Effect of Storage Conditions on the Quality Attributes of UV-C Light-Pretreated Plums (Prunus salicina cv. “Moscatel”)

Abstract

Plums are one of the most important stone fruits worldwide. Surprisingly, the effect of UV-C light on improving their bioactive compounds and its effect during storage has not been explored. This research aimed to assess the effect of UV-C light on the bioactive compounds and antioxidant capacity of plums, as well as to evaluate the storage conditions on the quality attributes of these fruits. Plums were UV-C light-irradiated (0, 0.175, and 0.356 kJ/m²) to analyze their effect on phenolic compounds, total anthocyanins, and antioxidant capacity. A selected dose of UV-C light treatment was applied to plums as a pretreatment to assess the effect of packaging (non-packed, packed in closed polyethylene boxes, and packed in closed polyethylene boxes with perforations) and temperature (5, 15, and 20 °C) on the quality characteristics of plums using a 3² experimental design. The results showed that phenolic compounds (3–10%), total anthocyanins (22–39%), and antioxidant capacity (8–15%) increased with the UV-C light treatment (0.356 kJ/m²). In storage, firmness remained constant, and color parameters (a* and b*) were reduced in all conditions, whereas weight loss was lower in plums stored in closed packages. Moreover, total anthocyanins and antioxidant capacity were enhanced under all storage conditions. The microbial load decreased due to the UV-C light treatment and remained constant during storage time (<100 CFU/g). Storing the plums at a low temperature in a closed package effectively preserved the quality attributes of plums for 40 days without affecting the sensory acceptance.

1. Introduction

The plum is a fruit that belongs to the Rosaceae family, which includes both the European (Prunus domestica L.) and Japanese (Prunus salicina Lindl.) species [1]. The popularity of plums among consumers has been increasing worldwide, with an annual production of over 12.6 million tons [2]. Although plums are generally recognized as a climacteric fruit, Minas et al. [3] have identified three types of physiological behaviors in plums: climacteric, suppressed climacteric, and non-climacteric. These behaviors are associated with a high respiration rate that affects postharvest quality, limits storage life, and influences fruit consumption [4,5]. To improve the storage life of plums, Khan et al. [6] indicated storing at low temperatures. However, to prevent the chilling injury associated with low temperature storage and enhance the shelf-life, the use of modified and controlled atmospheres, edible coatings, aqueous dip treatment with sodium nitroprusside (nitric oxide source), and staggered treatments has been proposed [5,7,8,9,10].

Plums are often consumed both fresh and dried. They are a rich source of bioactive compounds, such as flavonoids, phenolic acids, vitamin C, and carotenoids. These compounds possess strong antioxidant properties, which help protect cells from the oxidative damage that causes various chronic diseases, such as certain types of cancer, as well as inflammatory, neurodegenerative, and cardiovascular disorders [11]. In addition, it has been published that plums are useful in the treatment of digestive and blood circulation disorders [12]. In this regard, one of the main characteristics of plums is a higher concentration of anthocyanins (peel mainly) such as cyanidin-3-glucoside, cyanidin-3-rutinoside, cyanidin-3-xyloside, peonidin-3-glucoside, and peonidin-3-rutinoside [13].

Sanitizing fruits and vegetables before consumption is necessary for ensuring consumer safety. The use of disinfecting agents helps reduce microbial load at the beginning of the process. However, improper handling can lead to the rapid proliferation of microorganisms, reaching levels like the initial load [14]. Although chlorinated compounds are widely used in many countries, their use can lead to the formation of trihalomethanes, which pose health risks [15]. Therefore, numerous studies have been conducted to develop sanitizers and disinfection methods for fruits and vegetables [16]. One promising alternative is the use of physical treatments, such as ultraviolet-C light (UV-C light, “254 nm”), which can effectively disinfect cookware, equipment, and food [17,18]. In this context, Pérez-Ambrocio et al. [19] and Menaka et al. [20] established that UV-C light can be used as a postharvest technology to reduce the loss of fresh produce and enhance its quality characteristics. On the other hand, the UV-C light effect on microorganisms is at the DNA level, generating photo products such as pyrimidine dimers that block DNA transcription and replication, causing cell death [17]. Furthermore, in fruits and vegetables, this technology can act as an abiotic stress that induces the synthesis of secondary metabolites with antioxidant capacity (vitamins C and E, carotenoids, flavonoids, tannins, and phenolic acids) [21].

