tert-Butylhydroquinone alleviates postharvest endocarp browning of longan fruit by regulating antioxidant metabolism

doi:10.21203/rs.3.rs-4476184/v1

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tert-Butylhydroquinone alleviates postharvest endocarp browning of longan fruit by regulating antioxidant metabolism

https://doi.org/10.21203/rs.3.rs-4476184/v1

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Harvested longan fruit is prone to endocarp browning, which restricts preservation quality and shelf life. The antioxidant system defends against oxidative stress-mediated quality deterioration such as fruit browning. The study aimed to evaluate the effect of tert-Butylhydroquinone (TBHQ) on anti-browning ability of longan fruit in association with antioxidant capacity. The results indicated that application of 0.02% TBHQ significantly suppressed the progression of endocarp browning. In comparison with control, TBHQ treatment decreased the levels of hydrogen peroxide (H₂O₂), superoxide radical (O₂^−⋅), and malondialdehyde (MDA), and retained high levels of ascorbic acid (AsA), glutathione (GSH), total phenolics as well as 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging rate. Enhanced enzymatic activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), but inhibited polyphenol oxidase (PPO) and peroxidase (POD) activities were also observed in TBHQ-treated fruit. Gene expression analysis suggested oxidative stress-related genes including DlSOD, DlCAT, DlGR, and DlAPX were up-regulated after TBHQ treatment. The results suggest that TBHQ is effective in alleviating endocarp browning by increasing antioxidant capacity of longan fruit.

tert-Butylhydroquinone

longan fruit

postharvest

endocarp browning

antioxidant

Longan (Dimocarpus longan Lour.) fruit is nutrient-rich and attracts widespread popularity among consumers owing to its distinctive flavor, succulent texture, and multiple health benefits (Lin et al. 2020). However, longan fruit is susceptible to endocarp browning and pulp breakdown after harvest, causing a decline in storage quality and severe limitation in commercial trade (Li et al. 2019; Liu et al. 2021). Hence, developing new strategies is crucial for improving storage quality and prolonging shelf life of longan fruit.

Reactive oxygen species (ROS) are acknowledged as signaling molecules in plant cells and are involved in various physiological processes including ripening, senescence, and stress response to harsh environment (Decros et al. 2019). However, excess ROS would induce oxidative damage to protein, DNA, and lipid, which accelerates cellular dysfunction and causes postharvest physiological disorders (Tan et al. 2020). Mounting evidence suggests that sustained accumulation of ROS is the main factor that causes postharvest endocarp browning of longan fruit. Excessive amounts of ROS accelerate lipid peroxidation in membranes, resulting in the breakdown of cell structure and the following disruption of enzyme-substrate compartmentalization, which allows the interaction between polyphenol oxidases (PPOs) that located in cytoplasm and their phenolic substrates from vacuoles (Pan et al. 2021; Yan et al. 2022). The browning reactions are then triggered, PPOs catalyze continuous oxidation steps and form redox-active quinones, which subsequently react with amino acids, polyphenols, and proteins, and converted into brown polymers, melanin (Zhang et al. 2021). To neutralize the negative effects of ROS, organisms employ antioxidant defense systems to remove damaging radicals and recover oxidatively damaged lipid and protein (Liu et al. 2023). Postharvest treatments capable of enhancing organisms’ antioxidant defense systems are beneficial to alleviate postharvest browning and prolong shelf life of longan fruit (Corpas et al. 2022).

Tert-Butylhydroquinone (TBHQ) is a synthetic phenolic addictive commonly applied in food preservation. This chemical is low cost, wide availability, and high performance, and has been found in various food products that contain animal fats and lipids. Moreover, TBHQ is considered to be safe and can be directly consumed at concentrations no greater than 0.02%, according to the official guidance (Ramis-Ramos 2003). It’s evidenced that TBHQ exhibits superior antioxidant and anti-fungi capacity, thus is able to inhibit the oxidative deterioration of oils (Hung et al. 2019; Wang et al. 2021). However, there exists very scarce information and reports on its application in fruit preservation.

