Influence of postharvest putrescine application on respiration rate and physicochemical properties of tomato

Abstract

Background

Tomato (Solanum lycopersicum L.) is a species of vegetable that is widely consumed worldwide and has high nutritional value. However, during storage, quality losses occur, especially water loss, decay, acidity loss and vitamin reduction. In this study, the effect of putrescine applications was investigated in order to reduce quality loss in tomatoes during storage. Putrescine is a compound belonging to the polyamine class and provides potential benefits such as delaying fruit ripening, reducing respiration rate and preserving quality. Putrescine solutions were prepared at concentrations of 0.5 mM, 1 mM and 1.5 mM, and sprayed homogeneously onto the surface of tomato fruit for 15–20 s, kept at room temperature and then placed in storage conditions.

Results

In the study, the changes were observed in weight loss, decay rate, pH and titratable acidity rates in tomatoes as storage period increased. The weight loss rate increased up to 9.31%, putrescine applications reduced this loss to 4.24% especially with the highest dose of 1.5 mM. Putrescine was also effective in preventing fruit decay; at 1.5 mM dose, the decay rate decreased to 7.81%, while in the control group this rate was recorded as 8.76%. Putrescine applications also improved the content of organic acids and vitamin C. During storage, the decrease in organic acids slowed down and the loss of vitamin C remained at lower levels compared to the control group. In addition, putrescine applications maintained the acidic structure of the fruit by controlling the pH and titratable acidity. Respiration rate was kept low by putrescine, which delayed the fruit ripening process. All these findings show that putrescine maintains the fruit quality and extends the shelf life.

Conclusion

As a result, putrescine applications play an important role in reducing quality losses during the storage period of tomatoes. Putrescine particularly prevents fruit weight loss, decay, organic acid loss and vitamin C reduction. It also delays the ripening process by slowing down the fruit respiration rate and maintains the nutritional value of the fruit. This study suggests that polyamines such as putrescine offer a potential treatment option for fruit preservation and shelf life extension. Putrescine applications can reduce economic losses by maintaining quality under storage conditions, especially for fruit such as tomatoes.

Background

Tomato (Solanum lycopersicum L.) is a species of vegetable that is widely grown and consumed worldwide, providing high nutritional value and significant health benefits. It plays an important role in reducing the risk of cancer and cardiovascular disease, especially with the carotenoids it contains, such as β-carotene and lycopene [1, 2]. In addition, these compounds, which have antioxidant properties, reduce oxidative stress by preventing the accumulation of free radicals in the body [3]. Tomatoes are also rich in other important nutrients such as vitamin C, flavonoids and vitamin E [4]. Therefore, they have great economic importance both for fresh consumption and for the processing industry. However, the shelf life, quality and storage conditions of tomatoes are important factors that directly affect production efficiency and consumer satisfaction. Post-harvest quality losses are therefore one of the most important problems encountered in the production and consumption processes of tomatoes. Tomato is a species of vegetables that exhibits climacteric characteristics, that is, it continues to ripen after harvest. This characteristic increases the rate of deterioration of the tomato, limiting its shelf life [5, 6]. Climacteric fruit are characterized by the production of ethylene, which accelerates ripening, leading to rapid softening of the tomato, color change and water loss. The sensitivity of tomatoes in this process makes their storage and transportation processes quite difficult. Since the fruit has a high water content, quality losses can reach serious levels, especially when stored in hot and humid environments. The main problems encountered by tomatoes during storage include increased respiration rate, increased ethylene production, susceptibility to cold damage, microbial spoilage and wrinkles caused by dehydration [7]. Especially in developing countries, the post-harvest losses can reach up to 50% due to these problems [8]. Although cold storage is a common method for extending the shelf life of tomatoes, the susceptibility of tomatoes to cold damage limits the using of this method [9]. The various methods have been developed to reduce post-harvest quality losses. The cold storage helps extend the shelf life of tomatoes, but it is a method that requires caution because it is sensitive to low temperatures. The storage temperatures of 13 °C are recommended for early harvested tomatoes and 5 °C for more mature fruit [10]. However, it is a known fact that synthetic chemicals and fungicides used to preserve tomato quality can harm the environment and human health [11]. (Therefore, the development of more natural and environmentally friendly alternatives is gaining importance. The modified atmosphere packaging method is effective in extending the shelf life by regulating fruit respiration. This method slows down the aging process of the fruit by balancing the oxygen and carbon dioxide levels [9]. In addition, the edible coatings applied to the surface of tomatoes maintain quality by preventing microbial spoilage [12]. The various genetic studies have also allowed the development of varieties with longer shelf life by controlling the ripening processes of tomatoes [13]. However, the limitations and possible side effects of the such studies should be considered [14].

