Development of walnut-based multifunctional foods with encapsulation of phytochemicals
Creators: name: Liu, Qianru
Publisher: name: No Publisher Supplied
Year: 2022

description: As the global senior population and the age-associated dysfunction (such as digestion problems, obesity, cardiovascular health problem, and muscle loss) grow, offering them more fluid-like functional supplements are needed. Foods contain several types of bioactive components, such as essential amino acids, dietary fibers, antioxidants, and polyunsaturated fatty acids. The combinational intake of those substances can exert multiple activities, enhancing their physiological effects. Therefore, multifunctional foods (MFFs) with encapsulation of phytochemicals like antioxidants can provide seniors with several health benefits by the expression of multiple biological effects at one time. Walnuts (Juglans regia L.), which are distributed all over the world, especially prevalent in China, the US and Iran, are valuable sources of unsaturated fatty acids and proteins. Walnuts have also been identified as abundant sources of antioxidants (more than 20 mmol/100 g), polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs). Walnut oil contains approximately 55 v/v% of linoleic acid and 20 v/v% of oleic acid. Moreover, dietary fiber in the walnut meal can act as a prebiotic in preventing metabolic syndrome; the diet enriched in walnuts has been confirmed to be beneficial to patients with cardiovascular disease and obesity problems. Walnut products are, therefore, the ideal candidates as matrices of multifunctional foods. By encapsulating phytochemicals like natural antioxidants, the fortified multifunctional food products will not only own longer shelf life, but they are also beneficial to our health and easy for digestion when compared to raw walnuts and conventional food products. The dietary fiber from walnuts can also promote consumers’ colonic health by regulating the gut microbiota. My Ph.D. thesis focuses on the design and development of “all-in-one” walnut-based multifunctional food products for encapsulation of natural antioxidant - carnosic acid (CA) based on the O/W Pickering emulsion (PE) mechanism. The first section was conducted to develop the new methods of extraction and purification of walnut protein isolate (WNPI) from the defatted walnut flour (DWF) (obtained by the low-temperature continuous phase transition, largely protecting the native state of materials). The overall characteristics, conformation, and morphology of WNPI were investigated based on the amino acid analysis, SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), CD (circular dichroism), FT-IR (Fourier transform infrared), SAXS (small-angle X-ray scattering), and AFM (atomic force microscopy). Moreover, we also prepared two WNPI particles using genipin cross-linking and heat treatment, their application as potential Pickering stabilizers were then investigated. The modified WNPI particles all showed desired properties to stabilize PEs. In the second section, we used heat-induced WNPI particles as Pickering stabilizers to prepare PEs, the prepared PEs showed much stable storage stability. The PEs were then encapsulated with CA (CA-PEs). Except for evaluating the digestion and the release profiles of CA, the storage stability of CA-PEs was also investigated in terms of the lipid oxidative stability and rheological stability under different ionic strength and storage times. The results confirmed that PEs had significantly increased the bioaccessibility and absorption of CA. The encapsulation of CA could then, in turn, significantly increase the lipid oxidative stability. Such walnut protein-based PEs with CA encapsulation could be storage stable and antioxidant semi-liquid MFFs. In the third section, we conducted the fabrication and characterization of defatted walnut flour particles (DWFPs), and the highly relevant guidance to its further applications. DWFPs were prepared by a novel method - continuous phase transition extraction operated under low temperature (i.e., 50-65 °C) followed by 6-h media milling process, were spherical with an average size of 753.0 ± 27.8 nm. These particles were mainly composed of proteins (55.6 ± 0.2 wt%) and carbohydrates (24.0 ± 0.2 wt%) and demonstrated an ability to form a gel-like network structure in PEs. The visual observation and confocal laser scanning microscopy (CLSM) showed that the PE droplets stabilized by DWFPs had good stability over a prolonged storage time (i.e., 3-month storage). In the fourth section, the DWFPs were used as stabilizers to form high internal Pickering emulsions (HIPPEs) to encapsulate natural hydrophobic CA. Our results indicated that DWFPs could effectively stabilize HIPPEs. According to the characteristics (formation, microstructure, and stability) of DWFPs stabilized HIPPEs investigated via the combined confocal laser scanning microscopy (CLSM), cryo-scanning electron microscopy (cryo-SEM) and rheological measurements, HIPPEs exhibited excellent stability over a prolonged storage time (i.e., 3-month storage). The HIPPEs were then encapsulated with CA (CA-HIPPEs). The digestion and the release profiles of CA-HIPPEs in the upper gastrointestinal (GI) tract were evaluated with a combination of dynamic TNO’s gastrointestinal (TIM-1) model, pH-stat lipolysis model as well as the ex vivo permeability model - Franz cell and compared with that encapsulated in the bulk walnut oil. The results confirmed that HIPPEs had significantly increased the bioaccessibility and absorption of CA. The prepared walnut-based HIPPEs could be desired functional foods with long-term shelf life and significant health-beneficial effects. Lastly, to preserve the nutritional components as much as possible, the media-milling technique was applied to produce CA-loaded walnut dispersions, raw walnuts were then directly used as materials. The stability and CA’s bioaccessibility were then evaluated. Besides, CA-walnut particles (CAWPs) stabilized Pickering emulsions (CAWP-PEs) were fabricated as inks for 3-dimensional (3D) printing. Along with the milling process (0 - 16 h), the particle size of CAWPs gradually reduced. By simulating the whole digestive processes in the upper GI tract, the dynamic gastro-intestinal model - TIM-1 confirmed the increased CA’s bioaccessibility. CAWP-PEs were then prepared with optical microstructure and stability characterization. CAWPs concentrations (20 wt% and 30 wt%) and walnut oil fractions (v/v) were two key parameters to influence the formation of CAWP-PEs. Due to the thick barrier formed by CAWPs around oil droplets, CAWP-PEs were stable with ionic strength from 0 to 2000 mM, exhibiting excellent heating and freeze-thaw stability. CAWP-PEs with ionic condition (500 mM) contributed to more viscoelastic structures, facilitating 3D printing performance. The 3D printed products showed desired lipid oxidative stability. By combining media milling and 3D printing techniques, this work is significant in providing guidelines for the effective and sustainable production of customized multifunctional foods (MFFs) with desired stability.