INTRODUCTION

Throughout the ages, food preservation has been a never-ending challenge for humankind. The prevention of spoilage and harmful bacteria in fruits, vegetables and their products are the most important food safety problems. Food preservation is the process of extending the shelf life of raw materials or its processed forms. Thermal processing is a traditional approach for microbial or enzyme inactivation in the Food Industry (Jakob and Hensen, 2005). It has however an adverse impact on food quality, such as colour, flavour, taste and nutritional value. Although, thermal treatment helps kill vegetative organisms and certain spores, the quantity of nutritional loss, development of unpleasant flavours and deterioration of functional qualities of food products is related to the magnitude of treatment time and process temperature (Dolatowki et al., 2007). Recently, novel non-thermal technologies have been explored to inactivate microbes. However, the food composition and cellular activities are also affected by these non-thermal technologies. The food processor and eventually the consumer is concerned about pathogenic bacteria being removed. Chemical rinsing treatments are the most effective conventional methods for sanitization of fresh foods. But some of these agents such as chlorine are ineffective against some organisms, especially at high pH or against spore-forming microbes and can react with organic compounds to form trihalomethanes that are hazardous to human health as well as to the environment. As a result, emerging and innovative food preservation methods that can maintain food freshness while reducing microbial counts to the lowest possible level, without leaving any residual effects and at a cost-effective level have become a top priority for the food industry in recent years.

Hence, the focus has now been shifted to ozone, owing to its numerous applications in the food industry, such as sanitation of food plant, food surface hygiene, reuse of waste water, treatment and lowering Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) of food plant waste. Ozone has been shown to have bactericidal effects on a wide range of species, including bacteria and other surface spores, as well as vegetative cells. Ozone has the potential to meet industrial expectations (Khadre et al., 2001) and more research and commercial applications have proven that it can replace traditional sanitizing agents, while providing a better product quality (Graham, 1997). Food preservation through ozone is thus a non-thermal processing technology that helps in enhancing food safety without compromising on the quality and desirability of food products (Guzel-Seydim et al., 2004).

What is Ozone?

Schonbein discovered and named Ozone (O3) in 1840, which is an allotropic form of oxygen (O2). It is made up of the same atoms as oxygen (O2), but the atoms are joined in a different way. The presence of three oxygen atoms distinguishes it from “common oxygen”, which has only two. It has a low molecular weight (MW = 48 grams per mole) and three oxygen atoms organized chemically in a chain. The molecule is highly unstable at room temperature and exhibits higher oxidation potential than chlorine.

At room and refrigerator temperatures, ozone exists as a gas and it is slightly soluble in water. It degrades quickly (Manley and Niegowski, 1967), but its half-life in the gaseous state is longer than in aqueous solution (Rice, 1986). Ozone is moderately stable in air but highly unstable in water, where it decomposes quickly. Due to its short half-life, ozone gas cannot be stored and has to be produced onsite. The by-product of ozone processing is atmospheric oxygen and as such it does not leave any residues of its own. It has a pungent, distinctive odour that has been compared to “fresh air after a thunderstorm.” When produced from dried air, ozone is a blue gas, but when produced from high-purity oxygen, it is colourless. In 1997, the US Food and Drug Administration (FDA) declared ozone to be “Generally Recognized as Safe” (GRAS) for use in food processing (Graham, 1997). Furthermore, the US Food and Drug Administration (FDA) recognized and approved ozone as an antibacterial food additive in 2001.

Effect of Ozone on Microorganisms

The antimicrobial potential of ozone is associated with its high oxidation potential that induces lysis in the microbial cell constituents. The major target of ozonation has been considered to be the bacterial cell surface.

