Improvement of the quality parameters of cold stored food materials by the application of ultraviolet-C light

Thermal inactivation methods have negative effects on food materials, and this leads manufacturers to avoid using these methods. In consequence, cases affecting human health and food safety such as intoxications or outbreaks occur. Microbial safety, and sensory and shelf life stability of the food materials depend on the traditional preservation methods. However, consumers demand more fresh-like products with minimal processing and also a stable and safe food product. To prevent the occurring of food safety problems and human intoxications, and to avoid food quality degradation, alternative non-thermal inactivation and preservation methods are being developed. Non-thermal novel technologies such as; ultraviolet light, electrical field, magnetic field, ultrasound, ozone and high hydrostatic pressure are being studied and applied on food processing stages. These emerging technologies are considered as an alternative to respond to the most prospective consumer demand, minimally processed safe foods. For this reason, studies on novel food processing and preservation technologies contributes to the potential of these novel methods to substitute conventional methods. Novel preservation methods are projected to prevent microbial growth and extend shelf life, also to maintain the freshness of the food material. Applying one novel preservation method is generally not sufficient, so combination of preservation methods is required. Combination of an other preservation method, such as cold storage, with a novel method seems to be feasible to achieve the desired level of safety and quality. Inactivation of microorganism can be done by destruction of cells by heat treatment and by inactivation of the cells via novel physical methods as mentioned above. One of these non-thermal inactivation and preservation technologies is ultraviolet (UV) light application, which has been recognized for its germicidal effectiveness. Ultraviolet light applications are installed and demanded disinfection alternative for the production of drinking water. Besides the utilization of the method in drinking water production plants, Food and Drug Administration (FDA) approved the use of ultraviolet-C light application as an alternative to eliminate pathogenic bacteria from fruit juices, while preserving convenient amount of vitamins and entitled these kind of food products as "light processed". Ultraviolet light treatment of foods is a physical method of preservation which is free of waste and chemical residues. Therefore, this method is ecologically friendly, does not produce by-products and is safe to use. Based on the recent scientific data and engineering studies, ultraviolet light technology offers the enhancement of microbiological safety of food products and improvent of the quality parameters such as flavor, color and texture to a value closer to those of non-treated food materials. Application of UV-C light technology during storage simultaneously with cold storage at optimum temperatures causes the initial microbial load to decrease and also retards the microbial growth. The aim of this study is to identify the spoilage conditions of frequently cold stored food products such as red meat and tomato paste, and to determine the optimum UV-C light processing parameters which maximize the quality and shelf life of these food products. Various studies have been made to investigate effects of ultraviolet light processing on the properties of food materials. For this purpose, the effects of UV light on the quality of the food material are being investigated besides the effects on microorganisms present in food materials. Nutritional value, texture, flavor and color are the basic attributes of food material which is influential on the consumer choice. Such attributes of the food material should be remained unchanged during ultraviolet light application, therefore the studies made on the novel techniques should also tend towards controlling the stability of these attributes besides ensuring the microbiological safety of the food material. Ultraviolet light technology is used for different applications in the food industry. Equipment sterilization in milk industry, meat industry and bakery industry, sterilization of packaging materials such as boxes, tubes and bottles, and decontamination processing conveyors are the main applications of UV technology. Besides the affectivity of UV light on the sterilization of surfaces, there is a limited application field in food processing operations. However, studies on the practicality of UV light for the sterilization of food surfaces is gaining significant attention. Frequently studied food materials are ready to eat meat products, bread, eggs, fish, fruits, vegetables and powders. In general, ultraviolet light technology does not have adverse effects on food materials. But, when the food material is exposed by high doses of UV light, undesirable changes may occur. Changes and modifications made on the ultraviolet technology equipments would contribute to achieve process conditions which can reach high inactivation levels without adverse effects. For this reason, ultraviolet light application is a promising technology which can overcome the undesired effects of thermal processes. Successful studies and applications of ultraviolet light technology on the prevention of mould growth on fruit and vegetables, and on the improvement of shelf life of perishable fresh foods were made by researchers. Also, studies on the subject of improving the quality and shelf life of foods stored in cold such as veal, chicken, fish, milk and milk products, charcuterie products and canned foods are being made. In the present study, the effects of ultraviolet light application on the quality and shelf life of red meat and tomato paste was studied. UV application doses were chosen by searching the technical sources and testing initial samples as 1, 3, 5 and 8 minutes for meat samples and 1, 2.5 and 5 minutes for tomato paste samples. Fillet cut red meat and tomato paste samples were stored in the refrigerator at 4 °C after UV light application. Thiobarbituric acid reactive substances assay, pH and color assays, total viable mesophilic aerobic bacteria and lactic acid bacteria count assay, and sensory analyzes were made daily on red meat samples for 7 days. Tomato paste samples were stored in refrigerator for 19 days after UV application. Color and pH assays, titration acidity analyze, water soluble dry matter and Howard mould count assays were made on tomato paste samples at specific days. The potential of ultraviolet light application to prolong the shelf life of red meat depends on both the initial microbial load and also the processing stage in which the application is made. Microbial inactivation data obtained in this work shows that the lactic acid bacteria count can be reduced and corresponding sensory changes can be prevented when the UV light application is made in a refrigerator. Also the application dose should be chosen responsibly to both achieve the microbial inactivation and prevent the undesirable chemical and physical changes. Meat samples subjected to the highest dose (8 mins) were the ones which lost its redness most. These samples reached the highest hue angle value of h=1.30, and it can be said that the samples were browned. Low dose applications (1 and 3 mins) does not affect the TBARS value, while higher doses increases the level of oxidation products. Acceptability of the samples reached to the lowest level at 4th day. Samples subjected to UV light for 1 and 3 mins preserved their original color for longer, but the increase in the off-odor formation increased with the increasing doses. Considering the effects UV light on tomato paste samples, pH values rises by 1-1.5% during the self-life while the least rise was for control samples. Initial a*/b* color value was 1.47. According to this, it can be said that the product was not of high quality in the aspect of color. The effect of UV light on the original color of tomato paste was seen to be insignificant. When the mould surface zones were analyzed, 5 minutes of application had the most effective microbial inactivation. In the aspect of domestic consumption, application of UV light on tomato paste offers a promising potential for retarding surface moulding and extending shelf life. During the shelf life, visible surface mould, black spots or any other abnormal appearance was not seen in the sensory analyzes. It is concluded that the samples subjected to 2.5 minutes of UV application were in a more acceptable quality opposed to other applications and control samples. Different doses of ultraviolet applications can be studied, analyzed and applied to specific food materials and the optimum doses can be determined. Besides this, UV application partitions in refrigerators can be designed for various food materials and the rapid deterioration occurring after the package unsealed can be slowed down. The effects of UV light on different food materials are varied, the recommended optimum doses are of 0.2-0.6 J/cm2 for the food products investigated in this research. Applications on various food materials can be made in the ongoing researches, and this would be a significant contribution on the implementation of UV light application combined with household cold storage methods.