当前位置:首页 >> >>

Preparation and physical properties of soy protein isolate and


ARTICLE IN PRESS

HYDROCOLLOIDS
Food Hydrocolloids 21 (2007) 1153–1162 www.elsevier.com/locate/foodhyd

FOOD

Preparation and physical properties of soy protein isolate and gelatin composite ?lms
Na Caoa,b, Yuhua Fua,?, Junhui Hea
a

Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Zhongguancun Beiyitiao 2, Haidianqu, Beijing 100080, PR China b Graduate University of Chinese Academy of Sciences, Yuquanlu Jia 19, Shijingshanqu, Beijng 100049, PR China Received 13 July 2006; accepted 5 September 2006

Abstract Mechanical, swelling, and optic properties of composite ?lms prepared from soy protein isolate (SPI) and gelatin were investigated. With increasing gelatin ratio in composite ?lms, tensile strength (TS), elongation to break (EB), elastic modulus (EM) and swelling property of the SPI/gelatin composite ?lms increased. In addition, the ?lms became more transparent, and easier to handle. When the ratio of SPI:gelatin was 4:6–2:8, the TS, EB, and other properties of composite ?lm approached those of gelatin ?lm and were better than those of SPI ?lm. Particularly, the composite ?lm was more economic than gelatin ?lm, so it could be used as edible ?lm instead of gelatin ?lm for package. When the ratio of SPI:gelatin was 4:6, the in?uences of concentration of glycerin, pH value of SPI ?lm-forming solution, thermal-treatment temperature of SPI ?lm-forming solution and NaCl on mechanical and optic properties, and water content of composite ?lms were also studied. r 2006 Elsevier Ltd. All rights reserved.
Keywords: Composite ?lm; Edible ?lm; Soy protein isolate; Gelatin

1. Introduction Since late 1980s, edible ?lms have attracted much attention as food or druggery packaging. It is because edible ?lms may partly substitute for traditional plastic ?lms, most of which are not biodegradable. Edible ?lms can enhance food quality by acting as moisture, gas, aroma, and lipid barriers and by providing protection to a food product after the primary package is opened (Kim & Ustunol, 2001). Edible ?lms can be prepared from proteins, polysaccharides, lipids or the combination of these components. Among them, protein-based edible ?lms are most attractive. Firstly, they are supposed to provide nutritional value. Secondly, protein-based ?lms have impressive gas barrier and mechanical properties compared with those from lipids and polysaccharides (Ou, Kwok, & Kang, 2004).

?Corresponding author. Tel.: +86 10 82543539; fax: +86 10 62554670.

E-mail addresses: cao_na@mails.gucas.ac.cn (N. Cao), fuyuhua@mail.ipc.ac.cn (Y. Fu), jhhe@mail.ipc.ac.cn (J. He). 0268-005X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2006.09.001

As one kind of protein, gelatin obtained by partial degradation of collagen has gained more attention as edible ?lms for its abundance and biodegradability (Jongjareonrak, Benjakul, Visessanguan, Prodpran, & Tanaka, 2006). Gelatin has excellent ?lm-forming and good mechanical properties. In addition, it is unique among hydrocolloids in forming thermo-reversible with a melting point close to body temperature, which is particularly signi?cant in edible and pharmaceutical applications (Achet & He, 1995). However, as animal protein, gelatin is more expensive than plant protein, which to a certain extent inhibits its application as edible ?lm. Recent reports pointed out the use of soy protein isolate (SPI) to develop edible and biodegradable ?lms. SPI is abundant, inexpensive, biodegradable, and nutritional raw material. It is a mixture of proteins with different molecular properties. Among them, the 7 and 11 S fractions that make up about 37% and 31% of the total extractable protein have the capability of polymerization. Sulfhydryl groups of 11 S protein were reported to be responsible for the formation of disul?de linkages that results in the formation of a threedimensional network (Cho & Rhee, 2004; Sabato et al., 2001). Unfortunately, SPI has a light beany ?avor, its ?lm is

ARTICLE IN PRESS
1154 N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162

rather brittle, and has relatively poor mechanical properties. Previous experimental results showed that the properties of soy protein can be modi?ed by physical, chemical, or enzymatic treatments. Another approach to improve physical properties of biopolymer ?lms is to prepare composite ?lms. The properties of soy protein ?lms may be improved by blending with starch, sodium alginate, whey protein isolation, etc. (Rhim, Wu, Weller, & Schnepf, 1999; Sabato et al., 2001; Tang, Du, Zheng, & Fan, 2003). Despite numerous studies on ?lms of SPI and gelatin, respectively, there have been few reports on composite ?lms of SPI and gelatin. The objectives of this paper were to prepare composite ?lms based on SPI and gelatin, and to utilize effectively the functional merits of SPI and gelatin. The good mechanical properties and the property of melting in mouth instantly favor the use of gelatin ?lm as edible ?lm. The addition of gelatin into SPI could diminish undesirable ?avor and brittleness, improve mechanical properties of SPI ?lm. And the cost of composite ?lm is much lower than gelatin ?lm, and the composite ?lm is also more nutritional. This paper mainly studied the in?uences of the ratio of SPI and gelatin, concentration of glycerin, pH of SPI ?lm-forming solution, thermal-treatment temperature of SPI ?lm-forming solution and NaCl on the mechanical properties of SPI/gelatin composite ?lms. The swelling and optic properties of composite ?lms were also investigated. 2. Material and methods 2.1. Materials SPI (minimum 90% protein content on dry basis) was purchased from Daqing Sun Moon Star Protein Co., Ltd. (Daqing, China). Gelatin (type B, bovine bone) was purchased from Guang Dong Bright pearl Biology Industry Co., Ltd. (Guang Dong, China). NaCl, NaCO3, HAc, and glycerin were all analytical grade and purchased from Beijing Chemical Factory. MgNO3 ? 6HNO3 (A.R) was purchased from Beijing Shuanghuan Weiye Reagent Co., Ltd. 2.2. Preparation of composite ?lms Gelatin ?lm-forming solution (10%, w/w) was prepared as follows. Gelatin was hydrated at room temperature for 30 min, then dissolved in 50 1C water bath with mechanical stirring for about 20 min until completely dissolved, followed by addition of 0.1 g glycerin/g gelatin. The SPI ?lm-forming solution (10%, w/w) was prepared as follows. A certain amount of SPI was dissolved in deionized water, followed by addition of 0.1 g glycerin/g SPI. Then the solution was homogenized with a homogenizer for 2 min. After that, the solutions were strained through nylon cloth to remove small lumps (only minuscule amounts).

