Physical and sensory properties of gelatin from

Received: 15 January 2017

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Revised: 18 April 2017

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Accepted: 27 May 2017

DOI: 10.1111/jtxs.12280

RESEARCH ARTICLE

Physical and sensory properties of gelatin from seabass (Lates calcarifer) as affected by agar and j-carrageenan Sittichoke Sinthusamran1 | Soottawat Benjakul1 1 Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand 2

School of Chemical Sciences, University of Auckland, Auckland 1142, New Zealand 3

Riddet Institute, Palmerston North, New Zealand

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Yacine Hemar2,3

Abstract Physical and sensory properties of gelatin from skin and swim bladder of seabass (SK and SW, respectively) as affected by agar or j-carrageenan at 10 and 20% substitution were investigated. Hardness of both SK and SW gels containing agar increased with increasing level of agar. However, the addition of j-carrageenan lowered hardness of mixed gels. Springiness and cohesiveness of either SK or SW gels decreased as the level of both agar or j-carrageenan increased. Gelling and melting temperatures generally increased when the level of hydrocolloids was increased. The

Correspondence Soottawat Benjakul, Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand. Email: [email protected]

highest gelling (36C) and melting temperatures (43C) were obtained for SK added with 20%

Funding information Thailand Research Fund (under the Royal Golden Jubilee PhD Program to Sittichoke Sinthusamran), Grant/Award Number: PHD/0053/2553; Graduate School, Prince of Songkla University, Thailand; TRF Distinguished Research Professor Grant

Practical applications

agar and 20% j-carrageenan, respectively. However, the addition of both hydrocolloids at 10% affected gel microstructure differently. Furthermore, the addition of agar at 10% could increase the likeness score of sensory properties of gelatin gel. Therefore, the addition of hydrocolloids with appropriate level could improve the texture and sensory properties of gelatin from seabass.

Due to the poor gelling property of fish gelatin, compared to its mammalian counterpart, improvement of this property using the selected hydrocolloids can be a promising means. In this work, it was found that agar or j-carrageenan can be incorporated to fish gelatin to improve gelling, textural and sensory properties of gelatin from skin of seabass (Lates calcarifer). Both agar and j-carrageenan could increase gelling and melting temperatures of seabass gelatin. The incorporation of hydrocolloids (agar and j-carrageenan) could also improve the quality of fish gelatin gel, which in turn can widen the applications of fish gelatin in the food and other industries. KEYWORDS

agar, gelatin, hydrocolloids, j-carrageenan, sensory property, texture properties

1 | INTRODUCTION

(Benjakul et al., 2012; Sadowska, Kołodziejska, & Niecikowska, 2003). Currently, an increasing interest has been paid to alternative sources of

Gelatin is a fibrous protein extracted from collagenous material by ther-

gelatin, particularly from the by-products of fish processing (Kittiphat-

mal denaturation. It is one of the most versatile biopolymers and has a

tanabawon, Benjakul, Sinthusamran, & Kishimura, 2010; Sinthusamran,

wide range of applications in food, pharmaceutical, cosmetic and pho-

Benjakul, & Hemar, 2014). However, the application of fish gelatin is

tographic industries (Regenstein & Zhou, 2007). Gelatin has been primarily produced from the skin and bones of pig and cow. However, the outbreak of bovine spongiform encephalopathy (BSE), foot-andmouth disease (FMD), as well as bird flu have resulted in anxiety among users of gelatin from land animals (Benjakul, Kittiphattanabawon, & Regenstein, 2012). Additionally, gelatin obtained from pig cannot be consumed by Muslims and Jews, due to religious restrictions

limited, due to its poor gelling property, compared to its mammalian counterpart (Muyonga, Cole, & Duodu, 2004). Gelatin from different fish species have varying thermal and rheological properties such as gel strength, gelling, and melting temperatures (Sinthusamran et al., 2014). The textural and sensory properties of gelatin gels are greatly influenced by their rheological properties, which are governed by their chemical compositions and chain length (Benjakul et al., 2012;

This article was published on AA publication on: 5 June 2017.

J Texture Stud. 2017;1–9.

Kołodziejska, Kaczorowski, Piotrowska, & Sadowska, 2004).

wileyonlinelibrary.com/journal/jtxs

C 2017 Wiley Periodicals, Inc. V

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To improve the property of fish gelatin, some polysaccharides can

Sinthusamran, Benjakul, Hemar, and Kishimura (2017), respectively.

be used as co-gelators. Polysaccharides possess several functional

Before gelatin extraction, skin and swim bladder were soaked in 0.1 M

properties, especially gelation (Lau, Tang, & Paulson, 2000). However,

NaOH with a sample/solution ratio of 1:10 (w/v) in order to remove

the effectiveness of individual polysaccharide on the improvement of

non-collagenous proteins. The mixture was stirred continuously for 3

gelatin can vary, due to their compatibility. For example, the interaction

hr at room temperature (28–30C) using an overhead stirrer with a pro-

of charged gelatin and polysaccharide macroions leads to the formation

peller (W20.n IKA-Werke GmbH & CO.KG, Staufen, Germany). The

of polyelectrolyte complexes (Derkach, Ilyin, Maklakova, Kulichikhin, &

alkaline solution was replaced every 1 hr, 3 times. The residues were

Malkin, 2015). The mixtures between gelatin and various polysaccha-

then washed with tap water until a neutral or faintly basic pH of wash

rides, such as maltodextrin, pectin, alginate, j-carrageenan and agar

water was obtained. The deproteinized matters were then mixed with

have been previously investigated (Haug, Draget, & Smidsrød, 2004;

