Physicochemical properties of gelatin extracted from chicken deboner residue

Accepted Manuscript Physicochemical properties of gelatin extracted from chicken deboner residue Fatemeh Rafieian, Javad Keramat PII:

S0023-6438(15)00332-1

DOI:

10.1016/j.lwt.2015.04.050

Reference:

YFSTL 4639

To appear in:

LWT - Food Science and Technology

Received Date: 26 November 2014 Revised Date:

16 April 2015

Accepted Date: 19 April 2015

Please cite this article as: Rafieian, F., Keramat, J., Physicochemical properties of gelatin extracted from chicken deboner residue, LWT - Food Science and Technology (2015), doi: 10.1016/j.lwt.2015.04.050. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Physicochemical properties of gelatin extracted from chicken deboner residue

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Fatemeh Rafieian1,2, Javad Keramat2

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1 Wood Science and Engineering, Oregon State University, 119 Richardson Hall, Corvallis, OR 97331,

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USA.

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2 Department of Food Science and Technology, Isfahan University of Technology, Isfahan 84156-83111,

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Iran.

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Correspondence to: Fatemeh Rafieian [email protected])

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Abstract:

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The aim of this study was investigation of physicochemical properties of chicken deboner

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residue (CDR) gelatin in comparison with a commercial gelatin. A pretreatment with 6.73

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g/100 mL hydrochloric acid, followed by water extraction at 86.8 °C for 1.95 h was

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established as optimal conditions for obtaining gelatin from chicken deboner residue.

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CDR and commercial gelatin were evaluated in terms of proximate composition (ash,

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moisture, fat and protein), pH, pI, gel strength, viscosity, oil and water holding capacity

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(WHC), foaming properties (foam capacity and foam stability), turbidity, color (L*, a*, b*,

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C* and h°) and amino acid composition. Ash content, bloom, viscosity, pI, foam stability

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and WHC of CDR gelatin were significantly higher than commercial gelatin. There were

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no significant differences in fat and moisture content, L*, a* and h° factors and foam

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formation capacity between two gelatin samples.

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Keywords: Chicken deboner residue gelatin; Bloom; Viscosity; Foaming properties;

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Water holding capacity

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1. Introduction

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Gelatin has been widely used in the confectionary and gelatin desserts (such as fruit

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gummies, mallows, bar products), dairy products and pastries (such as stirred and

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thermally treated fermented milk products, ice cream and whipped desserts), meat and

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delicatessen products, beverages, photography and ink-jet printing, pharmaceutical and

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medicine.

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In large scale manufacture of gelatin, the primary raw material used, is the collagen found

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in cattle and pigs. In recent years the demand for non-porcine and non-bovine gelatin has

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increased due to the bovine spongiform encephalopathy (BSE) crisis and for religious and

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social reasons (Al-Saidi, Al-Alawi, Rahman, & Guizani, 2012). Production of gelatin

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from pig skins is not acceptable for Islam and Judaism and gelatin from beef is

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acceptable only if it has been prepared according to religious requirements. Fish gelatin is

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acceptable for Islam and with a minimum restriction for Judaism (Bae, Darby, Kimmel,

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Park, & Whiteside, 2009), but persisting residual odor in fish gelatin can cause problems

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especially when it is intended for use in mildly flavored products. Chicken deboner

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residue (CDR) is a major byproduct of the meat processing industry and it can be a

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valuable source of gelatin. In this work, the physicochemical properties of gelatin

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extracted from CDR under optimum conditions were investigated and compared with

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commercial gelatin.

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2. Materials and methods

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2.1 Materials

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Sodium chloride (NaCl) and sodium hydroxide (NaOH), hydrochloric acid and kaolin

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were of analytical grades and supplied by Merck KGaA (Darmstadt, Germany). Ion

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exchange resins and Whatman filter paper were purchased from Sigma–Aldrich Inc. (St

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Louis, MO, USA) and Kaolin was provided by Merck KGaA (Darmstadt, Germany).

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2.2. Methods

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2.2.1. Gelatin extraction procedure

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The dried and defatted samples were washed with tap water for removing the superfluous

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material.

