1. Work package (WP) 1:
We employed a dual modification strategy – a combination of pH-shifting and ultrasound (US) technology – for SPI modification; and employed alkaline or/and enzymatic treatments to modify pectin. Different modified SPI and pectin samples were then used to prepare the SPI-pectin complexes and conjugates.
The results showed that US remarkably enhanced the modification effect on SPI brought by pH-shifting. Dual modification on SPI also significantly accelerated the Maillard reaction, resulting in desirable structural and physicochemical properties of the final products. Furthermore, we found that the original pectin (without modification) was the optimum material for electrostatic complexation. However, an ideal grafting polysaccharide should possess a “moderate” Mw that is not too high to hinder the Maillard reaction, while still generating proper steric-hindrance effects for functional purpose. In this study, the enzymolysis pectin proved to be an optimum polysaccharide for conjugation with SPI.
Results exploitation: Results of this study will provide reference for material selection for preparation of protein-polysaccharide-based emulsifier in the industry and improve productivity, which will provide alternative low-cost additives for the food system.
2. WP2:
We employed a probe sonicator for complex/conjugate preparation. The reaction efficiency, yield, structural and functional properties of the final products prepared with and without US were compared.
The results indicated that the US cavitation effects resulted in structural modifications in both SPI and pectin, as well as enhanced their electrostatic interactions, which in combination contributed to the more desirable emulsifying properties of the complex. In addition, US significantly accelerated the grafting process and increased the surface hydrophobicity and emulsifying properties of the conjugates.
Results exploitation: The results indicated that US can be a desirable method for protein-polysaccharide complexation/conjugation, which could facilitate the application of US technology in the relevant industry. Furthermore, the incorporation of US into modern food processing could offer other significant benefits including high productivity, sustainability and greener processing.
3. WP3:
The SPI-pectin/β-carotene nanoemulsions were prepared with a microfluidizer. The relationship between the formation mechanisms of nanoemulsions and their delivery functions was analysed.
The results indicated that the complexation and conjugation of SPI with pectin significantly increased the stability and bioaccessibility of nanoemulsions. US treatment enhanced the stability of complexes/conjugates, resulting in better protective effects for β-carotene and more desirable controlled release. Furthermore, US increased the bioaccessibility for nanoemulsions stabilized by complexes. Despite the lower bioaccessibility of US-treated conjugates, US is still useful in accelerating the Maillard reaction and increasing the stability of the conjugates. In conclusion, US-prepared SPI–pectin complexes and conjugates have enormous potential in preparing emulsion-based systems for the delivery of hydrophobic nutrients, given their high stability and strong protective effects, as well as the high efficiency of the preparation procedures.
Results exploitation: In general, as the formation and preservation of electrostatic complexes have a strict requirement for pH, applications of the US-prepared complexes might be more suitable for acidic, liquid food matrices; applications of the conjugates are more flexible, which can be preserved in both solid and liquid states. This study advances the understanding of the delivery properties of protein–polysaccharide-based complexes and conjugates, as well as the merits that ultrasound provides when developing such binary systems.
4. Dissemination:
4.1 Conferences:
(1) 2023 MCAA Annual Conference and General Assembly, Córdoba, Spain, 24–25 February 2023.
(2) Ma, X., Miao, S. & Liu, D. Effects of structural modification of pectin by alkali or/and pectinase on the Maillard reaction with soy protein isolate. The 5th Food Structure and Functionality Symposium, Cork, Ireland, 18–21 September 2022. (Poster presentation)
(3) Ma, X. Functions and mechanisms of ultrasound in soy protein isolate (SPI)-pectin nanoemulsion preparation. The 1st Teagasc Food Research Day, Fermoy, Ireland, 28–29 September 2021. (Oral presentation)
4.2 Publications:
(1) Ma, X., Yan, T., Miao, S., Mao, L. & Liu, D. In Vitro Digestion and Storage Stability of β-Carotene-Loaded Nanoemulsion Stabilized by Soy Protein Isolate (SPI)-Citrus Pectin (CP) Complex/Conjugate Prepared with Ultrasound. Foods, 2022, 11(16), 2410.
(2) Ma, X., Chi, C., Pu, Y., Miao, S. & Liu, D. Conjugation of soy protein isolate (SPI) with pectin: effects of structural modification of the grafting polysaccharide. Food Chemistry, 2022, 387, 132876.
