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    A study of the abiotic factors influencing the biofilm and spore formation of dairy isolates of Geobacillus stearothermophilus and characterisation of spores based on their heat resistance : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Safety & Microbiology at Massey University, Palmerston North, New Zealand
    (Massey University, 2021) Kumar, Murali
    Geobacillus stearothermophilus, a Gram-positive thermophilic bacterium is an important contaminant in the dairy industry during milk powder manufacture. This bacterium is capable of survival and growth in sections of the milk powder manufacturing plant where higher temperatures (40-65 °C) prevail. They form biofilms on industrial processing surfaces and their spores are heat resistant. Although, these bacteria are not pathogenic, their presence is an indicator of poor plant hygiene and diminishes the quality of end products thereby incurring economic loss. Previous studies have focused on designing control strategies to prevent the biofilm and spore formation during milk powder manufacture but with limited success. This is largely attributed to the limited knowledge we possess on the biofilm and spore forming capacity of these thermophiles and the impact of abiotic factors. This study focussed on the role of abiotic factors viz. incubation temperature and total dissolved solids on the biofilm and spore formation of Geobacillus stearothermophilus A1, D1, P3 and ATCC 12980. The heat resistance of the spores was characterized and the effect of phosphate on the heat resistance of spores was discussed. The effect of temperature and total dissolved solids on the biofilm and spore formation was evaluated using a Centre for Disease Control (CDC) reactor in a milk environment. The results from the CDC study demonstrated that 65 °C is the most preferred temperature for biofilm and spore formation. Milk proteins influence the attachment of bacteria to the stainless steel surface with caseins having the greatest effect. The three strains were characterized based on their heat resistance and the effect of phosphate on the heat resistance of these spores was determined using atomic absorption spectroscopy (AAS). AAS demonstrated that phosphate when present in the heating medium causes release of cations from within the spore thereby lowering their heat resistance. In addition, the Calcium and Dipicolinic acid (DPA) content of these spores was determined and the DPA content was found to be associated with the heat resistance of spores. The heat resistance of spores obtained by a milk biofilm system under continuous flow was determined and compared with previous values obtained from spores prepared in a static laboratory medium. There is no significant difference (p ≤ 0.05) in the heat resistance of spores obtained by the biofilm in milk and by a sporulation medium. The results from spore formation under different temperatures and total solids will aid in the design of thermal processing steps aimed towards controlling the biofilm and spore formation of G. stearothermophilus during milk powder manufacture. The effect of phosphate on the heat resistance of spores, will aid in the design of a phosphate based cleaning agent to minimise product spoilage caused by the presence of spores of G. stearothermophilus. The results showing the similarity between the heat sensitivity of spores prepared in sporulating medium and a continuous flow CDC reactor using milk provide confidence in results on heat resistance taken from laboratory sporulating medium in terms of their relevance to the dairy industry.
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    Native milk fat globule membrane damage : measurement and effect of mechanical factors in milk powder processing operations : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology of Massey University
    (Massey University, 2005) Downey, Mark
    The goal of this work was to measure native milk fat globule membrane (NMFGM) damage in a number of processing operations within the milk powder manufacturing process. Analysis of the literature showed that NMFGM damage was not well understood, particularly as caused by processing operations within factories. Reliable methods of measuring NMFGM damage were not available: current methods had limited scope or were qualitative in nature. In the highly mechanised dairy industry, damage to the NMFGM can lead to serious quality and financial losses owing to consequences such as lipolysis and creaming. The aims of this work were to develop new techniques for measuring NMFGM damage, and to use these in assessing the effects of a number of operations within the milk powder process. The majority of time was spent on developing two new tests, the selective lipolysis (SL1) test and the particle size zoning (PSZ) test. The SL1 test measures a chemical consequence of NMFGM damage, that is the production of free fatty acids (FFAs). The PSZ test measures a physical consequence of NMFGM damage, that is the change in the fat globule size distribution. Controlled experiments were used to measure NMFGM damage in process operations including pumping, agitation, preheating and evaporation. For these operations, variables such as shear, time, temperature, air inclusion and cavitation were investigated. Surveys of two industrial milk powder plants were also conducted. The results showed that the SL1 and PSZ tests were reproducible, sensitive enough to detect NMFGM damage in a number of process operations, and, together, could give a reasonably comprehensive picture of NMFGM damage. The results of pumping and agitation experiments were consistent with previous research, but were more comprehensive. The effects on measured NMFGM damage of the presence of separated fat in foam or as churned fat have hardly been described by previous workers. Results for the effects of preheating and evaporation on NMFGM damage are new, and challenged the findings of previous research. The need to improve the flexibility and practicality of the SL1 and PSZ tests, so they can he used as widely as possible to gain a comprehensive picture of NMFGM damage across many dairy processes, was identified. Studies should be made to connect the results of the particle size zoning and selective lipolysis tests with product quality and process efficiency data from industrial sites.
