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1. INTRODUCTION

Both flavors and active ingredients such as vitamins impart important characteristics to products desirable to consumers in the marketplace. However, flavors and active ingredients can be lost or degraded during food processing, with the result of losing consumer benefit. However, critical components can be encapsulated using polymeric materials to prevent such losses. Polymers are typically applied in thin coatings which allows for a cost effective encapsulation with functional properties. Understanding the properties of thin barrier coatings is essential to obtain optimal encapsulation performance. The food and flavor industry have used polymeric materials for decades as bulking agents, viscosifiers, and barrier materials for various encapsulation systems. Materials such as sugar, maltodextrin, pectin and alginate can be used to create water soluble encapsulation systems. Pectin and alginate materials are of great interest to the flavor industry due to the cross-linkable nature of these natural polymer materials. Cross-linked pectin and alginate form hydrogel barriers which are water insoluble but water swellable. The swelling properties of hydrogel barriers can be manipulated by varying levels of chemical
cross-linking along these carbohydrate chains. Highly cross-linked polymer materials typically demonstrate minimized diffusion properties which creates an effective barrier reducing flavor loss during cooking processes. Lightly cross-linked polymers become less effective barriers due to increased diffusion properties. Flavor encapsulation systems containing hydrogels have been utilized in food to create products with increased flavor perception. However, flavors encapsulated in hydrogel systems typically need to be reformulated to preserve such a desirable perception. The swelling property of hydrogel barriers allows flavor components having a large affinity for water to be extracted from the encapsulation system while more hydrophobic flavor components remain encapsulated. The swelling property of hydrogel barriers is a large problem for the flavor industry because flavors are complicated mixtures of both hydrophilic and hydrophobic components. For example, typical fruit flavors contain numerous individual ingredients which impart a delicate balance and flavor profile. Individual cherry flavor ingredients have vegetable oil: water partition coefficients ranging from 4 to 1. A partition coefficient, denoted as P in this document, is the concentration ratio of a compound in two immiscible solvents at equilibrium. The P coefficient in this study is a measure of differential compound solubility between vegetable oil and water. The higher the P value the more hydrophobic the compound. Since most food applications are exposed to water over time, maintaining a balanced flavor profile is difficult. Creating an encapsulation system with reduced flavor diffusion properties would be beneficial for the flavor industry. The flavor industry creates encapsulation systems to address various food processing issues. Analyzing an encapsulation system typically entails “in-use” tests which only demonstrate whether or not the encapsulation system provides a benefit. A typical “in-use” test consists of making an encapsulation containing a flavor. The encapsulated flavor is then added to a food application and processed under normal cooking conditions. These tests only provide a result which is negative or positive. Since the encapsulation system is a complex product no data is provided on what aspect of the technology is providing the result. Also, the food application is very complex and also affects how the encapsulation performs. These facts leave the researcher asking “Have we created a better encapsulation or merely used the encapsulation in a more desirable environment?”.
Analytical experiments, such as encapsulation-dissolution testing, have been created to characterize the individual encapsulation systems in model food application environments. Valuable data has thus been obtained which can predict encapsulation performance in various applications. However, encapsulation performance is highly dependent on capsule particle size, polymer barrier thickness, polymer permeability, capsule structure and encapsulation makeup. Capsule performance is measured, with account for all the variables that affect encapsulation performance. Previously at the Givaudan Flavor Corporation attempts were made to study the diffusion and permeability properties of hydrogel films containing clay. Films approximately 25 to 200 microns were cast and cross-linked with the appropriate reagents. The method produced wrinkled films and inconsistent film thicknesses that only allowed for small pieces of the films to be analyzed. The irregular films produced irreproducible diffusion and permeability measurements. The analytical methodology used to characterize the films was tedious and involved the use of multiple analytical techniques. Each analytical technique contributed compounded errors which affected the accuracy of the data. The primary goal of the present study is to create thin hydrogel films whose diffusion and permeability properties can be measured easily with relative accuracy. Understanding flavor diffusion across thin hydrogel membranes will provide the basic knowledge for hydrogel encapsulation development. The films created were approximately 20μm thick, which replicates typical coating thicknesses used in the flavor industry. Creating thin films can be challenging due to the following circumstances: thin films become very brittle, brittle and cracked films lead to ineffective barriers, and thin films are hard to cast uniformly. The thin films created were uniform and reproducible which ensured a robust method and reliable data. For the present work, two calcium cross-linkable polymers were chosen for study. Alginate and pectin were chosen for their acceptance in the food and flavor industry.
The thin film hydrogels were characterized by micrometer film thickness measurements, Environmental Scanning Electron Microscope (ESEM), swelling
ratio.

