Stability of isoflavone phytoestrogens in fermented soymilk with Bifidobacterium animalis Bb12 during storage at different temperatures

Soy isoflavones in fermented soymilk with Bifidobacterium animalis Bb12 were stored at various temperatures (?80, 4, 24.8 and 37 °C) for 8 weeks and the concentration of isoflavones determined weekly using reverse‐phase high‐performance liquid chromatography (RP‐HPLC). The first‐order kinetic model was used to assess the degradation of each isomer at each storage temperature. Soymilk predominantly possesses high concentrations of isoflavone glucosides and very low concentration of bioactive aglycone component. During storage at various temperatures, concentrations of individual isoflavone isomers appeared to be significantly stable (P < 0.01). Interestingly, aglycones showed much smaller degradation constants compared with glucosides at all the storage temperatures studied. Genistein and daidzein were much more stable than glycitein and had almost similar degradation patterns, despite differences in their concentrations in the fermented soymilk. It was, however, observed that 4 °C was the most suitable storage temperature for the product in order to guarantee minimal degradation of bioactive isoflavone aglycones.     

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.     

Original article: Thermal dynamic properties of isoflavones during dry heating

Thermal stabilities of major soya isoflavones at different dry‐heating temperatures were determined in this study. The conversion of glucoside isoflavones to aglycone isoflavones was monitored as well. The thermal degradation of the isoflavones: glucoside form daidzin, glycitin, and genistin and aglycone form daidzein, glycitein, and genistein followed first‐order reaction kinetics at heating temperatures 100, 150, and 200 °C. The degradation rate constants of the six isoflavones were not significantly different at 100 °C. However, the constants increased with increasing heating temperature. The half‐life for the glucoside and aglycone isoflavones was from 144 to 169 min and 139 to 176 min at 100 °C, respectively. They decreased rapidly to 15.7–54.7 and 36.0–90.7 min when temperature increased to 150 °C. When heated at 200 °C, they further decreased to 5.8–6.0 and 15.7–21.2 min, respectively. The order of thermal stability from lowest to highest was glycitin < genistin < daidzin < glycitein < genistein < daidzein at temperature below 150 °C. However, their thermal stabilities were not different at 200 °C. The conjugated glucosides were cleaved from the isoflavones to produce their corresponding aglycones when heated at 150 °C or higher. The production of glycitein increased constantly and was the highest among the three aglycone isoflavones.     

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.     

Isoflavone Profile in Soymilk as Affected by Soybean Variety,Grinding, and Heat‐Processing Methods

Isoflavones impart health benefits and their overall content and profile in foods are greatly influenced at each step during processing. In this study, 2 soybean varieties (Prosoy and black soybean) were processed with 3 different grinding (ambient, cold, and hot grinding) and heating methods (traditional stove cooking, 1‐phase UHT, and 2‐phase UHT) for soymilk making. The results showed after cold, ambient, and hot grinding, the total isoflavones were 3917, 5013, and 5949 nmol/g for Prosoy; the total isoflavones were 4073, 3966, and 4284 nmol/g for black soybean. Grinding could significantly increase isoflavone extraction. The grinding process had a destructive effect on isoflavones and this effect varied with grinding temperature. Different heating methods had different effects on different isoflavone forms. Two soybean varieties showed distinct patterns with respect to the change of isoflavone profile during processing.     

Effect of thermal processing on available lysine,thiamine and riboflavin content in soymilk

Soymilk was heated over a range of temperatures (90–140°C) and times (0–6 h). The available lysine, thiamine and riboflavin content of the soymilk samples were determined. There was no significant change in available lysine during a 3 h heating period at 95°C. At elevated temperatures of 120 and 140°C, optimum heat processed soymilk gave higher measured values of available lysine than did soymilk processed at 95°C. Prolonged heating at 120 and 140°C caused a decline in available lysine. Kinetic data on the thermal degradation of thiamine and riboflavin in soymilk were fitted with first-order kinetics and the kinetic parameters were determined. © 1998 SCI.     

