Microbial degradation is directly affected by Tm , i.e. the lower the Tm , the higher the biodegradation of a toxicant such as free cyanide [31-33]. Beta vulgaris consist of 9.56 % carbohydrates, with betalains, phenolic compounds, including trace elements and minerals accounting for a larger percentage [34, 35]. The presence of betalains and phenolic compounds influence the microbial growth in BA samples since they degrade under different bioreactor operating conditions [36] from that of free cyanide, resulting in a slightly higher molecular weight of the F. oxysporum and thus, a higher Tm for BA samples. Similarly, interactions of molecular chains affect the change of enthalpy \((H)\) in melting with the internal energy accounting for the flexibility or otherwise of the samples studied, thus affecting the change of entropy \((S)\) in melting [37]. The highest \(H\) in melting for BCN samples was an indication of highest molecular interactions during free cyanide biodegradation.
Tan et al. [30] reported glass transition on reversible heat flow profile of MDSCTMafter the onset temperature which overlapped with the peak temperature. It was presumed that this was due to changes in the state of the starch molecules i.e. from being highly confined within the granular packing, to being disentangled as the order in which the molecules are arranged changed as the transition occurred. Glass transition could also be due to structural transitions of cellular materials at temperatures below freezing point of pure water including the influence of the underlying heating rate, modulation period and amplitude [17, 27]. There was no glass transition onF. oxysporum grown on glucose i.e. GA, this is similar to the previous report on the heat capacity of starch and glucose [14, 16]. It was evident that the substrate from which the biomass materials were formed, played a major role in the phase transition as can be seen that only cultures grown on Beta vulgaris (BA and BCN), had a glass transition.