Effects of gaseous ozone treatment on quality attributes of some foods during cold storage

Today, novel technologies in addition to cold storage come to to the fore as an alternative method of protection. The purposes of these technologies are to preserve food quality for longer time and to increase the shelf life of foods. Today, the rapid pace of work and intensity have limited the time for shopping. On the other hand, eating habits at home have changed, and there is a tendency towards eating out. In addition, an increase has been observed in the number of people living far away from shopping areas in town. Another issue is that the number of individuals living alone has increased today. In such cases, quality losses arise as the purchased products are stored in the cold storage equipments for prolonged periods, product safety may be affected, and economic losses occur as a result of disposal of unconsumable food products. Therefore, extensive studies are carried out today to design the household-type cold storage equipment in the best way to preserve the original features of the food products and the importance of the subject is increasing day by day. Meat and meat products, if manufactured under non-hygienic conditions, can cause serious problems for human health. As a result of various chemical and enzymatic reactions and microbial growth, products may be non-consumable. Among these, microbial growth affects the product shelf-life and food safety the most whereas the most influential factor on the development of microorganisms is the storage temperature. For this reason, cold-storage is of great importance especially for the preservation of the so-called "fresh food" groups, sales and domestic consumption stages in terms of product safety and long shelf-life. Nowadays the challenge customers are considering about is chemical preservatives that are used for extending shelf life and obtaining food safety. With the increase in the demands of consumers in the same way as fresh foods, especially the widespread use of non-thermal inactivation technologies increased in the food industry. In recent years, non-thermal applications such as UV-C light, ozone and magnetic field has gained importance in the food industry. Ozone technology is one of the alternative preserving methods of protection that gained considerable importance in recent years. With new regulations about ozone gas, which has characteristic and fresh smell and can be produced naturally in the atmosphere, this molecule has become significant alternative case against traditional methods, especially for the food industry. Ozone is a broad spectrum antimicrobial agent, effective against bacteria, molds, yeasts, and protozoa. Today ozone applications are used in many different areas. Especially during cold storage of fruits and vegetables, ozone treatment gives very good results for the inhibition of microorganisms. Ozone is one of the most powerful sanitisers. It was affirmed as Generally Recognised As Safe (GRAS) in the United States and approved by the Food and Drug Administration (FDA) as an antimicrobial agent that can be directly applied in the food industry. Ozone use may have many advantages in the food industry. There are numerous application areas of ozone in food industry such as food surface hygiene, sanitation of food plant equipment and reuse of waste water. While the destruction of bacteria by ozone has been studied extensively, relatively little information is available on the effect of various food components on the bactericidal and or fungicidal activity of ozone. Through the activity of ozone gas, it is believed to be applicable for the foods stored at household type cold storage equipment to preserve quality and increase storage time. Ozone has very high oxidation reduction potential, it acts as an oxidant for the cell wall constituents of microorganisms and oxidizes certain essential components e.g., unsaturated lipids, enzymes, proteins, nucleic acids. Destruction of large part of the membrane barrier causes leakage of cell contents, and the bacterial or protozoan cells lyse (unbind) resulting in gradual or immediate destruction of the cell. Most pathogenic and foodborne microbes are susceptible to this oxidizing effect. The aim of this study was to investigate the effects of ozone gas treatment on cold stored food groups which are beef and tomato paste. Taking into consideration of safety values and the literature data, ozone gas was applied with different concentrations at different time intervals to beef and tomato paste samples. Beef samples were treated with 1 and 1.8 ppm ozone concentrations in the specific compartments of cold storage equipment up to 60 minutes in order to determine the initial application period and concentration level. After the application of ozone gas, beef samples were stored at 4°C for 7 days by wrapping with stretch film. During this period, physical, chemical, microbiological and sensory quality changes of products were investigated and compared with the control group. Samples were evaluated according to the thiobarbituric acid (TBA), pH, sensory changes, color, total viable count and lactic acid bacteria levels. In the second part of the study, it was aimed to determine the required time intervals of ozone gas treatment throughout the storage period as 'periodic application time'. Ozone gas was applied to beef samples which are exposured to initial ozone application with the following periods: 12 h, 24 hours and 3-24 hours. After the initial application (t0 value: 1 ppm for 10 minutes), the same concentration and time procedure as 1 ppm ozone for 10 minutes was applied to the samples. Microbiological level of the products came with undesired results after the periodic application in a short time. Furthermore, tomato paste samples were treated with 0.5; 2.5; 5 ppm ozone concentrations for 10 minutes. After the application of ozone gas, tomato paste samples were stored at 4°C for 21 days. Samples were evaluated according to pH levels, sensory changes, total amount of acids, total dry matter, and mold growth. With 1 ppm ozone concentration for 10 minutes, better results were obtained in beef samples for color, TBA, pH, microbiologic and sensory evaluations than with control group and other applications. Increasing ozone concentration and exposure time in beef samples, increased TBA number as well. As a result of sensory analysis, long time and high concentration (1.8 ppm, 30 min and 1 ppm, 60 min) of ozone caused undesirable characteristics such as bad smell in beef samples. The periodic ozone application has decreased shelf life by accelerating microbiological growth. As a result of the analysis conducted in tomato paste samples, ozone application led to changes in the number of percent of moldy area amongs quality parameters. No significant change was observed in other parameters. The number of percent of moldy areas with high concentrations (5 ppm for 10 min) of ozone gas applied in tomato paste was less than control group and other treatments. In conclusion, no change was observed in sensory properties of tomato paste samples subjected to ozone gas and stored for 21 days.