Effects of dehydrofreezing conditions on tomato lycopene and kinetics of lycopene change in dehydrofrozen tomatoes during storage

Abstract In the study, the change in lycopene content of tomatoes, which were frozen either fresh or after being partially dehydrated with different methods (convective, osmotic, and vacuum dehydration) during the 6‐month storage at −20°C was investigated. In the freezing process, tomatoes were frozen at 2 m/s air flow velocity by convective method and at different freezing temperatures (−30, −35, −40°C) and cryogenic method up to the thermal center temperature of the samples reaches to −20°C. It was determined that the reaction representing the lycopene change during the storage process occurred in accordance with the first‐order kinetic model. The reaction rate constants ( k ) determined for the lycopene change during the storage process of the tomatoes frozen by the convective method were found to be affected by freezing conditions and the results revealed that the k value decreased with reducing temperature. It was found that the half‐life time of the lycopene change reaction during the storage period increased as the freezing temperature decreased in the tomatoes frozen by the convective method. In general, it was seen that in terms of lycopene preservation of tomatoes, freezing of tomatoes with cryogenic method after being dehydrated by vacuum and osmotic treatment gave better results The lycopene loss at the end of the 6‐month storage was determined to be 46.4% in the tomatoes frozen by the cryogenic method after being dehydrated by the osmotic treatment, whereas it was 64% in the samples that were freshly frozen at −30°C. Practical applications Dehydrofreezing is a food freezing method in which the foods are partially dehydrated and then frozen. Traditional freezing methods cause serious damage to the vegetal products. Reducing the water that will be frozen in the dehydrofreezing process allows to form ice crystals without damaging the cellular structure of vegetables. Because of the reduction of tissue damage, sensitive nutrients are less affected by process conditions. As a result; for food producers, dehydrofreezing technology seems to be more advantageous as it means less processing time, more weight product for unit volume and high quality products. In conclusion, according to the results, freezing the tomatoes by dehydrofreezing method gives better results to protect the tomato lycopene during storage.