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Article

Effect of Silver Nitrate (AgNO3) and Nano-Silver (Ag-NPs) on Physiological Characteristics of Grapes and Quality during Storage Period

by
Essam Elatafi
1,2 and
Jinggui Fang
1,*
1
College of Horticulture, Nanjing Agricultural University, Nanjing 210095, China
2
Department of Pomology, Faculty of Agriculture, Mansoura University, Mansoura 35516, Egypt
*
Author to whom correspondence should be addressed.
Horticulturae 2022, 8(5), 419; https://doi.org/10.3390/horticulturae8050419
Submission received: 8 March 2022 / Revised: 10 April 2022 / Accepted: 13 April 2022 / Published: 7 May 2022
(This article belongs to the Special Issue Advances in Improving Fresh Produce Quality and Postharvest Shelf Life)
Browse Figures
Versions Notes

Abstract

:
The aim of this study was to evaluate the effects of silver nitrate (AgNO3) and nano-silver (Ag-NPs) on the physiological and biochemical characteristics, and quality of grape bunches during a cold storage period. For investigations, two varieties of grapes were used, Shine Muscat and Kyoho, with different concentrations of AgNO3 and Ag-NPs on post-harvest dipping. The data indicated that AgNO3 and Ag-NPs enhanced the fruits’ longevity and quality. Depending on the data analysis, it was found that the lowest weight loss value was obtained from Ag-NP treated grapes, followed by AgNO3 treated grapes, while the highest loss occurred in the control grapes. Immersion of grape bunches in Ag-NPs was the best application for maintenance of overall storage quality for both cultivars. In the same trend, treatment with Ag-NPs produced the best results for soluble solids content (SSC), titratable acidity (TA), malondialdehyde (MDA) content, polyphenol oxidase (PPO), pyrogallol peroxidase (POD), and pectin methylestraese activity (PME). It was concluded that Ag-NPs and AgNO3 were helpful in maintaining the quality of grape bunches up to 30 days, while grape bunches under control conditions were spoiled with 30 days of cold storage.

1. Introduction

Grapes deteriorate quickly, due to their delicate texture and high-water content, making them difficult to store without treatment [1]. Nonetheless, interdisciplinary studies have made significant progress in postharvest technologies for long-term preservation of table grapes, allowing the table grape sector to attain a better supply–demand balance.
AgNO3 is one of chemical materials which was used for extending the storage life of unrooted cuttings of Pelargonium × hortorum at low temperatures [2]. In addition, AgNO3 was used for reducing the extent of postharvest losses in guava fruits and to extend the shelf life [3].
The broad antimicrobial effects of AgNO3 are well-known, since Ag+ ions replace the hydrogen cations (H+) of sulfhydryl or thiol groups (-SH) on surface proteins in the cell membranes of bacteria, which leads to loss of membrane integrity, causing death of a cell [4]. AgNO3 has the ability to induce toxicity in humans and other creatures [5], so it is not utilized in commercial vase solutions. Comparing silver nanoparticles to other silver forms, it was found that silver nanoparticles have a larger surface area to volume ratio, which may make them more effective as a biocide [6], while they also have lower toxicity effects [7].
8-hydroxyquinoline sulfate (8-HQS) is an essential preservative used as a germicide in the floral industry; it used as an antimicrobial and antifungal agent [8], as well as for increasing water intake by minimizing physiological stem obstruction [9].
Silver nanoparticles (Ag-NPs) could help cut flowers to last longer after they have been harvested. In acacia flowers, nano-silver had a positive influence on the longevity of cut flowers, because of their influence on ethylene inhibitor [10,11]. Silver is considered an inhibiting agent against microorganisms because of the high surface area to volume ratio of these particles [6,12,13]. In addition, Ag-NPs have been utilized for food sector, agriculture, horticulture, food science, food processing, nano-packaging, nano-sensors, and fruit and vegetable packaging [14,15]. In the post-harvest sector, Ag-NPs treatment suppressed the growth of microorganisms in a vase solution and reduced malondialdehyde (MDA) concentration, extending the vase life of gerberas [16]. Ag-NPs were developed as agents to enhance fruit ripening [17,18]. Moreover, it decreased sugar content in Lupinus termis L. and Oryza sativa L. [19,20].
According to Ghasemnezhad et al. [21], nanotechnology can be useful in the storage of vegetables and fruits in three ways: (A) Levels of disinfection and antimicrobials: Nanotechnology can almost eliminate the entrance of bacteria by moving the surface of the coated material of any microorganism or germs into food. Microbicides containing nanoparticles, such as vegetable oils and alcohol, are safe for human health and the environment. (B) Antioxidant protection: Keeping sensitive antioxidants such as vitamins A, D, E, and K, omega-3 fatty acids, and beta-carotene in good condition has long been a vital aspect in food preservation. Nanoparticles can be used to keep such materials from degrading during the manufacturing process and during storage. (C) Inhibiting and regulating enzyme activity: Nanotechnology plays a critical role in finding and developing enzymes for construction. By changing the structure of enzymes and adding additional active particles, nanotechnology can control their metabolism. Enzyme activity can be regulated in this manner.
Nanotechnology can be used to enhance the shelf life of fruits and vegetables, because it has yet to be connected to any significant side effects. Under the current circumstances, developing adequate grape fruit processing techniques is vital to ensuring their availability for fresh fruit markets and export. Chemical treatments with AgNO3 and Ag-NPs can reduce postharvest losses in grapes and extend shelf life. The purpose of this study was to evaluate the effect of AgNO3 and Ag-NPs on the physiological and chemical properties, and quality of grape bunches during prolonged cold storage, for enhancing the deterioration of the grapes.

