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Classification of hydrocolloids based on in vitro starch digestibility and rheological properties of Segoami gel
International Journal of Biological Macromolecules 104 (2017) 442–448
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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Classification of hydrocolloids based on in vitro starch digestibility and rheological properties of Segoami gel Da Sol Jung a , In Young Bae b , Im Kyung Oh a , Sang-Ik Han c , Sung-Joon Lee d , Hyeon Gyu Lee a,∗ a
Department of Food and Nutrition, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Republic of Korea, Republic of Korea Department of Food & Fermentation, Far East University, Gamgok, Eumseong, Chungbuk 369-700, Republic of Korea c Department of Functional Crop, National Institute of Crop Science (NICS), Rural Development Administration (RDA), Miryang 50424, Republic of Korea d Department of Food Bioscience & Technology, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 27 February 2017 Received in revised form 25 May 2017 Accepted 12 June 2017 Available online 13 June 2017 Keywords: Segoami Hydrocolloid Principle component analysis In vitro starch digestibility Rheological property
a b s t r a c t The influence of hydrocolloids on in vitro starch digestibility and rheological properties of Segoami (a new rice variety fortified with amylose and dietary fiber) gel was investigated in terms of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition levels (0.3–0.7% for rice flour weight) of hydrocolloids. In addition, the behavior of hydrocolloids was analyzed by principal component analysis (PCA) based on both properties of various Segoami-hydrocolloids gels. The first and second principle components (PC) explained 80.93% of the total variation; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively, implying that the two components provided a strong summary of the data. PC1, represented in vitro starch digestibility and was affected by the addition level of hydrocolloids: PC2, represented rheological parameters and was highly affected by the type of hydrocolloids. Moreover, there was a non-linear relationship between in vitro starch digestibility and rheological properties of Segoami-hydrocolloids gels. The hydrocolloids used in this study showed similar features according to the addition levels of hydrocolloids regardless of type. Segoami-0.5% arabic gum gel was the optimum preparation for retarding in vitro starch digestibility and maintaining rheological properties. © 2017 Published by Elsevier B.V.
1. Introduction Rice is a major cereal grain staple food across the world and has a high glycemic index (GI). Diets that mainly consist of white rice can lead to obesity and hyperlipidemia [1]. Therefore, to enhance the health functionality of rice, several challenges must be met to develop functional rice varieties. Segoami is a new rice variety which was fortified with amylose and dietary fiber in order to reduce GI. Many factors affect the functional properties of rice varieties, including granule structure, amylose contents, and amylose-amylopectin ratio [2]. Among them, amylose content is a key factor in controlling starch digestibility. Starchy foods with high amylose contents have been associated with reduced sensitivity to digestive enzymes, decreased blood glucose levels, and a reduced rate of gastric emptying [2,3]. For these reasons, Segoami, which is classified as
∗ Corresponding author at: 222 Wangsimni-ro, Seoul, 04763, Korea. E-mail address: [email protected] (H.G. Lee). http://dx.doi.org/10.1016/j.ijbiomac.2017.06.063 0141-8130/© 2017 Published by Elsevier B.V.
high-amylose rice, is expected to exhibit lower GI relative to other rice varieties. Hydrocolloids, generally known as either thickening or gelling agents, can be used to improve the texture and stability of foods and to retard starch digestibility [4]. Several reports have been published on the functionalities of hydrocolloids over long periods. The impact of rice starch on digestive patterns in the presence of hydrocolloids has been reported in mixed grain porridge, including arabic gum, rice starch dispersions with xanthan gum and guar gum, and rice coated with locust bean gum and agar [5–7]. Cooked rice in the presence of several hydrocolloids shows improvement in texture and starch digestibility [8]. Alginate in rice dough and noodles has been confirmed to have an effect on cooking quality and starch hydrolysis [9]. Rice starch suspensions mixed with xanthan, pectin, and agar have been examined in previous studies focusing on viscosity and starch digestibility [10]. These functionalities of hydrocolloids are expected to be synergetic with Segoami. When the two functional ingredients are applied in a food matrix, effective synergy will retard in vitro starch digestibility and improv processing quality.
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Therefore, the aims of this study were to investigate the effects of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition level (0.3–0.7% of rice flour weight) of various hydrocolloids on in vitro starch digestibility and rheological properties of Segoami gels and to classify these hydrocolloids based on both properties using principal component analysis (PCA). The results from this study will provide a fundamental understanding of the guidelines for selecting hydrocolloids that lower in vitro starch digestibility and maintain or improve rheological properties in the food applications of Segoami.
and amyloglucosidase (0.2 mL per gram of starch in the sample), the pH of the sample was adjusted to 6.0 using 1 M HCl, and the sample was incubated in a 37 ◦ C shaking water bath. Aliquots of 0.1 mL were withdrawn at 0, 30, 60, 90, 120, and 180 min during digestion. Each aliquot was replaced with 1.4 mL of absolute ethanol and centrifuged at 3000g for 3 min. The released glucose content of the supernatant was analyzed using the GOPOD kit. Levels of rapidly digestible starch (RDS) and slowly digestible starch (SDS) were measured after intestinal digestion for 30 min and 120 min, respectively, and resistant starch (RS) was the starch remaining after 180 min.
2. Materials and methods
C = C∞ 1 − e−kt
2.1. Materials The Segoami rice cultivar produced in 2014 was obtained from the National Institute of Crop Science (NICS), Rural Development Administration (RDA), Korea. The rice was ground and passed through a 100 mesh sieve. Gum arabic from the acacia tree (G9752), guar gum (G4129), gum locust bean (G0753), and xanthan gum from xanthomonas (G1253) were obtained from Sigma-Aldrich Co. (St. Louis, MO, USA). Sodium alginate (37094-01) was obtained from Kanto Chemical Co. (Tokyo, Japan). Pancreatin from porcine pancreas (P7545, activity 8 x USP/g), amyloglucosidase (A9913), and porcine bile extract (B8631) were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Total starch assay (K-TSTA) and glucose oxidase-peroxidase assay (GOPOD, K-GLUC) kits were obtained from Megazyme International Ireland Ltd. (Bray, Ireland).
