| To overcome the hazards in chemicals handling, high energy consumption and obstructions in waste water treatment related to nowadays cleaning system of dairy processing, environment-friendly and energy-saving approach for cleaning the dairy processing pipeline(DPP) was explored. In this research, evaluation method of contaminants in DPP, process of DPP cleaning with electrolyzed oxidizing water(AEOW) and mechanisms of DPP contaminants removal by AEOW were studied.(1) A chemical evaluation system including operations of sampling, pretreatment and determination was established for mapping the contaminants composition in DPP.Contaminants precipitated on inner wall of DPP was sampled by ultrasonic enhanced extraction with mixed solvent(3 mol/L phosphoric acid solution: heptane: ethanol =1:1:1.4, in volume), and then fractioned by pretreatment as well as determined by chemical analysis on content of saccharides, protein and fat. A rapid assay based on dual wavelength of ultraviolet absorption of milk fat was developed. After extraction and fraction as above, the absorbance at 204 nm and 230 nm of the milk fat extract was detected. Then the milk fat content could be determined with the equation of standard curve by feeding the difference between absorbance at 204 nm and 230 nm, by which the interference of various heat treatments on samples could be avoided. It was verified that the variation coefficients were less than 3% and the recovery were ranging from 95.6%~102.9% for liquid dairy samples. In addition, the method led to reliable result in determining the milk fat residues in pipe wall under various dariy processing conditions.(2)For contaminants formed under mild processing temperature(about 75 ℃),desirable cleaning efficiency could be achieved with all kinds of cleaning reagent including the EOWs and the traditionas. While the contaminants formed under high temperature(about 120℃) was the major target to clean since they were quite difficult to remove. Temperature plays important role in cleaning as the cleaning efficency improved significantly with the increasing of cleaning temperature. For saccharides in DPP contaminants, alkaline EOW and acidic EOW provided similar cleaning efficiency; while for protein and fat contaminants, alkaline EOW shown much better cleaning efficiency. A two-stage cleaning process with EOW was optimized by the orthogonal test, the result shown that by using alkaline EOW at 60℃ for 20 min of flushing in stage one and acidic EOW at 60℃for 20 min of flushing in stage two could achieve cleaning efficiency close to those of 2% NaOH, while the energy andchemical consumption could be saved remarkably.(3)The formation of high temperature(120 ℃) DPP contaminants was highly correlated with the calcium containing precipitate, which improved the roughness of DPP inner wall enhancing the heating and precipitation of protein and fat, thus improved the accumulation of denatured protein and trapped fat in DPP contaminants.In process of high temperature contaminants cleaning with EOW, a stage of dissolving was following the stage of swelling. 60℃was the appropriate temperature for high temperature contaminants swelling, the maximum swelling rates were 84.3% and10.8% as treated with alkaline EOW and acidic EOW, respectively. Cleaning efficiency was the combination effect of chemical force and mechanical force. For cleaning of highly soluble saccharides and protein, the major factor was mechanical force, which could be affected by flow rate and pipeline shape; while for insoluble protein and fat, the noticeable factor was chemical force involving the swelling ability,which was a shortcoming of EOW with the comparison of 2% NaOH yet.Overall, the promising future of EOW application in DPP cleaning was proven,while further researches on the process protocol and the cleaning mechanism were necessary to meet the requirements of nowadays dairy process completely. |
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