Obtaining tomato powder using innovative drying methods, determining the quality characteristics of the powdered product and investigation of its storage stability

In this thesis study, the aim was to produce tomato paste powder using two innovative drying technologies: Infrared-Assisted Refractance Window Drying (IRRWD) and Ultrasound-Assisted Refractance Window Drying (USRWD). To achieve this, an existing Refractance Window Drying (RWD) system in the department was modified by integrating an infrared (IR) lamp controlled by a pyrometer. There is no previous study in the literature on drying tomato paste using the IRRWD system. In this study, tomato paste adjusted to a spreadable consistency was dried under optimized conditions using four different drying approaches (excluding hot air drying), and the most suitable method for producing tomato powder was determined. For IRRWD, the independent variables optimized were: circulating water temperature (60–90 °C), paste spreading thickness (2–3 mm), and product surface temperature (30–36 °C). A response surface methodology (Design Expert software, Optimal Custom Design) was used to optimize for maximum lycopene content, minimum browning index, and shortest drying time. The optimal conditions were determined as: water temperature 82 °C, spreading thickness 2 mm, and surface temperature 32 °C. To shorten drying time in the IRRWD system, foam drying (FM-IRRWD) was also applied. For foam formation, soy and pea protein isolates were used as foaming agents at a total of 1.5% of the tomato paste. The ideal whipping duration and protein isolate ratios were optimized using Design Expert (optimal combined mixture design) to maximize foam stability and capacity. The optimal conditions were: 1-minute whipping time, 0.4% soy protein, and 1.1% pea protein. To prevent non-enzymatic browning, reduce aroma loss, and improve volatile stability in IRRWD, two additional trials were conducted: one with 0.5% ascorbic acid and one with 1% β-cyclodextrin added to the paste before drying. A control test was also performed using the RWD system without the IR lamp to assess the effect of IR. For the USRWD system, an existing ultrasonic water bath was covered with Mylar film, and drying was carried out at the same optimal temperature (82 °C) and thickness (2 mm), using ultrasonic power at 37–38 kHz. Conventional hot air drying (CHD) was also conducted for comparison. The physicochemical properties of tomato powders obtained from all methods were compared. The powders were stored at two different temperatures (4 °C and 25 °C), and changes in moisture content, water activity, color, HMF (5-hydroxymethylfurfural), total phenolics, lycopene, antioxidant activity, pH–titrable acidity, total sugars, ascorbic acid, and volatile compound composition were monitored. The drying times were as follows: IRRWD (40 min), FM-IRRWD (20 min), USRWD (50 min), RWD (55 min), and CHD (180 min). Lycopene content ranged from 157.54 to 257.53 mg/100g dry matter, with the highest levels in FM-IRRWD and USRWD powders. The lowest browning index was also recorded in these two methods. The highest antioxidant activity was found in the IRRWD sample with 0.5% ascorbic acid. Drying method had little effect on solubility, titratable acidity, and total sugar content, while total phenolics were higher in IRRWD and RWD powders. During storage, lycopene, ascorbic acid, and antioxidant activity significantly decreased, especially at 25 °C. HMF and total phenolic content increased. The main volatile component in all samples was 6-methyl-5-hepten-2-one, which decreased over time, more so at 25 °C. β-cyclodextrin was ineffective in preserving aroma components. Foam drying in the IRRWD system resulted in better aroma compound retention and lower HMF levels, indicating better suppression of non-enzymatic browning reactions. This approach was found to be the most effective for aroma stability. For the first time, drying kinetics and modeling were established for both IRRWD and USRWD systems using tomato paste, and the Newton model was identified as the best fit for both methods. Integration of IR into the RWD system significantly reduced drying time. Additionally, ascorbic acid addition and foam drying effectively mitigated the color degradation associated with IR, resulting in higher-quality tomato powder.