Putrescine is an aliphatic polyamine found in plants and plays a role in various biological processes such as fruit development, ripening, and response to biotic and abiotic stresses. Putrescine is among the major polyamines and is usually found in cationic form at pH 5–6 in plant cells. Polyamines are important compounds that regulate basic biological functions such as cell division and cell elongation in plants, as well as the aging processes of plants [15]. In this context, polyamines are thought to have anti-aging properties. However, in most fruit and vegetables, polyamine levels decrease during ripening and aging, which negatively affects fruit tissue properties and shelf life. For this reason, several studies have been conducted on the potential of exogenous polyamine applications to improve fruit quality. In particular, putrescine may help preserve fruit quality by delaying fruit ripening. Previous studies on tropical and subtropical fruit show that putrescine applications slow down ripening and extend fruit shelf life [16, 17]. In addition, due to the antioxidant properties of polyamines, they can also reduce the effects of reactive oxygen species formed during fruit ripening. This helps maintain fruit quality by preventing cellular damage caused by oxidative stress [18]. The protective effect of putrescine against oxidative damage in fruit tissue is a frequently emphasized topic in studies in this field. Especially the antioxidant properties of putrescine related to H₂O₂ and O₂ radicals can prevent oxidative damage in fruit tissue and increase fruit quality [19]. The effects of polyamines on fruit quality and shelf life have been investigated in many studies and the results in this area are quite promising. In fruit such as strawberries, plums, mangoes and apricots, putrescine and other polyamines have been shown to help extend fruit shelf life by delaying the ripening process [20]. However, no study has been found in the literature on putrescine applications in tomatoes. Therefore, examining the effects of putrescine applications on fruit quality and biochemical properties in tomatoes is of great importance to fill the knowledge gap in this area.

The aim of this study was to investigate the effects of postharvest putrescine applications on tomato fruit quality and biochemical properties. Evaluation of the potential effects of putrescine on the ripening process, shelf life and quality of tomatoes may allow the development of a new method to maintain this fruit fresh and in good quality for a longer period of time.

Materials and methods

The fruit of the ‘Depar’ tomato variety (Solanum lycopersicum L.) used in the study were harvested in the early hours of the morning during the ripening period in the field belonging to a producer in Düzce (Türkiye) province in 2024 year, and fruit that had reached the ripening stage and had homogeneous size and color characteristics were carefully selected. The harvested fruit were collected without damage and immediately transported to the laboratory of Ege University and Bolu Abant İzzet Baysal University, Faculty of Agriculture, Department of Horticulture. Putrescine solutions were prepared at concentrations of 0.5 mM, 1 mM and 1.5 mM. Each application was applied by spraying homogeneously on the surface of tomato fruit. After the putrescine solution was sprayed on the fruit surface for approximately 15–20 s, the fruit were kept at room temperature for a while and then taken to storage conditions. The control group was treated with only water without any chemical application. The study was designed with 3 replications, 10 fruits in each replication, and a total of 120 fruits were used for each treatment. The fruit were stored at 4 °C for 21 days at 0 ± 0.5 °C and 90% ± 5% RH, and the following analyses were performed every 7 days (7, 14 and 21 days) 3 replicate samples were used in each analysis.

Weight loss (%)

At the beginning of the cold storage, initial weights (Wi) of the fruit were determined by a digital scale with a precision of 0.01 g (Radwag, Poland). Then, on d 7th, 14th, and 21st days of the storage, final weights (Wf) were determined. The weight loss that occurs in fruit was based on the weight at the beginning of each measurement period and determined as a percentage through the equation given below (Eq. 1).

$$\:\text{WL}=\frac{Wi-Wf}{Wi}\times100$$

(1)

Decay rate (%)

Before the cold storage, 10 fruit were used in each replication and the total number of fruit (TF) was determined. Then, during each measurement period, the decayed fruit (DF) in each replication were determined. If the development of mycelium on shell occurred, the fruit were considered rotten. Finally, with the following equation (Eq. 2), the decay rate (DR, %) was detected [2].