0.05 M acetic acid at a sample/solution ratio of 1:10 (w/v) to swell the

& Larreta-Garde, 2009; Sinthusamran et al., 2016). When Panouille

collagenous material. The mixture was stirred at room temperature for

two biopolymers (protein and polysaccharides) are mixed together, dif-

2 hr. The swollen skin and swim bladders were washed using tap water

ferent behaviors can occur. In most cases, the mixtures of two or more biopolymers may lead to phase separation, which can be either associative (first phase being enriched in both polymers, the second one in solvent) or segregative (each phase being enriched with one of the two & Larreta-Garde, 2009). It was reported that biopolymers) (Panouille the addition of j-carrageenan into gelatin could improve the gelation rate, viscoelasticity, gel strength and melting temperature of the resulting mixture (Derkach et al., 2015). Sinthusamran, Benjakul, and Hemar (2016) reported that the addition of high levels of agar resulted in more brittle agar/gelatin gels. Failure stress of agar/gelatin gels increased as the levels of added agar increased (Sinthusamran et al., 2016). Lau et al. (2000) reported that the hardness of gellan/gelatin gels also increased as the level of added gellan increased. Seabass (Lates calcarifer) fish is of an economically importance to Thailand. Skin and swim bladder can be used for gelatin production, and their market values can be increased (Binsi, Shamasundar, Dileep, Badii, & Howell, 2009). To widen the uses of gelatin from seabass, the

until wash water became neutral or faintly acidic. To extract the gelatin, the swollen skin and swim bladders were mixed with distilled water at a ratio of 1:10 (w/v) with continuous stirring for 6 hr at 55 and 65C, respectively. The mixtures were filtered with two layers of cheesecloth. Then, the filtrates were mixed with 1% (w/v) activated carbon (Jacobi Carbons (Asia) Sdn Bhd, Penang, Malaysia) for 1 hr under continuous stirring for lowering fishy odor. The mixtures were centrifuged at 17,500 3 g for 15 min at 25C using a Beckman model Avanti J-E centrifuge (Beckman Coulter, Inc., Palo Alto, CA) to remove the insoluble material. The supernatants were filtered using a Buchner funnel with a Whatman No.4 filter paper (Whatman International, Ltd., Maidstone, England). Finally, the filtrates were freeze-dried using a freeze-dryer (CoolSafe 55, ScanLaf A/S, Lynge, Denmark) at 250C for 72 hr. Dry gelatins extracted from skin and swim bladder were referred to as “SK” and “SW,” respectively.

addition of some selected polysaccharides might improve the rheologi-

2.3 | Preparation of agar from Gracilaria tenuistipitata

cal, textural, and sensory properties of mixed gels. Nevertheless, there

The agar was extracted from the algae, Gracilaria tenuistipitata, follow-

is no information in the published literature on the textural and sensory properties of gelatin from skin and swim bladder of seabass as influenced by the addition of hydrocolloids. Therefore, the aims of this study were to investigate the impact of agar or j-carrageenan incorporation, at various levels, on the physical and sensory properties of gelatin from skin and swim bladder of seabass.

2 | MATERIALS AND METHODS

ing the method of Yarnpakdee, Benjakul, and Kingwascharapong (2015). Prior to extraction, dried algae were soaked in 5% NaOH, with an algae/solution ratio of 1:50 (w/v) for 24 hr at room temperature. The mixture was heated at 90C for 3 hr with continuous stirring using an overhead stirrer. After alkaline treatment, the algae were washed in tap water until a neutral pH was obtained. Finally, the pretreated algae were mixed with distilled water at a ratio of 1:50 (w/v) at 95C for 2 hr. The mixture was firstly filtered through a cheesecloth. The filtrate was

2.1 | Gelatins and j-carrageenan

further filtered under pressure using a Buchner funnel with a Whatman

All chemicals were of analytical grade. Fish gelatin produced from tila-

and allowed to gel at room temperature (25–26C). The gel was subse-

pia skin (240 bloom) was obtained from Lapi Gelatine S.p.A (Empoli,

quently frozen for 24 hr and thawed at room temperature for approxi-

Italy). Food grade bovine bone gelatin with a gel strength of 150–

mately 4 hr. Thereafter, the thawed gel was frozen for another 24 hr

250 g was purchased from Halagel (Thailand) Co., Ltd. (Bangkok,

prior to freeze-drying. The dried matter was blended and sieved (20

Thailand). j-Carrageenan powder with gel strength of 508 g (1.5% w/v,

mesh), and the powder was referred to as “agar.”

No. 4 filter paper. The filtrate was transferred into plastic container

at 20C) was procured from High Science Co, Ltd. (Songkhla, Thailand).

2.4 | Preparation of gelatin/hydrocolloids mixed gels 2.2 | Preparation of gelatin from seabass skin and swim bladder

Gelatins (SK or SW) and hydrocolloids (agar or j-carrageenan) were separately solubilized in distilled water at 60C and 95C, respectively.

