Science and Technology Indonesia
e-ISSN:2580-4391 p-ISSN:2580-4405
Vol. 10, No. 4, October 2025
Review Paper

Potential of Tropical Seaweed Carageenan in Applications of Soft Capsule as a
Replacement for Gelatin: A Review
Taufik Hidayat1,2* , Khaswar Syamsu1 , Titi Candra Sunarti1 , Mala Nurilmala3 , Lamhot Manalu2
1 Department of Agro-industrial Engineering, IPB University, Bogor, West Java, 16680, Indonesia
2 Research Center for Equipment Manufacturing Technology, National Research and Innovation Agency, South Tangerang, Banten, 15314, Indonesia
3 Department of Aquatic Product Technology, IPB University, Bogor, West Java, 16680, Indonesia
*Corresponding author: tauf023@brin.go.id

Abstract
Carrageenan, a natural sulfated polysaccharide extracted from red seaweed, has attracted considerable attention in the development
of drug delivery systems, particularly as a capsule-forming material. With its biodegradable, biocompatible properties and gel-forming
ability, carrageenan holds significant potential as a plant-based alternative to animal-derived gelatin. This review aims to evaluate the
potential of carrageenan, especially iota-carrageenan, in the production of soft capsules as a gelatin substitute, and to compare the
characteristics of hard and soft carrageenan-based capsules. In addition, formulation challenges and structural modification strategies
are discussed to improve the functional properties of carrageenan. Soft capsules are typically formulated using iota-carrageenan and
plasticizers such as glycerol to achieve optimal flexibility, while hard capsules utilize kappa-carrageenan due to its stronger gel texture.
Modifications such as depolymerization and blending with other polymers have been shown to enhance viscosity, elasticity, and
disintegration time of carrageenan capsules. However, several limitations remain, including high viscosity and slower disintegration
rates compared to gelatin-based capsules. Therefore, formulation optimization and improved extraction techniques are essential
for advancing carrageenan capsules as competitive alternatives in pharmaceutical applications. Looking forward, future research
should focus on optimizing low-cost and high-purity carrageenan extraction methods, engineering depolymerization processes,
and modifying kappa-carrageenan to exhibit iota-like flexibility. These approaches are expected to improve the feasibility of using
tropical seaweed-derived carrageenan as a sustainable and halal-compliant material for soft capsule shells.
Keywords
Carageenan, Red Seaweed, Seaweed, Soft Capsule Shell
Received: 15 December 2024, Accepted: 31 August 2025

https://doi.org/10.26554/sti.2025.10.4.1288-1300

1. INTRODUCTION
Algae are a diverse group of simple aquatic plants with a long
evolutionary history, widely distributed in various marine habitats. One significant subgroup of algae is seaweeds (macroalgae),
which are classified into red, brown, and green seaweeds based
on their pigmentation. The cell walls of red seaweeds are predominantly composed of sulfated polysaccharides such as carrageenan and agar, which play vital roles in structural support,
energy storage, and selective cation absorption (Pangestuti and
Kim, 2014) . Carrageenan is a major polysaccharide extracted
primarily from Kappaphycus alvarezii and Eucheuma denticulatum,
two red seaweed species widely cultivated in Southeast Asia,
including Indonesia (Imeson, 2009) .
Commercial carrageenan is typically classified into three
main types based on its structure and gel-forming properties:
kappa (𝜅), iota (𝜄), and lambda (𝜆 ). Kappa-carrageenan forms

strong and brittle gels in the presence of potassium ions; iotacarrageenan forms soft, elastic, and transparent gels in the
presence of calcium ions; and lambda-carrageenan does not
form gels and is generally used as a thickening agent in liquid
products (Pangestuti and Kim, 2014) .
Soft capsules are among the most commonly used oral
pharmaceutical dosage forms due to their ability to protect
liquid active ingredients from oxidation while improving patient compliance. These capsules can mask unpleasant tastes
and odors, provide airtight sealing, and rapidly disintegrate in
the stomach upon administration (Gullapalli and Mazzitelli,
2017) . Traditionally, soft capsules are made from gelatin derived from animal sources such as bovine or porcine collagen
(Nafchi et al., 2014) . However, gelatin poses several issues,
including dietary and religious restrictions (e.g., for muslim,
jewish, vegetarian, or vegan populations), as well as health concerns such as the risk of bovine spongiform encephalopathy

Hidayat et. al.

(BSE), thereby highlighting the need for plant-based and safer
alternatives (Gullapalli and Mazzitelli, 2017) .
Carrageenan has emerged as a leading candidate for replacing gelatin in capsule formulation in recent years. However,
it is important to note that not all types of carrageenan are
suitable for soft capsules. Although comparable to gelatin in
gel strength, Kappa-carrageenan is more appropriate for hard
capsule applications due to its brittle gel texture (Soraya et al.,
2024) . In contrast, iota-carrageenan is more suitable for soft
capsule applications because of its ability to form flexible and
elastic gels, which are essential for maintaining the mechanical integrity of soft capsules during processing, storage, and
administration (Hilliou, 2021; Pangestuti and Kim, 2014).
Despite these advantages, using iota-carrageenan in soft
capsule formulation still faces several technical challenges, including low solubility, high viscosity, and slower disintegration
time compared to gelatin capsules (Fauzi et al., 2020) . Additionally, the high molecular weight of carrageenan contributes
to poor solubility and excessive gel strength. To overcome
these limitations, strategies such as molecular depolymerization have been explored. For instance, Tecson et al. (2021)
utilized ultrasonic-assisted depolymerization, which successfully reduced the molecular weight of kappa-carrageenan by
96.33%, thereby improving its potential for drug delivery systems.
This review aims to evaluate the potential of iota-carrageenan,
derived from red seaweed, as a plant-based alternative to gelatin
for soft capsule applications. It will examine the physicochemical characteristics, formulation challenges, and possible strategies to enhance its pharmaceutical performance, including
structural modification and excipient combinations.
2. Characteristics of Tropical Seaweed
Several previous researchers have observed the chemical properties of seaweed in Indonesia. The chemical properties of
seaweed can be seen in Table 1.
The chemical composition of seaweed varies significantly
depending on species, habitat, harvest season, and initial processing methods. Table 1 presents the chemical profiles of
several tropical seaweed species commonly found in Indonesian waters and neighboring regions. Key chemical parameters
analyzed include moisture content, ash, protein, lipid, and
crude fiber levels. For example, Eucheuma cottonii, a significant source of kappa-type carrageenan, contains 7.21% protein,
0.47% lipid, and 8.52% crude fiber. These values indicate a
high fiber and low-fat content, favorable traits for carrageenan
extraction. The quality of the seaweed, how it is processed,
and the water’s environmental conditions all impact the carrageenan quality (Hajar and Parden, 2023) .
Other species, such as Sargassum polycystum, also show potential as raw materials, with ash contents ranging from 21.38%
to 30.78%. High ash content may reflect significant mineral
presence, but can also negatively affect the clarity and quality of
the final carrageenan product if not correctly managed during
processing. Ash content is an important factor in evaluating the
© 2025 The Authors.

