Journal of Scientific & Industrial Research

Vol. 61, July 2002, pp 504-509

Ozone: A Potent Disinfectant for Application in Food Industry -- An Overview

Ligimol James, A K Puniya, V Mishra and Kishan Singh*

Dairy Microbi o logy Division, National Dai ry Research Institu te, Kam al 132 001 , Haryan a, Indi a

Received: 12 February 2002; accepted: II March 2002

With the emergence of new microbial strains like Listeria , vi rulent E. coli, assorted viruses and accumulation of tox ic chemicals in environment increased attention has been given to the safe use of saniti zers, bleaching agents, pes ticides, etc. , in industri al process ing. The food industry, in particul ar, is in search of disin fectants that are effec tive against pathogens and are safe to use in specific applications. Ozone (0), is effecti ve against majority of microorgani sms tested and its applications in the food industry are related to decontamination of product surface and water treatment. Ozone has been used with success to inacti vate contaminant mi cro fl ora on meat, fruits, vegetabl es, and dry foods. Excessive use of ozone, however, may cause oxidation of some ingredients on food surface. Additional research is needed to optimi ze its use in food appli catjons. The pa­per reviews the various aspects of ozone as a di sin fec tant fo r different applicati ons in food industry.

Introduction

Ozone, a tri atomic form of oxygen , is an ex­

tremely potent oxidant having a broad antimjcrobial

spectrum. It is a blui sh gas with pungent and charac­

teri stic odour. Ozone has a molecular we ight of 48, boiling point of -111.9°C and a me lting po int of -

192.7°C at 1 atm. Ozone weighs 0.135 Ib/ft3, and has

a high oxidation potential of - 2.07 V.

Ozone is effective in decreasing the microbial

load, the level of toxic organic compounds, and the

bi ological oxygen demand in the environment. Ozone

decomposes spontaneously to oxygen, thereby, reduc­

ing the accumul ation of organic was te in the envi­

ronment. Thi s is considered to be an advantage of

ozone over other sanitizers as the use of the m results

in accumulation of wastes . Being a powerful oxidiz­

ing agent (l.S-times stronger than chlorine), it is a

viable di sinfec tant for ensuring the microbiological

safety and quality of food products. Ozone kill s wide

spectrum of bacteria like E. coli and Listeria, rapidl y

than traditionally used disinfec tants and is free of

chemical res idues. Moreover, it was g iven GRAS

(Generally Regarded As Safe) status by FDA in 1997, ensuring its use as a di sinfec tant '.

*Corresponding author

Antimicrobial Action of Ozollle

Ozone is potentially effective against bacteria ir

their vegetati ve as we ll as spore forms, fungi, proto

zoa,. and viruses (Table 1) . In the case of bacteria the

target sites are the bacteri al membrane glycoproteins

g lycolipids or certain amjno ac ids such as tryptophan

Besides, ozone also acts on the sulphydryl groups 0

certain enzymes, resulting in disruption of norma

cellular acti vit/. However the damage of viral nu

c1e ic ac id is the major cause of po liovirus-l inacti va . b 3 tlOn y ozone .

Bacteria - Ozone inactlvates both Gram-nega

tive and Gram-positi ve bacteria. Finch et al.4 have

studied the extent of inacti vation of E. coli, usin!

ozone at different doses and exposure times

Ozonated water has proved successfu l in reduc in!

surface-attached bacteria by more than 99 per cent:

and high concentrations (up to 1,500 r pm) of airbo rne

ozone have achieved simjlar dea th rates for E. col

and S. aureus5. Moore et al. 6 have evaluated the eff i

cacy of ozone as a di sinfectant of importance to the

da iry industry and observed inhibi tory effect of OZO J1(

on E. coli, Staphylococcus aureus, Serratia liquef a

ciells, Listeria innocua and Rhodotorula rubra Gram-negati ve bacteria were more sens itive to ozone

than Gram-pos iti ve organi sms. Si mjlar difference ir

JAMES et at.: OZONE - A POTENT DISINFECTANT 505

bacterial sensItIvIty 1.0 ozonated water has been

reported earlier7. According to FoegedingB, acidic pH

enhanced the lethality of ozone against the spores of

Bacillus and Clostridium, and that the spore coat is a

primary protective barrier against ozone. Addition of metallo-zeolites, ascorbic acid and isoascorbic acid

improved the inactivation of B. subtilis spores by

ozone treatment9. The combined treatment of gaseous

ozone and UV irradiation reduces contact time re­

quired for inactivation.

