Production of beta-glucosidase and hydrolysis of isoflavone phytoestrogens by Lactobacillus acidophilus, Bifidobacterium lactis, and Lactobacillus casei in soymilk

ABSTRACT:  The study determined β-glucosidase activity of commercial probiotic organisms for hydrolysis of isoflavone to aglycones in fermenting soymilk. Soymilk made with soy protein isolate (SPI) was fermented with Lactobacillus acidophilus LAFTI^® L10, Bifidobacterium lactis LAFTI^® B94, and Lactobacillus casei LAFTI^® L26 at 37 °C for 48 h and the fermented soymilk was stored for 28 d at 4 °C. β-Glucosidase activity of organisms was determined using ρ-nitrophenyl β-D-glucopyranoside as a substrate and the hydrolysis of isoflavone glycosides to aglycones by these organisms was carried out. The highest level of growth occurred at 12 h for L. casei L26, 24 h for B. lactis B94, and 36 h for L. acidophilus L10 during fermentation in soymilk. Survival after storage at 4 °C for 28 d was 20%, 15%, and 11% greater ( P < 0.05) than initial cell counts, respectively. All the bacteria produced β-glucosidase, which hydrolyzed isoflavone β-glycosides to isoflavone aglycones. The decrease in the concentration of β-glycosides and the increase in the concentration of aglycones were significant ( P < 0.05) in the fermented soymilk. Increased isoflavone aglycone content in fermented soymilk is likely to improve the biological functionality of soymilk.     

Effect of lactulose on biotransformation of isoflavone glycosides to aglycones in soymilk by lactobacilli

ABSTRACT:  Lactobacillus acidophilus 4461, L. acidophilus 4962, L. casei 290, and L. casei 2607 were used to hydrolyze isoflavone glycosides (IG) to biologically active forms—isoflavone aglycones (IA)—in soymilk (SM) prepared from soy protein isolate (SPI) and soymilk supplemented with 0.5% (w/v) of lactulose (SML). L. acidophilus 4461 utilized the highest level of lactulose (3.01 mg/mL) and L. acidophilus 4962 utilized the least (0.86 mg/mL) at 24 h of incubation. The pH values decreased to 4.00 to 5.00 in SML, while they remained relatively high (6.15 to 6.36) in SM. Supplementation with lactulose significantly ( P < 0.05) enhanced the viable counts of all the 4 Lactobacillus strains. At the end of incubation, the viable counts of Lactobacillus ranged from 8.08 to 8.25 log CFU/mL in SML compared to 6.99 to 7.11 log CFU/mL in SM. Supplementation with lactulose increased the biotransformation of IG to IA after 6 h of incubation. The presence of lactulose in the medium enhanced the biotransformation level of IG to IA by Lactobacillus up to 21.9%. The hydrolysis level of malonyl genistin and acetyl genistin in SML was much higher than in SM by all the 4 probiotic organisms. The biotransformation of IG to IA occurred rapidly during the 1st 12 h of incubation in both SML and SM. Among the 4 Lactobacillus strains, L. acidophilus 4461 biotransformed the highest level (88.8%) of IG to IA in SML compared to 68.2% in SM after 24 h of incubation.     

Phytase Activity from Lactobacillus spp. in Calcium-Fortified Soymilk

Abstract: The presence of phytate in calcium-fortified soymilk may interfere with mineral absorption. Certain lactic acid bacteria (LAB) produce the enzyme phytase that degrades phytates and therefore may potentially improve mineral bioavailability and absorption. This study investigates the phytase activity and phytate degradation potential of 7 strains of LAB including: Lactobacillus acidophilus ATCC4962, ATCC33200, ATCC4356, ATCC4161, L. casei ASCC290, L. plantarum ASCC276, and L. fermentum VRI-003. Activity of these bacteria was examined both in screening media and in calcium-fortified soymilk supplemented with potassium phytate. Most strains produced phytase under both conditions with L. acidophilus ATCC4161 showing the highest activity. Phytase activity in fortified soymilk fermented with L. acidophilus ATCC4962 and L. acidophilus ATCC4161 increased by 85% and 91%, respectively, between 12 h and 24 h of fermentation. All strains expressed peak phytase activity at approximately pH 5. However, no phytate degradation could be observed.     

