Optimisation of Ontaku/ Oshikundu: Pearl millet and sorghum malts quality and convinient premix development
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Date
2020
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University of Namibia
Abstract
Oshikundu/Ontaku is a nonalcoholic, acidic, opaque fermented beverage. It is comprised of pearl millet (Pennisetum glaucum (L.) R. Br) meal/flour, commonly known as mahangu, malts of pearl millet or sorghum (Sorghum bicolour (L.) Moench) and/or brans (pearl millet). Brewing of oshikundu remains an art in households with no empirical improvement of a controlled fermentation flow process to give a consistent product. Some of the major limitations to the formal commercialisation of this brew are the absence of standardised malting process that gives a consistent malt quality and microbial safety. The lack of standard ingredient ratios (flour/meal: malt: water) of brewing. Also, the sedimentation of adjunct particles at the bottom (dreg), thus creating the difference in viscosity of oshikundu. Well-defined fermenting microorganisms are not used, and the preparation method still relays on a laborious time-consuming process. Therefore, this study investigated conditions for malting, reduction of dreg, identification of fermenting microorganisms and formulation of ingredient ratio for an improved preparation process. Grains used in the study were collected from Omahenene Agricultural Research Station (2015 harvest), of the Ministry of Agriculture, Water and Forestry. Pearl millet varieties Okashana 2 (SDMV 93032), Kantana (landrace) and Kangara (SDMV 92040), while sorghum varieties are Macia (SDS3220) and landrace commonly referred to as red sorghum. Malts of the two cereals were prepared by steeping in static water at 20-22oC for 2 hours wet and 2 hours air-rest for a total of 8 hours and germinated at 30oC. Malts were dried between 50-55oC for 24 hours. Cereals germinative energy was above 90% as recommended for sorghum by the European Brewery Convention. Malting loss was high up to 30% in pearl millet varieties and Macia. Crude protein and fibre were found to increase following malting. Reducing sugars were not detected in nongerminated pearl millet grains. Malts reducing sugars were statistically significant (p ≤ 0.05) between cereals. The malt reducing sugars was as follows Macia> Red sorghum> Kantana>Okashana 2 = Kangara. Malting resulted in significantly increased free amino nitrogen (FAN) content. Kantana had the highest FAN followed by Macia malt. No amylolytic activity was detected in nongerminated grains irrespective of the cereal. Pearl millet was found not to contain condensed tannins. Malts had an unacceptable high aerobic plate count load above 6.3 Log cfu/g or (2 × 107 cfu/g) as specified for Southern African sorghum malts. However, results show that the malts were not contaminated by Salmonella spp., Shigella and coliforms. Regulated mycotoxins in malts were found to be below the legal limits. Cereal malts are not of safety concern from coliforms and mycotoxins under these malting conditions. Oshikundu is likely fermented by lactic acid bacteria (Lactobacillus. plantarum, L. pentosus, L. acidifarinae, L. paraplantarum, L. spicheri, L. namurensis, L. zymae, L. fermentum, L. brevis, L. delbrueckii subsp bulgaricus, L. buncheri, Leuconostoc gurlium and Pediococcus acidilactici) and yeast (Saccharomyces cerevisiae and S. paradoxus). However, the dynamics of LAB and yeast during fermentation are not known. The use of smaller amounts of dry ingredients and pre-gelatinisation of pearl millet meal in the process of making oshikundu significantly decreases total solids. This suggests that the amount of suspended particles in oshikundu that tend to settle during storage can also be reduced through this route, in the absence of consumer acceptability test. The study demonstrated a creative formulation of a dry powder premix for brewing oshikundu. Preliminary sensory evaluation showed that panellists extremely liked the ease of preparation method, where only water was required to be added to the premix. The study demonstrated that malting pearl millet and sorghum grains under set conditions gave malts of acceptable quality (reducing sugars, free amino nitrogen, alpha and beta amylase activity, phenolic content, radical scavenging activity, mycotoxins and microbial load). Also, a lower amount of pre-gelatinised adjunct can be used to achieve the same yield of oshikundu and at the same time reduce dregs. Also, ingredient ratios were formulated by the use of dry ingredients premix for making oshikundu that was easy to prepare.
Description
A research dissertation submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Science (Biochemistry)
Keywords
Oshikundu, Pearl millet, Sorghum malts