Introduction

Tomato (Lycopersicum esculentum) belongs to a family solanaceae [1]. Tomatoes are fruits but referred to as vegetables [2]. Tomatoes are one of the most cultivated and commercialized vegetable crop in the world [3-5]. The crop duration is relatively short, high yielding and is economically attractive. Its cultivation (area wise) is increased substantially in the recent past [6]. Tomatoes are mainly of three types; cultivars for industrial use, cultivars for fresh usage and cherry tomatoes [7]. It provides healthful and necessary nutrients in the human diet and is consumed either fresh as in salad or used as an ingredient in different food products [8-10].

Tomato contains 94-95% water and 5-6% organic compounds, of which almost one percent is seeds and skin [11,12]. The composition of tomatoes reveals that it contains substantial amount of vitamins, minerals, sugars, essential amino acids and dietary fibers. It is a rich source of iron, phosphorus, vitamin B and C [13-15]. It is very rich source of lycopene in the human diet, and among all dietary carotenoids, it has the highest antioxidative properties [6,16,17]. Tomatoes and products made from tomatoes are also the rich sources of quercetin and kaempferol, which exist together in the form of conjugates [18,19]. It also contains chlorogenic acid and a flavanone (naringenin). Tomatoes are ranked first in case of the total consumption of phenols [18].

The beneficial aspects of tomatoes in the human diet is mostly attributed to it protections against prostate cancer, cardiovascular diseases and neurodegenerative diseases, which is provided by lycopene, antioxidant and phyto-chemicals in the fruit [20-23]. Lycopene and other compound present in the fruit acts as a radical scavenger [24]. Anti-oxidant destroys and neutralizes free radicals, which results in the oxidative damages of the biological molecules i.e. lipids, protein and nucleic acids [25,26]. The presence of phenolic compounds functions as anti-allergic, anti-thrombotic and anti-inflammatory and plays an important role against neurological and cardiovascular disease [27]. The processed products made from tomatoes include purees, pastes, ketchup and juices. Their shelf life has been increased to a great extent by canning and drying [6,28]. It is very important to extend the shelf life of the tomatoes for domestic market and exporting [29]. Dehydration of tomato is one the oldest process used to overcome the losses of tomato by extending the storage life [20]. It can be preserved by different methods such as canning, bottling and by using chemical preservatives [30].

The usage of spices has increased significantly in the recent years because of its preservative role. Some studies provide information on their inhibitory role against microbial contamination [31-33]. Over all spices cannot help in the preservation of food. Some provide only flavor to food like vinegar, some act as an antimicrobial which help the food to preserve it for long time like salts and garlic. The usage of herbs in large quantity leads to high flavor, texture, when used in the commodities like soups; whereas when exposed to high quantity of salts no detrimental changes were observed [34]. Spices are used in tomato ketchup along with salt, sugar and vinegar with other optional ingredients (starches, onions, garlic etc.), where the proportion of tomato solids must not be less than 12% and is the most highly consumed products [35]. The current study is designed keeping in view the effect of natural additives i.e. spices and salt on the physicochemical, microbial and sensory attributes of tomato cubes during storage period.

Materials and Methods

Tomato, garlic, onion, salt, ginger, red pepper, turmeric powder, coriander powder and cumin powder were purchased from the local market at Peshawar, and were brought to the laboratory of Pakistan Council of Scientific and Industrial Research (PCSIR), Peshawar for research work.

Preparation of Tomato Cubes

Tomatoes were washed and the unwanted portions as well as diseased tomatoes were removed. The tomatoes were slashed into four equal halves and the pulp was extracted through Pulper machine. Garlic, onion and ginger were first peeled and cut into small pieces and the pulp were extracted through Pulper machine. Garlic, onion and ginger pulp as well as salt, red pepper, turmeric powder, coriander powder and cumin powder were mixed with the tomato pulp. The mixtures were then heated until the moisture content reduced to 22 percent. After heating, the mixtures were put in a cube shaped plastic mould. Then the cubes were placed in an oven at a temperature of 60 0C to avoid moisture absorption. The standard protocol of Amankwah et al. (2006) [36] was used by modifying the time for heat treatment and the amount of additives.

Physicochemical Analysis

Physicochemical properties such as total soluble solids, titratable acidity, moisture and ash contents were determined following the standard method of AOAC (2012) [37].

Sensory Evaluation

The 9-point hedonic scale of Larmond (1977) [38] was used for sensory evaluation. On the basis of experience in sensory analysis, 15 judges were selected. The quality characteristics including taste, color, flavor and overall acceptability were estimated by taking the mean value of final decision of the panelists. The panelist expresses the results in term of hedonic scale (1-9), where 9 exhibit strong liking and 1 express strong disliking.

Statistical Analysis

The data were analyzed statistically by using 2-factorial Completely Randomized Design (CRD) and means were separated by LSD test at 0.05% significant level [39].

Results and Discussion

Total Soluble Solids of Cubes

The effect of storage and treatments on total soluble solids of tomato cubes stored at room temperature is presented in Table 1, 2. Statistically analyzed data showed that storage and treatments had significant (p <0.05) effect on TSS of tomato cubes. The results showed that total soluble solids were significantly increased during storage. At initial day of storage of tomato cubes, total soluble solids were found in the range of 27.0 to 30.0. But on the other hand, after 90 days’ interval storage, total soluble solids raised (27.8-33.0). The results are similar to the findings of (Rohani et al. 1979) [40], who studied TSS of tomato paste in the range of 25.5 to 31.3. Total soluble solids fluctuate during storage due to different factors. Temperature is one of the main factors which affect total soluble solids during storage [41]. Similarly, total soluble solids are also related to moisture content i.e. increase in moisture content cause dilution effect of solids [42].

