The tomato fruits, Gelilea hybrid variety grown on farmers' open-field were used for the dehydration process. Galilea is a hybrid tomato variety released by Hazera Genetics Ltd., Israel (MANR, 2016) produced by Hazera Seeds Ltd, South Africa (Pty) and commercially supplied in Ethiopia by Greenlife Trading PLC. The variety is high-quality Roma-type fruit with a high yield and wide range of resistances, good for bush and stacking production, adapted for various climates, and suitable for processing (https://hazeraafrica.com/?s=galilea, October 2021). Thus, it is preferred by most of the producers and processing industries. Chemical and standards such as polyphenol standards (gallic acid, tannic acid, and catechin) with > 97.5% purity, FolinCiocâlteu reagent, aluminum chloride, oxalic acid, ascorbic acid, sodium nitrite, 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 6-dichlorophenol indophenol dye were also used.

The data generated from laboratory analysis were subjected to analysis of variance (ANOVA) using the GenStat 18th Edition (64 bit) statistical software and GraphPad 8.0.2. Treatment differences were determined using Fisher's LSD (Least Significant Difference Test) at a 5% level of significance.

Dehydration temperature significantly (P < 0.001) reduced moisture contents of dehydrated powders of tomato while dehydration time had no significant difference.

As it can be predicted, the maximum moisture content (92.58%) was obtained from fresh tomatoes (Table 1). The exclusive comparison of dehydrated tomatoes showed that the maximum moisture content (12.18%) was obtained at 70°C while the minimum (9.39%) was at 90°C dehydration temperatures. The decrease in moisture content with increasing temperature is accompanied by an increased percentage of TSS since it is the major component of dry matter. This result is supported by Abe-Inge et al. (2018). Food products with high moisture content are suitable for microbial development causing product spoilage. Therefore, such food products would have a shorter shelf life (Lewicki, 1998). Abdullahi et al. (2016) reported a reduced microbial growth on dehydrated tomatoes with lower moisture content. The lower moisture content of the tomato powder might reduce the probability of microbial development and potentially extends shelf life.

Both pH and TA were significantly (P < 0.01 and P < 0.001 respectively) influenced by dehydration temperature and time length. The maximum pH value (4.567) was recorded from fresh tomato fruits whereas the minimum (4.333) was obtained at 90°C with 13 h dehydration temperature and time length respectively. Dehydrated tomato powders showed a reduction in pH values compared with fresh fruits. pH values were decreasing along with the increasing dehydration temperature and time (Table 1). On the contrary, Alfeo et al. (2021) reported no significant difference in pH values among dehydration temperatures of 50, 60, and 70°C. However, a decrease in pH value has been reported by Yusufe et al. (2017) from tomato slices dehydrated at 90°C for 8 h.

Titratable acidity (TA) was also increased with increasing temperature and time length. The maximum TA (0.4967%) was obtained at 90°C dehydration for 11 h (Figure 2). This result was statistically similar with the same temperature but 13 h of dehydration time. Previous studies (Khazaei et al., 2008) also reported an increase in TA with increasing dehydration temperature. The increase in TA with dehydration temperature and time might be due that organic acids in dehydrated tomatoes became more concentrated. The minimum TA (0.0433%) was observed from fresh tomatoes followed by the lowest dehydration temperature of 70°C and 9 h dehydration time (0.2867%). When dehydration time is extended from 11 to 13 h at a constant temperature of 90°C, there was about a 20.13% reduction in TA content (Table 2). This might be due to acetic acid degradation by higher temperatures. This result is consistent with several studies (Khazaei et al., 2008; Aderibigbe et al., 2018) that reported degradation of citric acid at higher temperatures with extended dehydration time.

pH and titratable acidity (TA) contents are associated with the amount of citric acid. Citric acid is the most important acid present in tomatoes. A high value of citric acid is associated with a satisfactory acidic flavor (Yusufe et al., 2017). It has been reported that tomato fruits with below 4.5 pH values are desirable to cease the proliferation of microorganisms after industrial processing (Qiu et al., 2017). TA and pH are interrelated in terms of acidity but have different impacts on food quality. While TA influences more on the flavor and taste of products, pH provides a degree of strength of acidity (Ma et al., 2012; Aderibigbe et al., 2018). Lower pH provides more inhibition of microbial growth (Cases, 2021). So, acidity contributes to both food taste and food safety.

There was a significant (P < 0.001) change in vitamin C content of dehydrated tomato powders compared with fresh tomato fruits (Figure 3; Table 1). Vitamin C content significantly decreased with increasing temperature while dehydration time had no significant influence (Figure 3). The result is consistent with Dewanto et al. (2002) who testified a decreased vitamin C content with a dehydration temperature at 88°C. Many other authors (Ashebir et al., 2009; Arslan and Özcan, 2011; Basri and Aziz, 2012) also reported Vitamin C reduction with increasing temperature. It might probably be due to the thermos-sensitivity of ascorbic acid. Basri and Aziz (2012) justified that the decrease in vitamin C contents with increasing processing temperature is due to Vitamin C being a very heat-labile component. Thus, vitamin C retention is affected by thermal processing. Dewanto et al. (2002) further clarified that loss of vitamin C occurs primarily by chemical degradation involving oxidation of ascorbic acid into dehydroascorbic acid (DHAA); then, the DHAA is hydrolyzed into 2, 3-diketogulonic acid which finally forms nutritionally inactive products.