Schematic diagram showing antimicrobial mechanism due to ozone induced oxidation
Fig 1: Schematic diagram showing antimicrobial mechanism due to ozone induced oxidation

Two major mechanisms have been identified in ozone destruction of the target organisms: first mechanism is that ozone oxidizes sulphydryl groups and amino acids of enzymes, peptides and proteins to shorter peptides. Ozone further oxidizes polyunsaturated fatty acids to acid peroxides via the second mechanism. Cell breakdown and subsequent leakage of cellular contents are caused by ozone induced oxidation of unsaturated lipids in the cell membrane. The intense destruction and damage of nucleic acids can potentially cause cellular death. Ozone sensitivity is higher in thymine than in cytosine or uracil. Ozone also damages viral RNA and changes viral protein coat polypeptide chains (Kim et al., 1999; Guzel-Seydim et al., 2004).

Ultra-violet lamp method oxygen turns into ozone after it is hit with UV light from a UV bulb

Application of Ozone in the Food Industry

Today, Ozone is steadily replacing traditional sanitation methods, including chlorine, steam and hot water. It’s gaining popularity in the food processing sector as the safest, most cost-effective and chemical-free method of managing food safety (Aslam et al., 2020).

Applications of Ozone in Food Processing Sector

Ozone has been shown to deactivate a wide range of organisms, including bacteria, fungi, yeast, parasites and viruses, as well as oxidize natural organic compounds and synthetic chemicals like detergents, herbicides and composite pesticides (Graham, 1997; Guzel-Seydim et al., 2004; Gonçalves, 2009). Ozone has been utilized in the food processing sector to eliminate germs on a wide range of food products and contact surfaces, both as gaseous ozone and as dissolved in water (Aslam et al., 2021; Guzel-Seydim et al., 2004; Chawla et al., 2007; Gonçalves, 2009).

1. Ozone as a Preservative Tool for Food Safety and Hygiene in the Food Industry:

Ozone will influence any pathogen or contaminant that can be disinfected, changed or eliminated by an oxidation process. It has the highest oxidizing power of any molecule available for water disinfection, second only to elemental fluorine (Duguet, 2004; Gonçalves, 2009).

2. Fruits and Vegetables:

Microorganisms are natural contaminants of fresh produce and minimally processed fresh-cut items and they can come from a variety of places, including postharvest handling and processing (Beuchat, 1996). Fresh produce contains a complex mix of bacteria, fungus and yeast, the number and types of which are highly changeable (Zagory, 1999). The growth of the microbial population must be regulated to extend the shelf life of fresh fruits and vegetables (Ponce et al., 2003). Chlorine is the principal sanitizing agent used in the washing of fruits and vegetables (Ponce et al., 2003), but it also produces residual by-products such as trihalo-methanes, which are probable carcinogens (Fawell, 2000).

Treatment of Chinese cabbages with ozonated water (2.3 mg/L) for 60 minutes resulted in a greater than 90% reduction in total bacterial counts. Sarig et al. (1996) found that grapes exposed to ozone (8 mg/lt) for 20 minutes had significantly lower levels of bacteria, fungus and yeast. With ozone treatment, fungal deterioration in grapes during cold storage was minimized and shelf life was extended. During storage, onions were treated with ozone. There was a significant reduction in mould and bacterial counts with no change in chemical composition or sensory quality (Aslam et al., 2021).

Response Surface plot showing effects of ozone concentration (mg/l) and exposure time (min) on microbial degradation (log reductions) in whole peeled onion (Aslam et al., 2021).

3. Dried Fruits:

The overall count of mesophilic bacteria, coliforms, S. aureus and yeast/mould was reduced when ozone was given in gas form at three concentrations (1, 3, and 5 ppm) for four distinct periods (15, 30, 45 and 60 minutes) on Iranian date fruit, according to Najafi and Khodaparast (2009). The findings also suggested that a one-hour ozone treatment at 5 ppm could successfully reduce coliform and S. aureus counts in date fruits, but that longer exposure times are needed to eliminate total mesophilic bacteria and yeast/mould counts, which were statistically lower than those of untreated control samples.