$$\:\text{DR}=\frac{TF-DF}{TF}\times100$$

(2)

SSC, pH, acidity and fruit flesh firmness

The juice was obtained by squeezing 10 fruit with a blender and passing through cheesecloth. SSC was analyzed by digital refractometer (Atago PAL 1) by taking enough of the obtained juice sample. pH value was measured with a digital pH meter (Metler Toledo). To determine titratable acidity, juice sample was taken from the obtained fruit juice, diluted with 10 mL distilled water, and titrated with 0.1 mol L^-1 (N) sodium hydroxide (NaOH) until the pH reached 8.1, and the amount of NaOH consumed in the titration was taken. It was expressed in terms of citric acid. The firmness of the fruit was assessed by applying a digital penetrometer (LOYKA GY-3) to the opposite sides of the equatorial region of five fruit, ensuring the device’s point was perpendicular to the surface [21].

Respiration rate

Five fruit were placed in airtight containers, and after a 2-hour waiting period, the amount of CO₂ released into the atmosphere was measured using a Headspace Gas Analyser GS3/L device (Gasboard-3210Plus). The respiration rate was expressed as ml CO₂/kg⁻¹ h⁻¹. Respiration Rate = (Vj – Vf) x %CO2 × 10 / FW x T,

Vj = Jar volume, Vf = Fruit volume, FW = Fruit Weight (kg), T = Time (Hour).

Organic acids and vitamin C

Fruit sample (15 g) was homogenized with 0.009 N H₂SO₄ in a 1:1 ratio and mixed on a shaker for 1 h. The samples were centrifuged at 15,000 rpm for 15 min. The supernatant was filtered through a 0.45 μm membrane filter and then through a SEP-PAK C18 cartridge for HPLC analysis. Organic acids were analyzed using the method developed by Bevilacqua and Califano [22]. on an HPLC (Agilent HPLC 1100 series G 1322 A, Germany) equipped with an Aminex HPX-87 H, 300 mm x 7.8 mm organic acids column (Bio-Rad Laboratories, Richmond, CA, USA). Vitamin C content was determined using a Reflectoquant Plus 10 device (Merck RQflex Plus 10, Turkey). A 0.5 mL sample of the juice extract was diluted to 5 mL with 0.5% oxalic acid. The ascorbic acid test kit (Catalog No: 116981, Merck, Germany) was briefly immersed in the solution for 2 s, left to oxidize for 8 s, and measured in the device’s test adapter after 15 s. Results were expressed as mg per 100 g [2].

Individual phenolic compounds

Individual phenolic compounds were determined using the method by Rodriguez-Delgado et al. [23]. In this method, 5 g of tomatoes fruit samples were mixed with distilled water in a 1:1 ratio and centrifuged at 15,000 rpm for 15 min. The supernatants were filtered through a coarse filter, followed by a 0.45 μm membrane filter, and then injected into the HPLC (Agilent HPLC 1100 series G 1322 A, Germany). Chromatographic separation was performed using a DAD detector and a 250 × 4.6 mm, 4 μm ODS column (HiChrom, USA).

Statistical analysis

In this study, data were analyzed using two-way ANOVA through the statistical software SAS 9.1 (SAS Institute Inc., Cary, NC, USA). The research was designed according to a randomized block design with 3 replications. Differences between means were evaluated with Tukey’s test at a significance level of p < 0.05. Data analysis was performed using the SAS Version 9.1 statistical software package (SAS Institute Inc., Cary, NC, USA). Heatmap clustering analysis and principal component analysis were conducted with the Jmp Pro 17 statistical software package.

Results and discussion

Weight loss

As the storage period progressed the weight loss of tomato fruit increased. The weight loss rate at the end of storage was recorded as 9.31%. This shows that tomatoes lost water during storage and lost mass due to deterioration (Table 1; Fig. 1(A)). Water loss is a common problem, especially during the shelf life of fresh fruit and vegetables, because the loss of water in the fruit tissues causes fruit to dry out and therefore lose quality [24]. Putrescine applications showed a reducing effect on this weight loss. Especially the highest putrescine dose of 1.5 mM reduced the weight loss to 4.24% on day 21, creating a significant difference compared to the control group. Other putrescine doses (0.5 mM and 1 mM) also reduced the weight loss in a similar way, but the most significant effect was observed at the highest dose. It is shown that putrescine has an effect on preventing water loss, especially in fruit and vegetables, and thus maintains the quality of tomatoes during storage. These observations show that water loss and spoilage lead to weight loss during fruit storage, and at the same time putrescine reduces this loss (Table 1; Fig. 1).

