Behavior of functional compounds during freeze concentration of tofu whey

The liquid waste generated from tofu production, denominated as Tofu Whey (TW), contains important amounts of isoflavones that can be evaluated by various separation techniques. In this work TW was concentrated by falling-film freeze concentration from 1.9 to 15.5 °Brix, up to levels of 208 mg of isoflavones per 100 g solids. The levels of isoflavones, proteins, sugars, calcium and magnesium were determined both in the ice and in the concentrate obtained. It was found by rheological characterization that TW shows a Newtonian behavior at concentrations between 1.9 and 15.5 °Brix with freezing points of −0.6 to −2.7 °C.     

Freeze concentration of whey in a falling-film based pilot plant: Process and characterization

Falling-film freeze concentration is a technique for concentration of liquids by freezing the available water in the form of a layer of ice on a refrigerated surface. Processing at low temperatures keeps the organoleptic properties of the initial product. In this study the freeze concentration of whey was investigated as an technological alternative for the use of this byproduct of the dairy industry. Freeze concentration tests were carried out in pilot-scale equipment and the increase in soluble solids content of the whey and the amount and purity of the ice formed were analysed. Electrical conductivity, viscosity and freezing point of the concentrated whey were determined. The concentrate obtained had a solid concentration of up to 21.8 °Brix. The ice formed in the last stage of the freeze-concentration process had a lactose content of 11.3 g/L and protein content of 3.45%. The electrical conductivity of the ice formed increased exponentially to a value of 29.40 mS/cm. Freeze-concentrated whey of 10, 15, and 20 °Brix behaves as a Newtonian fluid in the temperature range of −4 °C-4 °C.     

Modelling of rheological behaviour of soursop juice concentrates using shear rate–temperature–concentration superposition

The effect of temperature and concentration on rheological behaviour of freeze dried soursop juice concentrates were investigated using a rheometer over a wide range of temperatures (10–70 °C) and concentrations (10–50 °Brix) at shear rates of 0–400 1/s. The Power law is the best fitted model to the rheological data due to the high value of coefficient of determination (R² = 0.9989). The soursop juice concentrates exhibited shear thinning or pseudoplastic behaviour with n < 1. The consistency coefficients dependency on temperature and concentration were well described by Arrhenius relationship and exponential relationship respectively. The flow activation energy of soursop juice concentrates were 8.32–30.48 kJ/mol. The superposition technique with Power law model sufficiently modelled the overall rheological characteristics of soursop juice concentrates into a single master curve using shift factors based on double shifting steps with R² = 0.9184. This technique also showed that the soursop juice concentrates increases in viscosity and pseudoplasticity behaviour with concentration.     

Progressive freeze concentration of orange juice in a pilot plant falling film

In the present study the cryoconcentration of orange juice was investigated, using a pilot plant unit for cryconcentration of liquids using a cold surface. The evolution in time of the concentration of solids in the juice and in the ice was analyzed during the process. It was found that the concentration of solids in the juice showed a linear increase in time at a rate of 0.75 °Brix/h until a final concentration of 28.8 °Brix. The concentration of solutes in the ice showed an exponential increase.Industrial relevanceThe freeze concentration allows dewatering orange juice at temperatures below the water's freezing point, which allows obtaining products of better quality. The freeze concentration is a technology that allows eliminating water from the juices at temperatures below the water's freezing point, which allows obtaining products of better quality. This work has applied this technology to concentrate orange juice, obtaining promissory results.     

Concentration of apple and pear juices in a multi-plate freeze concentrator

In this article we will examine the process for concentration of apple and pear juices as well as concentration of sugar solutions modelling pear juice (simulation fluid) using a descending film multi-plate freeze concentrator. It has been determined in advance the freezing point of those fluids in the working concentration and temperature intervals. In addition, different parameters were studied to allow tracking of the process of freeze concentration, such as ice accumulation, variation of the content of soluble solids in the solution and in the ice removed, ice production and energy consumption. The apple and pear juices tested showed similar behaviour, while the mixture of sugars used for simulation showed better behaviour, due perhaps to the absence of foam in the process and to the quicker formation of ice. It has been obtained concentrations of 30.2 and 30.8 °Bx with the apple and pear juices, respectively, and up to 32.7 °Bx with the simulation fluid.Industrial relevanceThe clarified juices usually are concentrated on an evaporation stage. In this stage the juice is subjected to high temperatures that cause undesirable reactions, such as non enzymatic browning and destruction of nutritive compounds. The freeze concentration is a technology that allows eliminating water from the juices at temperatures below the water’s freezing point, what allows obtaining products of better quality. In this work has been applied this technology to concentrate apple and pear juices, obtaining promissory results.     