2. Materials and Methods

2.1. Plant Material and Storage Conditions

This study was carried out to investigate the effect of different concentrations of AgNO3 and Ag-NPs on the physiological characteristics and quality of grape bunches during cold storage. These experiments were conducted on two varieties of grape, Shine Muscat and Kyoho, over a 30-day period of cold storage of grape bunches. During the 2019/2020 harvest season, grape bunches of Vitis vinifera L., cvs Shine Muscat and Kyoho, were purchased from a local market. The experiments were carried out in the Pomology department’s lab at Nanjing Agricultural University in Jiangsu Province, China.
Grape bunches were transported to the laboratory in polyethylene bags, to reduce water loss. Grape bunches were cleaned of any foreign matter and damaged berries before being placed in plastic boxes. The grape fruit samples were packed in a plastic box and kept in cold storage bunches fruits at 4 °C with 95 percent relative humidity for 30 days, until use.

2.2. Silver Nitrate (AgNO3) and Silver Nanoparticles (Ag-NPs) Preparation

AgNO3 and Ag-NPs were purchased from (Xilong Scientific Co., Ltd., Shantou, Guangdong, China and Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), all chemicals and solvents were applied as received, without further purification.
AgNO3 solution was prepared at concentrations of 5000 and 10,000 ppm in the laboratory. While, the nanoparticle solution was prepared at concentrations of 50 and 100 ppm.

2.3. Treatment of Research Work

The treatments were administered as follows: (1) untreated grape bunches (control), (2) treated grape bunches fruits with AgNO3 solution, and (3) treated grape bunches fruits with Ag-NPs solution. Grape bunches were dipped in water without any chemical materials for the control group. Grape bunches samples were dipped in 5000 ppm and 10,000 ppm of AgNO3 for 3 and 5 min, respectively, while grape bunches samples were dipped in 50 ppm and 100 ppm of Ag-NPs for 3 and 5 min. Bunches were exposed to the air for a few minutes after dipping, as shown in Table 1. The dried bunches were packed in 0.5 kg plastic boxes and kept in cold storage at 4 °C with 95% relative humidity for 30 days then three bunches were taken for each treatment, and different berries were selected on the 1st, 10th, 20th, and 30th day for the analysis of physical characters.

2.4. Quality Assessments

Juice from the randomly gathered berries was extracted with a hand press and filtered through cheesecloth. After a short centrifugation, the supernatants were collected for juice analysis. General quality assessment parameters of weight loss, firmness, soluble solid content (SSC) and titratable acidity (TA) storage life were determined by the methods described by AOAC [22].