Table 1 Effect of Putrescine treatments on quality properties of tomato fruits during storage

Fig. 1

Effect of putrescine application on wight loss (A), decay rate (B), solouble solid content (C), pH (D), titratable acidity (E) and respiration rate (F) of tomato fruits during storage

Polyamines such as putrescine prevent water loss by reducing the permeability of cell membranes [25]. In addition, polyamines can inhibit ethylene biosynthesis and reduce respiration, which can prevent weight loss by reducing the metabolic rate of fruit [26]. Additionally, polyamine applications can strengthen cell walls and thus prevent water loss inside fruit [27]. Previous studies also support the effects of putrescine applications on reducing fruit weight loss. Kablan et al. [28] suggested that carbon loss in the respiratoion cycle may lead to weight loss. The weight loss reducing effects of putrescine have also been reported in such studies. In particular, Barman et al. [29] stated that putrescine reduces weight loss and alleviates cold injury by decreasing the respiration rate in pomegranate fruit. In addition, Archana and Suresh [30] showed that putrescine applications in banana fruit, especially 0.5 µM spermidine dose, reduced weight loss. Similarly, Shanbehpour et al. [31] reported that 1.0 and 2.0 µM putrescine doses in Indian plums resulted in lower weight losses compared to the control group. Tas et al. [32] reported that putrescine applications in cornelian cherry fruit resulted in significant weight loss reductions associated with lower respiration rates.

Decay ratio

It has been observed that the rate of decay in fruit increased as the storage period progresses. This shows that long-term storage triggers decay and the fruit begin to deteriorate over time (Table 1; Fig. 1(B)). These findings support those reported by Cantín et al. [33] that fruit spoilage varies depending on the fruit type and variety, but generally increases with the length of storage time. Putrescine applications have a significant protective effect in terms of preventing decay. Especially at the 1.5 mM dose, the decay rate decreased to 7.81% on the 21st day, and this rate remained at 8.76% in the control group. The doses of 0.5 mM and 1 mM were also effective in reducing decay, and there were significant differences between putrescine application doses on 21st day of storage. These results confirm the positive effects of polyamines on fruit decay (Table 1; Fig. 1). Hanif et al. [34] stated that polyamines have anti-pathogenic properties and reduce decay rates. In addition, Martínez-Romero [35] reported that putrescine applications significantly reduced fruit decay and preserved fruit quality. This is consistent with the findings in a study by Khosroshahi et al. [20] showing that putrescine-treated strawberries were suitable for marketing after 12 and 14 days of storage. The mechanisms by which putrescine and other polyamines reduce decay are related to various biological processes. Polyamines enhance defense responses against pathogens in fruit tissues and promote the accumulation of protective compounds that inhibit decay. Yamakawa et al. [36] stated that polyamines function as signaling molecules that trigger defense mechanisms in plants. Furthermore, Champa et al. [26] suggested that polyamines increase pathogen resistance by combining with phenolic compounds and hydroxycinnamic acid amides. This mechanism explains the ability of putrescine to reduce fruit rot and cold damage. The effect of pt levels was obvious as shown in Fig. 1. In the studies conducted by Barman et al. [29] and Koushesh Saba et al. [37], it was reported that putrescine also reduced decay in fruit such as pomegranate and apricot. This shows that polyamines are similarly effective in different fruit species and putrescine offers a potential treatment option for application in various fruit species.

