Effect of pH and soybean flour heat treatment on the texture and colour of fortified roasted shredded cassava roots (garri)

The effect of adding soy protein on the texture and colour of garri, a West African cassava food, is evaluated. Garri is mostly pre-gelatinized and agglomerate starch product. The challenge lies in maximizing the protein supplementation without changing the textural characteristics. Three different soybean flours were used for fortification: toasted soy flour (TSF), isolated soy protein (ISP) and defatted soy flour (DSF). The soy flours were dispersed in water, and the pH of the dispersions adjusted to 6.5 and 4.5. Both boiled and unboiled dispersions were used. Fortification of garri with soy flour to a protein content of 15% w/w affected the texture of garri agglomerates. The addition of soy flour suspensions that were not boiled to the shredded cassava roots resulted in increase of hardness of swollen garri particles by a factor greater than 1.7 for ISP and DSF and a factor of 1.2 for TSF. Suitable pretreatment of the soy suspension in term of pH adjustment to 4.5 and boiling, restored the hardness to the level of non-fortified garri with all types of flour. Light microscopy of garri aggregates showed a positive correlation between the size and continuity of protein domains and hardness, where hard garri' consist of a system of starch in protein' and soft garri' consist in a system of protein in starch'. The hue turned more yellow and the darkness of fortified garri increased as consequence of the colours of the soy flours added