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Milk protein hydrogels: Milk protein hydrogels as carriers for bioactive substances: water-insoluble micro-capsule systems for stabilization and controlled release of ingredients from the bioakive bilberry
Project
Project code: AiF 15611 N
Contract period: 01.01.2008
- 31.12.2011
Budget: 256,900 Euro
Purpose of research: Applied research
Background:
Bilberries, especially wild bilberries, contain various groups of substances which have a positive impact on human health. Especially due to their high content of anthocyanins and polyphenols they exhibit the highest antioxidant capacity compared to all other fruits and vegetables and are therefore suitable additives for functional foods. However, many of these bioactive substances are relatively unstable. For use as additives they have to be stabilised against degradation at the environmental conditions prevalent in the most food products. After ingestion their release should take place in the gastrointestinal tract.
For stabilising the sensitive compounds and allowing their controlled release within the gastrointestinal tract the technology of microencapsulation can be used. However, little experience exists in the field of microencapsulation of secondary plant compounds in water insoluble matrices as functional food ingredients. The use of thermally crosslinked milk protein hydrogels as a matrix material can thereby be considered as a promising approach. Only few studies exist for microencapsulation using heat-induced gelation of milk proteins. For medical applications the use of milk protein-based hydrogels as a carrier matrix for the encapsulation of drugs has been investigated for some years. According to that milk proteins are safe in terms of health and offer ideal technological properties for matrix formation and thus exhibit a high potential for the encapsulation of bioactive substances.
The objective of the research project (Project 3 of the DFG/AiF-cluster 'Bioactive substances from microstructured multicapsule systems') is to develop and optimise techniques for the microencapsulation of bilberry extract and ingredients isolated therefrom by means of thermally induced water-insoluble milk protein hydrogels. The used microencapsulation method is based on a water-in-oil emulsification process.
Results:
Whey protein systems at pH 1.5 and pH 3 were selected for the encapsulation of the anthocyanin-rich bilberry extract because anthocyanins show their maximum stability at acidic pH. Gels with a protein concentration of 20 % were found to be optimal with respect to bilberry extract retention and technical feasibility. The optimum thermal impact for the thermal gelation of the whey protein solutions was heating to 80 °C for 10 min. By this means bilberry extract-loaded water-insoluble gels could be generated with a low thermal anthocyanin degradation. At both pH-values an encapsulation-related stabilisation of the anthocyanin fraction was determined during a storage period of 28 days compared to aqueous solutions with a better stabilisation at pH 1.5.
The microcapsule production from whey protein solutions was based on the w/o-emulsion method using a stirred tank and 6-blade impeller. With a dispersed phase content of the emulsion of 15 % and by addition of the emulsifier PCDL (phosphatidylcholine depleted lecithin) microcapsules with mean diameters of 20-180 μm could be produced. Microcapsules with a maximum bilberry extract content of 10 % could be produced just at pH 1.5. because at pH 3 adverse interactions between bilberry extract components and whey proteins occurred.
The antioxidative potential of the bilberry extract was determined by means of the TEAC (Trolox equivalent antioxidant capacity)-assay. During the production of microcapsules using the emulsifier PCDL specific PCDL-anthocyanin interactions occurred. These interactions resulted in a strong anthocyanin loss and a decrease of the antioxidative potential of the encapsulated bilberry extract. For this reason the further use of PCDL was avoided. The bilberry extract microencapsulated without using emuslifiers showed a high antioxidative potential. As nearly no anthocyanin deagradation occurred during heating, the observed decrease of antioxidave potential during microencapsulation can be traced back to the loss of other antioxidative bilberry extract components.
Cell culture assays of the cluster-project 7 at the Technische Universität Kaiserslautern confirmed the bioactivity of the microencapsulated bilberry extract. As demonstrated by in- vitro and ex-vivo experiments (cluster project 6 at the university of Halle, cluster project 7 and own experiments) the release from the whey protein matrices in an aqueous gastrointestinal environment was driven by diffusion and thus time-dependent. The delayed release of the encapsulated anthocyanins renders it possible to counteract a continuous degradation of the anthocyanins in the small intestine (desired location of anthocyanin release). Thus, the period during which a constant concentration of stable anthocyanin flavylium cations exists in the small intestine could be extended which is expected to improve the absorption and bioavailability of anthocyanins.
To avoid the diffusive loss of anthocyanins before reaching the location of release, the microcapsules were enterically coated. Shellac as well as low- and high-melting fats were used as coating materials. By this means, the diffusive release in the simulated digestive media could be reduced significantly. In addition to the stabilisation of the anthocyanins due to the encapsulation in thermal whey protein gels also the native whey proteins were found to have a stabilising effect on the anthocyanins, which counteracted the anthocyanin degradation at neutral pH. Therefore a further system based on the process of spray-congealing for the encapsulation of a non-denatured bilberry extract-whey protein solution was developed to exploit the observed stabilising effect. Futhermore a water-free encapsulation system for encapsulating bilberry extract-whey protein suspensions in lipid matrices was established. The different properties of the varying encapsulation systems allow the consideration of product-specific requirements for the selection of a suitable capsule type for food products. The various microencapsulation techniques consequently allow for the stabilisation and controlled release of the encapsulated bilberry extract.
Section overview
Subjects
- Food Processing
Collaborative Project
Bioactive Ingredients from microstructured Multi capsule systems
