Genetic diversity of wine Saccharomyces cerevisiae strains involved in spontaneous fermentations was studied by analysis of mitochondrial DNA restriction patterns. Yeasts were isolated at different stages of fermentations with must from three different white grapevine varieties, Albariño, Godello and Treixadura, which are autochthonous from Galicia. Nineteen different patterns out of a total of 446 strains analysed were identified, but only a few of them appeared at high frequency and therefore were able to lead the fermentation process. Some strains were common to all fermentations; however, most of them were a minority being only found at low frequency for one or two specific grape varieties. The dominant strain was different for each variety except in one case, suggesting that some strains are better adapted to certain must conditions.

Polymorphism and growth behavior of blends of a high-melting fraction of milk fat (HMF) and sunflower oil (SFO) formulated with and without the addition of sucrose esters (SE) P-170, P-1670, and S-170 were studied by pulsed 1 H NMR spectroscopy, X-ray diffraction, and polarized light microscopy. The effect of SE on the solid content maximum (S max ) or crystallization rate was observed only at low supercooling (values of ∆T below 15°C). The Avrami k n decreased as n values increased, indicating that SE inhibited growth and impeded nucleation. Addition of SFO modified the polymorphic behavior of milk fat, most likely owing to the increase in the C 54 fraction (mostly 18:1 cis) in crystals composition. P-170 and S-170 modified the polymorphic behavior of HMF when it crystallized in the α-form or in blends with up to 40% SFO at all crystallization temperatures (T c ) selected. Addition of P-170 and S-170 favored crystallization in the β'-form, and the appearance of the β-form was delayed. P-1670 had no effect on polymorphism. When HMF and the blends were crystallized under dynamic conditions, addition of P-170 and S-170 markedly decreased crystal sizes. P-1670, however, showed no effect on microstructure.Paper no. J11247 in JAOCS 83, 489-496 (June 2006). KEY WORDS:Avrami model, high-melting fraction of milk fat, isothermal growth, polymorphism, sucrose esters, sunflower oil, trans fat blends.Consumer concerns associated with the atherogenic effect of trans-FA limit the future of the hydrogenation process as a way to modify the solid-to-liquid ratio in vegetable oils/fats. As an alternative to hydrogenated vegetable oils, modification of high-m.p. stearins by blending with vegetable oils is becoming important, since shortenings with appropriate physical chemical properties and good nutritional characteristics that are free of trans-FA and rich in PUFA can be obtained (1-3). The crystallization kinetics and polymorphic behavior of fats (particularly the rate of crystallization and the rate of change from one polymorphic form to another) are very important since they affect the properties of the fat during processing (4). Emulsifiers are useful functional additives without which many food products could not be made. Emulsifiers typically act in multiphase systems in two ways. The first is as an emulsifying agent to enable two distinct phases to be combined in a stable quasi-homogeneous state for an indefinite length of time.The second function of an emulsifier is often to modify the behavior of the continuous phase of a food product so as to bring about a specific effect or benefit. Sucrose esters (SE) possess both lipophilic and hydrophilic properties. The nature of this property is often expressed as the hydrophilic/lipophilic balance (HLB) on a scale of 0 to 20, with low numbers indicative of the oil-like tendency (5). A few reports have described the effect of SE on induction time of crystallization and development of polymorphic forms of fats in bulk systems (2,6-8).Most of the work was done on hydrogenated oils. ...

Nucleation behavior of blended high-melting fractions of milk fat as affected by emulsifiersThe effect of highly hydrophobic emulsifiers, the palmitic sucrose ester P-170 (hydrophilic/lipophilic balance (HLB) = 1.0), the stearic sucrose ester S-170 (HLB = 1.0), the polyglycerol ester decaglycerol decastearate DAS 7S (HLB = 3.7) and the polyglycerol ester decaglycerol dodecabehenate DDB 750 (HLB = 2.6), on the nucleation of a high melting point milk fat fraction (HMF) and its blends with sunflower oil (SFO) was investigated by polarized laser light turbidimetry, X-ray diffractometry and polarized light microscopy (PLM). Addition of polyglycerol esters accelerated nucleation, giving shorter induction times for the same supercooling. On the contrary, sucrose esters inhibited nucleation since induction times were elongated in all conditions selected. Addition of emulsifiers modified the polymorphic behavior in the blends with SFO. The b' form was promoted especially with the addition of S-170. DAS 7S and DDB 750 promoted crystallization. PLM images showed many small crystals that did not appear in HMF images. Addition of P-170 and S-170 delayed nucleation and inhibited crystal growth. Crystals were notoriously smaller than the ones that appeared in HMF images. The Fisher-Turnbull model was used to calculate activation free energies of nucleation. In all cases, sucrose esters elevated the energy barrier for nucleation. Polyglycerol esters, however, if they had an effect on the energy barrier, lowered the values.

The effects of addition of the sucrose esters (SE) P-1670, P-170, and S-170 to a high-melting fraction of milk fat (HMF) and its blends with sunflower oil (SFO) on nucleation and growth were studied by laser polarized light turbidimetry and polarized light microscopy (PLM). The three SE delayed nucleation of HMF at the temperatures selected. P-1670 did not modify average crystal size after 3 h at crystallization temperature (T(c)) or crystal size distribution and modified crystallization kinetics only slightly. P-170 and S-170, however, markedly diminished crystal size and narrowed crystal size distribution. Activation free energies of nucleation at equivalent supercooling, calculated using the Fisher-Turnbull equation, significantly increased with addition of SE. According to these results, among the mechanisms described in the literature for fats or emulsions, the cocrystallization hypothesis is the one that better described the effects of sucrose esters on crystallization behavior in these systems.