Physicochemical Characterisation and Determination of the Effect of Temperature on the Amylase Activities of Germinated Sorghum and Maize Grains

Abstract

Maize and sorghum are staple foods in many African countries. Along with rice, they constitute the bulk of the cereals consumed by the populations of northern Côte d'Ivoire. These cereals are used either directly or indirectly in malted and/or fermented form in the preparation of several traditional foods and the production of alcoholic beverages such as dolo a local beverage. This study aims at the physicochemical characterization and the determination of the effect of temperature on the amylase activities of germinated cereal grains of corn and sorghum collected on the market of the city of Korhogo. To do this, the analysis of cereals germinated over 6 days revealed that amylase activities are optimal on the second day of germination with a diastatic power of 110.29 ± 1.8 IU / g of protein and 114.17 ± 2, 4 IU/g of protein respectively for sorghum and maize. The optimal temperatures are mesophilic and are between 40 and 50°C. Beyond these temperatures, amylase activities are denatured until they reach 20% relative activity after exposure to 65°C. During germinationsand at an acid pH, the levels of reducing sugars, polyphenols and tannins increased with the duration of germination. The results of this study revealed that certain physicochemical characteristics and the effect of temperature condition the obtaining of a malt likely to influence the quality of a traditional beer. The germination time set at 2 days makes it possible to obtain fermentable sugars during malting for the preparation of alcoholic beverages according to the production conditions of traditional vendors. For sugars, they increase from 0.39±0.035 mg/100g DM (Dry Matter) before germination to 0.86± 0.003 mg/100g DM on the 6th day of germination for sorghum. As for maize, these levels increase from 0.11± 0.014 mg/100g DM to 0.43± 0.02 mg/100g DM. The diastatic power is optimal on the 2nd day, 110.29 ± 1.8 IU/g of protein for sorghum and 114.17 ± 2.4 IU/g of protein for maize.