Titratable Acidity of Cubes

Titratable acidity of tomato cubes had significantly (p<0.05) different from each other. The results showed that higher acidity was found in LS0 (3.04 %) whereas lower total acidity (1.41%) was observed in LS5 at initial day of storage (Table 3). It was observed from the results that titratable acidity increased with the storage intervals in the range of 1.80 % to 5 %. Titratable acidity may be affected by the temperature and presence of sugar content in fruits and also influenced by the conversion of starch into sugar [43,44]. It might be increased by the influence of spoilage organisms which can secrete some substance into the samples [45].

Moisture (%) of Cubes

Statistical results indicate that treatments and storage period had significant (p<0.05) influence on moisture content of tomato cubes (Table 4). The moisture content was observed in the range of 21.44 % (LS3) to 23.35 % (LS1) at the storage of tomato cubes after 90 days. But at initial day of storage the moisture content was found in the range of 22.87 to 21.9%. The results indicated that moisture content decreased significantly during storage. The results are similar with the findings of the article by [46]. They observed moisture content of 16-27 % in tomato cubes. Moisture content of any food product during storage depends on the processing time and storage temperature [47]. Lodge and Whalley (1981) [48] concluded that moisture content and water activity are directly proportional to each other. The higher the moisture content the higher the water activity and vice versa.

Sensory Evaluation of Tomato Cubes

Color Measurement

The results of stored treatments of tomato cubes are presented in Table 5. Statistically both storage and treatments had significant (p <0.05) effect on color of tomato cubes. Maximum score of 7.56 was given to LS3, whereas minimum score of 5.90 was given to LS0 by the panelists. Maximum rating of 8.20 was observed at day one, while minimum rating of 5.55 was observed at 90 days’ storage interval. Throughout the storage, the highest fall in color was recorded in LS0 (48.72%), while lowest fall was observed in LS3 (20.24%). Lycopene is the color pigment of tomato, which is affected by the addition of sodium chloride and heat treatment [20]. It was also observed that the color of tomato product might also be influenced by drying time [49,50].

Taste

The effect of storage duration and treatments on taste of tomato cubes stored at room temperature is presented in Table 6. Statistically both storage and treatments had significant (p<0.05) impact on taste of tomato cubes. Higher score of 7.50 were obtained by LS4, whereas lower score of 6.34 were obtained by LS0 of tomato cubes. Maximum taste score (8.53) was observed at day one, while lowest taste score (5.82) was observed at day 90 of storage interval. Throughout the storage period, the highest fall in taste was recorded in LS0 (46.34%) while lowest fall was observed in LS3 (26.44%). Among treatments, maximum mean score was observed in treatment having fewer spices (8.14), while minimum was recorded (2.29) in the treatment having maximum concentration of spices. The result of analyzed samples showed a linear decrease for taste among treatments during storage periods. Increase in the concentration of spices beyond optimum amounts may, however, reduce the taste ratings thus requiring optimization. However, dried tomato was shown to maintain acceptable sweetness ratings within a study period of two months [51].

Flavor

Table 7 shows the impact of flavor on tomato cubes. Statistically both storage and treatments had significant (p<0.05) influence on flavor. LS3 was given maximum score (7.47) for flavor, whereas LS0 was given minimum score (6.44) by the sensory panels. Higher score for flavor (8.38) was observed at day one while lower score (5.70) was observed at 90 days of storage interval. During the storage period, highest fall in flavor score was recorded in LS0 (41.98%) while lowest fall was observed in LS3 (23.53%). Among the various samples, maximum mean score was recorded (8.05) in treatments having maximum proportion of spices, while minimum mean score was observed in treatments having minimum proportion of spices (4.71). The results pertaining to the response of flavor on the storage interval of the candies prepared from tomato paste. The mean scores of judges for flavor significantly decreased from 8.25 to 4.92 during storage [52].

Overall Acceptability

The impact of storage and treatments on over all acceptability of tomato cubes stored at room temperature are presented in Table 8. Statistically, both storage and treatments had significant (p<0.05) effect on over all acceptability of tomato cubes. LS3 got the highest acceptance score (7.77), whereas LS0 obtained the lowest acceptance scores (5.89) among the tomato cube samples. Likewise, higher overall acceptability (8.28) was observed at day one, while lowest (5.37) was observed at day 90 of storage interval. In the whole period of the storage, the maximum decline in overall acceptability rating was recorded in LS0 (49.37%) while lowest decline was observed in LS3 (19.77%) followed by LS4 (25.88%). Overall acceptability generally related to all sensory attributes. It is reported that the acceptability of fruits and vegetables is influenced by their flavor and taste. The overall acceptability of intermediate moisture product decreased significantly during keeping period [53]. Maximum mean score was recorded in samples having maximum amount of spices, while minimum mean score was observed in the sample having minimum amount of spices.

Conclusion

Tomato cubes were prepared by the addition of various spices and salt due to their preservative role. It was concluded that the sample LS3 was found best, followed by LS4 on the basis of physicochemical analysis, and sensory analysis. During storage a decrease in moisture color, flavor, taste and over all acceptability were observed, while an increase in TSS, acidity and ash content were observed. All the formulations are acceptable considerably, but the formulation that is used in LS3 is recommended for the preparation of tomato cubes.

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