APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Oct. 1976, p. 647-648
Vol. 32, No.
Copyright © 1976 American Society for Microbiology
4
Printed in U.S.A.
Electrochemical Sterilization of Beer R. E. WAGENER,* J. R. HELBERT, AND E. CHICOYE Research Department, Miller Brewing Company, Milwaukee, Wisconsin 53201
Received for publication 29 June 1976
Electrochemical inactivation of microorganisms was not achieved in beer but was achieved in physiological saline. Addition of carbohydrates or proteins to physiological saline prevented inactivation in this medium. Inactivation of microorganisms in aqueous medium is usually achieved by heat or chemicals. Since the pasteurization of beer requires substantial energy, alternative methods are desirable. High-voltage electrolytic processes have been used for microbial inactivation (G. E. Stoner, U.S. Patent 3,725,226, 3 April 1973), but they are impractical in beer due to product alteration. Stoner and Srinivasan (2), using a lowvoltage electrolytic process, found that proteinaceous matter adsorbed to an electrode. In a patent (no. 3,725,226) issued in 1973, he described a low-power system capable of inactivating bacteria, viruses, flukes, protozoa, endoparasites, fungi, nematodes, algae, and fungal spores. Organisms were adsorbed, inactivated, and then desorbed by an alternating current of relatively low voltage. At some applied potential the protein or polysaccharide in the coat of microorganisms adhered to the anode; denaturation or destruction followed. During the cathodic phase the organic matter desorbed (Stoner, U.S. Patent 3,725,226, 3 April 1973). An electrochemical sterilizer, as described by
Stoner, was built for use by The Research Laboratories for the Engineering Sciences at the University of Virginia. The reactor, shown in Fig. 1, had its own power supply designed to deliver a square wave at a frequency of one cycle per second and at 12 V above and below ground. This potential was applied between two electrodes, each having an area of 140 cm2. The total volume between the electrodes was 53 ml. The current density recommended as necessary for sterilization was 14 to 19 mA/cm2. Our results using this device with beer spoilage microorganisms are described below. Unpasteurized beer and saline solutions, to which beer spoilage microorganisms (1) had been added, were tested. A flow rate of 50 ml/ min through the reactor allowed an average residence time of 1 min. Samples, taken before and after passing through the reactor, were filtered through a membrane filter (Millipore Corp.) and incubated on Universal Beer Agar (1) at 25°C in a CO2 atmosphere. Colony counts were recorded after 7 days. Inactivation was incomplete in beer with a microbial load of 1.2 x 103 to 3.8 x 106 cells/liter.
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648
APPL. ENVIRON. MICROBIOL.
NOTES
TABLE 1. Electrochemical inactivation of microorganisms in various media Viable micoorganisms/liMedium
ter Before
Beer Beer Beer NaCl in beer (0.15 M) 1% (wt/vol) maltose in NaCl solution (0.15 M) 0.2% (wt/vol) protein in NaCl solution (0.15 M) NaCl (0.15 M) Na2SO4 (0.15 M)
1.2x 103 5.9 x 103 3.8 x 103 4.8 x 103
Inactivation (%) After
1.2x 5.3 x 3.3 x 3.1 x
103 103 106 103
0 10 13 35
2.4 x 104 2.1 x 104
13
1.9 x 104 1.8 x 104
5
3.5 x 106 1.0 x 102 1.4 x 107 1.1 x 107
99 21
This effect may be due to nonviable organic matter as the following observations suggest. Low levels of inactivation were obtained both with sodium chloride (0.15 M) in beer and with maltose (1%) or protein (0.2%) in physiological saline (Table 1). Inactivation equivalent to pasteurization was obtained in physiological saline, but not in sodium sulfate (0.15 M). These results suggest chloride may be important for inactivation. LITERATURE CITED 1.
2.
Barney, M. C., and J. R. Helbert. 1975. A microcolony method for rapid determination of contaminant microorganisms in beer. Tech Q. Master Brew. Assoc. Am. 12:23-27. Stoner, G., and S. Srinivasan. 1970. Adsorption ofblood proteins on metals using capacitance techniques. J. Phys. Chem. 74:1088-1094.
Vol. 32, No.
Copyright © 1976 American Society for Microbiology
4
Printed in U.S.A.