Feasibility of using dialysis for determining calcium ion concentration and pH in calcium-fortified soymilk at high temperature

Abstract: Dialysis was performed to examine some of the properties of the soluble phase of calcium (Ca) fortified soymilk at high temperatures. Dialysates were obtained while heating soymilk at temperatures of 80 and 100 °C for 1 h and 121 °C for 15 min. It was found that the pH, total Ca, and ionic Ca of dialysates obtained at high temperature were all lower than in their corresponding nonheated Ca‐fortified soymilk. Increasing temperature from 80 to 100 °C hardly affected Ca ion concentration ([Ca²⁺]) of dialysate obtained from Ca chloride‐fortified soymilk, but it increased [Ca²⁺] in dialysates of Ca gluconate‐fortified soymilk and Ca lactate‐fortified soymilk fortified with 5 to 6 mM Ca. Dialysates obtained at 100 °C had lower pH than dialysate prepared at 80 °C. Higher Ca additions to soymilk caused a significant (P≤ 0.05) reduction in pH and an increase in [Ca²⁺] of these dialysates. When soymilk was dialyzed at 121 °C, pH, total Ca, and ionic Ca were further reduced. Freezing point depression (FPD) of dialysates increased as temperature increased but were lower than corresponding soymilk samples. This approach provides a means of estimating pH and ionic Ca in soymilks at high temperatures, in order to better understand their combined role on soymilk coagulation.     

Effect of thermal processing on genistein,daidzein and glycitein content in soymilk

Soymilk was subjected to various heat treatments at 95, 121 and 140 °C for various lengths of time. The contents of the aglycones of isoflavone (daidzein, glycitein and genistein) of the soymilk were determined using C₁₈ reversed‐phase high‐performance liquid chromatography. Genistein showed greater stability to heat treatment than daidzein and glycitein. Both the daidzein and glycitein contents decreased rapidly during the early stage of heating, but on continued heating the rates of decrease were much slower. Heating may cause an increase or decrease in the genistein content of soymilk depending on the temperature and time used. Upon heating at 95 and 121 °C, there was an increase in the genistein content in the early stage of heating, possibly due the conversion of genistin to genistein. Heating at 140 °C for more than 15 s and prolonged heating at 95 and 121 °C, however, caused a slow decline in the genistein content. Copyright © 2006 Society of Chemical Industry     

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     

Sterilization and aseptic packaging of soymilk treated by ultra high pressure homogenization

Ultra high pressure homogenization (UHPH) was applied on soymilk to produce an aseptically packaged beverage. UHPH-treated soymilk (300 MPa, 80 °C inlet temperature and 144 °C/0.7 s at the homogenization valve) was compared with samples treated by ultra high temperature (UHT) at 142 °C for 6 s. After treatment, soymilk samples were aseptically packaged in coated paperboard cartons of 200 mL Tetra Brik containers. Tetra Brik containers were stored for 6 months at room temperature and analyzed at different days. Microbiological (total mesophilic aerobic bacteria, aerobic spores, Bacillus cereus, and enterobacteria counts), physical (dispersion stability and particle size distribution), chemical (hydroperoxide index and volatile profile evolution) and sensory analyses were performed on soymilks. Both UHPH and UHT soymilks did not present microbiological growth during storage. UHPH soymilk presented high colloidal stability and relevant decrease in hydroperoxide index during storage. On the other hand, almost all of the compounds associated to off-flavors were detected in the volatile profile of soymilk. Sensory results indicated that UHPH treatment did not produce changes in soymilk which could affect the panel perception for different UHT and UHPH soymilks and for selecting their preference.Industrial relevanceSoymilk constitutes one of the food industry sectors with the highest worldwide growth and its consumption has experienced a noticeable increase in the last years. The growing consumer demand for safe products, environmentally friendly processes and high quality nutritional foods has challenged the food industry to adapt the technological processes. This tendency impacts directly on traditional technologies, like heat treatments. In this sense, UHPH technology has been applied as an alternative to those thermal treatments. This research paper presents a comparative study between soymilk treated by UHPH and by UHT to produce a product stored at room temperature for 6 months. Results showed stable levels of oxidation, high physical stability, no microbial growth and a positive trend of sensory response during the period analyzed for UHPH soymilk. Moreover, the UHPH system was designed to work at continuous flow, allowing its application in several industrial food processes.     

Predicting the Heating Temperature of Soymilk Products Using Fluorescence Fingerprints

A novel measurement technique using fluorescence fingerprints (FFs) was developed to measure the degree of heat treatment applied to soymilk. FFs are a set of fluorescence spectra acquired at consecutive excitation wavelengths. Soymilk was heated at 50, 60, 70, 80, or 90 °C, for 10 min, and the samples were measured both in the liquid and freeze-dried forms. Partial least squares (PLS) regression models were constructed to predict heating temperature from the FFs of liquid soymilk and freeze-dried soymilk. Heating temperatures were predicted from soymilk FFs with root-mean-square errors of prediction (RMSEP) and R ²P of 7.20 °C and 0.92 and from freeze-dried soymilk FFs with RMSEP and R ²P of 9.00 °C and 0.89, respectively. The fluorescence of aromatic amino acids and Maillard products mainly contributed to the prediction models. FF measurement proved to be effective for the objective control of the soymilk heating process.     

