| Due to ever increasing trends in food safety, food manufacturers should take sanitary/ hygienic processes into key consideration. Typically, a routine cleaning-in-place (CIP) procedure is employed to sanitize food contact surfaces in enclosed food processors including plate heat exchangers. Water spraying and disinfectants are, in general, used to sanitize the outer surfaces of food preparation equipment and utensils such as conveyor, knife, and cutting board. The CIP process requires a tremendous amounts of electrical energy, water, and chemicals in use. The economic penalties associated with the CIP also include inevitable production losses caused by frequent process downtimes. It has been estimated that a dairy factory is required to spend 13% of its total energy usage for CIP processes. If not handled properly, most of the chemical disinfectants also cause negative effects to workers and food contact surfaces due to severe corrosion and irritation. Therefore, a series of nanoengineered food contact surfaces including nanoparticulate composite coatings were developed to overcome the intensive uses of water and chemicals in food processing environments by inhibiting the biofouling formulation. The overall goal of this research was to minimize the attachment of biofouling, including milk protein, bacterial cells, biofilms, and liquid food debris, onto a metal substratum using novel surface fabrication techniques based on the nanoscale surface characteristics and anti-fouling mechanism. Three innovative nanoengineered surfaces were designed and fabricated in accordance with a variety of biofoulants found in food processing, such as nanoparticulate composite coatings; an omhiphobic surface; and nanopatterned surfaces using electropolishing and anodization.;The superhydrophobic (SHB) and superhydrophilic (SHL) nanoparticulate composite surfaces were developed and evaluated with milk fouling and bacterial adhesion testing. The fouling occurrence during milk pasteurization was simulated and conducted in a single-channel prototyped plate heat exchanger. The effect of SHB carbon nanotubes (CNTs)-Teflon on the masses of deposited surface foulants was investigated. Water contact angle (WCA) of a stainless steel surface was dramatically increased from 71.2° (uncoated) to 141.1° (CNTs-Teflon coated). After 5 hours of pasteurization, only 30% of milk foulant (18.45 mg/cm2) was observed on the SHB surface, compared to uncoated steel (62.0 mg/cm2). For bacterial testing, the SHB (WCA 154.6°) and SHL titanium dioxide (WCA <5°) steel surfaces were exposed to Escherichia. coli suspension (3x108 CFU/mL) for an hour in both stagnant and dynamic environments. The enumeration of E. coli adhering to uncoated, SHB, and SHL steel substrates in stagnant and dynamic flow modes showed that the anti-adhesion effect of SHB was most pronounced after the dynamic test where the lotus effect was in place. As compared to the control, only 20% and 55% of adhering cells were remaining on the SHB and SHL surfaces, respectively. On the other hand, the stagnant test showed that anti-adhesion effect of a hydration layer which would act as a barrier between the cells and the fully wetted surface (SHL) was predominant; thus, 75% and 35% of bacterial cells were found on the SHB and SHL surfaces, respectively.;L. monocytogenes (1.9x108 CFU/mL) was used for bacterial adhesion testing of nanoengineered stainless steel surface, which may be more demanding for hygienic food processing equipment. The NS stainless steel surface was achieved by electropolishing the steel in a mixture of sulfuric and phosphoric acid. For NR stainless steel fabrication, the bare substrates were anodized in a mixture of perchloric acid and ethylene glycol to create two surfaces with two different in nanopore diameters ( 50 nm and 80 nm), so-called NP50 and NP80, respectively. Thereafter, the NS, NR50, and NR80 stainless steels were exposed to the L. monocytogenes solution in a stagnant environment for four hours. The enumerated average cell counts were 5x10 3, 5.0x101, and 2.8x101 CFU/cm2 for NS, NR50, and NR80, respectively. The results suggested that regardless of the substratum materials, nanoporous surface finishes could significantly inhibit the adhesion and attachment of L. monocytogenes. However, the statistical analysis indicated that the numbers of cells adhering to the 50 nm and the 80 nm nanoporous surfaces were not significantly different. The finding could be because besides the pore diameter, other surface parameters such as peak heights (or pillared magnitudes) and interpore distances might also play an important role on anti-adhesion of L. monocytogenes. (Abstract shortened by UMI.). |