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described in our previous study (Rafieian, Keramat, & Kadivar, 2013) and its

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physicochemical properties of CDR gelatin were investigated and compared to a

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commercial sample.

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2.2.2. Proximate composition

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Moisture, protein, fat and ash were estimated using AOAC official methods 925.09,

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955.04, 922.06 and 900.02 (AOAC, 1990), respectively. In the moisture content

57

determination, a drying temperature of 98-100 ºC for 5 h was used instead of the

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prescribed 135 °C.

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2.2.3. pH and isoelectric point (IEP) measurement

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pH was measured using a 1 g/100 mL solution cooled to 45 ºC. The isoelectric point was

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determined using the method described by Zaganiaris (2011) using mixed bed ion

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exchange resin [strong acid (Purolite C100) and base (Purolie A105)] for deionization.

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2.2.4. Gel strength

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The gel strength was determined according to the AOAC Official Method 948.21, using

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rheometry. A 6.67 g/100 g gel was formed by dissolving the dry gelatin in distilled water

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at 60 ºC, and cooling the solution in a refrigerator at 10 ºC (maturation temperature) for

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16-18 h (maturation time). The gel strength, expressed in bloom value was determined on

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The gelatin extraction was performed according to the optimal procedure

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a texture analyzer (Instron) with a load cell of 5 kN, cross head speed of 1 mm/s,

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equipped with a 12.7 mm diameter flat-faced cylindrical stainless steel plunger. The

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dimensions of the sample were 33 mm diameter and 60 mm height. Gel strength was

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expressed as maximum force (in g), necessary to give a 4-mm depression in the gelatin

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gels. Data represent the average of three determinations (AOAC, 1990).

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2.2.5. Viscosity

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The viscosities of gelatin solutions (6.67 g/100 g) were determined according to the

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Official Procedure of the Gelatin Manufacturers Institute of America, Inc. (GMIA) using

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an Oswald's viscometer (PSL Ltd., Wickford, UK) which was held in a water bath to

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maintain a constant temperature of 60 ± 1 ºC. The time required for 100 mL of solution

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to pass between two marks through the capillary tube of the pipette was determined as

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efflux time. The viscosity at 60 ºC of any sample was calculated as follows:

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Equation 1

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V = Viscosity, in millipoises (mP)

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A, B = A and B pipette constants

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t = efflux time (s)

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d = solution density, for a 6.67 g/100 g gelatin solution at 60 ºC d = 1.001 (Rafieian et al.

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2013).

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2.2.6. Water holding capacity (WHC)

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WHC was determined using the method outlined by Zarai, Balti, Mejdoub, Gargouri, and

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Sayari (2012) with slight modification. One gram of the samples weighed into a pre-

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weighed 50 mL centrifuge tube and was mixed with 50 mL of distilled water. The

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samples were then allowed to stand at 30 ± 2 ºC for 1 h before centrifuging at 450 g for

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20 min. After centrifugation the supernatant was decanted and centrifuge tube was

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drained for 30 min on a filter paper after tilting to a 45º angle and weighed. The WHC

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was expressed as grams of water held by 100 g of protein.

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2.2.7. Fat binding capacity (FBC)

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The above method was used for measuring the FBC, but instead of 50 mL distilled water,

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10 mL of corn oil was added to the samples. The fat binding capacity was expressed as

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grams of oil held by 100 g of protein.

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2.2.8. Foaming properties

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Foam capacity and foam stability

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The method of Kwak, Cho, Ji, Lee, and Kim (2009) with slight modification was

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employed for foam capacity measurements. Fifty milliliters (volume before whipping) of

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a 2 g/100 mL gelatin solution in distilled water was prepared. The sample was

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homogenized using a model A Polytron homogenizer at 10000 rpm for 5 min and rapidly

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transferred into a 250 mL graduated cylinder and the foam volume recorded. Foam

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capacity was calculated according to the following equation:

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Equation 2

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Foam stability was determined as the volume of foam remaining after 30 min, expressed

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as a percentage of the initial foam volume (Jridi, Lassoued, Nasri, Ayadi, Nasri, &

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Souissi, 2014). 5

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2.2.9. Turbidity

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A 0.1 g/100 mL gelatin solution was formed by dissolving the dry gelatin in distilled

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water at 60 ºC for 30 min. The sample absorbance was measured at wavelength of 660

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nm with a spectrophotometer (UV-visible spectrophotometer, Camspec Co., U.K.). A

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standard curve was prepared with 1, 3, 5, 7 and 9 mg/kg concentrations of Kaolin and

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turbidity was expressed in Kaolin mg/kg (See, Hong, Ng, Wan Aida, & Babji, 2010).

