Application of γ-aminobutyric acid in reducing the accumulation of off-flavor substances in fruits

Abstract

This invention belongs to the field of postharvest fruit preservation technology, specifically relating to the application of γ-aminobutyric acid (GABA) in reducing the accumulation of off-odor substances in fruits after harvest. This invention treats fruits with GABA before applying a coating agent, thereby reducing the accumulation of off-odor substances such as ethanol, acetaldehyde, or methanol. The results of the embodiments show that, in the application of GABA in reducing the accumulation of off-odor substances in fruits after harvest, GABA treatment can reduce the accumulation of off-odor substances in fruits subjected to hypoxia stress, especially those treated with coating agents, without having other effects on fruit quality.

Description

Technical Field

[0001] This invention belongs to the field of postharvest preservation technology for fruits, specifically involving the application of γ-aminobutyric acid in reducing the accumulation of off-flavor substances in fruits after harvest. Background Technology

[0002] The accumulation of off-flavor substances is one of the most common quality deterioration and adverse post-harvest physiological disorders in fresh fruit. This accumulation causes an alcoholic off-flavor in the fruit, primarily consisting of ethanol, acetaldehyde, and methanol, with ethanol being the most significant. Ethanol and acetaldehyde are products of ethanol fermentation metabolism. While they typically exist in trace amounts during post-harvest storage, they are induced to synthesize and accumulate under hypoxic stress, leading to the development of alcoholic off-flavors. Ethanol fermentation metabolism occurs under the action of two key enzymes, pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH), replacing mitochondrial respiration and allowing the glycolysis pathway to recycle NAD2. + ATP is produced to meet the energy metabolism needs of fruits under hypoxic stress. PDC and ADH are both hypoxia-responsive genes (HRGs), encoding proteins belonging to the anaerobic polypeptide family (ANPs). Under hypoxia, the ERF-VII transcription factor activates transcription by binding to hypoxia-responsive promoter elements (HRPEs) located on the promoter. Methanol originates from the demethylation reactions of biological macromolecules DNA and proteins, but the primary source is the demethylation of cell wall pectin by pectin methylesterases (PMEs). Methanol release increases due to cell wall damage in response to stress.

[0003] In postharvest citrus production, factors such as postharvest coating treatment, low-temperature storage, low oxygen concentration, high carbon dioxide concentration, high respiration rate, and high temperature can all cause hypoxia stress in the fruit. Postharvest coating treatment is widely used in citrus production. This technology forms an artificial wax film on the fruit surface, increasing its gloss and reducing moisture loss, thereby improving the fruit's appearance and maintaining its marketability. However, currently widely used coatings such as 402D Brightening Coating, while reducing moisture loss, hinder normal gas exchange during respiration, leading to the consumption of oxygen inside the fruit and the continuous accumulation of carbon dioxide produced by respiration. High carbon dioxide and low oxygen concentrations create hypoxia stress, inducing ethanol fermentation and resulting in alcoholic off-flavors. Furthermore, production practice shows that low-temperature storage can induce the accumulation of ethanol and acetaldehyde fermentation metabolites in citrus varieties such as Wogan, causing alcoholic off-flavors and severely affecting the fruit's marketability. The accumulation of postharvest off-flavor substances in citrus fruit severely restricts the application of postharvest production technologies such as coating agents and low-temperature storage, and has become a key factor limiting the high-quality development of the citrus industry. However, there is no effective way to control the accumulation of off-flavor substances in citrus fruits after harvest. Therefore, finding technical means to effectively control the post-harvest alcohol off-flavor of citrus fruits is urgently needed by the industry.