2.4.1. Weight Loss Measurement

The weight loss (%) of bunches was calculated using the following equation:
Weight   loss   ( % ) = M 0 −   M M 0 ∗ 100
where M is the mass of bunches during storage at 10, 20, and 30 days, and M0 is the mass of stored bunches at 0 day. Three bunches were used for the measurements.

2.4.2. Firmness

The berry firmness estimation was performed in triplicate using a digital penetrometer (GY-4 digital fruit penetrometer, Gtech Co., Ltd., Hongguang County, Jianxin Town, Fuzou, Fujian, China) and measuring the highest penetration force required for a 6-mm-diameter probe to penetrate into the berry to a depth of 5 mm at a rate of 5 mm/s1. The berries were placed perpendicular to the probe to allow penetration into the center, and the results were measured as the force in Newtons (N).

2.4.3. Soluble Solid Content (SSC)

Five berries from each bunch were combined and ground to obtain a homogeneous sample.
Total soluble solids (TSS) were determined in triplicate using a digital refractometer (3T, Atago Co., Ltd., Tokyo, Japan) at 20 °C, then a few drops from the juice were taken on prism of a refractometer and a direct reading was taken by reading the screen of the refractometer, and the results were expressed in °Brix.

2.4.4. Titratable Acidity (TA) Measurement

Five berries from each bunch were combined in triplicate and ground to obtain a homogeneous sample, then 5 mL of juice were taken for titration with 0.1 N sodium hydroxide (NaOH) to a phenolphthalein end point using a color indicator (clear to pink), and expressed as percentage of tartaric acid.
Titratable acidity (%) was calculated using the following equation:
TA = (T × M × 0.075)/V × 100
where
  • M = molarity of NaOH
  • T = titre of NaOH required (mL)
  • V = volume of sample used (mL)

2.5. Determination of Malondialdehyde (MDA) Content

A thiobarbituric acid (TBA) reaction was used to evaluate MDA levels, according to the method of Dipierro and Leonardis [23]. Fresh berry was ground into pieces, and 1-g samples were homogenized in a cooled mortar and pestle for 3 min with 10 mL of ice-cold 0.1 percent trichloroacetic acid (TCA). The homogenate was centrifuged for 10 min at 10,000× g. The supernatant was then thoroughly mixed with 4 mL of 10% TCA containing 0.25 percent TBA in a 1-mL aliquot. The mixture was promptly cooled and centrifuged at 10,000× g for 10 min after being incubated at 95 °C for 15 min. The absorbance of the supernatant was measured at 532 nm, and the absorbance at 600 nm was subtracted to adjust for nonspecific turbidity. Using an extinction value of 155 mM−1·cm−1 and an extinction coefficient of μmol/g FW, the concentrations of lipid peroxides and oxidatively changed proteins in plants were assessed in terms of MDA levels and expressed as μmol/g FW.

2.6. Determination of Polyphenol Oxidase (PPO)

Previous studies according to Tian et al. [24] on PPO activity were used as a guide, with a few tweaks. First, 2 g of tissue samples were homogenized in 10 mL of 0.1 mol/L PBS (pH 6.4) containing 0.2 g/L polyvinylpolypyrrolidone for 2 min at 4 °C. The suspension was centrifuged at 15,000× g for 30 min, and the supernatant was used to measure PPO activity with catechol as substrate at 398 nm. The reaction mixture contained 100 μL of extract, 0.004 mol H2O2, 0.1 mol PBS, and 0.5 mol catechol, in a total volume of 3.0 mL. The results were represented in units of U/g·min, with one unit equaling the rate of rise in absorbance per mass of protein per minute.

2.7. Determination of Pyrogallol Peroxidase (POD)

POD activity was determined using the information provided by Vicente et al. [25]. As previously stated, a crude extract was prepared. In a total volume of 3.0 mL, the reaction mixture contained 100 L of extract, 0.024 mol H2O2, 0.1 mol PBS, and 0.008 mol guaiacol. The enzyme activity was measured at 460 nm and 30 °C, with guaiacol as the substrate, and the results were expressed as U/g·min.