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2.2.10. Color measurement

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Samples were prepared according to sample preparation procedure for gel strength

118

determination. The color of the samples was measured with a Hunterlab colorimeter

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using Illuminant D65, model Txt-Flash. Measurement results were displayed in Hunter

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values of L*, a* and b*: L*, from black (0) to white (100); a*, from green (−50) to red

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(+50); b*, from blue (−50) to yellow (+50). Furthermore, colors were described in terms

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of C* and hº. C* (Chroma, also called saturation) is the attribute of color perception that

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expresses the amount of departure from a gray of the same lightness. All grays have zero

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saturation. The C*of a color is represented in an a*, b* color plane by the distance between

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the achromatic point and the (a*, b*) coordinates of a given color. hº (hue angle) indicates

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the position inside a quadrant of a color plane. C* and hº were calculated by Equations 3-

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4:

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Equation 3

Equation 4

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2.2.11. Amino acid analysis 6

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The amino acid content of CDR and commercial gelatins was measured by amino acid

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analyzer. The samples were hydrolyzed to yield free amino acids by the addition of

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10 mL HCl (6 mol/L) to 1 mg of gelatin at 110 °C for 24 h. Two different samples of the

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hydrolyzed gelatin solution as well as amino acids standards (20 µL) were analyzed by

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Pico-Tag Amino Acid Analyzer (Autosampler SIL 10A, Waters 600E System Controller,

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Waters 1525 Binary HPLC Pump and Waters 2487 Dual λ Absorbance Detector). Data

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acquisition and processing were accomplished with the Breeze Data Processing software.

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2.2.12. Statistical analysis

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All measurements were replicated three times and results were reported as mean ±

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standard deviation (SD). Data were subjected to statistical analysis by Student’s t-test and

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a value of P < 0.05 was considered significant.

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3. Results and discussion

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3.1. Proximate composition

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Data on proximate composition of the gelatin samples was expressed as grams (g) per

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100 g gelatin. Table 1 shows the proximate composition of CDR and commercial

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gelatins. The moisture content of two gelatin samples was statistically different at 5%

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level of significance (P < 0.05). Moisture content in the samples was well below the

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prescribed limit of 15 g/100 g for edible gelatin (GME, 2005). At moisture content of 6-8

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g/100 g, gelatin is very hygroscopic and it becomes difficult to determine the

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physicochemical attributes with accuracy (Shyni, Hema, Ninan, Mathew, Joshy, &

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Lakshmanan, 2014).

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There were no significant differences in the amount of protein, fat and ash between two

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samples (P > 0.05). The gelatin samples showed protein as the major component but they

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were almost free of fat, showing that the simple de-fattening method followed here has

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eliminated the fat content as desired. The gelatins were found to be high in ash content,

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above the recommended maximum of 2.6 g/100 g (Shyni et al. 2014). The ash content of

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gelatin varies with the type of raw material and the method of processing. In the case of

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CDR gelatin, purification was done only by filtration through Whatman No. 4 filter

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paper. Following this step by ion exchange treatment may be used for demineralizing or

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de-ashing of gelatins more effectively.

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3.2. pH and IEP measurement

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The pH of CDR gelatin (4.83 ± 0.12) was significantly lower than commercial gelatin

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(5.92 ± 0.09). This difference between pH of two gelatin samples may be due to the

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different gelatin extraction method employed during preparation procedures.

