**4. Enhancing the textural, structural, and cooking properties of fresh rice noodles using SPI and combined cross-linking technologies**

Gluconoδ -lactone (GDL) is a cyclic ester. It contains a lactone group and gradu- ally dissolves in water to form gluconic acid, causing a reduction in pH in food systems (**Figure 2**). It is widely used as an acidulant in yogurts, sausages, and different dessert mixes. GDL is used as a coagulant in the production of *tofu*, a soymilk curd [25, 26]. The introduction of GDL into protein alters the pH toward the isoelectric point and subsequently gels the proteins through electrostatic repulsion, salt-bridging, and noncovalent interactions, such as hydrogen bonding and van der Waals forces [27, 28]. The aggregation of protein in GDL-induced acidification of soymilk proteins occurred at pH 5.9 [29].

The combined control of the acidification and gelling of proteins by heat treatment creates a "cold gelation" [20, 30]. In the cold gelation process, aggregates and the formation of a protein network are separated in time. Cold gelation is made of two steps. First, at neutral pH well above the isoelectric point, low concentrations of native globular proteins are thermally treated, causing the native proteins to unfold and form disulfide cross-linked aggregates. The soluble aggregates formed were made possible due to net surface charge proteins and repulsive forces, which prevent random aggregation. Depending on the denaturation conditions, a stable dispersion of aggregates is obtained after cooling to room temperature. Secondly, an alteration in the quality of the solvent causes gelation. Typically, cold-set gels by acidification are stronger than salt-induced cold-set gels for the same protein concentration [31].

**Figure 2.** *Hydrolysis of GDL.*

SPI and MTG have been used to improve noodles' texture and mechanical properties, but a mixture of SPI, MTG, and GDL has never been tested to improve the texture and other properties in rice noodles. Rice flour-SPI noodles containing MTG and GDL were tested for various parameters to develop a gluten-free alternative to wheat flour noodles with comparable or better characteristics. Rice noodles were prepared to contain 5% SPI, were cross-linked with MTG (1% w/w rice flour), and cold-gelled using GDL (1% w/w rice flour). This restructured fresh rice noodle termed RNS-COM (SPI-rice noodle formed via combined crosslinking technology) showed heavier protein bands than a typical rice protein band, indicating the polymerization of proteins into bigger matrixes. The cooking time for RNS-COM was significantly lower than commercially available yellow alkaline noodles (YAN). No significant difference was found between the percentage cooking loss between the two. RNS-COM had better textural parameters, including hardness and chewiness, while compactness and tensile strength were comparable (**Figure 3**). Overall, the RNS-COM noodles performed better than regular rice noodles and can potentially be used in place of YAN [18]. The addition of SPI in rice noodles made them have better textural properties than the control (RN). Increased SPI cross-linking by MTG and GDL in RNS-COM gave a compact and robust protein matrix embedded with the starch granules within the rice noodles (data not shown).

SPI, MTG, and GDL are additives commonly used in the food industry to enhance foods' texture and physiochemical properties. Adding these additives to rice noodles makes them more palatable and may mimic those of wheat flour noodles, such as YAN. It is crucial to optimize the values of such additives to make the product marketable. Optimization is required for factors, including hardness, springiness, chewiness, tensile strength, and cooking time. It is suggested that an addition of SPI, 68.32 (g/kg of rice flour), MTG, 5.06 g/kg of rice flour), and GDL, 5.0 (g/kg of rice flour) improved the various parameters. The hardness of the final product with optimized values of SPI, MTG, and GDL was hardness (53.19 N), springiness (0.76), chewiness (20.28 J), tensile strength (60.35 kPa), and cooking time (5.15 min) [32].

### **Figure 3.**

*Standardized textural properties of rice noodles (RN = rice noodles with 100% flour, RNS-MTG = rice noodles with 5% SPI, crosslinked with 1% MTG, RNS-GDL = rice noodles with 5% SPI, gelled with 1% GDL, RNS-COM = rice noodles with 5% SPI, crosslinked with 1% MTG and gelled with 1% GDL).*

*Innovative Application of Soy Protein Isolate and Combined Crosslinking Technologies… DOI: http://dx.doi.org/10.5772/intechopen.103154*