2.8. Determination of Pectin Methyl Esterase Activity (PME)

PME enzyme activity was measured in frozen berries (50 g) using a titration technique developed by Anthon and Barrett [26].

2.9. Storage Life

The shelf life of grape bunches samples was calculated by counting the days when they remained acceptable for market, according to Mondal [27].

2.10. Statistical Analysis

The experiment was designed with two grape varieties with two chemical substances each, while one had two concentrations for two periods. Each treatment contained three replicates. A factorial randomized design was used. The data were analyzed using the CoStat software package (CoStat-Statistics _v6.3, CoHort Software, Birmingham, UK). Means and the values of two experiments were first subject to analysis of variance (two-way ANOVA), and significant difference between treatment means of repeated experiments were determined using analysis of Duncan’s multiple range test at p  < 0.05 probability [28,29].

3. Results

3.1. Effect of AgNO3 and Ag-NPs on the Weight Loss (%) in Shine Muscat (A) and Kyoho (B) Grape Varieties during 30 Days Cold Storage

It was shown from the data in Figure 1 that the highest percentage weight loss was obtained from Kyoho bunches in the control treatment after 30 days, while the lowest percentage weight loss was obtained with the Ag-NPs treatment at 100 ppm for 5 min after 10 days. On the other hand, the control treatments of Shine Muscat bunches recorded the significant differences from the other treatments after 30 and 20 days, respectively. In the same trend, the Ag-NPs at the same concentration as the previous on Shine Muscat bunches had the lower weight loss percentage than on Kyoho bunches. In general, we found that the Ag-NPs treatment at 100 ppm for 5 min had the best results in the weight loss percentage in the two varieties and for all periods.

3.2. Effect of AgNO3 and Ag-NPs on Firmness Force (N) in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

It was shown from the data in Figure 2 that the lowest firmness was obtained from Kyoho and Shine Muscat bunches in the control treatment after 30 days, and the differences between them were non-significant. However, the highest firmness was obtained by Ag-NP treatment at 100 ppm for 5 min after 10 days. On the other hand, the control treatments with Shine Muscat bunches recorded more significant differences than the other treatments after 20 and 30 days, respectively. In the same trend, the Ag-NPs at the same concentration as on the previous Shine Muscat bunches had higher firmness on Kyoho bunches. In general, we found that the Ag-NPs treatment at 100 ppm for 5 min had the best results for firmness, in the two varieties and for all periods.

3.3. Effect of AgNO3 and Ag-NPs on Soluble Solids Content (%) in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

It was shown from the results in Figure 3 that the highest SSC percentage was obtained from Shine Muscat bunches in the control treatment after 30 days. However, the lowest SSC percentage was obtained by Ag-NP treatment at 100 ppm for 5 min after 10 days. On the other hand, the control treatments in Shine Muscat bunches recorded more significant differences than the other treatments after 30 and 20 days, respectively. In the same trend, the Ag-NPs at the same concentration as on the previous Shine Muscat bunches had a lower the SSC percentage on Kyoho bunches. In general, we found that the Ag-NPs treatment at 100 ppm for 5 min had the best results for SSC percentage, in the two varieties and for all periods.

3.4. Effect of AgNO3 and Ag-NPs on Titratable Acidity (%) in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

As shown in Figure 4, the lowest percentage TA was obtained from Kyoho and Shine Muscat bunches in the control treatment after 30 days, respectively. However, the highest percentage TA was obtained by the Ag-NP treatment at 100 ppm for 5 min after 10, 20, and 30 days for the two varieties, and the differences between both of them were non-significant, except for the period after 10 days where the differences were significant. On the other hand, the control treatments in Shine Muscat bunches recorded more significant differences than the other treatments after 20 and 30 days, respectively. In the same trend, the Ag-NPs at the same concentration as on the previous Shine Muscat bunches had a higher TA percentage on Kyoho bunches. In general, we found that the Ag-NPs treatment at 100 ppm for 5 min had the best results in TA percentage, in the two varieties and for all periods.