Stability of β-glucosidase Activity Produced by Bifidobacterium and Lactobacillus spp. in Fermented Soymilk During Processing and Storage

ABSTRACT: Microorganisms possess endogenous enzymes, however the stability of these enzymes during storage in soymilk has not been studied. β-glucosidase is an important enzyme that could be used in the bioconversion of the predominant soy isoflavone glucosides to their bioactive aglycone forms. Fifteen probiotic microorganisms including bifidobacterium, Lactobacillus acidophilus , and Lactobacillus casei were screened for β-glucosidase activity using p-nitrophenyl-β-d-glucopyranoside as a substrate. Six strains were selected on the basis of β-glucosidase activity produced during fermentation of soymilk. The stability of the enzyme activity was assessed during incubation for up to 48 h and storage for 8 wk at frozen (-80°C), refrigerated (4°C), room (24.8°C), and incubation (37°C) temperatures. L. casei strains showed the highest β-glucosidase activity after 24 h of incubation followed by L. acidophilus strains, whereas bifidobacterium strains showedleast activity. However, p-glucosidase from Bifidobacterium animalis BB12 showed the best stability during the 48 h fermentation. Lower storage temperatures (-80°C and 4°C) showed significantly higher ( P < 0.05) β-glucosidase activity and better stability than that at higher temperatures (24.8°C and 37°C). The stability of β-glucosidase from these microorganisms should be considered for enzymic biotransformation during storage of isoflavone β-glucosides to bioactive isoflavone aglycone forms with potential health benefits.     

Using of Lactobacillus and Bifidobacterium to product the isoflavone aglycones in fermented soymilk

The study determined isoflavone aglycone contents in soymilk and sugar-soymilk fermented with a single culture of two strains of Lactobacillus paracasei, two strains of Lactobacillus acidophilus, and one strain of Bifidobacterium longum respectively at 37 degrees C for 24 h. Isoflavone concentration was analyzed by HPLC. The viable count of bacteria in all of the fermented soymilk ranged from 7 to 9 log CFU/ml. The isoflavone aglycone had a significant increase of 62%-96% of isoflavone in all of the fermented soymilk compared to 17% in non-fermented soymilk (P<0.05). The five strains of microorganisms produced lesser amount of isoflavone aglycones in fermented sucrose-soymilk than in other fermented soymilk.     

Skim milk powder supplementation affects lactose utilization, microbial survival and biotransformation of isoflavone glycosides to isoflavone aglycones in soymilk by Lactobacillus

Four probiotic bacteria, Lactobacillus acidophilus 4461, L. acidophilus 4962, Lactobacillus casei 290 and L. casei 2607, were used for fermentation of soymilk (SM) prepared from soy protein isolate (SPI) supplemented with skim milk powder (SMP) (SSM). Soymilk and reconstituted skim milk (RSM) were used as controls. Lactose utilization in SSM by these probiotic organisms ranged from 14.97 to 18.15mg/ml, compared to 14.12-16.06mg/ml for RSM. The pH in SSM dropped to 4.07-4.29 compared to 6.15-6.36 for SM and 4.10-4.96 for RSM. The microbial viable counts were also significantly enhanced by up to 0.98logCFU/ml by the supplementation of SMP to SM. The biotransformation level of isoflavone glycosides (IG) to isoflavone aglycones (IA) in SSM ranged from 81.4% to 85.1%, which was 13.9-19.0% higher than that for SM, after 24h of incubation. Most of IG in SSM was completely converted to IA, except malonyl glycitin and malonyl genistin. At the end of the incubation, IA comprised up to 76.8% of total isoflavones in SSM.     