Science and Technology Indonesia, 10 (2025) 1288-1300

nutritional value of seaweed. A high ash level makes seaweed
less suitable for human consumption, reducing its effectiveness
as a food source (Alghazeer et al., 2022) . Meanwhile, species
like Caulerpa racemosa and Caulerpa mexicana exhibit high protein levels (up to 20.79% in C. cupressoides), which may not be
ideal for carrageenan extraction due to differences in polysaccharide structure, but may be better suited for functional food
or dietary supplement applications.
These variations in chemical composition not only influence carrageenan content but also affect the extraction process,
yield efficiency, and the physical and chemical quality of the resulting carrageenan. For instance, seaweeds with high moisture
content are prone to faster degradation of bioactive compounds
if not promptly dried. In contrast, high protein and lipid levels
may contaminate the final product, requiring additional purification steps. Therefore, selecting the right seaweed species
ensures quality and production efficiency.
Moreover, environmental factors such as salinity, temperature, and nutrient availability in seawater also influence the
biosynthesis of bioactive compounds, including carrageenan.
As such, cultivation and post-harvest practices play an important role in determining the quality of seaweed biomass.
A thorough understanding of the chemical characteristics
of different seaweed species allows for optimizing appropriate
extraction strategies, including the choice of method, processing conditions, and necessary pre-treatments. The following
section will explore the various carrageenan extraction methods commonly used, and how these methods are adapted to
different seaweed compositions.
3. Extraction Method of Carrageenan
Carrageenan can be extracted using various methods such as
alkaline, enzymatic, or thermal extraction, each influencing its
structural and functional properties. Different extraction techniques affect the yield. Extraction using hot alkaline solvents
can reduce operational costs because it only requires simple
equipment and lower energy consumption. However, this process takes longer due to the use of large amounts of solvent,
which can cause waste of solution, increase the risk of microbiological contamination, and potentially damage high-value
microalgae cell components due to alkali exposure (Firdayanti
et al., 2023) . According to Jiang et al. (2022) , the resulting carrageenan results in low yields and the use of large amounts of
chemicals and water, thus increasing wastewater treatment costs
exponentially. Extraction methods can provide alternatives to
minimize the use of chemicals with microwaves, ultrasonics,
and enzymatic methods.
The microwave method has advantages including short curing time, suitability for heat-sensitive compounds, efficiency
and uniformity in heating, and high extraction yields. However, this technology has several disadvantages, such as relatively high costs, the potential risk of explosion, especially in
closed microwave systems, challenges in temperature control,
and the possibility of microwave leakage, which needs to be
managed properly to ensure safety and prevent health risks.
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Hidayat et. al.

Table 1. Chemical Properties of Dried Tropical Seaweeds

Types of Seaweed

Location

Water (%)

Ash (%)

Protein
(%)

Lipid
(%)

Crude
Fiber
(%)

S. polycystum

Teluk Kemang

13.70

21.38

8.65

3.42

13.55

Caulerpa cupressoides

Pacheco Beach

12.21

11.28

20.79

3.77

–

Caulerpa Mexicana

Pacheco Beach

10.70

7.79

18.06

1.52

–

Hypnea musciformis

Pacheco Beach

14.17

14.14

17.12

0.33

–

Solieria filiformis

Pacheco Beach

15.06

15.12

20.31

0.34

–

U. lactuca

Pameungpeuk
Waters

16.90

11.20

13.60

0.19

–

Gracilaria seaweed

Karawang

11.34

5.54

9.43

0.26

–

Gracilaria seaweed

Lombok

9.51

6.58

10.73

0.62

–

14.66

38.41

7.60

0.71

–

12.19

30.78

4.92

0.32

5.37

21.61

24.79

2.31

0.19

–

22.31

30.53

4.78

0.52

3.81

9.40

13.08

5.64

0.46

6.49

16.40

27.00

10.50

1.14

23.96

Caulerpa racemosa
S. polycystum
S. filipendulla
P.minor
S.oligocystum
P.tetrastomatoca

Tual, Southeast
Maluku
Kelanit waters of
Southeast Maluku
Kelanit waters of
Southeast Maluku
Kelanit waters of
Southeast Maluku
Kelanit waters of
Southeast Maluku
Kelanit waters of
Southeast Maluku

E. spinosum

Nusa Penida

19.55

24.26

6.04

0.012

15.12

E. spinosum

Takalar

21.27

23.66

7.33

0.032

18.56

Eucheuma cottonii

Tanjung Medang

–

14.22

7.21

0.47

8.52

E. striatum

Mimapropa region

35.30

16.44

–

–

–

K. alvarezii

Mimapropa region

35.70

18.55

–

–

–

E. denticulatum

Mimapropa region

38.67

16.22

–

–

–

The ultrasonic extraction method has advantages including
shorter drying time, more efficient use of solvents, improved
gel texture quality, and better temperature control capabilities.
However, this method also has several disadvantages, such as
the need for additional stirring due to uneven mixing depending on the viscosity of the sample, and the risk of reducing
the quality of the extract if the sonication process is carried

© 2025 The Authors.

