Extraction and Some Characteristics of Gelatin from Camel’s Skins

Gelatin is a natural protein originating from moderate hydrolysis of collagens. Collagen is obtained from skins, cartilage, bones and tendons from animals, such as cows (Abuibaid et al., 2020; Al-Hassan, 2020a; Zhou et al., 2022). Gelatin is a fat-free, cholesterol-free polymer originating from partially hydrolyzed collagen, where polypeptide bonds break down. It is widely used in food, pharmaceuticals and other industries for gelling, thickening, stabilizing and emulsifying. Its heat-reversible gel that melts near body temperature (Al-Hassan, 2020; Xu et al., 2017; Zhou et al., 2022). Major gelatin sources are extracted from pig’s skins, bovine hides and bones, which represent about 98% of global marketed gelatin. The remaining percentage (2%) gelatin was sourced from fish (Ahmed et al., 2020a; Al-Hassan, 2020). Gelatin types from the animal sources (i.e., pigs and cows) have been extensively marketed (Fawale et al., 2021; Kittiphattanabawon et al., 2010). Religious certificates (Halal in Islam or Jewish Kosher) and ethical concerns restrict gelatin consumption from porcine or bovine sources in many regions (Al-Hassan, 2020a; Kittiphattanabawon et al., 2010). Disease outbreaks, namely bovine spongiform encephalopathy (BSE), foot-and-mouth infections and swine flue have driven demands for safer gelatin sources (Ahmed et al., 2020a; Xu et al., 2017). Recently, fish gelatins are now  growing alternatives from processing wastes. (Ahmed et al., 2020a; Kittiphattanabawon et al., 2010; Zhou et al., 2022). In fact, fish gelatins had poorer quality, such as lower Bloom values (gel strength) and lower stability than the mammalian ones. Thus, they have limited applications (Ahmed et al., 2020a; Kittiphattanabawon et al., 2010). Mammalian gelatins have superior thermo-reversible gelling and water solubility and thus making them ideal for food and pharmaceutical applications (Abuibaid et al., 2020; Fawale et al., 2021). The U.S. gelatin market is expected to reach five billion USD by 2025, driving demand for nine hundred kilotons due to its use in functional foods and pharmaceuticals (Alipal et al., 2019). The food and other industries are prompted to search for alternative sources for halal gelatin from traditional origins of gelatins. At the large production scale, few halal alternatives from mammal sources are available as sources of gelatin production (Fawale et al., 2021). To this end, camel skins could supply gelatins that  meet religious needs. In Arabia and Africa, camels (one-hump, Camelus dromedarius) have been domestically raised for milk and meat sources and camel’s  skins could be alternative sources for gelatin (Al-Hassan, 2020a; Benyagoub et al., 2022; Demlie et al., 2023; Fawale et al., 2021). Worldwide, the camel population is about thirty five million and the wet skin is a major by-product representing up to 15% of slaughtered camels (Al-Hassan, 2020a; Fawale et al., 2021).  In fact, scarce information has been published on camel’s skin gelatin. Depending on the extraction method, there are the alkaline extracted gelatin (Type B) and the acid extracted type A gelatin from camel and other mammalian skins (Abuibaid et al., 2020; Ahmad et al., 2018, 2020; Al-Hassan, 2020b; Bessalah et al., 2023; Mulyani et al., 2017; Yu et al., 2016). Alkaline treatments weaken gelatin gel strength and thermal stability, take longer time and yield lower purity gelatins. Acid treatment releases more soluble proteins and fats efficiently (Mulyani et al., 2017).

This study investigates camel’s skin gelatin, covering extraction methods, composition and potential applications in food and pharmaceuticals. It highlights its properties, contributing to research on alternative gelatin sources.