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    Effect of homogenisation on milk fouling in a tubular heat exchanger : a thesis presented in partial fulfilment for the requirements for the degree of Master of Food Engineering, Massey University, Palmerston North, New Zealand
    (Massey University, 2004) Martinez-Sanchez, Monica
    Fouling of equipment surfaces in milk processing has been a costly problem for many years. In spite of an increasing body of knowledge of the fouling mechanism, the problem is not fully understood yet. Recent investigations suggest that the role of fat in whole milk fouling seems to be very important. The state and form of the fat globules, processing conditions as well as the orientation of heating surfaces may affect the fouling mechanism. Homogenisation of milk is known to cause disruption of fat globules and prevent creaming. The present work aimed to investigate the effect of homogenisation on the rate of fouling, composition and structure of fouling layers. Homogenised and un-homogenised milk were used as test fluids. Milk was heated from 4°C to 60°C in a plate heat exchanger then to 70°C and 80°C in a double pipe heat exchanger consisted of a horizontal and a vertical tube. The fouling rate in the double pipe heat exchanger was calculated and expressed as the rate of increase of the overall resistance to heat transfer, normalised using the initial heat transfer coefficient at the beginning of the run. Composition analysis of fouling layers was carried out using standard methods of moisture, ash, fat and protein tests. Resistance to deformation analysis was performed using texture tests; coverage measurement was determined by digital image analysis. Within the experimental conditions used in this work, the effect of homogenisation on the fouling rate could not be ascertained conclusively because of large variations in the values obtained but it had a significant effect in the composition of fouling layers. In all experimental runs, the amount of fat in the fouling layer was higher for un-homogenised milk compared to homogenised milk. In fact, the fat contents of fouling layers were found to be very high (between 30%-60% on a dry weight basis), which agrees with observations of other researches in New Zealand. The coverage and thickness of fouling layers were more influenced by the orientation of heated surfaces than by homogenisation. The strength of fouling layers is affected by their thickness, which decreases with increasing milk temperature.
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    Characterisation & process control of pumping systems in the dairy industry : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Technology at Massey University
    (Massey University, 2000) Dorsey, Mark Richard
    The interaction between control of pumping systems in the dairy industry and the performance of the process has been investigated. Pumping in a precooling system at Massey University No.1 Dairy Unit was chosen as a case study. The requirements of the precooling system were determined from previous work done by dairy technologists. Part of these requirements were that: i) microbial damage to milk must be minimised by good temperature control, specifically by cooling the milk down to 18°C immediately after milking as specified in the New Zealand Dairy Industry Farm Dairy Code of Practice (COP). ii) handling should be gentle to minimise damage to the milk fat globule membrane by avoidance of cavitation and foaming. However controlled pumping, which minimises damage to the fat globule membrane, has been reported to decrease the cooling capacity of the plate heat exchanger (PHE). The precooling system at No.1 Dairy Unit was modified to allow continuous monitoring of key process variables (temperatures, flows and pressures). These were logged continuously and automatically to allow analyses to be carried out for whole milking sessions. The analysis shows that the releaser pump in the precooling system at No.1 Dairy Unit was oversized. This resulted in the pump only operating for 10 to 50% of the time and consequent inefficient usage of cooling water. In general the average temperature of the milk entering the vat complied with the COP requirement. However, as a consequence of the pump control system, the instantaneous temperature at times exceeded the COP recommended temperature. The analysis showed that cooling of the milk held up in the PHE during the pump-off phase contributed significantly to the cooling performance of the system. The present set up of the releaser pump pumping regime is based on a fixed pump-on phase of 6 seconds. The pump starts when the milk level reached a predetermined level in the milk receiver tank, which holds the milk coming from the cows. The duration of the pump on phase was set so that there would always be a milk fluid head in the receiver tank; which was decided by the relative size of the pump and receiver tank. The present pumping regime did not make best use of the ability of the system to cool the milk held up in the PHE during the pump-off phase. By simply changing the pump-on phase to 3s, more milk could be held up during the pump off phase in the PHE, giving a 10% increase in efficiency in the use of the cooling capacity of the water. This was achieved without changing the size of the PHE or any additional capital investment. Synchronising the water with milk flow rate resulted in further gains in efficiency of cooling water usage but this resulted in an increase in the temperature of milk exiting the PHE. This conflict of goals made evident that an improvement in efficiency could only be attained by using cooler water, which could be achieved by additional equipment such as a cooling tower. However it is recommended that any modification to the process must be accompanied by a reanalysis of the performance of the system in conjunction with an appropriate control system to optimise the performance of the system.