4. Liquid Foods:

Until now, microbial studies have shown that by using ozone, it is possible to achieve mandatory 5-log reductions in spoilage and potentially harmful organisms most usually found with fruit and vegetable juices. Traditionally, ozone processing in the food industry has been done on solid foods using either gaseous treatment or ozonated water washing. However, since the FDA approved ozone as a direct food additive, its potential in liquid food applications has begun to be explored. While liquid food ozonation is still in its infancy, it has been used to process a variety of fruit juices, including apple cider (Choi and Nielsen, 2005; Steenstrup and Floros, 2004; Williams et al., 2005) and orange juice (Williams et al., 2005). (Angelino et al., 2003; Tiwari et al., 2008).

5. Spices:

Experimentally, Ozone has been used to decontaminate whole and crushed black peppercorns instead of ethylene oxide (Zhao and Cranston, 1995). The oxidation of volatile oil constituents in powdered black pepper was mild, while ozone had no effect on the volatile oils in whole peppercorns. Ozonation was recommended for industrial treatment of whole black peppercorns, because it efficiently decreased microbial burdens and did not induce considerable oxidation of the volatile oils (Zhao and Cranston, 1995). Inan et al. (2007) conducted research into the influence of ozone on the detoxification of aflatoxin B1 in red pepper. Various ozone concentrations (16, 33, 66 mg/l) and exposure periods were used to ozonize flaked and chopped samples (7.5, 15, 30, 60 min.). After 60 minutes of exposure to 33 mg/l ozone and 66 mg/l ozone respectively, the amount of aflatoxin B1 in flaking and chopped red peppers was reduced by 80% and 93% respectively.

6. Meat and Poultry:

Water is consumed in huge amounts by the poultry processing sector. The possibility of reusing poultry processing water has gained a lot of appeal for the industry. The use of ozonation for poultry carcass washing was approved by the USDA in 1996. Chang and Sheldon (1989) found that combining screening, diatomaceous earth filtration and ozonation resulted in the best water quality with the lowest overall microbial burdens (total coliforms, E. coli and salmonella reduced by 99 percent).

The effect of ozone treatment on microbiological contamination of pork was investigated by Jaksch et al. (2004). Ozone was used to treat commercial pork meat samples. The Proton-Transfer Reaction Mass Spectrometry (PTR-MS) technique was employed to investigate volatile emissions, with the signal observed at mass 63 (assumed to be a measure for dimethylsulphide) being utilized as a diagnostic of bacterial activity. Such a signal was shown to strongly grow with time for an untreated meat sample, whereas ozone-treated meat samples showed much lower emissions, implying that microbial activity had been greatly repressed by ozone treatment, resulting in an increase in meat shelf-life. Novak and Yuan (2004) used ozone to treat beef surfaces, then cooked the treated beef at 45-75°C to see if it affected entero-toxin producing Clostridium perfringens strains. Aqueous ozone treatment and heating at 45-75°C resulted in a reduction of 1-2 log CFU/g in C. perfringens, according to the authors. They also detected a decrease in spore count with the same treatments. However, the difference was minor, showing that the spores were considerably more resistant to ozone and thermal treatments. The scientists came to the conclusion that ozone treatment followed by heat treatment allowed for reductions at cooking temperatures that would not typically allow for such reductions.

7. Sea Foods:

Ozone application for fresh fish helps to suppress the unique scent, which can be unpleasant at times, giving the fish a healthier appearance (Gonçalves, 2009). Tilapia pre-treatment with ozone (6 ppm) extends the product’s shelf life by 12 days. The combination of ozone pre-treatment and 0°C storage appears to be a viable method of extending fish storage life (Nash, 2002; Gelman et al., 2005). When ozonized water was used for dipping and washing fish or fish fillets, the microbial flora was effectively reduced, while the product was unaffected (Tapp and Sopher, 2002; Gelman et al., 2005, Gonçalves, 2009). When live catfish and fillets were rinsed in ozonated water, they showed highly significant reductions in plate counts (Campos et al., 2006). In a time when efforts are being made to eliminate the use of commonly used chlorine, owing to its ability to form potential carcinogens when reacting with organic matter, ozonated water technology can be successfully used as a germicidal agent in seafood processing to extend the shelf life and quality of wild shrimp (Graham, 1997; Chawla et al., 2007). According to Chawla et al. (2007), soaking shrimp in 3 ppm O3 for 60 seconds enhanced the shelf life of shrimp stored in ice.

