Nutritional Qualities, Health Benefits and the Potential for Complementary Food Formulation of Three Types of Amaranthus Caudatus Grain Cultivated in Ethiopia as Affected by Processing

Amaranth is a valuable cereal crop with high biodiversity, distribution and productivity. Unlike other commonly utilized cereals, amaranth has high tolerance to arid conditions and poor soils, resistance to drought, pests and ability to adapt to environments that are not conducive to conventional cereals. The crop is underutilized in many parts of the world despite it has all the good attributes mentioned. Although it is known long time ago as a food and medicine in some parts of Ethiopia, it is still an underutilized crop and known as an “invasive weed’ by agricultural experts. Therefore, this study evaluates the nutritional qualities and health benefits of three different types of Amaranthus caudatus grain cultivated in SNNPR, Ethiopia for a possible use as an ingredient in complementary food formulation. The macro and micronutrient contents, mineral absorption inhibitors (IP6 and Iron binding polyphenols: galloyls and catechols), free and total amino acid profiles, protein fractions and digestibility, starch fractions and digestibility, bioactive compounds (total polyphenol, total flavonoid and γ-aminobutyric acid (GABA)) and antioxidant activity using DPPH and ABTS assays were determined. The effect of commonly utilized processing methods for cereal food preparation, popping and fermentation, on the overall nutritional qualities and health benefits was evaluated. Moreover, combining treatments such as soaking (at optimum pH and temperature for endogenous phytase enzyme) and malt addition was applied in order to see the quality changes consequent to phytate degradation and starch hydrolysis. The results of the study showed that amaranth has higher protein (14.0-15.5 g/100g DM) compared to maize, rice and barley but comparable with the content present in wheat and teff. The fat content is in the range of 7.5-7.7 g/100g DM and this value is two-fold higher than that present in commonly utilized cereals such as maize, barley, rice, sorghum, wheat and teff. The carbohydrate, acid detergent fiber, neutral detergent fiber and ash contents were in the range of 60-68, 5.5-14.2, 7.1-14.8 and 2.6-3.1 g/100g DM, respectively. Iron, zinc, calcium and magnesium contents were obtained in the range of 12-21, 2.7-3.4, 102-215, 292-340 mg/100g DM, respectively. A surprisingly too high IP6 content ranging from 1.85 to 2.20 g/100g DM was found in raw amaranth limiting its application for the formulation of infant foods. The content of galloyls and catechols were in the range of 93-143 mg TE/100g DM and 24-54 mg CE/100g DM, respectively. The high content of IP6 was decreased by 39 and 77% after popping and fermentation, respectively with subsequent improvement in estimated mineral bioavailability. However, the residual level is still high enough to demonstrate inhibition of mineral absorption. Fermentation also demonstrated a much larger, by 96-100%, degradation of iron binding polyphenols than popping. Experimental design aimed to achieve maximum phytic acid degradation by optimizing the best condition for enhanced activity of endogenous phytase using combined treatment of malt addition (10%) and soaking resulted in complete degradation of the phytic acid in 8.36 h at optimum temperature of 46 °C and pH of 5.2. The complete phytic acid degradation achieved in such relatively short period is due to the higher enzymatic activity of added malt, 3x higher than raw amaranth. Furthermore, the malt also favors the hydrolysis of starch and found to lower the apparent viscosity. This consequently improves the energy and nutrient density of amaranth porridge. The content of total essential amino acids, which include lysine, threonine, valine, leucine, isoleucine, histidine, sulphur and aromatic amino acid were in the range of 65.3-73.9, 35.0- 40.3, 41.3-48.3, 59.5-67.1, 34.9-39.4, 33.9-37.2, 66.5-79.5 and 88.4-99.4 mgg-1 protein, respectively. This result shows that all, except leucine in raw red and brown amaranth, are above WHO reference pattern for children aged 1-2 years. However, when the digestible fraction of the protein was considered the contribution to the daily essential amino acid requirement is decreased by 18-29%, the maximum decrease being for the brown amaranth due to its lower digestibility compared to the other two amaranth samples. Both popping and fermentation caused substantial decrease in cysteine, lysine and methonine contents. The content of free essential amino acid obtained was below 0.2% and the highest was for histidine. Popping decreased all the measured essential free amino acids due to volatilization but fermentation increased all the essential free amino acids due to hydrolysis of large polypeptide molecules. Separation of amaranth seed protein fraction based on Osborne classification demonstrates that albumin + globulin are the major and prolamin is the minor fraction which is in extreme contrast to teff and sorghum grains affecting the functional property during food formulation The free glucose (FG), total starch (TS), rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) contents of the three types of raw amaranth were found in the range of 0.64-0.67, 48-60, 27.4-33.2, 10.9-13.9 and 8.5-9.4 g/100 DM, respectively. Popping exhibited significant improvement in RDS, SDS and TS contents and no significant change on FG and RS content. On the other hand, fermentation increased the FG, RDS and SDS and decreased the TS and RS contents. Consequent to the increase in RDS and SDS, the starch digestibility also increased from 83 to 86 and 96% during popping and fermentation, respectively. The starch digestibility of the raw sample was relatively high and the further improvement during popping and fermentation was associated with degradation of phytic acid during both processing methods and enhanced microbial enzyme activity during fermentation. Moreover, both popping and fermentation modifies the rheological property of amaranth. Therefore, the energy density of gruel prepared from raw, popped and fermented amaranth was found to follow the order; fermented > popped > raw. Total polyphenol and total flavonoid contents were highest for the brown amaranth (257 mg GAE/100g DM and 680 µg CE/g DM) followed by red (158 mg GAE/100g DM and 600 µg CE/g DM) and white (146 mg GAE/100g DM and 520 µg CE/g DM). Antioxidant capacity (AC) that was determined using DPPH and ABTS assays also showed that brown amaranth had highest AC (43.29±3.22 and 93.08±0.72 mg TE/100g DM, respectively) followed by red (35.52±1.88 and 85.66±3.59 mg TE/100g DM, respectively) and white (16.65±1.54 and 79.61±1.43 mg TE/100g DM, respectively) amaranth. All processing methods, popping, germination and fermentation showed tremendous improvement on the antioxidant activity due to the production of maillard reaction products during popping and increased extractability of phenolic compounds during germination and fermentation. A remarkable increase in γ-aminobutyric acid (GABA), that has an antihypertensive and antidiabetic effect, was observed during germination and fermentation indicating that malted and fermented amaranth are preferred ingredient in functional food preparation especially for celiac patients due to the absence of gluten in amaranth. Realizing the good nutritional qualities of amaranth compared to commonly utilized cereals, the attempt made to prepare injera from a blend of teff and amaranth was successful with acceptable nutritional and sensory qualities until 20% amaranth blending thereby contributes to the actions to ensure food and nutrition security. Generally all the three types of cultivated Amaranthus caudatus grains were found to have good nutritional and health benefits, the brown amaranth being superior in many of the parameters analyzed. Moreover, the processing techniques applied were also contributed to the improvement in the nutritional quality and health benefits. However, due to the presence of high levels of phytic acid in the studied amaranth, utilizing them as an ingredient in complementary foods should be done with great caution. Selection and breeding of low phytic acid containing amaranth is also strongly recommended to exploit the potential of the crop