1. Publishable summary
In light of alarming reports on (the evolution of) the health condition of consumers in the
developed world, researchers invest much time and effort in the quest for ‘healthier’ foods.
Fortification of food products with bioactive food components (“nutraceuticals”) perfectly
fits in with this quest. However, the mere supplementation of these bioactive components
to a food product is often not that simple as those components are usually not very stable
or even incompatible with the food matrix. Supplementation of the bioactive components
in an encapsulated form is one of the strategies currently explored to overcome these
difficulties and challenges, and to design controlled release and target delivery systems.
Structured emulsions and biopolymeric particles have already proven promising for
enhancement of the nutritional profile of ‘liquid’ food systems. However, to date very little
work has been carried out using this approach for ‘low-moisture’ food products.
Furthermore, some food products would also benefit from a controlled release strategy for
quality improving components which do not primarily affect the nutritional quality of the
food, but have a substantial effect on the organoleptic quality.
This project aims at the rational design of structured lipid- or biopolymer-based systems as
carrier systems for application within ‘low-moisture’ food products, such as bread.
The objectives of this research project are twofold:
- production of food-grade emulsion-based and biopolymeric delivery systems with
distinct characteristics and identification of those properties which determine the
functional performance of the particles in real food products.
- Incorporation of emulsion-based and biopolymeric delivery systems into real food
matrices and unraveling the relation between the particle functionality and specific
particle properties in order to design systems with tailor-made functionality.
Three main encapsulation systems have been explored to date:
- Emulsions were produced using gluten hydrolysate samples with different properties.
Hereto, gluten was hydrolyzed to different degrees of hydrolysis (DH) using two peptidases
with distinct hydrolysis specificity, i.e. trypsin and alcalase. As expected, there was a clear
emulsion forming and stabilizing capacity difference between peptides produced with the
two peptidases. This can be (partially) explained by the different hydrolysis specificity of
both peptidases: while hydrolysis by trypsin generally occurs more specific and leaves the
hydrophobic patches in the amino acid sequence of gluten proteins intact, alcalase has a
much broader specificity and likely cleaves the hydrophobic patches which results in
peptides with reduced surface active properties. Emulsion droplets with a submicrometer
average diameter (10 w/v% corn oil) could be produced with 1.0 w/v% trypsin hydrolysates
with a DH of 3 and using a high pressure homogenizer. These emulsions were relatively
stable if the pH was distinct from the isoelectric point of the droplets. However, when using
emulsions as carrier system, there is always a lipid phase involved. This lipid phase will
most probably also have a tremendous effect on the processing and end product quality of
‘low moisture’ food products. Alternative encapsulation systems were, hence, explored.
- Biopolymeric particles can be made by liquid antisolvent precipitation (LAS), a
technique that relies on the reduction of the solvent power of the medium in which the
biopolymers are dissolved. Particle properties can be tightly controlled by selecting the
biopolymers and appropriate parameters during the particle production process.
 Water insoluble proteins such as gliadin and zein can be used to encapsulate
hydrophobic molecules (i.e. resveratrol and ascorbyl palmitate in this project). The
particles produced, however, are not very stable as protein particle suspensions are
generally stabilized through electrostatic repulsion which makes them very susceptible
to changes in pH or ionic strength. Additional stability can be achieved by including
proteins with flexible structures (e.g. sodium caseinate) or polysaccharides (e.g. pectin)
in the particle structure. Hereto, the particles can be coated after particle production by
electrostatic deposition or by coprecipitating the biopolymers dissolved in the
antisolvent phase during particle production. Pectin and sodium caseinate successfully
increased the stability of gliadin and zein particles, respectively. Furthermore, the
inclusion of these biopolymers in the particle structure had a tremendous effect on the
particle size and increased the encapsulation efficiency of the particles for resveratrol.
However, the particles, bare or uncoated, were still relatively unstable at pH conditions
commonly found in food. Conjugation of dextran to zein prior to particle production
resulted in the formation of particles that were stable over the entire pH range relevant
for food and at high ionic strength.
 Water soluble proteins (e.g. whey protein and gelatin) and polysaccharides (e.g.
octenyl succinate starch) were used to produce particles through LAS that could be
used to encapsulate hydrophilic compounds (i.e. anthocyanins, fluorescein
isothiocyanate (FITC) dextran and potassium iodate in this project). Particles produced
from water soluble biopolymers, however, tended to redissolve once reintroduced in an
aqueous phase. The particles could be stabilized through crosslinking of the
biopolymers or by coating them with water insoluble biopolymers such as gliadin. Most
of the crosslinking strategies explored adversely affected the integrity of the
encapsulated bioactive molecule or did not sufficiently improve the stability of the
particle structure. The coating strategy indeed improved the stability of whey protein
particles against redissolution. However, the encapsulation efficiency and retention
capacity of these particles for anthocyanins, i.e. low molecular weight molecules, were
limited. Conversely, the gliadin coated whey protein particles efficiently encapsulated
and retained high molecular weight molecules such as FITC dextran.
 Fluorescence quenching experiments were used to study interactions between proteins
and bioactive molecules such as anthocyanins and resveratrol. The quenching
experiments e.g. revealed that resveratrol interacts with zein through hydrogen bonds
while interactions with gliadin were dominated by hydrophobic interactions. These
results are very valuable as they shed light on the strength and nature of the interactions
and, hence, enable the design of protein particles with tailor-made properties and
functionality (encapsulation and release characteristics).
- Starch granules were used as alternative anthocyanin encapsulation systems. As the
pores of bare starch granules were very large relative to the anthocyanins, these molecules
readily diffused out of the granules. Starch granules were coated with proteins or lipids by
spray drying in order to restrict the diffusion of anthocyanins out of the granules. However,
none of the investigated coatings efficiently restricted the diffusion of the anthocyanins.
In conclusion, different encapsulation strategies and systems have been explored. All of
them hold promise to be used in real food products. This will be the focus of the research
conducted in the third and final year of this project. The identification of emulsion-based
and biopolymeric delivery systems suitable for bioactive and quality improving
components and with the desired functionality in food products will come to the benefit of
the design of healthier food products.