J. Home Econ. J pn. Vol. 44 No. 12 999-1005 (1993) Gelation and Melting of a Mixed Carrageenan-Gelatin Gel Reiko SHIMADA, Keiko KUMENO,* Hiro AKABANE * * and Nobuko NAKAHAMA * Junior College at Mishima, Nihon University, Mishima, Shizuoka 411, Japan * Japan Women's University, Bunkyo-ku, Tokyo 112, Japan * * Kantogakuin Women's Junior College, Kanazawa-ku, Yokohama 236, Japan The rheological changes in a mixture of two different gelling agents were studied. A 0.9% (w/v) ƒÈ-carrageenan solution (C(1)), a 4% (w/v) gelatin solution (G(1)) and mixed samples in three proportions were prepared. The gelling temperature and melting temperature were mea- sured. Changes in the dynamic viscoelasticity when the state of the gel changed were determined with a Rheolograph-Sol instrument, and the endothermic reaction during melting was also examined by DSC. The gelling and melting temperatures for C(1) were the highest among all the samples. These values for the mixed samples were reduced according to the decreasing ratio of carrageenan. Gelling and melting of the samples were observed when the storage modulus was in the range of 6-8 N/m2. This suggests that the change point for state exists in this range. The DSC result revealed that the peak heights of the mixed gelatin-carrageenan samples were lower and their shapes were broader than those of the pure samples. The peak temperature of the endothermic reaction and the melting temperature corresponded well. (Received February 2, 1993) Keywords: carrageenan/gelatin mixed gel, gelation, melting, DSC, dynamic viscoelasticity. bean gum, in different ratios, and have also reported INTRODUCTION rheological changes during gelling of pure samples.4) Both gelatin and carrageenan are widely used However, there is no information available about as gelling agents for cookery and food applications global changes in the gelling properties, including since both form a highly transparent gel. The both gelling and melting. gelling properties of these agents are, however, Thus, a Reolograph-Sol instrument equipped very different. Gelatin is often used for home with a computer-controlled temperature stabilizer cookery as it melts quickly in the mouth due to its was utilized to clarify changes in the viscoelasticity low melting point, but this property is trouble- (which is assumed to quantify the texture in the some when handling. While not melting very mouth) of the mixed gels during their gelling and well in the mouth, carrageenan is frequently used melting transitions. The gelling temperature, us- in commercial products because of its stability ing the laid-down test tube method, melting during transportation. Thus, it would be advan- temperature, using the upside-down test tube tageous to determine the optimal ratio of these method, and endothermic reaction during melting two gelling agents so as to obtain a gel with proper- were also measured to examine their relationships ties of good melting in the mouth and ease of to viscoelasticity. handling. To approach this goal, we investigated EXPERIMENTAL METHOD in this study the gelling properties of various gelatin-carrageenan mixtures in terms of melting Sample preparation in the mouth. κ-carrageenan CS-88 (San-ei Chemicals), alkali- Several studies have reported the different gel- treated gelatin A-U (Miyagi Chemicals) and su- ling properties obtained by mixing four gelling crose (Kanto Chemicals) were used. Their con- agents,1)-3) carrageenan, gelatin, agar and locust centrations were adjusted to 0.9% (w/v) for carra- ( 999 ) 1 J. Home Econ. Jpn. Vol. 44 No. 12 (1993) Table 1. Volumetric proportions of the mixed samples geenan, 4% (w/v) for gelatin and 40% (w/v) for were injected into test tubes with a diameter of 1.2 sucrose. cm, and maintained at 50°C for 30 min in a pro- Although too high for a table jelly, the sucrose grammed hot bath (Taiyo Chemicals). The tem- concentration of 40% was selected for our study perature was then decreased at a rate of 0.5°C per in order to make the result clearer.5' Five-hun- minute. One test tube was removed every minute, dred-milliliter samples were prepared by the laid down as shown in Fig. 1-a, and the distance method of Isozaki et al.,6) carrageenan being soaked migrated after 3 sec was measured. in distilled water for 1 h, and heated for 1 h at As the temperature fell, the sol became more 75°C and then for 30 min at 98°C (carrageenan. viscous, and the migration finally became zero. sample). Gelatin was soaked in distilled water for This happened when the sol in the very center 1 h and then heated for 30 min at 65°C (gelatin (0.6 cm