Samples and other materials
 
Fresh camel skins were obtained from a slaughterhouse in Al-Omran, 23 km northeast of the university campus. Adult male camels (2-year-old) were selected, as preferred for meat. Samples were stored at -20^oC before analysis. Analytical-grade chemicals were used and experiments ran from 2023-2024 in the Food  and Nutrition Department, College of Agricultural and Food Sciences.
 
Gelatin extraction
 
Skin preparations and gelatin extraction were done as reported previously (Chen et al., 2014; Ma et al., 2018; Yu et al., 2016). Thawed skin pieces (1 kg) were rinsed under tap water to remove dirt, lightly squeezed, then soaked in 10% NaCl (5 L) for six h at room temperature.

After NaCl treatment, skin pieces were washed with running tap water, then soaked in 3500/ ml of 2% Ca(OH)‚  for fifteen/ h. Hair was manually removed and residual fat and meat were trimmed using a knife and scraper. Washing continued until the pH of squeezed water reached ~6.7. Un-haired skins were cut into ~2x1x1/ cm pieces, placed in polyethylene bags and frozen at -20^oC for fifteen/ h. After thawing at 5^oC, pieces were soaked in 1% HCl (1:10) for fifteen min. Skin pieces became thicker (swollen) and lighter in color after acid treatments. They were washed thoroughly with water until near neutrality (pH 6.8). Gelatin was extracted from skin in DDW (1:10) at 60^oC for six/ h in a digital water bath, with occasional stirring. The extract was filtered through a five-layer cheesecloth to remove residues. Extracted clear gelatin was lyophilized at -55^oC (1.3 mBar) using a FreeZone Triad Freeze Dry System (Labconco, MO, USA), then oven-dried at 55oC until constant weight (<2% moisture). Final gelatin weight was recorded.
 
Extracted gelatin from skin
 
Gelatin (hereafter CG) yields from camel’s skin were calculated using the formula below:
 

 

 
Where,
W1 = Original weight of skin in g.
W2 = Powdered gelatin in g.
 
Proximate composition of CG
 
Moisture, fat and ash of GC were analyzed by AOAC methods 942.05 and 920.39. Protein was determined by the Kjeldahl method using a nitrogen factor of 5.55 (Al-Hassan, 2020a; Sompie et al., 2015). All tests were done in triplicate.
 
pH of CG
 
pH of triplicate 1% gelatin solutions at 55^oC was measured using an ATC pH meter (ThermoScientific, USA) following US Pharmacopoeia (GMIA, 2019). The pH meter was calibrated with pH 4 and 7 buffers.
 
UV-Visible spectrum of CG
 
A 1% gelatin solution was prepared in DDW at 40^oC and scanned at 200-400/ nm against a DDW blank using an Evolution 201 spectrophotometer (Thermo Scientific, USA). Commercial bovine gelatin was used for comparison.
 
Amino acid composition by HPLC analysis
 
Gelatin (80/ mg) was hydrolyzed with 10/ ml 6N HCl and 600 ml 1% phenol using a microwave digestion system at 150^oC for 90/ min (Messia et al., 2008; Tran Jeong 2017).  Filtered samples were diluted prior to HPLC injections. Protein digestates were analyzed following a reported protocol (Henderson et al., 2000). HPLC analysis was performed using an Agilent 1260 Infinity system with a quaternary pump and auto-sampler (Agilent Technologies, Santa Clara, CA, USA). A Zorbax Eclipse AAA column (3.5 mm, 4.6 x 150 mm) and OPA/FMOC derivatives of digested gelatin were used. Data were analyzed using Agilent ChemStation3 (Model G1656B). Amino acid concentrations were quantified with an Agilent amino acid standard (250/ pmol ml in 0.1 M HCl).
 
Turbidity of CG
 
Gelatin solution (6.67%) turbidity was measured at 620 nm (GMIA, 2019) using a ThermoScientific Evolution spectrophotometer.
 
Gel strength (bloom)
 
Bloom strength was tested (6.67% gelatin, 60^oC and cooling to 10^oC for 17h) per GMIA (2019) using a texture analyzer (TA Texture Analyser XT plus, Stable Micro System, England, UK). Triplicate experiments were conducted.
 
