Abstract
Carrageenan (CGN) is a high molecular weight (typically 200–800 kDa) polysaccharide derived from red seaweed. It is used as a food additive and as a functional excipient in pharmaceutical and nutraceutical products. In softgels, CGN can offer advantages over gelatin, including pH tolerance up to 12, thermal stability during processing (70–90 °C), and resistance to cross-linking. However, under extreme conditions, such as prolonged exposure to strong acid and temperatures exceeding 100 °C, CGN may degrade into low-molecular-weight fragments (<20 kDa), known as poligeenan, which has been linked to toxicological effects. This study investigates whether conditions used in softgel manufacturing or simulated gastrointestinal digestion could cause CGN to degrade into poligeenan or similar low-molecular-weight species. Iota carrageenan from three different batches used in food, nutraceutical, and pharmaceutical products was subjected to controlled stress conditions, including high temperature and low pH. Molecular weight distributions were measured using gel permeation chromatography (GPC). Carrageenan exhibited excellent thermal stability at 95 °C and 105 °C without significant molecular weight reduction when not exposed to acid. Under gastric-simulating conditions (pH 1.2 at 37 °C), moderate hydrolysis occurred, but fragments remained above the 20 kDa threshold. In contrast, combined acid and high-temperature treatment induced substantial degradation, yielding fragments under 20 kDa. No low-molecular-weight fragments consistent with poligeenan (<20 kDa) were observed under relevant conditions, reinforcing carrageenan’s safety profile for use as a functional excipient in controlled-release dosage forms and dietary supplements.
Highlights
- Carrageenan stability tested under softgel and GI-relevant stress conditions
- No poligeenan formed under gastric pH and softgel processing temperatures
- Degradation only observed under extreme acid and heat combinations
- Gel permeation chromatography used to track molecular weight shifts
- Supports carrageenan’s safety as a pharmaceutical excipient
Introduction
Carrageenan (CGN) is a high-molecular-weight, sulfated polysaccharide derived from red seaweed and commonly used as a multifunctional food additive and excipient in pharmaceutical and nutraceutical products [1]. It serves as a gelling, thickening, and stabilizing agent, with broad applicability in food, pharmaceutical and other industries. One of the applications of carrageenan is in softgel capsules and controlled-release systems. Carrageenans have also been reported to exhibit a range of biological activities, including antiviral, immunomodulatory, and antimicrobial effects, and have been investigated for biomedical applications such as tissue engineering and biomaterials development [2].
CGN exists in three primary forms: kappa (κ), iota (ι), and lambda (λ), which differ in sulfate content and gelling properties (Fig. 1). The functionality and safety of CGN are closely linked to its molecular weight distribution, which typically ranges from 200 to 800 kDa. Analytical studies, including gel permeation chromatography (GPC) coupled with inductively coupled plasma (ICP) detection, have confirmed that commercial food-grade or pharmaceutical-grade CGN lacks significant quantities of low-molecular-weight fragments associated with toxicity [1].
Despite its broad functionality, the safety of CGN has been debated due to its potential to degrade into low-molecular-weight components under the combined conditions of strong acidity and high temperature. Of particular concern is poligeenan (PGN), a chemically distinct degradation product with molecular weights below 20 kDa, formed through extended exposure of CGN to strong acid hydrolysis at elevated temperatures [3]. Poligeenan is not approved for food or pharmaceutical use due to its demonstrated pro-inflammatory and toxic effects [3,4].
Poligeenan (PGN) is not produced biologically and is not present in native carrageenan. Rather, it is generated through extensive acid hydrolysis of carrageenan under harsh, non-physiological conditions, typically at very low pH (about 0.9-1.3) and elevated temperatures above 80 °C for several hours. These conditions are substantially more severe than those encountered in the gastrointestinal tract or during standard softgel manufacturing. In humans, gastric pH under fasting conditions is generally about 1.3-3 and rises transiently after food intake before gradually returning toward baseline as gastric emptying proceeds. In addition, gastric residence time is limited, typically on the order of 3-4 h. Taken together, these conditions are not generally sufficient to produce the extensive hydrolysis required to convert carrageenan into poligeenan.