Soluble solids content, pH and titratable acidity

Although the increasing SSC ratio as the storage period progressed had a slight effect on increasing the SSC value, which was lower in 0.5 mM and 1 mM putrescine applications compared to the control group, generally similar SSC values were recorded among all applications. This result suggests that putrescine has no effect such as increasing sugar accumulation or accelerating ripening. When the effects of storage time and putrescine application were evaluated, the applications did not cause a significant change on SSC. However, the observation of the lowest SSC values on the 7th day and the highest on the 21st confirms the effects of storage time on fruit ripening and SSC (Table 1; Fig. 1(C)). This is in line with previous literature, emphasizing the effect of fruit ripening on SSC [38, 39]. The increase in SSCis the change in the metabolism of sugars and organic acids as a result of fruit ripening. The effect of putrescine application on this process is thought to be limited. Although these findings show that putrescine delays the ripening process, it does not show a significant effect in preventing the increase in SSC. The increase in SSC depends on the metabolism of sugars and the rate of cellular respiration [40]. Putrescine can slow down this process by inhibiting ethylene production, but it does not have a direct effect on SSC [41]. Previous studies have reported that putrescine applications failed to control changes in SSC in fruit species such as peach [42], papaya [34]. and plum [41]. In other studies, the slowing down of the conversion of sugars by putrescine had an effect on the ability to control SSC rates [17, 43].

The pH value increased as the storage period progressed. This indicates that acidity levels decreased over time and pH increased as tomatoes ripen. During ripening, acidity in the fruit decreased while pH increased. This is associated with a decrease in organic acids (especially citric acid) and an increase in sugars. Putrescine applications have shown a significant effect on pH. Especially at 0.5 mM and 1 mM doses, pH value was kept lower than the control group (Table 1; Fig. 1(D)). These findings reveal the potential of polyamines to control acidity [20]. Putrescine applications prevent the decrease of organic acids by slowing down the respiration rate and thus prevent excessive increase in pH. This is particularly linked to decreased ethylene production and slowed fruit ripening rates [41, 44]. Many studies have reported significant effects of putrescine applications on pH. For example, Khosroshahi et al. [20] observed that putrescine applications increased pH in strawberry fruit. Similarly, Kibar et al. [45] noted that putrescine applications increased pH in peach fruit.

Titratable acidity decreases with storage time. This can be explained by the decrease in acidity levels as tomatoes ripen and sugars increase. Putrescine applications were effective in maintaining acidity. On the 7th and 14th days, the titratable acidity was higher than the control group. This shows that putrescine prevents fruit from becoming less acidic by maintaining titratable acidity. The lowest titratable acidity values were observed on the 21st day of storage, indicating the natural effect of fruit ripening and the protective role of putrescine application (Table 1; Fig. 1(E)). The decrease in titratable acidity in fruit is related to the fruit respiration rate and the metabolism of organic acids. Putrescine slows down this process and maintains acidity, creating an effect to preserve the acidic structure in the fruit tissue [40]. Putrescine applications can inhibit the metabolism of acids by reducing the respiration rate in the fruit, which helps maintain titratable acidity. The positive effects of putrescine applications on acidity have been frequently reported in the literature, especially with their effects on slowing fruit ripening and maintaining titratable acidity. Khosroshahi et al. [20] reported that putrescine increased titratable acidity in strawberry fruit. Furthermore, Kibar et al. [45] showed that putrescine maintained the itratable acidity in peach fruit.

Respiration rate

As the storage period progresses, the metabolic activities in the fruit increase and the respiration rate increases accordingly (Table 1; Fig. 1(F). This increase is an indicator of the biochemical changes experienced during the storage process of tomatoes and shows that the oxygen consumption of the fruit increases and therefore their metabolism accelerates. This process increases the ripening rate of the fruit due to many factors such as metabolism of sugar and organic acids, water loss and changes in the cell Wall [46,47,48]. However, the research has shown that applications such as putrescine effectively slow down the respiration rate, thereby extending the shelf life of the fruit. Putrescine, especially when applied at 0.5 mM and 1 mM doses, was able to keep the respiration rates of the fruit at lower levels compared to the control group. It was observed that the respiration rate decreased as the putrescine application dose increased. This finding indicates that putrescine delays the fruit ripening process and has the capacity to control metabolic rates (Table 1; Fig. 1). Putrescine inhibits the production of ethylene, preventing the effect of this hormone to accelerate the ripening process [49]. The mechanisms behind the effect of putrescine in slowing down the respiration rate include delaying fruit ripening and thus reducing metabolic activities. Ripening increases the respiration process in fruit, causing a rapid decrease in organic acids along with other metabolic activities [50]. This mechanism may be associated with the slowing down of respiration rate and the reduction of cold damage severity in putrescine-treated fruit. For example, Barman et al. [51] reported that putrescine application delayed fruit ripening and slowed down the respiration rate in their study on mango fruit. Also, Khan et al. [52] reported that respiration rates were lower in putrescine-applied fruit compared to the control group in their study on plum fruit. Similarly, Hanif et al. [34] observed that putrescine reduced respiration rates in papaya, Razzaq et al. [53] in mango and Tas et al. [32] in kiwi fruit. Tekin et al. [48] reported that respiration rates decreased with guar and tara gum applications in tomato and similarly, the semi-permeable structure formed by putrescine on the fruit surface reduced respiration rates by regulating oxygen, carbon dioxide and moisture exchange [54,55,56]. However, there are also some studies that contradict these findings. Fawole et al. [25] stated in their study on pomegranate fruit that the respiration rate was higher in putrescine applications compared to the control group. The researchers stated that this result may have been due to the very high dose of putrescine applied to the fruit. This situation highlights the importance of the effect of dosage, as different doses may have different effects on the fruit. In conclusion, putrescine applications may be an effective method for reducing the respiration rate and extending the shelf life of fruit such as tomatoes. However, the effects of this application may vary depending on factors such as dosage, fruit type and storage conditions.

