Funcionalidad de hidrocoloides en la digestibilidad de emulsiones aceite/agua

This doctoral thesis focuses on the study of the physical properties and fat digestibility of hydrocolloid based emulsions to assess their application as fat substitutes in the reformulation of a healthier foodstuffs. Obtaining healthier foods can be achieved through different ways: by decreasing the amount of fat present or decreasing its digestibility, although a lipid profile improvement is also considered as a key factor. Taking this into consideration, emulsions formulated with different types of fat stabilized by different types of polymer matrices were designed, in order to evaluate the structural properties, digestibility and the functionality in their application in a final product, in particular filling creams. Semisolid vegetable oil in water emulsions stabilized with different types of hydrocolloids (cellulose ethers and xanthan gum) were designed. The rheological characterization of the emulsions showed different behaviour depending on the type of hydrocolloid used. This structural behavior was related to the resistance to digestion, that is, to the digestibility of the fat present. The fat released from the matrix after digestion is an indicator of structural resistance. More resistance will indicate a greater barrier exerted against a physical contact between the emulsified lipid and the digestive enzymes and, therefore, the generation of free fatty acids will be lower. Comparing with a control emulsion without hydrocolloid, all hydrocolloids were effective in reducing lipid digestibility, although differences were found according to their composition. In the case of xanthan gum, the reduction in lipid digestibility was enhanced with the presence of Tween 80 emulsifier. To evaluate the effect of the fat phase in the emulsion and in order to increase the plasticity, emulsions were prepared using fats with a higher content of saturated fatty acids, which are solid at room temperature, in particular anhydrous milk fat. Although these emulsions do not improve the lipid profile, they are an advantage because they have a fat content (47%), which is significantly lower than butter or conventional shortenings (80 %). It was demonstrated that it is possible to formulate cellulose ether emulsions with solid fat with spreadable characteristics and reduced fat content. The texture quality depended on the fat used, but also on the type of cellulose ether, that affected the morphology of the fat crystals and, consequently, the structural and thermal properties. The original compact structure of the fat was improved by the presence of hydrocolloids, and it was demonstrated that these emulsions allowed to obtain a stable product and plastic reduced in fat, softer than butter and spreadable at refrigeration temperature and room temperature. These emulsions could be used as a directly spreadable product or in food applications that require plastic properties. To evaluate the functionality of the low digestibility emulsions in a food matrix, these were applied as fat substitute in a filling cream. The creams were formulated with milk powder, water, sugar, starch and emulsions formulated with different types of fat (sunflower oil and palm oil) and different hydrocolloids (methylcellulose, hydroxypropylmethylcellulose and xanthan gum). The effect of the different emulsions on the structural properties and the digestibility of the final product was studied. The oral digestion produced a reduction of the consistency in all the samples, associated to the hydrolysis of the starch carried out by the α-amylase present in the saliva. This decrease was much more pronounced in the control cream without hydrocolloid, since in the creams with emulsion the networks of the hydrocolloids were not affected by the enzymatic effect and these continued to provide stability to the system. After the gastric phase, creams formulated with cellulose ether emulsions showed a decrease in consistency, mainly due to the dilution level of the system and not to gastric conditions (acid pH or presence of enzymes). However, in the cream with xanthan gum, the gastric conditions generated an increase in the consistency, as occurs with the isolated emulsion. The stage of intestinal digestion affected the structure of all the systems, although more notably in the control cream, in which the fat was digested almost completely by the action of the pancreatic lipase. As in emulsions, in creams the presence of the hydrocolloid acts as a physical barrier that confers structural stability and hinders the effective action of enzymes. To evaluate the industrial application, a thermoreological study of the different creams was carried out. The results showed important differences in viscosity and viscoelastic properties at room temperature. The cream with emulsion elaborated with a methylcellulose of high grade of methoxylation (MX) was different from the rest of the cellulose creams, with a behavior similar to the control cream based on starch. These differences detected in the initial consistency were significantly reduced at spreading speeds (higher shear rates). The evolution of the storage modulus (G') with the temperature showed different gelation temperatures depending on the chemical substitution of the cellulose ethers. At 45 °C the creams with methylcellulose A4M and MX are gelled, while the creams with hydroxypropyl methylcellulose gelled at a higher temperature. At 70 °C all the creams with emulsion are gelled and showed analogous characteristics both in flow and viscoelastic behavior. Therefore, the chemical substitution of cellulose ethers and temperature are key factors to consider in order to carry out the application of the creams studied as an alternative to conventional fats, taking into account the desired characteristics and the application process. Finally, the acceptability and sensorial attributes that described the cocoa creams with the emulsions formulated with all the hydrocolloids studied (methylcelluloses (MX and A4M), hydroxypropylmethylcelluloses (F4M and K4M) and xanthan gum were evaluated. The consumer's perception was evaluated through an acceptance test in which the tasters rated the samples according to general acceptability, appearance, color, taste and texture. The control cream was the sample that presented the best scores, although the emulsion cream of xanthan gum obtained similar scores in appearance, color and texture. To determine the sensory attributes that were best related to acceptability, a CATA questionnaire was carried out ("Check-All-That Apply"). Consumers marked the attributes that they considered appropriate to describe each sample and the frequency of mention of each of them were determined. The control cream was the one that most liked the consumers, although the cream formulated with the emulsion of xanthan gum showed an acceptability close to it. Both presented the best organoleptic qualities, such as sweet taste and creamy and smooth appearance. Although the MX cream presented attributes such as sweet taste, it was also considered too bright and with lumpy texture. On the other hand, creams made with A4M and K4M were characterized by their lumpy texture and gummy appearance, and their taste was evaluated negatively by the tasting panel.