Pii: s0308-8146(98)00258-

Dinh Huu Donga, Dong Thi Anh Daoa
aDepartment of Food Technology, Ho Chi Minh City University of Technology, Viet Nam E-mail: dinhhuudong06@gmail.com, dtanhdao@hcmut.edu.vn The traditional process of instant tofu production was adjusted to produce a high content of isoflavone and calcium instant tofu. The soaking time, the ratio of soy bean to water in soaking step and grinding step were studied. The isoflavone (Daidzein and Genistein) in tofu was increased when increased the soaking time and reached the highest content at 3.5 hours (1960,38μg Daidzein/g and ,2490,39 μg Genistein/g) . The ratio of soy bean to water in soaking step affected the isoflavone in the instant tofu. At the soy bean to water ratio of 1:4.5, the tofu had the highest isoflavone and calcium content. In addition, the additives had strong influence on the calcium content in tofu. The gluconate calcium at the concentration of 0.3% produced a tofu with high content. Keywords: tofu, coagulation, isoflavone, calcium gluconate
in soybeans improve the nutritional value of soybeans. The main isoflavone in soybeans naturally exist in the form of aglycones Isoflavones of soybeans exist in forms of aglycone (daidzein, genistein and glycitein), their glycoside forms (daidzin, genistein and isoflavone has received strongly glycitin) and their malonyl glycoside and concentration due to their bioactivity. The structural of isoflavone is similarity with 17-β-estradiol , therefore isoflavone is called phytoestrogen and act like a weak amount over the world, especially in Asia. 2011). Isoflavone has protective effect on Soybeans have processed to many kinds of products such as tofu (soybean curd), miso soybean. The process conditions strongly 2010). In addition, isoflavone has shown influenced the isoflavones of soybeans (Lee and Lee, 2009; Kao et al., 2004; Molamma Fiechter et al., 2011; Kazuhiro Nara et al., conditions also affected the yield of tofu and the isoflavone content in tofu (Kao et influence on the yield and quality of tofu ground nut. The high content of isoflavone (Kao et al., 2004). The aim of this study and to suggest an adjustment for process condition to produce soft tofu with high Yield, solid recovery and proximate content isoflavone and appropriately high 2.MATERIALS AND METHODS
2.1 Materials
soymilk. Moisture content was determined by drying 5 g of fresh tofu at 105oC in an air oven to constant weight (Tsai, Lan, Kao & calcium chloride, acid lactic) used in this determined by drying 10 ml ofthe whey at Kjeldahl method (AOAC,1975) on air-dried standards used in the HPLC analysis were tofu samples and using the factor N_ 6.25 to in forms of aglycone: Genistein (EC. 207- tofusamples was measured with a digital pH standards were supplied by Sigma-Aldrich meter with a glass electrode (Metrohm AG, 2.2 Methods
2.2.1 Soy milk and soy curd (tofu) The total isoflavone content in tofu was analyzed by HPLC. The isomeric glucoside, acetyl glucoside, Maloney glycoside were hydrolyzed in to free isoflavones: genistein and daidzein. The isoflavone acetonitril 58% was used as the extraction solvent and filtered to collect soymilk. In the soaking step, the influence of the ratio of soybeans tofu was studied at four levels :1:3, 1:3.5, Kjeldahl method using a protein conversion method, respectively. The ash contents were step, the influence of the ratio of soybeans – to – water (w/v) on REDM was studied digestion of the sample on a mixture of 4 curd were quantified in each experiment. included: calcium citrate, calcium 560 instrument (Perkin-Elmer Corp.). fumarate, calcium gluconate. The most Results were expressed on dry-matter basis. appropriate coagulant was further studied for the optimum concentration used. Each difference) intervals (p < 0.05) were calculated to evaluate significantly different 3. RESULTS AND DISCUSSION
shape were cut ver-468 Eur Food Res Technol (2008) 226:467–472123 tically 3.1.Effect of soaking time on the recovery
from a block of curd using a cylindrical efficiency of dry matter (REDM) and
isoflavone concentrations.
The soaking time was strongly affect the height with a metal disc (60 mmdiameter). REDM and isoflavone concentration. The REDM increased when extending the tocalculate the hardness, brittleness and soaking time (table 1 and chart 1). The increase of soaking time from 2.5 hours to 4 hours resulted in the increase of 9.56% of REDM. However, the REDM and isoflavone chewiness) using the instrument software content had no significant difference when soaking soybeans in 3.5 hours and in 4 hours. The enough period of soaking time allowed the swelling of tissues, the hydration loosened and broke down the matrix inside soybean. The soluble panellists evaluate the sensory attribute of components increasingly released when the the fresh tofu. Panellists were familiar soaking time was prolonged. The table 1, chart 1 and chart 2 have shown that the daidzein content and genistein content in soft tofu also enhanced to certain level. Extending the soaking time to 4 hours did panellists took 10–15 min to complete the not gain the significantly high content of rating of all the samples. Tofu was cut into isoflavone in comparison to 3.5 hours. The soaking time of 3.5 hours was chosen for attributes evaluated were colour, flavour , mouth feel and overall acceptability. For Table 1. Effect of soaking time on REDM each sample, panellists scored their liking point hedonic scale (1 = dislike extremely, Daidzein content Genistein content 2 = dislike very much, 3 = dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 41.625(±0.12)a 1828.22(±1.03) a 1965.76(±1.02) a = like moderately, 8 = like very much, and 44.325(±0.15)b 1855.91(±1.05) b 45.725(±0.14)c 1871.38(±1.06) c 1990.39(±1.03) c 46.025(±0.17)c 1885.82(±1.04) c 1998.65(±1.08) c The experiments was carried out in triple. ANOVAs (STATGRAPHICS 3.0 version software) were used to evaluate significant differences between treatments (p=0.05%). The LSD (least significance Table 2. Effect of the Ratio of soybean-to-
in each column with different superscripts water on REDM and the content of
are significantly different (p < 0:05). isoflavones
43.8(±0.20) 1863.36(±0.36) 1985.17(±0.60) 45.3(±0.17) 1868.10(±0.18) 1989.39(±0.81) 46.3(±0.16) 1872.48(±0.14) 1991.48(±0.57) 46.8(±0.19) 1881.59(±0.15) 1995.51(±0.45) Chart 1.Effect of soaking times and
performance on REDM
Chart 3: Effect of the ratio of soybeans- to-
water soaked by 3.5 hours on REDM
Chart 2. Effect of soaking times on
concentration of isoflavones
3.2. Effect of the ratio of soybean – to –
water on the recovery efficiency of dry

