Cleanability of Milk-Filmed Stainless Steel by Chlorinated-Detergent Solution1

Cleanability of Milk-Filmed Stainless Steel by Chlorinated-Detergent Solution 1 J. M. JENSEN

Department of Food Science, Michigan State University, East Lansing 48823 Abstract

Stainless steel test plates, with and without pretreatment in 100 p p m chlorine, were filmed with cold raw milk and washed by 16 detergents at 0.35% concentration. The detergents ranged from 0.016 to 0.102%, active alkalinity and 0 to 100 p p m available chlorine. Plates filmed with milk only were cleaned effectively by each nonchlorinated detergent, but high soil build-up, appearing as blue-brown color, accumulated when washed in alkaline solutions containing 25 p p m available chlorine. Less build-up occurred from 50 and 54 p p m chlorine and none from 75 and 100 ppm. Plates filmed with milk following pretreatment with 100 p p m chlorine accumulated high build-up when washed by alkaline detergent solutions. High build-up occurred as well using alkaline solutions supplemented with 25 ppm, and somewhat less with 50 ppm. None occurred when alkaline solutions contained 75 and 100 p p m chlorine. Soil build-up was caused by adhesive nonsoluble chloro-protein occurring in low concentration of chlorine ions. When the concentration of chlorine ions increased to 75 and 100 p p m the chloro-protein was solubilized and nonadhesive. Chlorinated detergents have been used extensively for washing stainless steel milk equipment in recent years. However, build-up of soil film and discoloration a p p e a r to have been linked with their use. Difficulty has been encountered in ascertaining the cause of film build-up by observing practices used in fal~n milk-houses. Consequently, the present study was undertaken to find particular causes and possible remedies for defective cleaning under closely supervised conditions. Review of Literature

Studies relating to the use 1 Michigan Agricultural Journal Article no. 4489.

of

Experiment

chlorineStation

supplemented detergent solutions have been reported by MacGregor et al. (4), Lewandowski (3), I~aufmann and Tracy (2), and Merrill et al. (6). All of these investigators found improved cleaning of stainless steel when chlorine compounds were used in detergent solutions. MacGregor et al. (4) recommended adding 25 to 100 p p m NaOCI to certain alkaline detergents for improved protein removal. Lewandowski (3) obtained brighter surfaces and a reduced tendency toward filming when chlorine compounds were blended with alkaline cleaner. I~aufmann and Traey (2) found one chlorinated alkali solution of two kinds used, which was capable of removing iridescent films from stainless steel. Merrill et al. (6) reported that the addition of NaOC1 to a 0.1% trisodium phosphate solution produced a significant increase in protein solubility. However, Ctaybaugh (1) found a residual film when milk cans were sanitized with chlorine solution prior to use. H e named the film chloro-protein. Furthermore, W r i g h t et al. (8) attributed solubility of milk protein to increased active alkalinity rather than to the effect of available chlorine. These workers reported 0.0091% and 0.0425% active alkalinity from 100 p p m Chlorox and chlorinated trisodium phosphate, respectively. Experimental Procedures

Special equipment used consisted of Number 4 finish, 6 by 9 cm stainless steel test plates, two styrene cylinders measuring 6 cmd by 20 cmh, and a motor-driven reciprocal shaker (Fig. 1) operated at eight 7.62-cm strokes per second. The cylinders were fitted with screwtop covers. Five plates from previous washing trials were used as standards for retained soil (Fig. 2). The density of filming was expressed by plus and minus symbols: -- -----No film. + --~ Slightly iridescent. + + = Definitely bluish. + + - b ~ Highly bluish-brown. ÷ + + ÷ --~ Intensely bluish-brown. New stainless steel plates were washed free of oil and pumice before experimental washing began. They were regarded clean when distilled water from rinsing adhered and drained evenly without streaking or beading. 248

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Seven-tenths-gram of detergent was placed in the cylinder used to perform the washing operation. I n selected instances 0.1-ml quantities of 10% NaOCI were added to the cylinders. Two hundred milliliters of distilled water at 62.8 C were used in each cylinder. The filmed plate was inserted and the cylinder closed with a screw-top eover. The shaker was operated three minutes per washing sequence, then the plate was transferred to a 250-ml beaker where softened, running tap water at 62 C rinsed it 30 seconds. Each plate was dried in an air blast

FIG. 1. Mechanical washing apparatus styrene cylinders.

