The effects of thermosonication (high intensity ultrasound coupled with thermal treatment), on the reduction of thermophilic spore-forming microorganisms and its effects on the solubility index in reconstituted skim milk powder (RSMP) were evaluated. Thermosonication was applied to RSMP at various solids concentrations, temperatures, and lengths of time based on commercial milk powder processing conditions. Microbial counts were determined prior to and after treatments to determine the log reduction of Geobacillus stearothermophilusvegetative cells and spores. Log reductions were recorded, and data were analyzed by response surface analysis. The log reductions induced by temperature and time without high intensity ultrasound (HIU) were compared to reductions observed with HIU. Thermosonication was also applied to RSMP to determine effects on solubility using a continuous flow cell system. Thermosonication yielded a significantly higher level of microbial destruction for both vegetative cells and spores than heat treatment alone. For experiments involving vegetative cells, the interaction of treatment time and temperature proved to have the greatest influence on microbial inactivation. In comparison, the interaction of total solids content and length of HIU treatment demonstrated the greatest effect on the increased log reductions for spores. The solubility of RSMP treated with HIU did not significantly differ from the solubility of RSMP not treated with HIU. Further data showed the implementation of HIU, or thermosonication, during milk powder processing would be most effective before and after the evaporation stage when the total solids content of product is 9.2% and 50% at 75°C and 60°C, respectively. Based on preliminary data, it is assumed HIU applied for 10 s at these two locations would produce an additive effect, thereby reducing overall microbial counts by 5.76 log and 0.51 log for G. stearothermophilus vegetative cells and spores, respectively, in the product prior to entering the drying stage. All research findings and observations suggest HIU, or thermosonication, to be a successful method for reducing microbial populations during milk powder processing without sacrificing skim milk powder solubility

MSCFST / Department of Food Science and Technology / Watermelon (Citrullus lanatus) juice is rich in phytochemicals that possess antioxidant properties which are known to have a positive contribution to human health. Colour, pH, total soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity are quality properties that characterise watermelon juice. However, these quality properties undergo some chemical changes throughout the stages of maturity of the fruit as well as during thermal processing. The aim of this study was to investigate the effects of maturity and filtration on the physicochemical properties (colour, pH, total soluble solids) and the phytochemicals (lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity) of fresh watermelon juice. It further investigated thermosonication effects on these quality properties using response surface methodology (RSM). RSM considering temperature (25 – 52ºC), time (2 – 10 min) and amplitude level (24.1 – 60 μm) at a constant frequency of 20 kHz were the independent variables while colour variables (L*, a* and b*, C* and h*), pH, total soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity were the dependent variables. Results showed that colour, pH, total soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity of watermelon fruit juice are maturity dependent. All the physicochemical and phytochemical properties increased with maturity. The combination of the CIELAB parameters (L*, a*, b*) was clearly explained by the Chroma (C*) and hue (hº). The (C*) and hº values of the watermelon fruit juice were significantly (p < 0.05) affected by the stages of maturity. The red colour was observed to be more saturated in the fully - ripe sample as indicated by the highest Chroma (7.35) values. The half - ripe sample which was observed to be pink - red had a C* of 5.88 while the lowest (4.32) value was observed from the unripe sample. The highest hº value was obtained from unripe sample (83.89), while lower value was observed from the fully - ripe (76.03) sample because of the saturation of the red colour in the fully - ripe sample. The total soluble solids also increased with stages of maturity 6.66 to 6.60 at half - ripe while at fully - ripe redness changed from 9.3 to 8.99 and TSS 8.37 to 8.02. Filtration has shown a significant (p < 0.05) on the C* and hº values. There was a higher retention of all dependent variables at lower thermosonication treatment (25ºC; 24.4 μm), especially the lycopene which increased by 127%. Model predictions for the colour properties and phytochemicals were closely correlated to the experimental results obtained. Prediction models were found to be significant (p < 0.05) with low standard errors and high coefficients of determination (R2). / NRF