Foam expansion (FE) and stability (FS)
 
FE of CG (1%) was assessed (40^oC, 35,000 rpm, 1 min) and compared to that of commercial bovine. FE measured volume increase and was recorded after 60 min (Abuibaid et al., 2020; Shahidi et al., 1995).
 
Fourier Transform Infrared Spectroscopy (FTIR)
 
FTIR spectra (4000-500 cm^-1, 4 cm^-1 resolution) of CG were obtained using KBr pellets (Abuibaid et al., 2020; Dai et al., 2020). The FTIR Affinity-1S (Shimadzu Corporation, Japan) was used for that purpose.
 
Data analysis
 
The results obtained of triplicate tests were processed using an Excel of MS Office 365.

Gelatin yield
 
Skin pretreatments yield two gelatin types; Type A (acid-soaked) and Type B (alkaline-soaked) (Al-Hassan, 2020a; Bahar et al., 2018; GMIA, 2012).

As shown in Table 1, the translucent gelatin (type A) constituted 5.4% ±2.11 of camel skin. The yield of CG extracted at 60^oC for 6h was closer to that mentioned by other researchers (Bessalah et al., 2023). Actually, there are very few reports on gelatin extraction from camel skins, by either acidic or alkaline processing of skins (Abuibaid et al., 2020; Ahmed et al., 2020b; Al-Hassan, 2020b; Bessalah et al., 2023). Depending on extraction temperatures and time, gelatin yield range was 9.5-28.6% (Ahmed et al., 2020). It was reported that 9.5% gelatin (camel skin) yield was obtained at 60^oC for five hours (Abuibaid et al., 2020). A similar yield (~9%) was also obtained under extraction temperature of 60^oC for six hours (Bessalah et al., 2023). An extreme gelatin yield (42%) from camel’s skin was reported (Al-Hassan, 2020b). It was stated that extraction conditions directly affected polypeptide chain length, functional properties and other quality parameters of gelatin (Al-Hassan, 2020). Harsh extraction conditions increased gelatin yield but reduced gel quality, while milder conditions improved gel properties despite lower yields (Abuibaid et al., 2020). In fact, in the present investigation a conventional protocol (Al-Hassan, 2020b; Alipal et al., 2019; Chen et al., 2014; Yu et al., 2016) of gelatin extraction at 60^oC for six hours was adopted. Regarding other sources, % yield of skin gelatin were 16.11, 15.95, 8.49 and 23.1%, from cows (Ahmad et al., 2018), goats (Fawale et al., 2021), rabbits (Yu et al., 2016) and fish (Sae-Leaw et al.,  2016), respectively.


 
pH of CG
 
The pH of gelatin solution was 3.89±0.13 (Table 1). The pH of gelatin from camel skins was 5.26 recorded during extraction at 71.9^oC for 3 m (Ahmed et al., 2020b). The pH values of other camel skin gelatins were 7.1 to 7.6 which were higher compared to bovine skin gelatin (pH 5.45) (Al-Hassan, 2020).
 
UV-Visible pattern of CG
 
Fig 1 shows the spectrum (200-400 nm) of CG solution. The bovine one also exhibited a maximum peak at 240 nm. The chromophore groups showed absorption at 210-240 nm indicated  presence of  peptide bond in gelatins (Das et al., 2017).


 
Composition of CG
 
Table 1 lists proximate composition of CG. Proteins were the major constituent (95.31%±0.94) in CG (Table 2). Their concentration was slightly higher than those reported by a previous publication where proteins ranged from 88.21 to 92.53% (Al-Hassan, 2020). From other animal species, protein contents were 89.8-91.3% for bovine, porcine and fish skin gelatins (Al-Hassan, 2020). Pretreatments of skin and extraction conditions would contribute to differences in protein contents of gelatin. Fat and ash were 1.19 and 1.07%, respectively (Table 1).