This work aimed to evaluate the role of TBHQ against endocarp browning of longan fruit combined with antioxidant capacity during postharvest storage. Specific analyses focused on basic quality parameters (endocarp browning index, pulp breakdown index, MDA content), ROS biosynthesis (contents of H₂O₂ and O₂^−⋅, activities and gene expressions of oxidase PPO and POD), endogenous antioxidant defense systems including enzymatic activities and gene expressions as well as non-enzymatic antioxidants. These results are helpful to provide a safe and effective strategy to maintain postharvest quality and extend shelf life of longan fruit.

2.1 Fruit materials and treatments

Longan fruit (Dimocarpus longan Lour.) were picked from an orchard close to Hongqi town in Haikou City, Hainan Province, China, and immediately transferred to our laboratory at Hainan University. Fresh fruit then underwent a 3-min sterilization by being immersed in 0.1% sporgon (w/v) solution. A total of 900 longan fruit with consistent size, maturity, and free of visible flaws were carefully chosen and divided randomly and equally into two groups. One was submerged in a 0.2 g L^− 1 TBHQ (w/v) solution at 25°C for 3 min. The other was subjected to a 3-min treatment with distilled water at the same temperature, and serving as control. The optimum concentration of TBHQ (0.2 g L^− 1) was determined based on our preliminary study of endocarp browning index and aril breakdown index using 0.05, 0.1, 0.2 and 0.5 g L^− 1 TBHQ.

After TBHQ or distilled water treatment, the fruit were air-dried and subsequently stored at the temperature of 25 ± 1°C and relative humidity of 85–90% for a duration of 8 days. Pericarp tissues were collected at intervals of 2 days, immediately frozen in liquid nitrogen, and preserved at − 80°C for further study. At every time point, three biological replicates were conducted for physiological parameters analysis.

2.2 Endocarp browning and aril breakdown index

Endocarp browning was assessed based on the browning area of inner pericarp, which could be divided into 6 grades, with 1 = no browning; 2 = less than 25% browning area; 3 = 25–50% browning area; 4 = 50–75% browning area; 5 = 75–100% browning area; 6 = All browning. Endocarp browning index = ∑ (browning scale × fruit number of corresponding scale) / (total fruit number).

Aril breakdown index was determined by referencing Chen et al. (2015) (Chen et al. 2015). According to the extent of aril breakdown area, breakdown index could be divided into 4 grades with 0 = no breakdown, 1 = less than 25% breakdown area, 2 = 25–50% breakdown area, 3 = 50–75% breakdown area, and 4 = more than 75% breakdown area. Aril breakdown index = ∑ (breakdown scale × fruit number of corresponding scale) / (total fruit number).

2.3 ROS and MDA analysis

O₂⁻· production rate was determined by following the procedure described in the study of Chen et al. (2020) (Chen et al. 2020b), and expressed as mmol min^− 1 kg ^− 1 on a fresh weight basis. The content of H₂O₂ was analyzed using an H₂O₂ content assay kit (G0112W, Grace Biotechnology Co. Ltd., Suzhou, Jiangsu, China) according to the protocols provided by manufacturer, and expressed as mmol kg^− 1 on a fresh weight basis. The malondialdehyde (MDA) content was determined according to the method of Lin et al. (2014) (Lin et al. 2014), and the results are presented as mmol kg^− 1 on a fresh weight basis.

2.4 Assay of DPPH scavenging rate

The assay of DPPH scavenging rate was conducted with reference to methods in Huang et al. (2022) with slight modifications (Huang et al. 2022). Briefly, 1 g of frozen pericarp powder was mixed with 5 mL of methanol. After homogenization, the mixture was subjected to centrifugation with 12 000 × g force, 30 min. The supernatant (2 mL) was collected and added to 2 mL of 0.1 mM DPPH. The mixture was then incubated at 25°C under dark conditions for 20 min. Absorbance at the wavelength of 517 nm was recorded.