Isoflavone phytoestrogen degradation in fermented soymilk with selected beta-glucosidase producing L. acidophilus strains during storage at different temperatures

Soymilk fermented with 3 selected Lactobacillus acidophilus strains were stored at various temperatures (-80 degrees C, 4 degrees C, 25 degrees C and 37 degrees C) for 8 weeks and the concentration of isoflavones determined weekly using RP-HPLC. The decreasing concentration of isoflavones in soymilk during storage due to degradation was found to fit the first order kinetics model. Isoflavone aglycones as well as isoflavone glucosides largely appeared to be stable during storage (P<0.01). Interestingly, the aglycone forms showed much smaller degradation as compared to glucoside forms at all the storage temperatures studied. Of the isoflavone aglycones, daidzein was found to be the most stable followed by genistein, while glycitein was least stable. Isoflavone aglycones such as glycitein, daidzein and genistein showed smaller degradation constants in fermented soymilk at lower storage temperatures (-80 degrees C and 4 degrees C) and higher degradation constants at higher storage temperatures (25 degrees C and 37 degrees C) with each strain. In contrast, glucosides glycitin and daidzin showed higher degradation at lower storage temperatures (-80 degrees C and 4 degrees C) and lower degradation at higher storage temperatures (25 degrees C and 37 degrees C). Storage temperature was therefore found to be very important in regulating the rate of degradation soy isoflavones in fermented soymilk.     

Transformation of isoflavone phytoestrogens during the fermentation of soymilk with lactic acid bacteria and bifidobacteria

In the present study, soymilk is fermented with lactic acid bacteria (Streptococcus thermophilus BCRC 14085, Lactobacillus acidophilus BCRC 14079) and bifidobacteria (Bifidobacterium infantis BCRC 14633, B. longum B6) individually, and in combination. The change in the content of various isoflavones (aglycones, glucoside, acetyl- and malonyl-glucosides) and the beta-glucosidase activity in soymilk during fermentation is investigated. It is observed that fermented soymilk contains a lower total isoflavone content (81.94-86.61 microg/ml) than soymilk without fermentation (87.61 microg/ml). Regardless of starter organism employed, fermentation causes a major reduction in the contents of glucoside, malonylglucoside and acetylglucoside isoflavones along with a significant increase of aglycone isoflavones content. The level of change in the content of various isoflavones and beta-glucosidase activity after fermentation varies with the starter organism. Among all the fermented soymilks tested, soymilk fermented with S. thermophilus showed the highest beta-glucosidase activity and the greatest increase in the contents of aglycones. The percentage of daidzein, genistein and glycitein to total isoflavone content in S. thermophilus-fermented soymilk increases from an initial 14.24%, 6.89% and 2.45%, respectively, to 36.20%, 28.80% and 12.44% after 24h of fermentation. Finally, the increase of aglycones and decrease of glucoside isoflavones during fermentation coincides with the increase of beta-glucosidase activity observed in fermented soymilk.     

Evaluation of enzymic potential for biotransformation of isoflavone phytoestrogen in soymilk by Bifidobacterium animalis,Lactobacillus acidophilus and Lactobacillus casei

Three strains of Lactobacillus acidophilus, two of Lactobacillus casei and one of Bifidobacterium were screened for β-glucosidase activity using ρ-nitrophenyl-β-d-glucopyranoside as a substrate and their potential for the breakdown of isoflavone glucosides to the biologically active aglycones in soymilk. Isoflavones quantification with HPLC and β-glucosidase activity were performed after 0, 12, 24, 36, and 48 h of incubation in soymilk at 37 °C. All six micro-organisms produced β-glucosidase, which hydrolysed the predominant isoflavone β-glucosides. There was a significant increase and decrease (P < 0.05) in the concentration of isoflavone aglycones and glucosides, respectively, in fermented soymilk. Based on the concentration of isoflavones during peak β-glucosidase activity, the hydrolytic potential was calculated. L. acidophilus 4461 had the highest aglycone concentration of 76.9% after 24 h of incubation, up from 8% in unfermented soymilk (at 0 h). It also had the best isoflavone hydrolytic index of 2.01, signifying its importance in altering the biological activity of soymilk.     