3.5. Effect of AgNO3 and Ag-NPs on Malondialdehyde (MDA) content in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

As shown from the results in Figure 5, the highest MDA content was obtained from Kyoho bunches in the control treatment after 30 days. However, the lowest MDA was obtained by the Ag-NP treatment at 100 ppm for 5 min after 10 days in Shine Muscat bunches. On the other hand, the control treatments in Shine Muscat bunches recorded more significant differences than the other treatments after 30 and 20 days, respectively. In the same trend, the Ag-NPs at the same concentration as on the previous Shine Muscat bunches had a lower MDA content on Kyoho bunches. In general, we found that the Ag-NP treatment at 100 ppm for 5 min had the best results for MDA content in the two varieties and for all periods.

3.6. Effect of AgNO3 and Ag-NPs on Polyphenol Oxidase (PPO) Activity in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

As shown from the results in Figure 6, the highest PPO activity was obtained from Kyoho bunches in the control treatment after 20 days. However, the lowest MDA was obtained by Ag-NPs treatment at 100 ppm for 5 min after 30 days in Shine Muscat bunches. On the other hand, the control treatments in Shine Muscat bunches recorded more significant differences than the other treatments after 20 and 10 days, respectively. In the same trend, the Ag-NPs at the same concentration as on the previous Shine Muscat bunches had a lower PPO activity on Kyoho bunches. In general, we found that the treatment of Ag-NPs treatment at 100 ppm for 5 min had the best results for PPO activity in the two varieties and for all periods.

3.7. Effect of AgNO3 and Ag-NPs on Pyrogallol Peroxidase (POD) Activity in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

According to the data in Figure 7, the highest POD activity was obtained from Kyoho bunches in the control treatment after 20 days. However, the lowest POD activity was obtained by Ag-NP treatment at 100 ppm for 5 min after 30 days in Shine Muscat bunches. On the other hand, the control treatments in Shine Muscat bunches recorded more significant differences than the other treatments after 20 and 10 days, respectively. In the same trend, the Ag-NPs at the same concentration as on the previous Shine Muscat bunches had a lower POD activity on Kyoho bunches. In general, we found that the Ag-NP treatment at 100 ppm for 5 min had the best results for POD activity in the two varieties and for all periods.

3.8. Effect of AgNO3 and Ag-NPs on Pectin Methylestraese Activity (PME) Activity in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

According to the data in Figure 8, the highest PME activity was obtained from Shine Muscat and Kyoho bunches in the control treatment after 30 days, and the differences between both varieties were nonsignificant in all periods. On the other hand, the lowest PME activity was obtained by Ag-NP treatment at 100 ppm for 5 min after 10 days in Shine Muscat bunches. On the other side, the control treatments in Shine Muscat bunches recorded more significant differences than the other treatments after 30 and 20 days, respectively. In the same trend, Ag-NPs at the same concentration as on the previous Shine Muscat bunches had a lower PME activity on Kyoho bunches. In general, we found that Ag-NPs treatment at 100 ppm for 5 min had the best results for PME activity in the two varieties and for all periods.

4. Discussions

4.1. Effect of AgNO3 and Ag-NPs on the Weight Loss (%) in Shine Muscat (A) and Kyoho (B) Grape Varieties during 30 Days Cold Storage

Weight loss is one of the important indicators of the quality of bunches of grapes during prolonged cold storage. Generally, it is clear that weight loss gradually increased significantly during the cold storage period especially for the control, and the effect of Ag-NPs and AgNO3 treatments were clear for reducing weight loss % in the treated samples, as shown Figure 1A,B. The control recorded a high value in weight loss % at end of cold storage, whereas the treated samples with Ag-NPs and AgNO3 were better and had less weight loss. These results conform with the studies conducted by [30], who proved that the lowest values for weight loss were in the coated date fruits (Hyani cv.); 34.9, 34.8, and 34.4% with PVA + 25 ppm Ag-NPs, PVA + 50 ppm Ag-NPs, and PVA + 100 ppm Ag-NPs, respectively, and the same results were obtained by other researchers [31,32,33,34].
In general, the findings were consistent with previous research that showed a reduction in weight loss caused by Ag-NPs, which acted as semipermeable barriers against oxygen, carbon dioxide, and moisture; reducing respiration, water loss, and oxidation reactions [30,35,36,37,38]. Ref. [39] reported in this context that the nanoparticles are responsible for creating a zigzag in the film structure, which obstructs the passage of permeates such as O2, Co2, and water vapor. In addition, the reduction in weight loss in berries treated with AgNO3 compared with the control was due to reduction or interruption in fruit respiration rate by AgNO3 and its stimulatory effect on fruit metabolism [40]. These results conform with the studies conducted by [41] in orange, ref. [42] in banana, and [3] in guava. Furthermore, soaking pieces of tomato pericarp in AgNO3 solution can inhibit ethylene, as well as reduce endogenous ethylene production [43].

