Effect of membrane property and operating conditions on phytochemical properties and permeate flux during clarification of pineapple juice

The effects of membrane property on the permeate flux, membrane fouling and quality of clarified pineapple juice were studied. Both microfiltration (membrane pore size of 0.1 and 0.2 μm) and ultrafiltration (membrane molecular weight cut-off (MWCO) of 30 and 100 kDa) membranes were employed. Membrane filtration did not have significant effects on the pH, reducing sugar and acidity of clarified juice whereas the suspended solids and microorganism were completely removed. The 0.2 μm membrane gave the highest permeate flux, total vitamin C content, total phenolic content and antioxidant capacity as well as the highest value of irreversible fouling. Based on these results, the membrane with pore size of 0.2 μm was considered to be the most suitable membrane for the clarification of pineapple juice. The optimum operating conditions for the clarification pineapple juice by membrane filtration was a cross-flow velocity of 3.4 ms⁻¹ and transmembrane pressure (TMP) of 0.7 bar. An average flux of about 37 lm⁻² h⁻¹ was obtained during the microfiltration of pineapple juice under the optimum conditions using batch concentration mode.     

Rotating Disk-Assisted Cross-Flow Ultrafiltration of Sugar Beet Juice

Rotating disk module (RDM)-assisted cross-flow ultrafiltration of sugar beet juice, obtained by cold pulsed electric field-assisted pressing, was studied in full recycling and concentration modes. Results of trans-membrane pressure (TMP) stepping tests with 10- and 50-kDa membranes showed that filtration flux increased with rotation speed and TMP until 1000 rpm and 4 bar. A slight variation of filtration purity was observed for a rotation speed range of 0–2500 rpm. A TMP increase resulted in purity reduction due to the formation of thicker fouling layer. A full recycling test study with a 10-kDa membrane confirmed the influence of TMP and rotation speed on filtration flux. A rotation speed of 1000 rpm and a TMP of 4 bar were selected for sugar beet juice purification, by concentrating juice from 13 to 1 L. The results of concentration mode tests revealed that, with a 10-kDa membrane, the filtrate purity could reach 95.6 ± 0.5 %, which was comparable to the purity of sugar beet juice purified by conventional liming-carbonation method. The flux decline in cross-flow filtration was still important, justifying more effective anti-fouling technologies investigation.     

Analysis of the fouling mechanisms during cross-flow ultrafiltration of apple juice

The purpose of this work was to study the fouling mechanisms of a Carbosep^® M8 membrane during the cross-flow ultrafiltration of apple juice. A new fouling model has been developed that simultaneously considers membrane blocking within the pores, at the pore mouths and by cake formation at the membrane surface. Membrane fouling by apple juice was due to internal pore blocking as well as cake formation. When operating ultrafiltration at a transmembrane pressure of 150 kPa and a cross-flow velocity of 7 m/s, fouling was minimal with a gradual decrease of the relative contribution of cake formation; however, transmembrane pressure still exceeds critical pressure. The fouling model predicts no cake formation at a cross-flow velocity of 7.4 m/s and a transmembrane pressure of 150 kPa or at a cross-flow velocity of 7.0 m/s and a transmembrane pressure of 120 kPa. Under these conditions, internal membrane blocking would be the only mechanism responsible for the decrease of permeate flux.     

Effects of pretreatment and various operating parameters on permeate flux and quality during ultrafiltration of apple juice

The central composite design with a quadratic model was used to investigate the effect of temperature (20–40 °C) and transmembrane pressure (TMP) (100–300 kPa) as well as pretreatment with gelatin and bentonite (0:0–300:1500 mg L^?1) on permeate flux and fouling resistance during ultrafiltration of apple juice. The changes in some physicochemical properties were also investigated. Pretreatment of apple juice with gelatin and bentonite and an increase in the temperature and TMP significantly improved the permeate flux. In general, physicochemical properties of apple juice other than polyphenolics were not affected by the applied parameters. Using 150 mg L^?1 of gelatin and 750 mg L^?1 of bentonite for fining significantly reduced the total phenolic content and so did the fouling resistance. Fouling resistance also decreased with increasing temperature, and increasing pressure increased the fouling resistance.     