Organic acids and vitamin C

The study investigated the effects of putrescine applications on organic acids and vitamin C in tomatoes and the results show that putrescine treatment plays an important role in preserving the quality of tomato fruit. A decrease in the levels of organic acids (citric, malic, tartaric, oxalic) was observed as the storage period progressed; this can be considered as a natural part of the ripening process of the fruit. The decrease in organic acids leads to the loss of acidic properties of the fruit and changes in the taste profile. Similarly, there has been a significant decrease in vitamin C levels, which can be explained as a result of the metabolism and ripening process of the fruit. Putrescine applications significantly improved the organic acid and vitamin C content during storage period. In particular, putrescine applications at doses of 0.5 mM and 1.5 mM slowed down the decrease in organic acid levels and helped preserve the acidic properties of the fruit. Although vitamin C content decreased with storage time in all treatments, putrescine treatments slowed down the loss of vitamin C compared to the control group and had a positive effect on the nutritional value of the fruit (Table 2). Putrescine is a compound known as a polyamine and has the capacity to delay fruit ripening and slow metabolic changes. Polyamines are biological compounds that exhibit ripening-slowing effects in fruit and vegetables. The effect of these compounds is to slow down fruit ripening through inhibition of ethylene production, reduce respiration rate and hence delay the depletion of organic acids [57] In particular, putrescine applications were able to maintain the levels of organic acids (especially citric, malic and tartaric acids) in the fruit higher for longer periods than in the control group. This finding suggests that putrescine is effective in preserving acidity by delaying the fruit ripening process (Table 2). The positive effects of putrescine applications on the content of organic acids and vitamin C have also been seen in similar studies. For example, Kibar et al. [45] stated that the organic acid and vitamin C content of peach fruit applied with putrescine was preserved for a longer time compared to the control group. Gupta and Jawandha [58] reported that malic, citric and quinic acids were the major organic acids in peach fruit and putrescine application significantly inhibited the loss of these acids. Similarly, Abbasi et al. [59] reported that 2 mM putrescine application reduced the loss of ascorbic acid in peach fruit. Erbas [60] reported that putrescine applications maintained the organic acid and vitamin C content in plum fruit during storage. Similarly, Ennab et al. [61] and Archana and Suresh [30] stated that vitamin C content was maintained more as putrescine doses were increased. Razzaq et al. [53] reported that putrescine applications in a study on mango preserved the vitamin C content in the fruit and extended the shelf life. These studies highlight the ability of putrescine to reduce the loss of organic acids and vitamin C by slowing down cellular metabolic activities and inhibiting respiration.

Table 2 Effect of Putrescine treatments on organic acids (oxalic g/kg) and vitamin C of tomato fruits during storage (mg/100 g)

