CLEANING KINETICS MODELING OF HOLDING TUBES FOULED DURING MILK PASTEURIZATION1

In the present study, 25 cm tubes fouled during pilot plant scale pasteurization of raw whole milk were cleaned with sodium hydroxide. The pasteurization conditions resembled those of the dairy industry. An optical sensor sensitive to the turbidity of suspended deposits removed by the cleaning solution was placed successively at the outlet of each fouled tube. Use of this sensor combined with a nonrecycled cleaning solution process enabled us to measure the cleaning rate on line. In these conditions it was observed that, at zero time, the cleaning rate was null. Based on the above observations a kinetic model of cleaning was established. It consists of two steps in series. The adhesive deposit passes through an intermediate state before being washed away by the cleaning solution. Each step is a first order reaction related to the mass of the adhesive deposit and the mass of the intermediate compound, respectively. Among the many physico-chemical parameters affecting the cleaning process, three major ones were studied; temperature, concentration and circulation rate of the soda solution. An empirical model of the rate constant was set up which takes into account those three parameters and the initial weight of deposit to be cleaned. A 1% increase in the amount of NaOH caused the same increase in the constant rate as 8°C or 0.5 m/s.     

处理L-苯丙氨酸发酵液污染膜的化学清洗研究

对处理发酵液后污染严重的聚偏氟乙烯(PVDF)中空纤维膜进行了化学清洗研究。实验中,通过电镜与红外定性分析了污染物成分,并确定了氧化剂高锰酸钾的使用条件,比较了氧化清洗的加酸前后及还原前后的清洗效果,并对清洗后的中空纤维膜进行了一系列的性能测试。最后进行了双向流工艺的在线中试研究。     

Polymers Decrease Cleaning Time of an Ultrafiltration Membrane Fouled with Pectin

An ultrafiltration system fouled by pectin solutions was used as a model system. The fouled membrane flux was fully restored by circulating 0.5% NaOH solution for 1 hr. By adding 0.003% polyethylene oxide) in 0.5% NaOH solution, the cleaning time required to fully recover flux of the fouled membrane was reduced to 2 min. The mechanism of improving cleaning efficiency may not be wholly attributed to the scouring effect of the polymer on the membrane surface. The cleaning and rinsing results suggest that polymers in cleaning solutions convert the pectin foulant into a foulant-polymer complex which could be readily rinsed from the membrane surface by water.     

污染微滤膜的超声波辅助清洗实验研究

超声波清洗技术用于清洗酵母菌溶液和大豆分离蛋白(ISP)溶液污染的聚偏氟乙烯(PVDF)微滤膜。实验中所用的超声波频率为40kHz,超声波的强度为1.43～2.85W/cm2。实验结果表明:对于酵母菌溶液污染的微滤膜超声波辅助水洗是恢复水通量的有效方法;而且超声波强度越高,达到相同FR(水通量恢复率)的清洗时间tc越短;但对于大豆分离蛋白溶液污染的微滤膜单纯用超声波辅助水洗的效果相对较差,而超声波辅助NaOH溶液的化学清洗的效果较好,在浓度为3g/L的NaOH溶液超声波辅助清洗6min即可使其FR值达到91%。     

SPINNING DISC MEASUREMENT OF TWO-STAGE CLEANING OF HEAT TRANSFER FOULING DEPOSITS OF MILK

The efficient and effective cleaning of milk protein – based deposits from heat transfer equipment is essential in the dairy industry. The aim of this study was to evaluate the effectiveness of two‐stage cleaning using acid and caustic. Stainless steel discs were fouled during heat transfer by skimmed milk and whey protein. The discs were then cleaned with acid and sodium hydroxide solutions under controlled mass transfer conditions using spinning disc techniques. The use of 0.5% nitric acid, and a commercial acid known as Triplex, as a rinse before caustic cleaning increased the cleaning rate by 2.5 times. The foulant was found to swell about 40% and calcium was leached out within 5 min after exposure to acid. The acid treatment is believed to cause a reduction in the viscosity, and hence an increase in dissolution, of the gel layer formed when caustic cleaning takes place.     

PVDF/PVC膜化学稳定性研究

采用干湿法纺制PVDF/PVC中空纤维膜,并进行化学稳定性测试。试验表明:PVDF/PVC中空纤维膜经过次氯酸钠溶液清洗之后,膜通量有所回升,且回升程度与溶液的浓度和作用时间有关系;PVDF/PVC中空纤维膜耐酸性和抗氧化性较好,耐碱性较差。同时分析污染后膜的情况,结果表明,化学清洗比水清洗更为有效,膜的抗污染性能有待进一步提高,为PVDF/PVC纤维膜的应用提供理论基础。     

Effect of ozone pretreatment on alkali cleaning of alumina fouled with bovine serum albumin

Pretreatment of alumina particles fouled with bovine serum albumin (BSA) by 0.3% (v/v) gaseous ozone markedly accelerated the removal of BSA during alkali cleaning through partial decomposition of the BSA molecule. The results suggest that ozone pretreatment can reduce the NaOH concentration required for adequate alkali cleaning by at least one order of magnitude.     

