Glycerol esters of rosin, commonly known as ester gums, are highly versatile resins used in adhesives, coatings, inks, and other markets. Their unique functionality has led to specialized food applications in beverages and chewing gum.
An interesting example is the use of glycerol ester of wood rosin (GEWR) as a beverage-weighting agent (BWA) for citrus-flavored beverages. This application was created by a long-term cooperative approach with beverage customers and regulatory agencies. Food applications require rigorous testing to demonstrate safety and compliance with all global standards. The safety of GEWR was originally established by rigorous toxicological testing and has been further proven by five decades of global use in beverage production. Active support of the regulatory process has demonstrated an ongoing commitment to product safety that’s a global expectation of consumers for all food additive manufacturers.
Scientific opinions by the European Food Safety Authority in 2010 and 2018 reiterated that a valid safety assessment of glycerol esters of rosin in food applications should consider species-specific differences and require appropriate compositional and toxicological data. The approval of the original GEWR, which is derived from longleaf and slash pines, was based on this foundation of testing that ensures food additive safety.
Beverage-Weighting Agent Technology
Many citrus-flavored beverages, such as carbonated soft drinks and sports drinks, are emulsions of flavor oils in water. These drinks are technically challenging, requiring the production of emulsions stable in the form of concentrate, syrup, and diluted beverage over a range of storage and handling conditions. Beverage instability results in oil droplets migrating to the surface of the liquid with undesirable effects on taste and appearance. Emulsion stability requires both an emulsifier and a BWA, with the BWA used to increase the density of the dispersed flavor oil phase, thereby reducing the density difference between the oil and aqueous phases and enhancing stability.
Glycerol esters of rosin are the best known and most commonly used weighting agents in the beverage industry. There are two distinct types on the market: GEWR and glycerol ester of gum rosin (GEGR). GEWR was identified in the 1960s as an ideal candidate for application as a BWA. This versatile resin, based on a natural and renewable feedstock, has excellent solubility in essential oils. An extensive process of applications development and product safety testing established GEWR as the predominant beverage-weighting agent in the market. GEGR has trailed in the footsteps of GEWR in an attempt to gain the same widespread market acceptance.
GEWR versus GEGR
Glycerol esters of rosin are used to modify the properties of diverse formulations in adhesives, coatings, inks, and food applications. Their broad compatibility and solubility encourage uses in a wide array of markets. The primary differences in GEWR and GEGR arise from the sourcing, pine species, and production processes used for their feedstock rosins. Rosins derived from different pine species can vary widely with respect to composition and physical properties, such as softening point, causing performance disparities in some end uses. Although GEWR and GEGR are used in many of the same markets, they are not interchangeable in all applications. GEGR traditionally has been less expensive than GEWR but is limited by less comprehensive regulatory approvals in areas such as beverages.
GEWR: Wood rosin is the natural resin produced by the solvent extraction of aged pine stumps followed by a liquid-liquid solvent refining process. This technology was developed in the first half of the 20th century. The feedstock is stump wood from longleaf (Pinus palustris) and slash (Pinus elliottii) pines grown in the southeastern United States. These stumps are left in the ground after harvesting of the pine trees for other uses and are a renewable resource. The refining process produces rosin of highly consistent quality, meeting purity specifications required by numerous end-use applications.
GEWR is produced by the reaction of food-grade glycerine with refined wood rosin at temperatures in the 260-280°C range. After the required acid number range has been reached, the product is purified by countercurrent steam stripping.
The above definition of GEWR is based entirely on the original wood rosin process that has been in continuous operation to this day. Its approval for use in beverages was the basis for the successful development and approval of GEWR as a beverage-weighting agent.
The wood rosin purification process was developed specifically for the longleaf/slash crude rosin originating in the southeastern United States. Since the extractives in pine stump wood have a wide range of structures and polarity, the composition of the wood rosin product will depend on the specific pine species and the extraction and refining solvents chosen—in other words, the pine species and extraction process determine the chemical identity of the rosin, which means the process for any new GEWR needs to be well defined, thoroughly documented, and understood by the regulatory authorities.