Sources
(Nazarudin et al.,
2021)
(Carneiro et al.,
2014)
(Carneiro et al.,
2014)
(Carneiro et al.,
2014)
(Carneiro et al.,
2014)
(Rasyid, 2017)
(Purwaningsih et al.,
2024)
(Purwaningsih et al.,
2024)
(Pangestuti and Kim,
2014)
(Erbabley and
Junianto, 2020)
(Erbabley and
Junianto, 2020)
(Erbabley and
Junianto, 2020)
(Erbabley and
Junianto, 2020)
(Felix and Brindo,
2014)
(Diharmi et al.,
2019)
(Diharmi et al.,
2019)
(Diharmi et al.,
2020)
(Abel and Tolentino,
2024)
(Abel and Tolentino,
2024)
(Abel and Tolentino,
2024)

out excessively (Firdayanti et al., 2023) . Enzyme-assisted extraction can reduce the use of alkali and increase extraction
yields. However, the carrageenan quality tends to be less than
optimal because the enzyme is susceptible to inactivation, and
its stability is difficult to maintain in a practical scale production
process (Jiang et al., 2022) .
The widely used extraction method is the alkali method be-

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Hidayat et. al.

Table 2. Yield Results with Different Carrageenan Extraction Methods

Extraction Method

Yield (%)

Sources

Alkali (Ca(OH) 2)
Alkali (NaOH)
Microwave Assisted Extraction (MAE) - KOH 3% (1:10)
MAE – KOH 3% (1:20)
MAE - NaOH 0,1N (1:10)
MAE - NaOH 0,1N (1:20)
Microwave Assisted Extraction – KOH 3%
Microwave Assisted Extraction - Aqueous
Ultrasonic Assisted Extraction (UAE) – NaOH
UAE – KOH
NAC-Alkali
Enzyme cellulase 0.2%, xylanase 0.2%, NAC-alkali
Alcalase 0.2% + NAC-alkali
Bead mill

24.7
21.0
68.90
25.61
52.87
37.32
16.6
21.5
33.73
76.70
23.8
35.5
27.8
67.86

(Jiang et al., 2022)
(Jiang et al., 2022)
(Kasim et al., 2023)
(Kasim et al., 2023)
(Kasim et al., 2023)
(Kasim et al., 2023)
(Vazquez-Delfin et al., 2014)
(Vazquez-Delfin et al., 2014)
(Mendes et al., 2024)
(Mendes et al., 2024)
(Naseri et al., 2020)
(Naseri et al., 2020)
(Naseri et al., 2020)
(Firdayanti et al., 2023)

cause it can produce good quality carrageenan, lower costs, and
the process is easier to implement on a large scale. However,
current carrageenan production has complex manufacturing
steps, such as the use of high concentrations of NaOH, and the
amount of water used is large and requires significant investments in wastewater treatment. Several studies have innovated
to overcome these problems. The carrageenan extraction process with Ca(OH) 2 for carrageenan extraction and CO2 for
neutralization as a substitute for the use of alkali (NaOH) has
been carried out by Jiang et al. (2022) and Liu et al. (2022) .
The results showed that the quality of kappa carrageenan produced by Ca(OH) 2 extraction was superior to the extraction
method with NaOH, such as increased gel strength, thermal
stability, and decreased viscosity. In addition, a study with
the same method on iota carrageenan showed results with a
gel texture, such as better hardness and elasticity compared
to the NaOH alkali extraction method, good thermal stability, and lower viscosity. In the study of Kasim et al. (2023) ,
using KOH as an extraction solvent typically yields a higher
amount of carrageenan than NaOH due to the higher molecular
weight of potassium ions relative to sodium ions. Additionally,
the efficiency of the extraction process is affected by both the
volume-to-material ratio and the concentration of the alkaline
solution used. The greater the volume and concentration of
the alkaline solvent used, the greater the yield of carrageenan
produced.
According to Jiang et al. (2022) , this is due to the absence of
preliminary alkali treatment. Without alkali, there is no conversion process of D-galactose-6-sulfate to 3,6-anhydrogalactose,
which affects the formation of helical bonds and the stability of
the molecular structure, so the resulting gel is not strong.
In another study by Firdayanti et al. (2023) , a mechanical
method, namely a bead mill, was used in carrageenan extraction. The results showed that the yield produced was higher,
reaching 67.86% in a short time, namely ±50 minutes, com-

© 2025 The Authors.

pared to the conventional method using alkali KOH. However,
the physicochemical characteristics, especially the gel strength
produced, were lower than those of the conventional method
with KOH solvent. Several other research results with different
extraction methods on the yield of carrageenan can be seen in
Table 2.
While numerous studies have explored diverse extraction
methods for carrageenan, a critical gap remains in correlating
extraction parameters with the functionality of carrageenan in
pharmaceutical applications, particularly capsule shell formation. High yield does not always translate into better gel properties or biocompatibility. For example, the bead mill method
provides exceptional yield but results in lower gel strength, limiting its use in soft capsule matrices that require mechanical
integrity.
Additionally, the scalability of enzymatic and ultrasonic
methods is yet to be validated in industrial settings, where cost,
energy efficiency, and chemical use must be optimized. In
this regard, green extraction technologies-such as enzymatic
or microwave-assisted extraction using minimal solvents-need
further exploration, especially within the framework of GMP
(Good Manufacturing Practice) compliance.
Future studies should focus on developing a standardized
extraction-performance evaluation framework that quantifies
yield and assesses gel strength, viscosity, sulfate content, and
biocompatibility in an integrated model. Such a framework
would bridge the gap between academic innovation and realworld pharmaceutical application.
4. Quality of Carrageenan from Tropical Seaweed Materials
Carrageenan is a stabilizer, thickener, and gel former in food
products. In the non-food industry, carrageenan is used as
a mixture for cosmetics, paints, and textiles, and is used in
the pharmaceutical industry (Shen and Kuo, 2017) . The carrageenan extraction process is done in an alkaline atmosphere
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Table 3. Characteristics of Carrageenan Quality

