Quantification of Isoflavones in Soymilk and Tofu from South East Asia

Figures & data

Figure 1 Chemical structures of parent isoflavones and respective glucosides in soybean.

Figure 2 Reversed-phase HPLC chromatogram of the six isoflavones in soy samples.

Figure 3 Correlation of protein and isoflavone levels for soymilk samples.

Table 1 Total isoflavone data (on wet weight basis) reported as microgram aglycon equivalents per gram of sample for soymilk, soft tofu, and firm tofu prepared by standard procedure

Soy product	Moisture (% ± SDb)	Proteina (%)	Daidzein (µg/gm)	Glycitein (µg/gm)	Genistein (µg/gm)	Total aglycons ± SDb
Soymilk	86.4 ± 0.01	3.30	2.746	2.170	1.771	6.687 ± 0.118
Soft tofu	89.8 ± 0.01	6.10	3.443	4.133	2.070	9.646 ± 0.183
Firm tofu	79.2 ± 0.01	10.05	7.306	4.153	4.916	16.376 ± 0.045
Milk type	Daidzin (µg/gm)	Glycitin (µg/gm)	Genistin (µg/gm)	Glucosides in aglycon-equivalents ± SDb		Total isoflavones ± SDb
Soymilk	84.14	9.84	99.08	119.60 ± 1.73		126.287 ± 1.70
Soft tofu	111.71	12.84	129.67	157.48 ± 0.340		167.13 ± 0.456
Firm tofu	147.80	17.34	197.78	224.97 ± 1.09		241.34 ± 1.05

^aProtein calculated from the BioRad protein assay.

^bSD is standard deviation and all values are the mean of 6 replicates from two plant trials of the respective soy food making.

Table 2 Total isoflavone data (on wet weight basis) reported as microgram aglycon equivalents per gram of sample for the commercially available soymilks

Milk type	Moisture (% ± SDb)	Proteina (%)	Daidzein (µg/gm)	Glycitein (µg/gm)	Genistein (µg/gm)	Total aglycons ± SDb
Brand A	96.0 ± 0.01	2.048	6.857	1.112	4.867	12.836 ± 0.17
Brand B	90.6 ± 0.01	2.858	3.635	0.117	1.717	5.469 ± 0.71
Brand C	85.2 ± 0.01	3.675	4.090	0.360	3.740	8.190 ± 0.04
Brand D	82.6 ± 0.01	3.700	1.327	0.092	0.957	2.377 ± 0.19
Brand E	86.2 ± 0.01	4.200	12.357	0.775	7.402	20.535 ± 0.08
Milk type	Daidzin (µg/gm)	Glycitin (µg/gm)	Genistin (µg/gm)	Glucosides in aglycon-equivalents ± SDb		Total isoflavones ± SDb
Brand A	44.23	8.41	49.92	63.58 ± 0.11		76.41 ± 0.28
Brand B	69.77	11.58	76.88	98.05 ± 1.54		103.52 ± 0.83
Brand C	102.56	11.56	143.18	159.52 ± 1.63		167.71 ± 1.60
Brand D	115.07	24.81	142.37	175.09 ± 1.17		177.46 ± 0.97
Brand E	136.72	11.95	140.12	178.72 ± 0.91		199.25 ± 0.99

^aProtein calculated from the BioRad protein assay.

^bSD is standard deviation and all values are the mean of four replicates.

Table 3 Total isoflavone data (on wet weight basis) reported as microgram aglycon equivalents per gram of sample for the commercially available tofu varieties

Tofu type	Moisture (% ± SDb)	Proteina (%)	Daidzein (µg/gm)	Glycitein (µg/gm)	Genistein (µg/gm)	Total aglycons ± SDb
Silken tofu	85.90 ± 0.01	5.280	2.440	ND	2.820	5.260 ± 0.24
Chinese tofu	89.60 ± 0.01	6.769	1.943	0.050	2.280	4.273 ± 0.02
Organic tofu	88.60 ± 0.01	6.536	4.260	0.040	2.500	6.800 ± 1.49
Braised tofu	67.40 ± 0.01	9.690	6.045	0.250	4.825	11.120 ± 0.07
Deep fried	74.40 ± 0.01	11.70	10.885	0.490	7.840	19.215 ± 0.72
Taw Kwa	74.40 ± 0.01	9.674	5.500	0.210	3.680	9.390 ± 0.12
Tofu	Daidzin (µg/gm)	Glycitin (µg/gm)	Genistin (µg/gm)	Glucosides in aglucon equivalents ± SDb		Total isoflavones ± SDb
Silken tofu	131.73	15.40	109.28	158.59 ± 2.77		163.85 ± 2.45
Chinese tofu	129.92	16.95	109.53	158.63 ± 3.26		162.91 ± 3.24
Organic tofu	139.77	16.14	120.67	171.10 ± 0.72		177.90 ± 2.22
Braised tofu	109.36	19.75	123.82	156.79 ± 9.23		167.91 ± 9.31
Deep fried	217.32	26.42	205.96	278.34 ± 4.84		297.55 ± 4.12
Taw Kwa	236.66	23.98	229.06	303.03 ± 2.74		312.42 ± 2.33

^aProtein calculated from the BioRad protein assay.

^bSD is standard deviation and all values are the mean of four replicates. ND = not detectable. All tofu samples analyzed were from the same manufacturer. “Silken” tofu, “chinese” tofu, and “organic” tofu are soft tofu varieties which is incorporated with whey and the difference between them being the type of coagulants used for its coagulation. “Organic” tofu uses organic soybean seeds. “Braised” tofu, “deep-fried” tofu, and “taw kwa” are firm tofu varieties.

Table 4 Correlations output from SPSS software obtained for soymilk samples

Protein	Isoflavone
Protein	Pearson Correlation	1	0.984a
Sig. (2-tailed)	—	0.002
N	5	5
Isoflavone	Pearson Correlation	0.984a	1
Sig. (2-tailed)	0.002	—
N	5	5

^aCorrelation is significant at the 0.01 level (2-tailed).