Composite ?lm-forming solutions of 10% total protein and 0.1 g glycerin/g protein were prepared by mixing different volumes of the above two solutions with the desired ratios of SPI to gelatin (10:0, 8:2, 6:4, 4:6, 2:8, 0:10). The solutions were then placed under ultrasonic for about 1 min to remove air bubbles. Finally, the solutions were coated on polyester plate and dried at ambient temperature. The ?nished intact ?lms were peeled and stored in certain climatic chambers. The ratio of SPI:gelatin 4:6 was selected to study the in?uences of some additives and preparation conditions on properties of the composite ?lms. 0, 0.1, 0.2, 0.3, and 0.4 g glycerin/g protein (g, w/w) were added, respectively, to gelatin and SPI ?lm-forming solution in order to select the appropriate addition of glycerin. The pH of SPI ?lmforming solution (0.1 g glycerin/g protein) was adjusted to about 6, 7, 8, 8.5, 9, and 10 with NaCO3 or HAc. The obtained solution was then mixed with a certain amount of gelatin ?lm-forming solution. SPI ?lm-forming solution (0.1 g glycerol/g protein, pH ? 8) was heated on a hot plate magnetic stirrer until its temperature reached 50, 60, 70, 80, and 90 1C, respectively. And kept at that temperature for about 20 min, then it was mixed with gelatin ?lm-forming solution. A certain amount of NaCl (7.02, 14.05, 28.09, 42.13, and 56.18 mg NaCl/g protein, respectively) was added to the composite ?lm-forming solution (pH of SPI solution was 8, 0.1 g glycerol /g protein) in order to study the in?uence of NaCl on properties of ?lms. 2.3. Mechanical properties Tensile strength (TS), elongation to break (EB) and elastic modulus (EM) of ?lms were measured on a microcomputer-controlled electronic testing machine (RGD-1, Shenzhen Reger Instrument Co. Ltd.) according to ASTM standard method D882-01 (ASTM, 2001). Samples were conditioned at 25 1C and 5073% relative humidity in a desiccator containing Mg(NO3)2 saturated solution for at least 2 days prior to analysis. A rectangular ?lm strip of 180 mm in length and 25 mm in width was used. The initial grip separation was set at 100 mm, and crosshead speed was set at 10 mm/min. The EM, the stress at break and the strain at break of the strips were measured in a static mode. The measurement was performed immediately after a sample was taken out from the desiccator. Tensile properties were calculated from the plot of stress (tensile force/initial cross-sectional area) versus strain (extension as a fraction of the original length) (Perez Gago & Krochta, 2001). TS was calculated by dividing the maximum load by the initial cross sectional area of the specimen (ASTM, 2001). EB was calculated by dividing the extension at rupture of the specimen by the initial gage length of the specimen (100 mm) and multiplying by 100 (ASTM, 2001). Elasticity Modulus, a measure of intrinsic ?lm stiffness, is the slope of the linear

ARTICLE IN PRESS
N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162 1155

range of the stress–strain plot (Mauer, Smith, & Labuza, 2000).TS, EB and EM measurements for each type of ?lm were repeated at least eight times, from which an average was obtained. 2.4. Film thickness Film thickness was measured with a micrometer with a sensitivity of 0.001 mm. Five to ten thickness measurements were carried out on each ?lm, from which an average was obtained. 2.5. Swelling property The ?lms were cut into a piece of 2.5 ? 2.5 cm in size and weighted in air-dried conditions (w1). They were then immersed in deionized water (25 1C) for 2 min. Wet samples were wiped with ?lter paper to remove excess liquid and weighted (w2). The amount of adsorbed water was calculated as Swelling ?%? ? 100?w2 ? w1 ?=w1 , where w2 and w1 were the weights of the wet and the airdried samples (Bigi, Panzavolta, & Rubini, 2004). The measurement was repeated three times for each type of ?lm, and an average was taken as the result. 2.6. Opacity measurement Film specimen was cut into a rectangle piece and placed in a spectrophotometer test cell directly, and air was used as the reference. A spectrum of each ?lm was recorded on an UV-Vis spectrophotometer (u-2001, Japan). The area under the absorption curve from 400 to 800 nm was recoded, and the opacity of ?lm was calculated by the following equation: Opacity ? A500 500=T; where A500 was the absorption at 500 nm, and T is the ?lm thickness (mm) (Cho & Rhee, 2004; Shiku, Hamaguchi, Benjakul, Visessanguan, & Tanaka, 2004). The measurement was repeated three times for each type of ?lm, and an average was taken as the result. 2.7. Water content Film samples were weighed (w1), dried at 105 1C for 24 h, weighted (w2) again. Water content (WC) was determined as the percentage of initial ?lm weight lost during drying and reported on a wet basis. WC ?%? ? 100?w1 ? w2 ?=w1 . Triplicate measurements of WC were conducted for each type of ?lm, and an average was taken as the result (Rhim, Gennadios, Weller, & Hanna, 2002).