8. Grains and Their Products:

Storage grains are vulnerable to a variety of insects, including Tribolium sithophilus and moths, which can cause significant damage and may evolve resistance to current insecticides. Ozone is an efficient insecticide, mycotoxin destroyer and microbial inactivator that have little or no influence on grain quality. Ozone has been shown to have particular advantages for grain processing, as well as addressing growing concerns about the use of toxic pesticides (Tiwari et al., 2010). According to the findings, treating grains with 50 ppm ozone for 30 days had no negative impact on the popping volume of popcorn, as well as the fatty acid and amino acid composition of soybean, wheat and maize. The milling features of wheat and maize, as well as the baking characteristics of wheat and the stickiness of rice were unaffected. In terms of baking and milling parameters, the use of ozonated water had no effect on the chemical and physical attributes of the parent flour. Furthermore, when wheat kernels were tempered with ozonated water, there was a significant drop in overall bacteria and yeast/mold populations.

9. Use of Ozone for Sanitization of Plant Equipment:

Several researches have been carried out to see how efficient Ozone has been against certain microbes that affect food processing plants. Canut and Pascual (2007) demonstrated that Ozone might be used as an alternative to other sanitizers in Cleaning-in-place (CIP) procedures in many sectors of the Food Industry with potential environmental benefits. Guillen et al. (2010) investigated the efficacy of ozone in a wine industry CIP system. A wine-transporting hose was subject to the following treatments: ozonated water at 28°C; hot water; peracetic acid; and a caustic soda solution containing peracetic acid in this study. The results showed that using ozonated water is more successful than using peracetic acid alone or using soda and peracetic acid together.

10. Dairy Industry:

Dairy Industry is one of the most delicate industries requiring a high level of hygiene to produce high-quality products that are free of physical, chemical and microbial hazards. Milk is a perishable foodstuff that is easily contaminated by germs. On dairy farms, ozone can significantly reduce chemical expenditures and completely eliminate hot water costs. Heacox D (2013) submitted a patent for an ozone delivery method, system and apparatus that uses ozonated water with ozone at a desirable level of 0.04-1.2 ppm to clean and disinfect dairy products, milking equipment and other surfaces in dairy environments. Scanning electron micrographs revealed that the ozonation cleaning technique cleaned the metal surfaces more effectively than the 40°C warm water treatment. According to the results of Compound Oxygen Request (COD) calculations, ozonated water removed 84 percent of milk build-ups from plates, while non-ozonated warm water removed only 51 percent of dairy soil elements.

Jorek U, et al. used pressurized ozone (5-35 mg/L for 5-25 minutes) to protect skim milk by reducing bacterial populations. The treatment appears to reduce the number of Psychrotrophs by more than 98%. Ozonation completely eliminated Listeria monocytogenes from both crude and marked milk samples, according to Sheelamary M, et al. Bacterial and contagious checks were reported to be reduced by up to 1 log10 cycle when exposed to ozone gas at 1.5 mg/L for 15 minutes.

Impact of Ozonation on Quality of Agro-products

Although, ozonation assures microbiological safety and pesticide degradation in agro products with a long shelf life, the end product’s physicochemical, nutritional and sensory quality must be guaranteed. The quality changes that occur when fresh fruits and vegetables are exposed to ozone provide a significant viewpoint on Ozone and its impact on fresh produce.

1. Sensorial Characteristics

Sensory features are frequently regarded as a quality indicator. Colour, smell, surface, taste and appearance are all important sensory elements that determine a customer’s preference. In most studies, ozone has been observed to non-significantly affect sensory quality of treated products. For example, in comparison to coriander treated with caustic electrolyzed water, P. Sintuya et al. observed that ozone treated coriander maintained better sensory quality.