Sample

Location

Eucheuma spinosum

Nusa penida

Eucheuma spinosum

Sumenep

Eucheuma spinosum

Takalar

Eucheuma cottonii

Bantaeng

K. alvarezii

Wongsorejo

Eucheuma cottonii

Banggai Beach

K. alvarezii

Karimun

Results
Yields: 25.81%, Ash: 29.03%, Gel strength:
32.73 g.cm-1
Yields: 34.81%, Ash: 29.57%, Gel strength:
43.30 g.cm-1
Yields: 37.16%, Ash: 28.26%, Gel strength:
54.14 g.cm-1
Yields: 7.73%, Moisture: 9.84%, Ash: 37.03%,
pH: 7.02
Yields: 36.11%, Moisture: 11.19%, Ash: 25.79%,
Viscosity: 42.33 cP
Yields: 34.51%, Ash: 36.28%, Viscosity: 1.700
cP, Gel strength: 52.37 g.cm-1
Yields: 34.3%, Moisture: 6.3%, Ash: 59.4%,
Viscosity: 8.20 cP, Gel strength: 94.45 g.cm-1

using alkaline solutions such as NaOH, Ca(OH) 2, or KOH.
The use of alkali in this extraction process helps the extraction of polysaccharides to be more perfect and accelerates the
elimination of 6-sulfate from monomer units to 3,6-anhydroD-galactose to increase gel strength and product reactivity towards protein (Campo et al., 2009; Hilliou et al., 2006; Uy
et al., 2005). The quality characteristics of carrageenan that
researchers have carried out in the last 5 years can be seen in
Table 3.
The type of species, cultivation location, and extraction
conditions greatly influences the quality of carrageenan produced from seaweed. Some parameters generally used to assess
carrageenan quality include yield, ash content, water content,
viscosity, gel strength, and pH. Evaluation of these parameters
is important to determine the suitability of carrageenan as a
raw material in pharmaceutical preparations, especially soft
capsules.
Yield analysis in previous studies showed that most of them
met the FAO yield standard of a minimum of 25%. Diharmi
et al. (2017), Firdaus et al. (2021), Ferdiansyah et al. (2023),
and Manuhara et al. (2016) showed that the yield produced
met the FAO standard with a yield range of 25 - 37%. According to Diharmi et al. (2017) , the difference in carrageenan
yield may be due to differences in growing areas. Various
factors in the growing regions may physiologically influence
carrageenan formation in the seaweed. The difference in environmental conditions, such as water temperature, pH, and
salinity in coastal areas of Nusa Penida, Sumenep, and Takalar,
may affect carrageenan formation in the seaweed. In addition,
the yield of carrageenan can be influenced by the extraction
conditions used. Sormin and Masela (2019) stated that carrageenan yield is influenced by several factors, including an
increase in pH resulting from the addition of an alkaline solution. Higher temperatures also contribute to increased yield, as
elevated heat allows for more efficient carrageenan extraction

© 2025 The Authors.

Sources
(Diharmi et al., 2017)
(Diharmi et al., 2017)
(Diharmi et al., 2017)
(Lestari et al., 2024)
(Firdaus et al., 2021)
(Ferdiansyah et al., 2023)
(Manuhara et al., 2016)

from seaweed.
Furthermore, alkaline treatment promotes the formation
of 3,6-anhydrogalactose during the extraction process. In the
study of Lestari et al. (2024) , the yield produced was very
low. The low yield of carrageenan can be influenced by several
factors, such as the use of too high an extraction temperature, which can reduce the yield of carrageenan. The higher
extraction temperatures may have resulted in polysaccharide
degradation (Webber et al., 2012) .
Water content is an essential parameter in determining
product stability during storage. Carrageenan with water content that is too high tends to be readily degraded by microbiology and physical factors. Previous research on the characteristics of carrageenan water content shows that it meets
the FAO standard, which is a maximum of 12%. The water
content of the seaweed used can influence the water content
of carrageenan. Carrageenan possesses strong water-binding
properties. Its polymer chains can form intertwined double helices, which enable the entrapment of free water molecules. As
the concentration of carrageenan increases, a greater amount of
water can be immobilized within its polymer network (Hamzah
et al., 2021) .
Ash content reflects the content of minerals and inorganic
salts in carrageenan. High ash content values '' can reduce
purity and affect the stability of pharmaceutical preparations.
Based on previous research data, most have met the FAO ash
content standard, which is 15% - 40%. According to Chan
et al. (2013) , the ash fraction in k-carrageenan consists mostly
of macro minerals, such as potassium, sodium, calcium, and
magnesium. Ash content is directly proportional to mineral
content. The ash content of carrageenan can be affected by
several factors. The alkali solution concentration used in carrageenan extraction can affect the ash content of carrageenan.
The higher the concentration used, the higher the ash content
of the carrageenan produced. Alkali solutions such as NaOH

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Table 4. FTIR Characteristics of Carrageenan

Types of Carrageenan
Kappa carrageenan

Iota carrageenan

IR Absorption Peak
(cm-1 )
3319
2930
1619
1428
1234
1159
1066
920
844
699
3369
2912
1214
1157
1066
927
848
802

Information

Sources

OH stretching
CH stretching
Asymmetric C=O stretching
Symmetrical band of COOSulfate stretching of SO
Bridge C-O stretching
C-O-C stretching
C-O-C of 3,6 anhydro-o-galactos
C-O-SO3 stretching
Sulfate on C-4 galactose
O-H stretch
C-H stretch
ester sulfate O-S-O symmetric
vibration
C-O bridge stretch
C-O stretch
C-O-C of 3,6 anhydro-o-galactos
-O-SO3 stretching vibration at
D-galactose-4-sulfate
-O-SO3 stretching vibration at
D-galactose-2-sulfate (DA2S)

(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Perumal and Selvin, 2020)
(Ghani et al., 2019)
(Ghani et al., 2019)

will adhere to seaweed during the extraction process. The increasing amount of sodium and other minerals attached to
seaweed during the extraction process increases the ash content
of the carrageenan produced. In addition, the longer the extraction time, the longer the seaweed will contact heat and the
extraction solution (Manuhara et al., 2016; Astuti et al., 2017).
According to Ferdiansyah et al. (2023) , alkaline solutions contain K+, Na+, and Ca2+, which are inorganic substances that
are not lost during heating. Ash content in carrageenan can
derive from macro and micro minerals absorbed or retained
in seaweed as a material for carrageenan.
The viscosity of carrageenan is directly related to its ability
to form gel and film systems. High viscosity values '' indicate a
long and complex molecular structure, which is very useful in
applications as soft capsule forming agents. The results of previous studies have shown that the viscosity of the carrageenan
obtained has met the FAO standard, which is a minimum of
5 cP. According to Astuti et al. (2017) , the viscosity of carrageenan can be affected by sulfate levels and is directly proportional to sulfate content. High sulfate content will produce high
viscosity, due to the ability of sulfate groups in carrageenan to
provide repulsive forces between negative charges along the
polymer chain. As a result, the molecular chain becomes stiff,
so that viscosity increases. In addition, molecular weight also
plays a role in increasing viscosity. The polymer BM shows the
average molecular chain length. The high BM of carrageenan
causes the distribution of sulfate groups in the polymer chain

© 2025 The Authors.