2.4. Predicted glycemic index The digestion kinetics and pGI (predicted glycemic index) of Segoami flour gel were estimated according to the procedure suggested by Miao et al. [12]. The kinetics of starch hydrolysis were estimated as follows: where C, C∞ , and k denote the hydrolysis degree at each time, the maximum hydrolysis extent, and the kinetic constant, respectively. The hydrolysis index (HI) was calculated by dividing the area under the hydrolysis curve of each sample by the corresponding area of a reference sample (fresh white bread). The predicted glycemic index (pGI) was estimated as follows: pGI = 39.71 + 0.549HI
2.2. Preparation of samples
2.5. Rheological measurements
The types and addition levels of hydrocolloids were selected according to the results of previous studies [6–10]. All hydrocolloids (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) were mixed with distilled water to make 0.3, 0.5 and 0.7% (w/w, dry weight basis of rice flour) solutions, and each was stirred continually at 500 rpm. The solutions of arabic gum, sodium alginate, and xanthan gum were dissolved by heating at 50 ◦ C for 30 min, 95 ◦ C for 10 min, and 60 ◦ C for 15 min, respectively. After heating, the solutions were cooled at room temperature. Locust bean gum and guar gum solutions were prepared by heating on a stir plate at 95 ◦ C or 85 ◦ C, respectively, for 5 min, followed by stirring overnight at room temperature. The Segoami was ground and passed through a 100 um-pore diameter sieve to prepare rice flour gels. The Segoami flour was dispersed into distilled water or hydrocolloid suspensions at a concentration of 10.71% for measuring viscoelasticity and in vitro starch digestion properties. Dispersions containing 5% Segoami flour were also prepared for measuring flow behavior. The mixtures were heated in a double boiler on hotplates for 5 min and then steamed in a stainless steel steam pan for 40 min.
Rheological measurements of samples were conducted using a controlled strain rheometer (RheoStress RS1, Thermo Haake, Karlsruhe, Germany) equipped with a parallel plate geometry 35 mm in diameter with a 1 mm gap. A fresh sample was placed between parallel plates and excess sample was removed smoothly by a spatula. All rheological measurements were performed in triplicate. Dynamic viscoelastic properties were determined over a frequency range of 0.1–10 Hz at 1% strain and 25 ◦ C. A linear viscoelastic region was monitored before performing a frequency sweep test. Viscoelastic parameters of elastic modulus (G ), viscous modulus (G ), and tan ␦ were extracted using the program of rheometer.
2.3. In vitro starch digestion To simulate small intestinal digestion, in vitro starch digestion was conducted in accordance with Minekus et al. [11]. Simulated intestinal fluid (SIF) was composed of 6.8 mL of 0.5 M KCl, 0.8 mL of 0.5 M KH2 PO4 , 42.5 mL of 1 M NaHCO3 , 9.6 mL of 2 M NaCl, and 1.1 mL of 0.15 M MgCl2 (H2 O)6 in 400 mL of distilled water. Pancreatin was diluted 1:5 (w/v) with SIF and centrifuged at 3000g for 20 min. The enzyme solution was prepared by dilution of 5 mL of pancreatin supernatant, 0.435 g of bile extract, and 2 mL of SIF. The sample was synthesized by mixing 5 g of 10.71% gel with 26 mL of prepared SIF, 40 uL of 0.3 M CaCl2 , 0.15 mL of 1 M NaOH, and 1.31 mL of distilled water. After the addition of enzyme solution
2.6. Statistical analysis All experiments were performed in triplicate and means and standard deviations are reported. Analysis of variance (ANOVA) was performed, and the means were separated by Duncan’s multiple range test (p < 0.05). Cluster analysis (CA) and principle component analysis (PCA) were performed on in vitro starch digestibility (RDS, SDS, RS, and pGI) and viscoelastic parameters (G , G , and tan ␦). Statistical analyses were conducted using SPSS software (ver. 21.0, IMB Corp., Armonk, NY, USA). 3. Results and discussion 3.1. In vitro starch digestibility of Segoami-hydrocolloids gels Fig. 1 demonstrates the effects of Segoami gels with various hydrocolloids on in vitro starch digestibility compared to control gels without hydrocolloids. The amount of released glucose was determined as reducing sugars released during starch hydrolysis by digestive enzymes. Glucose release decreased in all samples with hydrocolloids compared to control without hydrocolloids.
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Fig. 1. Effects of sodium alginate (A), arabic gum (B), guar gum (C), locust bean gum (D), and xanthan gum (E) on glucose release of Segoami gels with different addition levels and the glucose release curve of Segoami gels with various hydrocolloids at 0.5% addition level (F).
Specially, the addition of 0.5% hydrocolloids in Segoami gels displayed the greatest impact on reducing in vitro starch digestibility. Arabic gum was the hydrocolloid that most significantly lowered the amount of glucose released, followed by xanthan gum, sodium alginate, locust bean gum, and guar gum. Starch fractions by enzymatic digestion with or without hydrocolloids are presented in Table 1. RDS is the starch fraction that digests rapidly during digestion for 30 min in the small intestine, SDS is the starch fraction that digests slowly, between 30 and 120 min of digestion, and RS is the starch fraction that is resistant to digestion in the small intestine [13,14]. The addition of hydrocolloids in the Segoami flour reduced RDS and SDS, but increased RS at the same time. In gels with 0.5 and 0.7% hydrocolloids, the amount of RDS and SDS ranged from 40.06-46.35% and 15.7822.86%, respectively. The addition of 0.5-0.7% hydrocolloids may prevent rapid degradation of starch in Segoami. Conversely, the amount of RS was over the range of 32.83-42.82%, much higher than that of the control (31.20%). The higher RS of Segoami-hydrocolloids gels suggests that the addition of hydrocolloids can slow the rate of starch degradation. The RS values of samples with arabic gum were much higher compared to other hydrocolloids at same level. The pGI values for Segoami gels with or without hydrocolloids are also presented in Table 1. The pGI values of 0.5% hydrocolloids ranged from 78.3 to 81.5 and those of 0.7% hydrocolloids ranged from 80.7 to 83.7, considerably lower values than the control (84.5). When the hydrocolloid addition level was 0.3%, there was little or no impact on pGI values compared to control. The 0.5% hydrocolloid addition groups showed the lowest glucose release curve. When 0.7% hydrocolloid was added, however, the glucose release curves increased again. Hydrocolloids act as a barrier to digestive enzyme at a certain concentration, but at a higher concentration, hydrocol-
loids enhance swelling of starch granules and promote the rate of starch hydrolysis [4]. These significant effects on reducing starch hydrolysis may be because the arabic gum prevented the starch from contacting digestive fluids and thus decreased glucose production [6]. The swelling power of arabic gum is also related to starch digestion. One factor relating to reduced starch hydrolysis is the inhibition of starch swelling. Thus, the sensitivity to digestive enzymes increased with swelling power [16]. Song et al. [15] have established that arabic gum led to a decrease in the swelling power of rice starch dispersions, suggesting that arabic gum had low swelling power at high temperatures. In other words, the low swelling power of arabic gum may have contributed to the slow the rate of starch hydrolysis. However, further study is needed to confirm the relationship between swelling power and the retardation of starch digestion by arabic gum. The effects of hydrocolloids on the retardation of starch digestibility have been investigated in many other studies. Guar gum is believed to inhibit starch from accessing water in food systems, and consequently prevents starch gelatinization [16]. Alginate acts as a physical barrier that encapsulates the starch granule, and is known to reduce pGI [11]. LBG and xanthan gum also restrict the water in starch foods, increase the viscosities of digesta, or restrict the accessibility of digestive enzymes [17]. The variation of starch digestion patterns might be due to hydrocolloid differences, including molecular weight, branching, and ionic charge, all of which influence their digestion degree. A hydrocolloids-amylose interaction could facilitate the enzyme attack, or retard enzymatic hydrolysis by coating the surface of the starch granule as physical barrier. Therefore, the optimized combination of starch and hydrocolloid is important, based on their in vitro digestibilities.