2. Colour

Consumer preference is influenced by colour, which is a crucial parameter of agricultural products. Changes in colour are primarily caused by enzymatic (polyphenol oxidase and peroxidase) and non-enzymatic reactions that alter the concentration of natural pigments such as anthocyanins, chlorophylls and carotenoids. Ozone treatments have no effect on the colour of fruits and vegetables. Surintraporn C, et al. observed that gaseous ozone treatment (5.5 g.h-1 for 30 min) had no effect on the colour of dried chillies in a recent investigation.

3. Aroma

One of the possible disadvantages of ozone processing is the loss of aroma. Ozone treatment significantly reduces the fragrance of fresh food. Strawberry stored in ozone-enriched cold storage, for example, resulted in an irreversible loss of scent. The loss of aroma was due to the oxidation of volatiles released by the strawberries. The volatile esters emission in ozone-treated strawberries was reduced by 40%, according to Baur S, et al.

4. Firmness

Apples, carrots, kiwifruit, strawberries and tomatoes have all been proven to benefit from ozone preservation. Most of the studies in the literature have reported better retention of texture in aqueous ozone-treated samples as compared to control. For example, higher firmness than control samples were reported by Nayak et al. (2020) in strawberries (0.1 ppm, 2 min); Liu et al. (2021) in fresh-cut apples (1.4 mg/L, 5 min) and Aslam et al. (2021) in onion slices (5 ppm, 8 min).

Conclusion:

Fresh and fresh-cut fruits and vegetables are susceptible to microbial deterioration that can potentially cause serious health hazards. In order to ensure microbial safety, chlorine and bromine-based sanitizers have been conventionally used in the food industry. However, recent studies have highlighted the production of potentially carcinogenic by-products like trihalomethanes. As such, ozone is being considered to replace these agents, owing to its high oxidation potential that not only ensures comparable sanitizing efficiency as compared to chlorine, but also maintains a better product quality. It does not leave any by-products of its own and is produced from atmospheric oxygen that is abundantly available. In the Food Industry, it can have tremendous applications including shelf-life improvement of fresh foods, sanitization of equipment surfaces, removal of pesticides, fumigation of grains, etc. Recent information suggest that Ozone has a remarkable potential to increase the safety and quality of food , piquing the Food Industry’s attention. Overall, Ozone is considered a green technology in the food processing applications, since it leaves no hazardous residue on the product.

References:

1. Aslam, R., Alam, M. S., & Saeed, P. A. (2020). Sanitization potential of ozone and its role in postharvest quality management of fruits and vegetables. Food engineering reviews, 12(1), 48-67.

2. Prabha, V. I. T. H. U., BARMA, R. D., Singh, R. A. N. J. I. T., &Madan, A. (2015). Ozone Technology In Food Processing: A Review.

3. Hampson, B. C., & Fiori, S. R. (1997). Applications of ozone in food processing operations.In IOA PAG Conf., Lake Tahoe (pp. 261-267).

4. Chuwa, C., Vaidya, D., Kathuria, D., Gautam, S., & Sharma, S. (2020). Ozone (O3): An Emerging Technology in the Food Industry. Food Nutr J, 5, 224.

5. James, L., Puniya, A. K., Mishra, V., & Singh, K. (2002). Ozone: A potent disinfectant for application in food industry-an overview.

6. O’Donnell, C., Tiwari, B. K., Cullen, P. J., & Rice, R. G. (Eds.). (2012). Ozone in food processing. John Wiley & Sons.

About the Authors:
1. Jashanpreet Kaur
Graduate Student, Department of Food Science & Technology,
Punjab Agricultural University, Ludhiana – 141 004

2. Raouf Aslam
Doctoral Student and Senior Research Fellow,
Department of Processing & Food Engineering,
Punjab Agricultural University, Ludhiana – 141004
Email ID: raoufaslam@gmail.com

Disclaimer:

The views/opinions expressed by authors on this website solely reflect the author(s) and do not necessarily reflect the views/opinions of the Editors/Publisher. Neither the Editors nor the Publisher can be held responsible and liable for consequences that may arise on account of errors/omissions appearing in the Articles/Opinions.

Author

An editor by day & dreamer at night; passionately involved with both print and digital media; Pet lover; Solo traveller.

Write A Comment

two × 4 =