(Ghani et al., 2019)
(Ghani et al., 2019)
(Ghani et al., 2019)
(Ghani et al., 2019)
(Ghani et al., 2019) )
(Ghani et al., 2019)

to become homogeneous, so the repulsive force and viscosity increase (Komersová et al., 2022; Montoro and Francisca,
2019). According to Naseri et al. (2020), low viscosity can be
influenced by impurities bound to carrageenan, thus interfering with the extraction solution attacking the seaweed cell wall
to release carrageenan, thereby degrading the structure of the
carrageenan itself.
Gel strength is one of the critical parameters in soft capsule
formulation, because it determines the mechanical strength of
the capsule wall. The higher the gel strength value, the better
the material’s ability to form a stable and non-breakable capsule. The gel strength value produced is by the FAO standard,
which states that the gel strength value of carrageenan is 20500 g.cm-1 . This shows that the gel strength of carrageenan in
previous studies has met the FAO gel strength standard. K. alvarezii from Karimun showed the highest gel strength of 94.45
g.cm-1 , while E. spinosum from Nusa Penida had the lowest gel
strength of 32.73 g.cm-1 . However, the data above show that
the gel strength of the carrageenan produced is relatively low.
In addition to the physicochemical properties discussed
above, carrageenan’s FTIR (Fourier Transform Infrared Spectroscopy) characteristics are also crucial for determining its
suitability in capsule applications. FTIR analysis provides insights into the functional groups present in carrageenan, such
as sulfate esters and 3,6-anhydrogalactose, which directly influence its gelling behavior, solubility, and interaction with
other formulation components. Inaccurate functional group

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composition can result in inconsistent gel strength or poor filmforming ability, affecting soft capsules’ integrity, elasticity, and
disintegration performance. Therefore, FTIR characterization
is essential to ensure carrageenan’s consistency and functional
reliability in pharmaceutical capsule formulations. The FTIR
characteristics of carrageenan are presented in Table 4.
The FTIR analysis results showed that both kappa and
iota carrageenan have typical main functional groups, such as
hydroxyl (O–H), methylene (C–H), sulfate (SO3–), and 3,6anhydrogalactose groups, which are characteristic of the carrageenan structure. Kappa carrageenan, as reported by Perumal
and Selvin (2020) , showed a typical absorption peak at 920
cm-1 indicating the presence of 3,6-anhydro-𝛼-D-galactose
groups - an important group in the formation of a strong gel
structure. The peaks at 844 and 699 cm-1 indicate the presence
of sulfate bonds that contribute to solubility and gel-forming
capacity. Similarly, iota carrageenan analyzed by Ghani et al.
(2019) showed a similar absorption pattern, including peaks at
927 cm-1 and 848 cm-1 , confirming the presence of sulfate at
an important position in the galactose structure.
Iota carrageenan has more sulfate groups, as seen from the
additional peak at 802 cm-1 (sulfation at the 2-galactose position). This makes iota carrageenan more soluble and produces
a softer and more elastic gel. Kappa carrageenan has a stiffer
structure due to its lower sulfate level and high proportion of
3,6-anhydrogalactose. As a result, it forms a strong and brittle
gel, suitable for hard capsules or solid matrices.
Carrageenan types can be classified according to the presence of 3,6-anhydro bridges on the four-membered galactose
residue and the position and number of sulfate groups (Vandanjon et al., 2023) . FTIR spectra reflect the unique structural features of carrageenan, which consists of repeating disaccharide
units made up of 3-linked D-galactopyranose (G-units) and
either 4-linked D-galactopyranose (D-units) or 4-linked 3,6anhydro-D-galactopyranose (DA-units). The classification of
carrageenan is based on the presence of the 3,6-anhydro bridge
on the 4-linked galactose unit and the number and position of
sulfate groups attached to the sugar backbone. These structural
differences give rise to distinct FTIR absorption patterns for
each carrageenan type. Traditionally, carrageenans are categorized as kappa (𝜅; G4S–DA), iota (𝜄; G4S–DA2S), and lambda
(𝜆 ; G2S–D2S,6S). Their respective sulfate substitutions and
the presence or absence of anhydro bridges influence their
chemical properties and functional behavior in applications.
Additionally, the precursors of kappa and iota carrageenan—
known as mu ( 𝜇) and nu (𝜈), respectively-contain sulfate groups
at the C-6 position (D6S), which can be converted into DAunits through alkaline treatment. These structural elements
are typically detected by characteristic FTIR peaks, particularly
in the regions corresponding to sulfate stretching and C–O–C
vibrations, which are critical for assessing the type and quality
of carrageenan (Boulho et al., 2017) .
Each type of carrageenan exhibits specific FTIR absorption
bands related to the position of sulfate esters and the presence
of 3,6-anhydro bridges. The presence of sulfate esters is con© 2025 The Authors.