果汁冷冻浓缩过程中冰晶形成规律的研究

本研究测定了橙汁和菠萝汁的冰点曲线,并以此探讨在果汁冷冻浓缩时水分冻结率的变化规律。结果表明,果汁在开始冻结的温度附近结冰率变化最大;以后逐渐减慢。橙汁和菠萝汁的最大冰晶生成区分别是-0.8～-7.9℃和-0.7～-6.7℃。冷却介质温度越低,冰晶的生长速度越快,但最终冰晶尺寸越小。当介质温度为-10℃左右时,可获得较大的冰晶尺寸。本文也研究了搅拌作用及果汁预处理因素对冰晶生长的影响。     

Calculation process for the recovery of solutes retained in the ice in a multi-plate freeze concentrator: Time and concentration

Fractionated thawing was studied as a method to recover solutes incorporated in the ice obtained in a cryoconcentrator. Thawing times and solute concentration in the ice were determined at several thawing temperatures.Ice sheets used for the thawing studies were obtained by cryoconcentrated solutions of sugars and simulated juice at initial concentrations of 5 to 20 °Brix. The ice sheets produced contained levels of solutes between 1.0 and 9.0 °Brix.Fractionated thawing was performed at temperatures of 20 to 30 °C while maintaining geometrical similarity for the test samples. By fractionated thawing more than 60% of the solutes retained in the ice was recovered in 34%, of the total thawing time.The procedure presented allows the determination of the solute concentration achieved in the various thawing fractions and predicts the thawing time required for a given form factor, melting temperature and the solute mass fraction in the ice.Industrial relevanceThe freeze concentration is a technology that allows eliminating water from liquid foods at temperatures below the water's freezing point, which allows obtaining products of better quality. Fractionated thawing was studied as a method to recover solutes incorporated in the ice, improving the global efficiency of a freeze concentration process by optimal recovery of the solutes retained in the ice. It also provides estimations of the energy used for thawing. This work continues the research in falling film freeze concentration technology which we have submitted and published in this journal. This work contributes to increase the global process efficiency.     

Spray evaporation of liquid foods

‘Spray evaporation’ based on the principle of adiabatic humidification was examined as an evaporation technique for the concentration of two types of representative liquid foods, namely, fruit juice and milk. The concentration of apple juice could be increased from 10.0 to 13.0 °Brix by this technique without application of heat utilizing the humidity potential to an extent of 89%. Employing heated process air during processing increased the amount of water evaporation owing to increased saturation humidity level, enabling higher concentrations to be achieved in apple juice (48 °Brix), reconstituted milk (29 °Brix) and single toned milk (22 °Brix). Feed flow rate had an inverse effect on the final concentration under otherwise similar conditions. Evaporative cooling associated with spray evaporation actually delivered the concentrate at a relatively lower temperature. By manipulating the operating conditions, humidity potential could be utilized to the extent of 55% with heated process air. The spray evaporation technique seemed to have a good potential for the concentration of liquid foods.     

Freeze‐drying concentration of Rangpur lime juice

The use of freeze‐drying for concentrating lime Rangpur juice was investigated. This procedure allowed obtaining concentrated Rangpur lime juices between 23 and 51.3 °Brix, without affecting their organoleptic and nutritional characteristics. The efficiency of the procedure was inversely related to the film thickness of the matrix to be lyophilised. The sublimation speed per unit area diminished with the reduction in the residual moisture content of the juice. The mathematical model that fitted to the concentration procedure allowed to predict the time required for concentrating Rangpur lime by freeze‐drying starting from samples of different thickness. When compared with other citric juices evaluated, the Rangpur lime juice was the most suitable for freeze‐drying concentration. The results could be used to devise optimal industrial freeze‐drying cycles for processing Rangpur lime juices at different concentrations.     