Effects of Storage Conditions on the Stability of Isoflavone Isomers in Lactic Fermented Soymilk Powder

In this study, the powder of the Streptococcus thermophilus-fermented soymilk was stored under five conditions for 10 weeks: (1) at 25 °C with no added desiccant or deoxidant, (2) at 25 °C with added deoxidant, (3) at 25 °C with added desiccant, (4) at 25 °C with both deoxidant and desiccant added, and (5) at 4 °C with both deoxidant and desiccant added. It was found that the isoflavone content of the fermented soymilk powder declined during storage depending on storage condition and the kind of isoflavone isomer. The highest residual of isoflavone was found with the fermented soymilk powder stored at 4 °C with deoxidant and desiccant. Under this storage condition, total isoflavone, β-glucosides, acetylglucosides, malonylglucoside, and aglycone isoflavone in fermented soymilk powder showed residuals of 89.7%, 83.5%, 87.8%, 61.0%, and 93.1%, respectively, of its original content after 10 weeks of storage. Meanwhile, the smallest respective residuals of 71.2%, 29.3%, 47.9%, 51.8%, and 79.2% were noted with powder stored at 25 °C with neither deoxidant nor desiccant. However, the percentage of aglycone, the bioactive isoflavone, increased from an initial value of 77.95% to 86.76% in this sample.     

Kinetic model for studying the conversion and degradation of isoflavones during heating

The conversion and degradation of isoflavones during dry or moist heating at 100, 150 and 200 °C, for varied lengths of time, were kinetically studied. Results showed that, at the early stage, all the reaction rates of malonylgenistin (MG), acetylgenistin (AG), genistin (G), and genistein (Ge) increased with increasing temperature and fitted a first-order model, when the concentration changes during heating were analyzed using HPLC. For dry heating, the conversion of MG to G exhibited the highest rate constant (h⁻¹), followed by MG to AG, AG to G, AG to Ge, G to Ge and MG to Ge. Moist heating showed the same phenomenon; however, the last three conversions were not observed. In addition, MG had the highest degradation rate, followed by G, Ge and AG during dry heating, while the reversed trend occurred for moist heating. Moist heating was more susceptible to conversion and degradation of isoflavones than dry heating. The correlation coefficients (r²) ranged from 0.664 to 0.987 for moist heating and 0.688–0.960 for dry heating. The kinetic model developed in this study can be used to predict the concentration changes of isoflavones during dry heating and moist heating.     

Isoflavone profiles of soymilk as affected by high-pressure treatments of soymilk and soybeans

High hydrostatic pressure was applied to hydrated soybeans (100–700 MPa, 25 °C) and soymilk (400–750 MPa; 25 and 75 °C) to assess its effect on isoflavone content, profile and water-extractability. Neither pressure level nor initial treatment temperature affected soymilk isoflavone content. However, combined pressure and mild thermal treatment modified the isoflavone distribution. At 75 °C, the isoflavone profile shifted from malonylglucosides toward β-glucosides, which was correlated to the effect of adiabatic heating. When pressure was applied to the hydrated soybeans, the soymilk isoflavone concentration varied between 4.32 and 6.06 μmol/g. The content of protein decreased and fat increased in soymilks prepared from pressurized soybeans with increasing pressure level.     

Neohesperidin Dihydrochalcone Stability in Aqueous Buffer Solutions

The degradation of neohesperidin dihydrochalcone (NHDC) in solution was studied at different temperatures (30–60°C) and pH values (l–7). Pseudo-first order kinetics were observed across the temperature and pH range. Maximum stability was at pH 3–5. These data may be used to predict sweetener stability to typical conditions prevailing during manufacture and storage of beverages and to food processing at high temperatures. Results indicate NHDC would be stable throughout the normal shelf-life of soft drinks and would also withstand pasteurization and UHT processes.     

