Kwang Yeon Lee

Rheological and gelation properties of rice starch modified with 4-α-glucanotransferase

Rheological measurements were performed to characterize rice starch modified with 4-alpha-glucanotransferase (4alphaGTase) isolated from Thermus scotoductus, in terms of effects of the enzyme and starch concentration on flow behavior, gel strength, and melting and gelling kinetics of the modified rice starch. Consistency index decreased and flow behavior index increased with the level of enzyme treatment, and at high level of enzyme treatment, it demonstrated Bingham plastic behavior. As the level of enzyme decreased and the starch concentration increased, gelation time decreased and the final gel strength increased significantly. Regardless of treatment variables, all the modified starch gels melted at similar temperature.

Chemical composition and physicochemical properties of barley dietary fiber by chemical modification.

Chemical modification of dietary fiber (DF), extracted from whole grain barley, was carried out to obtain cross-linked (CL) DF, carboxymethyl (CM) DF, and hydroxypropyl (HP) DF. The DF components, physicochemical properties, and subsequent influence on the in vitro digestibility of wheat starch gels were comparatively investigated. The redistribution of fiber components from chemically modified DF was observed. An increase in the total DF (TDF) content of CL- and HP-DF was observed, which was mainly due to an increase of insoluble DF. Carboxymethylation led to an appreciable increase of soluble DF (1.17-6.20%) but TDF contents slightly decreased. Chemical modification of barley DF led to increases in arabinose (7.1-11.5%) and xylose (10.7-17.5%), but glucose contents decreased (67.4-79.9%). The treatments, especially carboxymethylation, effectively (P<0.05) increased hydration properties (e.g. water solubility, swelling power, and water absorption index). Substitution of 5% wheat starch with CL-, and HP-DF led to decreased in vitro digestibility in comparison to the control starch. Our results suggest that chemical modification improve the DF characteristics of barley and to exploit its potential application as a functional ingredient in fiber-rich products.

Effect of hydrocolloids on the pasting and rheological characteristics of resistant starch (type 4)

The pasting and rheological properties of resistant starch-type 4 (RS4) and hydrocolloid mixtures were characterized at 2 different concentrations (0.1 and 0.5%, w/v). When RS4 was mixed with 2 hydrocolloids (pectin and xanthan gum), there was the overall tendency that both swelling power and solubility of the RS4 suspensions significantly increased. Steady shear measurements showed that the RS4 and hydrocolloid samples exhibited shear-thinning behaviors which could be well characterized by the Power law model. A dramatic increase in the viscosity by xanthan gum was also observed, compared to pectin. In addition, dynamic oscillatory tests indicated that the RS4 and hydrocolloid mixtures exhibited more elastic properties with less frequency dependence, compared to RS4 alone. Also, the viscosities of the RS4 suspensions during pasting increased with increasing concentrations of the hydrocolloids used and these effects became significantly dominant when xanthan gum was incorporated.

Comparative effects of slowly digestible and resistant starch from rice in high-fat diet-induced obese mice

The effects of optimized slowly digestible starch (SDS) and resistant starch (RS) from rice starch on weight gain and lipid metabolism in mice (C57BL/6J mice) fed a high-fat diet were investigated. The optimum conditions for SDS were obtained at the pullulanse concentration (X1) of 498 μL, storage temperature) (X2) of 47°C, and A/C cycle (X3) of 5, and for RS, were determined to be 838 μL (X1), 62°C (X2), and a cycle of 3 (X3) using response surface methodology (RSM). Mice fed SDS and RS for 6 weeks showed both significantly decreased weight gain and fat pad weight (p<0.05). Significant decrease in total lipid, triglyceride, and cholesterol concentrations in serum and liver was observed in both SDS and RS group compared to HFD groups (p<0.05). Although both of intake SDS and RS significantly contributed to beneficial effects, RS groups was more effective than SDS group in all parameters.

Changes in Quality Characteristics of Tofu with Freezing Treatment of Soybeans

The aim of this study was to investigate the influence of length of freezing time (−18°C for 5 or 24 h) on the quality characteristics of tofu. The yield and moisture content of tofu obtained from frozen soybean were lower than control tofu. Tofu made from frozen soybeans showed higher hardness, gumminess and chewiness than the control. Freezing treatment also made the microstructure of the tofu more uniform than the control. However, after 24-h freezing, hardness decreased and the microstructure of tofu appeared to form pores. Sensory evaluation showed that mouth-feel decreased with an increase of freezing time. Among all of tofu frozen at −18°C, 5-h freezing treatment showed the highest overall acceptability. These results indicate that the length of time that soybeans are frozen before making tofu affects the quality of tofu.