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Table 1 Starch fractions and pGI of Segoami gels with various hydrocolloids in different addition levels. Addition level (%)
Control Sodium alginate
Arabic gum
Guar gum
Locust bean gum
Xanthan gum
0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7
Starch fraction (%)
pGI
RDS
SDS
RS
45.61 ± 1.56ab 46.33 ± 5.61a 43.54 ± 1.07abc 43.77 ± 3.59abc 43.93 ± 0.69abc 40.06 ± 1.45c 43.32 ± 1.39abc 45.23 ± 2.29ab 42.27 ± 1.51abc 43.91 ± 1.95abc 46.35 ± 2.26a 43.83 ± 1.53abc 43.87 ± 2.34abc 43.66 ± 1.55abc 41.35 ± 2.60bc 44.13 ± 1.74abc
23.19 ± 2.92a 18.68 ± 2.83ab 15.78 ± 1.99b 18.37 ± 3.32ab 19.03 ± 3.58ab 17.12 ± 1.07b 19.06 ± 1.73ab 20.91 ± 4.06ab 17.98 ± 1.13ab 20.45 ± 3.51ab 20.83 ± 1.31ab 17.10 ± 1.53b 19.84 ± 5.09ab 18.96 ± 1.87ab 18.31 ± 2.84ab 22.86 ± 3.63a
31.20 ± 4.42c 34.99 ± 4.63abc 40.68 ± 2.83ab 37.86 ± 6.66abc 37.04 ± 4.09abc 42.82 ± 2.15a 37.63 ± 2.78abc 33.87 ± 6.06bc 39.75 ± 1.32ab 35.64 ± 5.40abc 32.83 ± 3.38bc 39.07 ± 0.27abc 36.30 ± 7.42abc 37.39 ± 3.29abc 40.34 ± 2.99ab 33.02 ± 4.35bc
84.52 ± 3.03a 83.20 ± 2.89ab 80.21 ± 1.99ab 82.51 ± 5.56ab 82.74 ± 2.89ab 78.28 ± 2.00b 80.87 ± 2.14ab 83.47 ± 3.12ab 81.21 ± 1.59ab 83.73 ± 3.78ab 84.32 ± 1.46a 81.46 ± 1.19ab 82.41 ± 3.10ab 81.21 ± 2.84ab 80.74 ± 0.99ab 82.58 ± 2.36ab
Means with different letters in the same column are significantly different at p < 0.05.
3.2. Dynamic viscoelastic property of Segoami-hydrocolloids gels Fig. 2 represents the changes of G and G of Segoami gels mixed with different hydrocolloids in the frequency range from 0.1 to 10 Hz at 25 ◦ C. The magnitudes of G and G increased with frequency and G was higher than G over the frequency range tested. These features indicated that all tested samples showed weak gel-like behavior [18]. It is also well known that the addition of hydrocolloids causes noteworthy effects on the magnitudes of G , but does not affect those of G [19]. As shown in Table 2, the magnitudes of G’ and G at 1 Hz are different. These results are consistent with studies on starch or flour-hydrocolloids mixture systems [20,21]. There was a significant difference between G’ of Segoami-xanthan gum gels and other hydrocolloids. In other words, the Segoami gels with xanthan gum became more elastic due to the extended rod conformation of xanthan gum in solution [22]. The values of tan ␦ (G /G’) <1 or >1 represent mostly elastic or viscous behavior. The tan ␦ values of all samples were lower than 1, suggestive of a highly elastic gel. Furthermore, increasing the addition level of hydrocolloids led to an increase in tan ␦ values, except for arabic gum and guar gum, although there were no significant differences within hydrocolloid types or addition levels compared to the control [18,20].
3.3. Principle component analysis and cluster analysis Principle component analysis (PCA) and cluster analysis (CA) were conducted to confirm the factors, that affected in vitro starch digestibility and rheological properties of Segoami gels, and to classify all tested hydrocolloids based on these properties. The relationships between in vitro starch digestibility and rheological properties in the context of the addition of hydrocolloids are demonstrated in Fig. 3. The first and second principle components (PC) explained 80.93% of the total variance; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively. This result implies that two components provided a strong summary of the data. The factors of in vitro starch digestibility, including RDS, SDS, and pGI were located close together, while rheological properties containing G , G , and tan ␦ were located to the upper left of the cluster of in vitro starch digestibility. As shown in Fig. 3 (A), RS is placed on the opposite side of the clusters, including RDS, SDS, and pGI, and also located close to the gels with 0.5% addition of hydrocolloids, indicating that RS contributed to the low pGI of those samples.
