PhD PUBLIC DEFENSE (Hybrid)

Title: Rheological characteristics of wheat-cassava composite flour and quality of the composite bread

Name: Manano John (Reg. No.16/U15132/GDFT/PE)
Supervisors: 1. Prof. Ogwok Patrick
2. Assoc. Prof. Byarugaba-Bazirake G.W.

Abstract

Uganda is a major producer of cassava in Africa. Cassava has great potential as a raw material for agro-industry. Currently, utilization of cassava is limited to semi-processed products through the informal sector. The overall objective of the study was to assess the potential of wheat-cassava composite flour as an industrial raw material for bread production in Uganda, and thus enhance cassava utilisation. Consequently, the study assessed the chemical composition of five major cassava varieties. Proximate composition, minerals and anti-nutritional factors were determined using standard methods. Minerals were determined by Atomic Absorption Spectrophotometry (AAS) and cyanogenic glucoside by Picrate Paper Kit. High quality cassava flour was prepared and utilised as partial wheat substitute for product formulation. Rheological characterisation of the composite flour/dough was carried out using the Mixolab, Consistograph and Alveograph. Physical and sensory evaluation of bread produced from the composite flours was performed under standard procedures. Bread quality attributes were correlated with rheological characteristics of flour dough.

Moisture content of the cassava varieties ranged from 5.43 to 10.87 %; ash ranged from 1.05 to 2.39 %; crude fibre from 1.06 to 1.18 %; crude protein ranged from 0.74 to 1.51 %; crude lipid ranged from 0.39 to 0.63 %; and starch contents ranged from 66.72 to 84.42%.

The mineral contents (mg/kg): calcium ranged from 13.15 to 16.56; iron ranged from 0.002 to 0.01; zinc ranged from 0.56 to 0.87; magnesium ranged from 3.58 to 3.88; and copper ranged from 0.002 to 0.14. The contents of anti-nutrients (mg/kg): cyanogenic glucosides ranged from 30 to 800; phytates ranged from 661.33 to 984.64; oxalates ranged from 90.6 to 227.8; and tannin ranged from 0.18 to 0.33. Cassava varieties contained higher levels of cyanogenic glucosides than recommended by Ugandan and East African Standards making them unsafe in the primary form for direct utilization as food and food raw materials for industries. The low levels of essential minerals, iron, zinc and copper necessitates fortification of cassava flour used as human food. The high content of phytates and oxalates in cassava requires some form of processing (thermal treatment or fermentation) before consumption to reduce their chelating effects on minerals. The high starch levels in the cassava varieties make them valuable raw materials for starch and starch-related industries.

Bread quality, expressed as overall acceptability, was positively correlated with mixolab parameters protein weakening (C2), (r = 0.732),  dough stability  (r = 0.749), and dough development time (DDT),  (r = 0.585); alveograph parameters tenacity/resistance (P), (r = 0.675) and deformation energy (W), (r = 0.640) and consistograph parameter maximum pressure (PrMax), (r = 0.913). Results showed that bread of acceptable quality can be processed using composite containing 20 % cassava flour. Rheological properties of flour can thus be used to assess the suitability of flour for bread making. The economic value of cassava can, therefore, be realised through the industrial processing of cassava-based products.

Keywords: composition, anti-nutrients, cassava varieties, composite flour, bread, sensory, physicochemical, rheology, mixolab, alveograph, consistograph, correlation

ACCESS DETAILS:

Venue: Central Lecture Block, Room 101

Date: 18th February 2022 Time: 9:00 Am

Join Us Online Via Zoom: https://kyu-ac-ug.zoom.us/j/93690773443?pwd=ZklRM2s3c3FvRFFzeWczbHFYQVV6UT09

Meeting ID: 936 9077 3443 Passcode: Kyu2022