The Contributing Effect of Apple Pectin on the Freezing Point Depression of Apple Juice Concentrates

Frozen apple juice concentrate was prepared using conventional procedures. Response surface methodology was used to statistically model the results. A regression equation was derived as a function of Brix and pectin concentration. The results of this investigation indicated that pectin contributed to the freezing point depression of apple juice concentrate, the effect of which was greater with increasing concentration. The untreated apple juice concentrate (with pectin intact) had a lower freezing point compared to the depectinized juice. The freezing point of apple juice concentrate decreased as the apples ripened as would be expected due to an increase in soluble pectin.     

Metabolomes of the psychrotolerant bacterium Listeria monocytogenes 10403S grown at 37 °C and 8 °C

Listeria monocytogenes is a food-borne pathogen with the ability to grow at refrigeration temperatures. Knowledge of the mechanisms involved in low temperature growth is incomplete and here we report the results of a metabolomics investigation of this. The small molecule contents of L. monocytogenes 10403S grown at 37 °C and 8 °C were compared by gas chromatography/mass spectrometry (GC/MS). Over 500 peaks were detected in both 37 °C and 8 °C-grown cells, and 103 were identified. Of the identified metabolites, the concentrations of 56 metabolites were increased (P < 0.05), while the concentrations of 8 metabolites were decreased at low temperature. Metabolites increasing in concentration at 8 °C included amino acids, sugars, organic acids, urea cycle intermediates, polyamines, and different compatible solutes. A principal component analysis (PCA) was used to visualize and compare the matrix containing the data in 6 samples, and this clearly identified the 37 °C and 8 °C metabolomes as different. The results indicated that an increase in solute concentrations in the cytoplasm was associated with low temperature adaptation, which may be a response to chill stress with the effect of lowering the freezing point of intracellular water and decreasing ice crystal formation.     

鸭梨的冻结特征及影响因素分析

运用自制热镀锡膜铜-康铜热电偶测温方法测定了鸭梨果实不同部位的冻结曲线,对鸭梨果实与汁液的冻结特点作了比较,并对冰点温度与部分品质参数的关系进行了探讨.试验结果表明,鸭梨果实的冻结曲线有3种形式,典型的形式具有过冷点、初始冰点、平衡冰点、终止冰点等关键特征点;果实不同部位的过冷点和冰点温度及其出现的时间顺序存在差异,越靠近果心,冻结速率越小,冰点温度越高;果实与果汁冻结特征的不同点在于果实有“特征小段”而果汁没有,且果汁较果实容易冻结;在一定范围内,鸭梨果实冰点温度与可溶性固形物含量呈极显著负相关,而与单果重、硬度相关性不显著.     

The effect of pre-treatment on the anthocyanin and flavonol content of black currant juice (Ribes nigrum L.) in concentration by reverse osmosis

Reverse osmosis process for the concentration of black currant juice was carried using AFC-99 tubular membrane at 30 °C and 45 bar. The contents of selected flavonols and anthocyanins were analyzed after centrifugation; enzyme treatment by Panzym Super E and by Rohapect berry followed by centrifugation; and ultrafiltration black currant juices and juice concentrates. The total soluble solid (TSS) content of the juices increased from the initial 17.6–17.9 °Brix to 24–24.8 °Brix in the case of the centrifuged juice in the concentration process. Similarly, it increased from 14.5–15.5 °Brix to 23.1–23.4 °Brix for the Panzym Super E treated juice, and from 16.1–16.9 °Brix to 22.5–23.1 °Brix for the Rohapect berry treated black currant juices. The ultrafiltered juice had the lowest initial TSS content between 14.1 and 14.9 °Brix and it increased to 22.1–23.1 °Brix. The average permeate fluxes during the concentration process were 7.3 L m⁻² h⁻¹ for the centrifuged juice, 11.9 L m⁻² h⁻¹ for the Panzym Super E treated juice, 9.2 and 13.1 L m⁻² h⁻¹ for the Rohapect berry treated and ultrafiltered juice, respectively. Analysis indicated that the enzymatic treatment resulted in the increase of anthocyanin and flavonol content of the juices. The centrifugation process decreased the amount of anthocyanins and flavonols to some extent. The juice clarified by ultrafiltration had significantly lower concentrations of anthocyanins and flavonols, while the juices treated by Panzym Super E had the highest levels of these flavonoids. This study recommends enzymatic pre-treatment by Panzym Super E, since it improves the permeate flux in reverse osmosis during the concentration process, and results in a juice concentrates highest in anthocyanins and flavonols.     