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The IEP of gelatin molecules is defined as the pH value at which the net average charge

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due to ionization of the acidic and basic groups is zero. The isoelectric point of CDR and

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commercial gelatins was 7.63 ± 0.30 and 5.11 ± 0.41, respectively. These results agreed

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with Aewsiri, Benjakul, Vinessanguan, & Tanaka (2008) who reported that type A

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gelatin as produced by the acid process has an IEP in the range of pH 6 and 9 whilst

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alkaline-produced gelatin of type B has an IEP at pH 4.8 - 5.4. These differences result

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from the partial deamination of glutamine and aspargine to glutamic acid and aspertic

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acid, respectively, during the alkaline pre-treatment of the raw materials.

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3.3. Gel strength

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The gel strength is one of important criteria which determine the quality of gelatin as

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required by manufacturer. It is a measure of the hardness, stiffness, firmness and

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compressibility

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of

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strength or bloom value, gelatin is categorized in terms of low (< 120 g), medium (120-

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200 g) and high (> 200 g) bloom. The gel strength values of CDR and commercial

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gelatins were 520 ± 10.00 g and 290 ± 10.00 g, respectively, and both of them were

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classified as high bloom gelatins. The commercial gelatin bloom strength was

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significantly (P < 0.05) lower than that of CDR gelatin. This may be attributed to the

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lower proline (Pro) and hydroxyproline (Hyp) content in commercial gelatin (see Table

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4). These two amino acids are particularly important for the gelling effect. Triple helical

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structure stability in renatured gelatins has been reported to be proportional to the total

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content in pyrrolidine imino acids; given that it is the Pro + Hyp rich zones of the

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molecules that are most likely to be involved in the formation of nucleation zones.

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However, although Pro is important, Hyp is believed to play a singular role in the

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stabilization of the triple-stranded collagen helix due to its hydrogen-bonding ability

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through its -OH group (Gime´nez, Go´mez-Estaca, Alema´n, Go´mez-Guille´n, &

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Montero, 2009). The gel strength of fish gelatin has been reported in a wide range of 124-

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426 bloom, compared to 200-300 bloom for bovine or porcine gelatin (Karim & Bhat,

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2009), much lower than the values obtained for CDR gelatin in the present study.

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3.4. Viscosity

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Viscosity is the second most important commercial physical property of a gelatin (Amiza

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& Siti Aishah, 2011). The viscosity of CDR gelatin was 5.55 ± 0.19 cP and much higher

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than commercial gelatin, 2.90 ± 0.17 cP. These values are in close agreement with those

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previously reported viscosity values (from 2.0 to 7.0 cP for most gelatins and up to 13.0

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cP for specialized ones). The viscosity of gelatin solutions is partially controlled by

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molecular weight and polydispersity. It also has been reported that the molecular weight

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distribution has greater impact on viscosity compared to the amino acid composition of

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the gelatin (Mahjoorian, Mortazavi, Tavakolipour, Motamedzadegan, & Askari, 2013).

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Lower viscosity of commercial gelatin might be due to the presence of peptide chains

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with low molecular weight as a result of over- hydrolysis of the collagen during the

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pretreatment step. Gelatin solution with a low viscosity usually yields a short and brittle

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texture gel, while high viscosity gelatin solution yields a tough and extensible gel that has

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a higher commercial value (Norziahn, Kee, & Norita, 2014); so for many applications,

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gelatins of high viscosity are preferred given that other properties are equal (Zhou,

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Mulvaney, & Regenstein, 2006).

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3.5. WHC

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WHC refers to the ability of the protein to imbibe water and retain it against gravitational

211

force within a protein matrix. It is positively correlated with water-binding capacity (Foh,

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Amadou, Foh, Kamara, & Xia, 2010). Interactions of water with proteins are very

213

important in the food systems because of their effects on the flavor and texture of foods.

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The water-absorption capacity can increase with heat treatment, due to the increased

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proportion of low molecular weight proteins with a high percentage of charged amino

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acids and to partial denaturation, unfolding and insolubilization. Intrinsic factors affecting

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water binding of food protein include size, shape, amino acids composition, protein

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conformation, surface hydrophobicity/polarity (Foh, Amadou, Kamara, Foh, & Xia,

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2011), and the presence of lipids, carbohydrates and amino acid residues on the surface,

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since most non-polar amino acid residues and polar groups are not hydrated in the interior

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(Bouaziz, Rassaoui, & Besbes, 2014).