GEGR: Gum rosin is produced by tapping living pine trees. The oleoresin exudate is collected, filtered, and distilled to remove turpentine, leaving gum rosin as the product. This rosin is sourced from a variety of pine species in China, Brazil, Indonesia, Mexico, Vietnam, and other countries. GEGR is produced in a manner similar to GEWR, although manufacturing processes and final product form may vary significantly depending on the supplier.
Much compositional variability is found in gum rosin sourced from different pine species and geographical locations. Use of GEGR as a beverage-weighting agent has been complicated by incomplete compositional and toxicological data. Understanding the composition of a natural raw material like rosin is critical in order to meet regulatory standards.
Food additive safety is verified by national and international regulatory agencies. The regulatory process has been a key driver in the successful development of the BWA market.
The FDA approved GEWR for use in beverages in the early 1960s. During the review and approval process, a suggestion was submitted that the product be referred to by the broader term of “glycerol ester of rosin.” Since available data didn’t support this proposal, this suggestion was rejected, and “glycerol ester of wood rosin” was adopted. This was an early acknowledgement that the source of the feed rosin was important and that all glycerol esters of rosin could not be considered equivalent based on superficial similarities. The FDA ultimately approved GEGR use in beverages in 2005, followed by Health Canada in 2010, but multinational regulatory agencies have not followed suit due to incomplete compositional and toxicological information.
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) carried out a comprehensive evaluation of GEWR produced from P. palustris and P. elliottii beginning in 1974. JECFA took a conservative approach to evaluating and approving this material as a food additive, and the original manufacturer of GEWR initiated a long-term program of analytical and toxicological testing at JECFA’s request. From the beginning, JECFA emphasized the need to more fully characterize the material from which the glycerol ester of rosin was prepared, including specifying the species of pine tree used. The rigorous evaluation process culminated in 1991 with specifications for GEWR under International Numbering System (INS) 445.
In 2008, FDA requested that JECFA consider the extension of INS 445 approvals to GEGR. The basis was a claim of chemical equivalence between GEGR and GEWR to justify relying on the extensive toxicological testing done on the original GEWR product. JECFA maintained a consistent, science-based approach in its evaluation of this request. During evaluation of the GEGR petition, the committee noted that the chemical composition of GEGR varies depending on the pine species, geographical differences, and the techniques used in the processes of rosin production. JECFA noted that limited data was available on the variability of the resin acid composition of GEGR in commerce and that complete information on the composition and ester distribution of GEGR had not been submitted. Therefore, officials were not able to claim similarities to GEWR. JECFA was unable to establish specifications and an allowable daily intake for GEGR due to the lack of information.
GEWR is the only glycerol ester of rosin approved for use in beverages by the European Food Safety Authority (EFSA). EFSA was petitioned by T&R Chemicals, Inc., in 2008 for the approval of GEGR as a beverage-weighting agent under E 445. A claim of chemical equivalence was put forth by the petitioner to justify use of the original GEWR toxicity test data. The EFSA Scientific Panel on Food Additives and Nutrient Sources Added to Food (ANS) reviewed the proposal and concluded that the available data was too limited to evaluate GEGR’s safety as a food additive. The panel couldn’t verify chemical equivalence of GEGR and GEWR due to the lack of critical information on composition, so toxicological data for GEWR could not be used for read-across to GEGR.
The EFSA issued a scientific opinion in 2018 after completing a re-evaluation of GEWR as a food additive. The EFSA noted that the toxicological studies that were the basis for E 445 and INS 445 approvals were based on GEWR produced from a mixture of the two species: P. palustris and P. elliottii. No comparable toxicological studies were available for GEWR originating from other pine species, and insufficient compositional information was available for those variations. Given this lack of information, determining chemical equivalence of GEWR from other pine species with GEWR originating from P. palustris and P. elliottii wasn’t possible, making read-across of toxicological data invalid.
The long-term success of GEWR as a beverage-weighting agent has required continued engagement with and active support of the regulatory process. This should be an expectation for any responsible food additive manufacturer, whether attempting to bring a new product to market or to support an existing product.
Merck is research and development manager at DRT. Reach him at firstname.lastname@example.org. Kennedy is senior vice president of Technology & Innovation at DRT. Reach him at email@example.com.