Science and Technology Indonesia, 10 (2025) 1288-1300

firmed by firm peaks near 1240 cm-1 (S=O stretching), while
the appearance of bands around 930 cm-1 and 1070 cm-1 indicates the presence of 3,6-anhydrogalactose (DA), which is
essential for gel formation. The classification of carrageenan
types can be further refined through FTIR spectral interpretation. According to literature, a peak at approximately 1240
cm-1 corresponds to sulfate esters and is typical of iota, kappa,
and nu carrageenan. A band near 1070 cm-1 is linked to C–O
stretching in DA units, while the 930 cm-1 peak is a strong
marker for DA-specific vibrations in iota and kappa. Furthermore, 905 cm-1 is unique to iota carrageenan, indicating sulfate
at C-2 of DA (DA2S), while 867 cm-1 , 825–830 cm-1 , and
815–820 cm-1 are characteristic of nu carrageenan, related to
sulfation at various positions of galactose. The 845 cm-1 band,
found in all three types, is associated with C-4 sulfation on
galactose (G4S) (Vandanjon et al., 2023) .
5. Application of Carrageenan to Capsule Shells
The quality of carrageenan from tropical seaweed in Indonesia
shows that the carrageenan produced meets FAO standards.
Carrageenan is mainly used in the pharmaceutical sector to
make capsule shells. The use of carrageenan in making capsule
shells functions as the leading gel former, which provides structure and strength to the capsule shell. Besides carrageenan, it
is usually used with additional ingredients such as starch, glycerin, or sorbitol to produce physical and mechanical properties.
Capsules are divided into hard capsules and soft capsules. According to the Ministry of Health of the Republic of Indonesia
(2020) , the difference between hard capsules and soft capsules
is that hard capsules consist of a body and lid, are available in
empty form, the contents are usually solid. Still, they can also
be liquid, can be used orally, and have only one shape, while soft
capsules are one unit; it is always filled, usually liquid or solid,
can be oral, vaginal, rectal, and topical, and comes in various
shapes. According to Zhou et al. (2023) , the incorporation of
plasticizers such as glycerol and sorbitol is crucial in enhancing
the mechanical properties and stability of polysaccharide-based
soft capsules, indicating the significance of these additives in
capsule formulation. Images of hard and soft capsules can be
seen in Figure 1.
Carrageenan, especially iota and kappa types, has been
widely explored in manufacturing soft and hard capsules. Data
shows that every kind of carrageenan produces different capsule
characteristics, depending on the polymer structure and application form. In the manufacture of soft capsules, carrageenan
can form a gel that is quite elastic and flexible when combined
with other components. However, to produce capsules with
optimal mechanical properties (flexible, not brittle, and not
easily broken), carrageenan needs to be combined with additional materials. In the study of capsule shell manufacture by
Perwatasari et al. (2025) , 1.5% iota carrageenan was used with
additional materials such as hydroxypropyl starch, glycerol, and
sorbitol. Zheng et al. (2023) used kappa carrageenan, sodium
alginate, and carboxymethyl starch. In their study, Pudjiastuti
et al. (2020) combined 𝜅-carrageenan with starch and kappa
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Hidayat et. al.

Figure 1. Hard Capsules (Left) and Soft Capsules (Right) (Hij Machinery, 2019)
Table 5. Characteristics of Carrageenan Capsules

Types of
Carrageenan

Types of Capsules

Results

Iota carrageenan

Soft capsule

13.56 mm

Kappa carrageenan

Hard capsule

22.56 mm

Iota carrageenan

Soft capsule

7.48 mm

Kappa carrageenan

Hard capsule

7.18 (body), 7.37
(cap) mm

Iota carrageenan

Soft capsule

0.49 g

Kappa carrageenan

Hard capsule

0.12 g

Iota carrageenan

Soft capsule

25.89 min

Iota carrageenan

Soft capsule

66.44 min

Kappa carrageenan
Kappa carrageenan
Kappa carrageenan

Soft capsule
Hard capsule
Hard capsule

15 min
36.21 min
18.47 min

Kappa carrageenan

Hard capsule

12.80 min

Kappa carrageenan

–

25.79 min

Tensile strength

Iota carrageenan

Soft capsule shell
sheet

2.3 Mpa

Stickiness

Iota carrageenan

Soft capsule shell
sheet

1500 gf, "1,755
kg/force"

Viscosity

Iota carrageenan

Soft capsule shell
sheet

1800 cP

Scanning Electron
Microscopy (SEM)

Kappa carrageenan

Hard capsule shell

(Fauzi et al., 2020)

Iota carrageenan

Soft capsule shell

(Perwatasari et al.,
2025)

Parameter
Length
Width

Heavy
Leakage time

Disintegration

© 2025 The Authors.

Sources
(Perwatasari et al.,
2025)
(Fauzi et al., 2020)
(Perwatasari et al.,
2025)
(Fauzi et al., 2020)
(Perwatasari et al.,
2025)
(Fauzi et al., 2020)
(Perwatasari et al.,
2025)
(Perwatasari et al.,
2025)
(Zheng et al., 2023)
(Soraya et al., 2025)
(Fauzi et al., 2020)
(Pudjiastuti et al.,
2020)
(Pudjiastuti et al.,
2020)
(Hidayat et al.,
2024)
(Hidayat et al.,
2024) and (Djafar
et al., 2024)
(Hidayat et al.,
2024)

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Hidayat et. al.