Recovery of bioactive compounds in kiwifruit juice by ultrafiltration

Food quality is not only a function of nutritional values but also of the presence of bioactive compounds exerting a positive effects on human health.This research was undertaken to study the influence of the ultrafiltration (UF) on the composition of some bioactive compounds of the kiwifruit juice in order to develop a natural product which can be used to fortify foods and beverages. At the same time the effect of transmembrane pressure (TMP) and temperature on the permeate flux was also investigated in order to identify the optimal operating conditions for the processing of the juice. An optimal TMP value occurred at 0.6–0.65 bar in different conditions of cross flow velocities. Steady-state permeate fluxes increased linearly with temperature in the range 20–30 °C.The kiwifruit juice was clarified in optimal operating conditions, according to the batch concentration mode, up to a final volume reduction factor (VRF) of 2.76.The analyses of flux decay according to fouling models reported in the literature revealed that the formation of a cake layer covering the entire surface of the membrane is the main cause of the membrane fouling.Most bioactive compounds of the depectinised kiwifruit juice were recovered in the clarified fraction of the UF process. The rejection of the UF membrane towards total phenolics was 13.5%. The recovery of glutamic, folic, ascorbic and citric acids, in the clarified juice, with respect to the initial feed, was dependent on the final VRF of the UF process: an increase of the VRF determines an increase of these compounds in the clarified juice. The rejections of the UF membrane towards these compounds were in the range 0–4.3%.

Industrial relevance

Among different substances contained in the kiwifruit a primary role, in the safeguard of the human health, is carried out by some bioactive compounds such as ascorbic, folic, citric, glutamic acids and polyphenols.This research was undertaken to study the influence of ultrafiltration on the composition of these compounds in order to develop a natural product which can be used to fortify foods and beverages.     

Fluid dynamic gauging of microfiltration membranes fouled with sugar beet molasses

Fluid dynamic gauging (FDG) was used to track the thickness of the cake layer formed during the microfiltration of a 45° Brix molasses solution using a 1.5 μm polysulphone membrane. A simultaneous measure of flux and deposit thickness throughout the full membrane operating cycle is reported. Asymptotic fouling thicknesses of ca. 100 μm are developed after 30 min of filtration. Accordingly, flux declines are severe at ca. 93%. Permeate line closed (PLC) operation leads to the complete removal of the deposit layer, and the recovery of 60% of the flux. However, permeate line open (PLO) operation leads to only a 50% flux recovery and an asymptotic deposit thickness of 10 μm. An initial increase and subsequent reduction in flux during chemical cleaning has also been recorded for both acid and alkali cleaning regimes. Effective cleaning regimes for membranes fouled by molasses require an alkali stage followed by an acid stage.     

Performance assessment of membrane distillation for skim milk and whey processing

Membrane distillation is an emerging membrane process based on evaporation of a volatile solvent. One of its often stated advantages is the low flux sensitivity toward concentration of the processed fluid, in contrast to reverse osmosis. In the present paper, we looked at 2 high-solids applications of the dairy industry: skim milk and whey. Performance was assessed under various hydrodynamic conditions to investigate the feasibility of fouling mitigation by changing the operating parameters and to compare performance to widespread membrane filtration processes. Whereas filtration processes are hydraulic pressure driven, membrane distillation uses vapor pressure from heat to drive separation and, therefore, operating parameters have a different bearing on the process. Experimental and calculated results identified factors influencing heat and mass transfer under various operating conditions using polytetrafluoroethylene flat-sheet membranes. Linear velocity was found to influence performance during skim milk processing but not during whey processing. Lower feed and higher permeate temperature was found to reduce fouling in the processing of both dairy solutions. Concentration of skim milk and whey by membrane distillation has potential, as it showed high rejection (>99%) of all dairy components and can operate using low electrical energy and pressures (<10 kPa). At higher cross-flow velocities (around 0.141 m/s), fluxes were comparable to those found with reverse osmosis, achieving a sustainable flux of approximately 12 kg/h·m² for skim milk of 20% dry matter concentration and approximately 20 kg/h·m² after 18 h of operation with whey at 20% dry matter concentration.     