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WHC of CDR gelatin (859.00 ± 60.02 g/100 g) was higher but not statistically different

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than commercial gelatin (816.66 ± 16.50 g/100 g). These values were much higher

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compared to the previously reported results by Shyni et al. (2014) for gelatin from the

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skins of skipjack tuna (Katsuwonus pelamis), dog shark (Scoliodon sorrakowah), and

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rohu (Labeo rohita) that can be attributed to the higher amounts of hydrophilic amino

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acids and hydroxyproline content.

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3.6. FBC

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Fat-binding capacity is a functional property that is closely related to texture and other

230

food quality properties through the interaction between oil and other components. The

231

ability of proteins to absorb and retain fat and to interact with lipids is important in food

232

formulations and its importance depends on the type of food. This property is affected by

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protein source, processing conditions, composition of additive, particle size and

234

temperature. The FBC of both gelatins were determined. The findings revealed that CDR

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gelatin had a lower FBC (67.26 ± 7.97 g of oil/100 g) than commercial gelatin (123 ±

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7.54 g of oil/100 g). These values were low compared to the mean values reported by

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Bougatef, Balti, Sila, Nasri, Graiaa, and Nasri (2012) for extracted gelatin from fish skin

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and halal bovine gelatin. The difference in FBC may be due to variation in the presence

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of nonpolar side chains, which bind the hydrocarbon side chain of oil. Ninan, Abubacker,

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and Jose (2011) reported that the degree of exposure of the hydrophobic residues were

241

responsible for the high FBC. According to Table 4, the hydrophobic amino acids,

242

tyrosine, leucine, valine, and isoleucine represented 6.4, 23.5, 20.8, and 9.8 mg/g of CDR

243

gelatin, respectively, which were slightly lower to those from commercial gelatin (7.3,

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24.7, 21.2 and 9.9 mg/g, respectively).

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3.7. Foaming properties

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Foams are two phase systems, with gaseous phase dispersed in an aqueous continuous

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one. Foaming requires a large interfacial area to facilitate the incorporation of air to the

248

liquid phase. In food products proteins are the main surface active agents that play a

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crucial role in air entrapment by decreasing surface tension at the air-liquid interface. An

250

example would be cohesive force of water molecules that tend to collapse a bubble, and

251

give resistance to shearing/tearing with high level of stretching capacity. So when protein

252

solution whipped or stirred vigorously air is pulled down into solution, and when it tries

253

to escape up, flexible protein surface forms a bubble. Foams become unstable due to

254

three physical processes:

255

(a) Bubble disproportionation: bubbles reduce in size with time because air diffuses from

256

the interior, which is at a higher pressure compared with the atmosphere.

257

(b) Lamellae (foam cell) rupture: bubbles coalesce quickly due to pushing and pulling

258

forces causing holes formation between two bubbles.

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(c) Drainage: the drainage water around the bubbles naturally drains down to the liquid

260

layer removing protein from the films around the bubble, which eventually becomes too

261

thin to support bubble (Ibidapo & Erukainure, 2012). Drainage of liquid in the

262

intervening films between bubbles due to gravity and Laplace capillary pressure

263

differences results in thinning of films. When the film thickness attains a critical value,

264

film rupture occurs as a result of the strong van der Waals attraction in such thin films

265

and the two bubbles coalesce (known as binary coalescence) to form a single bigger

266

bubble. Similarly, a bubble can coalesce with its bulk gas at the top interface which is

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called interfacial coalescence. Thus both binary and interfacial coalescences of bubbles

268

result in reduction of number of bubbles. The latter reduce the volume of the foam.

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Gelatin is commonly used as a foaming agent in commonly used foods such as

270

marshmallows and a type of premixed coffee beverage. This makes foam formation

271

ability and foam stability important for widespread application. Foaming properties of

272

protein could be influenced by protein source, intrinsic properties of protein, its

273

compositions and conformation in solution and at the air/ water interface (Raja Mohd

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Hafidz, Yaakob, Amin, & Noorfaizan, 2011). These properties of CDR and commercial

275

gelatins are shown in Table 2. Foam formation ability of CDR gelatin was higher than

276

commercial gelatin. The values observed in the present study were similar to gelatin of

277

analytical grade from porcine skin (280 mL/100 mL), gelatin of food additives grade

278

from porcine skin (290 mL/100 mL), and gelatin from shark cartilage (260 mL/100 mL)

279

in the work of Cho, Kwak, Park, Gu, Ji, Jang, Lee, and Kim (2004) but far higher than

280

those reported for bovine (93 mL/100 mL) and porcine skin gelatins (90 mL/100 mL)

281

(Raja Mohd Hafid et al. 2011).