2.8. Statistical analyses Statistical data were analyzed using Microsoft Excel 2000 and Origin 6.1. Student’s t-test was applied to compare the averages of properties with a level of 95% con?dence interval. 3. Results and discussion 3.1. Mechanical properties 3.1.1. The effects of SPI/gelatin ratio on the mechanical properties of composite ?lms The effects of SPI/gelatin ratio on TS, EB and EM of composite ?lms are showed Fig. 1. The results displayed that TS, EB and EM of the composite ?lms signi?cantly increased as the gelatin content increased. For example, TS, EB and EM of the SPI/gelatin ? 8:2 ?lm increased from 25.55 MPa, 2.64%, and 1280.00 MPa to 44.60 MPa, 3.32%, and 1861.16 MPa as compared with the SPI/ gelatin ? 2:8 ?lm. In contrast, SPI ?lm (concentration of 10% protein, 0.1 g glycerin/g protein) was rather brittle and hard to handle. When the gelatin content increased in composite ?lm, the ?lm became more transparent, homogeneous, ?exible and easier to handle. Gelatin ?lm has better mechanical properties than SPI ?lm. This fact may be attributed to the protein/protein interaction, which is determined by hydrogen bonds or by electrostatic interaction and/or by hydrophobic nature. These interactions are ultimately in?uenced by both the sequence of amino acid residues and by the threedimensional size of the entire network (Mariniello et al., 2003). Gelatin can form a soft, ?exible and elastic gel (Lee, Shim, & Lee, 2004). Gelatin has a ?brous tertiary structure then forms a triple helical, cross-linked quaternary structure. Among natural polymers, gelatin is probably most analogous to a synthetic polymer because of its linear structure, fairly limited monomer composition and its polydispersity (Simon-Lukasik & Ludescher, 2004). On the other hand, SPI is a complex mixture of proteins with widely different molecular properties. Most soy proteins are globulins (Cho & Rhee, 2004). Thus SPI has a less organized matrix. In the gelling and ?lm forming process, gelatin can renature and, re-acquire part of the triple helix structure of the collagen, which is a protein with a high degree of organization. Consequently, ?lms produced from gelatin can have a more organized network as compared to those made from SPI (Chambi & Grosso, 2006). Li, Kennedy, Jiang, and Xie (2006) and Xiao, Lu, Gao, and Zhang (2001) found increase in the TS and EB when gelatin was blended with konjac glucomannan. And they suggested that this result might be attributed to such factors as the hydrogen bonding interaction between the two polymers, the plasticizing effect of water absorbed in the ?lms. It was found in the current work that gelatin could enhance the strength and ?exibility of SPI/gelatin composite ?lm. The above increase of ?lm TS and EB

ARTICLE IN PRESS
1156 N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162

Tensile Strength (MPa)

80 60 40 20

(a)

4.0 3.5 3.0 2.5 2.0 1.5

Elongation (%)

(b)

Elastic Modulus (MPa)

3000 2500 2000 1500 1000

(c)

10:0

8:2

6:4 SPI:Gelatin

4:6

2:8

0:10

Fig. 1. Tensile strength (a), elongation to break (b), and elastic modulus (c) of composite ?lms as function of SPI/gelatin ratios (containing 0.1 g glycerin/g protein) Error bars show 795% con?dence interval.

blending SPI and gelatin may be attributed to the presence of intermolecular interactions between SPI and gelatin molecules. The amidogen and carboxyl of SPI and gelatin might form hydrogen bonding interactions between the two polymers. In this paper, the SPI:gelatin ratio of 4:6, at which the ?lm appeared much transparent and easily handled, was chose to investigate the properties of composite ?lm. And 0.1 g glycerin/g protein was also added as plasticizer to overcome ?lm brittleness and to obtain freestanding ?lms. 3.1.2. The effects of pH values of SPI ?lm-forming solution on mechanical properties of composite ?lms The effects of pH on mechanical properties are showed in Fig. 2. The ?gures revealed that TS and EM of composite ?lms ?rstly increased and then declined with increasing the pH value of SPI ?lm-solution from 6 to 10. And the maximum values appeared at pH 8.5, at which TS reached 49.45 MPa compared with 34.08 MPa at pH ? 7. We also found that EB of the composite ?lms increased with increasing the pH value of SPI ?lm-forming solution. Brandenburg, Weller, and Testin (1993) compared properties of SPI ?lms at pH 6, 8, 10, and 12. They found that pH 6 gave the lowest TS and EB, while higher pH gave higher TS and EB. Rhim et al. (1999) also reported that treatments with alkali and heating/dehydration could modify physical properties of SPI ?lms. Usually, two important processes were used to prepare ?lms. One was wet process based on dispersion or solubilization of proteins, the other was dry process based on thermoplastic