2.5 Assays of antioxidant enzyme activities

To determine the activities of SOD, CAT, APX, and GR, 1 g of frozen pericarp powder was homogenized in various buffers. Details are described in the study of Zhang et al. (2015) (Zhang et al. 2015).

SOD activity was determined according to the inhibition capacity of SOD on nitro blue tetrazolium (NBT) photoreduction. One unit (U) of SOD activity was defined as the amount of enzyme used to inhibit the reduction of 50% NBT per min monitored at the wavelength of 560 nm.

CAT activity was assessed by recording the alternation of absorbance at 240 nm based on its decomposing capacity on H₂O₂. One unit (U) of activity was defined as the amount of enzyme which catalyzed the degradation of 1 nmol of H₂O₂ every min.

APX activity was determined by measuring the alternation of absorbance at 290 nm caused by APX-catalyzed oxidation of ascorbic acid after adding H₂O₂. One unit (U) of APX activity was defined as the enzyme amount required for oxidation of 1 µmol of ascorbic acid every min.

The activity of GR was assessed by tracking the glutathione-dependent oxidation of NADPH at 340 nm. One unit (U) of activity was defined as the GR amount required to oxidize 1 nmol of NADPH every min.

MDHAR and DHAR activities were measured by following protocols provided by kits of G0213F and G0212F acquired from Suzhou Grace Biotech. One unit (U) of MDHAR activity was defined as the enzyme amount that is required to oxidize 1 nmol of NADH every min. One unit (U) of DHAR activity was defined as the amount of enzyme that generated 1 nmol of AsA every min.

2.6 PPO, POD activities assays

PPO activity was assessed using an enzymatic assay kit of PPO-1-Y bought from (Comin Biotech Co. Ltd, Suzhou, Jiangsu, China) with reference to the protocols provided by the manufacturer. One unit (U) of activity was defined as the amount of PPO that gave rise to an increment in absorbance of 0.005 every min.

POD activity was analyzed with reference to methods described in Tian et al. (2022) (Tian et al. 2022). One unit (U) of enzyme was defined as the amount of POD that was required to induce a rise in absorbance of 0.01 at 470 nm every min.

2.7 Total phenols, GSH, and AsA analysis

The concentrations of GHS and AsA were determined by following approaches described in Zhang et al. (2018) (Zhang et al. 2018). Absorbance at 412 and 534 nm were measured. GSH and ASA were expressed as mmol kg^− 1 and g kg^− 1 on a fresh weight basis, respectively.

2.8 RT-qPCR analysis

Total RNA of pericarp tissues was extracted using a cetyltrimethylammonium bromide (CTAB)-based method reported in Nian et al. (2021) (Nian et al. 2021). The purified RNA served as a template for reverse transcription to synthesize the first strand cDNA by using FastKing First Strand cDNA Synthesis Kit (KR118, Tiangen Biotech Co. Ltd., Beijing, China). Primers used in qPCR reactions were designed using Primer 6.0, which were listed in Table 1. The reaction system with 20 µL total volume of RT-qPCR was prepared by following the protocol of FastKing One Step RT-PCR Kit (KR123, Tiangen Biotech). After preparation, RT-qPCR was conducted using CFX96 Real-Time PCR system (Bio-Rad, Hercules, CA, USA). The relative expression levels were determined based on the 2^−ΔΔCT method. DlActin was chosen as the reference gene, whose expression was used as internal control.

Table 1

Primer sequences for RT-qPCR.
Gene	Forward	Reverse
DlActin	ACCACTACTGCTGAACGGGAAA	GCCTCCAACTCCTGCTCATAGT
DlSOD	GCACCACCAGAAGCATCACCAG	TGCCCTCCGCCGTTGAACTT
DlCAT	AACGTGTTGTCCATGCAAGAGG	CGGAGGATGATAGGCGTCTGAA
DlAPX	TCACGAGGCTAACAACGGTCTT	ACAGCAACAACTCCAGCCAACT
DlGR	CGCAACTACGACTTCGACCTCT	AGCTCGCAGACGGCAACAGA

2.9 Statistical analyses

Data were presented as mean value ± standard error (SE) based on measurements from three repeated experiments. The statistical program SPSS 22.0 was employed for means comparison using independent samples t-test analysis. Asterisk denoted significant differences between control and TBHQ-treated group (*P < 0.05, **P < 0.01). Graphs in this study were prepared by using Origin 9.1.

