Can microencapsuation be used to deliver bacteriostatic compounds?
Organic acids are used to reduce the pH in the small intestine of simple stomach animals such as pigs and poultry diets in order to provide a greater resistance to pathogenic bacterial infections. Post weaning diarrhea is one of the most frequent causes of heavy economic losses in pig herds. Before 2006, health strategies widely used antibiotic growth promoters to reduce enteric infections and the occurrence of pathogens able to adhere to intestinal mucosa. These are added to feed for piglets from birth to weaning with the aim of improving the composition. The increased use of antibiotics has given rise to a fear of the development of resistant pathogenic bacterial strains and residual contamination of the food chain with antibiotics. This has led to the adoption of safety measures and a gradual withdrawal of antibiotic promoters from pig diets. Because the use of antibiotics as growth promoters has been banned in certain countries and that the expansion of this policy to other countries can now be expected, intensive research has focused on the development of alternative strategies with the aim of maintenance of animal health and performance.
Various natural materials, many of which are commercially available, have been investigated as efficient alternatives to antibiotic growth promoters. Organic Acids and essential oils are viable alternatives. In 2007 Piva and coworkers working with piglets in which a diet containing microencapsulated organic acid was fed at a 10 fold lower dose rate compared to the normal dose of unprotected organic acid demonstrated a similar response in the rate of piglet diarrhea. This means that a lower dose of protected microencapsulated organic acid was effective and economical in reducing the number of piglet diarrhea.
Besides antimicrobial function, organic acids and their salts have a beneficial effect on digestibility, nutrient resorption and performance of weaned and growing piglets. Antimicrobial effects can be explained by two mechanisms. First, by a pH fall below 6 in the stomach, which inhibits the growth of pathogenic microorganisms such as coliforms and, secondly, the ability of organic acids to penetrate in their non-dissociated form through the bacterial wall and destroy some specific microorganisms. Bactericidal or bacteriostatic effects of organic acids consist above all in a direct effect of the organic acid anions on bacterial cell walls. For organic acids to function as effective bacteriostat they must be delivered and dissociate in the large intestine where most harmful bacteria such as E.coli reside. They cannot release in the small intestine alone.
Animal studies where microencapsulated organic acid preparations have been used show an increase in villi height, a decrease in the number of piglet diarrhea and better feed conversion which means higher average weight gain. In totality, microencapsulation is being used to deliver compounds with bacteriostatic properties. These compounds such as organic acids, Zin Oxide and others are available commercially.