Emulsion-based encapsulation systems stabilized with insect proteinsproduction with premix microporous emulsification

Resumen

Encapsulation is a means of protection, preservation, and delivery of bioactive and/or sensitive compounds, such as antioxidants, aromas and flavours, which is widely applied in food, pharmaceutical, biomedicine, and cosmetic industries. Amongst the existing strategies, encapsulation of the target active compounds within the structure of single and multiple emulsions is chosen in this thesis on account of the high encapsulation efficiency and the good compatibility with different media. The purpose of this thesis is to assess the use of both sustainable materials and technologies to produce emulsions and emulsion-based solid microcapsules as a means of encapsulation of ingredients for food applications. Specifically, single and double emulsions stabilised with sustainable protein sources have been produced by a low-energy high-throughput emulsification technology to encapsulate essential oils and polyphenols. The low-energy high-throughput technology is based on the use of dynamic membranes of tunable pore size (DMTS), which consists of a layer of glass microbeads supported by a nickel metal microsieve. The thickness and interstitial void diameter of the DMTS system can be tuned by selecting the microbeads size and the amount of microbeads for the bed. Emulsions are produced by premix emulsification mode, where a coarse emulsion is refined by pressing it through DMTS system several times (cycles). The target droplet size distribution of the refined emulsions can be controlled mainly by tuning interstitial void diameter, thickness of the bed, applied pressure, number of cycles, and viscosity of the emulsion. A case study on the valorisation of an agri-food by-product, carob pulp, has been implemented by coupling two low-energy membrane technologies: forward osmosis and membrane emulsification. A phenolic solution obtained through water extraction from carob pulp was concentrated via forward osmosis, and the polyphenol concentrate was encapsulated in the inner water phase (W1) of a water-in-oil-in-water (W1/O/W2) emulsions stabilized with whey protein isolate (WPI) by premix emulsification with DMTS. The study combines for the first time both membrane techniques for food by-product valorisation, allowing to assess the basis for the production of W1/O/W2 emulsions with the DTMS system. The research showed the importance of balancing the osmotic pressure between two aqueous phases which is a key of a successful encapsulation for this specific type of system. The polyphenol loaded W1/O/W2 emulsions could be further processed by spray drying to produce solid microcapsules. After rehydrating the solid microcapsules, the structure of the W1/O/W2 emulsion was partially recovered. The results of this study show the potential of combining membrane-based processes to concentrate and encapsulate bioactive compounds as a strategy to valorise agri-food products under mild process conditions. Aiming for the use of more sustainable ingredients in the food industry in general and in encapsulation applications in particular, the techno-functional properties of proteins from edible insects are evaluated. Edible insects, an EU novel food, have nutritional, economic, and environmental benefits, therefore they are interesting replacers for animal proteins, such as dairy proteins, for feed and food applications. Black soldier fly (BSF, Hermetia illucens) is one of the insects having higher organic to mass conversion rate. BSF protein concentrate (BSFPC) was obtained from aqueous extraction followed by acid precipitation at pH 4-4.3, and characterized on the amino acid profile, and nitrogen content. Techno-functional properties of the BSFPC including solubility, water binding capacity, oil binding capacity, foaming capacity, foam stability, emulsifying activity and interfacial tension were assessed, and compared to whey protein isolate (WPI). The BSFPC exhibited comparable or higher emulsifying activity values than WPI for the same concentrations, hence showing the potential for emulsion stabilisation. Sunflower oil and lemon oil emulsions with different oil fractions (20, 30, and 40%) stabilised with BSFPC or WPI were produced by the DMTS system. It was proved that BSFPC stabilises sunflower oil-water emulsions similarly to WPI, but with a slightly wider droplet size distribution. For lemon oil emulsions, BSFPC showed better emulsifying performance than WPI, specially for the highest oil fraction. Lesser mealworm (Alphitobius diaperinus) is one of the high-profile edible insects. Fractionation of insect meals to obtain a lipid and a protein fraction involves several steps. Defatting is the first step of the fractionation process that is usually carried out by solvent extraction. To more sustainable extraction processes, hexane was compared with greener solvents such as ethanol, iso-propanol, and 2-methyltetrahydrofuran. The impact of the solvent on the extraction yield, the lipid profile, and the emulsifying activity of the resulting protein was assessed. It was proven that defatting is feasible with greener solvents and the emulsifying ability of the lesser mealworm protein concentrate (LMPC) remains the same regardless of the solvent used during defatting. LMPC was further evaluated as emulsifier to stabilize W1/O/W2 emulsions and compared to a plant protein (pea protein isolate, PPI) and WPI. It was found that LMPC is able to stabilize W1/O/W2 emulsions comparably to whey protein and pea protein when using a premix emulsification with DMTS. Environmental stresses such as temperature (-20 ºC, 4 ºC, 25 ºC, 37 ºC, 65ºC and 90 ºC), pH (1.5, 4.0, 6.5-7.0 and 8.0), and osmotic pressure unbalance between W1 and W2 (10-fold water dilution of W2, 50 mM and 250 mM NaCl added to W2) were applied to assess the stability of the emulsions, and the storage stability at certain conditions (25 and 4ºC) were examined for 2 weeks. Under acidic conditions, LMPC shows similar performance as whey protein and outperforms pea protein. Under alkaline conditions the three proteins perform similarly, while the LMPC-stabilized emulsions are less able to withstand osmotic pressure differences. The LMPC stabilized emulsions are also more prone to droplet coalescence after a freeze-thaw cycle than the WPI-stabilized ones, but they are most stable when exposed to the highest temperatures tested (90 ºC). From the results it is clear that LMPC has the ability to stabilise multiple emulsions and encapsulate a polyphenol. As for enhancing the shelf-life of emulsions entrapping polyphenols and stabilised with LMPC, WPI or PPI, the thesis shows a first approach to the production of solid microcapsules from polyphenol loaded W1/O/W2 emulsions by spray drying or freeze drying. Regardless of the drying technique and protein used as emulsifier, the produced solid microcapsules are able to retain the structure of W1/O/W2 emulsions after rehydration. The results of this work demonstrate the potential of insect proteins as a feasible alternative to animal proteins, and will contribute to further implementation of insect ingredients in food, feed, pharmaceutical, biomedicine, and cosmetic applications. In particular, the surface-active properties of insect proteins, able to stabilise different emulsion-based encapsulation systems, open the possibility to develop a new range of sustainable food-grade amphiphilic emulsifiers.