[0004] Gamma-aminobutyric acid (GABA) is a widely distributed four-carbon non-protein amino acid. In animals, it functions as an inhibitory neurotransmitter and acts as a signaling molecule. In plants, abiotic stresses such as hypoxia, high temperature, and drought, as well as biotic stresses such as herbivorous damage and pathogen infection, induce GABA accumulation. GABA is considered an effective mechanism in plants to respond to various external changes, internal stimuli, and ionic environments such as pH, temperature, and external predator stimuli. However, no research has shown a relationship between GABA and the production of off-flavor substances in fruits. Summary of the Invention

[0005] The purpose of this invention is to provide an application that reduces the accumulation of off-flavor substances in fruits after harvest. This application can reduce the alcohol off-flavor of fruits after harvest, improve the flavor quality of fruits, and enhance the commercial performance of fruits.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides the application of γ-aminobutyric acid (GABA) in reducing the accumulation of off-flavor substances in fruits subjected to hypoxia stress.

[0008] Preferably, the fruit is treated with a coating agent.

[0009] Preferably, the coating agent is a 402D coating agent.

[0010] Preferably, the odorant includes ethanol, acetaldehyde, or methanol.

[0011] Preferably, the fruit is a citrus fruit.

[0012] The present invention also provides a postharvest preservative for citrus fruits, wherein the preservative contains GABA.

[0013] The preferred postharvest preservative for citrus is an aqueous solution containing GABA, with a GABA concentration of 0.2 mM to 0.5 mM.

[0014] The present invention also provides a method for reducing the postharvest alcohol odor of fruit. The method is to soak citrus fruits without obvious external damage in a 0.2mM-0.5mM GABA aqueous solution for 2-5 minutes, and then dry the fruit surface before storage.

[0015] Preferably, the fruit surface is dried and then coated with wax, and stored at room temperature.

[0016] Beneficial effects:

[0017] 1) Safety and Health: GABA is a natural non-protein amino acid and is classified as a Generally Recognized As Safe (GRAS) compound by the U.S. Food and Drug Administration (FDA). Furthermore, GABA itself is beneficial to human nutrition and health, directly regulates muscle tone, and has mood-stabilizing and blood pressure-lowering effects.

[0018] 2) Significant effects: Examples show that the present invention can significantly reduce the accumulation of acetaldehyde and ethanol during the storage of citrus fruits, reduce the alcoholic odor of the fruits, improve the commercial performance of the fruits, and enhance the application value of postharvest production technologies such as coating treatment and low-temperature storage.

[0019] 3) High commercial potential: GABA is easy to synthesize and relatively inexpensive. This invention is the first to apply this compound to the regulation of alcohol off-odors during post-harvest storage of fruits, and it has broad application prospects for fruits such as citrus and kiwifruit that are prone to off-odors. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 For Example 1, the content of off-flavor substances in Wenzhou mandarin oranges after harvest is as follows: A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content.

[0022] Figure 2 For Example 2, the postharvest off-flavor substances, TA, and TSS of Wenzhou mandarin oranges are: A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content; E: titratable acid (TA) content; F: soluble solids (TSS) content.

[0023] Figure 3 For Example 3, the postharvest off-flavor substances, TA, and TSS of 'Lunwan' navel orange fruit are: A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content; E: titratable acid (TA) content; F: soluble solids (TSS) content.

[0024] Figure 4 The following are the postharvest off-flavor substances, TA, and TSS of Wenzhou mandarin oranges: A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content; E: titratable acid (TA) content; F: soluble solids (TSS) content. Detailed Implementation

[0025] This invention provides the application of γ-aminobutyric acid in reducing the accumulation of off-odor substances in fruits after harvest, which can reduce the accumulation of off-odor substances, including ethanol, acetaldehyde or methanol, in fruits subjected to hypoxia stress.

[0026] This invention also provides a postharvest preservative for citrus fruits with GABA as the main component. The preservative is an aqueous solution of GABA at a concentration of 0.2 mM to 0.5 mM.

[0027] This invention also provides a method for reducing the postharvest alcoholic odor of fruit, specifically including the following steps:

[0028] First, select the fruit material: choose healthy citrus fruits that are uniform in size, have no obvious external damage, and have reached commercial maturity;

[0029] The fruit is then processed, including the following two methods.

[0030] Treatment method 1: The GABA aqueous solution is 0.2mM-0.5mM. Soak the fruit at room temperature for 2 minutes, dry the fruit surface, apply wax, and store at room temperature.