Conversion of isoflavone glucosides to aglycones in soymilk by fermentation with lactic acid bacteria

ABSTRACT:  Four lactic acid bacteria (LAB), Lactobacillus paraplantarum KM, Enterococcus durans KH, Streptococcus salivarius HM and Weissella confusa JY, were isolated from humans and tested for their capabilities of converting isoflavone glucosides to aglycones in soymilk. Changes in growth, pH, and titratable acidity (TA) were investigated during fermentation at 37 °C for 12 h. After 6 to 9 h of fermentation, each population of 4 LAB reached 10⁸ to 10⁹ CFU/mL. The initial pH of 6.3 ± 0.1 decreased while the TA of 0.13%± 0.01% increased as fermentation proceeded, resulting in the final range between 4.1 ± 0.2 and 4.6 ± 0.1 for pH and between 0.51%± 0.02% and 0.67%± 0.06% for TA after the 12 h of fermentation. The glucoside concentrations were significantly decreased in soymilks fermented with either L. paraplantarum KM, S. salivarius HM, or W. confusa JY with fermentation time ( P < 0.05). L. paraplantarum KM was the best in percent conversion of glucosides to corresponding aglycones, resulting in 100%, 90%, and 61% hydrolysis of genistin, daidzin, and glycitin, respectively, in 6 h. Consequently, the aglycone concentrations in soymilk fermented with L. paraplantarum KM were 6 and 7-fold higher than the initial levels of daidzein and genistein, respectively, after 6 h of fermentation. Changes in the daidzin and genistin levels were not significant in soymilk fermented with E. durans KH. The rates of hydrolysis of glucosides varied depending on the species of LAB. Especially, L. paraplantarum KM seems to be a promising starter for bioactive-fermented soymilk based on its growth, acid production, and isoflavone conversion within a short time.     

6 株乳酸菌在豆乳中的发酵特性

以干酪乳杆菌（Lactobacillus casei）、短乳杆菌（L. brevis）、嗜酸乳杆菌（L. acidophilus）、植物乳杆菌（L. plantarum）、鼠李糖乳杆菌（L. rhamnosus）和保加利亚乳杆菌（L. bulgaricus）分别发酵豆乳,测定发酵期间pH值、滴定酸度、游离氨基氮,发酵结束后的活菌数和质构参数,并且对所得产品进行感官评价。结果表明：发酵过程中前5 株菌发酵豆乳的pH值显著下降,而L. bulgaricus下降缓慢,发酵24 h pH值仅为5.2。这6 株菌发酵产品的活菌数均达到1.0×108 CFU/mL以上。结果表明L. casei、L. brevis、L. acidophilus和L. plantarum发酵得到的产品的坚实度、稠度、黏度、黏附性指数均较高,感官评定结果表明这4 株菌发酵豆乳产品得分均较高,容易被消费者接受,适合用于生产发酵豆乳产品。     

HYDROLYSIS OF ISOFLAVONE PHYTOESTROGENS IN SOYMILK FERMENTED BY LACTOBACILLUS AND BIFIDOBACTERIUM COCULTURES

This study evaluated the hydrolysis of isoflavones in soymilk fermented at 37C for 48 h by four different Lactobacillus and Bifidobacterium cocultures. The hydrolysis of isoflavone β-glucosides significantly increased ( P <  0.05) the bioactive aglycones from 36 to over 90% of total isoflavones in soymilk fermented with any of the four Lactobacillus and Bifidobacterium cocultures as compared with unfermented soymilk. Compared with three other cocultures of Lactobacillus and Bifidobacterium, fermentation of soymilk with the Lactobacillus paracasei/Bifidobacterium longum cocultures yielded better isoflavone hydrolytic potential (Otieno-Shah index) and the highest β-glucosidase activity after 12 h of incubation.

