Analytical techniques for nucleation studies in lipids: advantages and disadvantages

CERDEIRA, CANDAL, HERRERA

JOURNAL OF FOOD SCIENCE

Institute of Food Technologists

Lugar: Chicago, USA; Año: 2004 vol. 69 p. 185 - 191

0022-1147

Crystallization is generally considered a two step process. The first step, nucleation, involves the formation of molecular aggregates with a critical size great enough to become stable. During the second step, nuclei grow and develop into crystals. Distinguishing between nucleation and growth constitutes a major challenge in lipid crystallization studies. Thus, it is of great importance to discuss the information obtained from the different techniques that are usually used to study nucleation behavior such as nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), rheological techniques, light-scattering techniques such as turbidimetry and scanning diffusive light scattering (SDLS), polarized light microscopy (PLM), and laser polarized optical sets such as laser polarized-light turbidimetry (LPLT). Techniques to describe the nucleation process must be very sensitive to disregard growth. When crystallization is followed by methods such as DSC, NMR and rheological measurements, at times, small amounts of crystals are present in the melt before any solids are detected. Clearly, at this stage, well beyond the induction time for nucleation, these methods are measuring crystal growth. Techniques of low sensitivity for solid fat contents lower than 0.1% must not be used to evaluate nucleation effects. Sensitive turbidimeters with detectors that saturate below 0.3% solid fat content give good results as do scanning diffusive light-scattering equipment. Although the PLM technique is sensitive enough for these kinds of studies, an understanding of important basic concepts is essential. Laser optical sets are the most appropriated methods to study nucleation in fats systems.