away from the test tube wall) gelled, sample). The carrageenan and gelatin samples indicating a difference between the temperature of prepared in this way were mixed in the volume the water bath and the gelling temperature. To ratios shown in Table 1, these being 3:1, 1 :1 and produce the most realistic value possible, we 1:3 (mixed samples). decided to take the temperature of the water bath Both pure carrageenan and gelatin samples were when the length of migration was 2 mm and to use also prepared with sucrose by using the method already stated, but the volume of water for each sample was decreased beforehand so that the subsequent sugar addition would give the same final volume. Sugar was added, and each sample was then heated for a further 30 min. The carra- geenan-sucrose and gelatin-sucrose sols were mixed in the volume ratio of 1 :1 (mixed sample with sucrose). The abbreviations shown in Table 1 will be used throughout the remainder of the paper. Measurement The laid-down test tube method and the upside- down test tube method are illustrated in Fig. 1. (a) (b) 1. Gelling temperature Fig. 1. Measurement of gelling temperature by the The method of Takebayashi et al." with some laid-down test tube method (a) and of melting modifications was employed to measure the gelling temperature by the upside-down test tube temperature. Aliquots of the sample sol (5 ml) method (b) 2 ( 1000) Gelation and Melting of a Mixed Carrageenan-Gelatin Gel this as the gelling temperature ( TO for the laid- down test tube method. 2. Melting temperature The melting temperature was measured by the upside-down test tube method (Tanii et al.8)). First, 5-ml aliquots of the sample sols were injected into test tubes with a diameter of 1.2 cm. The test tubes were maintained at 10•Ž for 3 h until the contents had gelled, and were then placed upside-down in a water bath at 20•Ž (Fig. 1-b). The temperature of the water bath was then Fig. 2. Gelling temperatures of the samples increased by 0.5•Žper minute. The temperature of the water bath at which the gel collapsed was taken as the melting temperature ( Tm). 3. Viscoelasticity A Rheolograph-Sol instrument (Toyo Seiki; 3 Hz, + / -50 ƒÊm) was utilized to measure the dynamic viscoelasticity. A sample (1.5 ml) was cooled at a rate of 0.5•Ž per minute to 5•Ž, and the gelled sample obtained was then heated until it melted. Changes in the viscoelasticity during gelling and melting were consecutively measured. 4. Endothermic reaction The endothermic reaction of the samples with- out sucrose was measured during melting by DSC (Rigaku DSC 8240). A sample (25 mg) was prepared in a sealed aluminium cup, and water Fig. 3. Melting temperatures of the samples was used as a reference. Measurements were conducted while increasing the temperature at a rate of 2•Ž per minute from 5•Ž to 78•Ž. RESULTS AND DISCUSSION by carrageenan, which started gelling more quickly Temperature for gelling and melting than gelatin. The gelling temperatures of the To gelling temperatures from the laid-down test samples with sucrose were 4•Ž to 12•Ž higher than tube method are shown in Fig. 2, those of samples those of the samples without sucrose. Since the C(1) and G(1) without sucrose being around 30•Ž two lines in Fig. 2 (SC(1) to SC-G(1:1) and C(1) and 18•Ž, respectively. The mixed gels had an to C-G(1 :3)) are nearly parallel, the gelling tem- intermediate gelling temperature. The higher perature for the samples with sucrose is also as- the carrageenan concentration, the higher the gel- sumed to have been affected by the carrageenan ling temperature for the mixed gel samples (C(1), concentration. C-G(3:1), C-G(1:1), C-G(1:3)). Although data The melting temperatures by the upside-down are not presented, the gelling temperature for test tube method are shown in Fig. 3, those for sample C-G(1 :1) and that of the pure 0.45% samples C(1) and G(1) being 50•Ž and 30•Ž, (w/v) carrageenan sample (which had the same respectively. The melting temperature tended to carrageenan concentration as that of the C-G(1 :1) increase as the concentration of carrageenan sample) were the same. This shows that gelatin increased, as was the case with the gelling tempera- had no influence on the gelling temperature of the ture. This suggests that the gel fell from the test mixed samples, probably because carrageenan has tube wall only when the carrageenan started to a higher gelling temperature than gelatin. The melt, and that the effect of gelatin on the melting gelling of the mixed sample was therefore controlled temperature was small. The melting temperature ( 1001) 3 J. Home Econ.