Process Optimization and Quality Characterization of Tef Flour for The Industrial Manufacturing of Injera

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Addis Ababa University


Tef [Eragrostis tef (Zucc.)Trotter] is an Ethiopian indigenous tropical cereal crop and it has been cultivated for many years in Ethiopian highlands. Tef injera making in industry scale holds a significant economic and social interest but requires a thorough study of how the process variables affect the product quality. Tef is the main staple in the country mostly used to make injera. Injera is Ethiopian flat bread which is mostly made from tef flour. The general objectives of this thesis was optimizing injera making process (milling, kneading and Absit or scolded dough preparation) and identify the quality characteristics (tef flour and dough which includes flour functional and textural properties, dough rheological properties, injera sensorial quality and starch digestibility of injera) of tef flour, dough and injera for industrial manufacturing by 1) investigating the effects of mill type (hammer, disc, and blade), kneading conditions and injera absit preparation on injera sensorial quality; 2) assessing the effect of mill type and kneading conditions on starch digestibility, tef dough fermentation kinetics and phytate to mineral molar ratio;3) studying tef flour characteristics and its dough rheological properties as affected by mill type; and 4) introducing software based inhere quality evaluation technique. Standard methods were adopted for all analysis and determinations. Injera made with disc mill flour had higher overall sensorial acceptability (6.6) than that obtained from hammer mill (4.2) and blade mill (4.1) flours. The injera made with blade mill flour obtained the lowest rapidly available glucose (52.6) and rapidly digestible starch (47.3). Based on its higher injera overall acceptability and moderate starch digestibility, DM flour was preferred. Tef flour from blade mill had contained higher BD (0.77 g/mL) and FC (12.67 mL). On the other hand, flours from disk mill had higher WSI (7.94 g/100g) while lower was for hammer mill (4.17 g/100g). A lower value (64%) of dispersibility was recorded on flour from disk mill. The highest hardness (2.09 N) and gumminess (0.75N) was recorded tef gels from blade mill. Tef flour prepared from hammer mill showed significantly lower values of G’1 and G”2 and higher values of Tan δ than other mill type flours. Tef flours from disk mill had significantly higher peak and breakdown viscosity but lower trough viscosity values. Tef dough stickiness and forward extrusion was significantly (p<0.05) affected by mill types. Tef flour from disk mill yielded with the highest percentage of WSI indicates suitability to produce higher quality tef dough for injera making than other mill types. Changes in kneading conditions (time/speed) showed important variation on injera RAG and RDS content. Flavonoid, total phenolic content and phytate were also significantly varied at different kneading time-speed combinations. Injera sensory quality was also significantly varied due to the changes in kneading conditions. Tef dough kneading method was optimized at kneading speed of 6 (800 rpm) with 3 minutes of kneading time which has higher desirability to give 8-9 point hedonic scale of injera overall acceptability. In addition to kneading conditions, absit preparation method (water to fermented dough ratio) was found to affect the quality of tef injera. Absit preparation method was also optimized with a combination of 100 ml of batter to 900 ml of water to gives the higher desirability in terms of injera overall acceptability. The effect of mill type and kneading speed-time combinations on fermentation kinetics and phytate/mineral molar ratio were significant. The outcome of introducing software for the determinations of injera number of eyes was found effective; its result difference to human eye determination was insignificant. In general, transformation of traditional injera making process to industry level requires an intense investigation on mill type, dough kneading conditions and absit preparation methods, as these significantly affects tef flour characteristics, dough rheological properties and injera quality. On the other hand, software based injera quality evaluation is an important aspect to be considered in injera making industries to assess product quality and improve production yield.



Quality Characterization, Tef Flour, Manufacturing of Injera