4.2. Effect of AgNO3 and Ag-NPs on Firmness in Shine Muscat (A) and Kyoho (B) Grape Varieties during 30 Days Cold Storage

Determining the firmness level of fruit is one way to find out the characteristics of fruit maturity. As shown Figure 2A,B, it is clear that the firmness level gradually decreased during cold storage period, especially with controls, while the firmness level was higher in samples treated with Ag-NPs and AgNO3. These findings are consistent with previous research on tomato fruits conducted by [44].
The decrease in the firmness level of the berries of grape was due to a change in the composition of the cell wall constituents, due to the breakdown of insoluble protopectin into soluble pectin, causing softening to occur [45]. The increase of pectin reduces the cell wall cohesion power that binds cells to one another. As a result, the fruit firmness will decrease, and the fruit becomes soft.
According to [46], Ag+ ions from AgNO3 and Ag-NPs solutions, which inhibit the formation of 1-aminocyclopropane-1-carboxylic acid (ACC), will inhibit the formation of ethylene hormone, which can accelerate the maturity process. When the maturity process is inhibited, then the degradation of protopectin into pectin, which dissolves in water, will also be inhibited, so that the increase in the hardness value will be more stable.

4.3. Effect of AgNO3 and Ag-NPs on Soluble Solids Content (°Brix) in Shine Muscat (A) and Kyoho (B) Grape Varieties during 30 Days Cold Storage

The data in Figure 3A,B show the SSC during cold storage periods. Where the SSC of all samples was increased during the storage periods. These results are in line with those reported by [47], who mentioned that the SSC of fruits continuously increased with the progress of cold storage periods. The results in Figure 3A,B indicate that the SSC was significantly increased in control berries of grapes compared to those treated with Ag-NPs and AgNO3. These results can be explained in that dipping in solutions of Ag-NPs and AgNO3 regulates the internal atmosphere, by forming a semipermeable film [48]. As a result of this, respiration rate and SSC are decreased, due to slower carbohydrates hydrolysis into sugars [49,50,51]. Additionally, the SSC increased in control samples, due to the higher rate of evaporation and respiration from the grape surface [36].
The increase in SSC may be a consequence of cell-wall degradation or the degradation of other polysaccharides present in the fruit. Another elucidation for the observed increase in the SSC is the considerable loss of water during storage [52]. However, the treated berries experienced only a very slight increase of SSC, and the treatment with Ag-NPs was effective in retardation of the metabolic process and oxygen permeation [53]. Our results are in agreement with those reported by [54], who found that, during postharvest storage, apricots undergo a rise in respiration, which results in an increase in SSC by the loss of water as a result of dehydration during storage.

4.4. Effect of AgNO3 and Ag-NPs on Titratable Acidity (%) in Shine Muscat (A) and Kyoho (B) Grape Varieties during 30 Days Cold Storage

In general, the values of titratable acidity decrease with time during cold storage, this may be due to the consumption of organic acids in the breathing process, with a slow decrease observed with treated samples [55]. This is evident from the obtained results in Figure 4A,B. The titratable acidity was significantly reduced in control samples of berries stored at 4 °C, compared to treatments with Ag-NPs and AgNO3. The results depicted a much lower decrease in titratable acidity in treated grapes with Ag-NPs and AgNO3 compared to the control, which is due to the slower respiration rate and conversion of organic acid into sugars during metabolic processes [48]. Minimum titratable acidity was observed in the control, while the maximum titratable acidity was observed in berries treated with Ag-NPs at 100 ppm for 5 min. Similar results were revealed by [42]. Retention of acidity by application of a coating material in fruits and vegetables was reported in previous studies [56]. Fresh fruit under low temperature and storage demonstrated slow respiration and metabolic reaction, which resulted in a high rate of titratable acidity retention [37].

