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An experimental design generated dairy gels with a single strawberry flavour varying in: native or modified tapioca starch; two levels of starch, milk fat and sucrose; and presence or absence of K-carrageenan. Volatiles headspace concentrations differed significantly (p < 0.001) with K-carrageenan dominant factor with a single fat level and with two fat content. Sensory scoring of strawberry intensity, in a fractional factorial design, showed significant influence of sucrose but not fat but with significant interaction.

There is conflicting information on the mechanical properties and ageing kinetics of starch-water-glycerol systems. This makes understanding the changes occurring on storage of edible products difficult to predict. The work described in this thesis looks at model systems consisting of thermomechanically extruded plasticized starches (waxy maize, rice and wheat) and commercial products. The objectives of the work were to evaluate how the presence of polyols effects glass transition temperature (Tg), sorption isotherms, diffusion rates and texture parameters and to create models that could be used to predict behaviour. Very similar results were obtained for the starch samples except that monolayer (ma) values were higher for the waxy maize starch than for the wheat and rice. The waxy maize also was more brittle at equivalent moisture content when compared to the other two starches. Glycerol had a major impact on the water absorption. For RHs > 70% more water absorbed up by samples containing glycerol while the opposite occurred at RHs <60%. Monolayer values for GAB and BET confirmed this finding. The behaviour could be predicted if an interaction factor <1 was used in weight fraction models. Tg of the samples was measured by DSC and also by using predictive models, where the ten-Brinke Karas equation was found to give the best predictions. A value that was found to be most beneficial for the prediction of retrogradation was (storage temperature minus Tg). Change in texture was associate with (T-Tg), although the brittle ductile transition occurred 40°C below T-Tg=O. Diffusivity values increased with plasticizer level up to 8*10 3 m'z/s. There was an apparent fall in values when the samples were above Tg. However, it is suggested that this is due to sample geometry change rather than a change in diffusion mechanism. The Tg values also were found to be a good predictor of the type of change occurring in the model systems and food products during storage. Below Tg physical aging (enthalpy relaxtion) could be seen in the samples and retrogradation of the starch occurred above Tg. The rates of retrogradation were not affected by glycerol content directly and knowledge of Tg and storage temperature were sufficient to predict the retrogradation. Products became stiffer on storage and this was associated with molecular reassociation of the starchy component, but control of the moisture was also critical as water still dominated product behaviour even in the presence of glycerol.

MSCFST / Department of Science and Technology / Heat-moisture treatment (HMT) is a physical modification that alters the physicochemical properties of starch without changing its molecular structure. The objective of the study was to investigate the influence of HMT on the functional, colour and thermal properties of bambara groundnut (BG) starch. A central composite rotatable design comprising two independent factors (temperature and time) was used for the study. The central composite rotatable design was generated using Design-Expert software version 8.0.1.0. Bambara starch extraction was done by milling BG into flour (5 Kg), suspension in 15 L, 0.3% sodium hydroxide and centrifugation followed by washing using distilled water. The starch was then HMT treated in an air oven at 80 - 120 °C for 30 - 90 min under 15 % moisture content (MC) (HMT 15), 25% MC (HMT 25) and 35% MC (HMT 35). The highest L* and WI values for HMT treated BG starch were observed at HMT 80 °C for 30 min under 15% MC; 100 °C for 60 min (25% MC); and 100 °C for 17.57 min (35% MC) while the lowest was observed in HMT 100 °C for 102.43 min (15% MC); 120 °C for 90 min (25% MC); and 120 °C for 90 min (35% MC). In HMT 15-BG starch, the gelatinisation parameters onset (To), peak (Tp) and concluding temperature (Tc) of the samples decreased as treatment time and temperature increased whereas gelatinisation enthalpy of BG starch increased with increase in HMT treatment temperature and time. In HMT 25-BG starch Tp, and gelatinisation enthalpy of the starch increased with increase in HMT treatment temperature and time. While in HMT 35-BG starch, To, Tp, Tc and gelatinisation enthalpy of the starches decreased with increase in HMT treatment temperature and time. In HMT 15-BG starch, the water absorption capacity (WAC), solubility and swelling power (SP) decreased as treatment time and temperature increased while oil absorption capacity (OAC) of the starch increased with increase in HMT treatment temperature and time. In terms of HMT 25-BG starch, the WAC and OAC increased as HMT treatment time and temperature increased while SP and solubility of the starch decreased with increase in HMT treatment temperature and time. In HMT 35-BG starch, OAC, solubility and SP decreased as treatment time and temperature increased while WAC of the starch increased with increase in HMT treatment temperature and time. The optimum HMT conditions for BG starch were found to be 80 °C for 30 min (HMT 15), 105.74 °C for 30 min (HMT 25), and 113.16 °C for 30 min (HMT 35). Desirability of the obtained optimum conditions were 0.63 (HMT 15), 0.56 (HMT 25) and 0.64 (HMT 35). Information obtained from scanning electron micrograph indicates oval and round shape for bambara starch granules, with varying sizes. The range of the granule size width was 4.2 – 4.7 mm and 10 μm for length. The modified starches showed some changes in granule morphology as they seem to disintegrate with application of HMT. Unmodified and HMT - BG starches showed characteristic FTIR bands linked with common starches. All the samples displayed complex vibrations in the region below 1000 cm-1 due to the skeletal vibrations of the glucose pyranose ring. Statistical analysis on colour, thermal and functional properties of HMT 15-BG, HMT 25-BG and HMT 35-BG starch showed that effects of temperature and treatment time had no significant (p ≥ 0.05) effect on these properties of HMT-BG starch. However, treatment time had a significant linear effect (p ≤ 0.05) on swelling power, for HMT 15-BG starch. In HMT 35-BG starch, WAC was significantly affected by quadratic effect of temperature and time while solubility was significantly affected by linear effect of time and quadratic effect of temperature. / NRF