A study on degradation kinetics of ascorbic acid in drumstick (Moringa olifera) leaves during cooking

The kinetics of ascorbic acid degradation in drumstick (Moringa olifera) leaves as well as in pure ascorbic acid solutions at the initial concentrations present in drumstick leaves over a temperature range of 50–120 °C (isothermal temperature process) has been studied. The degradation kinetics of ascorbic acid was also evaluated in normal open‐pan cooking, pressure‐cooking and a newly developed and patented fuel‐efficient eco cooker (non‐isothermal heating process). The ascorbic acid degradation followed first‐order reaction kinetics where the rate constant increased with an increase in the temperature. The temperature dependence of degradation was adequately modelled by the Arrhenius equation. A mathematical model was developed using the isothermal kinetic parameters obtained to predict the losses of ascorbic acid from the time–temperature data of the non‐isothermal heating/processing method. The results obtained indicate the ascorbic acid degradation is of similar order of magnitude in all the methods of cooking. Copyright © 2005 Society of Chemical Industry     

Thermal degradation of deoxynivalenol during maize bread baking

The thermal degradation of deoxynivalenol (DON) was determined at isothermal baking conditions within the temperature range of 100–250°C, using a crust-like model, which was prepared with naturally contaminated maize flour. No degradation was observed at 100°C. For the temperatures of 150, 200 and 250°C, thermal degradation rate constants (k) were calculated and temperature dependence of DON degradation was observed by using Arrhenius equation. The degradation of DON obeyed Arrhenius law with a regression coefficient of 0.95. A classical bread baking operation was also performed at 250°C for 70?min and the rate of DON degradation in the bread was estimated by using the kinetic data derived from the model study. The crust and crumb temperatures recorded during bread baking were used to calculate the thermal degradation rate constants (k) and partial DON degradations at certain time intervals. Using these data, total degradation at the end of the entire baking process was predicted for both crust and crumb. This DON degradation was consistent with the experimental degradation data, confirming the accuracy of kinetic constants determined by means of the crust-like model.     

Thermal kinetics of pungency loss in relation to the quality of pickled garlic

The kinetics of the loss of pungency (enzymatically formed pyruvate) from garlic slices during heating was investigated at selected temperatures (60, 65, 70 and 75 °C) with the aim of optimizing the water blanching treatment in the processing of pickled garlic. For each temperature, after a lag period, pungency appeared to decrease in two phases as heating progressed. The first and more important phase, which was used for the calculation of the kinetic parameters, followed first‐order kinetics. The calculated z‐value (9.4 °C) was significantly lower than z‐values generally reported for degradation of quality factors in foods. The effectiveness of thermal treatment to eliminate pungent flavour and inhibit green discolouration increased with increasing temperatures. Optimum blanch treatment was reached at 80 °C for 1.1 min. Pyruvate determination was shown to be a better indicator of pungency than allicin determination in blanched garlic slices.     

Gelation enhancement of soy protein isolate by sequential low‐ and ultrahigh‐temperature two‐stage preheating treatments

The effects of combined two heating steps with low (LT, 60 °C for 1 h) and ultrahigh (UHT, 130 or 140 °C for 4 s) temperatures on the thermal gelation of soy protein isolate (SPI) were studied. UHT pretreatments significantly increased protein solubility and enhanced the gelling potential of SPI. Yet, the two‐stage preheating treatment with LT and then UHT‐130 °C had a most remarkable effect: the gel strength of the SPI₆₀₊₁₃₀ sample was, respectively, 1.45‐, 1.64‐ and 3.19‐fold as strong as those of SPI₆₀, SPI₂₅₊₁₃₀, and SPI₂₅. In comparison with single LT or UHT treatments, this two‐stage heating also produced greater amounts of soluble protein aggregates stabilised predominantly by disulphide bonds and hydrophobic forces, contributing to the improved gel network structure.     

Solid phase microextraction of stale flavour volatiles from the headspace of UHT milk

Solid phase microextraction (SPME) offers a solvent‐free and less labour‐intensive alternative to traditional flavour isolation techniques. In this instance, SPME was optimised for the extraction of 17 stale flavour volatiles (C3–11,13 methyl ketones and C4–10 saturated aldehydes) from the headspace of full‐cream ultrahigh‐temperature (UHT)‐processed milk. A comparison of relative extraction efficiencies was made using three fibre coatings, three extraction times and three extraction temperatures. Linearity of calibration curves, limits of detection and repeatability (coefficients of variation) were also used in determining the optimum extraction conditions. A 2 cm fibre coating of 50/30 µm divinylbenzene/Carboxen/polydimethylsiloxane in conjunction with a 15 min extraction at 40 °C were chosen as the final optimum conditions. This method can be used as an objective tool for monitoring the flavour quality of UHT milk during storage. Copyright © 2005 Society of Chemical Industry