3.1. Endocarp browning index, aril breakdown index

Endocarp browning occurs in deteriorated longan fruit, and is one of the main factors that restrict shelf life of fresh product (Long et al. 2022; Sun et al. 2022). Our study found that endocarp browning index in control fruit increased continuously at 25 ℃, with values from 1 to 2.62 after 8 d storage (Fig. 1A). In comparison, exogenous TBHQ treatment significantly decelerated the browning development, and the browning index in TBHQ-treated fruit raised from day 2 and reached to 2.12 at day 8 which was 19.1% lower than in control fruit.

Aril breakdown is another noticeable feature of quality deterioration in harvested longan fruit (Thavong et al. 2010; Wu et al. 2022). Aril breakdown index was calculated based on the average breakdown area that occupies picked fruit, which reflects breakdown severity of edible tissues. Consistent with browning development, aril breakdown index showed continuous increasement in both two groups. However, TBHQ treatment notably suppressed the advancement of aril breakdown as indicated by delayed increases in aril breakdown index (Fig. 1B).

Chemicals that exhibit antioxidant property are supposed to have positive effect on fruit preservation. It has been reported that application of antioxidants such as propyl gallate, α-lipoic acid, sodium para-aminosalicylate, and hydrogen water has successfully alleviated pericarp browning of longan and litchi fruit (He et al. 2021; Li et al. 2019; Li et al. 2018; Lin et al. 2018; Liu et al. 2022b). TBHQ is another well-known antioxidant compound, approved as a food additive widely used in oil preservation. However, its effect on fruit preservation is unknown. In this study, we found TBHQ with percent concentration 0.02% (a safe intake concentration) is effective in suppressing endocarp browning and aril breakdown of longan fruit under ambient conditions, suggesting the great potential of TBHQ in fruit preservation.

3.2 ROS production, MDA content, and DPPH scavenging rate

ROS are highly reactive metabolites derived from oxygen during mitochondrial respiration. Its imbalance between production and removal results in oxidative stress which contributes to cellular senescence and affects storage quality of harvested fruit (Tang et al. 2021). H₂O₂ and O₂⁻· are the major ROS involved in oxidative stress. As observed in Fig. 2A, the H₂O₂ content presented overall increase with fluctuation during storage, rising from an initial value of 27.63 mmol kg^− 1 to the peak of 34.13 mmol kg^− 1 at day 2, following a drop to 28.41 mmol kg^− 1 at day 6 and a subsequent increase to 31.53 mmol kg^− 1 at day 8. TBHQ treatment inhibited the production of H₂O₂, with H₂O₂ content at days 2, 4, and 6, being 5.2%, 9.1%, and 11.4% lower, in comparison with control. The production rate of O₂⁻· rose steadily during storage regardless of treatment, but at day 6, the O₂⁻· production rate was 3.8% lower in TBHQ-treated fruit, compared to control.

MDA is a peroxidation biomarker of membrane lipid caused by oxidative damage (Chomkitichai et al. 2014; Zhang et al. 2022). As observed in Fig. 2C, the MDA content increased steadily and showed analogous tendencies in both control and TBHQ-treated fruit, but the latter had average 17.53% lower values than the former from day 4 to day 8 storage.

DPPH test can be used to assess the antioxidant defense capacity of postharvest fruit by determining ROS scavenging potential (Chen et al. 2020a). In this work, the DPPH scavenging rate in control fruit presented an overall decline trajectory with fluctuation during storage (Fig. 2D). TBHQ treatment enhanced the DPPH scavenging rate at days 4 and 6, which was 1.0% and 1.62% higher than control fruit, respectively (Fig. 2D).