Physiochemical, antioxidant and whitening properties of extract from root cortices of mulberry as affected by membrane process

Extract from root cortices of mulberry (Morus alba, L.) was separated into permeate and retentate fractions using a membrane system equipped with either a microfiltration membrane or one of four molecular weight cut-off ultrafiltration membranes. The effects of membrane process at volume concentration ratio (VCR)=4 on the physiochemical characteristics, the contents of active compounds, antioxidant ability, and whitening capability (tyrosinase inhibitory activity) in permeate and retentate were evaluated. The clarification degree, antioxidant effects, and whitening capability of the permeates increased as compared to those of feed. In addition, permeate treated with a 0.45 μm microfiltration membrane exhibited less fouling layer and specific resistance (αpC_B=622.8 m⁻²×10⁻⁶) and thus had a higher permeate flux than treated with other ultrafiltration membranes (αpC_B=786.1-1025.3 m⁻²×10⁻⁶). A higher content of active compounds, such as chlorogenoic acid and p-hydroxybenzoic acid may explain higher antioxidant and whitening capabilities in permeate of extracts from root cortices of mulberry.     

Identification of optimal membrane morphological parameters during microfiltration of mosambi juice using low cost ceramic membranes

In this work, experimental investigations were carried out for the identification of optimal membrane morphological parameters (pore size distribution, average pore size and porosity) during microfiltration (MF) of mosambi juice using low cost ceramic membranes. Four different low cost ceramic membranes with different pore diameters (d_m) and porosities (?) were subjected to MF studies to evaluate the effect of d_m and ? on permeation characteristics (permeate flux and juice quality) of centrifuged mosambi juice (CJ) and enzyme treated centrifuged mosambi juice (ETCJ). Subsequently, a convenient factor namely effective permeable area factor (?_md_m²) was evaluated to provide greater insights in the fouling phenomena. Various physio-chemical properties such as colour, clarity, pH, citric acid content, density, total soluble solid (TSS) and alcohol insoluble solids (AIS) were measured for both feed and permeate juice samples to evaluate the effect of ?_md_m² on juice quality. Typical permeate fluxes were observed to vary from 5.78 × 10⁻⁶ to 13.45 × 10⁻⁶ m³/m² s for CJ and 14.07 × 10⁻⁶ to 60.64 × 10⁻⁶ m³/m² s for ETCJ at 82.7 kPa (ΔP) for different membranes whose ?_md_m² varied from 0.249 to 0.783 μm². Among different membrane pore blocking models, flux decline by cake filtration was found to be the best fitted model. The cake filtration model constant (k_c) was found to vary with ΔP and ?_md_m² and was empirically correlated. Phenomenological models were proposed to illustrate the dependency of total hydraulic resistance of membrane on ?_md_m², ΔP and time (t). Based on experimental as well as theoretical investigations, membranes with ?_md_m² up to 0.443 μm² for CJ and 0.294 μm² for ETCJ and a ΔP of 82.7 kPa were recommended for MF of mosambi juice.     

The effect of ultrasound waves on the efficiency of membrane clarification of pomegranate juice

Pomegranate juice has a turbid appearance, which poses difficulties in its concentration process. Membrane clarification can be used to clarify pomegranate juice; however, membrane fouling reduces the permeate flux, limiting its effectiveness. Ultrasound at 30 kHz was used to reduce membrane fouling. Results were compared with the data obtained for membrane clarification without ultrasonic treatment at the same temperature. Results showed that permeate flux increased with ultrasonic treatment. Evaluation of different membrane fouling characteristics showed that the total membrane resistance fell due to the reduction in irreversible fouling and cake resistance. However, ultrasound did not affect the thick caking produced in membrane processing at low feed‐flow rates. Evaluation of the physicochemical properties of pomegranate juice showed that ultrasound can decrease antioxidant activity due to the reduction in total anthocyanin content. Also, total soluble solid content and acidity of pomegranate juice changed with ultrasonic treatment.     

