Tef as industrial crop for food processing. Unlocking its latent potential and flour handling characteristics

Resum

Recently, tef [Eragrostis tef (Zucc.)Trotter] grain is attracting the attention of the modern food industry since it is a gluten-free grain encompassing highly appreciated nutritional advantages. However, as a relatively new raw material for most countries other than Ethiopia, a deep study on its inherent characteristics related to processing is still needed for its use in various food applications across the globe. The engineering characteristics and techno-functional properties of tef grain flours from three varieties (DZ-01-99, DZ-Cr-37 and DZ-Cr-387) were studied. Their potential in gel like food and breadmaking applications was explored. Commercial wheat (whole and refined) and rice flours were included as references. Tef variety and mill type had important effects on flour granulation, bulk density and starch granule which dictate the hydration and pasting properties. Different granulation of tef grain flour induced different in vitro starch digestibility. Tef grain flours were less flowable than the reference flours and their flow and packing properties were more sensitive to water activity. Tef grain flours led to sigmoidal sorption isotherms with estimated monolayer water content of 0.053 (BET model) and 0.057 (GAB model) g water/g dry solids. No differences among the three tef varieties were observed on their flour starch gelatinization enthalpies that were higher than that of wheat and similar to rice. The amylopectin recrystallization extent after 7 days of storage at 4oC was significantly higher in tef flour gels than in wheat ones. The minimum flour concentration required for gel formation from the three tef varieties was 6-8%, similar to wheat flour. The gels formed from the tef cultivars showed solid-like behavior indicating their ability of forming self-supporting gels. The dependence of viscoelastic moduli with concentration fulfilled a power law. The Avrami model was successfully fitted to the textural parameters evolution of tef grain flours gels with time. Important differences were observed among tef and rice and wheat flours, probably contributed by their differences in protein, starch, lipid and fiber constituents. The measured gelling properties suggest that tef grain flours would be suitable ingredients in gel food formulations. Incorporation of tef flours to wheat dough matrices visibly affected the dough structure by reducing the viscoelastic moduli values and the maximum stress they can tolerate before the composite structure is broken, and increasing the dough instantaneous and retarded elastic compliances. The effect of dose was not always significant in the parameters measured. On average, the DZ-Cr-37 supplemented doughs exhibited higher elastic and viscous moduli, lower compliances and higher steady state viscosity and led to significantly lower volume breads. Tef incorporation up to 30% gave ciabatta type breads with higher volume than the control bread (100% wheat). Tef incorporation led to breads with enhanced mineral contents and lower starch digestion rate index. DZ-01-99 (brown tef) supplemented breads had higher flavonoid content and larger anti-radical scavenging activity than those blended with the remaining varieties and higher than the control bread. In general, the results revealed the importance of the variety and the mill on flour engineering and techno-functional properties and confirmed the suitability of tef as an ingredient in the formulation of new cereal-based foods.