| dc.description.abstract | In recent years, freeze concentration (FC) or cryoconcentration has gained great popularity, due to is an emerging and environment friendly concentration technology, since exhibit low energy requirement, high separation and mainly, the process occurs at sub-zero temperatures, allowing to obtain an excellent quality and high solute concentration. FC is based on the principle that an aqueous solution is concentrated by partially or completely freezing water to ice; and then, the concentrated liquid and ice fraction (very pure ice) are separated. In particular, block FC has some advantages compared the other techniques (suspension and film FC), because the separation step is simpler and construction and equipment operation is uncomplicated. The concentrated solute in conventional block FC has been obtained by gravitational methods, also called passive or natural thawing, but the overall efficiency is relatively low. Hence, external forces (also called assisted techniques) could be added to the FC process to improve the concentration process. The hypothesis of this work is that it is possible to improve the final concentration, bioactive compounds and process parameters (efficiency, percentage of concentrate and solute recovered) by adding external forces (centrifugation and vacuum) to the cryoconcentration process from fruit juice. In the present thesis, vacuum and centrifugation were established as assisted techniques in block FC under different freezing conditions, temperatures, time of processing (vacuum) and cycles (centrifugation) to concentrate solutes and to protect bioactive components in the cryoconcentration of fresh blueberry and orange juice. In addition, the different cryoconcentration conditions were studied to improve the separation efficiency, percentage of concentrate and solute yield of the concentration process. Fresh juice samples were radial or unidirectional frozen (freezing conditions) at -20 and -80 °C (temperature condition) for 12 h. To force the separation of concentrated solutes from the ice fraction, the frozen juice was rapidly removed from the freezer and transferred to a suction stage at 80 kPa during 120 min (vacuum process) and to a centrifuge at 20 °C for 15min at 4000 rpm (1600 RCF) by three cycles (centrifugation process). In general, this study has shown that the integration of assisted techniques (vacuum and centrifugation) can improve the block FC performance in the elaboration of concentrated solutions from fresh blueberry and orange juice. The treatment presented the best results (low solute occlusion in the ice, high solute concentration and high process parameters) was -20 °C/unidirectional over the other conditions (-80 °C and radial). In vacuum process, the results indicated (in the first minutes of suction), an increased in concentrated fraction with a value of 63 and 48 °Brix, equivalent to an increase of 3.8 times in the total polyphenol content (76% of retention) and 4.1 times in the ascorbic acid content (73% of retention) for blueberry and orange juice, respectively, compared with the fresh juice. In centrifugation, as the cryoconcentration cycles progressed, the bioactive components increased significantly. After the third cycle, the total polyphenol (blueberry) and ascorbic acid (orange) content in the concentrate showed retention close to 70% of the initial value. Additionally, vacuum- and centrifugation-assisted block cryoconcentration improved the process parameters, achieved values near of 83%, 38% and 0.33 kg of sample obtained per 1 kg of initial sample and 65%, 65% and 0.75 kg of sample obtained per 1 kg of initial sample for efficiency, the percentage of concentrate and solute yield in the first minutes of suction and after the third cycle, respectively. Thus, the high process parameters with assisted techniques in block freeze concentration are a consequence of using an external driving force that improves the separation of concentrated solute from the ice fraction in comparison to passive or gravitational thawing. Finally, we can conclude that the use vacuum or centrifugation in block freeze concentration is an effective external force to obtain a final solute rich in bioactive components and to enhance the process parameters such as efficiency, percentage of concentrate and solute yield. | |