PRACTICAL APPLICATIONS

Isoflavones are known as phytoestrogens because they are present in soy products and have estrogen-like activity. During fermentation, the majority of glucoside isoflavones in soymilk are converted to bioactive aglycones via microorganism-derived β-glucosidase. In human intestines, aglycone isoflavones are absorbed faster and in greater amounts than their glucosides. Using probiotic Lactobacillus and Bifidobacterium cocultures to ferment soymilk efficiently increases the bioactive aglycone concentrations. Hence, fermenting soymilk with this coculture could enhance the nutritional value of the product.     

Content composition and antioxidant activity of isoflavones in commercial and homemade soymilk and tofu

BACKGROUND: Isoflavones, found in soymilk and tofu, are one of the phytochemicals in soy‐based products that may promote good health. Homemade tofu and various homemade soymilk samples were made using different soaking, grinding, and cooking methods. The homemade samples were compared to commercial tofu and soymilk for total isoflavone content and composition as well as their antioxidant capacity. All samples were freeze‐dried and extracted with a 58% acetonitrile solution which was subsequently used to determine the isoflavone content by reverse‐phase high‐performance liquid chromatography. The antioxidant activity of extracts was determined using a modified 2,2‐azino‐bis‐(3‐ethylbenzthiazoline‐6‐sulfonic acid) method and total antioxidant capacity was reported as ascorbic acid equivalents. RESULTS: The total isoflavone, aglycone, and antioxidant levels were significantly higher in homemade soymilk and tofu (1571 µg) than in commercial samples. Homemade soymilk made by the extended boiling method yielded the highest total isoflavone (2567 µg) and glucoside (1525 µg) content. A strong positive correlation was observed between the total isoflavone, aglycone conjugates, and genistein series concentration and antioxidant capacity of soymilk. CONCLUSION: Increased moist heating time yielded the highest concentration of total isoflavones as well as aglycone conjugates and the genistein series. Increasing the duration of boiling can increase the isoflavone content of both homemade and commercial soymilk and tofu. Copyright © 2007 Society of Chemical Industry     

Biotransformation of Isoflavones by Bifidobacteria in Fermented Soymilk Supplemented with D-Glucose and L-Cysteine

ABSTRACT: Soymilk prepared using soy-protein isolate supplemented with D-glucose and L-cysteine was fermented with 4 strains of Bifidobacterium. Enumeration of bifidobacteria and quantification of isoflavones using HPLC were performed at 0, 12, 24, 36, and 48 h of incubation. Supplementation did not significantly enhance ( p > 0.05) the growth of bifidobacteria between 0 and 12 h, but did after 12 h. The increase in concentration of isoflavone aglycones and equol was significantly lower ( p < 0.05) in supplemented soymilk after 24 h when compared to plain soymilk. Supplementation increased the concentration of aglycones by 0.796 mg/100 mL in soymilk fermented with B. animalis between 12 and 24 h, and the population by 1.27 log₁₀ CFU/mL ( p < 0.05).     

Enzymic Transformation of Isoflavone Phytoestrogens in Soymilk by β-Glucosidase-Producing Bifidobacteria

ABSTRACT: Five strains of bifidobacteria were screened for β-glucosidase activity using p-nitrophenyl-β-D-glucopyranoside as the substrate, and selected strains were used to ferment soymilk. Enumeration of viable bifidobacteria and quantification of isoflavones using HPLC were performed at 0, 12, 24, 36, and 48 h of incubation. Four strains produced β-glucosidase. B. pseudolongum and B. longum -a displayed the best growth in soymilk, with an increase of 1.3 log₁₀ CFU/mL after 12 h. B. animalis, B. longum -a, and B. pseudolongum caused hydrolysis of isoflavone malonyl-, acetyl- and β-glucosides to form aglycones, and transformed daidzein to equol in soymilk. Fermentation of soymilk with Bifidobacterium sp. resulted in a significant increase (p < 0.05) in the concentration of aglycones.     