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    The effect of lactose source on the stickiness of dairy powders : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Bioprocess Engineering
    (Massey University, 2006) Murti, Rosalind A
    The particle gun provides a valuable method to investigate powder stickiness properties. This method gives reproducible results when used under constant testing conditions and allows the isolation of factors influencing stickiness behaviour such as velocity and angle of impact. The (T-Tg)critical and rate of stickiness development obtained from the particle gun method were functions of the air velocity, angle of impact, powder aw and ambient air conditions. Under constant testing conditions (feed rate of 0.3 g.s -1, air velocity of 20 m.s-1, ambient air at < 50%RH, room temperature and constant powder aw (T-Tg)critical was reproducible within ± 0.8°C while the rate of stickiness development was reproducible within ± 0.45 %deposition/°C. The results obtained from the particle gun were consistently higher than the fluid bed results and can be explained by the different impact time and force experienced by the particles. Particle gun results can successfully be used to predict blockages in cyclones provided the appropriate correction is made for particle impact force and time. Blockage data from Te Rapa D5 indicates that the critical T-Tg where blockages occur in the cyclones is 27°C for SMP. Currently D5 is running satisfactorily for SMP at a T-Tg value of 28°C. Under these operation conditions the cyclone wall temperature results in a T-Tg value of 33°C. the same (T-Tg)critical value predicted by the particle gun for standardised SMP. This implies that the cyclone is operating correctly at the maximum T-Tg value before particles become sticky enough to cause blockage problems. Protein standardisation of milk powder via the addition of milk permeate or lactose solution had no detectable effect on the stickiness characteristics of SMP or WMP as measured by the particle gun or the fluid bed rig. No difference was seen in either the bulk or surface composition of the milk powder. This provides evidence to dispel speculation by operators that permeate standardisation produces a more difficult to handle powder.
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    Investigation of minimum flow conditions for milk products in falling-film evaporators : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology at Institute of Technology and Engineering, Massey University
    (Massey University, 2001) Paramalingam, Shabeshe
    Multiple-effect evaporators are widely used in dairy industries to concentrate milk, which will be further processed in spray driers to produce powder. Compared to the evaporation stage the drying stage consumes a lot of energy. So, from an energy-saving point of view it is important to remove as much water as possible in the evaporation stage. In producing milk powder about 90% of the water removal takes place in the evaporating stage. The operational conditions must be satisfied within the falling film evaporators in order to have continuous production. One of the constraints to the optimisation of the falling-film evaporator is found to be the minimum peripheral flow (Brenmuhl, 1999). Violation of this constraint could cause fouling due to film break-up within the evaporator tubes. Fouling due to film break-up is a major concern in the operation of falling-film evaporators (Brenmuhl, 1999; Winchester, 2000; Paramalingam et al., 2000). Insufficient flow is found to be the cause of film break-up (Hartley & Murgatroyd, 1964; Chung and Bankoff, 1979; Paramalingam, 1999; Hughes & Bott, 1991). To avoid fouling due to film break-up the flow rate along the tubes should not be less than a minimum flow necessary to sweep off the dry patches. This flow is known as the advancing minimum flow, where the flow can no longer advance to cover a dry area. For the safe operation of falling-film evaporators it is also important to know the minimum flow below which film break-up occurs. This minimum flow is known as the retarding minimum flow, where the flow can no longer support a full film and the film retards leaving a dry area. The purpose of this study is to determine the minimum flows for milk products and for water. To this end two models are used, proposed by Hartley and Murgatroyd (1964) and Hoke and Chen (1992) to predict film break-up and therefore minimum flows.