Effect of whey protein concentration on the fouling and cleaning of a heat transfer surface

In the studies of fouling and cleaning of heat exchange surfaces in dairy plants, whey protein deposits and heat induced whey protein gels (HIWPG) are considered as suitable model material to simulate the proteinaceous based type “A” milk fouling. Protein concentration of the fouling solution may significantly influence the formation of milk deposits on heat exchange surfaces, hence affecting the cleaning efficiency. In this study, a laboratory produced heat induced whey protein gels (HIWPG) and a pilot plant heat exchanger fouling/cleaning were used to investigate the effect of protein concentration on formation and cleaning of dairy fouling. Here, HIWPGs made from different protein concentrations were formed in capsules and then dissolved in aqueous sodium hydroxide (0.5 wt%). The dissolution rate calculation based on the UV spectrophotometer analysis. In the pilot-scale plant study, whey protein fouling deposits were formed by recirculating whey protein solutions with different concentrations through the heat exchange section in different runs, respectively. The deposit layers were then removed by recirculating aqueous sodium hydroxide (0.5 wt%) and the cleaning efficiency was monitored in the form of the recovery of heat transfer coefficient while both fluid electric conductivity and turbidity were monitored as indications of cleaning completion. It was found that increasing the protein concentration of the HIWPG significantly increased the gel hardness and the dissolution time. In addition, increasing the protein concentration significantly increased both, the amount of the fouling on the pilot-scale plant and the time required to clean the fouling deposit.     

正渗透膜污染的影响因素及清洗效果研究

为研究正渗透(FO)浓缩过程中的膜通量衰减规律,本文以牛血清白蛋白(BSA)为特征污染物,研究了正渗透过程中原料液的离子强度及BSA浓度、膜方位等参数不同时FO膜的污染规律,以提高膜通量和截留率为目标,对驱动液的种类、浓度,料液流速进行了优化,并优化了适宜的膜清洗方案.结果表明:原料液中离子强度越大,FO膜的初始通量越...     

Mesure en ligne de l'encrassement et du nettoyage d'un sterilisateur UHT industriel

An on-line fouling sensor for industrial heat exchangers used in food processing has been designed. Its principle is based on the evaluation of disturbances in the hydrodynamic functioning of the heat exchanger due to fouling. It was tested on an industrial plate heat exchanger used for UHT milk sterilization (10 m³ h⁻¹) to indicate the degree of fouling (α) in the heat-recovery section (milk temperature increasing from 80 to 120°C) and in the heating section (milk temperature increasing from 120 to 140°C). The final values of α can reach about 0·5 for each section. Furthermore, quality has a not insignificant effect on the kinetics of fouling and degree of deposition. The sensor is also able to measure fouling during cleaning processes. Thus, the cleanliness of the sterilizer can be evaluated. The sensor opens the way for the complete control and optimization of cleaning processes.     

Whey Protein-Based Gel as a Model Material for Studying Initial Cleaning Mechanisms of Milk Fouling

The dissolution kinetics and mechanical properties of whey protein concentrate (WPC) gels were investigated as part of a general study on cleaning mechanisms of milk fouling. The dissolution results showed that the WPC gel is a suitable model material to simulate milk fouling and the dissolution process is a major factor controlling the cleaning process. The hardness, elastic modulus, and fracture load of the WPC gels decreased significantly when they were treated with alkaline solution, indicating that certain physical and chemical changes occurred in these treated gels; as a result, different dissolution rates were observed. The results obtained in this article provide a good foundation for further studies on the cleaning mechanisms of milk fouling using WPC gels.     

The role of surface tension of re-used caustic soda on the cleaning efficiency in dairy plants

During the cleaning in place with recycled cleaning solutions, an increase of suspended solids (SS) and a decrease of the surface tension (γ) of caustic soda (NaOH) solutions were observed for various types of dairy equipment. The decrease of γ was shown to result from the chemical reactions of the milk protein and fat with the cleaning solutions. In this work, the respective roles of SS and γ on the cleaning efficiency, cleanliness and cleaning rate were determined. The cleaning test consisted of an ultrafiltration membrane fouled with skimmed milk and cleaned using four NaOH-based solutions: newly prepared NaOH (high γ), re-used NaOH (low γ) with and without pre-clarification and a newly prepared commercial detergent solution. In the range of γ (28.7–74.0 mJ m⁻²) and SS (0.0–1.7 g kg⁻¹) studied, the cleaning efficiency and the membrane hydraulic cleanliness were similar (0.91–0.94 and 0.69–0.71, respectively). However, it was found that solutions with a low γ resulted in a much faster cleaning rate. The presence of SS was mainly detrimental to the cleaning rate. For an efficient cleaning rate, high pH and low γ were important. A re-used NaOH solution with both low γ and SS was as fast as the commercial detergent solution at the same temperature (50 °C).     