植物乳杆菌58发酵豆乳产大豆异黄酮苷元条件的优化

本研究通过测定植物乳杆菌58在不同碳源中的生长和产β-葡萄糖苷酶情况,筛选菌株的最适碳源,并确定接种至豆乳的最佳时间。在接种量、糖含量、发酵时间和发酵温度等单因素实验基础上,根据Box-Behnken中心组合原理进行响应面实验设计,以大豆异黄酮苷元含量为指标,进一步优化菌株58发酵豆乳产大豆异黄酮苷元条件。结果显示,植物乳杆菌58生长和产β-葡萄糖苷酶的最适碳源为乳糖,酶活达0.66 U/m L,显著高于果糖、蔗糖、葡萄糖和麦芽糖(p<0.05)。菌株在乳糖碳源中培养18 h产酶活力最佳,达0.75 U/mL,且生长情况良好。响应面优化实验得出发酵豆乳大豆异黄酮最佳转化条件为:接种量3.80%,糖含量5.80%,发酵温度38.10℃,发酵时间9.80 h。此条件下,大豆异黄酮苷元含量预测值达68.63 mg/L,与实验值68.16 mg/L相比差异不显著,表明构建二次模型的科学性和准确性,与优化前(59.64 mg/L)相比提高15.07%,有助于乳酸菌发酵豆乳中大豆异黄酮糖苷向高生物活性和利用度大豆异黄酮苷元的转化。     

Probiotic Cheddar Cheese: Influence of Ripening Temperatures on Proteolysis and Sensory Characteristics of Cheddar Cheeses

ABSTRACT:  Bifidobacterium longum 1941, B. animalis subsp. lactis LAFTI^® B94, Lactobacillus casei 279, Lb. casei LAFTI L26, Lb. acidophilus 4962, or Lb. acidophilus LAFTI L10 were used as an adjunct in the production of Cheddar cheeses, which were ripened at 4 and 8 °C for 24 wk. Effects of ripening temperatures and probiotic adjuncts on proteolysis and sensory evaluation of the cheeses were examined. Higher ripening temperature increased the level of proteolysis in the cheeses. Product of proteolysis and organic acids released during ripening were shown to be important for the flavor of Cheddar cheeses. There were positive and significant correlations between the levels of soluble nitrogen, lactic, acetic, and butyric acids, percentage hydrolysis of α_s1-CN and β-CN to the scores of cheddary flavor ( P < 0.05). Scores for sour-acid and vinegary flavors were higher in cheeses with the addition of Bifidobacterium sp. or Lb. casei 279 ripened at 8 °C. The scores were positively and significantly correlated to the level of lactic, acetic, and free amino acids in the cheeses ( P < 0.05). The results show that both 4 and 8 °C have potential for use in the ripening of probiotic Cheddar cheeses.     

Enhancing the Biotransformation of Isoflavones in Soymilk Supplemented with Lactose Using Probiotic Bacteria during Extended Fermentation