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    Whole milk fouling of heated surfaces : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Engineering at Massey University
    (Massey University, 2000) Bennett, Hayden Albert Edward
    Whole milk fouling of surfaces within dairy products processing plants, especially that which occurs on heat treatment equipment, is an important operating problem, threatening the quality of product and reducing thermal and mechanical efficiency of equipment. A fouling monitoring system was developed using a commercial heat flux probe and temperature sensor. The fouling monitor was installed in two unit operations of a custom built milk powder pilot plant. The unit operations replicated heat treatments found in plate heat exchangers and falling film evaporators. The research plate heat exchanger consisted of six miniature plate heat exchangers or modules in series. Individual modules could be isolated at any point during a run allowing access to the fouling deposit. The research falling film evaporator was a flat plate attached to a steam chamber and milk weir box. The onset and build-up of whole milk fouling on the evaporator plate was viewed through a sight window installed in the evaporator casing. Trials conducted with the research plate heat exchanger showed that the monitoring system could detect whole milk fouling in terms of a reduction in the overall heat transfer coefficient. This reduction was shown to directly correspond to an increase in fouling deposit thickness. For the same bulk milk temperature, the fouling rate decreased significantly when the surface was unheated compared with heated surfaces. This observation lead to a set of experiments that manipulated the start up procedure on both the milk and heating medium side of the research plate heat exchanger. More fouling was observed on plates after air start up (on the milk side) than on plates after water start up. Similarly, Surface Conditioning by Operational Protocol (SCOP) extended the fouling induction period. The SCOP trials compared steady state heating with unsteady state heating during start-up. Similar amounts of fouling were observed on plates removed from the steady state heated modules after 30 minutes and on plates removed from the unsteady state modules after 9 hours. These results indicate that the state of the stainless steel surface when the. milk first makes contact has an important effect on the subsequent rate of fouling. It is recommended that future work aims to identify which milk components deposit first onto the surface and what influence they have on inhibiting or facilitating fouling. The fouling monitoring system successfully estimated the extent of fouling for all of the trials. Industry trials for the fouling monitoring system, particularly on heated surfaces are recommended. The system will allow local areas of intense fouling to be mapped within the processing plants. A number of recommendations are presented concerning future work associated with start up procedure manipulation, evaporator trials and seasonal variation trials.