Toxicological concern around poligeenan arises from its well-documented pro-inflammatory activity in experimental systems. Unlike high-molecular-weight carrageenan, poligeenan has been associated with gastrointestinal injury, activation of innate immune signaling, disruption of epithelial barrier integrity, oxidative stress, and alterations in gut microbial composition [5]. Proposed mechanisms include activation of Toll-like receptor-mediated pathways and downstream NF-kB signaling, resulting in increased expression of pro-inflammatory mediators such as IL-8, TNF-a, and IL-6. Poligeenan has also been reported to reduce tight junction protein expression, which may increase intestinal permeability, and to promote oxidative and microbial changes that can further amplify inflammatory responses.
Confusion surrounding CGN’s safety has been exacerbated by the historical use of the term “degraded carrageenan,” which led to toxicological findings derived from poligeenan being misattributed to CGN [3]. Although regulatory authorities such as the U.S. Food and Drug Administration (FDA), the Joint FAO/WHO Expert Committee on Food Additives (JECFA), and the European Commission have concluded that CGN is safe under intended use conditions [3,5,6], concerns persist regarding its stability during digestion or processing. Specifically, questions remain as to whether human gastrointestinal conditions or standard softgel manufacturing processes could induce hydrolytic degradation of CGN to poligeenan-like fragments.
Numerous pharmacokinetic studies have demonstrated that CGN is not systemically absorbed and is excreted unchanged in feces following oral administration in rats, guinea pigs, and primates [3,[7], [8], [9], [10], [11], [12], [13]]. Even in models colonized with human gut microbiota, no significant biotransformation or molecular weight reduction has been demonstrated [3,10]. Nonetheless, in vitro studies using highly sulfated λ-carrageenan (which contains three sulfate groups, compared to two in ι-carrageenan and one in κ-carrageenan) have reported inflammatory responses in cultured epithelial cells. However, these effects have not been consistently replicated in in vivo models or human studies [6,11,12].
A review of the literature revealed no studies directly examining whether carrageenan undergoes molecular weight degradation under actual softgel manufacturing or gastrointestinal physiological conditions, or whether such conditions could lead to the formation of poligeenan.
To address this gap, the present study aimed to assess whether iota-carrageenan degrades into low-molecular-weight fragments, specifically those consistent with poligeenan (<20 kDa), under physiologically relevant or softgel processing conditions. For this reason, gel permeation chromatography (GPC) was selected as the primary analytical method because it directly measures molecular weight distribution and enables detection of low-molecular-weight degradation products. Three commercial lots of iota-carrageenan were subjected to controlled stress conditions involving elevated temperature, acidic pH, and their combinations. Molecular weight distributions were measured using gel permeation chromatography (GPC), a sensitive technique for detecting polymer fragmentation. This study focused on qualitative comparisons of molecular weight distribution profiles, reporting observed shifts in peak molecular weight (Mp) and distribution patterns as indicators of degradation trends across treatment conditions and time points.
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Design of Experiment
Three batches of commercially available iota-carrageenan (GENUTINE® Carrageenan, supplied by CP Kelco) were utilized to assess the variability of this naturally derived material. These samples were not standardized, meaning no dextrose was added to alter their gel strength and viscosity. Dextrose can appear as low molecular weight fractions in tests, possibly being mistaken for poligeenan. To evaluate its stability, carrageenan samples from three different lots underwent three distinct treatment conditions: 1) elevated temperature alone; 2) acid treatment at physiological temperature; and 3) acid treatment at elevated temperature.
Soo Ah Jin, Qi Fang, Karunakar Sukuru, Do softgel manufacturing or gastric conditions break down carrageenan into poligeenan?, Biochemistry and Biophysics Reports, Volume 47, 2026, 102645, ISSN 2405-5808, https://doi.org/10.1016/j.bbrep.2026.102645.