Specific phenolic compounds

Phenolic compounds are important compounds that determine the health benefits and quality of tomatoes and the loss of these compounds during storage is generally associated with processes such as oxidation and spoilage. In this context, the study examines the effects of different storage periods (at harvest, on the 7th, 14th, and 21st days of storage) and putrescine treatment on the preservation of phenolic compounds. For most of the phenolic compounds, a general decrease was observed with increasing storage time. The amounts of compounds such as catechin, gallic acid, chlorogenic acid, caffeic acid and protocatechuic acid decreased with storage time. For example, the amount of catechin decreased from 61.89 mg/kg to 54.22 mg/kg, while the amount of gallic acid decreased from 2.60 mg/kg to 1.72 mg/kg from harvest to 21st day. Putrescine application helped to maintain phenolic compounds. The significant improvements were seen in some compounds, especially at low concentrations (0.5 mM). For example, on the 7th of storage, the decrease in the amount of catechin was lower with 1 mM putrescine compared to the control group. A similar effect was observed with compounds such as protocatechuic acid. Putrescine appears to have a protective effect on the phenolic compounds of tomatoes during storage. Catechin, which was 61.89 mg/kg at harvest, decreased to 54.22 mg/kg on the 21st day, but putrescine treatment kept catechin levels higher, especially on the 7th day of the storage. 0.5 mM putrescine treatment increased catechin levels to 70.32 mg/kg on the 7th day of the storage. Gallic acid also decreased during storage. However, putrescine treatment produced a limited increase in gallic acid levels. Chlorogenic acid was one of the compounds that showed the most significant decrease. However, putrescine treatment maintained this compound at higher levels on the 7th day of the storage. Caffeic acid is also lost, but the effect of putrescine treatment is more limited. Protocatechuic acid is one of the compounds that is lost the most. However, putrescine treatment also preserved this compound better, reaching a level of 3.94 mg/kg on day 7. Putrescine delays biochemical changes by inhibiting ethylene production in fruit (Tables 3 and 4). Ethylene is a gas that accelerates ripening, and inhibiting its production allows the fruit to remain fresh for a longer period of time. The effectiveness of putrescine in preserving phenolic compounds is related to this mechanism. In addition, the ability of putrescine to eliminate reactive oxygen species helps prevent phenolic compounds from undergoing oxidation [62, 63]. The antioxidant properties of putrescine help to maintain phenolic compounds in particular, since phenolic compounds are compounds that increase the antioxidant capacity of fruit. The effect of putrescine application on preventing the loss of phenolic compounds may also be associated with the inhibition of phenol oxidase enzymes. Phenol oxidase causes the oxidation of phenolic compounds, causing their loss. It is possible that putrescine slows down the loss of phenolic compounds by inhibiting these enzymes. Kibar et al. [45] stated that phenolic compounds in peach fruit decrease during storage, but putrescine application prevents this loss. In particular, putrescine application at a dose of 1.6 mM prevented the loss of phenolic compounds more. In this study, it was stated that putrescine prevented the loss of phenolic acids in peach fruit and the 1.6 mM dose was the most effective. Similarly, Yang et al. [64] reported that putrescine protects phenolic compounds in kiwi fruit and increases antioxidant activity. In addition, Bal [65] and Mirdehghan et al. [66] reported that putrescine protects phenolic compounds in cherry and pomegranate fruit and slows down the loss of these compounds during storage. Dursun and Bal [67] reported that putrescine positively affects the total flavonoid and phenolic substance content in plum fruit.

Table 3 Effect of Putrescine treatments on phenolic compounds of tomato fruits during storage (mg/kg)

Table 4 Continuation of Table 3 (mg/kg)

Heatmap, PCA and crelation analyses

In this study, the effect of putrescine application on fruit quality traits, organic acid content and individual phenolic content in tomatoes during storage was revealed. PCA (Principal Component Analysis), Heatmap and correlation analysis methods were used for statistical evaluation of the obtained data. While PCA detects changes in the parameters used in the research and highlights the most important features, Heatmap analysis is a powerful statistical method that reveals the evaluation of all applications and features within the scope of the study [68, 69] PCA and Heatmap hierarchical clustering analysis are widely used to explain the degree of influence of change models among the examined characteristics in many cold storage studies [70,71,72].The two principal components in the PCA analysis, which revealed the changes in fruit quality traits and organic acids during storage and the effect of putrescine applications on this change, explained 84.14% (PC1 + PC2) of the total variation. In the PCA plane, acidity, vitamin C and organic acids generally tended to decrease as storage time increased, while pH, SSC, respiration rate, weight loss and dacay rate from fruit quality traits increased as storage time increased. Fruit quality traits showed a more intense distribution than organic acids. It is seen that the groups constituting all doses in putrescine application largely overlapped (Fig. 2).