Suppressed levels of ROS and MDA and enhanced DPPH scavenging ability suggested the positive effect of TBHQ in alleviating oxidative stress, which might be responsible for attenuation of endocarp browning and quality maintenance of postharvest longan fruit. In consistent, the positive correlation between reduced oxidative stress and alleviated browning development after postharvest treatments has also been evidenced in pear, apple, litchi, and longan fruits (He et al. 2021; Jung and Choi 2020; Lin et al. 2014; Zhai et al. 2018).

3.4 PPO and POD activities

PPO is the main enzyme involved in enzymatic browning by catalyzing the oxidating reaction of phenolic substances to form quinones, which are substrates of brown polymers (Liu et al. 2022a; Pan et al. 2021). Its activity affects the progression of pericarp browning. In our work, PPO activity in control fruit showed an overall increasing tendency with initial value of 3.56 × 10⁴ U kg^− 1 to 1.58 × 10⁵ U kg^− 1 at day 8. TBHQ treatment suppressed the increasement of PPO activity, with notable results, 22.6% and 14.7% lower than control at days 4 and 8 (Fig. 3A).

POD also associates with the onset of fruit browning since it catalyzes the oxidation and polymerization of phenolic substances with H₂O₂ (Zhang et al. 2015). In control longan fruit, POD activity rose initially from 4.77 × 10⁴ U kg^− 1 to the peak of 1.10 × 10⁵ U kg^− 1 at day 4, then decreased to 2.42 × 10⁴ U kg^− 1 at day 8 (Fig. 3B). The application of TBHQ suppressed POD activity and resulted in significant lower values at days 2 and 6 (Fig. 3B).

PPO and POD are considered as the action targets to control the progression of enzymatic browning in postharvest fruit. Appropriate postharvest strategies offer a promising way to suppress PPO and POD activities. Lin et al. (2013) reported propyl gallate treatment alleviated longan fruit browning which could be ascribed to the decreased PPO and POD activities (Lin et al. 2013). TBHQ treatment is also useful in PPO and POD inhibition.

3.5 Total phenols, GSH, and AsA contents

Aerobic organisms have integrated antioxidant systems to defend against oxidative damage triggered by ROS stress and maintain cellular redox homeostasis (Meitha et al. 2020; Zhu et al. 2022). The antioxidant system consists of two parts, endogenous non-enzymatic and enzymatic antioxidants. Non-enzymatic antioxidants are represented by low-molecular-weight compounds, including phenolics, ASA and GSH (Yun et al. 2021). In this work, total phenolics content in control fruit raised initially from 1.63 g kg^− 1 and attained the maximum of 1.87 g kg^− 1 at day 6, then dropped to 1.59 g kg^− 1 at day 8 (Fig. 3C). In comparison, TBHQ-treated fruit presented noticeably higher levels of total phenolics than control at days 4 and 8 (Fig. 3C). AsA content in both groups displayed a decreasing trajectory during storage. TBHQ treatment impeded the decrease of AsA content in the last 4-d storage with values of 8.4% and 11.4% higher than control fruit at days 4 and 6 (Fig. 3D). The GSH content of control fruit dropped from 1.58 mmol kg^− 1 to 1.16 mmol kg^− 1 within the first 4 d, followed by an increment to 1.34 mmol kg^− 1 at day 6, then decreased to 1.03 mmol kg^− 1 at day 8 (Fig. 3E). Comparatively, fruit with TBHQ treatment exhibited significantly higher levels of 13.3% in average GSH content during 4–8 d of storage (Fig. 3E).

Phenolics are secondary metabolites, capable of scavenging oxygen free radicals in response to oxidative environment (Bai et al. 2022). AsA is regarded as a ROS detoxifying chemical and facilitates the decomposition of H₂O₂ under the action of APX (Wang et al. 2018a; Zhou et al. 2022). GSH is a cofactor for glutathione peroxidase and involves in the transformation of oxidated ASA to its active reduced form (Cai et al. 2011). These endogenous non-enzymatic antioxidants contribute to the enhanced ROS scavenging ability of longan fruit and attenuate postharvest endocarp browning. TBHQ treatment markedly increased these antioxidants to reduce fruit deterioration. Consistent with our results, higher levels of endogenous AsA, GSH, or phenolics were observed in apple polyphenols-, L-cysteine- or exogenous AsA-treated postharvest fresh products, which led to decreased ROS levels, and thus retarded fruit browning and senescence (Ali et al. 2016; Liu et al. 2021; Su et al. 2019).