Gelatins were extracted from the skin and the swim bladder of seabass

Solutions of agar (GA) or j-carrageenan (KC) were mixed with gelatin

according to the methods of Sinthusamran et al. (2014) and

solution to obtain a mixed solution with 10 and 20% gelatin

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substitution. Those samples were named as: SK-10GA, SK-10KC, SW-

the tubes were weighed (m2) again after discarding the supernatant.

10GA, or SW-10KC, for SK and SW gelatin mixed with GA or KC to

The percentage of syneresis was calculated as follows:

obtain 10% substitution. Similarly, SK-20GA, SK-20KC, SW-20GA, or SW-20KC refer to SK and SW gel containing GA or KC with 20% sub-

Syneresis ð%Þ5

ðm12m2Þ 3100 m1

(2)

stitution. Total solid content of all solutions was 6.67% (w/v). The mixtures were transferred to cylindrical molds with a 3 cm diameter and 2.5 cm height. The molds were incubated at refrigerated temperature

2.5.4 | Determination of gelling and melting temperatures

for 18 h. The mixed gel samples were then subjected to analyses and

Gelling and melting temperatures of gelatin and gelatin-hydrocolloid

compared to commercial bovine gelatin (BG) and commercial fish gela-

mixtures were measured following the method of Sinthusamran et al.

tin (FG).

(2014). The measurement was performed using a RheoStress RS1 rheometer (HAAKE, Karlsruhe, Germany) in the oscillatory mode. The

2.5 | Analyses

measuring geometry used was a stainless steel 60 mm diameter parallel plate and the gap was set at 1.0 mm. All samples were incubated at

2.5.1 | Texture profile analysis

60C for 30 min. Then the solution (2.9 mL) was loaded on the Peltier

Texture profile analysis (TPA) was performed using a TA-XT2 texture

plate and equilibrated at 60C for 5 min before measurements. The

analyzer (Stable Micro Systems, Surrey, UK) with a load cell of 50 kg,

measurements were conducted at a constant frequency of 1 Hz, and a

equipped with a 5.0 cm diameter flat-faced cylindrical aluminum probe.

constant applied stress of 3 Pa. The samples were cooled from 60 to

Gel samples were placed on the instrument’s base, and the tests con-

5C and subsequently heated to 90C at a constant rate of 1.0C/min.

sisted of two compression cycles with a time interval of 5 s. TPA

The gelling and melting temperatures were calculated, where tan d

textural parameters were measured at 8–10C using a crosshead speed

became 1 (d 5 458).

of 1.0 mm/s and 50% compression of the original sample height. Hardness (the maximum force peak on the first compression cycle), springiness (the height recovered during the time between the end of the first compression and the start of the second compression), cohesiveness (the ratio of the area under the first and second compression), gumminess (the hardness multiplied by cohesiveness), and chewiness (the hardness multiplied by cohesiveness and springiness) were calculated from the force–time curves generated for each sample (Lau et al., 2000; Yang, Wang, Jiang, Oh, Herring, & Zhou, 2007).

2.5.2 | Determination of gel color The color of gel samples was measured by a Hunter lab colorimeter (Color Flex, Hunter Lab Inc., Reston, VA). L*, a*, and b* values indicating lightness/brightness, redness/greenness, and yellowness/blueness, respectively, were recorded. The colorimeter was warmed up for 10 min and calibrated with a white standard (L* 5 90.77, a* 5 21.27, and b* 5 0.50). Total difference in color (DE*) was calculated according to the following Equation 1 (Gennadios, Weller, Hanna, & Froning, 1996): qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi (1) DE 5 ðDL Þ2 1 ðDa Þ2 1 ðDb Þ2

2.5.5 | Sensory evaluation Fifty non-trained panelists (aged between 25 and 40 years) were selected. They were the students and staffs from the Department of Food Technology, who were acquainted with gelatin products. Gel samples were cut into a bite-size (1 cm thickness and 2 cm diameter) and coded with three-digit random numbers. Gel samples (8–10C) were served on dishes at room temperature under a fluorescent daylight-type illumination. The samples stored at 4C were removed from the refrigerator and served to the panelists within 2–3 min, in which the core temperature was not above 10C. The panelists were asked to evaluate for the appearance, color, odor, texture, melting characteristic, and the overall liking of gel samples using a 9-point hedonic scale (1, extremely dislike; 2, very much dislike; 3, moderately dislike; 4, slightly dislike; 5, neither like nor dislike; 6, slightly like; 7, moderately like; 8, very much like; 9, extremely like) (Meilgaard, Carr, & Civille, 2006). Between samples, the panelists were asked to rinse their mouth with filtered water.

where DL*, Da*, and Db* are the differences between the correspond-

2.5.6 | Microstructure analysis of gelatin gel

ing color parameter of the sample and that of the white standard.