[0031] Treatment method 2: The GABA aqueous solution is 0.2mM-0.5mM. Soak the fruit at room temperature for 2 minutes, dry the fruit surface, bag each fruit individually, and store at a low temperature of 5℃-8℃.

[0032] To further illustrate the present invention, the application of γ-aminobutyric acid provided by the present invention in reducing the accumulation of off-flavor substances in fruits is described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1

[0034] The test samples were early-maturing Satsuma mandarins, collected from commercial orchards in Yiling District, Yichang City, Hubei Province. Fruits of uniform size and without obvious external damage were selected and divided into two groups for later use.

[0035] The experimental group was soaked in a 0.2 mM GABA aqueous solution for 2 minutes, while the control group was soaked in tap water for 2 minutes. After the fruits were naturally air-dried, half of the fruits from each group were manually and evenly coated with a commercial 402D coating agent. After the wax coating was naturally air-dried, the fruits were stored at room temperature, and samples were taken periodically during storage to test fruit quality indicators.

[0036] The results show ( Figure 1 Compared to uncoated fruit, coating treatment significantly induced the accumulation of ethanol, acetaldehyde, and methanol, the off-flavor substances in Satsuma mandarin oranges, with ethanol accumulation being the highest, several times higher than acetaldehyde and methanol. For coated Satsuma mandarin oranges, compared to the control, GABA treatment significantly reduced the content of coating-induced off-flavor substances ethanol, acetaldehyde, and methanol on day 14 of storage; on day 21 of storage, the accumulation of ethanol and methanol was also significantly reduced in coated fruit treated with GABA. Furthermore, for uncoated citrus fruit, GABA treatment promoted the accumulation of fermentation metabolites ethanol and acetaldehyde. These results indicate that GABA can significantly reduce the accumulation of coating-induced off-flavor substances ethanol, acetaldehyde, and methanol, and alleviate postharvest alcoholic off-flavors in fruit.

[0037] Figure 1 In this context, AD represents A: fruit appearance; B: ethanol content; C: acetaldehyde content; and D: methanol content. All data are mean ± standard error. The t-test was used to compare differences between two groups (significance level: *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001), and ANOVA was used to compare differences among multiple groups. CK: Soaking in tap water for 2 min; GABA: Soaking in 0.2 mM GABA aqueous solution for 2 min; 402D: Soaking in tap water and drying followed by treatment with commercial 402D brightening coating agent; GABA+402D: Soaking in GABA and drying followed by treatment with commercial 402D brightening coating agent.

[0038] Example 2

[0039] The test samples were commercially ripe Wenzhou mandarins, collected from commercial orchards in Yiling District, Yichang City, Hubei Province. Fruits of uniform size and without obvious external damage were selected and divided into three groups for later use.

[0040] Three groups of citrus fruits were soaked for 2 minutes each in 0.5 mM GABA, 0.5 mM GABA synthesis inhibitor DL-2-allylglycine (ALGLY) aqueous solution, and tap water, respectively, with the tap water treatment group serving as the control. After the fruits were naturally air-dried, half of the fruits from each group were manually and evenly coated with a commercial 402D coating agent, with the coated fruits soaked in tap water serving as the control. The coated fruits were stored at room temperature after the wax coating was naturally dried, while the uncoated fruits were individually bagged and stored at room temperature. Samples were taken periodically during storage to determine fruit quality indicators.

[0041] The results show that ( Figure 2 The coating treatment significantly induced the accumulation of fermentation metabolites ethanol and acetaldehyde, especially ethanol, in Wenzhou mandarin oranges. For coated Wenzhou mandarin oranges, on the 10th day of storage, the ethanol and acetaldehyde contents in fruits coated after soaking in GABA aqueous solution were significantly lower than those in fruits coated after soaking in tap water (control). However, the ethanol and acetaldehyde contents in fruits coated after treatment with the GABA synthesis inhibitor DL-2-allylglycine showed no significant difference compared to the control. For uncoated fruits, on the 10th day of storage, the ethanol content in the GABA-treated group was significantly increased compared to the control. Furthermore, compared to fruits coated after soaking in tap water, the GABA-treated coating treatment had no significant effect on the titratable acid (TA) and soluble solids (TSS) content of citrus fruits. These results indicate that GABA treatment can delay the accumulation of ethanol and acetaldehyde, the off-flavor substances induced by coating treatment, reduce postharvest alcoholic off-flavors, and improve the marketability of the fruit.