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for at least five minutes before repeating the soiling and washing cycle. Soiling and washing cycles were repeated 40 times p e r plate to show the accumulative effect of milk soiling and washing treatments. Active alkalinity of detergent solutions was determined by titrating 10 ml of 0.35% detergent solutions with 0.25 • H2S04 from a 5-ml mieroburette and using four drops of 1.0% phenolphthalein indicator. Approximately 0.5 g Na~S20~ crystals was dissolved in solutions containing chlorine before testing for active alkalinity. The p i t of 0.35% detergent solutions at 20 C was made using a Beckman Expandomatic p H meter. Sixteen trial-plates were filmed with raw milk only. An additional 16 plates were filmed with 100 p p m chlorine ahead of filming with milk and designated chloro-protein films, as shown in Table 1. The source of chlorine was 10% NaOC1, diluted to 100 p p m C1 in distilled water. These plates were submerged one minute, then dried five minutes in an air blast. Milk films were prepared by submerging the stainless steel plates in prestirred cold raw milk, testing approximately 3.4% f a t and 12% total solids. The plates were drained and dried five minutes. Since Merrill (5) showed that fihns retained from single immersion in skimmiik were closely reproducible by gravimetric measurement, no attempt was made to determine the weight of retained films. Sixteen different detergent products were used (Table 1). Detergents A, B, C, and D were commercially prepared and marked expressly for cleaning milk pipelines and bulk tanks. Detergents A, B, and C were labeled Chlorinated without showing their chlorine concentration. Detergent D consisted of mixtures of condensed sodium phosphate and surfactants:. The

FIG. 2. Standards used for designation of film retention on stainless steel plates. Interpretation of symbols: -- Completely clean and bright. + Slightly iridescent. +Jr Definitely yellowlsh-blue. ++-k Highly bluish-brown. +-k++ Intensely bluish-brown. JOURNAL OF DAIRY SCIEI~CE ~rOL. 58, NO, 2

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TABLE 1. Effect of certain chemical characteristics of detergent solutions on the build-up of milk-soil films. Rating* of soil retention film: ChloroMilk protein

Detergent

Chemical characteristic of detergent NaOH pH

C1

A B C D

(%) 0.051 0.050 0.017 0.016

11.50 10.85 9.20 9.20

(ppm) 55 25 15 0

+ -~--{--{--{---

-kq--b -l--b-i-q-{-+-4--b -b-i--i-

D D D

0.017 0.017 0.01S

9.20 9.20 9.28

25 50 75

T-F-{-+ +-l--

++-{--F -}-÷ --

D

0.018

9.28

100

--

X-/ X-2 X-3 X-4

0.042 0.035 0.059 0.099

9.90 9.90 11.30 10.40

0 0 0 0

-----

X-1 X-2 X-3 X-4

0.044 0.038 0.061 0.102

9.90 9.90 11.30 10.40

100 100 100 100

--{--{--~-+ -~--4--{--4-}--1-+-{-b-{-q-+

a Fihn retention and color: -- None. + Slight (slightly iridescent). + + Definite (definitely bluish). + + + Pronounced (highly bluish-brown). + + + + Very pronounced (intensely bhfishbrown). X-1 to X-4 series of detergents were prepared for information about the composition of alkaline materials used and to observe the effect of increased active alkalinity on milk soil removal. The percentage of ingredients used in Xseries detergents follows:

Analysis of available chlorine concentration was made by titrating 50 ml of 0.35% detergent solutions with 0.1 ~, Na~S~O~ as described in Methods of Analysis of Milk and Its Products (7). Detergent solutions were supplemented with

Detergent

CaL gon

Sodium rectasilicate

Sodium carbonate

X-1 X-2 X-3 X-4

50 50

10 10 20

30

Liquid, 10%, sodium hypochlorite was used as the source of chlorine for supplementing detergent solutions and preparing 100 ppm available chlorine sanitizing solution. Dichloroisoeyanurate was used only in the proprietary Detergents A, B, and C. The word chlorine is used in the text, as in common usage, without intending it to be interpreted as elemental chlorine. JOURNAL OF DAIRY SCIEI'~CE "VOL 53, 170. 2

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Trisodium phosphate

Surfactant

30 70

10 10 10 10

chlorine by adding NaOC1 directly from 10% stock solution. Thus, 0.1 ml 10% ~aOC1 contributed approximately 25 p p m available C1 in 200 ml of solution. By this procedure detergent solutions were made with approximately 25, 50, 75, and 100 ppm available chlorine. Results and Discussion The effect of chemical characteristics of de-

