Methods and compositions for producing hydrogel capsules coated for low permeability and physical integrity

Abstract

Methods and compositions for producing hydrogel capsules enveloped with at least one coating layer is disclosed. The coating formulations deposited on the surface of the capsules can improve the physical integrity and the water-retention properties of the alginate beads. The coating formulations can be sequentially applied in various combinations to obtain desirable properties, such as improved physical integrity, mechanical strength, and low permeability, that can extend the shelf-life of the capsules when incorporated into various consumer products.

What is claimed is: 
     
         1 . A method of preparing capsules with improved water retention, comprising:
 preparing hydrogel capsules having a diameter of 1 to 5 mm and comprising one or more optional additives and a polymer selected from the group consisting of alginates, pectins, carrageenan;   applying a coating to the capsules to form capsules with improved water retention that exhibit water retention of at least 40% after three days at 23 degrees C. and 50% relative humidity.   
     
     
         2 . The method of  claim 1 , further comprising treating the capsules by contacting the capsules with a solution having a pH below 5. 
     
     
         3 . The method of  claim 1 , wherein the coating comprises a polymeric coating, the method further comprising treating the capsules by heating the capsules to a temperature above a glass transition temperature of the polymeric coating. 
     
     
         4 . The method of  claim 3 , wherein the heat treatment comprises heating the capsules in air for at least 5 minutes at a temperature of at least 60 degrees C. or at least 120 degrees C. 
     
     
         5 . The method of  claim 1 , further comprising applying a second coating to the capsules. 
     
     
         6 . The method of  claim 5 , wherein the second coating is a wax coating. 
     
     
         7 . The method of  claim 6 , wherein the wax is selected from the group consisting of polyester wax, carnauba wax, and paraffin wax. 
     
     
         8 . The method of  claim 6 , wherein the coating is a polymeric coating, the step of applying the second coating comprising freezing the capsules having the polymeric coating and contacting the frozen capsules with molten wax. 
     
     
         9 . The method of  claim 5 , wherein the second coating comprises (acrylamidomethyl)cellulose acetate propionate. 
     
     
         10 . The method of  claim 1 , wherein the coating is formed from a methacrylic acid and ethyl acrylate copolymer dispersion. 
     
     
         11 . The method of  claim 1 , wherein the coating is of (acrylamidomethyl)cellulose acetate propionate. 
     
     
         12 . The method of  claim 1 , wherein the capsule comprises an additive selected from the group consisting of flavorants, tobacco, antioxidants, medicaments, nutraceuticals, cell culture medium, cosmetics, agrochemicals, disinfectants, detergents, and dyestuff. 
     
     
         13 . The method of  claim 1 , wherein the capsules exhibit water retention of at least 90% after three days at 23 degrees C. and 50% relative humidity. 
     
     
         14 . The method of  claim 1 , wherein the polymer is alginate. 
     
     
         15 . The method of  claim 1 , wherein the coating is wax. 
     
     
         16 . The method of  claim 1 , further comprising inserting the capsules in cigarette filters. 
     
     
         17 . The method of  claim 1 , wherein the coating is a film forming latex. 
     
     
         18 . The method of  claim 1 , wherein the capsules include a core containing tobacco extract. 
     
     
         19 . The method of  claim 1 , wherein the capsules include an alginate hydrogel matrix and a coating of methacrylic acid-co-ethyl acrylate latex. 
     
     
         20 . The method of  claim 1 , wherein the capsules include a core containing at least one flavorant.