The microstructure of gels from SK and SW without and with GA and KC at 10% substitution, prepared as previously described, was visual-

2.5.3 | Determination of syneresis

ized using scanning electron microscopy (SEM). Gelatin gels having a

Gel syneresis was determined as described by Banerjee and Bhatta-

thickness of 2–3 mm were fixed with 2.5% (v/v) glutaraldehyde in

charya (2011). All gelatin or gelatin-hydrocolloid solutions (30 mL) were

0.2 M phosphate buffer (pH 7.2) for 12 hr. The samples were then

poured into 50 mL graduated centrifuge tubes and their masses (m1)

rinsed with distilled water for 1 hr and dehydrated in ethanol with

were recorded. The solutions were allowed to cool at room tempera-

serial concentrations of 50, 70, 80, 90, and 100% (v/v). Dried samples

ture for 15 min, followed by incubation at 4C for 12 hr to form the gel.

were mounted on a bronze stub and sputter-coated with gold (Sputter

The resulting gels were equilibrated at room temperature for 3 hr

coater SPI-Module, West Chester, PA). The specimens were observed

before centrifugation at 2,150 3 g at 25C for 10 min using a Beckman

with a scanning electron microscope (JEOL JSM-5800 LV, Tokyo,

Coulter centrifuge (Palo Alto, CA). After centrifugation, gels along with

Japan) at an acceleration voltage of 20 kV.

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Hardness, springiness, cohesiveness, gumminess and chewiness of gel from seabass skin, and swim bladder gelatins mixed with agar or carrageenan at different levels

TA BL E 1

Hardness (N)

Springiness (cm)

Cohesiveness

Gumminess (N)

Chewiness (N 3 cm)

BG

34.77 6 0.17E

0.98 6 0.00A

0.89 6 0.00A

30.88 6 0.12E

34.09 6 0.22E

FG

34.00 6 0.22E

0.97 6 0.01A

0.90 6 0.01A

30.62 6 0.25E

33.12 6 0.21E

Gelatin sample

Level/hydrocolloid

SK-

0 10GA 20GA 10KC 20KC

44.01 6 0.40cD 50.18 6 0.78bC 62.95 6 1.16aA 35.02 6 1.17dE 34.77 6 0.75dE

0.98 6 0.01aA 0.97 6 0.00bAB 0.95 6 0.00cBC 0.97 6 0.01aA 0.96 6 0.00bAB

0.89 6 0.01aA 0.86 6 0.00bB 0.72 6 0.01dE 0.84 6 0.01bB 0.75 6 0.02cD

39.06 6 0.74cD 42.96 6 0.49bC 45.48 6 1.51aB 29.28 6 1.18dEF 26.13 6 1.38eG

43.13 6 0.47cD 48.45 6 0.73bC 59.72 6 1.13aA 34.11 6 1.38dE 33.55 6 0.86dE

SW-

0 10GA 20GA 10KC 20KC

42.28 6 0.48cD 48.92 6 2.01bC 60.00 6 4.18aB 35.02 6 1.17dE 36.07 6 0.02dE

0.98 6 0.00aA 0.97 6 0.01abAB 0.94 6 0.03cC 0.98 6 0.00aA 0.97 6 0.00abA

0.88 6 0.01aA 0.85 6 0.00bB 0.81 6 0.00cC 0.85 6 0.01bB 0.80 6 0.01cC

37.29 6 0.81cD 41.79 6 1.84bC 48.74 6 3.40aA 30.60 6 0.54dE 27.71 6 0.41dFG

41.48 6 0.47cD 47.25 6 1.70bC 56.55 6 5.73aB 34.26 6 1.24dE 34.82 6 0.13dE

Note. Values are presented as mean 6 SD (n 5 3). Different lowercase letters in the same column within the same gelatin sample indicate significant differences (p < .05). Different uppercase letters within the same column indicate significant differences (p < .05). Numbers (10, 20) in front of GA or KC represent concentration (%) of hydrocolloids added. BG 5 bovine gelatin; FG 5 fish gelatin; SK 5 seabass skin gelatin; SW 5 seabass swim bladder gelatin; GA 5 agar; KC 5 j-carrageenan.

2.6 | Statistical analysis

containing j-carrageenan might be associated with the phase separation between the two biopolymers present in the mixed gel. It was

All experiments were run in triplicate using three different lots of samples. Data were subjected to analysis of variance (ANOVA) and mean comparisons were carried out using the Duncan’s multiple range test (Steel & Torrie, 1980). A Randomized Complete Block Design (RCBD) was used for analysis of acceptance test. Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS for

previously reported that the addition of carrageenan induced phase separation in mixed gelatin/carrageenan gel (Doublier, Garnier, Renard, & Sanchez, 2000). In the present study, agar was found to be more efficient in increasing the hardness of gelatin gel, compared to carrageenan. Therefore, the gel strength of gelatin was dependent on the levels and the type of hydrocolloids added.

windows: SPSS Inc., Chicago, IL).

3.1.2 | Springiness

3 | RESULTS AND DISCUSSION

The gelatin and gelatin mixed with agar or j-carrageenan gels at different levels have different springiness as shown in Table 1. Springiness is

3.1 | Textural properties of gelatin gel as affected by agar and K-carrageenan 3.1.1 | Hardness

a perception of gel “rubberiness” in the mouth, and indicates how much the gel structure is broken by the initial compression (Lau et al., 2000). Springiness of gelatin (BG, FG, SK, and SW) gels alone was in the range of 0.97–0.98. Springiness of SK gel decreased with increas-

Hardness of gels from various gelatins and gelatins mixed with agar or j-carrageenan at different levels is shown in Table 1. Hardness of SK and SW samples was 44.01 and 42.28 N, respectively. Their hardness was higher than that of BG (34.77 N) and FG (34.00 N) gels (p < .05). On the other hand, Boran, Mulvaney, & Regenstein (2010) reported that porcine and bovine gelatin gels have higher

ing level of agar (p < .05). When j-carrageenan was higher than 10%, springiness of mixed gel decreased (p < .05). However, there was no difference in springiness among all gels (p < .05), except for SK and SW containing agar at 20%, which showed a lower springiness value (p < .05). It was reported that polysaccharides with less springiness such as low-methoxyl pectin, carrageenan and agar gels might break

hardness than fish gelatin. Hardness is related to the strength of gel

down more easily during compression than gelatin gel (Lau et al.,

structure under compression (Boran et al., 2010; Lau et al., 2000).