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tergent solutions on the cleanability of milksoiled stainless steel is shown in Table 1. Milk films fixed on stainless steel plates were removed entirely by chlorine-free alkaline solutions and by detergent solutions containing 75 or 100 ppm available chlorine. These films were not removed entirely by solutions with 25 or 50 ppm chlorine. Consequently, build-up increased as soiling and washing cycles increased. Plates, pretreated in 10O p p m chlorine solutions and dried, retained especially high buildup of film in contrast to nonchlorine-treated plates. This effect was particularly shown as plates were washed by solutions of less than 50 ppm chlorine. The plates were made entirely clean by using detergent solutions containing 75 and 100 ppm chlorine. Of special interest was the observation that active alkalinity, in the range of 0.016 to 0.099%, did not prevent high accumulation of filming. Consequently, the change in active alkalinity of 0.002 to 0.003% by addition of 100 ppm chlorine from NaOC1 (Table 1), was considered to have no effect on cleaning the plates. Furthermore, no difference in removal of milk film was discernible from differences of p H in the detergent solutions. The concentration of available chlorine in detergent solutions was differentially effective in changing the pattern of cleaning milk-filmed plates. Twenty-five parts per million of chlorine, either from dichloroisocyanurate or from NaOC1, yielded high film build-up. Build-up decreased when using 50 ppm chlorine and was absent when using 75 and 100 ppm chlorine. One conjectures that differences in film build-up were related to the nature of milk protein following its reaction with the different concentrations of chlorine ions. A film subjected to 25 p p m chlorine was adhesive and insolvent to alkaline solutions; that exposed to 50 ppm chlorine was less adhesive and more soluble, whereas the chloro-protein at 75 and 100 ppm was completely soluble. The residual filming on Number 4 Finish plates varied in color according to the intensity of build-up. When film retention was barely detectible the coloring was faintly brown~ then became bluish and iridescent with further increase in build-up. Dense fihns were intensely bluish-brown. Summary and Conclusion Two kinds of soil films, raw milk and chloroprotein, were used to make cleanability studies of Number 4 Finish stainless steel. Raw milk fihns were prepared by drying raw milk on stainless plates after submersion in milk.

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Chloro-protein films were prepared similarly, bub plates were sanitized in 100 p p m available chlorine from NaOC1. Raw milk films were removed effectively from stainless plates washed in nonchlorinated alkaline solutions, but film build-up occurred on plates washed in chlorinated-alkaline solutions limited to 25 or 50 ppm available chlorine. When the concentration of chlorine was increased to 75 ppm the plates were completely cleaned. Alkaline detergents alone, testing 0.16 to 0.99% active alkalinity, were ineffective in removal of chloro-protein films. When supplemented with 75 to 100 ppm available chlorine, complete removal of the film was obtained. Evidence from the study strongly supports the value of chlorine ions for cleaning milksoiled equipment, but shows a need for more chlorine-bearing compound than is presently found in many commercially prepared chlorinated detergents. No difference in chloroprotein soil removal was attributable to changes in active alkalinity concentration. References (1) Claybaugh, G. A. 1950. Investigation of detergency applicable to mechanical milk can washing. M.S. thesis, Michigan State University, East Lansing. (2) Kanfmann, O. W., and P. H. Tracy. 1959. Formation and removal of an iridescent discoloration in cleaned-in-place pipelines. J. Dairy Sci., 42: 1883. (3) Lewandowski, T. 1959. CIP cleaners. 5 pp. (mimeo.) Proe. 28th Ann. Meet., Washington State College Inst. Dairying, Pullnlan.

(4) MacGregor, D. R., P. ~. Elliker, and G. A. Richardson. 1954. Effect of adding hypochlorite on detergent activity of alkaline solutions in recirculation cleaning. J. Milk :Food Technol., 17: 136. (5) Merrill, E. P. 1961. Detergency of chlorinated trisodium phosphate on milk-protein soils from stainless steel and glass. Ph.D. thesis, Michigan State University, East Lansing. (6) Merrill, E. P., J. M. Jensen, and S. T. Bass. 1962. Detergency effects of trisodium phosphate with and without sodium hypochlorite on milk-protein soils. J. Dairy Sci., 45 : 613. (7) Milk Industry Foundation. 1964. Laboratory Manual Methods of Analysis of Milk and Its Products. (Third printing.) 838 pp. plus X X I V . Washington, D.C. (8) Wright, E. O., W. S. LaGrange, C. Dennis, E. W. Bird, and D. I=L Hotchkiss. 1967. Protein solubilization by chlorinated cleaners. J. Milk Food Technol., 30: 310. JOURNAL OF DAIaY SCIEI~CE VOL. 53, No. 2