Fig. 2

Relationship between organic acids and quality traits of tomato fruits during storage and determination of statistical effect of putrescine application by PCA method

Phenolic compounds generally showed changes during storage. The variation in the principal component analysis, which revealed the effect of putrescine application on this variability, was determined as 77.3% (PC1 + PC2). While caffeic decreased on the 7th day of storage, other phenolic compounds, especially catechin, quercetin and ferulic, increased. Gallic, chlorogenic, o-coumaric, p-coumaric and protocatechuic, as well as catechin, quercetin and ferulic contents were found to show parallel changes during storage. When the putrescine doses were grouped, it was observed that there was overlap between the groups (Fig. 3).

Fig. 3

Analysis of the effect of putrescine application on phenolic contents of tomato fruits during storage by PCA method

Heatmap analysis was performed to reveal the interaction between putrescine application and storage periods and the effect of this interaction on the quality characteristics and organic acid and individual phenolic contents of tomato fruit. As a result of the analysis, it was determined that the applications showed different distribution according to storage periods. In general, the combinations of application and storage periods were divided into two main groups. The 7th to 14th days of the applications and the harvest and 7th day period results of the control application were in one group, while the 14th to 21st days of the control application and the 21st day of the applications were in the other group. The traits examined in the study were divided into two groups. Fruit quality traits of tomato fruit (weight loss, respiration rate, SSC, decay rate and pH) were in one group, while individual phenolic and organic acid content traits were in the other group (Fig. 4).

Fig. 4

Analysis of the effect of putrescine application on quality properties, organic acids and phenolic contents of tomato fruits during storage by Heatmap method

The determining the relationship between the traits examined in the studies is of great importance for researchers. Significant positive and negative correlations were determined among the traits examined in the study. Fruit quality traits in general (except acidity), organic acids and individual phenolic compounds exhibited positive correlations among themselves. Weight loss, an important quality parameter in storage studies, showed negative correlations with organic acids and individual phenolic contents, while it showed positive correlations with other fruit quality traits except acidity. Weight loss showed the highest negative correlations with o-coumaric (r=-0.88), caffeic and vitamin C (r=-0.87), protocatechuic (r=-0.84) and citric (r=-0.83) traits, while it showed the highest positive correlation with respiration rate (r = 0.93). Decay rate, which is one of the important parameters during storage, exhibited significant negative correlations among protocatechuic (r=-0.89), citric (r=-0.88), chlorogenic, caffeic and oxalic (r=-0.86). Organic acids and individual phenolic compounds exhibited positive correlations. The highest positive correlations were found between ferulic and quercetin (r = 1.00) among organic acids and citric and malic (r = 0.96) among individual phenolic compounds (Fig. 5).

Fig. 5

Correlation between quality characteristics, organic acid and phenolic compounds. The color scale fading from red to blue indicates correlation values from − 1 to + 1, and the circle size illustrates the redundancy of the correlation. *, **, and *** indicates significance at p ≤ 0.05, p ≤ 0.01, and p ≤ 0.001, respectively. Cat: catechin, Gal: gallic, Chl: chlorogenic, Caf: caffeic, Prot: protocatechuic, p-Co: p-coumaric, O-Co: o-coumaric, Que: quercetin, Fer: ferulic, WeL: wight loss, DcR: decay rate, SSC: solouble solid contents, Aci: acidity, ReR: respiration rate, Cit: citric, Mal: malic, Tar: tartaric, Oxa: oxalic and VitC: vitamin C

Conclusion

This study shows that putrescine applications significantly reduce quality losses during the storage period of tomatoes. Putrescine was particularly effective in preventing fruit weight loss, decay, organic acid loss and vitamin C reduction. With the highest dose application (1.5 mM), the quality of the tomatoes was preserved and these losses were controlled during the storage period. The delayed loss and quality preservation at the applied 1.5 mM concentration is probably due to the more effective inhibitory role of this dose on cellular metabolism. This concentration is more effective in reducing oxidative stress and slowing down enzymatic degradation processes compared to lower doses. In addition, putrescine slowed down the fruit respiration rate, delayed the ripening process and maintained the nutritional value of the fruit. These findings reveal the effects of putrescine in improving fruit quality and extending shelf life. In conclusion, it appears that polyamines such as putrescine can be an effective preservation agent in the storage of sensitive fruit such as tomatoes and that these applications offer a potential method to extend the shelf life of fruit and vegetables in the food industry. Putrescine applications can contribute to preventing food losses and reducing economic losses by providing an alternative to keep tomatoes fresh and nutritious.