matter (REDM) and isoflavone contents.
Soybeans were soaking in 3.5 hours with various water level and then was went into coagulant. The table 2 demonstrated that the soybean – to – water ratio strongly affected the REDM but had slightly effect Chart 4.Effect of soaking times on
on and the content of isoflavones in the concentration of isoflavones
soft tofu. The chart 2 show that the REDM drastically increased 8.5% at the ratio of 1:4.5 in comparison to the ratio of 1.3. However the isoflavone content slightly between two cases: the ratio 1:4 and 1:4.5. soft tofu also enhanced about 2.5% with the increasing of water level. Therefore the ratio of 4 was used for the properly absorbed and health - usefull in human bodies: Calcium fumarate, calcium citrate and calcium gluconate. The calcium gluconate showed the best recovery of 3.3. Effect of the ratio of soybean-water
calcium in soft tofu than the others when grinding on REDM
used at the same concentration (table 3). Table 3. The effect of coagulants to total
concentration of calcium in soft tofu
Chart 5: Effect of the ratio of
soybeans- to- water grinding on REDM
the ratio 1:6 and 1:7. Therefore the ratio of 1:6 was used for the next experiments. 3.4. Effect of coagulant on calcium
concentration in the soft tofu
calcium were usually used to produce tofu. However, the types of coagulants Chart 6. The effect of coagulant on total
determined the structure of tofu and the calcium concentration in the soft tofu
concentration of calcium in the final product. The soluble content strongly loss in the coagulation (Kao et al, 2004). Three various concentration. The concentration of types of coagulant with concentration of calcium gluconate increased resulted in the increase of calcium in the final products. the ability of calcium retaining in soft The calcium gluconate concentration of 0.3 and 0.4% did not gave the significant difference on the calcium content in soft 0.3% calcium gluconate was chosen for the Conclusions
Table 4. Effect of calcium gluconate
In conclusion, the isoflavone content in soft concentration to the calcium content of
tofu depended on the process condition. The soft tofu.
swelling and the ability of release of soluble content in soybean. The ratio of soybeans – to – water caused the significant difference during the process. However, the isoflavone content could be optimized by change the process condition. The soaking time of 3.5 hours with the ratio of soybean – to – water of 1:4 showed the ability to retain highest isoflavone in soft tofu. The coagulant type and coagulant concentration influenced the structure and the calcium content of soft tofu. The calcium gluconate was used at the appropriated high calcium content in soft REFERENCES
[1] De-Fu Ma, Li-Qiang Qin, Pei-Yu Wang, Chart 7.The effect of calcium gluconate
intake increases bone mineral density in the concentration to the calcium content of
spine of menopausal women: Meta-analysis soft tofu.
of randomized controlled trials. Clinical tofu increasing strongly when added calcium gluconate from 0.1% to 0.3%, but increasing( chart 7). The concentration of pressure liquid chromatography method for Perera, Suresh Valiyaveettil. (2006). Effect Application to analyze isoflavone levels in of different coagulants on the isoflavone Food Research levels and physical properties of prepared firm tofu. Food Chemistry 99, 492–499. [3] Kao T.H. , Y.F. Lu, H.C. Hsieh, B.H. and tofu. Food Research International 37. composition of isoflavone in rice-koji miso. [4] Kazuhiro Nara , Ken-ichi Nihei, Yasuo Biomedicine &Pharmacotherapy. Available [6] Lee, H.P., Gourley, L., Duffey, S.W., Dietary effects on breast-cancer risk in (2009). Effects of oven-drying, roasting, isoflavone distributions in soybeans. Food

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