The Lipid Peroxide Content and Aokusami (Beany Flavor) of Soymilk
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Food Sc'i. Technol Res., 10 (3), 328-3_ 3_ _3, 2004 Technical paper Effect of Heat Treatment on the Lipid Peroxide Content and Aokusami (Beany Flavor) of Soymilk Hiroshi END0,1 Masahiro OHN0,2 Katsuo TANJI,3 Shinji SHIMADA4 and Kentaro KANEKO IFukushima Technology Centre Aizuwakamatsu Technical Support Centre, 88-], Shimoyanagihara, Tsuruga, Ikki-machi, Aizuwakamatsu-shi, Fu.kushima 965-0006 Japan 2Fukushima Technology Centre, 1-12, Machiikedai, Kooriyama-shi, Fukushima 963-0215 Japan -?Fukushima Prefecture Agricultural Experiment Station, 20, 14,akamiyamae, Tomita-machi, Kooriyama-shi, Fukushima 963-8041 Japan 4National [nstitute of Crop Science, 2-/-]8 Kannondai, Tsukuba, Ibaraki 305-8518, Japan 5Faculty ofApplied Life Science, Nippon veterinary and Animal Science University, 2-27-5 Sakai, Musashino-shi, Tokyo 180-8602 Japan Received February 23, 2004; Accepted June 4. 2004. With the objective of minimizing aokusami (beany flavor), which is an undesirable aspect of soymilk flavor, we studied the effects of heating on lipid peroxide content, a factor contributing to the beany flavor. We also prepared various desserts containing soymilk using this heating process, and evaluated the effects of heating by sensory test. The lipid peroxide content of soymilk prepared from soaked and swollen soybeans steamed at 75'C in a relative humidity of 80-90% for 10 minutes was substantially lower than that in soymilk prepared from soybeans which lacked lipoxygenase and was 14% or less that of non-heat-treated soybeans. Additionally, the lipid peroxide content of soymilk prepared by blanching soaked and swollen soybeans in boiling water for 30 seconds was comparable to that found in soymilk prepared from lipoxygenase-lacking soybeans. The beany flavor of custard pudding, Bavarian cream, and Annin tofu prepared with soymilk obtained from heat-treated soybeans was significantly improved. Keywords: soy bean, soymilk, Iipid peroxide, beany flavor. Soybeans have long played a pivotal role in the food blanching method in hot water at 99.3'C (Seth & Nath, culture of Japanese people as a foodstuff with a high nutri- 1 988); and the microwave heating method (Wang & Toledo, tive value. Recent research has shown that soybean protein 1987). However, all these methods share the problems of has a cholesterol-lowering effect (Anderson et al., 1995), heating-induced insolubilization of protein and an associ- that soybean saponin has anticancer activity (Kennedy, ated decrease in protein extraction rate (Ediriweera et al., 1995), and that soybean isoflavones have inhibitory effects 1 987). Omura and Takechi ( 1990) proposed heating soaked on breast cancer and prostate cancer (Peterson & Bernes, and swollen, peeled soybeans in hot water at 70'C for 5 l 99 1 ; Peterson G & Bernes S, 1 993) as wel] as a preven- min. However, because the peeling process is associated tative effect on osteoporosis (Tsuchida et al., 1999). Given with detachment of the hypocotyls (Endo et al., 2003a), the above, processed foods made from soybeans are valued this process is unsuitable for the preparation of raw mate- as a source of isoflavones. Soybeans are used in numerous rials for high-isoflavone soymilk. foods, including tofu, natto, miso, soy sauce, and soymilk. The present research was performed with the objective Soymilk is consumed as a beverage, and is also used as an of minimizing aokusami (beany flavor), which is an unde- ingredient in the making of jellies, custard puddings, and sirable aspect of the flavor of soymilk and other soymilk- other desserts. However, the distinctive aokusami (beany related drinks. We studied the effects of heating on lipid flavor) produced by lipoxygenase has a major impact on peroxide content, which contributes to the beany flavor, and consumer preference. Minimizing the beany flavor is there- we prepared desserts made with soymilk processed in this fore a key challenge in widening the use of soymilk. manner to investigate its effects on flavor. Several methods have been proposed for deactivating lipoxygenase: the hot water-added grinding method (Echigo Materials and Methods et al., 1991 ), in which soybeans are soaked in hot water at Test soybeans The following soybean varieties tested 70'C and then homogenized in hot water at 95'C; the were grown, screened, and dried at the Fukushima Prefecture Agricultural Experiment Station: Suzuyutaka, Tohoku 126 (high-isoflavone soybean, Endo et al., 2003b), Tohoku 1 35 E- mail : [email protected], jp (lipoxygenase-lacking soybean; hereafter, Iipoxygenase- Effect of Heat Treatment on the Lipid Peroxide Content and Aokusami of Soymilk 329 lacking soybean), Tohoku 139 (low-allergen soybean strain; The Suzuyutaka variety of soybeans was used for this test. hereafter, Iow-allergen soybean), Shinanokuro (black Soybeans that had been soaked and swollen for 16 h at 20*C soybean), Aomame 4 (blue soybean), and commercially- were blanched in boiling water for l0-40 s, and soymilk available lchihime (Tochigi Prefecture-origin; Iipoxyge- was then prepared using the heat-squeezing method with a nase-lacking soybean). 