This result predicts a non-linear relationship between in vitro starch digestibility and rheological properties. Furthermore, PC1 correlated positively with RDS, SDS, and pGI, while PC2 correlated positively with G , G , and tan ␦. These results confirmed that PC1 primarily explained factors related to in vitro starch digestibility, whereas PC2 primarily explained rheological properties of Segoami-hydrocolloids gels. Fig. 3 (B) shows that samples of the same addition level of hydrocolloids are located along the PC1 axis, 0.5% on the left side, 0.7% in the middle, and 0.3% on the right side. This means that factors of in vitro starch digestibility were highly affected by hydrocolloids addition level. In contrast, the factors of rheological parameters were highly affected by hydrocolloid type, because the samples of different hydrocolloids at the same addition level were dispersed along the PC2 axis. Gels containing 0.7% hydrocolloids were scattered along the PC2 axis in contrast to the 0.3 and 0.5% additions. The 0.7% addition level may strongly change the rheological properties relative to in vitro starch digestibility. To develop healthy rice products with lower GI, it is useful to apply hydrocolloids that not only retard starch hydrolysis effectively, but also minimally affect rheological properties [8]. Therefore, the samples with lower scores based on PC1 and similar control scores based on PC2 were selected. Among the selected samples, 0.5% arabic gum was located in a similar position to the control on PC2 and the furthest from the control on PC1. Consequently, 0.5% arabic gum with Segoami appeared to be most likely to be helpful in the food industry. The dendrogram and classification of clusters following CA are presented in Fig. 4. All Segoami-hydrocolloids samples were classified into four clusters. All samples were divided into several clusters in terms of their similarity. The results of CA showed that cluster 1 was comprised of five samples, cluster 2 included eight, and cluster 3 had two, while cluster 4 contained only one sample. The samples in cluster 1 were comprised of Segoami gels with 0.3% hydrocolloids or without hydrocolloids. cluster 2 samples were classified as samples with the addition of 0.5 and 0.7% hydrocolloids. Similarly, the members of the third cluster were made up 0.5% sodium alginate and 0.5% arabic gum. Finally, the cluster 4 sample was comprised of 0.7% xanthan gum. The Segoami-hydrocolloid gels studied in this paper were categorized according to the addition level of hydrocolloids, regardless of type. Through cluster analysis and PCA, the relationship between hydrocolloid concentration and type, rheological properties, and in vitro digestibility was shown. The rheological properties were characterized by the different types of hydrocolloids, and in vitro starch digestibilities were grouped by
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Fig. 2. Effects of sodium alginate (A), arabic gum (B), guar gum (C), locust bean gum (D), and xanthan gum (E) on elastic modulus (G , solid symbols) and viscous modulus (G , open symbols) of Segoami gels with different addition levels.
Table 2 Dynamic viscoelastic properties of Segoami gels mixed with various hydrocolloids in different addition levels at 1 Hz, 25 ◦ C.
Control Sodium alginate
Arabic gum
Guar gum
Locust bean gum
Xanthan gum
Addition level (%)
G’ (Pa)
G” (Pa)
tan ␦
0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7
460.13 ± 42.79bc 424.39 ± 29.69c 460.71 ± 44.81bc 479.74 ± 59.18abc 450.41 ± 78.81bc 520.06 ± 46.42abc 519.67 ± 45.70abc 445.20 ± 39.54bc 482.89 ± 57.60abc 511.74 ± 72.10abc 522.61 ± 8.08abc 511.59 ± 27.01abc 537.34 ± 38.73ab 475.92 ± 55.10abc 489.42 ± 25.35abc 570.23 ± 76.23a
105.71 ± 12.36ab 79.33 ± 14.73b 92.83 ± 3.56ab 120.79 ± 39.47ab 87.77 ± 4.11b 106.48 ± 27.04ab 91.62 ± 10.22ab 92.91 ± 9.61ab 120.55 ± 44.55ab 107.21 ± 1.31ab 88.00 ± 3.25b 113.93 ± 15.42ab 116.09 ± 44.73ab 107.73 ± 22.47ab 118.61 ± 19.61ab 134.91 ± 28.75a
0.23 ± 0.01a 0.19 ± 0.03a 0.20 ± 0.02a 0.25 ± 0.07a 0.20 ± 0.04a 0.20 ± 0.04a 0.18 ± 0.03a 0.21 ± 0.01a 0.25 ± 0.10a 0.21 ± 0.03a 0.17 ± 0.01a 0.22 ± 0.02a 0.21 ± 0.07a 0.22 ± 0.02a 0.24 ± 0.03a 0.24 ± 0.05a
Mean values with different letters in the same column differ significantly at p < 0.05.
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Fig. 3. Loading (A) and score plot (B) of Segoami gels with different type and addition levels of hydrocolloids based on in vitro starch digestibility and rheological property.
the different concentrations of hydrocolloids. Therefore, the optimized combination between hydrocolloids and Segoami enabled the development of processed products to improve health-related functionality and food quality. 4. Conclusions The effects of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition levels (0.3, 0.5, and 0.7%) of hydrocolloids on in vitro starch digestibility and rheological properties of Segoami gels were investigated. Multivariate analysis, including principle component analysis (PCA) and cluster analysis (CA) were used to examine the influence of hydrocolloids on two variables and to group similar types of hydrocolloids. The first and second principle components (PC) explained 80.93% of the total variance; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively, implying that two components provided a strong summary of the data. PC1 correlated positively with RDS, SDS, and predicted glycemic index (pGI), while PC2 correlated positively G , G , and tan ␦. This confirmed that PC1 primarily explained factors relating to in vitro starch digestibility, whereas PC2 primarily explained rheological properties of Segoami-hydrocolloids gels. The samples of the same hydrocolloids at different addition levels were scattered along the PC1 axis, indicating that factors of in vitro starch digestibility were highly affected by the addition level of hydrocolloids. In contrast, the factors of rheological parameters were highly affected by the type of hydrocolloids, as the samples of different hydrocolloids at same addition level were
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Fig. 4. Tree diagram (A) and clusters (B) on score plot of Segoami gels with different type and addition levels of hydrocolloids based on in vitro starch digestibility and rheological property.
dispersed along the PC2 axis. These results suggested that there was a non-linear relationship between rheological properties and in vitro starch digestibility of Segoami-hydrocolloid gels. Moreover, the hydrocolloids used in this study showed similar features according to their addition level, regardless of the type. In particular, 0.5% arabic gum was the optimal addition for retarding in vitro starch digestibility and maintaining its rheological properties. Acknowledgements This work was carried out with the support of “Cooperative Research Program for Agriculture Science & Technology Development (Project title: Development of specialty rice cultivar based on rice starch and its materials for commercialization, Project No. PJ01125305),” Rural Development Administration, Republic of Korea. References [1] A.-Y. Lee, S.-K. Yeo, J.H. Lee, H.-W. Kim, Y. Jia, M.H. Hoang, H. Chung, Y.-S. Kim, S.-J. Lee, Hypolipidemic effect of Goami-3 rice (Oryza Sativa L. Cv. Goami-3) on C57bl/6 j mice is mediated by the regulation of peroxisome proliferator-activated receptor-␣ and-␥, J. Nutr. Biochem. 24 (2013) 1991–2000. [2] H.-J. Chung, Q. Liu, L. Lee, D. Wei, Relationship between the structure, physicochemical properties and in vitro digestibility of rice starches with different amylose contents, Food Hydrocolloids 25 (5) (2011) 968–975.
