The Complex Modification And Mechanism For Baking Cassava Flour

In African countries,health problems caused by the consumption of gluten(gluten allergy)and the high economic costs of importation of wheat by African countries has prompted the important need for indigenous alternatives to wheat flour for the production of baked products.Cassava(Manihot esculenta Crantz)is a major food staple in tropical and sub-Saharan Africa with flour and starch being its main products which can be utilised as functional ingredients in the production of baked foods.However,native cassava starch is deficient in bioactive compounds and has poor thermal stability and high amylose retrogradation tendency,while cassava flour has a low protein content and is deficient in structural amino acids.These deficiencies make cassava flour and starch incapable of producing leavened bread of acceptable quality.An approach in improving the quality inadequacies of flour and starch is through modification of their microstructure.In this regard,novel dry-heat-moisture treatment and pressurised steam-heat-moisture treatment conditions combined with structure-enhancing additives were used to modify cassava flour and starch in order to develop suitable baking cassava flour and starch.Dry-heat-moisture modification methods for cassava flour and starch were developed.Process variables such as moisture,dry-heat temperature and treatment time conditions were optimised in relation to quality characteristics of cassava flour and starch using a three-variable Box-Behnken design based on response surface methodology.The derived optimal dry-heat-moisture treatment conditions for cassava flour was 250 g/kg moisture,90°C and 45 min and that for cassava starch was 270 g/kg moisture,120°C and 21 min were consequently derived and their effect on structural,functional,viscoelastic and gelatinisation thermal characteristics of cassava flour and starch were studied.It was revealed that the optimal dry-heat-moisture treatment conditions decreased the granule volume-based diameter(D^[4.3])of cassava flour(56%)and increased that of cassava starch(468%).Relative crystallinity of cassava flour was increased(7%)and that of cassava starch was decreased(9%)by the treatment.The structural changes induced by the treatment conditions led to decrease in gelatinisation enthalpy((?)H)of cassava flour and starch.Furthermore,the application of the treatment increased peak viscosity(55%and 36%),gelatinisation onset temperature(Tonset)to conclusion temperature(Tendet)range(7%and 32%)and elasticity(6%and 30%)of cassava flour and starch.The treatment of cassava starch was effective in decreasing amylose retrogradation ability(setback viscosity,17%).Pressurised steam-heat-moisture modification methods for cassava flour and starch were developed.Process variables namely moisture,pressurised steam temperature and treatment time conditions were optimised in relation to quality characteristics of cassava flour and starch using a three-variable Box-Behnken design based on response surface methodology.The derived optimal pressurised steam-heat-moisture treatment method for cassava flour was 150 g/kg moisture,120°C(2 Bar)for 10 min and that for cassava starch was 190 g/kg moisture,120°C(2 Bar)for 20 min were consequently derived and their effect on structural,functional,viscoelastic and gelatinisation thermal characteristics of cassava flour and starch were studied.It was revealed that the optimal steam-heat-moisture treatments decreased D^[4.3]of cassava flour(60%)and increased that of cassava starch(188%).The treatment increased the relative crystallinity of cassava flour(50%)and decreased that of cassava starch(40%).The structural changes induced by the treatment led to decrease in(?)H of cassava flour and starch.The treatment increased peak viscosity(15%)and elasticity of cassava starch while decreasing those of cassava flour.However,the treatment was effective in increasing Tonset-Tendet ranges(23%and 9%)and decreasing breakdown viscosity(22%and 7%)and setback viscosity(56%and 25%)of cassava flour and starch.In order to improve the structural and functional properties of cassava flour and starch modified by the optimised dry-heat-moisture treatment and pressurised steam-heat-moisture treatment conditions to meet the quality requirements of baked food,cassava flour and starch were complexed with different emulsifiers and hydrocolloids additives using the optimised dry-heat-and steam-heat-moisture treatment conditions,respectively.The effect of additive type and additive concentration on the swelling,pasting properties and amylose retrogradation ability of the cassava flour and starch-additive complexes were studied.Cassava flour complexations with guar gum(GG)and sodium stearoyl lactylate(SSL)at 1 g/kg concentration,respectively,as well as cassava starch complexations with diacetyl tartaric acid ester of mono-diglycerides(DATEM)and SSL at 1 g/kg concentration,respectively,produced the best quality characteristics and thus,their structural and functional,thermal and viscoelastic characteristics were studied.It was revealed that cassava flour formed cooperative complexation interactions between cassava flour with GG and SSL leading to increase in granule surface agglomeration,complexation index((?)H,23%-36%),thermal stability(Tonset-Tendet range,22%-51%),relative crystallinity(5%-19%),and decrease in D^[4.3](48%-73%),amylose retrogradation tendency(setback viscosity 43%-64%)and swelling properties.On the other hand,cassava starch formed non-cooperative interactions with DATEM and SSL leading to decrease in complexation index((?)H 2%-34%),increase in granule surface agglomeration,in relative crystallinity(4%-15%),D^[4.3](225%-326%),gel elasticity(tan?),thermal stability(Tonset-Tendet range,3%-42%),as well as decrease in and thermomechanical stability(breakdown viscosity 23%-57%).Regardless of heat-moisture treatment condition,cassava flour and starch complexations with SSL elicited better paste thermomechanical stability and gel resistance to structural deformation.Bread-making performance of all derived modified cassava flours was evaluated by blending them with wheat flour at a ratio of 30:70.The dough rheological characteristics,bread physical,structural and textural characteristics including bread amylopectin retrogradation kinetics of all modified cassava flour-wheat flour blends were compared with those of native cassava flour-wheat flour and wheat flour.It was revealed that optimal dry-heat-moisture treated cassava flour-SSL complex blend elicited the best bread characteristics as it exhibited higher dough stability(11%),loaf specific volume(26%)and bread crumb grain porosity(19%),as well as lower bread crumb hardness(19%)and loaf density(20%)than those of native cassava flour-wheat flour blend.All modified cassava flours were effective in decreasing the amylopectin retrogradation kinetics performance of cassava-wheat flour blend,with optimal steam-heat-moisture treated cassava flour-SSL complex having the greatest effect.The novel methods presented in this study were effective in improving the bread-making deficiency of cassava flour,thus producing modified cassava flours which can effectively replace wheat flour at 30%replacement level for the production of acceptable leavened pan bread.These proposed methods are based on readily-available low-cost green technologies which can easily be adopted in flour or starch processing systems.The outcomes from this study are of great significance for the effective use of cassava resources in achieving food security in African countries.