[0042] Figure 2 In this table, AF represents A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content; E: titratable acid (TA) content; and F: soluble solids (TSS) content. All data are mean ± standard error. Differences between two groups were compared using t-tests (significance levels: *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001), and differences among multiple groups were compared using analysis of variance. CK: Soak in tap water for 2 min; GABA: Soak in 0.5 mM GABA aqueous solution for 2 min; 402D: Soak in tap water and air dry, then treat with 402D coating agent; ALGLY: Soak in 0.5 mM GABA synthesis inhibitor DL-2-allylglycine for 2 min; 402D: Soak in tap water and air dry, then treat with commercial 402D bright coating agent; GABA+402D: Soak in 0.5 mM GABA and air dry, then treat with commercial 402D bright coating agent; ALGLY+402D: Soak in 0.5 mM DL-2-allylglycine and air dry, then treat with commercial 402D bright coating agent.

[0043] Example 3

[0044] The test samples were commercially mature 'Lunwan' navel oranges, collected from commercial orchards in Zigui County, Yichang City, Hubei Province. Fruits of uniform size and without obvious external damage were selected and divided into two groups for later use.

[0045] The experimental group soaked citrus fruits in a 0.5 mM GABA aqueous solution for 2 minutes, while the control group soaked citrus fruits in tap water for 2 minutes. After natural air drying, half of the fruits from each group were manually and evenly coated with a commercial 402D coating agent. The coated fruits soaked in tap water served as the control. Fruits with the wax coating were stored at room temperature after natural air drying, while uncoated fruits were individually bagged and stored at room temperature. Samples were taken periodically during storage to determine fruit quality indicators.

[0046] The results show ( Figure 3 From day 5 of storage, ethanol began to accumulate in coated fruits, but within 5 days, the ethanol content in coated and uncoated fruits was not significantly different. In the early stages of rapid ethanol accumulation, namely days 5 and 9 of storage, the ethanol content in GABA-treated coated fruits was significantly lower than the control. However, as storage time increased, the ethanol content in GABA-treated coated fruits showed no significant difference from the control. These results indicate that GABA can delay the accumulation of citrus off-flavor substances induced by coating and reduce postharvest alcoholic off-flavors. Furthermore, contrary to the results of GABA-treated coated fruits, the ethanol content in GABA-treated uncoated fruits was significantly higher than the control in both the early and late stages of storage, indicating that GABA treatment can induce ethanol fermentation metabolism to some extent under normoxic conditions.

[0047] Figure 3 In the table, AF represents A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content; E: titratable acid (TA) content; and F: soluble solids (TSS) content. All data are mean ± standard error. The t-test was used to compare differences between two groups (significance level: *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001), and ANOVA was used to compare differences among multiple groups. CK: Soaking in tap water for 2 min; GABA: Soaking in 0.5 mM GABA aqueous solution for 2 min; 402D: Soaking in tap water and drying followed by 402D coating agent treatment; GABA+402D: Soaking in 0.5 mM GABA and drying followed by 402D coating agent treatment.

[0048] Example 4

[0049] The test samples were commercially ripe Wenzhou mandarins, collected from commercial orchards in Yiling District, Yichang City, Hubei Province. Fruits of uniform size and without obvious external damage were selected and divided into two groups for subsequent experiments.

[0050] The experimental group underwent GABA immersion treatment: citrus fruits were immersed in a 0.5 mM GABA aqueous solution for 2 minutes, while the control group was immersed in tap water for 2 minutes. Half of the fruits in the experimental group were manually and evenly coated with a commercial 402D coating agent. One-third of the fruits in the control group were manually and evenly coated with a commercial 402D coating agent containing 0.5 mM GABA.

