Microencapsulação de Lactobacillus acidophilus utilizando extrato de soja e maltodextrina

Abstract

Microencapsulation is a particle coating technology, whereby smaller capsules are obtained. Among the microencapsulation methods, the spray drying is distinguished by being simple and inexpensive technique, that has been studied with the aim of improving the survival of probiotic microorganisms incorporated into foods. However, the protection offered by spray drying to the probiotic cells depends, among other factors, on the material used in the formation of microcapsules, which should keep the active microorganism until the time of consumption, protecting it from hostile conditions of production and storage of food, and during their passage through the digestive tract. Vegetable proteins, especially soy, pea, maize, wheat and sunflower has gained prominence because they are low-cost and renewable materials, in addition to having different functional properties are considered potentially suitable for use as wall material in the microencapsulation of active compounds . Soy proteins have been prominent in the food industry as the best substitute for animal protein due to its functional properties and its high nutritional value. The soybean extract powder is composed in major proportion of protein and carbohydrates, also containing oligosaccharides that may act as prebiotic stimulation of the growth of microorganisms. Besides the wall material composition, process conditions under which the microencapsulation happens have an important influence on the viability of encapsulated bacteria. Thus, the study aimed to optimize the microencapsulation by spray drying of L. acidophilus La-5, using soybean extract powder and maltodextrin as encapsulating agents, by selecting the optimal conditions of drying air inlet temperature, maltodextrin/soybean extract powder ratio in the composition of the wall material and system feed flow, in order to maximize the microorganism survival to the microencapsulation, as well as characterize the microcapsules and monitor cell viability during storage. The effects of the variables on the survival of the microorganism were studied through the application of experimental design, Central Composite Rotatable Design (CCRD). The microcapsules were submitted to analysis of size and morphology, moisture content, water activity, hygroscopicity and Fourier Transform Infrared Spectroscopy (FTIR). The thermal behavior of the particles was evaluated by Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG). The study of the microcapsules stability included the enumeration of viable cells of L. acidophilus and determining the water activity of the samples for 45 days storage at 4 ° C.The maximum yield of the microencapsulation was 83% and the process conditions that allow higher cell viability corresponded to 87ºC air inlet temperature, maltodextrin/soy extract powder ratio 0.67 (w.w-1) and feed flow rate of 0.54 L.hr-1. The adequacy of the model obtained through the CCRD was validated experimentally. The variables used in the experimental design had a significant effect on the yield microencapsulation and on the physical characteristics of powder obtained. Soy extract ratios superior to maltodextrin in the wall material composition were favorable to the survival of the culture. On the other hand, high air inlet temperatures and feed flow rate decreased the yield of microencapsulation. The drying air temperature and the feed flow rate also reduced water activity and moisture of the microcapsules, while the maltodextrin improved the hygroscopic properties of the particles. The microcapsules had a mean diameter of 4.97 μm and 8.82 μm, rounded shape and irregular surface with presence of concavities and flattening, common characteristics of dried products by spray drying. Through the DSC, TG and FTIR analyzes it was observed a possible interaction between the agents encapsulating and the cells of L. acidophilus. The particles are thermally stable at temperatures below 100ºC and the results suggested that microcapsules can protect microorganisms against heat and dehydration. During the storage period, the reduction in cellular viability of L. acidophilus was lower in microcapsules containing a higher proportion of soybean extract in the composition of the wall material. The water activity was within the recommended values in all treatments until the thirtieth day of storage. At the end of the storage period, the microcapsules produced in optimal conditions indicated by the experimental design showed appropriate water activity and high cell viability, indicating that soybean extract, combined with maltodextrin is an effective wall material in keeping the viability of L. acidophilus and a potential encapsulating agent for the development of probiotics microcapsules with high stability.