Abstract
The effects of cellulose nanocrystals (CNC) and microcrystalline cellulose (MCC) on the gel properties and microstructure of glucono-δ-lactone-induced soy protein isolate (SPI) gels were investigated. The water-holding capacity, gel strength, and viscoelastic modulus of CNC–SPI gels were positively associated with CNC concentration from 0 to 0.75% (w/v). In contrast, MCC–SPI gels exhibited decreased water-holding capacity, gel strength, and viscoelastic modulus. All composite gels displayed high frequency dependence and the typical type I (strain thinning) network behavior. Changes in viscoelasticity under large strain were correlated with differences in the microstructure of SPI composite gels. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) showed that CNC were more evenly and steadily distributed in the protein matrix and formed a compact network structure. In contrast, MCC–SPI gels exhibited a discontinued and rough gel network with some large aggregates and pores, in which MCC was randomly entrapped. Fourier transform infrared spectroscopy (FTIR) and molecular forces results revealed that no new chemical bonds were formed in the gelation process and that the disulfide bond was of crucial importance in the gel system. With the addition of CNC, electrostatic interactions, hydrophobic interactions, and hydrogen bonds in the SPI gel network were significantly strengthened. However, the incorporation of MCC might obstruct the connection of the protein network. It is concluded that both cellulose type and concentration affect gelling properties.
Highlights
Soy protein isolate (SPI), which mainly contains globulins glycinin (11S) and βconglycinin (7S), has been extensively used in the food field due to its high nutritive values and functional properties [1]
This study found no clear changes in soy protein isolate (SPI) gel spectra, indicating that no new chemical bonds formed in the gelation process
The effects of addition of CNC and microcrystalline cellulose (MCC), which could act as potential functional ingredients, on acid-induced SPI gels were investigated
Summary
Soy protein isolate (SPI), which mainly contains globulins glycinin (11S) and βconglycinin (7S), has been extensively used in the food field due to its high nutritive values and functional properties [1]. As a plant-derived protein, SPI has attracted widespread attention due to its low cost, low pollution, low toxicity, and renewable property compared with animal-based proteins [2,3]. It has been demonstrated that polysaccharides can alter the functional properties of protein gels, resulting in the formation of resultant composite gels with different microstructural, mechanical, and sensory properties [6]. The protein–polysaccharide interactions can be either adverse or beneficial to the formation of gels depending on their nature, addition amount, and ratio as well as the gel conditions [7]. It is vital to systematically investigate protein–polysaccharide interactions in order to design and develop the desired texture and expand the applications of gels
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