Phase Separation and Gelation of Biopolymers in Confined Geometries

Many biopolymer mixtures exhibit segregative phase separation that generates regions enriched in one polymer and depleted in the other. Today, much is known of how phase separating biopolymer systems behaves in bulk phase, and the final morphology can be controlled and tailored with high precision. However, few experimental studies have examined such systems in restricted geometries, where the system might be affected and limited by surrounding surfaces. Restricted geometries may be of importance for the properties of multi-phase materials, such as foods and composite materials. In this thesis the effects of confinements on phase separating and gelling biopolymer mixtures has been investigated, with emphasis on the phase separation kinetics and the final morphology. Two biopolymer systems were used; gelatin–maltodextrin and whey protein isolate–gellan gum mixtures. Various types of restricted geometries such as microdroplets, parallel cover glasses, and networks of cellulose fibres were used to evaluate the effects of confinements. The structural evolution and the final microstructures were characterized by confocal laser scanning microscopy and image analysis. The findings showed that the size of a confinement had a marked impact on the resulting microstructure in both systems. The morphology observed within the studied confinements differed from those seen in the bulk phase and included core-shell, Janus-like microstructures in microdroplets and columnar structures in confinements with solid surfaces. In the whey protein isolate–gellan gum system, the structural evolution was similar inside large microdroplets and the bulk phase. It was also found that when the characteristic wavelength of the spinodal decomposition was comparable to the size of the confinement, a structure transition took place and core-shell structures were obtained. Furthermore, the confinement size influenced the initiation of the phase separation in the gelatin–maltodextrin system. Use of conventional emulsification and a microfluidic technique to produce microdroplets was also evaluated. The former method allowed examination of microstructures in emulsion droplets of different sizes within a single sample, ensuring the same composition and thermal history. Monodisperse microdroplets with highly reproducible internal morphology were generated using microfluidics. The internal microstructure was designed using different cooling protocols to control the phase separation and gelation kinetics, and the biopolymer concentration. Homogeneous (no phase separation), discontinuous, and bicontinuous microstructures were observed. The effects of confinement on the internal morphology were investigated by performing elastic Lennard-Jones simulations, which showed good correlation with the experimental structures. Initial studies of the relationship between the microstructure and the diffusion properties of phase separated gels provided promising results, which opens new possibilities to control such properties in microdroplets through careful design of the internal morphology. To summarize, the work underlying this thesis has demonstrated that exploitation of phase separated systems within confined geometries offers great potential to tailor materials with new functionalities

Effects of confinement on phase separation kinetics and final morphology of whey protein isolate-gellan gum mixtures

The final microstructure of a phase separating and gelling biopolymer mixture is affected by physical confinement, because the structure evolution is limited by the surrounding surfaces. Here, we used various confining geometries such as microdroplets, parallel cover glasses, and networks of cellulose fibers to analyze the structure evolution and final morphology of mixtures of whey protein isolate (WPI) and gellan gum. The results were evaluated by confocal laser scanning microscopy (CLSM) and 2D fast Fourier transform (FFT) image analysis. This showed that the final morphology within the restricted geometry is determined by the characteristic wavelength of the bicontinuous bulk microstructure in relation to the dimensions of the confinements. The growth of the characteristic wavelength in the WPI-gellan gum system has two different regimes, which are similar in the bulk phase and large microdroplets. The growth is then kinetically trapped by the gelation. In microdroplets with a smaller dimension than the characteristic bulk wavelength, the growth of the spinodal structure is observed to collapse as the characteristic wavelength approaches the microdroplet diameter. This results in a core-shell structure with WPI present at the interface. Furthermore, 3D reconstructions of CLSM images from the parallel glass confinement showed that the bicontinuous structure is converted to columnar structures interconnecting two wetting layers at the glass surfaces. Similar columnar structures are observed between cellulose fibers. The present findings demonstrate that it is important to understand the impact of confinement on phase separation and gelation in order to control the final microstructure

Effect of anthocyanins on lipid oxidation and microbial spoilage in value-added emulsions with bilberry seed oil, anthocyanins and cold set whey protein hydrogels

The objective of this work was to explore the storage properties of a structured oil-in-water emulsion containing both water- and fat-soluble bioactive compounds from bilberries (Vaccinium myrtillus L.). Bilberry seed oil (BSO) was dispersed in a continuous aqueous phase of anthocyanins (AC) and whey protein isolate. The microstructure was evaluated using light microscopy and the effect of anthocyanins on lipid oxidation and microbial growth was investigated. The results showed that it was possible to generate a stable emulsion structure that resisted phase separation during 25 weeks of storage. Gas chromatography–mass spectrometry measurements of the fatty acids in the BSO during storage showed that AC had a protective effect against lipid oxidation. The AC did not have an antimicrobial effect against the investigated strains Zygosaccharomyces bailii (ATCC 42476) and Aspergillus niger (ATCC 6275 (M68)).This research was financially supported by the ERA-Net, SUSFOOD project ‘Sustainable &amp; Healthy: Development of sustainable processing technologies for converting by-products into healthy, added-value ingredients and food products’, Swedish Research Council Formas , Grant: 2014-49</p

Child and maternal benefits and risks of caseload midwifery – a systematic review and meta-analysis

Abstract Background It has been reported that caseload midwifery, which implies continuity of midwifery care during pregnancy, childbirth, and the postnatal period, improves the outcomes for the mother and child. The aim of this study was to review benefits and risks of caseload midwifery, compared with standard care comparable to the Swedish setting where the same midwife usually provides antenatal care and the checkup postnatally, but does not assist during birth and the first week postpartum. Methods Medline, Embase, Cinahl, and the Cochrane Library were searched (Nov 4th, 2021) for randomized controlled trials (RCTs). Retrieved articles were assessed and pooled risk ratios calculated when possible, using random-effects meta-analyses. Certainty of evidence was assessed according to GRADE. Results In all, 7,594 patients in eight RCTs were included, whereof five RCTs without major risk of bias, including 5,583 patients, formed the basis for the conclusions. There was moderate certainty of evidence for little or no difference regarding the risk of Apgar ≤ 7 at 5 min, instrumental birth, and preterm birth. There was low certainty of evidence for little or no difference regarding the risk of perinatal mortality, neonatal intensive care, perineal tear, bleeding, and acute caesarean section. Caseload midwifery may reduce the overall risk of caesarean section. Regarding breastfeeding after hospital discharge, maternal mortality, maternal morbidity, health-related quality of life, postpartum depression, health care experience/satisfaction and confidence, available studies did not allow conclusions (very low certainty of evidence). For severe child morbidity and Apgar ≤ 4 at 5 min, there was no literature available. Conclusions When caseload midwifery was compared with models of care that resembles the Swedish one, little or no difference was found for several critical and important child and maternal outcomes with low-moderate certainty of evidence, but the risk of caesarean section may be reduced. For several outcomes, including critical and important ones, studies were lacking, or the certainty of evidence was very low. RCTs in relevant settings are therefore required