properties of proteins under low water conditions. In the wet process, pH was a very important factor. In general, the dispersion was easily made at pH47 to unfold the protein. Sensitivity of proteins to pH change was usually associated with a high content of ionized polar amino acids (Swain, Biswal, Nanda, & Nayak, 2004). Treatments of SPI at high pH had resulted in hydrolyzed, denatured products which were more soluble and gel free in solution. Denaturation of protein was known to change the shape of the protein from globular to extended chain, thus more protein–protein interactions would occur (Brandenburg et al., 1993). In our experiment, the pH values of the SPI ?lm-forming solutions were about 6, 7, 8, 8.5, 9, and 10, respectively. After mixed with gelatin ?lm-solutions, the pH values of the mixtures were 5.87, 6.48, 7.02, 7.28, 7.50, and 9.33, respectively. Gennadios, Brandenburg, Weller, and Testin (1993) found that ?lm formation was inhibited by poor protein dispersion around the isoelectric pH region of SPI (pH 4.5). It was because that SPI coagulated, rather than dispersed, at pH 4–5. At pH values away from the isoelectric region, protein denatures, unfolds, and solubilizes, exposing sulfhydryl and hydrophobic groups. Such groups associate upon drying to form disul?de and hydrophobic bonding forces. SPI ?lms of higher TS were produced at pH values above the protein’s isoelectric point. (Gennadios et al., 1993). In Fig. 2, the fall of TS of SPI/gelatin composite ?lms when the pH value of SPI ?lm-forming solution changed from 8.5 to 10 was also observed. This may be explained by

ARTICLE IN PRESS
N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162 1157

Tensile Strength (MPa)

50 45 40 35 30 25 5 4 3 2 1

(a)

Elastic Modulus (MPa)

Elongation (%)

(b)

2000 1800 1600 1400

(c)

6

7

8 pH

9

10

Fig. 2. Effect of pH of SPI ?lm-forming solution on tensile strength (a), elongation to break (b), and elastic modulus (c) of SPI:gelatin ? 4:6 composite ?lm containing 0.1 g glycerin/g protein Error bars show 795% con?dence interval.

two reasons. One was that more Na2CO3 (used to adjust pH values) absorbed more water, whilst water could act as plasticizer for protein. The other was that TS of gelatin ?lm appeared maximum when pH of ?lm-forming solution was about 7 according to our previous study (Cao, Fu, & He, 2006). It could be concluded that the properties of composite ?lms were better at the pH value of 8–9 of the SPI ?lmforming solution. 3.1.3. The effect of thermal-treatment temperature of SPI ?lm-forming solution on mechanical properties of composite ?lms The in?uences of thermal-treatment of SPI ?lm-forming solution on TS, EB and EM of composite ?lms are showed in Fig. 3. Clearly, TS, EM and EB of composite ?lms increased as the temperature increased from about 46–90 1C. For example, TS increased from 46.88 to 59.44 MPa after the SPI ?lm-forming solution was heated at 90 1C. Thermal-treatment of protein ?lms and coatings or ?lmforming protein solutions noticeably affected ?lm properties. Thermal treatments of proteins at alkaline pH promoted formation of intra- and intermolecular crosslinks (Kim, Weller, Hanna, & Gennadios, 2002). Rhim, Gennadios, Handa, Weller, and Hanna (2000) observed that heat induced cross-linking contributed to increased strength and reduced extendibility of SPI ?lms. Stuchell and Krochta (1994) reported that quatemary structures of 7 and 11 S proteins of SPI could be disrupted by heat treatment. Heating also denatures secondary and tertiary

structures of proteins and allows possible disul?de interchange among protein molecules. Their result was that heated SPI ?lms had decreased water vapor permeability, and increased EB and solubility of protein when compared to unheated ?lms. Studies also showed that heat curing improved the mechanical toughness and moisture resistance of cast protein ?lms made from corn zein, wheat gluten, collagen, whey protein, and soyprotein, etc. (Garci’a & Sobral, 2005; Hernandez-Munoz, Villalobos, & Chiralt, 2004; Kim et al., 2002). During heat treatment, parts of three-dimensional structure of 11 S were unfolded, and parts of the hydrophobic residues, –SH groups, and S–S bonds, which were buried inside before heating, were exposed to water. When the molecular distances were close enough to each other, intermolecular polymerization occurs through molecular forces of –SH, S–S interchange reaction, and /or hydrophobic bonds, resulting in an intermolecular network (Cao & Chang, 2001). Heating favored soy protein cross-linking by disrupting the protein structure and exposing sulfhydryl and hydrophobic groups (Sabato et al., 2001). So, after SPI ?lmforming solution was heat-treated, the mechanical properties of SPI/gelatin composite ?lm were improved. 3.1.4. The effects of concentrations of glycerin on mechanical properties of composite ?lms Plasticizers are one of the basic additives of ?lm forming polymers. They reduce intermolecular forces, increase the mobility of biopolymer chains. Addition of a plasticizing agent is necessary in order to overcome the brittleness of ?lm, to improve ?ow and ?exibility, and to increase

ARTICLE IN PRESS
1158 N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162

Tensile strength (MPa)

60 55 50 45

(a)

Elongtion (%)

4.0 3.6 3.2 2.8

(b)

Elastic modulus (MPa)

2600 2400 2200 2000

(c)

45

50

55

60

65

70

75

80

85

90

Temperature (°C)
Fig. 3. Tensile strength (a), elongation to break (b), and elastic modulus (c) of SPI/gelatin ? 4:6 composite ?lms containing 0.1 g glycerin/g protein as function of thermal-treatment of SPI ?lm-solution (pH ? 8). Error bars show 795% con?dence interval.