Both the sole implementation and interaction of dehydration temperature and duration of time significantly (P < 0.001) influenced the TSS content of dehydrated tomatoes (Table 2). The maximum TSS content (7.433 °Brix) (Figure 4) was recorded when tomatoes are dehydrated at 80°C for 11 h which was statistically at par with 90°C^*11 h, 80°C^*13 h and 90°C ^*13 h. Whereas the minimum TSS (4.467°Brix) was observed from fresh tomatoes followed by dehydration at 70°C for 9 h. This result was in line with Alfeo et al. (2021) who observed an increased TSS with increasing temperature (50 to 60 then up to 70°C). Ashebir et al. (2009) also reported increased TSS with increasing temperature from 55, to 65 to 75°C. TSS content is one of the most crucial quality parameters in processed tomatoes. 50–65% of soluble solid contents are sugars, glucose and fructose, and their amount and proportion influence the organoleptic quality of tomatoes (Basri and Aziz, 2012). Thus, increased TSS with temperature and dehydration time might assure that there was a decrease in moisture content. On the other hand, dehydration temperatures beyond 80°C decreased the TSS content even though the change was not significant. Consistently, TSS contents were reportedly decreased after 80°C and extended dehydration time (Khazaei et al., 2008; Yusufe et al., 2017). The higher temperatures along with longer dehydration time lengths may be attributed to degrade sugars (Basri and Aziz, 2012).

There was a significant difference (P < 0.001) in the lycopene content of fresh and dehydrated tomatoes as well as within dehydrated tomatoes. Increasing dehydration temperature from 70 to 80°C significantly increased lycopene content (Table 3; Figure 5). On the other hand, dehydration time and its interaction with temperature had no significant difference. It may indicate that lycopene degradation is more sensitive for a higher temperature than time length.

The apparent increase in lycopene after dehydration is attributed to the loss of water and concentrated lycopene in the dehydrated product. Basri and Aziz (2012) reported similar findings. Maximum lycopene content (0.4512 mg/100 g) was obtained at 80°C dehydration temperature for 11 h (Table 3) whereas the minimum (0.2 mg/100 g) was recorded from fresh tomato fruits. This finding is in line with Dewanto et al. (2002) who observed an increased lycopene content up to 88°C. However, lycopene content was declined at 90°C despite the reduction was not significant (Figure 5). It may also indicate that extreme temperatures damage the lycopene pigments. This assumption is in agreement with Akanbi and Oludemi (2004) who reported lower lycopene contents in processed tomatoes. Amaya (1997) stated that the red color appears when lycopene is formed in the tomato fruit fibers. The attractive red color of the tomato fruit and its products is due to the presence of lycopene (Basri and Aziz, 2012). Therefore, dehydration methods with higher lycopene contents can be considered best for consumer preference.

Product color is another quality parameter that needs to be maintained during tomato processing. There was no significant difference in the color of fresh fruits and tomato powders dehydrated at lower dehydration temperatures for a shorter time length. However, significantly different L^*, a^* and b^* values of tomato powders were observed at interaction effects of higher temperatures and longer dehydration times, i.e., 80°C ^*11 h, 80°C ^*13 h, 90°C ^*11 h, and 13°C ^*13 h. When the temperature was increased with time length, the L^* (brightness), a^* (redness) and b^* (yellowness) values were decreased (Table 3). In line with this result, Arslan and Özcan (2011) reported reduced L^*, a^* and b^* values of dehydrated tomatoes compared with fresh fruits. Ashebir et al. (2009) and Arslan and Özcan (2011) also reported decreased L^* values of tomato slices with increasing dehydration temperature. The reduction in brightness (L^* value) of dehydrated products is likely. The color change can be either due to pigment degradation or browning reaction or both during dehydration (Akanbi and Oludemi, 2004; Mwende et al., 2018). The color change is associated with quality reduction. Hence dehydration of tomatoes with higher temperatures may reduce consumers' acceptability.

Significant (P < 0.01) changes have been observed in the rehydration ratio of dehydrated tomato powders in response to dehydration temperature and time length. The maximum rehydration ratio (4.347) was recorded at the maximum temperature (90°C) with 13 h time length, followed by the same temperature with 11 h time length (Figure 6; Table 2). Rehydration is the process of moisturizing a dehydrated material with abundant water (Lewicki, 1998). It is also considered as a measure of structural injury to the processed product caused by dehydration (Singh and Heldman, 2014). Whereas rehydration represents the ability of the same product for restoring its fresh quality in rehydration solution (Zhang et al., 2017). Consequently, the increased rehydration ratio with increasing temperature and time duration implies that the physical structure of tomato powder was not harshly damaged by increased temperature and time. So that it was able to promote better reabsorption and reconstitution of the product. Ghavidel and Davoodi (2010) reported similar findings from solar and tunnel dehydration methods. Farooq et al. (2020) observed a bit less rehydration ratio ranging from 1.51–1.82 for hot-air-dehydrated tomato powders. The difference is attributed to differences in a variety having different dry matter content. Dehydrated powders with higher dry matter content have lower moisture content so a higher rehydration ratio (Farooq et al., 2020). Increased attraction of water results in increased flow into the tissue and therefore improved rehydration (Ghavidel and Davoodi, 2010).