3.6 Antioxidant enzymes activities

Enzymatic antioxidants are of importance to shield fruit from oxidative stress by scavenging ROS. To investigate ROS scavenging ability of enzymatic antioxidants, we analyzed the activities of SOD, CAT, APX, GR, DHAR, and MDHAR.

As shown in Fig. 4A, SOD activity in control declined initially from 1.32 × 10⁶ U kg^− 1 to 1.12 × 10⁶ U kg^− 1 at day 2, followed by a 4-d increment to 1.21 × 10⁶ U kg^− 1, and slightly decreased to 1.17 × 10⁶ U kg^− 1 at day 8. After TBHQ treatment, SOD activity exhibited a similar trajectory, but was averaging 6.4% higher than control during days 2 to 6 (Fig. 4A). CAT activity in control declined gradually from 2.49 × 10⁵ U kg^− 1 to 7.73 × 10⁴ U kg^− 1 throughout storage. TBHQ treatment suppressed the decrement in CAT activity and maintained an averaging 26.8% higher level from days 2 to 6, in comparison with control (Fig. 4B). APX activity steadily increased from 1.31 × 10⁵ U kg^− 1 initially to 2.29 × 10⁵ U kg^− 1 at day 8 in control fruit. TBHQ treatment induced a more rapid increment of APX activity, which was averaging 13.9% higher than control from days 2 to 6 (Fig. 4C). GR activity in control fruit increased initially from 1.52 × 10⁵ U kg^− 1, and reach a peak of 4.16 × 10⁵ U kg^− 1 at day 6, then dropped to 3.14 × 10⁵ U kg^− 1 at day 8 (Fig. 4D). Comparatively, higher GR activity was observed after TBHQ treatment, with values 1.29- and 1.17-fold higher than control at days 4, and 6, respectively (Fig. 4D). MDHAR activity in control fruit decreased continuously over 6 d from 5.47 × 10⁴ U kg^− 1 to the minimum of 3.11 × 10⁴ U kg^− 1 (Fig. 4E). TBHQ-treated fruit maintained higher MDHAR activity, which was averaging 36.4% higher than control at days 6 to 8 (Fig. 4E). DHAR activity in control fruit decreased initially from 1.89 × 10⁵ U kg^− 1 to 1.37 × 10⁵ U kg^− 1 at day 4, then increased to the peak value of 1.86 × 10⁵ U kg^− 1 at day 6, then declined to 1.64 × 10⁵ U kg^− 1 at day 8 (Fig. 4F). Fruit with TBHQ treatment showed increased DHAR activity. Compared to control fruit, significant difference was observed at days 6 and 8, with values of 21.4% and 16.5% higher after TBHQ treatment (Fig. 4F).

SOD, CAT, APX, GR, DHAR, and MDHAR are essential enzymatic antioxidants directly and/or indirectly involved in scavenging ROS (Zhu et al. 2014). Among them, SOD catalyzes the dismutation reaction of O₂⁻· to form H₂O₂, which is decomposed into H₂O and O₂ under the action of CAT (Wang et al. 2018b). APX, GR, MDHAR, and DHAR participate in the ascorbate-glutathione cycle, which provides reducing power to regenerate reduced GSH and AsA (Pan et al. 2022). Li et al. (2019) addressed that the activation of antioxidant enzymes contributes to the reduced oxidative damage and the alleviated endocarp browning of longan fruit (Li et al. 2019). In this study, TBHQ treatment led to high levels of SOD, CAT, APX, GR, DHAR, and MDHAR, which might be linked to the suppression of enzymatic browning induced by oxidative stress.