toughness, strength and impact resistance of ?lm coating, and to prevent it from cracking during packing and transportation (Aydinli & Tutas, 2000; Barreto, Pires, & Soldi, 2003). A variety of plasticizers were commonly used in edible ?lms, including glycerol, polyethylene glycol 400 (PEG), sorbitol, propylene glycol and ethylene glycol. Polar groups (?OH) along plasticizer chains are believed to develop polymer–plasticizer hydrogen bonds that replace the polymer–polymer interactions in the biopolymer ?lms. Molecular size, con?guration and total number of functional hydroxyl groups of the plasticizer as well as its compatibility with the polymer could affect the interactions between the plasticizer and the polymer. Due to its small size, glycerin was more effective (Yang & Paulson, 2000). The in?uence of glycerin concentration on the mechanical properties of SPI:gelatin ? 4:6 composite ?lm is showed in Fig. 4. It displayed that TS, EM decreased and EB increased signi?cantly with increase of glycerin. Thus, addition of glycerin to edible ?lm increased extensibility of the ?lm, whilst reduced the mechanical strength. Without glycerin, the composite ?lms tended to be brittle and dif?cult to handle, which mainly resulted from the brittleness of SPI. Brandenburg et al. (1993) also found that SPI ?lms made without plasticizer were extremely brittle and shattered upon handling. However, there would be white residues on the surface of composite ?lms with more than 0.3 g glycerin/g protein. This is just as PEG (more than 66.7%) plasticized gellan ?lms, which has been referred to as ‘bloom’, and may be explained by the same reason. This generally occurs when the plasticizer

concentration exceeded its compatibility limit in the polymer. This incompatibility will cause phase separation and physical exclusion of the plasticizer (Yang & Paulson, 2000). Furthermore, addition of glycerin above 0.3 g glycerin/g protein had resulted in sticky and wet ?lms. This was because ?lm with a higher concentration of plasticizer absorbed more moisture due to an overwhelming hydrophilicity of the plasticizer (Cho & Rhee, 2002). As showed in Fig. 5, the water content of SPI:gelatin ? 4:6 composite ?lm increased signi?cantly with increasing glycerin. So, the appropriate amount glycerin for SPI:gelatin ? 4:6 composite ?lm was 0.1–0.2 g glycerin/g protein.

3.1.5. The effects of concentrations of NaCl on mechanical properties of composite ?lms From Fig. 6, it could be concluded that the effect of NaCl on the TS, EB and EM of composite ?lm was similar to that of plasticizer. The addition of NaCl probably changed interaction between SPI and gelatin. With increasing concentration of NaCl, the composite ?lm became more opaque. When addition of NaCl exceeded 28.09 mg/g protein, the composite ?lm became whiter, which was caused by NaCl particles crystallized in the ?lm. The composite ?lm also became sticky, this was because NaCl could easily absorb water. As showed in Fig. 7, increasing concentration of NaCl resulted in increase of the water content of ?lm. And water is an effective plasticizer for protein ?lms (Sothornvit & Krochta, 2001).

ARTICLE IN PRESS
N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162 1159

Tensile Strength (MPa)

50 40 30 20 10

(a)

Elongation (%)

50 40 30 20 10 0 2500

(b)

Elastic Modulus (MPa)

2000 1500 1000 500 0

(c)

0.0

0.1

0.2 glycerin/ protein (g,w/w)

0.3

0.4

Fig. 4. Effect of concentration of glycerin on tensile strength (a), elongation to break (b), and elastic modulus (c) of SPI: gelatin ? 4:6 composite ?lm Error bars show 795% con?dence interval.

18 16 14 water content (%) 12 10 8 6 4 0.0 0.1 0.2 0.3 0.4

3.3. Opacity evaluation of composite ?lms From Table 1, could be seen that when the ratio of SPI/ gelatin changed from 8:2 to 0:10, the opacity of the composite ?lms decreased. From optic sensory with naked eyes, with increasing the gelatin content of the composite ?lms, there were less SPI small particles in ?lms. Thus the ?lms became more transparent. And the odor of soy of composite ?lms was limited. Brandenburg et al. (1993) pointed out that SPI was clear in appearance; however, insoluble partitles may be present. Commercial processing methods for SPI may have caused this insolubilization. Cho, Park, Batt, and Thomas (2006) mentioned that SPI was produced from defatted soy meal by alkali extraction followed by acid precipitation (pH 4.5). Due to the fact that acid precipitation decreases the nitrogen solubility of soy proteins by their denaturation and aggregation, SPI had limited solubility. Table 2 showed that when the pH of SPI ?lm-forming solution was 8, 8.5, 9, the opacity of composite ?lms declined, and the ?lms were quite transparent and homogeneous. When the pH value of SPI ?lm-forming solution was 6, the composite ?lm became whiter and more opacus. These opacity of SPI/gelatin composite ?lms mainly lied on the insolubility of SPI. Brandenburg et al. (1993) found that SPI ?lms prepared at pH 6 were opaque, and contained many insoluble particles, which is possibly due to the insolubility of soy proteins at that pH. In contrast, those ?lms prepared at pH 8, 10, and 12 were transparent. Treatment with alkali could make SPI more

glycerin/ protein (g,w/w)
Fig. 5. Effect of concentration of glycerin on water content of SPI: gelatin ? 4:6 composite ?lm Error bars show 795% con?dence interval.

3.2. In?uences of SPI/gelatin ratios on swelling properties of composite ?lms The in?uence of SPI/gelatin ratios on swelling properties are shown in Fig. 8. With increasing the gelatin content in composite ?lm, the degree of swelling capacity of the ?lm increased. This might be ascribed to the fact that gelatin could swell more strongly in water than SPI.

