RESUMEN
In this study we investigated the combined effect of shearing and cooling rate in the rheology of organogels developed in high oleic safflower oil by (R)-12-hydroxystearic acid (HSA), its primary amide derivative [(R)-12-hydroxyoctadecanamide, HOA], and the N-octadecyl derivative of HOA [(R)-N-octadecyl-12-hydroxyoctadecanamide, OHOA]. The experimental set up to develop the organogels involved: 1). The use of quiescent (0s-1) or shearing (300, 600, and 1200s-1) conditions during cooling the gelator solutions (2%) just until achieving the gelator's melting temperature (TM) in the vegetable oil, to then continuing the cooling under static conditions until achieving 15°C) The use of cooling rate protocols involving a constant cooling rate of 1°C/min (CR1) or 10°C/min (CR10) in the shearing and static stages, or variable cooling rates in each stage (i.e., VR1-10 or VR10-1). The elasticity of the organogels (G') was measured while cooling under static conditions, once the systems achieved 15°C, and after 60min at this temperature. The rheological results obtained at 15°C showed a cooling rate and molecular weight-dependent effect of shearing on G'. We propose that the molecular relaxation time of gelator molecules, and its increase as molecular weight increases and as temperature decreases, plays an important role on the gelator's susceptibility to go through a shear induced crystallization process. Therefore, high molecular weight molecules like OHOA (551.97Da) would remain stretched by shearing longer times than HSA (300.49Da) and HOA (299.49Da). Thus, when shearing was applied while cooling at the higher cooling rate (i.e., CR10 and VR10-1), the stretched OHOA molecules would lead to the development of mesophase precursors that upon further cooling under quiescent conditions, crystallize developing a well-structured organogel. In contrast, stretched low molecular weight molecules (i.e., HSA and HOA) with shorter relaxation time would dissolve back to the isotropic state during cooling. Additionally, the rheological results of HSA and HOA organogels suggested that the shear induced crystallization process might be dependent on the gelator polarity also. These results show that the application of shear and the extent of its application as temperature decreases until achieving TM, have important implication on the self-assembly of gelator molecules, and therefore in the organization and rheology of the three-dimensional crystal network of the organogel.
Asunto(s)
Frío , Geles/química , Reología , Cristalización , Elasticidad , Tecnología de Alimentos , Peso Molecular , Transición de Fase , Aceite de Cártamo/química , Estearatos/química , TermodinámicaRESUMEN
The medium optimization for the production of the Geobacillus thermoleovorans CCR11 thermoalkalophilic lipase was carried out in shake flask cultures using safflower high oleic oil. In the first step of optimization, a two level fractional factorial design allowed the identification of the concentration of nutrient broth and temperature as the main variables significantly affecting lipase production (P<0.05). In a second step, a D-optimal design was applied to determine the variables optimal values, defined as those yielding maximal lipase production in shaken flasks, thus demonstrating that the optimal concentration of nutrient broth was 3.8 g/l and the optimal culture temperature was 39.5°C. The model was experimentally validated, yielding a lipase production of 2283.70 ± 118.36 U/mL which represents a 6.7-fold increase in comparison to the non-optimized medium.
Asunto(s)
Proteínas Bacterianas/biosíntesis , Geobacillus/enzimología , Geobacillus/crecimiento & desarrollo , Lipasa/biosíntesis , Modelos Biológicos , Aceite de Cártamo/química , Aceite de Cártamo/farmacologíaRESUMEN
It has been previously reported that Polifat KA-02 (fatty acids derived from safflower oil) prevents the pigment cholelithiasis produced by vitamin A in the golden hamster. In order to establish whether the saturation or the unsaturation of Polifat is directly related with its preventive action, in the present study the effect of the hydrogenation of the derivative on this preventive action was tested. Two experiments were carried out in which the animals received the different experimental diets ad libitum during 70 days. In the 1st. experiment the effect of the additions to the lithogenic diet (Rodents Chow + 25,000 UI% of retinol acetate) of 18% of crude safflower oil, or 15% Polifat, or 15% hydrogenated Polifat (approx. 80% saturation) were assayed. In the 2nd. experiment the effect of a more hydrogenated Polifat KA-02 (greater than 99%) was tested. The results of the 1st. experiment showed that the lithogenic diet produced a high incidence (90.5%) of animals with gallstones, which was very similar (100%) to that produced by the crude safflower oil, whereas the additions of normal and hydrogenated Polifat completely prevented the formation of gallstones. The 2 forms of Polifat produced a considerable hepatomegaly. The absorption of vitamin A, measured as total hepatic vitamin A, was higher in the 3 groups that received extra lipids in their diets. The results of the 2nd. experiment fully confirmed the findings related to the hydrogenated Polifat. It is concluded that hydrogenated Polifat KA-02 prevents, as normal Polifat does it, the pigment cholelithiasis in the golden hamster produced by vitamin A.