Preparation,Characterization And Application Of Peony Seed Protein-Based Emulsions

Protein-based emulsion is a kind of emulsion prepared with protein particles as stabilizer,which has the advantages of biodegradability and good biocompatibility and has been widely used in food and other fields.In this thesis,peony seed protein isolate and peony seed albumin were extracted from peony seed meal.Amino acid content,thermal denaturation temperature,surface hydrophobicity and other properties of the two proteins were analyzed.The peony seed protein isolate treated with transglutaminase(TGase)was used as a stabilizer for the preparation of protein-based emulsions.The physicochemical properties and stability of peony seed protein isolate emulsions(PSPIEs)were characterized,and the effects of PSPIEs on the stability of peony seed oil(PSO)were also investigated.Peony seed albumin-pullulan composite particles(PSAPs)were prepared by cross-linking peony seed albumin with pullulan,and the particles were used in the preparation of peony seed albumin-pullulan emulsions(PPEs).The physicochemical properties and stability of PPEs and their effects on the stability of PSO were studied.Moreover,the PSPIEs and PPEs were used for loading β-carotene to study the effects on light stability,thermal stability,antioxidant activity and bioavailability ofβ-carotene.(1)Peony seed protein isolate and peony seed albumin were extracted from peony seed meal by alkaline-soluble-acid-precipitation and water-soluble-acid-precipitation.The protein content of the protein isolate and the albumin were 73.83% and 87.12%,respectively,according to Kjeldahl method.The results of sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the molecular weight distribution of protein isolate and albumin was dense around 25 kDa and 35 kDa.Both the protein isolate and the albumin had high thermal denaturation temperature and high thermal stability.The surface hydrophobicity of the albumin was higher compared to the protein isolate.(2)The enzyme crosslinked protein dispersions of different pH were prepared by treating the protein isolate with TGase.PSPIEs of different pH were prepared by highspeed homogenization of enzyme crosslinked protein dispersions with PSO.pH 5 enzyme crosslinked protein dispersion with PSO were found to be unable to form homogeneous and stable emulsion,while pH 3-PSPIEs,pH 7-PSPIEs and pH 9-PSPIEs were stable without phase separation or oil emission.The average droplet sizes and micrographs showed that the droplet diameter of the emulsions decreased with the pH increased.Rheological results showed that PSPIEs showed shear thinning behavior and the emulsions had an elastic gel structure.Good storage stability,ionic strength stability,temperature stability and centrifugal stability of PSPIEs were found by storage at room temperature for 35 days,addition of Na Cl,heating,refrigeration and centrifugal treatment.Studying of the oxidation rate of PSO dispersed in PSPIEs versus pure PSO revealed that the oxidation rate of PSO dispersed in PSPIEs was slower and PSPIEs could be used to protect PSO.(3)PSAPs were prepared by cross-linking albumin with pullulan,and PPEs with different oil-phase mass fractions were prepared using PSAPs as stabilizer and PSO as the oil phase.The effect of oil-phase mass fraction on the physicochemical properties of PPEs was investigated.The micrographs showed that the droplet size of PPEs increased with the increase of oil-phase mass fraction.Rheological tests showed that PPEs exhibited shear thinning.The stability study shows that the other stability test samples have good stability except the phase separation phenomenon of PPEs-1 after heat treatment.PPEs could also protect PSO and inhibit the oxidation of PSO.(4)pH7-PSPIEs and PPEs-5 were used to load β-carotene to investigate the effect on the properties of β-carotene.The results showed that thermal stability of β-PSPIEs/β-PPEs was higher than that of β-PSO.The loading in PSPIEs/PPEs could also improve the photostability of β-carotene.The results of antioxidant activity showed that the antioxidant activity of β-PSPIEs/β-PPEs was higher than that of β-carotene as well as the blank emulsions.This indicates that the combined samples have higher DPPH free radical scavenging capacity than the single samples.In vitro simulated gastrointestinal digestion showed that loading of β-carotene into PSPIEs/PPEs also improved its bioavailability.The above results showed that the protein isolate and albumin extracted from peony seed meal can successfully prepare oil-in-water emulsion,and the emulsions have good stability.The emulsions could protect PSO and inhibit its oxidation.Emulsions as functional factor carriers could also improve the stability and bioavailability of β-carotene.This can greatly improve the application scope and added value of peony seed meal.It also provides two possible excellent carriers for β-carotene.