bioaccessibility;the excipient emulsions stabilized by OSA modified starch stable emulsions(8.08%)showed the lowest ?-carotene bioaccessibility.As for lutein,compared to the control(no lipids),the excipient emulsions stabilized by of sodium caseinate and tween 20 had no significant impact on its bioaccessibility(p>0.05);the excipient emulsions stabilized by OSA modified starch showed a significantly lower bioaccessibility than the control(p<0.05).(4)The influence of heating process on the bioaccessibility of carotenoids in spinach.The raw and blanched spinach were co-digested with the excipient emulsions using a simulated GIT.The results showed that the heating process of spinach had no significant impact on the physical properties(particle size,?-potential)and chemical properties of emulsion/spinach mixtures(p>0.05),but significantly impact the bioaccessibility of carotenoids(p<0.05).The blanching may limite the transfering of carotenoids from food matrix to the mixed micelles and result in a lower carotenoids bioaccessibility compared to the raw spinach.(5)Impact of mixed oil phase on carotenoids bioaccessibility.MCT oil and corn oil,each showed the greatest ability at enhancing the bioaccessibility of lutein and ?-carotene,were selected and formulated in a ratio of 1:1(w/w)to form another excipient emulsion.The excipient emulsions contained the mixed oil phase of MCT oil and corn oil simultaneously significantly increased the bioaccessibility of lutein(from 20.88% to 41.91%)and ?-carotene(from 6.84% to 25.04%)from spinach compared with the control(no oil)(p<0.05).Above all,the particle size,composition of oil phase and emulsifier type of the excipient emulsion and the processing of spinach have significant influence on the bioaccessibility of carotenoids.Additionary,these factors have significantly different effects on the bioaccessibility of different lipophilic carotenoids.Among them,the composition of the oil phase seems have the most important influence on the bioaccessibility of carotenoids.It suggests we should firstly take the composition of oil phase into consideration when we design the excipient emulsion.Moreover,mixed oil phases can be used to design excipient foods that optimize the bioaccessibility of compounds with different polarities from natural sources.Secondly,the particle size and the emulsifier type should be optimized.In practical applications,the processing method of fruits and vegetables should also be taken into consideration,and the excipient emulsion could be designed in various forms(such as salad dressing or sauce),so as to better play the role of the excipient emulsion. |
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