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International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Classification of hydrocolloids based on in vitro starch digestibility and rheological properties of Segoami gel Da Sol Jung a , In Young Bae b , Im Kyung Oh a , Sang-Ik Han c , Sung-Joon Lee d , Hyeon Gyu Lee a,∗ a
Department of Food and Nutrition, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Republic of Korea, Republic of Korea Department of Food & Fermentation, Far East University, Gamgok, Eumseong, Chungbuk 369-700, Republic of Korea c Department of Functional Crop, National Institute of Crop Science (NICS), Rural Development Administration (RDA), Miryang 50424, Republic of Korea d Department of Food Bioscience & Technology, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 27 February 2017 Received in revised form 25 May 2017 Accepted 12 June 2017 Available online 13 June 2017 Keywords: Segoami Hydrocolloid Principle component analysis In vitro starch digestibility Rheological property
a b s t r a c t The influence of hydrocolloids on in vitro starch digestibility and rheological properties of Segoami (a new rice variety fortified with amylose and dietary fiber) gel was investigated in terms of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition levels (0.3–0.7% for rice flour weight) of hydrocolloids. In addition, the behavior of hydrocolloids was analyzed by principal component analysis (PCA) based on both properties of various Segoami-hydrocolloids gels. The first and second principle components (PC) explained 80.93% of the total variation; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively, implying that the two components provided a strong summary of the data. PC1, represented in vitro starch digestibility and was affected by the addition level of hydrocolloids: PC2, represented rheological parameters and was highly affected by the type of hydrocolloids. Moreover, there was a non-linear relationship between in vitro starch digestibility and rheological properties of Segoami-hydrocolloids gels. The hydrocolloids used in this study showed similar features according to the addition levels of hydrocolloids regardless of type. Segoami-0.5% arabic gum gel was the optimum preparation for retarding in vitro starch digestibility and maintaining rheological properties. © 2017 Published by Elsevier B.V.
1. Introduction Rice is a major cereal grain staple food across the world and has a high glycemic index (GI). Diets that mainly consist of white rice can lead to obesity and hyperlipidemia [1]. Therefore, to enhance the health functionality of rice, several challenges must be met to develop functional rice varieties. Segoami is a new rice variety which was fortified with amylose and dietary fiber in order to reduce GI. Many factors affect the functional properties of rice varieties, including granule structure, amylose contents, and amylose-amylopectin ratio [2]. Among them, amylose content is a key factor in controlling starch digestibility. Starchy foods with high amylose contents have been associated with reduced sensitivity to digestive enzymes, decreased blood glucose levels, and a reduced rate of gastric emptying [2,3]. For these reasons, Segoami, which is classified as
∗ Corresponding author at: 222 Wangsimni-ro, Seoul, 04763, Korea. E-mail address: [email protected] (H.G. Lee). http://dx.doi.org/10.1016/j.ijbiomac.2017.06.063 0141-8130/© 2017 Published by Elsevier B.V.
high-amylose rice, is expected to exhibit lower GI relative to other rice varieties. Hydrocolloids, generally known as either thickening or gelling agents, can be used to improve the texture and stability of foods and to retard starch digestibility [4]. Several reports have been published on the functionalities of hydrocolloids over long periods. The impact of rice starch on digestive patterns in the presence of hydrocolloids has been reported in mixed grain porridge, including arabic gum, rice starch dispersions with xanthan gum and guar gum, and rice coated with locust bean gum and agar [5–7]. Cooked rice in the presence of several hydrocolloids shows improvement in texture and starch digestibility [8]. Alginate in rice dough and noodles has been confirmed to have an effect on cooking quality and starch hydrolysis [9]. Rice starch suspensions mixed with xanthan, pectin, and agar have been examined in previous studies focusing on viscosity and starch digestibility [10]. These functionalities of hydrocolloids are expected to be synergetic with Segoami. When the two functional ingredients are applied in a food matrix, effective synergy will retard in vitro starch digestibility and improv processing quality.
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Therefore, the aims of this study were to investigate the effects of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition level (0.3–0.7% of rice flour weight) of various hydrocolloids on in vitro starch digestibility and rheological properties of Segoami gels and to classify these hydrocolloids based on both properties using principal component analysis (PCA). The results from this study will provide a fundamental understanding of the guidelines for selecting hydrocolloids that lower in vitro starch digestibility and maintain or improve rheological properties in the food applications of Segoami.
and amyloglucosidase (0.2 mL per gram of starch in the sample), the pH of the sample was adjusted to 6.0 using 1 M HCl, and the sample was incubated in a 37 ◦ C shaking water bath. Aliquots of 0.1 mL were withdrawn at 0, 30, 60, 90, 120, and 180 min during digestion. Each aliquot was replaced with 1.4 mL of absolute ethanol and centrifuged at 3000g for 3 min. The released glucose content of the supernatant was analyzed using the GOPOD kit. Levels of rapidly digestible starch (RDS) and slowly digestible starch (SDS) were measured after intestinal digestion for 30 min and 120 min, respectively, and resistant starch (RS) was the starch remaining after 180 min.
2. Materials and methods
C = C∞ 1 − e−kt
2.1. Materials The Segoami rice cultivar produced in 2014 was obtained from the National Institute of Crop Science (NICS), Rural Development Administration (RDA), Korea. The rice was ground and passed through a 100 mesh sieve. Gum arabic from the acacia tree (G9752), guar gum (G4129), gum locust bean (G0753), and xanthan gum from xanthomonas (G1253) were obtained from Sigma-Aldrich Co. (St. Louis, MO, USA). Sodium alginate (37094-01) was obtained from Kanto Chemical Co. (Tokyo, Japan). Pancreatin from porcine pancreas (P7545, activity 8 x USP/g), amyloglucosidase (A9913), and porcine bile extract (B8631) were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Total starch assay (K-TSTA) and glucose oxidase-peroxidase assay (GOPOD, K-GLUC) kits were obtained from Megazyme International Ireland Ltd. (Bray, Ireland).