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Foam stability was significantly lower (P < 0.05) in commercial gelatin when compared

283

to CDR gelatins. It has been suggested that reduced foam stability may be due to

284

aggregation of proteins which interfere with interactions between them and water needed

285

for foam formation (Cho et al., 2004).

286

3.8. Turbidity

287

Turbidity may be due to insoluble or foreign matter in the form of emulsions or

288

dispersions which have become stabilized due to the protective colloidal action of the

289

gelatin, or to an isoelectric haze. Raja Mohd Hafidz et al. (2011) reported that gelatin

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solutions have a maximal turbidity at the IEP that protein molecules tend to form

291

aggregate and less water interacts with the protein molecules. The turbidity of CDR and

292

commercial gelatins was 5.94 ± 0.56 and 6.31 ± 0.32, respectively. The difference was

293

not considered to be statistically significant.

294

3.9. Color measurement

295

Color is an important quality factor directly related to the acceptability of food products,

296

and is an important physical property to report for extracted gelatins but does not

297

influence the functional properties. The color of gelatin depends on the nature of the raw

298

material used in its preparation and also whether the gelatin represents a first, second or

299

final extraction (Jakhar, Reddy, Maharia, Devi, Reddy, & enkateshwarlu, 2012).

300

Instrumental color measurements of the gelatins are as shown in Table 3. There was no

301

significant difference between ‘a’ and h° values of CDR and commercial gelatins (P >

302

0.05) but CDR gelatin gave significantly higher ‘L’ but lower ‘b’ (less yellowish) and C*

303

values than did commercial gelatin (P < 0.05).

304

3.10. Amino acid analysis

305

Table 4 shows the amino acid composition of CDR and commercial gelatins. Glycine was

306

the most abundant amino acid in commercial (295 mg/g) and CDR gelatins (311.5 mg/g).

307

They were essentially low in tyrosine, methionine and isolucine, while tryptophan,

308

histidine and cysteine were not detectable. Imino acids (Pro and Hyp) impart

309

considerable rigidity to the collagen structure and that a relatively limited imino acid

310

content should result in a less sterically hindered helix and may affect the dynamic

311

properties of the gelatin (Amiza & Siti Aishah, 2011). Nikoo, Xu, Benjakul, Xu,

312

Ramirez-Suarez, Ehsani, Kasankala, Duan, and Abbas (2011) also reported that the

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stability of collagen and gelatin is proportional to their total imino acid and glycine

314

contents. Gelatins with a lower amount of imino acid content have a higher critical

315

concentration and lower melting point, compared to those containing a high amount of

316

them (Mine et al. 2010). Cross-links or junction zones in gelatin are formed by ordered

317

triple helices, like the parent collagen. It has been reported that the substitution of glycine

318

in a tripeptide GLY-X-Y by alanine alters the conformation with a local untwisting of the

319

triple helix because close packing of the chains near the central axis is not possible

320

(Mine, Eunice, & Jiang, 2010). For close packing of the triple helix, small glycine

321

molecules are required to occupy every third position (Cheng, Rashid, Yu, Yoshizumi,

322

Hwang, & Brodsky, 2011). Mine et al. (2010) reported that effective formation and

323

stabilization of the collagen triple helix structure requires the presence of the repeating

324

sequence (GLY-X-Y) where X and Y can be any amino acid with an average of at least

325

one proline or hydroxyproline in every other triplet. Thus, GLY-PRO-Y, GLY-X-HYP

326

and GLY-PRO-HYP are important for the stabilization of the collagen structure; the

327

transition temperature of (GLY-X-HYP)n is higher than that of (GLY-PRO-Y)n (Badii &