[0051] As shown in the figure ( Figure 4 Compared to untreated fruit, the coating treatment induced a significant accumulation of ethanol, a fermentation metabolite, in Wenzhou mandarin oranges as early as day 5 of storage. In contrast, in 'Lunwan' navel oranges in Example 3, ethanol accumulation in large quantities under coating treatment only occurred on day 9 of storage. This indicates that coating treatment more readily induces the accumulation of ethanol in Wenzhou mandarin oranges compared to 'Lunwan' navel oranges. Similar to the results in Example 3, GABA treatment significantly reduced the accumulation of ethanol induced by coating treatment. On days 10, 15, and 20 of storage, the ethanol content in fruit treated with GABA-soaked coating was significantly lower than the control. However, adding GABA to the 402D coating agent was less effective than soaking the fruit in GABA. The ethanol content in the GABA-added 402D coating agent treatment was significantly lower than the control on day 10 of storage, but significantly higher on days 5 and 15. Furthermore, the ethanol content in the GABA-treated group was significantly higher than that in the control group on days 5, 10, and 20 of storage; the acetaldehyde content in the GABA-treated group was also significantly higher than that in the control group on days 10 and 20 of storage. This indicates that GABA promotes ethanol fermentation metabolism in fruits when it is not induced by hypoxia stress. Compared with fruits treated with tap water followed by 402D coating agent, the TA content in fruits treated with 402D coating agent containing GABA was significantly higher than that in the control group at all storage stages. There was no significant difference in TA content between the GABA-treated and control groups in Wenzhou mandarin oranges. These results indicate that GABA inhibits the high-activity ethanol fermentation metabolism induced by hypoxia and promotes the low-activity ethanol fermentation metabolism under normoxic conditions. In addition, although the combined treatment of GABA with the coating agent could not effectively delay the accumulation of postharvest off-flavor substances in citrus fruits, it enhanced the effect of GABA in delaying the degradation of organic acids in Wenzhou mandarin oranges after harvest, which was superior to the effects of GABA soaking treatment and GABA soaking followed by coating agent treatment.

[0052] Figure 4In the table, AF represents A: fruit appearance; B: ethanol content; C: acetaldehyde content; D: methanol content; E: titratable acid (TA) content; and F: soluble solids (TSS) content. All data are mean ± standard error. The t-test was used to compare differences between two groups (significance level: *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001). Analysis of variance was used to compare differences among multiple groups. CK: Soaking in tap water for 2 min; GABA: Soaking in 0.5 mM GABA aqueous solution for 2 min; 402D: Soaking in tap water and drying followed by 402D coating agent treatment; GABA+402D: Soaking in GABA and drying followed by 402D coating agent treatment; 402D(GABA): Soaking in tap water and drying followed by 402D coating agent treatment containing 0.5 mM GABA.

[0053] As demonstrated by the above embodiments, in the application of γ-aminobutyric acid (GABA) of the present invention in reducing the accumulation of off-flavor substances in fruits after harvest, GABA treatment can reduce the accumulation of off-flavor substances in fruits subjected to hypoxia stress, especially those treated with coating agents, without having other effects on fruit quality. While the GABA in this invention promotes ethanol fermentation metabolism in untreated fruits, it inhibits ethanol fermentation metabolism in treated fruits.

[0054] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. The application of γ-aminobutyric acid in reducing the accumulation of off-flavor substances in citrus fruits, characterized in that, The fruit was subjected to hypoxia stress; The odorous substance is ethanol, acetaldehyde, or methanol.

2. The application according to claim 1, characterized in that, The citrus fruit was treated with a coating agent.

3. The application according to claim 2, characterized in that, The coating agent is 402D coating agent.

4. A method for reducing postharvest alcoholic odor in citrus fruits, characterized in that, The method involves immersing citrus fruits without obvious external damage in a 0.2mM-0.5mM γ-aminobutyric acid aqueous solution for 2-5 minutes. After immersion, the fruit surface is dried and then coated with wax before storage at room temperature.

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