Dead end ultra-filtration of sugar beet juice expressed from cold electrically pre-treated slices: Effect of membrane polymer on fouling mechanism and permeate quality

Purification of raw sugar beet juice expressed at ambient temperature (20 °C) from pretreated sugar beet slices by pulsed electric field (E = 600 V·cm^− 1, t_PEF = 10 ms, T = 20 °C) was studied on the laboratory scale by dead-end ultrafiltration tests. Polyethersulfone (PES) and Regenerated Cellulose (RC) membranes with the same nominal molecular weight cut-off of 30 kDa were used. Experiments were carried out in unstirred and stirred (at rotation speed of 500 rpm) mode at constant trans-membrane pressure of 2 bar. The effects of the membrane polymer (Polyethersulfone and Regenerate Cellulose) on the filtration flux and the permeate quality were studied. In order to identify the fouling mechanism, the filtration kinetics was modeled using combined fouling models. Results showed that the filtration productivity (filtration flux) and selectivity (rejection ratio of impurities) depended on the membrane polymer. The juice filterability was better with Regenerated Cellulose (RC) membrane while the polyethersulfone (PES) membrane ensured a better retention of impurities (colorants, proteins and colloids), leading to a higher juice purity. Experimental and models data adjustment showed that combined models were preferable to investigate the fouling mechanism for both unstirred and stirred filtration. The desirable sugar purity (95–96%) of filtrate implies the potential application of a novel process (PEF treatment-cold pressing-ultrafiltration) for sugar industrial production.Industrial relevancePre-treatment by pulsed electric field PEF allowed cold or mild extraction of sucrose from sugar beet roots. The combination of PEF and ultra-filtration allowed high yield sucrose extraction and purification with less energy consumption. Membrane fouling analysis led to better filtration producibility. The obtained data can be useful for optimization of the sucrose production with high yield in industrial extraction processes.     

Reverse osmosis concentration of press liquid from orange juice solid wastes: Flux decline mechanisms

Orange juice production produces high amount of solid waste. An alternative for these wastes is their pressing with lime to obtain a press liquor stream and a dried solid for cattle feeding. The press liquor (around 10 °Brix) is traditionally concentrated up to 70 °Brix (citrus molasses) by multiple effect evaporation. In this investigation, reverse osmosis is evaluated as an alternative for press liquor preconcentration. Two synthetic feed solutions were studied, one included pectin in its composition (WP) and the other lacked pectin (WOP) to simulate a previous depectinization of WP. The concentration process was evaluated in terms of some selected parameters (chemical oxygen demand, total soluble solids, total dissolved solids and osmotic pressure). The fouling mechanism as well as the membrane resistance to the permeate pass were assessed. It was found that for later stages of concentration cake filtration was the dominant fouling mechanism while for earlier stages, the mechanism found was the complete pore blocking. The presence of pectin not only maximized the membrane fouling but also led to worse permeate quality.     

Synergistic effect of particle size,shear rate and driving-force during microfiltration of fruit juices: Toward a relevant choice of pretreatments and filtration conditions

With an objective to recommend relevant operating conditions for fruit juice microfiltration, the combined effect of particle size, shear rate and driving-force on fouling was studied. The filterability of three orange juices with different granulometry was estimated at pilot scale under different shear rates and driving forces (flux or TMP, in immersed and side-stream membrane configuration respectively). In flux-driven filtrations, fluxes to avoid an intense fouling were identified (below 5–10 L.h⁻¹.m⁻² for studied juices) and the role of juice granulometry on fouling highlighted. In TMP-driven filtrations, whatever the juice granulometry, steady-state fluxes were TMP-independent but shear rate dependent (around 10 and 30 L.h⁻¹.m⁻², for 4500 s⁻¹ and 15500 s^-1 respectively). The results demonstrated that, whatever their granulometry, juice filterability was higher in low shear rate flux-driven filtrations, than in high shear rate TMP-driven ones, which relativizes the relevance of crossflow filtration.     