Electrochemical Sterilization of Beer R. E. WAGENER,* J. R. HELBERT, AND E. CHICOYE Research Department, Miller Brewing Company, Milwaukee, Wisconsin 53201
Received for publication 29 June 1976
Electrochemical inactivation of microorganisms was not achieved in beer but was achieved in physiological saline. Addition of carbohydrates or proteins to physiological saline prevented inactivation in this medium. Inactivation of microorganisms in aqueous medium is usually achieved by heat or chemicals. Since the pasteurization of beer requires substantial energy, alternative methods are desirable. High-voltage electrolytic processes have been used for microbial inactivation (G. E. Stoner, U.S. Patent 3,725,226, 3 April 1973), but they are impractical in beer due to product alteration. Stoner and Srinivasan (2), using a lowvoltage electrolytic process, found that proteinaceous matter adsorbed to an electrode. In a patent (no. 3,725,226) issued in 1973, he described a low-power system capable of inactivating bacteria, viruses, flukes, protozoa, endoparasites, fungi, nematodes, algae, and fungal spores. Organisms were adsorbed, inactivated, and then desorbed by an alternating current of relatively low voltage. At some applied potential the protein or polysaccharide in the coat of microorganisms adhered to the anode; denaturation or destruction followed. During the cathodic phase the organic matter desorbed (Stoner, U.S. Patent 3,725,226, 3 April 1973). An electrochemical sterilizer, as described by
Stoner, was built for use by The Research Laboratories for the Engineering Sciences at the University of Virginia. The reactor, shown in Fig. 1, had its own power supply designed to deliver a square wave at a frequency of one cycle per second and at 12 V above and below ground. This potential was applied between two electrodes, each having an area of 140 cm2. The total volume between the electrodes was 53 ml. The current density recommended as necessary for sterilization was 14 to 19 mA/cm2. Our results using this device with beer spoilage microorganisms are described below. Unpasteurized beer and saline solutions, to which beer spoilage microorganisms (1) had been added, were tested. A flow rate of 50 ml/ min through the reactor allowed an average residence time of 1 min. Samples, taken before and after passing through the reactor, were filtered through a membrane filter (Millipore Corp.) and incubated on Universal Beer Agar (1) at 25°C in a CO2 atmosphere. Colony counts were recorded after 7 days. Inactivation was incomplete in beer with a microbial load of 1.2 x 103 to 3.8 x 106 cells/liter.
I
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I I1½
-I
11&" t
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:
i I -i
zi
;
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- ZZ4 i
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I FIG. 1. Electrochemical reactor. Dimensions: 13/8 by 41/2 by 111/2 inches (3.5 by 11.4 by 29.2 cm). 647
648
APPL. ENVIRON. MICROBIOL.
NOTES
TABLE 1. Electrochemical inactivation of microorganisms in various media Viable micoorganisms/liMedium
ter Before
Beer Beer Beer NaCl in beer (0.15 M) 1% (wt/vol) maltose in NaCl solution (0.15 M) 0.2% (wt/vol) protein in NaCl solution (0.15 M) NaCl (0.15 M) Na2SO4 (0.15 M)
1.2x 103 5.9 x 103 3.8 x 103 4.8 x 103
Inactivation (%) After
1.2x 5.3 x 3.3 x 3.1 x
103 103 106 103
0 10 13 35
2.4 x 104 2.1 x 104
13
1.9 x 104 1.8 x 104
5
3.5 x 106 1.0 x 102 1.4 x 107 1.1 x 107
99 21
This effect may be due to nonviable organic matter as the following observations suggest. Low levels of inactivation were obtained both with sodium chloride (0.15 M) in beer and with maltose (1%) or protein (0.2%) in physiological saline (Table 1). Inactivation equivalent to pasteurization was obtained in physiological saline, but not in sodium sulfate (0.15 M). These results suggest chloride may be important for inactivation. LITERATURE CITED 1.
2.
Barney, M. C., and J. R. Helbert. 1975. A microcolony method for rapid determination of contaminant microorganisms in beer. Tech Q. Master Brew. Assoc. Am. 12:23-27. Stoner, G., and S. Srinivasan. 1970. Adsorption ofblood proteins on metals using capacitance techniques. J. Phys. Chem. 74:1088-1094.