6-fold volume of water added. Soybean heat-treatment method and soymilk prepara- Measurement of lipid peroxide content To 0.5 g of tion Suzuyutaka was used as the raw material. 32-mesh or finer soybean powder ground in a compact Control group: Soybeans were soaked and swollen in milling machine (AS One Corporation; Wonder Blender water at 20'C for 16 h, and soymilk was then prepared using WB- I ), soymilk, or each of the soymilk desserts was added the heat-squeezing method with the addition of water (6: I , 10 mL of distilled water, and the mixture was ice-cooled water weight: soybean weight) (Endo et al., 2003a, simi- while being homogenized for I min using a Polytron homog- larly hereafter). enizer. The homogenate was allowed to stand for 60 min Test- I : Soybeans were air-dried for 10 min at 75'C (DK- at 4'C, after which the lipid peroxide content was assayed 600T incubator; Hitachi Corp.), rinsed with water, and by the DETBA (1,3-diethyl-2-thiobarbituric acid) method soymilk was then prepared by the same method as that (Suda et al., 1994). described for the control group. Preparation and sensory evaluation of soymilk desserts Test-2: Soybeans were steamed for 10 min at 75'C in a Desserts were made using soymilk prepared from Tohoku relative humidity of 80-90% (MTH-4400 constant tem- 126 soybeans, and a sensory evaluation of the beany flavor perature and humidity chamber; Sanyo) and rinsed with was undertaken. Using the heat-squeezing method with a water. Soymilk was then prepared by the same method as 6-fold volume of water added, soymilk was prepared from that described for the control group. soybeans blanched in boiling water (1000C) for 30 s after Test-3: Soybeans that had been soaked and swollen in being soaked and swollen in water at 20'C for 16 h. Desserts water for 16 h at 20'C were steamed for 10 min at 75'C in were prepared using standard recipes, with milk partly a relative humidity of 80-90% and rinsed with water, after replaced with soymilk (Table 1). Pudding was made using which soymilk was prepared using the heat-squeezing pudding mix (Nisshin Foods), Bavarian cream using method with the addition of water (6:1, water weight Bavarian cream mix (Nisshin Foods), and Annin tofu using soybean weight). Annin tofu mix (Heichinsei) (Table 1). Test-4: Soybeans were heated for 60 min in hot water at Sensory evaluation was performed using a five-point 750C and rinsed with water, after which soymilk was rating scale (1: Strong; 2: Moderately strong; 3: Weak; 4: prepared using the heat-squeezing method with the addition Almost none; 5: None whatsoever) to score the beany flavor of water (6: 1, water weight: soybean weight). of soymilk (Furukawa, 1994). Panelists comprised 15 staff Test-5: Soybeans that had been soaked and swollen for members from the Aizu-Wakamatsu Technical Support 16 h in water at 20'C were blanched for 2 min in hot water Center (ages 25=56 years; 12 men and 3 women). Sensory (10:1, water weight: soybean weight) at 750C, and then evaluation was repeated twice and the mean scores were rinsed with water, after which soymilk was prepared using determined. Differences between samples were tested for the heat-squeezing method with the addition of water (6: I , significance using two-way ANOVA (Furukawa, 1994). water weight : soybean weight). Measurement of extraction rates ofprotein and solid Test-6: Soymilk was prepared using the same method as matter The extraction rates of protein and solid matter in that described for the control group, except that the soybeans soymilk were measured according to a previously described were homogenized with hot water at 95'C. method (Endo et al., 2003a). Blanching in boiling water and preparation of soymilk Table 1. Material composition of various desserts prepared by mixing the soymilk. Soymilk and Milk (g) Soymilk dessert Mix*1(g) Yolk (g) Water (g) Soymilk'2 Processed soynulk 3 Milk Custard pudding 1) 400 2) 60 200 200 3) 200 200 Bavarian cream 1) 400 2) 70 18 200 200 3) 200 200 Annin tofu 1) 300 2) 84 300 150 l 50 3) 150 150 * I : Mix is an essential factor in the making of each dessert which is composed of sugar, polysaccharides and other ingredients. *2: Soymilk was prepared by the heat squeezing method in which soybean seeds were homogenized by adding 6.0 times more water to them after soaking in water for 16 hrs. *3: The soybean seeds were heated for 30 sec in 100'C hot water after soaking in water and then prepared in soymilk the same way as *2. 330 H. ENDO et al Results and Discussion proportional to that of lipid peroxide (Furuta et al., 1996), Lipidperoxide content ofsoybeans and soymilk Table and that the beany flavor of soymilk prepared from all 2 presents data on the lipid peroxide content of 7 varieties lipoxygenase-lacking soybeans is less than that of soymilk of soybean and soymilk.