Impact of Processing Techniques on Nutrient and Anti-Nutrient Content of Grain Amaranth (A. albus)

Abstract

Grain amaranth (Amaranthus albus) is a pseudo cereal consumed in various parts of the world especially in Africa, India, Nepal and some non-native regions. It has attracted increasing interest over recent decades because of its nutritional and functional properties. Reducing anti-nutrients level in the grain prior to consumption can increase the bioavailability of nutrients. Therefore, this calls for increased efforts towards evaluation of how different processing technologies can improve the bioavailability and absorption of nutrients. Traditionally, amaranth grain is boiled, popped, roasted, or milled to make gruel for consumption. This study investigated the impact of dry and wet heat processing techniques on the nutrient and anti-nutrient contents of grain amaranth. Proximate composition and anti-nutrients content were determined using standard procedures. Protein digestibility was determined after enzyme digestion while starch gelatinization was evaluated using light microscopic techniques The dry heating processes used included roasting(160ºC 10min) and popping(190ºC 15s)while the wet heating techniques included boiling whole grains   and slurries(100ºC 25min). Generally, the effects of dry and moist heat processing with regards to loss and retention of the nutrients differed significantly (p>0.05), with only the roasting retaining more of the nutrients than boiled seed flour. A pronounced reduction in the anti-nutrient content (tannins, oxalates, and phytates) was observed in the case of boiling as compared to roasting and popping.  Boiling and slurring resulted in, 86.2% and 92.6% increase in protein digestibility respectively whereas roasting reduced it to 66.3% as compared to raw grains (74.8%). Dry heating resulted in partial gelatinization of starch unlike wet processing which showed complete gelatinization. These results indicate that wet processing techniques are superior to dry processing techniques in terms of nutrient bioavailability

Keywords: Grain amaranth, gelatinization, protein digestibility, anti-nutrient