Ultrafiltration in Food Processing Industry: Review on Application,Membrane Fouling,and Fouling Control

Ultrafiltration process has been applied widely in food processing industry for the last 20 years due to its advantages over conventional separation processes such as gentle product treatment, high selectivity, and lower energy consumption. Ultrafiltration becomes an essential part in food technology as a tool for separation and concentration. However, membrane fouling compromises the benefits of ultrafiltration as fouling significantly reduces the performance and hence increases the cost of ultrafiltration. Recent advances in this area show the various intensive studies carried out to improve ultrafiltration, focusing on membrane fouling control and cleaning of fouled membranes. Thus, this paper reviews recent developments in ultrafiltration process, focusing on fouling mechanisms of ultrafiltration membranes as well as the latest techniques used to counter membrane fouling.     

Evaluation of a fluorescence and infrared backscatter sensor to monitor acid induced coagulation of skim milk

A prototype sensor that employs both ultraviolet excited fluorescence and infrared light backscatter was evaluated as an in-line process analytical technology (PAT) tool to monitor acid induced coagulation kinetics of skim milk. Coagulation experiments were carried out at 32 °C using three concentrations of glucono-delta-lactone (GDL). Measurement of storage modulus (G′) of acidified skim milk gel was used as a reference rheological method to monitor the coagulation kinetics. Prediction models were developed to predict the times required for acidified skim milk coagulum to reach selected G′ values (0.5 Pa, 1 Pa, 5 Pa, 10 Pa and 15 Pa) using time parameters extracted from the ultraviolet excited fluorescence and infrared light backscatter profiles. A strong correlation was observed between the predicted times developed using time parameters extracted from the prototype sensor profiles and the measured G′ times extracted from the rheometer (R² = 0.97, standard error of prediction = 2.8 min). This study concluded that the prototype fluorescence and infrared backscatter sensor investigated combined with the developed rheological prediction model can be used as a potential PAT tool for in-line monitoring of coagulation kinetics in the manufacture of acid induced milk gels.Industrial relevanceThe prototype fluorescence and infrared backscatter sensor investigated in this study combined with the developed rheological prediction model can be employed to monitor and control coagulation kinetics in a wide range of dairy processing applications including fresh cheese varieties and yoghurt manufacture.     

THE FOULING AND CLEANING OF ULTRAFILTRATION MEMBRANES DURING THE FILTRATION OF MODEL TEA COMPONENT SOLUTIONS

Proteins and polyphenols are the principal fouling constituents in the ultrafiltration (UF) of black tea liquor. The aim of this study was to determine the relative importance of individual components in the fouling process, to investigate any synergetic interactions that were occurring and to compare the cleaning characteristics of different fouled membranes. A 30‐kD molecular weight cutoff polysulfone UF membrane in dead‐end mode was challenged with model solutions of tea components. Model solutions consisted of tea proteins, theaflavins (TFs), thearubigins and caffeine. Sodium hydroxide was used as a cleaning reagent. Permeate flux decline curves were presented for single components and mixtures. Individual component transfer fluxes and rejections were also presented. An unexpected finding was that protein in a mixture with TFs could permeate the membrane to a degree, while a protein solution in the absence of the polyphenol was completely rejected. The inspection of membranes fouled by different solutions revealed different foulant morphologies. Membrane cleaning with 0.2 wt % sodium hydroxide was generally found to be effective.     

陶瓷膜处理乳酸菌发酵液的膜清洗研究

研究了在不同操作压力下乳酸菌发酵液的渗透通量随时间的变化,以及污染后的陶瓷膜的清洗情况, 同时也考察了用陶瓷膜分离乳酸菌发酵液的效果。结果表明,渗透通量与操作压力、时间有密切关系；清洗过程中,纯水的温度、清洗剂的浓度以及清洗时间等都会影响膜通量的恢复率。     

Facilitation of cleaning of alumina surfaces fouled with heat-treated bovine serum albumin by ozone treatment