Fungi -Yeasts appear to be more sensitive than

molds to ozone treatments. Restaino et al.7 have re­

ported considerable reduction in the populations of

Candida albicans and Zygosaccharomyces bacilli, by

ozonated water, whereas, in the case of Aspergillus niger spores, less reduction was noticed 10. Moore et

al. 6 have studied inhibitory effect of ozone on many

microorganisms and found yeast more resistant than bacteria towards ozone activity.

Viruses - Ozone is a potentially virucidal

agent, inactivates viruses on short exposure and at

low concentration. Viruses associated with cells or

cell fragments are more resistant to ozone compared to purified virus II . In a continuous flow of ozonation

systems the cell-associated poliovirus and cox­

sackievirus samples demonstrated survival. Ultra­

sonic treatment did not increase inactivation of the cell associated enteric viruses. Herbold et aL. 12 have

tested the resistance of viruses and bacteria to ozone

in steadily flowing water at 20°C and pH 7. The order

of resistance was poliovirus 1 < E. coli < hepatitis A

virus < Legionella pneumophila serogroup 6 < B. subtilis spores.

Protozoa - Ozone is more effective than chlo­

rine against Cryptosporidium and Giardia. Wickra­manayake et al.13 have reported that Naegleria gru­

beri cysts were more resistant to ozone than Giardia muris. Korich et al. 14 reported> 90 per cent reduction

in the population of intestinal parasite, Cryptospor­

dium parvwn, within 1 min at 1 mg/L ozone in ozone demand free water.

Ozone - An Alternative to Chlorine

Hypochlorite salts of chlorine have been suc­cessfully used to sanitize utensils and equipments in

dairy and other food-processing industries. Hypochlo­

rites, being inexpensive GRAS substances, can be safely used in different food applications and have

been proved as effective disinfectants. But chlorine

compounds have some drawbacks that limit their use

in food applications. Toxic or carcinogenic chlorine

compounds can be formed in water as a result of

chlorination, e.g. trihalomethane in drinking water is

formed by the reaction of free chlorine with soluble

organic compounds. Ozone, compared to chlorine

shows stronger and more rapid antimicrobial action

against spores, fecal and pathogenic microorganisms

and viruses. Due to its spontaneous decomposition to

oxygen, ozone does not remain in water for a longer duration, hence, may be considered as a process

rather than an additive, with no safety concerns about

consumption of residual ozone in foods. By-products of ozone treatment of foodstuffs are similar to normal

oxidation products, and are less likely to have delete­

rious health effects than the by-products of chlorine.

Molecular ozone has a half-life (12 h) in air but in

water its stability depends on the amount of ozone­

demanding material in the water. Its half-life in water

at room temperature is only 20 min, and it decom­

poses into simple oxygen with no safety concerns

about consumption of residual ozone in the treated food product l5

. However, as in the case of any other

disinfectant, ozone also has a disadvantage of using it

as a disinfectant as it is extremely unstable. More­over, mechanisms of decomposition of ozone are

complex and are dependent on factors like type of

radicals formed and organic matter present in the me­dium that initiate, promote or inhibit the radical chain

reaction. Hence, it is difficult to generalize that a par­

ticular concentration of ozone at a given time will

always be effective in inhibiting microorganisms in

the food product l 6 (Table 1). Excessive use of ozone may result in surface oxidation of food l

? and in some

cases it may promote oxidative spoilage. Like other

oxidizing gases, it is potentially harmful at high con­centration for a sufficient duration to human beings. The "Threshold Limit Value - Long Term Exposure

Limit" for ozone exposure in the work place is 0.1

ppm for 8-h d140 h work week, as recommended by the 'American Conference of Govemmental Indus­trial Hygienists ' and approved by 'Occupational

506 JSCI IND RES VOL 61 JULY 2002

Table 1 - Inactivation of different groups of microorganisms by ozone!" 19

Groups of microorganisms Inactivation (log 10) Treatment Time (min) Concentration (mglL) Reference(s)