Effect of modified dietary fiber extracted from wholegrain wheat on the physicochemical and cake properties

Dietary fiber (DF) extracted from whole wheat was chemically modified by cross-linking (CL), carboxymethylation (CM), and hydroxypropylation (HP) and their physicochemical properties and baking performance were evaluated. CM contributed to the increase in soluble DF (SDF) contents and water solubility. While CL and HP contributed to the decrease in water solubility as insoluble DF (IDF) contents increased. In comparison to the chemically modified DF, CLDF deteriorated textural and physical properties of cakes. On the other hand, the cakes with CMDF and HPDF had improved cake qualities such as appearance, higher volume and lower hardness compared to cake with native DF. Consequently, this study suggested that the chemical modifications of wheat DF can effectively regulate the IDF/SDF ratio and total dietary fiber (TDF) contents, resulting in the change of physicochemical properties of them. When applied to cake, modified wheat DF diversified the physicochemical properties and quality by a functional group.

Suitability of TEMPO-oxidized oat β-glucan for noodle preparation

Native oat β-glucan (N-BG) and the oxidized derivative β-glucan (Oxi-BG) were incorporated into noodles and preparation characteristics (pasting, cooking, and textural properties) were investigated. N-BG caused an increase in the pasting parameters of wheat flour, and values were increased by Oxi-BG. Noodles containing either N-BG or Oxi-BG had higher cooked weights, cooked volumes, and water absorption values than controls. Raw noodles containing either N-BG or Oxi-BG showed high L values. Cooked noodles lacking BG exhibited higher L values. N-BG-containing noodles had textural properties similar to controls. Noodles prepared with Oxi-BG had higher textural parameter values than N-BG noodles, except for hardness.

Effect of different pH conditions on the in vitro digestibility and physicochemical properties of citric acid-treated potato starch

The objective of this study was to investigate the influence of citric acid (CA) treatment (10, 20, and 30% of dry starch weight) under different pH conditions (3.5, 4.5, and 5.5) on the physicochemical properties, in vitro digestibility and prebiotic effects of potato starch. With the CA content increased, the degree of substitution of CA-starch treated at pH 3.5 and 4.5 wad significantly increased i.e. from 0.125 to 0.418 and from 0.078 to 0.167, respectively (p<0.05), except for starch treated at pH 5.5 (from 0.023 to 0.030). The resistant starch (RS) content of CA-starch was effectively increased compared to pH control made by changing pH from 3.5 to 5.5 with hydrochloric acid alone. The results of X-ray diffraction and swelling power were affected by pH condition, whereas they were less affected by the percentage of CA. Swelling power of treated starch also significantly decreased as the pH level decreased (p<0.05). Probiotic bacteria B. bifidum and L. acidophilus grown in medium with citrate starch showed substantial viability. These results suggest that pH conditions of CA modification substantially affect the degree of CA substitution, physicochemical properties, and nutritional value.

Effect of different chemical modification on the physicochemical properties of fiber-enriched polysaccharides isolated from wholegrain rice and buckwheat

Dietary fiber (DF) isolated from wholegrain flours (brown rice and buckwheat) were chemically modified by cross-linking (CL), carboxymethylation (CM) and hydroxypropylation (HP). The modified DF was evaluated for its physicochemical characteristics based on compositions, hydration properties and interactions of wheat starch/DF system. The changes in total dietary fiber (TDF) content of were found to be chemical modification-dependent. CM contributed to the increase in soluble dietary fiber (SDF) contents and water solubility. On the contrary, CL and HP significantly increased the insoluble dietary fiber (IDF) contents, resulted in reduced water solubility. Hydration properties of both native and modified buckwheat DF were higher than all rice DF counterparts. In the interaction with wheat starch, starch hydrolysis was low in samples with high TDF contents (CL≈HP>CM≈ native). It was concluded that characteristics of modified cereal DF depended on the presence of functional groups rather than sources of wholegrain.