4.5. Effect of AgNO3 and Ag-NPs on Malondialdehyde (MDA) Content in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

Reactive oxygen species (ROS) accumulation was able to cause and exacerbate oxidative damage to lipids during fruit and vegetable preservation, forming toxic products such as MDA, a secondary end product of polyunsaturated fatty acid oxidation [57].
As a result, MDA is commonly used as an indicator to assess the progress of fruit ripening, as it represents the level of lipid peroxides and the structural integrity of plant membranes; and, according to this trend, we found that the Ag-NPs treatment at 100 ppm for 5 min had the best results for MDA content in the two varieties and for all periods, as shown in Figure 5A,B.

4.6. Effect of AgNO3 and Ag-NPs on Polyphenol Oxidase (PPO) Content in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

PPO activities increased significantly in all treatments after 20 days during cold storage at Figure 6A,B. Enzymatic browning, which occurs primarily as a result of the oxidation of phenolic compounds and contributes to quality loss [58], as well as significant economic loss, due to consumer unacceptability, is one of the most important causes of color deterioration in fruits. PPO is the primary enzyme responsible for the browning reaction, because it can catalyze the hydroxylation of monophenols to o-diphenols and the oxidation of o-diphenols to o-quinones. Based on this, we found that the treated with Ag-NPs at 100 ppm for 5 min had the best results in the PPO activity in the two varieties and for all periods.

4.7. Effect of AgNO3 and Ag-NPs on Pyrogallol Peroxidase (POD) Activity in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

In all treatments, the POD activity increased gradually and peaked on day 20, as shown in Figure 7A,B, because diphenols can act as reducing substrates in the POD reaction, and it is another oxidoreductase enzyme involved in enzymatic browning [59]. Peroxidases have been shown to participate in a variety of physiological processes, such as lignification and wound healing [60]. Biles [61] explained the role of POD in damaged tissues, describing its involvement in cell wall cross-linking and in pathogen-infected tissues. As a result, increasing POD activity in treated grape fruits would reflect the progression of tissue damage during storage, whereas lower POD activity in grapes with nano-silver indicated that these fruits experienced less damage than the controls.

4.8. Effect of AgNO3 and Ag-NPs on Pectin Methylestraese (PME) Activity in Shine Muscat and Kyoho Grape Varieties during 30 Days Cold Storage

According to the results in Figure 8A,B, the samples treated with 100 ppm for 5 min with Ag-NPs had the lowest enzyme activity during storage. Activity continued to increase during prolonged cold storage, indicating that those bunches of grapes had a slower ripening process than the others. This behavior may correlate with O2 consumption, since this plays a key role in the maturation process, where the coatings made with Ag-NPs showed the lowest O2 consumption rate, according to Garcia-Betanzos [62].

5. Conclusions

Based on this research, it can be concluded that increasing the concentration of inhibitor solution of Ag-NPs and AgNO3 can reduce the effect of a prolonged cold storage period on various responses, including weight loss, soluble solids content (SSC), and inhibited the activity of PPO, POD, and PME, had and the highest values of firmness and acidity. Therefore, postharvest Ag-NPs at 100 ppm for 5 min may be used as chemical means to extend the storage life of processed grapes with an alleviating effect on physiological and chemical disorders.
Previously, there were not many papers published about using (AgNO3 and Ag-NPs) nanoparticles in grapes postharvest. Our paper is the first to use the AgNO3 and Ag-NP nanoparticles to improve grape bunches. Currently and in the future, we recommend further research about the ability of nanoparticles to improve the quality and quantity of grape bunches and their consumer viability.

