Nucleation in food colloids

Abstract

Nucleation in food colloids has been studied in detail using Ultrasound Spectroscopy. Our data shows that classical nucleation theory (CNT) remains a sound basis from which to understand nucleation in food colloids and analogous model systems using n-alkanes. Various interpretations and modifications of CNT are discussed with regard to their relevance to food colloids. Much of the evidence presented is based on ultrasound velocity spectrometry measurements which has many advantages for the study of nucleating systems compared to light scattering and NMR due to its sensitivity at low solid contents and its ability to measure true solid contents in the nucleation and early crystal growth stages. Ultrasound attenuation spectroscopy also responds to critical fluctuations in the induction region. We show however, that a periodic pressure fluctuation such as a quasi-continuous (as opposed to a pulse comprising only a few pressure cycles) ultrasound field can alter the nucleation process, even at very low acoustic intensity. Thus care must be taken when using ultrasound techniques that the measurements do not alter the studied processes. Quasi-continuous ultrasound fields may enhance or suppress nucleation and the criteria to determine such effects are derived. The conclusions of this paper are relevant to colloidal systems in foods, pharmaceuticals, agro-chemicals, cosmetics and personal products.

Applications of ultrasonics in food science - novel control of fat crystallization and structuring

“…During the manufacture of a fatty spread an oil-in-water emulsion is first produced in which crystal nucleation is initiated. The transformation from the disordered liquid state to an embryonic then stable solid nucleus was recently discussed in [10] and what appears there will not be repeated here.…”

“…At the molecular scale, ultrasound (both high and low power) may influence nucleation [10], at low power the effects are predictable due to the rectification of heat transfer from a quasi-static pressure field changing the energy barrier to nucleation. The effect of high power, whilst undeniable, is far less predictable and in practice can only be developed empirically, this being the case over all length scales.…”

“…Once crystal growth ensues the heat evolved raises the temperature, reducing undercooling and removing the energy barrier to crystal growth which pumping from the quasistatic acoustic field reduces or increases [10].…”

“…However, it has recently been shown that under some special circumstances, even low power ultrasound may be material altering [10].…”

Crystallization of Femtoliter Surface Droplet Arrays Revealed by Synchrotron Small-Angle X-ray Scattering

“…Droplet arrays offer the unique possibility to study droplets within a closed system and are frequently utilized within microfluidics to study a broad range of physical and biological processes. − One such process is the crystallization of and within droplets, which is a burgeoning area with applications in food science, pharmaceuticals, and high-throughput screening of protein crystallization. , Within food science, the crystallization of emulsion droplets has been studied owing to its influence on physical properties which impact the flavor, stability, texture, and appearance of foods. Given that many bioactive components are lipophilic, food-grade lipids have also attracted interest for their potential as nanoparticles for the delivery of active ingredients. , Triacylglycerol (TAG) nanoparticles, in particular, are being explored owing to their ability to protect bioactives from degradation and prevent bioactive crystallization, which can significantly lower their bioavailability. , The performance of the lipid carriers is also critically dependent on the crystallization properties of the lipid and its active component. − …”