carrageenan with alginate. Fauzi et al. (2020) combined kappa
carrageenan with maltodextrin (6:1) and added sorbitol. Soraya et al. (2025) used 22.5 g of kappa carrageenan, primogel,
and Tween 80. Djafar et al. (2024) combined carrageenan
with starch, glycerol, and sorbitol. Hidayat et al. (2024) used a
combination of iota carrageenan, modified starch, and glycerol.
Previous research regarding the characteristics of the capsules
produced can be seen in Table 5.
The process for making hard and soft capsule shells is different. Hard capsule shells can be dipped by mixing carrageenan
with distilled water and stirring them using a magnetic stirrer at
a temperature of 95°C until they are homogeneous. Then the
plasticizer is added to the solution and stirred. Next, the hot
plate is turned off, and printing begins. The molding process is
carried out by inserting the capsule shell tool into the solution
for 3 seconds, then removing and drying it. After drying, the
capsule is released from the mold and cut to the cap and shell
body size. Unlike hard capsules, divided into body and cap,
soft capsules are made, filled, and sealed in one process. When
making soft capsules, the gel strength required is lower than
that of hard capsules (Rowe et al., 2009) . In a beaker, soft
capsule shell films are made by mixing water with plasticizers (glycerol and sorbitol) and carrageenan. The mixture was
heated using a homogenizer for 30 minutes. After that, starch
is added, stirred, and heated to a temperature of 95°C. The
dough homogenized to a milky white color tends to be clear,
printed on 1.5 mm thick acrylic, and the surface is smoothed
(Djafar et al., 2024) .
The process for making hard and soft capsule shells is different. Hard capsule shells can be made by dipping them by
mixing carrageenan with distilled water and stirring them using
a magnetic stirrer at a temperature of 95°C until they are homogeneous. Then the plasticizer is added to the solution and
stirred. Next, the hot plate is turned off, and printing begins.
The molding process is carried out by inserting the capsule shell
tool into the solution for 3 seconds, then removing and drying
it. After drying, the capsule is released from the mold and cut
to the cap and shell body size. Unlike hard capsules, divided
into body and cap, soft capsules are made, filled, and sealed
in one process. When making soft capsules, the gel strength
required is lower than that of hard capsules (Rowe et al., 2009) .
In a beaker, soft capsule shell films are made by mixing water
with plasticizers (glycerol and sorbitol) and carrageenan. The
mixture was heated using a homogenizer for 30 minutes. After
that, starch is added, stirred, and heated to a temperature of
95°C. The dough homogenized to a milky white color tends
to be clear, printed on 1.5 mm thick acrylic, and the surface is
smoothed (Djafar et al., 2024) .
Iota carrageenan-based soft capsules have average dimensions of 13.56 mm in length and 7.48 mm in width, weighing
0.49 g. The leakage and disintegration times were quite long,
25.89 minutes and 66.44 minutes, respectively, indicating
good structural resistance to environmental conditions (Perwatasari et al., 2025) . These characteristics are reinforced with
a tensile strength of up to 2.3 MPa and an adhesion level (stick© 2025 The Authors.

Science and Technology Indonesia, 10 (2025) 1288-1300

iness) of up to 1,755 gf, indicating flexibility and mechanical
strength that is close to or even equal to gelatin (Hidayat et al.,
2024; Djafar et al., 2024) . Disintegration that exceeded the
standard in the Perwatasari et al. (2025) study can be caused by
the solid matrix formed by modified cassava starch combined
with iota carrageenan, which provides structural integrity and
prolongs the breakdown process.
According to Hidayat et al. (2024) , the more glycerol is
used, the tensile strength value of the soft capsule shell film will
increase. The results obtained have met the Japanese Industrial
Standard, namely a minimum tensile strength value of 0.39
MPa. The mixture of iota carrageenan with plasticizer showed
better thermal stability and tensile strength properties. In addition, increasing the amount of glycerol used will increase the
stickiness and viscosity of the capsule shell film. The increasing composition of iota carrageenan, starch, and glycerol can
increase the viscosity of the capsule shell film.
On the other hand, kappa carrageenan is more widely applied in hard capsules, with longer dimensions (22.56 mm)
and varying disintegration times depending on the formulation,
ranging from 12.80 to 36.21 minutes (Fauzi et al., 2020; Pudjiastuti et al., 2020; Soraya et al., 2025) . In the study of Soraya
et al. (2025) , an evaluation was conducted related to the dynamics of disintegration of seaweed capsules containing several
additional materials, such as Polyvinylpyrrolidone, Primogel,
Sodium Croscarmellose, and Sodium Carboxymethylcellulose. The results showed that using primogel in soft capsules
would result in lower capsule swelling ability, resulting in faster
destruction caused by reduced water retention and a less watersaturated matrix.
On the other hand, kappa carrageenan is more widely applied in hard capsules, with longer dimensions (22.56 mm)
and varying disintegration times depending on the formulation, ranging from 12.80 to 36.21 minutes (Fauzi et al., 2020;
Pudjiastuti et al., 2020; Soraya et al., 2025) . In the study,
Soraya et al. (2025) conducted an evaluation related to the dynamics of disintegration of seaweed capsules containing several
additional ingredients such as Polyvinylpyrrolidone, Primogel, Sodium Croscarmellose, and Sodium Carboxymethylcellulose. The results showed that the use of primogel in soft
capsules would result in lower capsule swelling ability resulting
in faster destruction, which was caused by reduced water retention and a less water-saturated matrix. In the study of Fauzi
et al. (2020) , it was shown that the manufacture of hard capsules based on carrageenan combined with maltodextrin and
sorbitol will produce a capsule swelling rate 3.6 times higher
than gelatin capsules under rapid dissolution conditions in a
weak acid medium. This indicates a good ability to withstand
disintegration compared to gelatin capsules. In the study of
Pudjiastuti et al. (2020) , the combination of carrageenan with
alginate and with starch was compared. The results showed
that carrageenan capsules with a combination of starch had
a stiffer structure than carrageenan capsules combined with
alginate. This is because starch is a semicrystalline material
containing the crystalline form of the amylose structure and
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Hidayat et. al.

