Pressure-shift nucleation: A potential tool for freeze concentration of fluid foods

Abstract

Pressure-shift nucleation (PSN) has been evaluated as a potential substitute of the crystallization step at the scraped surface heat exchanger in conventional freeze concentration. To do that, PSN experiments were carried out at different pressure and temperature conditions in orange juices of several concentrations. After crystallization, the final concentration reached and the size and shape of the ice crystals formed were measured. The results obtained showed that the higher the pressure and the lower the temperature employed in the PSN experiments, the higher is the final concentration in the juice and the smaller the ice crystals formed. Four important advantages of pressure-shift nucleation over conventional crystallization were found: temperature in the pressure vessel can be relatively high if pressure is increased enough, the desired concentration can be achieved in the whole sample quasi-instantaneously just after expansion, ice crystals produced are round in shape without pockets and indentations and they are homogeneously distributed throughout the sample. Industrial relevance: Freeze concentration is the most advantageous technique to obtain high quality food concentrates without appreciable loss in taste, aroma, color, or nutritive value. However, it is hardly employed in the food industry mainly due to economic aspects of the technology. In the last decades, many efforts have been made to improve the crystallization phase, the most expensive step in freeze concentration, without definitive success. The results obtained in this paper show that pressure-shift nucleation presents a number of advantages over the traditional crystallization step at the scraped surface heat exchanger which can be exploited to improve the industrial freeze concentration process.

Multi-plate freeze concentration: Recovery of solutes occluded in the ice and determination of thawing time

“…The concentration reached with this system is between 45 and 55 °Brix (Lee and Leem, 1998; Van Weelden, 1994). To reduce SSHE costs, Habid and Farid (2006) suggest the use of a liquid-solid fluidized bed instead of an SSHE and Otero et al. (2012) suggested increasing the pressure in nucleation stage.…”

Progressive Freeze Concentration for Volume Reduction of Produced Water and Biodiesel Wastewater

“…Thus, the solutes were diffused and they escaped the freezing front. At -10°C coolant temperature, the structure of produced ice was fragile and dendritic where the solute would easily be trapped, thus resulting in a higher value of K. Besides, the nucleation of ice did not easily occur at high temperature [29], causing the ice crystal to grow in an unorganized pattern [30]. The coolant temperature of -10°C cannot provide adequate cooling for the ice crystal to be formed in a perfect shape due to the low degree of supercooling.…”

Review on Progressive Freeze Concentration Designs

“…SFC system consists of crystallization, growth and separation of ice crystals (Otero et al, 2012;Sánchez et al, 2009) where it comprises of a scraped-surface heat exchanger (SSHE) and a recrystallizer (Lemmer et al, 2001;van Nistelrooij, 2005).…”