The Biodegradation Of Tannins And The Application Of Tannins In Oil-In-water Emulsions

Tannins are naturally occurring secondary metabolites from plants,which has good bioactivity.Tannins can form complexes with some food ingredients?e.g.alkaloids,metal ions,proteins and polysaccharides?.The interaction between tannins and food ingredients often results in the change of appearance?e.g.clarification?and physicochemical properties?e.g.emulsify,oxidative stability,digestibility and so on?,which influence the food quality,nutritive value and bioactivity in food systems.Therefore,reasonable avoidance and utilization of the interaction between tannins and food ingredients are of great significance for the developing of tannins in food industry.This study consists of two parts:?i?tannins were degraded by biodegradation technology to avoid the interaction between tannins and food ingredients and improve the appearance of food systems,?ii?the interaction between tannins and biomaterials was used to improve the physicochemical properties of food ingredients?e.g.emulsifying property,oxidative stability and digestibility?.These researches would provide the theoretical and technical support for the comprehensive utilization of tannins in food industry.The main results are as follows:?1?The tannins were degraded by biodegradation technology.The fermentation products of tannic acid?TA?by Aspergillus carbonarius FCYN212 were isolated and identified.Two major chemical components were obtained:gallic acid?GA?and 3,4,6-tri-O-galloyl-D-glucose?TGG?.GA and TGG exhibited stronger free radical scavenging ability and ferric-reducing power than butylated hydroxyanisole?BHA?.TGG also exhibited good inhibitory activity against the enzymes??-amylase and?-glucosidase?responsible for starch digestion.TGG isolated from a fermented TA product has been shown to be a good antioxidant and enzyme inhibitor.?2?The tannase was immobilized by glutaraldehyde conjugation to amino-functionalized chitosan-coated magnetic nanoparticles?Fe₃O₄-CS NPs?.Fe₃O₄-CS NPs are spherical or ellipsoidal with an average diameter of 5.97±1.25 nm.The stability and functionality of free and immobilized tannase were compared.Both forms of tannase exhibited the same optimal temperature of 30°C,whereas the optimal pH value of immobilized tannase?pH 4.5?was lower than that of the free tannase?pH 5.5?.The pH and thermal stabilities of immobilized tannase were significantly better than those of the free tannase.Immobilized tannase retained over 50%of its initial activity after repeated utilization for eight cycles.Furthermore,the immobilized tannase effectively improved the clarity and color of black and green tea infusions.?3?Colloidal complexes were successfully prepared by TA and oat beta-glucan?BG?.TA-BG complexes were spherical and very sensitive to environmental factors?e.g.pH,ionic strength,and temperature?.Oil-in-water emulsion was prepared that was stabilized by TA-BG complexes.Emulsions formed using only BG?1%?contained large droplets that were unstable to flocculation and coalescence.The stability of the emulsions?pH 5?could be enhanced by optimizing the ratio of TA-to-BG used to form them,i.e.,TA/BG=0.5.Meanwhile,emulsions stabilized by TA-BG complexes?TA/BG=0.5,pH 5.0?remained stable over a range of environmental conditions:pH5?9,NaCl<100 mM,temperatures<70?C.These results may increase the breadth of applications of TA and BG as a functional ingredient in foods.?4?Complexes were fabricated by TA and pea protein?PP?and then their ability to act as antioxidant emulsifiers in flaxseed oil-in-water emulsions were studied.TA and PP can spontaneously assemble into complexes in aqueous solution.High temperature could lead to the aggregation of TA-PP complexes when TA content was up to 0.1%.These TA-PP complexes could be used to prepare flaxseed oil-in-water emulsions containing relatively small oil droplets.The presence of the TA improved the physical and oxidative stability of the emulsions,but the TA level used should be optimized depending on the application.For instance,emulsions stabilized by 0.5%TA-PP complexes had good oxidative stability but were prone to aggregation at higher storage temperatures.Additionally,TA-PP complexes altered the rate and extent of lipid digestion in the emulsions.In particular,0.3%TA-PP complexes retarded the initial stages of lipid digestion,but had little impact on the final extent of lipid digestion.These results have important implications for the design of plant-based delivery systems for encapsulating and protecting polyunsaturated fatty acids.?5?Quillaja saponin?QS?was used as an emulsifier to prepare flaxseed oil-in-water emulsion.The impact of TA on the oxidant stability of emulsions with or without pro-oxidant Fe?II?was investigated.The chelates between TA and Fe?II?have color at pH 5 and 7.TA addition in emulsions was shown to effectively inhibit temperature or Fe?II?-induced lipid oxidation,and maintain the stability of emulsions.In addition,the oxidation rate of lipid was different at different pH,and the oxidation rate decreased in the following order:pH 3>pH 5>p H 7.The oxidation rate of lipid was extremely fast because of the week chelating ability of TA and Fe?II?at pH 3.0.Therefore,the lipid oxidation in emulsion could be inhibited when TA content was up to 0.1%.However,0.01%TA can effectively inhibit lipid oxidation at pH 5 and 7.These results provided a theoretical basis for the application of TA as an antioxidant in emulsion systems.?6?The impact of TA on digestibility,?-carotene?BC?bioaccessibility and storage stability of flaxseed oil-in-water emulsions with two plant-based emulsifiers?quillaja saponin,QS and arabic gum,AG?was investigated.The droplets in the QS-emulsions containing 0.1%TA were highly flocculated in the stomach phase.This impacted the initial lipid digestion,but did not impact the final extent lipid digestion.TA addition had no significant influence on BC bioaccessibility in QS-and AG-emulsions.Additionally,TA addition was shown to effectively inhibit temperature-induced BC degradation.These results have important applications for the formation of functional foods and beverages that can control lipid digestion and protect oil-soluble bioactive components.