328

Howell, 2006). The total imino acid contents of CDR and commercial gelatins were

329

about 218 and 190 mg/g, respectively. The amount of proline in CDR gelatin, 120.7

330

mg/g, was higher than in commercial gelatin (115.1 mg/g). The same as proline, the

331

amount of hydroxyproline was also higher in CDR gelatin (97.1 mg/g) than that in

332

commercial gelatin (74.7 mg/g). So it can be deduced that the degree of cross-linking and

333

gel strength of CDR gelatin is to be higher than that of commercial gelatin according to

334

the contents of glycine, proline and hydroxyproline. Furthermore the amount of serine,

335

which has a free hydroxyl group, was higher in CDR gelatin; Hydrogen bonds between

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water molecules and free hydroxyl groups of amino acids in gelatin also influence gelatin

337

gel strength (Raja Mohd Hafidz et al. 2011).

338

4. Conclusion

339

CDR gelatin is classified as high bloom gelatin (bloom > 250). High gel-strength gelatins

340

do have superior water absorbing properties and gel melting temperature to low bloom

341

gelatins and for these reasons alone they should be preferred in dairy products, gelatin

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dessert and jellied meat production. CDR gelatin has also higher viscosity and foam

343

properties than commercial gelatin that makes it suitable for preparation of marshmallow

344

because a good marshmallow gelatin should be high in bloom and viscosity and have

345

good whipping qualities. Based on the comparison with commercial one, the gelatin

346

extracted from CDR was proven to exhibit superior characteristics and are potentially to

347

be utilized as alternative sources of mammalian gelatins and may be used in various

348

applications in the food, pharmaceutical, and photographic industries.

349

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ACCEPTED MANUSCRIPT Table 1. Proximate composition of CDR and commercial gelatins Moisture Protein Fat Ash

CDR gelatin (%) Commercial gelatin (%) 8.89 ± 0.19a 8.19 ± 0.16b a 85.67 ± 0.76 86.20 ± 0.63a 0.80 ± 0.06a 0.72 ± 0.00a a 4.41 ± 0.14 4.15 ± 0.06a

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Values are the means ± SD of triplicates. Means within a row with same letter are not significantly different (P > 0.05).

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ACCEPTED MANUSCRIPT Table 2. Foam formation capacity and foam stability of CDR and commercial gelatins.

CDR gelatin Commercial gelatin

Value ± SD Foam formation capacity Foam stability (%) (%) 323 ± 25a 44.00 ± 5.29a b 224 ± 16 2.24 ± 0.41b

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Means within a column with same letter are not significantly different (P > 0.05).

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ACCEPTED MANUSCRIPT Table 3. Hunter L-a-b values of CDR and commercial gelatins Commercial gelatin 53.92 ± 1.81b a 1.24 ± 0.13 b 10.76 ± 0.22 b 10.84 ± 0.23 a 1.46 ± 0.01

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Chicken deboner residue gelatin a 68.22 ± 2.34 a 0.89 ± 0.20 a 9.37 ± 0.41 a 9.41 ± 0.43 a 1.48 ± 0.02

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Means within a row with same letter are not significantly different (P > 0.05).

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ACCEPTED MANUSCRIPT Table 4. Amino acid analysis of CDR and commercial gelatins

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Chicken deboner residue gelatin (mg) 74.5 65.8 40.5 97.8 311.5 97.1 9.8 23.5 31.5 9.1 33.4 120.7 21.6 12.1 6.4 20.8

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Alanine Arginine Aspargine Glutamine Glycine Hydroxyproline Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tyrosine Valine

Commercial Gelatin (mg) 69.5 66.5 42.8 97.1 295 74.7 9.9 24.7 32.1 7.5 36.2 115.1 17.5 13.5 7.3 21.2

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We extracted gelatin from chicken deboner residure (CDR) under optimized conditions. Optimal conditions were as follows: soaking in 6.73 g/100mL HCl & water extraction at 86.8 °C for 1.95 h

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Physicochemical properties of extracted gelatin were investigated. Bloom and viscosity of CDR gelatin were higher than commercial one.

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Commercial gelatin had higher foam stability & water holding capacity compared to CDR gelatin.