 
Amino acid composition by HPLC analysis
 
Amino acid concentrations in CG are listed in Table 2. The amino acid glycine (15.2%) was the predominant one. That corroborated previous reports where glycine was the major amino acid in gelatin extracted from camel’s skin (Ahmed et al., 2020; Al-Hassan, 2020). Meanwhile, glycine was also the major amino acid in gelatin from cow’s skin (18.18%) and in rabbit skins (22.2%) (Ahmad et al., 2018; Yu et al., 2016). Besides glycine, proline represented 12.26% of CG (Table 2). It was reported that proline was the second most abundant amino acid in gelatin from different sources (Ahmed et al., 2020b; Al-Hassan, 2020a; Yu et al., 2016). It is noteworthy to mention that functional properties of gelatins (e.g., gel strength) were associated to amino acid composition of proteins (Al-Hassan et al., 2021; Chen et al., 2014; Yu et al., 2016).

Clarity of gelatin
 
Turbidity of gelatin was related to insoluble and foreign matters (GMIA, 2012). The  absorbance (A) of CG solution was  0.25±0.11 (Table 3) and thus gelatin of our study was more transparent than those previously reported (Abuibaid et al., 2020; Al-Hassan, 2020a). Gelatine turbidity resulted from colloid particles or aggregates (GMIA, 2012). Additionally, higher temperature and longer extraction time elevated carbonyl-amino reactions in non-enzymatic browning (Abuibaid et al., 2020).


 
Gel strength of CG
 
Bloom measures gelatin strength and serves as a key quality indicator. As seen in Table 3, gel strength of CG was about 176 g. The gel strength is low (<150 g), medium (>150-220 g) and high (>220-300 g) (Ahmed et al., 2020). The gel strength of gelatins from camel skin extracted under different conditions were 196-293 g (Abuibaid et al., 2020). Despite the difference in the extraction conditions of camel skin, the bloom value of skin from the present study (Table 3) was very similar to that reported by Abuibaid et al., (2020). A highest gel strength (239 g) took place at 60^oC for 5 hours. Higher temperatures and longer times reduced Bloom values (Abuibaid et al., 2020). Lowest gel strength (72-122) of camel skin gelatin extracted at 75^oC for 3 h (Al-Hassan, 2020b) corroborated a previous finding on detrimental effects of higher temperature on gel strength of camel’s skin gelatin (Abuibaid et al., 2020). The gel strengths of gelatin from other skin sources were 554.90 for bovine (Ahmad et al., 2018), 320 for porcine (Chen et al., 2014) and 410 for rabbit  (Liu et al., 2019). For commercial demands, gelatins with  gel strengths of 50-260 g are used in some food, beverages, pharmaceuticals and other applications (Ahmed et al., 2020b; Alipal et al., 2019).
 
Foaming expansion (FE) and stability (FS)
 
The FE of CG solution (1%) was 134%±3.5 (Table 3). It was higher than those extracted at 60°C for 5-7h (Abuibaid et al., 2020; Bessalah et al., 2023). Camel skin gelatins showed higher FS values than bovine and porcine ones (Abuibaid et al., 2020). A very low FE (10%) was reported for camel skin gelatins (Ahmed et al., 2020). The FS of CG was 130%±14.1 (Table 3). Lower FS values (<110) were mentioned for camel skin gelatins (Abuibaid et al., 2020; Bessalah et al., 2023). Previous reports mentioned % FS  of 43% for bovine gelatin and 155% for goat skin gelatin (Abuibaid et al., 2020). Both FE and FS were associated with protein ability to migrate, adsorb and reorient at the air-water interface (Abuibaid et al., 2020). They are linked to their hydrophobic characteristics of proteins. Hydrophobic protein group increases may improve their functional properties (Ahmed et al., 2020b). Commercial bovine gelatin showed higher FE (164%) than CG but lacked FS (Table 3).
 
