Browsing by Author "Srichantra, Arunee"
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- ItemModeling of the break process to improve tomato paste production quality : a thesis presented in partial fulfilment for the degree of Master of Engineering in Bioprocess at Massey University(Massey University, 2002) Srichantra, AruneeThe pectic enzyme, Pectinmethylesterase (PE) and Polygalacturonase I and II (PGI and PGII), in the tomato fruit released after crushing during tomato processing reduce the viscosity of tomato paste by breaking down the insoluble pectin in the cell wall. To achieve higher viscosity tomato paste, the cold break (<60°C) or hot break (>60-95°C) processes can be used to inactivate the pectic enzyme and to achieve higher viscosity tomato paste. The study of tomato solids and PG enzyme activity showed that the levels of insoluble solids, total solids, pectin, and °Brix in Ferry Morse tomatoes were independent of fruit ripeness. The amount of PG enzymes was high in orange and dark red tomatoes and the activity of PG enzymes increased as a function of ripeness, from green to dark red. In the dark red tomato, the inactivation of PG enzyme activity was required to retain the level of pectin. Cold break temperatures below 60°C can not inactivate the PG enzyme activity. The PG enzymes started to be denatured when the hot break temperature was above 65°C and be completely destroyed when the break temperature was above 80°C. A mathematical model of the break process was formulated and Matlab programme was used to predict the effect of break temperatures on the pectin and PG enzyme concentration of the tomato pulp in the break tank for any inputs of feed rate (the flow rate to the break tank), feed ripeness, and residence time. The model was used to demonstrate the understanding and the optimisation of break process performance. Longer residence time of dark red tomato pulp in the break tank can decrease pectin fraction residual and increase enzyme inactivation in the tank temperature range 40 to 60°C. The pectin fraction remaining increased when the tank temperature was above 60°C because of the inactivation of PG enzymes. At 80°C there was no effect of residence time, the pectin fraction residual increased and reached 90% and enzyme fraction residual decreased to 10%. The effect of mixed tomato ripeness between the ripe fruit (orange and dark red) with the unripe fruit (green, breaker, and turning), the level of PG enzymes in the break tank decreased and affected on the higher pectin fraction remaining. Lower break temperature can be therefore used in this process to inactivate the low amount of PG enzyme and to achieve the same extent of pectin hydrolysis. The interruption of the feed coming into the break tank during tomato processing can increase the pectin fraction remaining and the enzyme fraction remaining in a new steady state when the feed was turned on.
- ItemStudies of UHT-plant fouling by fresh, recombined and reconstituted whole milk : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Engineering(Massey University, 2008) Srichantra, AruneeThe objective of this study was to investigate the effects of preheat treatments on fouling by fresh whole milk (FWM), recombined whole milk (RCB) and reconstituted whole milk (Recon) in the high-temperature heater of indirect UHT plants. Various preheat treatments prior to evaporation during milk powder manufacture were applied to skim milk powder (SMP, 75 °C 2 s, 85 °C, 155 s and 95 °C, 155 s) and whole milk powder (WMP, 95 °C, 33 s). These preheat treatments were so-called “evaporator preheat treatments”. Skim milk powder (SMP) and whole milk powder (WMP) were derived from the same original batch of pasteurised FWM to remove the effects of the variation in milk composition between different milk batches. These SMPs were recombined with anhydrous milk fat and water to prepare RCB, and WMPs were reconstituted with water to prepare Recon. Then, (homogenized) FWM, RCB and Recon were subjected to various preheat treatments (75 °C, 11 s, 85 °C, 147 s and 95 °C, 147 s) prior to UHT processing. These preheat treatments were so-called “UHT preheat treatments”. Temperature difference (hot water inlet temperature – milk outlet temperature) was taken as a measure of the extent of fouling in the high-temperature heater. The slope of the linear regression of temperature difference versus time (for two hours of UHT processing) was taken as fouling rate (°C/h). Increasing both evaporator and UHT preheat treatments resulted in increasing fouling rate and total deposit weight for all three whole milk types for several milk batches. In the case of FWM, there was no reduction in fouling rate with increasing UHT preheat treatment whether FWM was homogenized then preheated, preheated then homogenized or not homogenized at all. These findings, which are wholly consistent and well replicated, are in apparent conflict with the results of most previous comparable studies. Possible reasons for this are explained. Further investigations of the effects of homogenization relating to the role of whey protein on the surface of the fat globules showed that whey protein associated with the membrane covering the surface of fat globules for homogenized then preheated FWM, RCB and Recon and that association increased with increasing heating process stage. The increasing association of whey protein with the milk fat globules membrane with increasing severity of heating process stage became faster when preheat treatment was more severe: the association of whey protein plateaued on intermediate temperature heating when the milks were preheated at 75°C, 11 s and on preheating when the milks were preheated at 95°C, 147 s. In the case of FWM, the thickness of the membrane covering the surface of fat globules for homogenized then preheated FWM, which increased with the severity of heating process stage, was greater than the thickness of the membrane in preheated then homogenized FWM. Preheating then homogenization resulted in the greater interfacial spreading of small molecules on the surface of fat globules, i.e. whey protein or small molecules from the disintegration of casein micelles during preheating. Possible basic mechanisms for UHT fouling in the high-temperature heater include: the reduction in the solubility of calcium phosphate and the deposition of protein as fat-bound protein and non-fat-bound protein. When non-fat-bound protein in milk plasma deposited, it could be a carrier for the deposition of mineral, such as, the precipitate of calcium phosphate in the casein micelles or the deposition of complexes between whey protein and casein micelles.