Plant protein structure design and its potential substitution of dairy proteins in gelation systems

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Tang, Qi
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University College Cork
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Plant-based proteins are gain attention as versatile alternatives to dairy-derived proteins as functional ingredients in food formulations due to their greater sustainability and lower production costs, and health benefits. However, in-depth knowledge about the structural and functional knowledge of plant and dairy proteins under different pH conditions and the modifying technologies for binary plant and dairy proteins have rarely reported. The study investigated the pH-dependent behavior of structural, and functional properties, especially thermal gelation performance, of plant protein and dairy proteins. Moreover, the study also explored the modifying strategies on the gelation performance of lentil-dairy binary protein gels treated with by heating and microbial transglutaminase. The studies focused on the influence of different pH levels on the structural, surface properties and functional properties of different plant proteins and dairy proteins. Findings demonstrated that dairy proteins generally showed brighter color (higher L* and lower a* and b*), higher solubility, emulsification properties, and foaming capacity compared to plant proteins, whereas plant proteins displayed superior foaming stability and water holding capacity. The thermal gelation performance of plant proteins and dairy proteins are also showed that the disulfide bond formation was attributed to partial 11S acidic and basic subunits of plant proteins (soy, pea, lentil, and chickpea). The disulfide-bonded aggregation was attribute to partial β-Lg and α-La in WPI, which was inhibited at acidic conditions but facilized under higher pH conditions, whereas in CM, κ-casein and αs2-casein might involve in this process. Moreover, the highest gel performance of SPI and CPI were peaked at pH 9, but that of LPI at pH 3, whereas no self-standing gel formed for PPI at the same protein concentration (14%, w/w) over the test pH conditions. For dairy protein, whey protein showed the superior gel performance at pH 7, whereas that was observed optimum at pH 3 for casein micelles. The modification strategies were further explored by subjecting plant and dairy binary protein mixtures to heating and microbial transglutaminase treatment and demonstrated that only certain fractions (legumin acidic and basic subunits) in LPI involved in disulfide-mediated polymerization, whereas almost all fractions in WPI were involved, but that of CM was hindered during heating treatment. However, the 11S acidic subunit and 7S vicilins in LPI were involved in Gln-Lys isopeptide bond formation when subjected to MTGase treatment, whereas that was hindered in WPI but promoted in CM. The binary protein gel performance demonstrated that the application of heating treatment could result in the formation of self-standing gels when replacing whey protein with lentil protein. Nevertheless, when aiming to substitute casein micelles with lentil protein with good gel performance, microbial transglutaminase treatment was found to be a more effective modifying method. Furthermore, a higher ratio of casein micelles to lentil protein can lead to a significant enhancement in gel performance, resulting in improved mechanical properties, rheological properties, water-holding capacity, and the development of more homogeneous and compact microstructures. Remarkably, when substituting 25% casein with lentil protein, similar gel performance with casein alone was observed when mediated by microbial transglutaminase treatment. The findings of this study offer a profound comprehension of the distinctions between plant proteins and dairy proteins regarding their structural and functional properties under varying pH conditions. Furthermore, this research provides different modifying strategies for substituting dairy proteins with plant proteins, thereby broadening the potential applications of plant proteins in diverse food formulations.
Plant protein , Dairy protein , Structure , Modification , Gelation property
Tang, Q. 2023. Plant protein structure design and its potential substitution of dairy proteins in gelation systems. PhD Thesis, University College Cork.
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