2.1 Procedures – Laboratory Testing Equipment Preparation

2.1.1 Film Sheet Preparation

Three Baker’s Secret medium cookie sheets were purchased from a local grocery store. The measurements of the cookie sheets were 43.2cm X 27.9cm X 1.9cm with an estimated surface area of 1205.3 cm2. The cookie sheets were lightly scuffed under water with an abrasive sponge to partially remove the Teflon™ coating from the sheets. Partially removing the Teflon™ coating allowed the polymer solutions to wet the surface creating a uniform polymer film.

2.1.2 Leveling Film Sheet Apparatus
A leveling apparatus was created to ensure a level surface for use with the film sheets. The leveling apparatus was created using medium-density fiberboard and spring-loaded clamps. The base measurements of the leveling apparatus were 96.5 cm X 63.5 cm X 2.0 cm. The clamping system consisted of two pieces of 86.4 cm fiberboard strips attached to the base of the leveling apparatus 43.5 cm apart. Three spring-loaded clamps were applied to each strip at the desired distance to ensure three film trays could be clamped to the apparatus. The leveling apparatus was then stored in a fume hood and adjusted with shims to ensure a level surface.

2.2 Procedures – Sample Preparation
2.2.1 Creating 1.0% Sodium Alginate Solutions
Approximately 990.0g of distilled water (pH 6.5) was added to a 2000mL Waring blender and mixed using a Cole-Parmer solid state power controller set to 30% power. 10.0g of sodium alginate was weighed into a weigh boat and gently dispersed into the distilled water. The sodium alginate solution was mixed for 15 minutes to ensure that the polymer was completely dissolved. During the mixin process the sodium alginate gelled, increasing the solution viscosity and entrapping air in the solution. . The sodium alginate solution was allowed to remain in the blender with no mixing for 30 minutes to ensure air bubbles would not be present in the solution.

2.2.2 Creating Calcium Alginate Films
Approximately 250.0g of the 1.0% sodium alginate solution was poured into a lightly scuffed cookie sheet and allowed to stand in a fume hood for 24 hours on a leveling apparatus. The 1% sodium alginate solution delivered 2.5g of sodium alginate across 1205 cm2 of surface area on the cookie sheet. As the water evaporated from the sodium alginate solution a thin film of sodium alginate was deposited on the surface of the cookie sheet. A 2.0% calcium chloride solution was prepared by adding 5.0g of calcium chloride to 245.0g of distilled water (pH 6.5) in a 400mL beaker containing a stir bar. The 2% calcium chloride solution was stirred for 30 minutes using a stir plate. Approximately 250.0g of the 2.0% calcium chloride solution was poured into the cookie sheet containing the sodium alginate film and allowed to stand for 30 minutes. The 2% calcium chloride solution delivered 5g of calcium chloride to 2.5g of sodium alginate.
The calcium displaced the sodium in the alginate film forming a cross-linked water insoluble calcium alginate film. The calcium chloride solution was then decanted from the cookie sheet. The cookie sheet containing the cross-linked alginate film was rinsed three times with 250.0g of distilled water (pH 6.5). The cookie sheet was placed in a fume hood and allowed to stand for 24 hours. The film was slowly peeled off the cookie sheet. Thin uniform calcium alginate films were created containing no wrinkles or high spots. The film was cut into 5cm X 5cm squares and stored in a sealed container. The dried calcium alginate film demonstrated a moisture content of 1.8 to 2.3%.

2.2.2 Creating Calcium Alginate Films
Approximately 250.0g of the 1.0% sodium alginate solution was poured into a lightly scuffed cookie sheet and allowed to stand in a fume hood for 24 hours on a leveling apparatus. The 1% sodium alginate solution delivered 2.5g of sodium alginate across 1205 cm2 of surface area on the cookie sheet. As the water evaporated from the sodium alginate solution a thin film of sodium alginate was deposited on the surface of the cookie sheet. A 2.0% calcium chloride solution was prepared by adding 5.0g of calcium chloride to 245.0g of distilled water (pH 6.5) in a 400mL beaker containing a stir bar. The 2% calcium chloride solution was stirred for 30 minutes using a stir plate. Approximately 250.0g of the 2.0% calcium chloride solution was poured into the cookie sheet containing the sodium alginate film and allowed to stand for 30 minutes. The 2% calcium chloride solution delivered 5g of calcium chloride to 2.5g of sodium alginate.
The calcium displaced the sodium in the alginate film forming a cross-linked water insoluble calcium alginate film. The calcium chloride solution was then decanted from the cookie sheet. The cookie sheet containing the cross-linked alginate film was rinsed three times with 250.0g of distilled water (pH 6.5). The cookie sheet was placed in a fume hood and allowed to stand for 24 hours. The film was slowly peeled off the cookie sheet. Thin uniform calcium alginate films were created containing no wrinkles or high spots. The film was cut into 5cm X 5cm squares and stored in a sealed container. The dried calcium alginate film demonstrated a moisture content of 1.8 to 2.3%.