Facilitation of cleaning of alumina (A12O3) particles fouled with heat-treated bovine serum albumin (BSA), which contains sulfhydryl groups on the molecule, by gaseous ozone was studied. With increasing temperature of heat treatment, the amount of adsorbed BSA onto A12O3 surfaces increased, whereas the rate of BSA desorption during alkali cleaning decreased markedly, resulting in the larger amounts of BSA remaining on 12O3 surfaces. No significant amounts of BSA were removed from A12O3 surfaces by alkali cleaning alone when treated at temperatures above 120 degrees C. Before alkali cleaning, the heat-treated, BSA-fouled AI2O3 at 150 degrees C were treated with 0.05 to 0.30% (vol/vol) gaseous ozone at room temperature. Ozone pretreatment markedly accelerated the rate of BSA desorption during subsequent alkali cleaning. The effect of ozone pretreatment on BSA removal depended on the concentration of ozone and treatment time and hence on the total amount of ozone supplied. The molecular weight (MW) of desorbed BSA during alkali cleaning without ozone pretreatment coincided with the MW of the native BSA, whereas the MW of desorbed BSA during the combined ozone-alkali cleaning was lower than the MW of the native BSA. This indicated that the heat-treated BSA molecules adsorbed on A12O3 were partially decomposed into some fragments by ozone pretreatment, resulting in the facilitation of the removal of BSA during alkali cleaning.     

REMOVAL KINETICS OF BACILLUS CEREUS SPORES FROM STAINLESS STEEL PIPES UNDER CIP PROCEDURE: INFLUENCE OF SOILING AND CLEANING CONDITIONS

Cleaning efficiency is of prime importance for food industries to ensure both the quality and safety of the products. The removal kinetics of Bacillus cereus spores adhering to unheated stainless steel pipes was studied under turbulent flow conditions (Reynolds’number of 77500 and 116300) in order to be close to those encountered in industrial practice. The experimental data was fitted using a hyperbolic tangent model. Variance analysis was then performed to underline any potential effects on the kinetics of the processing parameters, such as soiling conditions, soiling media and mean walls shear stress during cleaning. A significant influence of the adhesion medium (milk or saline) is shown at the level of spore removal (P < 0.001). This trend could probably be explained by the change in the surface properties of spores and stainless steel surfaces when covered by milk macromolecules. After milk soiling in turbulent flow conditions, removal efficiency was enhanced by a factor of 2.5 to remove 50% of the initial spore contamination and by a factor of 2 for the remaining spores after 30 min of cleaning. No effect of the two mean wall shear stresses (9.4 and 19.1 Pa) has been identified. The removal kinetic model proposed here could now permit the effect on the cleaning efficiency of a wide range of CIP conditions to be tested.     

Surfactant cleaning of ultrafiltration membranes fouled by whey

A polyethersulphone ultrafiltration membrane was prepared for concentration of whey. The membrane was fouled by whey and the effect of different cleaning agents on flux recovery of the fouled membrane was studied. The optimum cleaning procedure for membrane regeneration was elucidated. The results showed that a combination of surfactants (anionic, cationic and nonionic) may be employed as the optimum cleaning agent for maximum flux recovery. The fluorescence studies revealed that the cationic surfactant interact with proteins by breaking the intra‐chain hydrophobic bonding and providing electrostatic repulsion. Changing the alkyl chain from dodecyl to hexadecyl increases the interaction of surfactant–protein. Dodecyltrimethylammonium bromide (DTAB) provided a weak interaction with whey proteins than to tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB). All data obtained in this study support a surfactant–protein interaction in which hydrophobic forces play a dominant role. The nonionic surfactants poly(oxyethylene) isooctyl phenyl ether (TX‐100) and anionic surfactants SDS interact with amino acids in the inner protein structure thus denaturate tertiary protein structure and reduce hydrophobic interaction of proteins by membrane surface.     

Cleanability of soiled stainless steel as studied by atomic force microscopy and time of flight secondary ion mass spectrometry

The hygienic status of food contact surfaces can deteriorate with wear. Effective cleaning regimes must remove any adsorbed organic material as well as microorganisms. Previous work has determined the extent of surface wear occurring on a stainless steel surface within the food industry, and we have reproduced representative samples in vitro. Two surface analytical techniques, atomic force microscopy and time of flight secondary ion mass spectrometry were combined with fluorescence microscopy to give detailed analysis of stainless steel surfaces fouled with starch and milk powder, then cleaned with water either by a spray or brushing method. It was found that the surface cleanability is affected by the cleaning regime and the surface roughness, not only the average vertical roughness but also by the shape of the surface defects, with sharp scratches more difficult to clean than wider surface defects. Spray cleaning with distilled water was found to be a selective method by preferentially removing proteinaceous material more easily than fatty acid ester material. The analytical techniques employed provided information on selective cleanability and surface topography at a hitherto unexplored level, and the information gained may be of value in the design and investigation of novel cleaning regimes and hygienic surfaces.