2000). The incorporation of polysaccharides into gelatin gel could

The hardness of both SK and SW gels increased as the level of agar

therefore reduce the springiness of mixed gel. The incorporation of

added increased (p < .05). The highest hardness was observed for

agar (10%) or carrageenan (10 and 20%) into either SK or SW gels had

SK-20GA gel (p < .05). In contrast, when j-carrageenan was incorpo-

no marked impact on springiness of resulting mixed gels (p > .05). How-

rated into SK or SW gels, the resulting mixed gel showed a decrease

ever, the addition of agar at a level higher than 10% lowered the

in hardness, regardless of the gelatin types (p < .05). Nevertheless,

springiness of gelatin gels from seabass skin and swim bladder.

there was no difference in hardness between gelatin gels containing 10 and 20% j-carrageenan (p > .05). The results indicate that SK or

3.1.3 | Cohesiveness

SW gels containing agar had the higher hardness than those mixed

Cohesiveness of different gelatin gels without and with agar or

with j-carrageenan (p < .05). The lowered hardness of mixed gel

j-carrageenan at different levels is presented in Table 1. Cohesiveness

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of FG, BG, SK, and SW gel sample was 0.90, 0.89,0.89, and 0.88,

3.1.5 | Chewiness

respectively, which were higher than those of SK or SW gels with

Chewiness is related to the energy required to masticate a solid food

added agar or j-carrageenan (p < .05). Cohesiveness is a measure of

to a state ready for swallowing (Yang et al., 2007). Chewiness of both

the degree of difficulty in breaking down the internal structure of the

SK and SW gels increased with increasing levels of agar (p < .05) (Table

gel (Lau et al., 2000). For a given gelatin, cohesiveness of gels

1). Nevertheless, chewiness of gel decreased when the carrageenan

decreased with the increasing level of agar or carrageenan (p < .05).

content was increased (p < .05). SK and SW containing agar gels have

Furthermore, at the same level of hydrocolloids used, no difference in

higher chewiness than BG and FG samples (p < .05). The lowest chewi-

cohesiveness is observed for both SK and SW gels. On the other hand,

ness was found in both SK and SW gels containing 10 and 20%

Lau et al. (2000) reported that the incorporation of gellan into gelatin

j-carrageenan (p < .05). The highest chewiness was found for SK gel

resulted in the increase in cohesiveness of the gel structure. In this

added with 20% agar (p < .05). The result suggested that the incorpora-

study, the internal structure of gelatin gel alone could be more difficult

tion of agar into gelatin gel more likely affected the chewiness of mixed

to break, when compared to gelatin gel containing hydrocolloids, espe-

gel. Gel from channel catfish skin gelatin with the higher chewiness

cially at higher levels (20%). Generally, most of the gel matrix is not

was considered as a better quality gel (Yang et al., 2007). Thus, the

broken during the first compression, and more energy is required to

addition of agar into SK and SW gelatins could improve the chewiness

break the remaining gel matrix during the second compression, leading

of resulting gels.

to an increased toughness (Lau et al., 2000). Therefore, agar and j-carrageenan addition decreased the cohesiveness of gelatin gels from seabass skin and swim bladder.

3.2 | Color The color of gels from various gelatins without and with agar or j-carrageenan at different levels expressed as L*, a*, b*, and DE* is shown in Table 2. In general, FG and BG gels had a higher lightness (L*-

3.1.4 | Gumminess

value), compared with SK and SW gels as well as all gelatin gels mixed

Gumminess is the energy required to break down a semi-solid food

with hydrocolloids (p < .05). The L*-value of gelatin-hydrocolloid gels

ready for swallowing (Yarnpakdee et al., 2015). Gumminess of

decreased when the content of both agar and j-carrageenan increased

gelatin gels in the absence and presence of agar or j-carrageenan at

(p < .05). However, no differences in L*-value between SW gels

different levels is shown in Table 1. For both SK and SW gels,

containing 10 and 20% agar were observed (p > .05). Among all gel

gumminess increased as the levels of agar increased (p < .05).

samples, SW gels with 10 or 20% agar and 20% j-carrageenan showed

However, when j-carrageenan was added into gelatin gel, gummi-

the lowest L*-value, compared with others gelatin samples (p < .05).

ness of mixed gels decreased (p < .05). Decrease in gumminess of

The lowest redness (a*-value) was found in FG gel (–1.81), followed by

gelatin/carrageenan mixed gel is related to the decrease in hardness

BG gel (0.73) (p < .05). SK gel had higher a*-value than SW gel

of the gels (Table 1). The highest gumminess was observed in SW

(p < .05). The incorporation of agar or carrageenan into gelatin gel

gels containing 20% agar, compared to other gel samples (p < .05).

increased a*-value of SK and SW gel (p < .05). The yellowness (b*-

The result suggests that the incorporation of agar increased the

value) of mixed gel decreased as levels of agar or carrageenan

gumminess of gelatin gels.