2.2.2 Creating Calcium Alginate Films
Approximately 250.0g of the 1.0% sodium alginate solution was poured into a lightly scuffed cookie sheet and allowed to stand in a fume hood for 24 hours on a leveling apparatus. The 1% sodium alginate solution delivered 2.5g of sodium alginate across 1205 cm2 of surface area on the cookie sheet. As the water evaporated from the sodium alginate solution a thin film of sodium alginate was deposited on the surface of the cookie sheet. A 2.0% calcium chloride solution was prepared by adding 5.0g of calcium chloride to 245.0g of distilled water (pH 6.5) in a 400mL beaker containing a stir bar. The 2% calcium chloride solution was stirred for 30 minutes using a stir plate. Approximately 250.0g of the 2.0% calcium chloride solution was poured into the cookie sheet containing the sodium alginate film and allowed to stand for 30 minutes. The 2% calcium chloride solution delivered 5g of calcium chloride to 2.5g of sodium alginate. The calcium displaced the sodium in the alginate film forming a cross-linked water insoluble calcium alginate film. The calcium chloride solution was then decanted from the cookie sheet. The cookie sheet containing the cross-linked alginate film was rinsed three times with 250.0g of distilled water (pH 6.5). The cookie sheet was placed in a fume hood and allowed to stand for 24 hours. The film was slowly peeled off the cookie sheet. Thin uniform calcium alginate films were created containing no wrinkles or high spots. The film was cut into 5cm X 5cm squares and stored in a sealed container. The dried calcium alginate film demonstrated a moisture content of 1.8 to 2.3%.

2.2.3 Creating 1.0% pectin solutions
Approximately 990.0g of distilled water (pH 6.5) was added to a 2000mL Waring blender and mixed using a Cole-Parmer solid state power controller set to 30% power. 10.0g of pectin was weighed into a weigh boat and gently dispersed into the distilled water. The pectin solution was mixed for 15 minutes to ensure that the polymer was completely dissolved. During the mixing process the pectin gelled, increasing the solution viscosity and entrapping air. The pectin solution was allowed to stand in the blender with no mixing for 30 minutes to ensure air bubbles would not be present in the solution.

2.2.4 Creating calcium pectinate films
Approximately 250.0g of the 1.0% pectin solution was poured into a lightly scuffed cookie sheet and allowed to stand in a fume hood for 24 hours on a leveling apparatus. The 1% pectin solution delivered 2.5g of pectin across 1205cm2 of surface area on the cookie sheet. As the water evaporated from the pectin solution a thin film of pectin was deposited on the surface of the cookie sheet. A 2.0% calcium chloride solution was prepared by adding 5.0g of calcium chloride to 245.0g of distilled water (pH 6.5) in a 400mL beaker containing a stir bar. The 2% calcium chloride solution was stirred for 30 minutes using a stir plate. Approximately 250.0g of the 2.0% calcium chloride solution was poured into the cookie sheet containing the pectin film and allowed to stand for 30 minutes. The 2% calcium chloride solution delivered 5g of calcium chloride to 2.5g of pectin. The calcium reacts with the galacturonic acid in the pectin film forming a cross-linked water-insoluble calcium pectinate film. The calcium chloride solution was then decanted from the cookie sheet. The cookie sheet containing the cross-linked pectin film was rinsed three times with 250.0g of distilled water (pH 6.5). The cookie sheet was placed in a fume hood and allowed to stand for 24 hours. The film slowly peeled off the cookie sheet. Thin uniform calcium pectinate films were created containing no wrinkles or high spots. The film was cut into 5 cm X 5 cm squares and stored in a sealed container. The dried calcium pectinate film demonstrated a moisture content of 2.1 to 2.5%.
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