Process optimisation of the bitter gourd (Momordica charantia) concentrated juice preparation for a freeze‐dried powder

Bitter gourd (Momordica charantia), a commonly consumed vegetable in South Asia, eastern‐South Asia, China, Japan, Korea peninsula, Caribbean Sea isles etc., is used as an adjunct in the management of diabetes mellitus. In this study, in order to find the effective ways of producing bitter gourd freeze‐dried powder, the concentrated juice of bitter gourd was produced through enzymatic process (EP), ultra filtration (UF), reverse osmosis and vacuum concentration technology. Results indicated that total saponins, total sugar and pH value in bitter gourd juice were almost unchanged after EP and after UF (P ≥ 0.05). However, UF decreased the turbidity and improved transmittance of juice (P < 0.05). When compared with the vacuum concentration alone, the combined process of reverse osmosis followed by vacuum concentration had 3.33 folds of production efficiency and 1.725 times of vitamin C content in concentrated juice. With freeze‐drying microscope system, the eutectic point of the freeze‐dried product of bitter gourd juice was detected to be ?37.5 °C, which was important to optimise lyophilisation parameters. The freeze‐drying microscope system was more accurate than the conventional electric resistance method in detecting the eutectic point of freeze‐dried product.     

Effect of chitosan on the stability and properties of modified lecithin stabilized oil-in-water monodisperse emulsion prepared by microchannel emulsification

The effect of chitosan (CHI) on the stability of monodisperse modified lecithin (ML) stabilized soybean oil-in-water (O/W) emulsion was investigated. Monodisperse emulsion droplets with particle size of 24.4 ± 0.7 μm and coefficient of variation below 12% were prepared by microchannel (MC) emulsification using a hydrophilic asymmetric straight-through MC silicon 24 × 24 mm microchip consisting of 23,348 microchannels. The stability of the ML stabilized monodisperse emulsion droplets was investigated as a function of CHI addition at various concentration, pH, ionic strength, thermal treatment and freezing-thawing treatment by means of particle size and ζ-potential measurements as well as microscopic observation. The monodisperse O/W emulsions were diluted with CHI solution at various concentrations to a final droplet concentration of 1 wt% soybean oil, 0.25 wt% ML and 0–0.5 wt% CHI at pH 3. Pronounced droplet aggregation was observed when CHI was present at a concentration range of between 0.01 and 0.04 wt%. Above this concentration range, flocculations were less extensive, indicating some restabilization. ML stabilized emulsions were stable at a wide range of NaCl concentrations (0–1000 mM) and pH (3–8). On the contrary, in the presence of CHI, aggregation of the emulsion droplets was observed when NaCl concentration was above 200 mM and when the pH started to approach the pKa of CHI (i.e. ∼6.2–7.0). Emulsions containing CHI were found to have better stability at high temperature (>70 °C) in comparison to the emulsion stabilized only by ML. With sucrose/sorbitol as cryoprotectant aids, emulsions with the addition of CHI were found to be more resistant to droplet coalescence as compared to those without CHI after freezing at −20 °C for 22 h and thawing at 30 °C for 2 h. The use of CHI may potentially destabilize ML-stabilized O/W emulsions but its stability can be enhanced by selectively choosing the appropriate CHI concentrations and conditions of preparation.     

Simultaneous estimation of the thermophysical properties of three kinds of fruit juices based on the measured result by a transient heat flow probe method

The thermophysical properties of three kinds of fruit juices (grape juice, orange juice, and pineapple juice) were measured at various temperatures (10–50 °C) and concentrations (10–50%). A new method for the simultaneous determination of thermophysical properties using a modified version of current probe theory method was proposed. The temperature changes of the probe upon insertion in the sample were fitted to an approximate solution of the heat conduction equation, and the values of two parameters in that solution were determined. Using the values of these parameters, the thermal conductivity and thermal diffusivity of each sample were determined. The specific heat of each sample was estimated from the definition of thermal diffusivity. These thermophysical properties were expressed as a function of concentration and temperature.     