3.7 Gene expression of DlSOD, DlCAT, DlAPX, and DlGR

To measure the expression levels of genes that involve in ROS metabolism, we extracted total RNA and conducted RT-qPCR. Results are shown in Fig. 5. Different from the fluctuating trajectory of SOD activity, DlSOD expression in control fruit raised initially, and peaked at day 4 with 2.3-fold increases, then dropped dramatically to 0.4-fold at day 8. TBHQ treatment significantly elevated the expression of DlSOD at days 2 and 4, which was 1.7- and 2.5-fold of that in control fruit (Fig. 5A). Similarly, the DlCAT expression in control fruit declined sharply in the first 2 d and reached to 9.3-folds, then decreased to 0.6-fold at day 8. TBHQ treatment significantly upregulated the expression of DlCAT which was 3.4 times of that in control at day 2 (Fig. 5B). Notably, the changing tendency of DlCAT expression was also different from CAT activity. For DlAPX, TBHQ-treated fruits maintained higher expression levels during the first 6 d of storage, by averaging 35.68% higher than control, which is consistent with the changing trend of APX activity (Fig. 5C). Similar to DlSOD, DlGR expression presented an upward tendency in the first 4 d, then slightly declined in the latter storage. TBHQ treatment significantly upregulated DlGR expression, with values of 2.91- and 2.11-folds higher than control at days 2 and 4 (Fig. 5D). The overall trend of DlGR expression was in accordance with GR activity, though the peak value of GR activity was 2 d later in comparison with DlGR expression. The difference between enzymatic activity and gene expression might be explained by the imbalance between biosynthesis and degradation of enzyme, and the complicated regulation in transcription and translation process (Wen et al. 2023). The expression of genes relevant to ROS metabolism was stimulated by TBHQ, thereby reinforcing the antioxidant system and the preservation quality of longan fruit.

In conclusion, application of TBHQ effectively suppressed the endocarp browning of longan fruit at 25°C storage. This treatment alleviated oxidative stress, which might be linked to its positive effect in enhancing ROS-defensing system by upregulating gene expression of antioxidant enzymes, improving enzymatic oxidant activities, as well as maintaining high levels of non-enzymatic oxidants. The proposed mechanism of TBHQ-induced quality maintenance in postharvest longan fruit is presented in Fig. 6. Our study suggested that TBHQ might be a promising chemical in fruit preservation due to its inducing effect in antioxidant capacity.

Author Contribution

Zhiqian Yu performed the experiments and wrote the main manuscript. Wenjing Kang performed formal analysis. Zhengke Zhang reviewed this manuscript. Ziqin Yang acquired funding for this project. Yueming Jiang reviewed this manuscript. Yonggui Pan supervised this project, and reviewed this manuscript. Jiali Yang conceptualized this project, acquired funding, critically reviewed and revised this manuscript.

Funding

This work was supported by Natural Science Foundation of Hainan Province, China (223RC403 and 323RC535), Collaborative Innovation Center of Hainan University (XTCX2022NYC07), and Hainan Provincial Key Laboratory of Food Nutrition and Functional Food (KF202207).

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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tert-Butylhydroquinone alleviates postharvest endocarp browning of longan fruit by regulating antioxidant metabolism

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Abstract

Figures

1. Introduction

2. Materials and methods

2.1 Fruit materials and treatments

2.2 Endocarp browning and aril breakdown index

2.3 ROS and MDA analysis

2.4 Assay of DPPH scavenging rate

2.5 Assays of antioxidant enzyme activities

2.6 PPO, POD activities assays

2.7 Total phenols, GSH, and AsA analysis

2.8 RT-qPCR analysis

2.9 Statistical analyses

3. Results and discussion

3.1. Endocarp browning index, aril breakdown index

3.2 ROS production, MDA content, and DPPH scavenging rate

3.4 PPO and POD activities

3.5 Total phenols, GSH, and AsA contents

3.6 Antioxidant enzymes activities

3.7 Gene expression of DlSOD, DlCAT, DlAPX, and DlGR

4. Conclusion

Declarations

References

Additional Declarations

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