| Orange peel,as one of the byproducts generated in orange juice production,contains such functional active compounds as pectin,essential oil,flavone,carotene,mineral and vitamins,showing a big potential in food filed especially food colloids.However,most of current studies use chemical means or modification methods to extract these functional components from peels to prepare colloidal systems,which not only increases the cost,but also is not suitable for "clean-label" principle.Therefore,the objectives of this study were aimed to use orange peel as raw material to develop a natural colloid system which contains various components via mechanical treatments.The physical characteristics and stability mechanism of the natural colloid system were investigated.In addition,the natural colloid was innovatively added to commercial foods,explored its impacts on the sensory quality,functional characteristics and storage stability of foods.Finally,it was evaluated that healthy function of natural colloid,which lays a foundation for the development of related functional products.This study aims to provide theoretical and technical support for the deep utilization of orange peel.The following are main results.(1)Fresh orange peel,ponkan peel,tangerine peel,pomelo peel and lemon peel as raw materials were used to prepare the natural colloid by colloid milling,respectively.The stability test and microstructure observation showed that natural orange peel-prepared colloid had the lowest TSI(Turbiscan stability index)value and formed a specific network structure.Additionally,the natural orange peel-prepared colloid,after processed by HPH,showed a decrease in its particle size,increase in charge and improvement in apparent viscosity,thus the whole system became more stable.Moreover,adding natural orange peel prepared-colloid to commercial orange juice and yogurt significantly reduced the TSI value,improving the storage stability of orange juice and yogurt.(2)Addition of 5% orange essential oil to the natural orange peel-prepared colloid showed that oil droplets could be stabilized by polysaccharide aggregates.Besides,some oil droplets could be stabilized by free protein particles.Use of ethanol to classify this system,ethanol-extracted supernatant(ES)was identified as flavonoids and alcohol precipitate(EP)was dietary fiber.The results of interfacial tension and rheology exhibited that the stability of the colloid system was mainly due to low interfacial tension and high viscosity of EP.In addition,it had been proved that this system was natural polysaccharidebased colloid.The measurements of ζ-potential of the natural colloid treated with acid,alkali,Na Cl,urea and SDS,together with the observation of its appearance and microstructure,showed that the intermolecular forces of natural orange peel-prepared colloid were mainly hydrophobic interaction and electrostatic interaction.(3)Electronic eye,electronic nose and electronic tongue tests were applied to the sensory quality of commercial orange juice and yogurt products with the natural polysaccharide-based colloid was supplemented.Brighter appearance in color and more orange flavor were formed after adding the natural polysaccharide-based colloid to orange juice and yogurt products,respectively.Also,it had little effect on the taste of orange juice and yogurt.Of course,presence of the natural colloid prepared by orange peel improved the DPPH free radical-scavenging rate of orange juice and yogurt products.(4)EP extracted from the natural orange peel-prepared colloid exhibited good the oil binding capacity,cation-exchanging capacity and cholesterol-binding capacity.The survival rate showed that EP had little effect on the growth of Hep G-2 cell lines between 0 and 200 μg/m L.Oil-red-O staining showed that 200 μg/m L EP obviously inhibited lipid to accumulate in Hep G-2 cell lines.Compared to model group,Hep G-2 cells treated with EP up-regulated the gene expression levels of AMPKα,PPARα,PPARγ,LXRα and APOA1,while down-regulated the gene expression levels of SREBP1 c,FAS and ACC.Western blot analysis of upstream key genes showed that relative protein expression levels of SREBP1 c and LXRα in EP-treated Hep G-2 cells increased,compared with oleic acid-induced Hep G-2cell lines.These results implicated that EP might reduce intracellular lipid accumulation through adjusing the expression of AMPK/SREBP1c/ACC/FAS pathway and PPARγ/LXRα/ABCA1/ABCG1 pathway.In-vitro human colon fermentation showed that,compared with control group,EP altered the composition of the microbial community,increased the abundance of beneficial bacteria such as Bifidobacterium,Lactobacillus,Roseburia,Blautia and Faecalibacterium,which are short chain fatty acids(SCFAs)producers.At the same time,it also reduced the abundance of potential pathogens(Bacteroides,Ruminococcus,Dorea and Escherichia).Above all,EP had a certain probiotic function for intestinal health.In conclusion,this study presents a new insight for high value-added utilization of orange peel,and provide a practicable technology for orange-peel fine processing.Morever,this study will present more theoretical guiding for developing new high-efficiency biocompatible food-grade natural colloid and related health food. |
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