Author Contributions

Conceptualization, E.E. and J.F.; methodology, E.E.; performed the experiment, E.E.; software, E.E.; validation, J.F.; formal analysis, E.E.; investigation, E.E.; resources, E.E.; data curation, E.E.; writing—original draft preparation, E.E.; writing—review and editing, J.F.; supervision, J.F.; project administration, J.F.; funding acquisition, J.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Key Research and Development Program (2019YFD1000101) National Natural Science Foundation of China (31872047).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Data sets analyzed during the current study are available from the authors on reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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Horticulturae 08 00419 g001a 550Horticulturae 08 00419 g001b 550
Figure 1. Effect of AgNO3 and Ag-NPs on the weight loss (%) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
Figure 1. Effect of AgNO3 and Ag-NPs on the weight loss (%) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
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Figure 2. Effect of AgNO3 and Ag-NPs on Firmness Force (N) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
Figure 2. Effect of AgNO3 and Ag-NPs on Firmness Force (N) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
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Figure 3. Effect of AgNO3 and Ag-NPs on Soluble Solids Content (%) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
Figure 3. Effect of AgNO3 and Ag-NPs on Soluble Solids Content (%) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
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Figure 4. Effect of AgNO3 and Ag-NPs on Titratable Acidity (%) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
Figure 4. Effect of AgNO3 and Ag-NPs on Titratable Acidity (%) in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
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Figure 5. Effect of AgNO3 and Ag-NPs on malondialdehyde (MDA) content in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
Figure 5. Effect of AgNO3 and Ag-NPs on malondialdehyde (MDA) content in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
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Figure 6. Effect of AgNO3 and Ag-NPs on Polyphenol Oxidase (PPO) in Shine Muscat (A) Kyoho (B) of grape varieties during 30 days cold storage.
Figure 6. Effect of AgNO3 and Ag-NPs on Polyphenol Oxidase (PPO) in Shine Muscat (A) Kyoho (B) of grape varieties during 30 days cold storage.
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Figure 7. Effect of AgNO3 and Ag-NPs on Pyrogallol Peroxidase (POD) activity in Shine Muscat (A) and Kyoho (B) of grape varieties during 30 days cold storage.
Figure 7. Effect of AgNO3 and Ag-NPs on Pyrogallol Peroxidase (POD) activity in Shine Muscat (A) and Kyoho (B) of grape varieties during 30 days cold storage.
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Figure 8. Effect of AgNO3 and Ag-NPs on Pectin methylestraese (PME) activity in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
Figure 8. Effect of AgNO3 and Ag-NPs on Pectin methylestraese (PME) activity in Shine Muscat (A) and Kyoho (B) grape varieties during 30 days cold storage.
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Table
Table 1. Experimental treatments with silver nitrate and silver nanoparticles of different concentrations for different periods on Shine Muscat and Kyoho grape.
Table 1. Experimental treatments with silver nitrate and silver nanoparticles of different concentrations for different periods on Shine Muscat and Kyoho grape.
GroupsTreatments
T0Control (water without chemical)
T1AgNO3 5000 ppm for 3 min
T2AgNO3 5000 ppm for 5 min
T3AgNO3 10,000 ppm for 3 min
T4 AgNO3 10,000 ppm for 5 min
T5Ag-NPs 50 ppm for 3 min
T6Ag-NPs 50 ppm for 5 min
T7Ag-NPs 100 ppm for 3 min
T8Ag-NPs 100 ppm for 5 min
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Elatafi, E.; Fang, J. Effect of Silver Nitrate (AgNO3) and Nano-Silver (Ag-NPs) on Physiological Characteristics of Grapes and Quality during Storage Period. Horticulturae 2022, 8, 419. https://doi.org/10.3390/horticulturae8050419

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Elatafi E, Fang J. Effect of Silver Nitrate (AgNO3) and Nano-Silver (Ag-NPs) on Physiological Characteristics of Grapes and Quality during Storage Period. Horticulturae. 2022; 8(5):419. https://doi.org/10.3390/horticulturae8050419

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Elatafi, Essam, and Jinggui Fang. 2022. "Effect of Silver Nitrate (AgNO3) and Nano-Silver (Ag-NPs) on Physiological Characteristics of Grapes and Quality during Storage Period" Horticulturae 8, no. 5: 419. https://doi.org/10.3390/horticulturae8050419

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