increased (p < .05). However, the addition of agar at 10% had no

TA BL E 2

Color (L*, a*, b*, and DE*) of gel from seabass skin gelatin and swim bladder gelatins mixed with agar or carrageenan at different

levels Gelatin sample

Level/hydrocolloid

L*

BG

64.41 6 1.71B

FG

74.47 6 2.29A

a* 0.73 6 0.11H 21.81 6 0.07I

b*

DE*

31.00 6 1.13A

41.74 6 0.34G

9.64 6 0.35I

20.51 6 1.90H

SK-

0 10GA 20GA 10KC 20KC

55.40 6 0.72aC 52.22 6 0.69bD 48.69 6 0.01cE 52.60 6 0.60bD 41.50 6 0.32dG

1.66 6 0.08dG 3.36 6 0.56bC 3.61 6 0.03bB 3.78 6 0.03cB 4.30 6 0.16aA

25.44 6 0.21aC 24.77 6 1.21aC 19.47 6 0.11cE 23.85 6 0.17bD 19.43 6 0.13cE

44.82 6 0.49dF 47.52 6 0.10bcD 48.26 6 0.04bD 46.64 6 0.40cE 57.60 6 0.25aA

SW-

0 10GA 20GA 10KC 20KC

53.09 6 0.39aD 39.38 6 0.51cH 38.10 6 0.28cH 45.32 6 1.18bF 38.15 6 0.34cH

2.02 6 0.03dF 2.72 6 0.16cE 3.13 6 0.18bCD 3.21 6 0.12bCD 3.80 6 0.10aB

26.29 6 0.3aB 15.50 6 0.11dG 11.52 6 0.18eH 23.40 6 0.68bD 18.08 6 0.19cF

47.53 6 0.30dD 55.61 6 0.53bB 55.97 6 0.23bB 53.41 6 0.17cC 57.80 6 0.17aA


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Therefore, the incorporation of carrageenan and agar in gelatin gel increased the syneresis of the resulting mixed gels.

3.4 | Gelling and melting temperature Gelling and melting temperatures of various gelatins without and with agar or j-carrageenan at different levels are shown in Table 3. Gelling and melting temperatures of various gelatins were in the range of 16.74–21.99C and 25.21–31.67C, respectively. Among all gelatin (without hydrocolloids), BG exhibited higher gelling and melting temperatures, compared with SK, SW, and FG samples (p < .05). The lowest gelling (16.74C) and melting (25.21C) temperatures were found in F I G U R E 1 Syneresis of gel from seabass skin and seabass swim bladder gelatins mixed with agar or carrageenan at different levels. BG: bovine gelatin, FG: fish gelatin, SK: seabass skin gelatin, SW: seabass swim bladder gelatin, GA: agar, KC: j-carrageenan. Bars represent the standard deviation (n 5 3). Different lowercase letters on the bars within the same gelatin sample indicate significant differences (p < .05). Different uppercase letters on the bars indicate significant differences (p < .05)

impact on the b*-value of SK gel (p > .05). The highest b*-value (31.00) was found in gel from BG gel (p < .05). The higher yellowness in gelatin gel from bovine bone might be affected by the harsher extraction process required for bone due to its complex structure, leading to the formation of coloring components (Kittiphattanabawon et al., 2016). For total difference in color value (DE*-value), FG gel exhibited the lowest DE*-value (20.51), compared to other gel samples (p < .05). DE*-value of gel increased when agar or carrageenan contents were increased (p < .05). SK gel generally had higher DE*-value than SW gel. The result suggested that color of individual hydrocolloids as well as the interaction between biopolymer affected the color of mixed gels. It can be inferred that the addition of either agar or j-carrageenan had an impact on the color of gelatin gel.

3.3 | Syneresis Syneresis of gels from different gelatins in the absence and presence of agar or j-carrageenan at various levels after storage for 12 hr at room temperature (25C) is shown in Figure 1. Syneresis is the phenomenon of liquid being exuded from a gel and this is basically undesir-

FG (p < .05). No difference in gelling and melting temperatures was observed between SK and SW gels (p > .05). In general, the differences in setting and melting temperature of gelatin are governed by molecular weight distribution (Muyonga et al., 2004; Sinthusamran et al., 2014). Gelling and melting temperatures of SK or SW mixed with agar increased as the level of agar increased (p < .05), except for gelatin mixed with 10% agar. Gelling temperature of gelatin gel containing j-carrageenan increased as the level of j-carrageenan increased (p < .05). The results suggested that the interaction between gelatin and hydrocolloids (agar and j-carrageenan) could enhance gelation of the mixtures as indicated by the increased gelling and melting temperatures. Derkach et al. (2015) reported that the gelation rate of gelatin increased with increasing concentration of j-carrageenan. This might be associated with the formation of polyelectrolyte complexes. The increase in the melting temperature with increasing j-carrageenan was also reported by Pranoto, Lee, and Park (2007). Nevertheless, SW gels containing j-carrageenan (10 and 20%) had no impact on melting temperatures (p > .05). Among all gel samples, the highest gelling Gelling and melting temperatures of seabass skin and swim bladder gelatins mixed with agar or carrageenan at different levels

