PRESERVATION OF GRAPE TOMATOES
Tomato is a summer fruit. In our country, the use of fresh tomatoes in other seasons is ensured by cultivating in the summer. Tomatoes are imported and exported to different regions. Storage and protection methods also vary according to the conditions of use. One of the most used methods is Freezing. This method facilitates the use of tomatoes picked in summer in other seasons. Since the vitamin C (Ascorbic acid) in tomato content is phenolic and carotenoid (especially lycopene), it has an important place in human health. Especially during the pandemic, its importance has become more evident. Grape tomatoes should be stored at 10°C and above in order to prevent chilling injury after harvest.
The method of preservation by freezing is one of the methods that provides the best preservation of the natural structure, appearance, color, flavor and composition of foods. While the activities of enzymes found naturally in the structure of the food and various chemical reactions slow down significantly in frozen foods, microbial developments stop completely. The basic principle of the freezing process is to transform the water in the grape tomato into ice crystals so that the food is not affected by chemical, enzymatic and microbiological spoilage. With this method, it is aimed to preserve the long-term quality food of freshly picked tomatoes. Because tomatoes are a very perishable food.
Freezing can be done in many different ways.
Freezing with atmospheric pressure is one of the methods for long-term protection. Slow deterioration is seen in this freezing process. These; Freezing temperatures occur with crystallization of water, microbial growth reactions. However, it may cause mechanical and chemical deterioration in cellular tissues due to cell dehydration and ice crystal formation. As a result of these reactions, nutrient loss, color change and tissue deterioration occur.
The isochoric freezing system prevents the formation of ice in the food and allows it to be preserved at temperatures below freezing. At the same time, the isochoric system consists of a fixed-volume chamber that can withstand pressures. In the preliminary stage, tomatoes are immersed in isotonic liquid and brought to sub-freezing temperature. The principle of this method is that ice is formed in the solution during freezing. The volume of ice increases, increasing the pressure in the room. In this way, the outer surface of the food remains undissolved. Consequently, the food can be stored below freezing temperature without the formation of ice. This is impossible with other conventional preservation methods. This method has been found to be more energy efficient during storage and transportation than traditional preservation methods.
As a result of the research, there is not much difference between grape tomatoes kept at -2.5°C in fresh and isochoric methoda. It has been observed that the outer surfaces of tomatoes stored in cold (tradtional preserving at 10C) are wrinkled and dehydrated. They did not see much change in the color changes of the stored samples, but the view of the change was found to be yellow. Experts attributed this to enzymatic oxidative reactions to the reduction of carotenoid content in frozen tomatoes.
The ascorbic acid (Vitamin C) content of fresh grape tomatoes is approximately 196 mg / 100 g db. Tomatoes preserved in isochoric environment have shown that they retain their ascorbic acid properties for four weeks. In addition, losses in ascorbic acid properties occurred after two weeks in the isobaric and IQF method.
Lycopen is an important ingredient in tomatoes because of its antioxidant properties and its red color. As a result of the isochoric method, it was observed that 90% of the lycopene property of the tomato stored for 4 weeks was preserved. It has been observed that these changes are due to enzymatic activations because lycopene in tomatoes; It can be oxidized by the presence of enzymes such as peroxidase, catalase and lipase.
According to the researches, the positive effects of the isochoric storage method on tomatoes have been observed. It is an important method of preserving its content as well as physical deterioration that may occur outside the tomatoes.
References
1. Bilbao-Sainz, Cristina, et al. “Preservation of grape tomato by isochoric freezing.” Food Research International 143 (2021): 110228.
2. Rahman, M. Shafiur, and Jorge F. Velez-Ruiz. “Food preservation by freezing.” FOOD SCIENCE AND TECHNOLOGY-NEW YORK-MARCEL DEKKER- (1999): 259–284.
3. Ukponmwan, Ifueko. “Preservation of Tomatoes.” 5th International Conference on Biomedical Engineering and Technology: Preservation of Tomatoes. Vol. 81. 2015.