ARTICLE IN PRESS
1160 N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162

Tensile Strength (MPa)

50 40 30 20 (a)

Elongation (%)

6 5 4 3 (b)

Elastic Modulus (MPa)

2000 1750 1500 1250 1000 0 (c) 10 20 30 40 50 60

w (NaCl): w (protein)/(mg/g)
Fig. 6. Effect of NaCl on tensile strength (a), elongation to break (b), and elastic modulus (c) of SPI:gelatin ? 4:6 composite ?lm containing 0.1 g glycerin/g protein, pH of SPI ?lm-solution was 8. Error bars show 795% con?dence interval.

1100

12
1000

Water content (%)

11
Swelling (%)

900 800 700 600 500

10

9

8 0 10 20 30 40 50 60
400 10:0 8:2 6:4 4:6 2:8 0:10

w (NaCl): w (protein)/(mg/g)
Fig. 7. Effect of NaCl on water content of SPI: gelatin ? 4:6 composite ?lm containing 0.1 g glycerin/g protein, pH of SPI ?lm-solution was 8. Error bars show 795% con?dence interval.
SPI: Gelatin

Fig. 8. Swelling capacity of composite ?lms as function of SPI/gelatin ratios (containing 0.1 g glycerin/g protein) Error bars show 795% con?dence interval.

soluble, so ?lm appearance could be generally improved. Cho et al. (2006) also pointed out SPI ?lm formed at neutral pH showed uneven surfaces with unsolubilized particles, and protein solubility was increased by creating alkaline condition. In our experiment, as pH was 10, the ?lm became a little opacus compared to those prepared at pH 8, 8.5, 9, respectively. This may be because of partly crystallization of Na2CO3 that was used to adjust pH values in the course of ?lm forming.

When the temperature of thermal-treatment increased, the composite ?lms became more transparent and homogeneous by naked eyes. As showed in Table 3, heat-curing SPI ?lm-forming solution could decrease opacity of composite ?lms. In our experiment, higher temperature favored SPI dispersion in solution, thus increased the solubility of SPI. Stuchell and Krochta (1994) reported that

ARTICLE IN PRESS
N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162 Table 1 Opacity and absorption of composite ?lms as function of SPI/gelatin ratios (containing 0.1 g glycerin/g protein) SPI/Gelatin ratio 10:0 8:2 6:4 4:6 2:8 0:10 Absorption at 500 nm 0.06170.0070 0.38670.0071 0.20670.0127 0.19670.0205 0.19070.0014 0.045070.0014 Opacity 1.32670.1541 5.67670.1039 3.32370.2280 3.06370.1167 2.63970.0198 1.18470.0372 1161 Table 4 Opacity and absorption of composite ?lms as function of NaCl (pH of SPI ?lm-solution was 8) w (NaCl):w (protein)/(mg/g) 0 7.02 14.05 28.09 42.13 56.18 Absorption at 500 nm 0.10170.0092 0.08070.0028 0.09970.0042 0.18070.0022 0.62170.0134 0.72470.0184 Opacity 1.94270.1256 0.17470.0614 2.30470.0922 3.00070.03512 7.76370.1679 8.61970.2188

Values were given as average7standard deviation.

Values were given as average7standard deviation.

Table 2 Opacity and absorption of composite ?lms as function of pH of SPI ?lmforming solution pH 6 7 8 8.5 9 10 Absorption at 500 nm 0.60570.0495 0.19670.0205 0.10170.0092 0.07870.0028 0.08370.0014 0.11670.0064 Opacity 7.03570.0681 3.06370.1167 1.94270.1256 1.77370.0642 1.80470.04618 2.32070.1273

Values were given as average7standard deviation.

Table 3 Opacity and absorption of composite ?lms as function of thermaltreatment temperature of SPI ?lm-forming solution (pH of SPI ?lmsolution was 8) Temperature (1C) 46 (untreated) 50 60 70 80 90 Absorption at 500 nm 0.10170.0092 0.06770.0014 0.06170.0021 0.05970.0014 0.05670.0022 0.05470.0028 Opacity 1.94270.1256 1.59570.03365 1.38670.04815 1.31170.05289 1.27370.0069 1.20070.0098

Values were given as average7standard deviation.

heat treatment produced a ?lm which was smoother and more transparent than unheated SPI ?lms. As re?ected in Table 4, NaCl increased the opacity of composite ?lms except the addition of 7.02 mg NaCl/g protein. This exception was probably attributed to good dispersion of the small amount of NaCl. From optic sensory with naked eyes, the composite ?lms became more whiter and opaque when too much NaCl was added, because of crystallization of NaCl. 4. Conclusions SPI and gelatin composite ?lms could be used as edible ?lms. The composite ?lms utilized most effectively the functional behavior of SPI and gelatin. Gelatin ?lms had better mechanical properties and the properties of melting

in mouth instantly. But compare to plant protein SPI, gelatin was more expensive. In addition, SPI was much nutritional, and the addition of gelatin could diminish the undesirable ?avor of SPI, and improve properties of SPI ?lm. The mechanical, swelling and optic properties of composite ?lms (containing 0.1 g glycerin/g protein) made of SPI and gelatin were affected by the SPI/gelatin ratio. As the proportion of gelatin increased, TS, EB, and EM, swelling capacity of the composite ?lms increased, and the ?lms became much more transparent, easier to handle. So, gelatin could enhance ?lm strength and ?exibility. The properties of the composite ?lm prepared with a SPI:gelatin ratio of 4:6–2:8, approached to those of gelatin ?lm and were better than those of SPI ?lm. In addition, the ?lm was cheaper than gelatin ?lm. At a SPI:gelatin ratio of 4:6, adding 0.1 g glycerin/g protein, the ?lms appeared transparent and could be easily handled. The TS, EB, and EM of the ?lm were 33.65 MPa, 3.19%, 1540.61 MPa. At this ratio, with increase of concentrations of glycerin and NaCl, the EB and water content of composite ?lms increased, whilst TS, EM decreased. The appropriate amount of glycerin for SP/gelatin composite ?lms was 0.1–0.2 g glycerin/g protein, which could break the brittleness of ?lm, improve ?exibility and toughness. When the pH of SPI ?lm-forming solution was 8–9, the properties of composite ?lms were better. And thermal-treatment (50–90 1C) of SPI ?lm-forming solution could produce excellent mechanical and homogeneous ?lms.