the amorphous form of branched amylopectin. At the same
time, sodium alginate is a straight, unbranched polymer composed of two types of sugar acids- 𝛽 -D-mannuronic acid (M)
and 𝛼-L-guluronic acid (G)-which are connected through a
type 1→4 glycosidic bond. The overall structure is amorphous
or irregular. This causes the disintegration time of the starch
combination carrageenan capsule to be higher than that of the
alginate combination carrageenan capsule.
SEM (Scanning Electron Microscopy) characteristics of
carrageenan-based capsule shells conducted by Fauzi et al.
(2020) showed the presence of pores on the surface of the film,
while on the surface of the gelatin capsule shell film there were
no pores at the same magnification scale, so it can be concluded
that the pores of the carrageenan-based capsule shell are larger
than the pores of the gelatin capsule shell. The nature of the
carrageenan hydrogel causes these pores. In addition, the more
elastic mechanical properties of gelatin capsules can be seen
from the minimal cracks or break patterns in the SEM image.
In contrast, carrageenan capsules tend to be more fragile and
show more precise indications of microcracks. This difference
affects stability, release of active substances, and compatibility
in pharmaceutical and supplement applications.
These data indicate that both iota and kappa carrageenan
can produce capsules with competitive physical and mechanical properties, even without using gelatin. With formulation
optimization, carrageenan from tropical seaweed can qualify as
a base material for soft capsules, especially in terms of tensile
strength, viscosity, and shape stability.
6. Challenges Associated with Carrageenan Soft Capsules
In the development of plant-based soft capsules, selecting the
appropriate type of carrageenan is crucial to the success of the
formulation. Carrageenan consists of various kinds-namely,
kappa, iota, and lambda-each with distinct structural and rheological properties. Studies conducted by Ock et al. (2020) and
Oishi et al. (2018) have shown that iota-carrageenan is the most
suitable type for soft capsule production. Iota-carrageenan is
extracted through alkaline treatment from the red seaweed
Eucheuma denticulatum and possesses a structure rich in sulfate
groups-particularly 4-sulfate on D-galactose and 2-sulfate on
3,6-anhydro-D-galactose-which contributes to the formation
of elastic and flexible gels (Necas and Bartosikova, 2013) .
In contrast, kappa-carrageenan is more commonly used in
hard capsule formulations. Previous studies have indicated that
kappa-carrageenan, derived from seaweed, is a promising nongelatin alternative for hard capsules due to its gel strength and
viscosity comparable to gelatin (Soraya et al., 2024) . However,
the rheological characteristics required for soft capsules are
significantly more demanding, as they require gelling agents
with higher viscosity and elasticity (Naharros-Molinero et al.,
2024) .
Unlike kappa-carrageenan, which forms brittle and rigid
gels, iota-carrageenan produces softer and more elastic gels
(Alves et al., 2010) -a desirable feature for soft capsules that demand high flexibility and adequate mechanical strength (Hilliou,
© 2025 The Authors.

Science and Technology Indonesia, 10 (2025) 1288-1300

2021) . Thus, iota-carrageenan is considered more appropriate
for use as the primary material in soft capsule shells than other
carrageenan types.
Despite these advantages, using iota-carrageenan in soft
capsule formulations still encounters several technical and functional challenges, such as high viscosity, slow disintegration
time, poor solubility due to high molecular weight, and suboptimal mechanical strength. Carrageenan, particularly at effective
concentrations, tends to have high viscosity, complicating soft
capsules’ molding and filling processes. Excessive viscosity may
also hinder drug release from the capsule. A proposed solution is molecular depolymerization. For instance, Tecson et al.
(2021) demonstrated that ultrasonic-assisted depolymerization
significantly reduced carrageenan’s molecular weight and viscosity, up to 96.33% from its initial molecular weight, thereby
improving flow properties and accelerating disintegration.
Carrageenan-based capsules also tend to exhibit longer
disintegration than gelatin capsules (Gullapalli and Mazzitelli,
2017) , potentially delaying drug release and absorption. One
practical approach to address this is bacterial fermentation, as
Li et al. (2024) demonstrated, using marine bacteria Shewanella
sp. to depolymerize iota-carrageenan. After fermentation, the
apparent viscosity of the carrageenan was reduced by up to
84.10%, contributing to enhanced solubility and faster disintegration.
The complex structure of carrageenan also limits its solubility, hindering active compounds’ efficient release in the
digestive tract (Song et al., 2023) . In addition to depolymerization, formulation strategies such as the addition of co-polymers
or solubilizing agents—such as sodium alginate, glycerol, and
sorbitol—can improve solubility and facilitate a more uniform
distribution of active ingredients within the gel matrix, as reported by Perwatasari et al. (2025) . Furthermore, soft capsules
require shells that are both flexible and mechanically robust.
Unmodified carrageenan gels may be too brittle or weak. The
addition of film-forming agents and cross-linkers such as maltodextrin (Fauzi et al., 2020) has been shown to enhance the
gel strength of kappa-carrageenan. Similarly, combining carrageenan with modified starch or glycerol can improve capsule
elasticity and mechanical stability.
7. Future Research: Using Seaweed as A Substitute for
Gelatin In Soft Capsule Shells
Exploration of the development of capsules with seaweed carrageenan to replace gelatin is progressing. Several previous
studies have observed how tropical seaweed in Indonesia can
produce carrageenan of good quality and meet standards. The
quality of the carrageenan produced can be influenced by the
type of seaweed used, the age at which the seaweed is harvested,
the location of the seaweed habitat, and the extraction process
used, including the materials, temperature, and time used during extraction. The material used in the seaweed extraction
process is an alkaline solution. The quality of the carrageenan
produced can be applied as a thickener and gelling agent to be
used as a substitute for gelatin.
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Research on making capsule shells from carrageenan has
been widely carried out. If we look at the application of carrageenan in hard capsule shells, it meets the standards, and the
quality produced is similar to commercial capsules. Several researchers have researched making soft capsule shell films. Soft
capsule shells usually use carrageenan, starch, glycerol, and,
in some studies, even sorbitol. The type of carrageenan that
can be used in making soft capsule shells is iota carrageenan.
Iota carrageenan produced by previous researchers has shown
good carrageenan quality and meets standards. So it can be
used as raw material to make soft capsules. Future research
should be directed at developing plant-based soft capsules primarily from high-quality, low-cost seaweed with little or no
contaminants (chemical or microbial). An alternative to producing soft capsule shells for future research is engineering the
depolymerization process of iota carrageenan and modifying
kappa carrageenan, such as iota carrageenan. Carrageenan soft
capsule shells have comparable properties to commercial soft
capsule shells, thus showing good potential as an alternative to
gelatin soft capsule shells.
8. CONCLUSIONS
Iota carrageenan derived from tropical seaweed shows strong
potential as an alternative to gelatin in soft capsule formulations due to its ability to form elastic gels, biocompatibility,
and capacity to produce flexible films. However, key challenges
remain, including high viscosity, limited solubility, and slow
disintegration. Studies have demonstrated that structural modification (via fermentation or depolymerization), the addition of
plasticizers, and blending with other polymers such as modified
starch can significantly enhance the mechanical and functional
properties of carrageenan-based films. With optimized formulation and processing, carrageenan holds great promise as a
halal, environmentally friendly, and competitive material for
plant-based soft capsule development in modern drug delivery
systems.
9. ACKNOWLEDGEMENT
The authors are very grateful to the National Research and
Innovation Agency (BRIN) for funding the housing program
at the BRIN research and agricultural organization.
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