FTIR properties of CG
 
FTIR spectroscopy analyzes material structures, like gelatin, by identifying functional groups through infrared spectrum bands (Abuibaid et al., 2020; Bessalah et al., 2023).  Proteins consist of amino acids linked by amide bonds, with polypeptides exhibiting nine characteristic IR absorption bands, amide-A, B and I-VII (Nur Hanani et al., 2012). Fig 2 shows Amide A (3444 cm^-1), 3291 cm^-1, 1628 cm^-1 and 1559 cm^-1 bands. Gelatins from various sources showed IR absorption bands in the Amide region. The bands at 3285, 1632, 1550 and 1238 cm^-1 corresponded to Amide-A, glycine/water molecules, Amide I, II and III, respectively (Nur Hanani et al., 2012). Amide-A signified NH-stretching with hydrogen bonding; amide I, C=O stretching/hydrogen bonding with COO; amide II, N-H bending and C-N stretching; amide III, in-plane C-N, N-H, or CH2 vibrations (Nur Hanani et al.,  2012). FTIR spectrum (Fig 2) was very similar to those reported for camel skin gelatin. They were Amide A (3400-3300 cm^-1), band at 3309.38 cm^-1 (O-H stretching), Amide I at 1647.98 cm^-1 resulting from C-O stretching and band at 1543.13 cm^-1 representing amide II (-NH twisting mode) (Al-Hassan, 2020). Additionally, the presence of amide III band based on spectral features such as CN stretching vibration, NH deformation from amide linkages and wagging vibration from CH2 groups from amino acids glycine and proline (Al-Hassan, 2020). As reported by for camel skin gelatin (Bessalah et al., 2023), the absorption for hydrogen bonded N-H associated to amid A amide was at 3362 cm^-1. FTIR showed the absorption band at 1656 cm^-1 for C=O stretching (Amide I). GC (Fig 2) shows camel skin gelatin with similar FTIR spectra for Amide I, II, III and Amide-A to those of a previous report (Bessalah et al., 2023). Camel skin gelatins extracted under different conditions displayed a similar FTIR spectra (Abuibaid et al., 2020) to those of CG (Fig 2). The Amide A band in camel gelatin (3307-3315 cm^-1) occurred from N-H stretching with H-bonding. Gelatins generally show a broad Amide A band (3300–3400 cm^-1) with free N-H stretching (Abuibaid et al., 2020). The Amide-B band (2924 cm^-1)  in camel gelatin indicated C-H and -NH3+ stretching (Abuibaid et al., 2020). The Amide I (1629 cm^-1) and II (1548 cm^-1) wavenumbers reported earlier (Abuibaid et al., 2020) were very similar to those obtained from the present study on CG (Fig 2). The wavenumbers between 1238-1244 cm^-1 were associated with Amide III (Abuibaid et al., 2020). The Amide III indicated the a-helical transformation to a random coil structure which will result in the loss of triple helix structure. Furthermore, the amide-III peak represented a blend of N-H deformation and C-N stretching vibrations originating from amide linkages along with a response due to vibrations caused by CH2 groups from the glycine back-bone and proline side chains (Abuibaid et al., 2020). Amid A bands (3286-3291 cm^-1) and water molecules in beef, pork and Tilapia fish gelatins were reported (Nur Hanani et al.,  2012).

CG as an underutilized resource, offers sustainable potential for food, pharmaceutical and packaging applications. Its unique properties (clarity, gel strength, foaming) and cultural acceptability address limitations of traditional sources. CG-based films show promise for food preservation against oxidative degradation.

The present study was supported by the Deanship for Scientific Research (DSR) at the King Faisal University, Saudi Arabia, for funding this research through the project number KFU251318.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All animal procedures for experiments were approved by the Committee of Experimental Animal care and handling techniques were approved by the King Faisal University, Saudi Arabia (KFU-REC-2025-ETHICS3050).

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.