References
Achet, D., & He, X. W. (1995). Determination of the renaturation level in gelatin ?lms. Polymer, 36(4), 787–791. ASTM. (2001). Standard test method for tensile properties of thin plastic sheeting. Annual book of ASTM standards. Designation D882-01. Philadelphia: ASTM, American Society for Testing Materials. Aydinli, M., & Tutas, M. (2000). Water sorption and water vapour permeability properties of polysaccharide (Locust Bean Gum) based edible ?lms. Lebensmittel-Wissenschaft und-Technologie, 33(1), 63–67. Barreto, P. L. M., Pires, A. T. N., & Soldi, V. (2003). Thermal degradation of edible ?lms based on milk proteins and gelatin in inert atmosphere. Polymer Degradation and Stability, 79(1), 147–152.

ARTICLE IN PRESS
1162 N. Cao et al. / Food Hydrocolloids 21 (2007) 1153–1162 pectin—soy ?our ?lms obtained in the absence or presence of transglutaminase. Journal of Biotechnology, 102(2), 191–198. Mauer, L. J., Smith, D. E., & Labuza, T. P. (2000). Water vapor permeability, mechanical, and structural properties of edible X -casein ?lms. International Dairy Journal, 10(5&6), 353–358. Ou, S. Y., Kwok, K. C., & Kang, Y. J. (2004). Changes in in vitro digestibility and available lysine of soy protein isolate after formation of ?lm. Journal of Food Engineering, 64(3), 301–305. Perez Gago, M. B., & Krochta, J. M. (2001). Lipid particle size effect on water vapor permeability and mechanical properties of whey protein/ beeswax emulsion ?lms. Journal of Agricultural and Food Chemistry, 49(2), 996–1002. Rhim, J. W., Gennadios, A., Handa, A., Weller, C. L., & Hanna, M. A. (2000). Solubility, tensile, and color properties of modi?ed soy protein isolate ?lms. Journal of Agricultural and Food Chemistry, 48(10), 4937–4941. Rhim, J. W., Gennadios, A., Weller, C. L., & Hanna, M. A. (2002). Sodium dodecyl sulfate treatment improves properties of cast ?lms from soy protein isolate. Industrial Crops and Products, 15(2), 199–205. Rhim, J. W., Wu, Y., Weller, C. L., & Schnepf, M. (1999). Physical characteristics of a composite ?lm of soy protein isolate and propyleneglycol alginate. Journal of Food Science—Engineering and Processing, 64(1), 149–152. Sabato, S. F., Ouattara, B., Yu, H., D’Aprano, G., Tien, L. C., Mateescu, M. A., et al. (2001). Mechanical and barrier properties of cross-linked soy and whey protein based ?lms. Journal of Agricultural and Food Chemistry, 49(3), 1397–1403. Shiku, Y., Hamaguchi, P. Y., Benjakul, S., Visessanguan, W., & Tanaka, M. (2004). Effect of surimi quality on properties of edible ?lms based on Alaska Pollack. Food Chemistry, 86(4), 493–499. Simon-Lukasik, K. V., & Ludescher, R. D. (2004). Erythrosin B phosphorescence as a probe of oxygen diffusion in amorphous gelatin ?lms. Food Hydrocolloids, 18(4), 621–630. Sothornvit, R., & Krochta, J. M. (2001). Plasticizer effect on mechanical properties of X -lactoglobulin ?lms. Journal of Food Engineering, 50(3), 149–155. Stuchell, Y. M., & Krochta, J. M. (1994). Enzymatic treatments and thermal effects on edible soy protein ?lms. Journal of Food Science, 59(6), 1332–1337. Swain, S. N., Biswal, S. M., Nanda, P. K., & Nayak, P. L. (2004). Biodegradable soy-Based plastics: Opportunities and challenges. Journal of Polymers and the Environment, 12(1), 35–42. Tang, R., Du, Y., Zheng, H., & Fan, L. (2003). Preparation and characterization of soy protein isolate–carboxymethylated konjac glucomannan blend ?lms. Journal of Applied Polymer Science, 88(8), 1095–1099. Xiao, C., Lu, Y., Gao, S., & Zhang, L. (2001). Characterization of konjac glucomannan–gelatin blend ?lms. Journal of Applied Polymer Science, 79(9), 1596–1602. Yang, L., & Paulson, A. T. (2000). Mechanical and water vapor barrier properties of edible gellan ?lms. Food Research International, 33(7), 563–570. Bigi, A., Panzavolta, S., & Rubini, K. (2004). Relationship between triplehelix content and mechanical properties of gelatin ?lms. Biomaterials, 25(25), 5675–5680. Brandenburg, A. H., Weller, C. L., & Testin, R. F. (1993). Edible ?lms and coatings from soy protein. Journal of Food Science, 58(5), 1086–1089. Cao, N., Fu, Y., & He, J. (2006). Preparation of gelatin ?lm and its properties. Journal of East China University of Science and Technology (Natural Science Edition), 32(10), 50–54. Cao, Y. M., & Chang, K. C. (2001). Edible ?lms prepared from water extract of soybeans. Journal of Food Science, 67(4), 1449–1454. Chambi, H., & Grosso, C. (2006). Edible ?lms produced with gelatin and casein cross-linked with transglutaminase. Food Research International, 39(4), 458–466. Cho, S.Y., Park, J.-W., Batt, H.P., Thomas, R.L. (2006). Edible ?lms made from membrane processed soy protein concentrates. LWT— Food Science and Technology [available online 23.03.2006]. Cho, S. Y., & Rhee, C. (2002). Sorption characteristics of soy protein ?lms and their relation to mechanical properties. Lebensmittel-Wissenschaft und-Technologie, 35(2), 151–157. Cho, S. Y., & Rhee, C. (2004). Mechanical properties and water vapor permeability of edible ?lms made from fractionated soy proteins with ultra?ltration. Lebensmittel-Wissenschaft und-Technologie, 37(8), 833–839. Garci’a, F. T., & Sobral, P. J. do A. (2005). Effect of the thermal treatment of the ?lmogenic solution on the mechanical properties, color and opacity of ?lms based on muscle proteins of two varieties of Tilapia. Lebensmittel-Wissenschaft und-Technologie, 38(3), 289–296. Gennadios, A., Brandenburg, A. H., Weller, C. L., & Testin, R. F. (1993). Effect of pH on properties of wheat gluten and soy protein isolate ?lms. Journal of Agriculture and Food Chemistry, 41(11), 1835–1839. Hernandez-Munoz, P., Villalobos, R., & Chiralt, A. (2004). Effect of thermal treatments on functional properties of edible ?lms made from wheat gluten fractions. Food Hydrocolloids, 18(4), 647–654. Jongjareonrak, A., Benjakul, S., Visessanguan, W., Prodpran, T., & Tanaka, M. (2006). Characterization of edible ?lms from skin gelatin of brownstripe red snapper and bigeye snapper. Food Hydrocolloids, 20(4), 492–501. Kim, K. M., Weller, C. L., Hanna, M. A., & Gennadios, A. (2002). Heat curing of soy protein ?lms at selected temperatures and pressures. Lebensmittel-Wissenschaft und-Technologie, 35(2), 140–145. Kim, S.-J., & Ustunol, Z. (2001). Solubility and moisture sorption isotherms of whey-protein-based edible ?lms as in?uenced by lipid and plasticizer incorporation. Journal of Agriculture and Food Chemistry, 49(9), 4388–4391. Lee, K. Y., Shim, J., & Lee, H. G. (2004). Mechanical properties of gellan and gelatin composite ?lms. Carbohydrate Polymers, 56(2), 251–254. Li, B., Kennedy, J. F., Jiang, Q. G., & Xie, B. J. (2006). Quick dissolvable, edible and heatsealable blend ?lms based on konjac glucomannan– gelatin. Food Research International, 39(5), 544–549. Mariniello, L., Di Pierro, P., Esposito, C., Sorrentino, A., Masi, P., & Porta, R. (2003). Preparation and mechanical properties of edible