Mathematical modeling of crossflow microfiltration of diluted malt extract suspension by tubular ceramic membranes

The practical application of microfiltration in brewing industry is hindered by severe membrane fouling and subsequent permeate flux decline. A theoretical and experimental study on the effect of operating parameters, which influence the crossflow microfiltration of beer and beer quality was performed. A mathematical model is developed to better understanding of the fouling layer characteristics. The experiments were conducted for different ranges of pressures, temperatures and shear rates. An optimum transmembrane pressure of 1.1 bar is suggested to maximize both the steady state and average permeate fluxes. The results of numerical simulation were in a good accordance with the experimental data.     

陶瓷膜和有机膜超滤处理荔枝汁和膜垢分析及荔枝汁品质研究

应用陶瓷膜和有机膜对荔枝汁进行澄清实验,并进行采用总循环模式(TRM)研究跨膜压力(TMP)和循环流量(Qf)对膜通量(Qp)的影响,确定其各自的最优水平;采用批处理模式(TBM)研究这两个参数最优水平的组合工艺。澄清工艺中：无机陶瓷膜效果优于有机聚醚砜膜,最佳工艺条件为陶瓷膜组件、TMP 0.3MPa、Qf 40L/min。研究在TBM下,膜垢的形成原因,对微分方程--＝k(J－Jlim)J2－n进行拟合,拟合R2为无机膜0.8812和0.8478;有机膜为0.9048,并分析膜垢的形成的模式：有机膜的膜垢主要是层垢(n＝0),无机膜的膜垢形成主要是层垢和部分并在膜垢的综合情况(n＝0,n＝1)。并研究TBM模式下,总糖、总果胶、总蛋白、抗氧化活性等影响果汁品质的物质的动态过程,结果表明：在P＜0.05,无机膜在品质的保持比如总糖、抗氧化活性、总酚的截留滤等方面强于有机膜,其余的品质无显著差异。     

EFFECT of pH and ENZYMATIC TREATMENT ON MICROFILTRATION and ULTRAFILTRATION of TANGERINE JUICE

Tangerine (Citrus reticulata blanco) juice clarification by crossflow microfiltration and ultrafiltration using polysulphone flat sheet membranes with nominal molecular weight cut off of 25,000, 50,000, 100,000 and 0.1 μm, 0.2 μm pore sizes was studied. the juice was pretreated by polygalacturonase and pH adjustment. the treated juice was clarified with a laboratory scale filtration unit with effective filtration area of 14 cm². Filtration conditions were transmembrane pressure of 93 to 194 kPa, crossflow velocity of 0.96 to 3.5 m/s and 25°C. Membrane performance was evaluated in terms of volume flux and clarity (% transmittance) of the permeate. Pretreatment of the juice by polygalacturonase and adjustment to pH 2 with HCl resulted in a clearer supernatant than enzyme treatment alone. Maximum flux was obtained with the 0.1 μm microfiltration membrane. Flux increased with transmembrane pressure and crossflow velocity. Flux at 194 kPa and 3.5 m/s was 69 L per square meter per hour. Permeate clarity was better at higher transmembrane pressure and lower velocity, due to the effect of the polarized/fouling layer of solute on the membrane surface, which acted as a secondary “dynamic” filter.     

Influence of operating conditions on membrane fouling in crossflow microfiltration of particulate suspensions

The effects of the operating conditions on the crossflow microfiltration (CFMF) of particulate suspensions were investigated. Lactalbumin particles were used as the feed material. Experiments were carried out in constant transmembrane pressure (TMP) mode using tubular ceramic membrane modules. All important parameters (internal and surface fouling, cake mass, height, porosity, and particle size distribution (PSD)) were estimated to provide a more complete understanding of the process than has been attempted before. Lactalbumin particles which are highly irregular in shape and widely size distributed formed an adhesive cake on the membrane surface during CFMF. The porosity and particle size of the deposited cake decreased with time of filtration. The value 100 kPa was found to be optimum with respect to the permeate flux in the studied range of TMP. Particle size classification effects of TMP and crossflow velocity (CFV) were demonstrated. The results of this study provided a possible explanation to the contradictory reports on the effect of CFV on the steady-state flux and the time required to obtain it. Significantly, the internal fouling first decreased with increasing CFV and then increased above 1.5 m s⁻¹. This is attributed to the particles size classification effect of CFV. A process was developed based on the observed effects of the operating parameters on the CFMF performance that enables operation at very low internal fouling and high flux for as long as 160 min. The developed process has the potential to become commercial if coupled with backflushing.     