BacteriumE. coli 3.0 19 02.2 40Legionalla pneumophila 4.5 20 0.32 41Salmonella typhimurium 4.3 1.7 0.23 42YeastCandida parapsilosis 2.7 1.7 0.23 42

VirusBacteriophage J2 0.7 10 0.10 43Enteric virus 1.7 29 4.10 40Human rota virus 0.7 10 0.31 43Poliovirus type 1 2.0 10 0.20 43ProtozoaCryptosporidium parvum 1.0 05 01.0 14

Safety and Health Administration'. The "ThresholdLimit Value - Short Term Exposure Limit" is 0.3ppm for 15 min without suffering from physical irri-tation or other acute effects'8. However, ozone has thelowest value compared to other gases, like CO2, N2•

and O2. Therefore, it can be safely used in variousfood applications. Although ozone treatment is ex-pensi ve than chlorination but hazards of storing oftoxic chlorine in populated areas, handling and dis-posal of corrosive chemicals required for on-site gen-eration of chlorine, and the safety concerns aboutorganic chlorine by-products favours ozone as a saferdisinfectant".

Applications in Food Industry

Applications of ozone include, increased yieldof certain crops, preserving raw agricultural producesduring storage and transport, and sanitizing waterused for washing equipment and packaging". How-ever, effectiveness of ozone vary widely dependingon the nature and composition of food surface, typeof microbial contaminant, and the degree of attach-ment of microorganisms with food".

Meat and Meat Products - Research conductedby various workers on ozone's impact on beef so far,however, is still inconclusive. It was reported thatwashing of beef carcasses with plain water followedby ozonated water was more effective than that oftreatment with trisodium phosphate, acetic acid or asanitizer'", On the contrary, Reagan et al?' havefound that treatment with ozone was an improvement

I

over control but it showed no advantage over conven-tional washing in reducing microorganisms.

Dairy Products -The possibility of using ozoneas a mold inhibitor in cheese ripening rooms andpackaging materials without affecting the chemicaland sensory qualities of cheeses was studied. Shiler etal.22 have also suggested a method of ozonation forripening and storing cheese to inactivate contaminat-ing microflora, without any damage to cheese-packaging materials. For good results, ozonization iscarried-out for 1-3 hid at a cone. of 0.08 to 0.1 flg/Lof air with an intervals of 2 to 12 h, and after every 10to 30 d the chambers are treated with at a concentra-tion of 8 to 12 flg/L of air for 2 to 4 h.

Dry Foods - Naitoh et al.23 have obtained 1 to3 logs reduction in count of Bacillus and Micrococcusof cereal grains, peas, beans and spices on treatmentwith < 50mg/L ozone. In general, longer exposuretime and lower temperature resulted in higher micro-bicidal activity in dry foods. Ozone concentration of< 5 ppm can be used effectively without oxidativechanges in lipid containing foods. In a microbial de-contamination study of spices by ozone, a slight « 1log) microbial inactivation with 30 to 145 mg/L re-sidual ozone was noticed by Zagon et al.": Ozonedecreased essential oil content in some spices,thereby having a negative impact on sensory quali-ties. Galdun et al.25 tested the effect of ozone on gar-lic during long-term cold storage. Ozone treatmentincreased the yield of stored garlic by 3.7 per cent anddecreased damage to the product by Penicillium.

JAMES el at.: OZONE -A POTENT DISINFECTANT 507

With 15 mg/L for 30 min, ozone effectively de­creased the A. flavus population and its aflatoxin in dried SOUp26. Maeba et al.27 have confirmed the de­

struction and detoxification of aflatoxins B" G" B2 and G2 (50 t!g/mL in 4 per cent dimethyl sulphoxide).

Produce Industry -The number of produce as­sociated food-borne out-breaks and an increase in cases of illness due to pathogens is becoming com­mon phenomena. Moreover, losses in the fresh pro­duce industry that is attributable to microbial spoilage between the time of harvest and consumption is esti­mated to be as high as 30 per cenes. Hence, there is a need for an effective and safe antimicrobial agent in the produce industry. Ozone can be a simple answer

to it, as it can be successfully used in several applica­tions in the produce industry.

(a) Treatment of Process Water - Ozone has been proven to be a good alternative of chlorine for disin­fection and sterilization of process water used by food industr/9. 3o

. It is capable of destroying chlorine by­products, pesticides and organic compounds in the process water without leaving any toxic residues. De­pending on the source applications of ozone to proc­ess water range from 0.5 to 5 ppm with less than 5 min contact time. Ozone can also be used to remove iron, manganese, and sulphur and to control taste and odour of fresh water. This application ensures con­tinuous availability of high quality water free of mi­croorganisms and toxic chemicals for the produce . d IS In ustry .

(b) Fruit and Vegetable Washing - One way to

maintain the safety of fresh produce is to wash vege­tables and fruits using ozonated water. Kim et al. 16

have used ozonated water to wash shredded lettuce and obtained 2-log cfu/g reduction in total plate counts. Ozone is particularly found active against E. coli, the food pathogen of most concern to the pro­duce industr/ s.

(c) Preservation of Fruit and Vegetable - Another important use of ozone in produce industry is to deodorize fruits and vegetables during cold storage l7

.

Ozone is used to prevent microbial activity on sur­faces and extend the shelf-life of fruits and vegeta­bles ls

. The shelf-life of potatoes could be extended to as long as 6 months at 6 to 14°C and 93 to 97 per cent

relative humidity with 3 ppm of ozone without affect­ing the qualit/ I

. Ozone can also be used for increas­ing the shelf-life of blackberries, by preventing fungal growth without causing any observa~le defects, and surface colour of berries for 12 d (ref. 32). Ozone can be effectively used to slow down the fruit and vegeta­

ble ripening process during cold storage. During rip­ening, many fruits, such as bananas and apples, re­lease ethylene gas, which speeds up the ripening process. Ozone is very effective in removing ethylene

through chemical reaction to extend the storage life of many fruits and vegetables 17

•

Recycling of Process Water

Nearly, 50 billion gallons of fresh water is used annually by the produce industry, hence the quantity of fresh water consumed should be reduced because of rising costs of water and wastewater treatment dif­ficulties in handling large water volumes and prob­lems of disposal. Ozone can be a good option for the treatment of water for recycling, as it has been used to disinfect, to remove colour, odour and turbidity, and to reduce the organic loads of wastewater29. 30. Ozone

can be used for recycling process water in other in­dustries, particularly in poultry sector. However, fur­ther research is needed on wastewater from the pro­

duce industr/ s.

Miscellaneous Applications

Sander33 has developed an ozone treatment for fruit juices and liquid dairy products that minimizes possible quality deterioration. Rojek et al .34 have at­tempted to use pressurized ozone to decrease the mi­

crobial population of skim milk. Treatment of whey and apple juice also produced favourable microbial reduction. Greene et al.2 have proved effectiveness of ozone against biofilms of milk spoilage bacteria, such as P. fluorescens and Alcaligenes faecalis on stainless steel plates. Moore et al.6 have recommended ozone as an effective terminal disinfectant, if applied after adequate cleaning. Ozone was found to be effective on airborne microorganisms in different air disinfect­ing systems. Ozone can also be applied for preventing secondary contamination during bread manufactur­ing35

. Aerial conta-minants, such as Bacillus sp. and Micrococcus sp. in the plastic film processes were

508 J SCI IND RES VOL 61 JULY 2002

reduced.", Use of an UV air, cleaner for the steriliza-tion and deodorization of the air in refrigerators, sig-nificantly destroyed or reduced organisms on foodpreparation surfaces and inhibited development ofcold-tolerant bacteria and pseudomonads on foods".

The 'Food and Drug Administration' recognizesOzonation, as GRAS for treatment of bottled waterfor drinking when used in accordance with goodmanufacturing practices+'. Israel uses ozonation tocontrol post-harvest decay of table grapes39

. Ozonedeconta-mination of beef carcasses is also being usedin the US21

• Hence, ozone is having worldwide rec-ognition in an array of food commodities and thespectrum of applications can be further enhanced.

Conclusion

Ozone has certain attracti ve characteristics forbeing used as a safer sanitizer in food processing. In-vestigations on disinfection of foods and sanitizingsurfaces of vegetables, fruits, etc. support ozone as apowerful disinfectant. However, studies are still re-quired to define inherent factors that contribute to theresistance of some microorganisms to ozone.

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