赞助商链接
相关文章:
浙江大学教师岗位申请(推荐)表_图文
Detergents on the Adhesiveness and Thermal Properties of Soy Protein Isolate....Tilley*. Characterization of sorghum protein extract. (In preparation for J....
大豆分离蛋白溶解性和乳化活性影响因素的研究(20101029)
Key words: Soy protein isolate; Solubility; Emulsifying Properties 中图分类号: 中图分类号: 献标识码: 献标识码: 文章编号: 文章编号: 大豆分离蛋白(Soybean...
大豆异黄酮雌激素效应的研究
Isoflavone2rich soy protein isolate attenuates bone loss in the lumbar spine of periminopausal wom2 en[J ] . AmJ Clin Nutr ,2000 ,72 (3) :8442852...
生物酶在植物蛋白饮料中的应用
soy protein isolate[J].J>agric.Chem,1990.38(12):651~656 [7]Qi H,Hettiarachchy M, Kalapathy N S .Solubility and emulsifying peoperties if soy ...
碳酸钙晶须用量对胶黏体系性能影响的研究
大豆分离蛋白( SoyProtein Isolate,简称 SPI)是 以大豆为原料经过加工制成的[2]。 用大豆分离蛋 白制成的大豆蛋白胶黏剂有一定的粘接性能,能够 粘接木材,纸张...
蛋白质的改性论文
,1997, 60: 357~363 [4] Barman.B.G.,HansenJ.R;Mossey A.R 二 Modification of the Physical Properties of Soy Protein Isolate by Acetylation.J....
生物质材料木材胶粘剂的发展
Preparation of dopamine-grafted soy protein isolate (SPI-DA). Reaction ...Thermal properties and adhesiveness of soy protein modified with cationic ...
营养与食品卫生专业词汇 10
sorghum 高梁 sour milk 酸奶 soya-bean milk 豆浆 soy bean 大豆 soy protein concentrate 浓缩大豆蛋白 soy protein isolate 分离大豆蛋白 specific dynamic action...
河工大 双语 重点
6. Factors affecting physical characteristic of ...5 . What are Soybean Protein Isolates? By ...How many functional properties do vegetable protein...
婴幼儿配方米粉的研制
soy protein isolate powder 20%, rice 50%, 20% egg yolk powder, ... suitable for infants and young children's physical and dietary ...
更多相关标签: