**4. Biological modifications**

*Grain and Seed Proteins Functionality*

compared to the conjugates formed at 90 °C.

Forming protein-polysaccharide based conjugates through glycation or Maillard

participated in the Maillard reaction. Conjugation was indicated to alter the secondary structure, decreasing the α-helix content due to heat-induced unfolding of the molecule and attachment of dextran. Fluorescence spectra were used as an indicator to monitor the changes in tertiary structure. The authors proposed that conjugation induced unfolding of mung bean protein up to a certain extent and increased the flexibility of protein structure. Solubility of the conjugates formed at 2–3 h was reported to be increased compared to mung bean protein due to the increased number of hydrophilic moieties introduced by the grafted dextran. However, a slight decrease in solubility was observed with increasing graft time due to formation of insoluble protein aggregates. Emulsifying activity and stability indices of conjugates followed a similar trend and first increased compared to the native mung bean protein and then decreased with increasing graft time. Initial increase in emulsifying activity and stability indices was attributed to improved solubility and flexibility due to conjugation. The possible mechanism behind impaired emulsifying properties observed with increasing graft time was explained by heat induced protein aggregation and reduction of interfacial activity of mung bean protein with increased attachment of dextran. The authors reported that conjugates formed at 80 °C with lower glycosylation degrees and browning showed better functionality

Wang et al. [28] investigated the effect of ultrasound treatment on conjugation of mung bean protein isolate and glucose. Similar to the study of Zhou et al. [29], the authors reported that Maillard reaction resulted in changes in the secondary structure of mung bean protein. Furthermore, ultrasound-treated conjugates were reported to have a less compact tertiary structure compared to the heat-treated conjugates and the native protein. Application of ultrasound treatment in Maillard reaction was indicated to form conjugates with a higher degree of glycosylation and improved solubility. Higher solubility observed in ultrasound-treated conjugates was attributed to two factors: breaking of insoluble aggregates and addition of more hydrophilic groups due to enhanced conjugation with the ultrasonication treatment. Similarly, ultrasound-treated conjugates showed better emulsifying activity and stability compared to heat-treated conjugates due to dispersion of aggregates and improved mobility of the protein molecule. Jin et al. [30] also investigated the effect of ultrasound treatment on conjugation of black bean protein isolate and glucose via Maillard reaction. Ultrasound treatment was reported the increase the reaction rate indicated with a higher degree of glycation at a shorter time. FTIR profile of the samples indicated that ultrasound-treated conjugates lost more ordered secondary structure (α-helix and β-sheet content) compared to the heat-treated conjugates. Alterations in protein structure resulting in increased unordered structure content were reported to improve the flexibility of the molecule and hence, emulsifying properties. Changes in fluorescence spectra indicated that the Maillard reaction resulted in alterations in the tertiary structure and ultrasonication treatment further increased the extent of these changes. Moreover, ultrasound-treated conjugates were reported to show higher surface hydrophobicity, improved solubility, emulsifying activity and stability indices compared to the heat-treated conjugates and the native protein. In another recent study, Zha et al. [31] formed conjugates between pea protein and gum Arabic and monitored the changes in functional properties

reaction has been indicated as a promising method for modification of protein functionality [34]. Zhou et al. [29] formed conjugates between mung bean protein isolate and dextran at 80–90 °C for changing durations of 1–6 h. Electrophoretic profile of mung bean protein showed that both vicilin and legumin subunits

**3.2 Maillard reaction**

**94**

Functional properties of legume proteins can be improved via various biological methods including enzymatic hydrolysis, cross linking and fermentation. A brief summary of the findings of recent studies focusing on biological modification of legume proteins is presented in **Table 3**.



#### **Table 3.**

*Summary of recent studies on biological modification of legume proteins for improved functionality.*