2.4. Predicted glycemic index The digestion kinetics and pGI (predicted glycemic index) of Segoami flour gel were estimated according to the procedure suggested by Miao et al. [12]. The kinetics of starch hydrolysis were estimated as follows: where C, C∞ , and k denote the hydrolysis degree at each time, the maximum hydrolysis extent, and the kinetic constant, respectively. The hydrolysis index (HI) was calculated by dividing the area under the hydrolysis curve of each sample by the corresponding area of a reference sample (fresh white bread). The predicted glycemic index (pGI) was estimated as follows: pGI = 39.71 + 0.549HI
2.2. Preparation of samples
2.5. Rheological measurements
The types and addition levels of hydrocolloids were selected according to the results of previous studies [6–10]. All hydrocolloids (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) were mixed with distilled water to make 0.3, 0.5 and 0.7% (w/w, dry weight basis of rice flour) solutions, and each was stirred continually at 500 rpm. The solutions of arabic gum, sodium alginate, and xanthan gum were dissolved by heating at 50 ◦ C for 30 min, 95 ◦ C for 10 min, and 60 ◦ C for 15 min, respectively. After heating, the solutions were cooled at room temperature. Locust bean gum and guar gum solutions were prepared by heating on a stir plate at 95 ◦ C or 85 ◦ C, respectively, for 5 min, followed by stirring overnight at room temperature. The Segoami was ground and passed through a 100 um-pore diameter sieve to prepare rice flour gels. The Segoami flour was dispersed into distilled water or hydrocolloid suspensions at a concentration of 10.71% for measuring viscoelasticity and in vitro starch digestion properties. Dispersions containing 5% Segoami flour were also prepared for measuring flow behavior. The mixtures were heated in a double boiler on hotplates for 5 min and then steamed in a stainless steel steam pan for 40 min.
Rheological measurements of samples were conducted using a controlled strain rheometer (RheoStress RS1, Thermo Haake, Karlsruhe, Germany) equipped with a parallel plate geometry 35 mm in diameter with a 1 mm gap. A fresh sample was placed between parallel plates and excess sample was removed smoothly by a spatula. All rheological measurements were performed in triplicate. Dynamic viscoelastic properties were determined over a frequency range of 0.1–10 Hz at 1% strain and 25 ◦ C. A linear viscoelastic region was monitored before performing a frequency sweep test. Viscoelastic parameters of elastic modulus (G ), viscous modulus (G ), and tan ␦ were extracted using the program of rheometer.
2.3. In vitro starch digestion To simulate small intestinal digestion, in vitro starch digestion was conducted in accordance with Minekus et al. [11]. Simulated intestinal fluid (SIF) was composed of 6.8 mL of 0.5 M KCl, 0.8 mL of 0.5 M KH2 PO4 , 42.5 mL of 1 M NaHCO3 , 9.6 mL of 2 M NaCl, and 1.1 mL of 0.15 M MgCl2 (H2 O)6 in 400 mL of distilled water. Pancreatin was diluted 1:5 (w/v) with SIF and centrifuged at 3000g for 20 min. The enzyme solution was prepared by dilution of 5 mL of pancreatin supernatant, 0.435 g of bile extract, and 2 mL of SIF. The sample was synthesized by mixing 5 g of 10.71% gel with 26 mL of prepared SIF, 40 uL of 0.3 M CaCl2 , 0.15 mL of 1 M NaOH, and 1.31 mL of distilled water. After the addition of enzyme solution
2.6. Statistical analysis All experiments were performed in triplicate and means and standard deviations are reported. Analysis of variance (ANOVA) was performed, and the means were separated by Duncan’s multiple range test (p < 0.05). Cluster analysis (CA) and principle component analysis (PCA) were performed on in vitro starch digestibility (RDS, SDS, RS, and pGI) and viscoelastic parameters (G , G , and tan ␦). Statistical analyses were conducted using SPSS software (ver. 21.0, IMB Corp., Armonk, NY, USA). 3. Results and discussion 3.1. In vitro starch digestibility of Segoami-hydrocolloids gels Fig. 1 demonstrates the effects of Segoami gels with various hydrocolloids on in vitro starch digestibility compared to control gels without hydrocolloids. The amount of released glucose was determined as reducing sugars released during starch hydrolysis by digestive enzymes. Glucose release decreased in all samples with hydrocolloids compared to control without hydrocolloids.
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Fig. 1. Effects of sodium alginate (A), arabic gum (B), guar gum (C), locust bean gum (D), and xanthan gum (E) on glucose release of Segoami gels with different addition levels and the glucose release curve of Segoami gels with various hydrocolloids at 0.5% addition level (F).
Specially, the addition of 0.5% hydrocolloids in Segoami gels displayed the greatest impact on reducing in vitro starch digestibility. Arabic gum was the hydrocolloid that most significantly lowered the amount of glucose released, followed by xanthan gum, sodium alginate, locust bean gum, and guar gum. Starch fractions by enzymatic digestion with or without hydrocolloids are presented in Table 1. RDS is the starch fraction that digests rapidly during digestion for 30 min in the small intestine, SDS is the starch fraction that digests slowly, between 30 and 120 min of digestion, and RS is the starch fraction that is resistant to digestion in the small intestine [13,14]. The addition of hydrocolloids in the Segoami flour reduced RDS and SDS, but increased RS at the same time. In gels with 0.5 and 0.7% hydrocolloids, the amount of RDS and SDS ranged from 40.06-46.35% and 15.7822.86%, respectively. The addition of 0.5-0.7% hydrocolloids may prevent rapid degradation of starch in Segoami. Conversely, the amount of RS was over the range of 32.83-42.82%, much higher than that of the control (31.20%). The higher RS of Segoami-hydrocolloids gels suggests that the addition of hydrocolloids can slow the rate of starch degradation. The RS values of samples with arabic gum were much higher compared to other hydrocolloids at same level. The pGI values for Segoami gels with or without hydrocolloids are also presented in Table 1. The pGI values of 0.5% hydrocolloids ranged from 78.3 to 81.5 and those of 0.7% hydrocolloids ranged from 80.7 to 83.7, considerably lower values than the control (84.5). When the hydrocolloid addition level was 0.3%, there was little or no impact on pGI values compared to control. The 0.5% hydrocolloid addition groups showed the lowest glucose release curve. When 0.7% hydrocolloid was added, however, the glucose release curves increased again. Hydrocolloids act as a barrier to digestive enzyme at a certain concentration, but at a higher concentration, hydrocol-
loids enhance swelling of starch granules and promote the rate of starch hydrolysis [4]. These significant effects on reducing starch hydrolysis may be because the arabic gum prevented the starch from contacting digestive fluids and thus decreased glucose production [6]. The swelling power of arabic gum is also related to starch digestion. One factor relating to reduced starch hydrolysis is the inhibition of starch swelling. Thus, the sensitivity to digestive enzymes increased with swelling power [16]. Song et al. [15] have established that arabic gum led to a decrease in the swelling power of rice starch dispersions, suggesting that arabic gum had low swelling power at high temperatures. In other words, the low swelling power of arabic gum may have contributed to the slow the rate of starch hydrolysis. However, further study is needed to confirm the relationship between swelling power and the retardation of starch digestion by arabic gum. The effects of hydrocolloids on the retardation of starch digestibility have been investigated in many other studies. Guar gum is believed to inhibit starch from accessing water in food systems, and consequently prevents starch gelatinization [16]. Alginate acts as a physical barrier that encapsulates the starch granule, and is known to reduce pGI [11]. LBG and xanthan gum also restrict the water in starch foods, increase the viscosities of digesta, or restrict the accessibility of digestive enzymes [17]. The variation of starch digestion patterns might be due to hydrocolloid differences, including molecular weight, branching, and ionic charge, all of which influence their digestion degree. A hydrocolloids-amylose interaction could facilitate the enzyme attack, or retard enzymatic hydrolysis by coating the surface of the starch granule as physical barrier. Therefore, the optimized combination of starch and hydrocolloid is important, based on their in vitro digestibilities.