ANALYSIS OF THE FOULING MECHANISM IN MICROFILTRATION OF ORANGE JUICE

The purpose of this work is theoretical and experimental evaluation of fouling effects on flux performance in clarification of freshly squeezed orange juice by cross-flow microfiltration. To identify optimum operating conditions to minimize fouling effects, juice was microfiltered on a laboratory scale plant varying axial velocity and transmembrane pressure difference. The observed flux decay was modeled using a modified form of the differential equation used to describe classical dead-end filtration processes. The mechanism of fouling during cross-flow microfiltration was identified by estimation of the model parameters according to a nonlinear regression optimization procedure. Analysis of the results revealed that the separation process is controlled by a cake filtration fouling mechanism as the juice is fed at relatively low velocity (i.e., Re = 5000) and the system is operated at low transmembrane pressure difference. In these operating conditions the permeate flux decays within the first 20–30 min to gradually achieve a limit value. At higher Reynolds number (Re = 15,000), an increase in applied transmembrane pressure (i.e., from 0.3 to 1 bar) allows the limit permeate flux to increase by a factor of about 4. In these conditions the filtration process is controlled by a complete pore blocking fouling mechanism, and the permeate flux becomes approximately invariant with respect to time, and a negligible decay may be observed. Evaluation of specific energy consumption involved in the filtration process is reported.     

A physicochemical investigation of membrane fouling in cold microfiltration of skim milk

The main challenge in microfiltration (MF) is membrane fouling, which leads to a significant decline in permeate flux and a change in membrane selectivity over time. This work aims to elucidate the mechanisms of membrane fouling in cold MF of skim milk by identifying and quantifying the proteins and minerals involved in external and internal membrane fouling. Microfiltration was conducted using a 1.4-μm ceramic membrane, at a temperature of 6 ± 1°C, cross-flow velocity of 6 m/s, and transmembrane pressure of 159 kPa, for 90 min. Internal and external foulants were extracted from a ceramic membrane both after a brief contact between the membrane and skim milk, to evaluate instantaneous adsorption of foulants, and after MF. Four foulant streams were collected: weakly attached external foulants, weakly attached internal foulants, strongly attached external foulants, and strongly attached internal foulants. Liquid chromatography coupled with tandem mass spectrometry analysis showed that all major milk proteins were present in all foulant streams. Proteins did appear to be the major cause of membrane fouling. Proteomics analysis of the foulants indicated elevated levels of serum proteins as compared with milk in the foulant fractions collected from the adsorption study. Caseins were preferentially introduced into the fouling layer during MF, when transmembrane pressure was applied, as confirmed both by proteomics and mineral analyses. The knowledge generated in this study advances the understanding of fouling mechanisms in cold MF of skim milk and can be used to identify solutions for minimizing membrane fouling and increasing the efficiency of milk MF.     

Combinatorial optimality of membrane morphology and feedstock during microfiltration of bottle gourd juice

The combinatorial optimality of membrane morphology and process parameters during dead end microfiltration of bottle gourd juice have been addressed in this article. Saw dust and kaolin based low cost ceramic membranes with varied morphology have been chosen to evaluate upon their microfiltration performance. For the chosen membranes, fresh, paper filtered and centrifuged juice samples were considered along with transmembrane pressure differential as process parameters. Combinatorial optimality was based on flux decline trends, fitness of fouling models, irreversible and reversible fouling data, irreversible permeation resistance and nutritional analysis of the permeate samples. An interesting feature of the article had been with respect to feed constitution playing a critical role in influencing the optimal choice of membrane morphology and transmembrane pressure differentials. Among all cases, paper filtered bottle gourd juice, 0.75 μm membrane and 137.9 kPa transmembrane pressure were found to be the best choice in terms of minimal irreversible fouling, lowest protein content, good clarity, good polyphenol and antioxidant activity in the permeate and appropriate flux.