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    Standardisation of cultured butter processing for smallscale production : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Albany, New Zealand
    (Massey University, 2015) Shi, Jia
    Summary: Butter is one of the most popular dairy products that have been transformed from a cottage industry to successful large scale productions. In western countries, consumption of butter has slowly overtaken margarine as the most popular spread. Different kinds of butter are now available on the markets, of which sweet cream butter and salted butter constitute significant proportions. The popularity of cultured cream butter is mainly attributed to its unique flavour and nutritional properties. Butter contains large amounts of β-carotene (provitamin A carotenoid) and is characterised by the buttery flavour due to the presence of diacetyl as well as other organic aroma compounds. Although butter has been produced successfully in large scale commercial processing, small scale productions still exists in small communities and for use in specialised products. New Zealand, like in many other western countries, is dominated by small to medium scale food processing enterprises which produce speciality foods for discerning markets. The domestic market in New Zealand enjoys a variety of dairy products which includes cultured butter. Some small food processing enterprises in outlying areas of New Zealand produce their own cultured butter to cater for the local businesses and their inhabitants. Thus, the main objective of this project was to standardise small scale production of cultured butter using kitchen/domestic scale equipment. Fresh cream (40% fat) used to produce cultured butter was fermented by a mixed lactic starter culture (Lactococcus lactis subsp. lactis biovar. diacetylactis and Leuconostoc cremoris) following a modified standard method. The cream was pasteurised at 95°C/5 min, rapidly cooled to 8°C, and then starter culture (2%) was added. The cream was held at 8°C/2 h to initiate the formation of low melting point fat crystals. The temperature of the cream was then increased to 20-21°C, and held at this temperature for further 2 h to melt fat crystals with high melting point and recrystallise the crystals. The temperature was then decreased to 16°C/2 h to form pure fat crystals. This was then followed by slightly decreasing the temperature to 15°C for butter churning in a K5SS KitchenAid Heavy Duty (USA) churning mixer. Buttermilk (100 mL) was collected and stored at 4ºC for analysis and the remained buttermilk in the butter churn was drained. The butter grains were washed with distilled water to remove any residual buttermilk. Final cultured butter (product) was packed in heavy duty aluminium foil and stored at 4ºC for 21 days. Cultured butter was produced on three different occasions commencing in August 2014 (batch 1), September 2014 (batch 2), and October 2014 (batch 3). Various analyses and measurements were conducted during processing and storage to monitor the shelf life stability of the butter. Standard methods were used to measure chemical, physical, consumer sensory acceptance of the products and presence of coliforms were enumerated by Violet Red Bile Agar. Thus, fat content in buttermilk was determined by the Mojonnier test to calculate churning efficiency. Colour was measured by colourimetry, while texture analysis was determined by the TA.XT2 Texture Analyser. Water droplet size of butter was examined by confocal laser scanning microscope after staining with Nile Red and Acridine Orange. The cultured butter samples were also evaluated by consumer sensory panellists using hedonic scaling of six sensory attributes (smoothness, hardness, spreadability, melting rate, buttery flavour, and overall acceptance). Data were plotted on graphs and also analysed by analysis of variance (P<0.05), linear regression and interaction plot. There were significant differences (P<0.05) in moisture content of the three batches of butter which ranged from 13.90 to 19.19%. Although the moisture content of two batches (1 and 3) of butter was slightly higher than the standard (16%), it was within expected range. Manual washing butter grains after churning to remove water droplets may be inefficient to remove water droplets on the surface of butter. Most of the water droplets had a diameter of 5 μm which is desirable to inhibit the growth of spoilage microorganisms. No coliforms were detected in the cultured butter, indicating good hygiene standard during production. There were significant differences (P<0.05) in hardness of the three batches of cultured butter. Batch 2 had higher hardness than the other two batches, probably attributed to its low moisture content. The fat content of cultured butter of the three batches ranged between 75% and 80%, which was slightly lower than the expected 80%. However, the results were reasonable, considering the higher moisture content of the butter. The cultured butter was well accepted by sensory panellists. Linear regression and interaction plot showed that spreadability and buttery flavour had significant effects (P<0.05) on the overall acceptance of the butter. The products were spreadable, presumably due to higher moisture content. The buttery flavour could be attributed to the aroma compounds produced by lactic acid bacteria through citrate metabolism during cream ripening. The dominant hue in the butter was yellowness, which slightly decreased during storage, presumably due to the loss of β-carotene. The pH of butter samples (5.3 to 5.8) during storage was slightly higher than in previous studies (4.7-5.2). The higher pH may be caused by poor acid production of the leuconostoc in the mixed culture. Cultured butter was successfully processed using a kitchen/domestic churning mixer. The churning efficiency of the equipment was lower than the expected range. The butter had good keeping quality and was well accepted by sensory panellists. The quality of the butter during storage was probably attributed to the optimal size of water droplets, which were successfully measured by the confocal laser scanning microscope method modified in this study.