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Table 1 Starch fractions and pGI of Segoami gels with various hydrocolloids in different addition levels. Addition level (%)
Control Sodium alginate
Arabic gum
Guar gum
Locust bean gum
Xanthan gum
0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7
Starch fraction (%)
pGI
RDS
SDS
RS
45.61 ± 1.56ab 46.33 ± 5.61a 43.54 ± 1.07abc 43.77 ± 3.59abc 43.93 ± 0.69abc 40.06 ± 1.45c 43.32 ± 1.39abc 45.23 ± 2.29ab 42.27 ± 1.51abc 43.91 ± 1.95abc 46.35 ± 2.26a 43.83 ± 1.53abc 43.87 ± 2.34abc 43.66 ± 1.55abc 41.35 ± 2.60bc 44.13 ± 1.74abc
23.19 ± 2.92a 18.68 ± 2.83ab 15.78 ± 1.99b 18.37 ± 3.32ab 19.03 ± 3.58ab 17.12 ± 1.07b 19.06 ± 1.73ab 20.91 ± 4.06ab 17.98 ± 1.13ab 20.45 ± 3.51ab 20.83 ± 1.31ab 17.10 ± 1.53b 19.84 ± 5.09ab 18.96 ± 1.87ab 18.31 ± 2.84ab 22.86 ± 3.63a
31.20 ± 4.42c 34.99 ± 4.63abc 40.68 ± 2.83ab 37.86 ± 6.66abc 37.04 ± 4.09abc 42.82 ± 2.15a 37.63 ± 2.78abc 33.87 ± 6.06bc 39.75 ± 1.32ab 35.64 ± 5.40abc 32.83 ± 3.38bc 39.07 ± 0.27abc 36.30 ± 7.42abc 37.39 ± 3.29abc 40.34 ± 2.99ab 33.02 ± 4.35bc
84.52 ± 3.03a 83.20 ± 2.89ab 80.21 ± 1.99ab 82.51 ± 5.56ab 82.74 ± 2.89ab 78.28 ± 2.00b 80.87 ± 2.14ab 83.47 ± 3.12ab 81.21 ± 1.59ab 83.73 ± 3.78ab 84.32 ± 1.46a 81.46 ± 1.19ab 82.41 ± 3.10ab 81.21 ± 2.84ab 80.74 ± 0.99ab 82.58 ± 2.36ab
Means with different letters in the same column are significantly different at p < 0.05.
3.2. Dynamic viscoelastic property of Segoami-hydrocolloids gels Fig. 2 represents the changes of G and G of Segoami gels mixed with different hydrocolloids in the frequency range from 0.1 to 10 Hz at 25 ◦ C. The magnitudes of G and G increased with frequency and G was higher than G over the frequency range tested. These features indicated that all tested samples showed weak gel-like behavior [18]. It is also well known that the addition of hydrocolloids causes noteworthy effects on the magnitudes of G , but does not affect those of G [19]. As shown in Table 2, the magnitudes of G’ and G at 1 Hz are different. These results are consistent with studies on starch or flour-hydrocolloids mixture systems [20,21]. There was a significant difference between G’ of Segoami-xanthan gum gels and other hydrocolloids. In other words, the Segoami gels with xanthan gum became more elastic due to the extended rod conformation of xanthan gum in solution [22]. The values of tan ␦ (G /G’) <1 or >1 represent mostly elastic or viscous behavior. The tan ␦ values of all samples were lower than 1, suggestive of a highly elastic gel. Furthermore, increasing the addition level of hydrocolloids led to an increase in tan ␦ values, except for arabic gum and guar gum, although there were no significant differences within hydrocolloid types or addition levels compared to the control [18,20].
3.3. Principle component analysis and cluster analysis Principle component analysis (PCA) and cluster analysis (CA) were conducted to confirm the factors, that affected in vitro starch digestibility and rheological properties of Segoami gels, and to classify all tested hydrocolloids based on these properties. The relationships between in vitro starch digestibility and rheological properties in the context of the addition of hydrocolloids are demonstrated in Fig. 3. The first and second principle components (PC) explained 80.93% of the total variance; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively. This result implies that two components provided a strong summary of the data. The factors of in vitro starch digestibility, including RDS, SDS, and pGI were located close together, while rheological properties containing G , G , and tan ␦ were located to the upper left of the cluster of in vitro starch digestibility. As shown in Fig. 3 (A), RS is placed on the opposite side of the clusters, including RDS, SDS, and pGI, and also located close to the gels with 0.5% addition of hydrocolloids, indicating that RS contributed to the low pGI of those samples.