ABSTRACT: Soymilk (SM) lacks lactose; hence supplementation of SM with lactose is likely to enhance the growth of probiotic bacteria and biotransformation of isoflavone glycosides to isoflavone aglycones. In this study, 11 strains of probiotic bacteria including Lactobacillus rhamnosus, L. salivarius, L. plantarum, L. acidophilus, L. paracasei, HOWARU L. rhamnosus, L. delbrueckii subsp. bulgaricus, Bifidobacterium lactis type Bi-07, B. longum, HOWARU B. bifidum, and B lactis type Bi-04 were inoculated individually or as mixed cultures into SM and soymilk supplemented with lactose (SML). A total of 2% of lactose was added to 1 L of SM with the aim of improving the growth of probiotic organisms and promoting the biotransformation of isoflavone isomers to bioactive isoflavone aglycomes. Samples of SM were incubated at 37 °C and 10 mL aliquots of SM were taken at 0, 24, 48, and 72 h to monitor the growth of probiotic bacteria and changes in isoflavone contents using high-performance liquid chromatography (HPLC). Results indicated that SML fermented with probiotics had higher viable counts by >2.4 log CFU/mL than that in SM at the end of the 72 h fermentation period. Mixed cultures grew at different rates and in general Lactobacilius spp. had >1.02 log CFU/mL more cells than Bifidobacterium spp. at the end of the fermentation period. The total aglycone content in SM at 72 h of fermentation was 0.924 mg/100 mL, whereas that in SML was 1.623 mg/100 mL. Addition of lactose not only improved the growth of probiotic bacteria in SM but also enhanced the biotransformation of isoflavone glucosides to the more bioactive isoflavone aglycones. Mixed cultures did not improve the biotransformation of bioactive isoflavones when compared to single cultures.     

Profiling and quantification of isoflavones in soymilk from soy protein isolate using extracted ion chromatography and positive ion fragmentation techniques

Dietary supplements on soy based foods and beverages are increasingly gaining prominence all over the world. In this study, liquid chromatography coupled with positive electrospray ionisation tandem mass spectrometry (LC-ESI-MS) and diode array detection was used for the quantitation and characterisation of isoflavones in fermented and unfermented soymilk made from soy protein isolate SUPRO 590. Bifidobacterium animalis ssp. lactis Bb12 was used for the fermentation of soymilk. The isoflavones were found to produce characteristic radical ions as well as molecules of H₂O, CO₂, a sugar unit, and an alcohol through collision-induced fragmentation. Product ion fragments revealed unique fragmentation pathways for each isoflavone compound. Characteristic fragmentation of different isoflavones were unequivocally identified and differentiated. The occurrence of aldehydes such as pentanal, ethanal and methanal was shown to be specifically linked with isoflavone aglycones, daidzein, genistein and glycitein, respectively. Main glycosides such as genistin, daidzin and glycitin as well as the acetyl-, and malonyl forms also showed respective aglycone ions in their spectra fragmentation. Thus positive ion fragmentation was important in the absolute confirmation of isoflavones and to reveal the occurrence of other related compounds such as aldehydes in soymilk.     

Role of microbial strain and storage temperatures in the degradation of isoflavone phytoestrogens in fermented soymilk with selected β-glucosidase producing Lactobacillus casei strains

Soymilk fermented with 2 Lactobacillus casei strains were stored at various temperatures (80 °C, 4 °C, 24.8 °C and 37 °C) for 8 weeks and isoflavone concentration analysed at weekly intervals using RP-HPLC. The degradation of each isoflavone compound at each storage temperature was found to fit first order kinetic model. Aglycone as well as glucosides generally appeared to be stable during storage (P < 0.01) at the 4 storage temperatures. Aglycone forms had smaller degradation constants compared to glucosides at all storage temperature and in the presence of both microorganisms. Specifically, aglycones showed a unique trend of smaller degradation at lower storage temperatures (−80 °C and 4 °C) than at higher temperatures (24.8 °C and 37 °C). Glucoside genistin was least stable at all storage temperatures compared to other isoflavones in the fermented soymilk with each strain while aglycone daidzein was the most stable. L. casei 2607 in fermented soymilk stored at 4 °C after 8 weeks gave the least degradation for daidzein of a mere 3.78% loss from 9.53 to 9.17 ng/μL. L. casei 2607 showed greater hydrolytic potential than L. casei ASCC 290 as denoted by higher degradation of isoflavone glucosides in fermented soymilk at lower storage temperatures.