Effect of previous enzymatic recirculation treatment through a tubular ceramic membrane on ultrafiltration of model solution and apple juice

The process of ultrafiltration of a model solution and 12% soluble solids apple juice containing pectins through tubular membranes of 100 and 300 kDa (1 and 3 channels) was studied. Furthermore, in order to obtain a higher permeate flow, the fluids were previously treated with pectinolytic enzymes recirculating through a tubular membrane at different concentrations and treatment times. The permeate flow was analyzed with respect to time and the influence of enzymatic treatment on different parameters: viscosity, density, absorbance at 420 nm, reducing sugars, °Brix, color and pH. Depectinization increased the permeate flow for the model solution and apple juice with 67.52% and 53.11% when the pectinolytic enzyme preparation re-circulated across the tubular membrane. Using the lowest concentration of enzyme treatment and the longest recirculation treatment, an increase in permeate flow was obtained leading to a more favourable clarification process and economic benefits.     

Fermentation pH and temperature influence the cryotolerance of Lactobacillus acidophilus RD758

The effects of 3 fermentation temperatures (30, 37, and 42°C) and 3 fermentation pH (4.5, 5, and 6) on the cryotolerance of Lactobacillus acidophilus RD758 were studied in relation to their fatty acid composition. Cryotolerance was defined as the ability of the cells to recover their acidification activity after freezing and frozen storage at −20°C. Better cryotolerance was obtained in cells grown at 30°C or at pH 5; these cells showed no loss in acidification activity during freezing and a low rate of loss in acidification activity during frozen storage. On the other hand, cells grown at 42°C or at pH 4.5 displayed poor cryotolerance. The membrane fatty acid composition was analyzed and related to the cryotolerance using principal component analysis. The improved cryotolerance observed during the freezing step was associated with a high ratio of unsaturated to saturated fatty acids, a low C18:0 content, and high C16:0 and cyclic C19:0 relative concentrations. High resistance during frozen storage was related to a high cycC19:0 concentration. Finally, the low cryotolerance observed after fermentation at pH 4.5 was explained by a low C18:2 content.     

Loss of rutin and antioxidant activity of asparagus juice caused by a pectolytic enzyme preparation from Aspergillus niger

We found that a commercial pectolytic enzyme preparation from Aspergillus niger (pectinase AN) contained laccase activity that decreased rutin content and antioxidant activity of asparagus juice. This research investigated the effects of pH, temperature, and concentration of pectinase AN on pectinase AN’s laccase activity to decrease rutin content and antioxidant activity of asparagus juice. Asparagus juice was incubated with pectinase AN at different pHs (3.2, 4.5 and 5.8), temperatures (25, 37, and 50 °C) and enzyme concentrations (0.1%, 0.5% and 1%). Rutin content and antioxidant activity of samples was determined by HPLC and 2,2′-diphenyl-1-picrylhydrazyl (DPPH) free radical method, respectively. The rate of loss of rutin and antioxidant activity of asparagus juice was smaller at pH 3.2 than at pH 4.5 and pH 5.8, smaller for 0.1% pectinase AN than 0.5% and 1% pectinase AN. The rate of loss of rutin of asparagus juice was greater at 25 °C than at the other two temperatures. Pectinase AN can decrease rutin content and antioxidant activity of asparagus juice at the selected conditions. But rutin content and antioxidant activity of asparagus juice produced using pectinase AN could be less decreased at pH 3.2 and 0.1% of enzyme with less than 2 h of incubation time. This information was helpful for juice industry to produce juices with high antioxidant activity using pectinase AN.     

果汁冷冻浓缩中生物冰核的成冰作用及初步应用

介绍了冰核细菌促进成冰的机制,并结合国外有关报道和我们的研究结果,论述了冰核细菌在食品冷冻浓缩中导致冰晶形成的结构、冷冻效率、应用前的预处理及食用级冰核细菌在果汁中的应用情况,最后展望了未来的研究方向。