This result predicts a non-linear relationship between in vitro starch digestibility and rheological properties. Furthermore, PC1 correlated positively with RDS, SDS, and pGI, while PC2 correlated positively with G , G , and tan ␦. These results confirmed that PC1 primarily explained factors related to in vitro starch digestibility, whereas PC2 primarily explained rheological properties of Segoami-hydrocolloids gels. Fig. 3 (B) shows that samples of the same addition level of hydrocolloids are located along the PC1 axis, 0.5% on the left side, 0.7% in the middle, and 0.3% on the right side. This means that factors of in vitro starch digestibility were highly affected by hydrocolloids addition level. In contrast, the factors of rheological parameters were highly affected by hydrocolloid type, because the samples of different hydrocolloids at the same addition level were dispersed along the PC2 axis. Gels containing 0.7% hydrocolloids were scattered along the PC2 axis in contrast to the 0.3 and 0.5% additions. The 0.7% addition level may strongly change the rheological properties relative to in vitro starch digestibility. To develop healthy rice products with lower GI, it is useful to apply hydrocolloids that not only retard starch hydrolysis effectively, but also minimally affect rheological properties [8]. Therefore, the samples with lower scores based on PC1 and similar control scores based on PC2 were selected. Among the selected samples, 0.5% arabic gum was located in a similar position to the control on PC2 and the furthest from the control on PC1. Consequently, 0.5% arabic gum with Segoami appeared to be most likely to be helpful in the food industry. The dendrogram and classification of clusters following CA are presented in Fig. 4. All Segoami-hydrocolloids samples were classified into four clusters. All samples were divided into several clusters in terms of their similarity. The results of CA showed that cluster 1 was comprised of five samples, cluster 2 included eight, and cluster 3 had two, while cluster 4 contained only one sample. The samples in cluster 1 were comprised of Segoami gels with 0.3% hydrocolloids or without hydrocolloids. cluster 2 samples were classified as samples with the addition of 0.5 and 0.7% hydrocolloids. Similarly, the members of the third cluster were made up 0.5% sodium alginate and 0.5% arabic gum. Finally, the cluster 4 sample was comprised of 0.7% xanthan gum. The Segoami-hydrocolloid gels studied in this paper were categorized according to the addition level of hydrocolloids, regardless of type. Through cluster analysis and PCA, the relationship between hydrocolloid concentration and type, rheological properties, and in vitro digestibility was shown. The rheological properties were characterized by the different types of hydrocolloids, and in vitro starch digestibilities were grouped by
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Fig. 2. Effects of sodium alginate (A), arabic gum (B), guar gum (C), locust bean gum (D), and xanthan gum (E) on elastic modulus (G , solid symbols) and viscous modulus (G , open symbols) of Segoami gels with different addition levels.
Table 2 Dynamic viscoelastic properties of Segoami gels mixed with various hydrocolloids in different addition levels at 1 Hz, 25 ◦ C.
Control Sodium alginate
Arabic gum
Guar gum
Locust bean gum
Xanthan gum
Addition level (%)
G’ (Pa)
G” (Pa)
tan ␦
0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7 0.3 0.5 0.7
460.13 ± 42.79bc 424.39 ± 29.69c 460.71 ± 44.81bc 479.74 ± 59.18abc 450.41 ± 78.81bc 520.06 ± 46.42abc 519.67 ± 45.70abc 445.20 ± 39.54bc 482.89 ± 57.60abc 511.74 ± 72.10abc 522.61 ± 8.08abc 511.59 ± 27.01abc 537.34 ± 38.73ab 475.92 ± 55.10abc 489.42 ± 25.35abc 570.23 ± 76.23a
105.71 ± 12.36ab 79.33 ± 14.73b 92.83 ± 3.56ab 120.79 ± 39.47ab 87.77 ± 4.11b 106.48 ± 27.04ab 91.62 ± 10.22ab 92.91 ± 9.61ab 120.55 ± 44.55ab 107.21 ± 1.31ab 88.00 ± 3.25b 113.93 ± 15.42ab 116.09 ± 44.73ab 107.73 ± 22.47ab 118.61 ± 19.61ab 134.91 ± 28.75a
0.23 ± 0.01a 0.19 ± 0.03a 0.20 ± 0.02a 0.25 ± 0.07a 0.20 ± 0.04a 0.20 ± 0.04a 0.18 ± 0.03a 0.21 ± 0.01a 0.25 ± 0.10a 0.21 ± 0.03a 0.17 ± 0.01a 0.22 ± 0.02a 0.21 ± 0.07a 0.22 ± 0.02a 0.24 ± 0.03a 0.24 ± 0.05a
Mean values with different letters in the same column differ significantly at p < 0.05.
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Fig. 3. Loading (A) and score plot (B) of Segoami gels with different type and addition levels of hydrocolloids based on in vitro starch digestibility and rheological property.
the different concentrations of hydrocolloids. Therefore, the optimized combination between hydrocolloids and Segoami enabled the development of processed products to improve health-related functionality and food quality. 4. Conclusions The effects of type (sodium alginate, arabic gum, guar gum, locust bean gum, and xanthan gum) and addition levels (0.3, 0.5, and 0.7%) of hydrocolloids on in vitro starch digestibility and rheological properties of Segoami gels were investigated. Multivariate analysis, including principle component analysis (PCA) and cluster analysis (CA) were used to examine the influence of hydrocolloids on two variables and to group similar types of hydrocolloids. The first and second principle components (PC) explained 80.93% of the total variance; PC1 and PC2 explained 50.40% and 30.53% of the total variance, respectively, implying that two components provided a strong summary of the data. PC1 correlated positively with RDS, SDS, and predicted glycemic index (pGI), while PC2 correlated positively G , G , and tan ␦. This confirmed that PC1 primarily explained factors relating to in vitro starch digestibility, whereas PC2 primarily explained rheological properties of Segoami-hydrocolloids gels. The samples of the same hydrocolloids at different addition levels were scattered along the PC1 axis, indicating that factors of in vitro starch digestibility were highly affected by the addition level of hydrocolloids. In contrast, the factors of rheological parameters were highly affected by the type of hydrocolloids, as the samples of different hydrocolloids at same addition level were
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Fig. 4. Tree diagram (A) and clusters (B) on score plot of Segoami gels with different type and addition levels of hydrocolloids based on in vitro starch digestibility and rheological property.
dispersed along the PC2 axis. These results suggested that there was a non-linear relationship between rheological properties and in vitro starch digestibility of Segoami-hydrocolloid gels. Moreover, the hydrocolloids used in this study showed similar features according to their addition level, regardless of the type. In particular, 0.5% arabic gum was the optimal addition for retarding in vitro starch digestibility and maintaining its rheological properties. Acknowledgements This work was carried out with the support of “Cooperative Research Program for Agriculture Science & Technology Development (Project title: Development of specialty rice cultivar based on rice starch and its materials for commercialization, Project No. PJ01125305),” Rural Development Administration, Republic of Korea. References [1] A.-Y. Lee, S.-K. Yeo, J.H. Lee, H.-W. Kim, Y. Jia, M.H. Hoang, H. Chung, Y.-S. Kim, S.-J. Lee, Hypolipidemic effect of Goami-3 rice (Oryza Sativa L. Cv. Goami-3) on C57bl/6 j mice is mediated by the regulation of peroxisome proliferator-activated receptor-␣ and-␥, J. Nutr. Biochem. 24 (2013) 1991–2000. [2] H.-J. Chung, Q. Liu, L. Lee, D. Wei, Relationship between the structure, physicochemical properties and in vitro digestibility of rice starches with different amylose contents, Food Hydrocolloids 25 (5) (2011) 968–975.
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