TA BL E 3

Gelatin sample

Gelling temperature

Melting temperature

BG

21.99 6 0.58E

31.67 6 0.66C

FG

16.74 6 0.97H

25.21 6 0.71E

SK-

0 10GA 20GA 10KC 20KC

19.87 6 1.10dFG 20.87 6 1.04dEF 28.92 6 0.85bC 25.2610.42cD 36.27 6 0.41aA

28.98 6 0.58cD 31.58 6 0.81bC 43.40 6 1.89aA 31.30 1 0.83bC 33.97 6 0.56bB

SW-

0 10GA 20GA 10KC 20KC

18.62 6 0.46eG 20.76 6 0.65dEF 27.71 6 0.57bC 24.38 6 1.01cD 33.27 6 0.84aB

28.55 6 0.57cD 30.82 6 1.00bC 42.66 6 0.87aA 28.97 6 0.56cD 28.45 6 0.45cD

able for gel product (Haug & Draget, 2011). In general, gelatin gel alone (BG, FG, SK, and SW) showed a lower syneresis than those mixed with agar or j-carrageenan (p < .05). Syneresis of mixed gels increased when agar or carrageenan at level higher than 10% were added (p < .05). The incorporation of agar or carrageenan at 10% had no impact on syneresis of mixed gels (p > .05). The highest syneresis was found in SK and SW gels containing 20% j-carrageenan (p < .05). The presence of carrageenan at higher level (20%) might decrease interaction between the gelatin and carrageenan molecules. This might result in a non-ordered network, which had poorer water holding capacity as indicated by the increased syneresis. However, Banerjee and Bhattacharya (2011) reported that an increase in the levels of hydrocolloids (gellan and agar) decreased the syneresis of gelatin mixed gel.

Level/ hydrocolloid


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7

temperature was found in SK gel containing 20% j-carrageenan, while

caused by the increased gel turbidity, resulting in a decreased lightness

SK or SW gels containing 20% agar showed the highest melting tem-

value (Table 2). Texture likeness score of mixed SW gels increased

perature (p < .05). Mixed gels were more thermally stable, especially

when agar or j-carrageenan at a level of 10% was incorporated

when agar at high level was present. This was evidenced by the

(p < .05), except for SW gel containing 20% carrageenan. The addition

increased melting temperature of resulting gels. Increase in gelling tem-

of both hydrocolloids into gelatin gel likely affected the gel texture,

perature of gelatin gel containing polysaccharide (k-carrageenan) could

especially the hardness (Table 1). Nevertheless, the addition of both

be related to water distribution between gelatin and polysaccharide

hydrocolloids at 10% had no impact on texture likeness score of SK

(Tolstoguzov, 1995). Additionally, the increasing concentration of gela-

gels. Drastic increase in hardness of mixed gel negatively affected the

tin also affected melting and gelling temperatures of gelatin (Osorio,

textural properties of gelatin gel as shown by the decreased likeness

Bilbao, Bustos, & Alvarez, 2007). The result suggested that both agar

score of the texture of the gel containing 20% hydrocolloids. However,

and j-carrageenan strongly affected the thermo-stability of gelatin and

the addition of both hydrocolloids at 20% had no effect on the likeness

the level of both hydrocolloids played a role in the complexation of the

score of melting characteristic of both gelatins (SK and SW gels) (p >

mixed gel systems.

.05). The addition of hydrocolloids at optimum level could improve the melt-in-mouth property during ingestion of gelatin gel, which is a

3.5 | Sensory properties

unique characteristic of gelatin gels (Zhou & Regenstein, 2007). SK gel

Scores of appearance, color, odor, texture, melting characteristic and overall likeness of gels from BG, FG, SK, SW, and SK or SW mixed with agar or j-carrageenan at different levels are presented in Table 4. In general, BG and FG gel samples showed no differences in likeness scores for all attributes (p > .05). Appearance, color, odor, texture, and melting characteristic likeness scores of SK and SW gel alone showed

added with 10% agar had the comparable overall likeness, compared to FG gel (p > .05). Therefore, the addition of hydrocolloid at an optimum level might be used to improve the sensory properties of gelatin gel from seabass skin and swim bladder.

3.6 | Gel microstructure

similar result to that of BG and FG gel samples (p > .05). Moreover, no

Microstructures of BG and FG as well as SK and SW gels without and

differences in appearance, color, odor, and texture likeness between

with agar or j-carrageenan at 10% are illustrated in Figure 2. The

FG and SK samples were observed (p > .05). Melting characteristic like-

microstructure of gel is believed to be directly related to the strength

ness scores of SK gel containing agar or j-carrageenan at 10%

of gel, which is governed by the conformation and chain length of gela-

increased (p < .05). Moreover, there was no difference in appearance,

tin (Benjakul, Oungbho, Visessanguan, Thiansilakul, & Roytrakul, 2009).

odor and texture likeness scores between SK gel and SK gel with

Generally, all gelatin gels showed sponge or coral-like structures. SK

added agar or j-carrageenan at a level of 10% (p > .05). Nevertheless,

and SW gel exhibited similar gel network, with a finer structure and

the addition of either agar or j-carrageenan at 10% increased the melt-

denser strands in the gel matrices, when compared to BG and FG gels.

ing characteristic likeness score of the gelatin samples. Decreases in

This could be related to the higher hardness of SK and SW, in compari-

appearance and color likeness score of mixed gels were more likely

son with BG and FG (Table 1), which also exhibit thinner strands

Likeness score of appearance, color, odor, texture, melting characteristic, and overall of gel from seabass skin and swim bladder gelatins mixed with agar or carrageenan at different levels

