Determination of hmf kinetics in different temperature and duration combinations of two commercial tomato pastes

In this study, the effects of heat treatments applied at different temperatures and times on two different tomato paste samples obtained from a local market in Bursa were investigated. In the experimental study, dry matter, pH, water activity, color (L*, a*, b*, C*, h), glucose, fructose, sucrose and hydroxymethylfurfural (HMF) contents of the pastes were analyzed after heat treatment at 150, 170 and 190 °C for 0, 5, 10, 15, 20, 25 and 30 min. The average contents of glucose, fructose and sucrose were measured in the ranges of 1.99–2.33; 2.12–2.41; and 0.17–0.22 g/100 g dry matter, respectively. In the color analyses, the L* value increased slightly with time, but decreased as the temperature increased, approaching the initial value again. As the temperature increased, a decrease of 26.5–34.5–32.7% in a* value, 39.3–49.5–49.5% in b* value, 30–41–55% in C* value and 15–17.5–16% in Hue value was observed. These changes show that the color of the tomato paste darkens, loses its brightness and the red-yellow tones decrease. HMF is evaluated as an indicator of the severity of processing and quality changes in foods exposed to heat treatment. Due to its toxic effects, monitoring of HMF levels in foods is of great importance for health. As expected in this study, an increase in the amount of HMF was observed as the processing time increased. The average HMF levels increased in the range of 30.24–58.75 mg/100 g dry matter. HMF formation was detected in both high temperature-short time and low temperature-long time conditions; however, it was determined that this formation occurred faster at high temperatures. Therefore, decreasing the temperature and extending the time limits the formation of HMF while affecting the product quality less. As a result of kinetic analyses, it was determined that HMF formation obeys zero-order reaction kinetics. Reaction rate constants (k) were determined as 0.78–1.05–1.72 mg/100 g dry matter min for the first paste and 0.78–1.23–1.74 mg/100 g dry matter min for the second paste at 150, 170 and 190 °C, respectively. Activation energies (Ea) were calculated as 32.00 kJ/mol and 32.50 kJ/mol, respectively; frequency factors (k₀) were calculated as 6634 and 8103 mg/100 g dry matter min. In addition, although the correlation between HMF and other parameters changed as the temperature increased, it was found that it generally showed a negative correlation with sugar contents at all temperatures. In further studies, it may be aimed to determine the process conditions where HMF formation is minimized by using different heat treatment techniques (e.g. microwave, infrared or vacuum heat treatment).