Rheological behaviour of pullulanase-treated guar galactomannan on co-gelation with xanthan

The present study involves the use of non-specific enzyme pullulanase (from Bacillus acidopullulyticus) to remove galactose residues from guar galactomannan to obtain modified guar galactomannan mimicking the functional properties of locust bean gum. The modified guar galactomannan blended with xanthan exhibited the rheological behaviour of elastic modulus (G′) greater than viscous modulus (G″) with a decrease in tan δ value similar to locust bean gum/xanthan blend. Also a twofold increase in the magnitude of elasticity compared to xanthan alone suggested the synergistic interaction with formation of three dimensional networks. The modified guar galactomannan with galactose content of 21% and M:G ratio 1:3.8, almost akin to locust bean gum, showed a better interaction with xanthan. Dynamic stress sweep study of modified guar galactomannan/xanthan blend with increased yield stress of 800 dynes/cm² also indicated the synergistic behaviour. Modified guar galactomannan also revealed the maximum synergistic interaction with xanthan at a mixing temperature of 60 °C than at 20 °C, 30 °C, 40 °C and 50 °C, respectively. Modification of guar galactomannan by pullulanase is an alternative route to produce galactose-depleted guar galactomannan with enhanced rheological functionalities on co-gelation with xanthan, as a cost effective replacement to locust bean gum.