TA BL E 4

Attributes Gelatin sample

Level/ hydrocolloid

Appearance

Color

Odor

Texture

Melting characteristic

Overall

BG

7.30 6 1.45ABC

7.40 6 1.14ABC

7.30 6 1.38ABC

7.30 6 0.92ABC

6.70 6 1.22ABCD

7.43 1 0.87AB

FG

7.80 6 1.11A

7.40 6 2.06ABC

7.50 6 1.40A

7.70 6 1.22A

7.50 6 1.15A

7.80 1 1.11A

SK-

0 10GA 20GA 10KC 20KC

7.40 6 0.82abAB 8.00 6 0.79aA 6.05 6 1.85dEFG 6.80 6 1.70bcBCD 6.60 6 0.50cdCDE

7.00 6 1.21bcBCD 8.10 6 0.85aA 6.25 6 1.83cDE 6.90 6 1.41bcBCD 7.10 6 1.07bBC

6.80 6 1.39abABC 7.40 6 1.31aAB 6.00 6 1.84bD 6.70 6 1.59abABCD 6.00 6 1.84bD

7.30 6 0.66abABC 7.50 6 1.47aAB 6.75 6 1.07bcBCD 7.60 6 0.94aA 6.60 6 1.39cCD

6.58 6 1.29bcBCD 7.30 6 1.22aABC 6.60 6 1.27bcBCD 7.50 6 0.69aA 6.50 6 1.79cCD

7.15 6 1.17bB 7.90 6 0.85aA 6.45 6 1.28cCDE 7.30 6 1.03abAB 6.40 6 1.05cDE

SW-

0 10GA 20GA 10KC 20KC

7.50 6 0.95aAB 6.00 6 1.17bcEFG 5.80 6 1.20bcFG 6.45 6 1.47bDEF 5.60 6 1.23cG

7.70 6 0.92aAB 5.90 6 1.41cE 5.60 6 1.31cE 6.75 6 0.97bCD 5.80 6 1.28cE

7.10 6 1.25aABC 6.50 6 1.32aCD 5.10 6 1.33bE 6.60 6 0.97aBCD 5.20 6 1.82bE

6.70 6 0.85bBCD 7.45 6 0.93aAB 6.40 6 1.73bD 7.25 6 1.02aABC 6.60 6 1.31bCD

6.40 6 1.85bD 7.35 6 0.8aAB 6.40 6 1.85bD 6.80 6 1.24abABCD 6.10 6 1.48bD

7.00 6 1.03aBCD 6.85 6 0.88a BCD 5.70 6 1.30bF 6.85 6 1.09aBCD 5.90 6 1.25bEF


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strength. Formation of j-carrageenan aggregate occurred separately and those aggregates were localized between gelatin networks. This could disturb the continuous gelatin network, leading to the decrease in the hardness of the mixed gels (Table 1).

4 | CONCLUSIONS Both agar and j-carrageenan affected the textural properties of gelatin gels. Gelling and melting temperatures of gelatin gel increased as the level of hydrocolloids increased. The addition of 10% agar in gelatin was recommended to improve the textural and gelling properties as well as sensory properties of gelatin from both seabass skin and swim bladder.

ACKNOWLEDG MENTS The authors would like to express their sincere thanks to Thailand Research Fund under the Royal Golden Jubilee PhD Program to Sittichoke Sinthusamran (PHD/0053/2553) and the Grant-in-Aid for dissertation from Graduate School, Prince of Songkla University, Thailand for financial support. The TRF Distinguished Research Professor Grant was also acknowledged.

ET HICAL STATEMENTS Conflict of Interest: The authors declare that they do not have any conflict of interest. Ethical Review: This study does not involve any human or animal testing. Informed Consent: Written informed consent was obtained from all study participants.

RE FE RE NCE S

F I G U R E 2 Microstructures of gel from seabass skin and swim bladder gelatins mixed with agar or carrageenan at 10%. BG: bovine gelatin, FG: fish gelatin, SK: seabass skin gelatin, SW: seabass swim bladder gelatin, GA: agar, KC: j-carrageenan. Number of 10 in front of GA or KC represents concentration (%) of hydrocolloids added. Magnification: 3,0003

(Figure 2). An ordered gel matrix structure with larger strands was reported to be related to the higher gel strength (Yang Wang, Zhou, & Regenstein, 2008). The differences in gel microstructure of gelatin are also strongly affected by the distribution of a-, b-, and g-chains in gelatin (Sinthusamran et al., 2014). When agar (10%) was incorporated into gelatin gel, the gel network of SK or SW gel had a more compact and denser network structure with less voids, compared to SK or SW gels alone. This result correlates with the higher hardness of SK or SW gels containing 10%, compared with SK or SW gel alone (Table 1). Agar and gelatin might form interpenetrated networks via hydrogen bonds between the two biopolymers (Tian, Xu, Yang, & Guo, 2011). This could result in a denser gel structure, with an increased gel network

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How to cite this article: Sinthusamran S, Benjakul S, Hemar Y. Physical and sensory properties of gelatin from seabass (Lates calcarifer) as affected by agar and j-carrageenan. J Texture Stud. 2017;00:1–9. https://doi.org/10.1111/jtxs.12280