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    Evaluation and development of chemical solutions for membrane cleaning in the dairy industry : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Science at Massey University
    (Massey University, 1999) D'Souza, Nisha Maria
    Membranes must be cleaned regularly to remove organic material deposited on the surface from the food or biological fluids processed. Cleaning is a compulsory step in maintaining the permeability and selectivity of the membrane and is also necessary to return the plant to its original capacity, to avoid bacteriological contamination, and to produce products with a long shelf-life. Without cleaning, the flux of solution through the membrane would decline to uneconomic levels. Caustic, acidic and enzymatic based cleaners may be used for membrane cleaning. Such cleaners affect the lifetime and performance of a membrane and should thus be surface-active, soluble, rinsable, non-corrosive, safe, effective and easy to use. The primary objective of work carried out was to evaluate a range of cleaning chemicals and cleaning regimes on a pilot-scale. Cleaning regimes employing conventional caustic and acidic cleaners, and enzymatic detergents have been evaluated for a Desal ultrafiltration membrane. The membrane was reproducibly fouled during the processing of skim milk and skim milk concentrate on a pilot-scale plant supplied by Tuchenhagen (N.Z.) Limited and compared favourably with an industrial plant. A spiral wound membrane of polyethersulfone with an active area of 7.4 m and a 10,000 molecular weight cut-off was selected. A transmembrane pressure of 2.5 bar, a retentate flow rate of 60%, a temperature of 18.5°C, and a recirculation flow rate of 7 m was kept constant during filtration. A combination of flux recovery after cleaning and solute resistance removal was used to assess cleaning performance. Higher flux recoveries (87.3-93.6%) were achieved with surfactant based formulations compared with enzymatic detergents. This was attributed to the wetting action of surfactants which when used in conjunction with a high strength blended alkali solution, aided the convective cleaning solution flow through the membrane pores. Enzymatic cleaning was found to be milder to the membrane. While the enzyme-sanitiser regime yielded good flux recoveries (68.4-87.3%), the enzyme-acid and acid-enzyme regimes were not capable of restoring membrane permeability, resulting in low flux recoveries 64.2-78.9%. The acid in these regimes caused the membrane pores to shrink, restricting the ability of the enzymatic detergent or rinse water to penetrate the foulant and remove it. Based on these results, a new formulation (DR292) with more surfactant action was developed and evaluated. Flux recovery using this new formulation increased by 3.5%. Regimes incorporating non-ionic surfactants and high strength alkali solutions were found to successfully restore membrane permeability because a higher level of surfactant was obtained from the mixture. Further experiments using enzyme-acid and acid-enzyme regimes, and the new formulation need to be trialed on new membranes to determine their long-term effect on membrane permeability and selectivity.
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    Surface modifications to increase dairy production run length : a thesis presented in partial fulfilment of the requirements for the degree of Master of Chemical Engineering at Massey University, [Manawatū], New Zealand.
    (Massey University, 2013) Runwal, Siddharth
    Fouling is the build-up of undesired deposits on surfaces. In the dairy industry, fouling is mainly seen in heat exchangers where dairy fluid is heated or concentrated. It is one of the primary reasons for restricted run length, causing financial losses from downtime, the use of cleaning chemicals and reduced product quality. Fouling is a complex process and is due to number of factors including the properties of the heat transfer surface. A silica based coating is known to alter the surface properties. This study was carried out to investigate the effect of a silica based coating on fouling by whole milk in a falling film evaporator. Seven independent trials were conducted. In each trial, a control run was carried out followed by a full cleaning of the equipment and then either another control run or a coating run with pasteurized milk from the same batch. There was a six hour interval between the start of the control run and start of the coating run. Since prolonged milk storage may have some effect on fouling rate, control-control runs were carried out to see the effect of prolonged storage. The results obtained from control-control runs were used in analysing the effect of the coating on fouling rate. All coating trials showed consistently lower fouling rate as compared with corresponding control trials. The Pearson’s correlation coefficient of 0.83 showed a strong effect of coating on the fouling rate. Further, a regression analysis gave a p-value of 0.033, indicating that, at the 96.7% level of confidence, coating reduced the fouling rate. The extent of reduction in fouling rate varied from trial to trial. It was estimated that the coating had the potential to increase the run length by a maximum of 34% under the conditions these experiments were carried out.