Recently, the demand and consumption of fruits and vegetables, whether raw or fresh cut, have increased [22]. However, after harvesting, fruit and vegetables may suffer several physicochemical (dehydration and oxidation), microbiological (spoilage), and physiological (respiration, transpiration, ripening, and senescence) changes, which can reduce their quality characteristics if handling and storage conditions are inadequate [23]. In fruit and vegetables, storing at low temperatures can slow down microbial growth and reduce their enzymatic and metabolic activities. However, to meet consumer demands, it is essential to manage chilling injury and dehydration. Proper packaging can help mitigate chilling injuries, dehydration, metabolic changes, and microbial growth in fruit and vegetables. Additionally, packaging can modify the internal atmosphere by changing the concentrations of oxygen (O₂) and carbon dioxide (CO₂), which may extend the shelf life of certain food products [24].

According to the author’s knowledge, the use of UV-C light as a pretreatment to induce the synthesis of antioxidant compounds and its effect on the quality attributes of plums during storage have not been explored. Therefore, this study aimed to evaluate the effect of UV-C light on the bioactive compounds and antioxidant capacity of plums, as well as the impact of storage conditions on their quality attributes.

2. Materials and Methods

2.1. Fruit Material

Fresh plums (Prunus salicina cv. ‘Moscatel’) were acquired from a local farm in Puebla, Mexico. The fruits were harvested at commercial maturity and selected based on their homogeneous light red color (L* = 27.0 ± 2.0, a* = 25.4 ± 4.6, b* = 4.6 ± 0.9) and being free from physical and microbiological apparent damages. The fruits were washed with distilled water, gently dried with absorbent paper, and used for further analysis.

2.2. Chemical Reagents

Folin–Ciocalteu reagent, gallic acid, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and tartaric acid were purchased from Sigma–Aldrich (St. Louis, MO, USA). Standard plate count and potato dextrose agar were purchased from Difco (MD, USA). Ethanol, methanol, and hydrochloric acid were obtained from J.T. Baker (Phillipsburg, NJ, USA).

2.3. UV-C Light Treatment

The UV-C light equipment used in this study was assembled at the Benemerita Universidad Autonoma de Puebla, Puebla, Mexico. The equipment consists of a chamber (60 × 60 × 60 cm) of stainless steel containing six (one per side) UV-C lamps (Model G15T8, General Electric, CT, USA). A grid was inserted in the middle of the chamber (Figure 1). Ten fruits (13–20 g each) were placed separately on the grid to be totally covered on their surface by the UV-C light. The UV-C lamp intensity was measured on the grid using a digital radiometer (model DT-1309, London, UK). The plums were UV-C light treated (in triplicate) at room temperature (22–24 °C) for 0 (control), 30, and 60 s, corresponding to doses of 0, 0.175, and 0.356 kJ/m², respectively (the doses were selected according to preliminary tests). The effect of the UV-C light treatments on the bioactive compounds and antioxidant capacity of the plums was immediately evaluated.

2.4. Storage Conditions

The plums were treated with a selected UV-C light dose to evaluate the effect of storage conditions on the quality characteristics. The fruits were divided into nine groups and stored according to a 3² general factorial design (Design-Expert program 6.0.6, Stat Ease Inc., Minneapolis, MN, USA) with storage temperatures (5, 15, and 20 °C) and packaging (non-packed, packed in closed polyethylene boxes, and packed in closed polyethylene boxes with 21 perforations of 0.5 cm in diameter each) as independent variables (Figure 1). Ten fruits per treatment were placed into seven crystal polyethylene boxes, each measuring 15 × 15 × 10 cm (2250 cm³), and then stored at the selected conditions. The evaluation of the storage conditions was conducted in duplicate. The quality attributes of plums, including physicochemical characteristics, weight loss, firmness, color, microbial counts, phenolic compounds, total anthocyanins, and antioxidant capacity, were assessed every five days until their appearance (weight loss and color change) was inadequate for consumption.

2.5. Weight Loss

The weight loss during storage was conducted by weighing four plums using a PA313 analytical balance (Ohaus Co., Zurich, Switzerland). Weight loss was calculated according to Equation (1).

(1)$WL=100-\left({\displaystyle \frac{W_i-W_f}{Wi}}\times 100\right)$

where WL is the weight loss (%), W_i is the weight at the beginning of the storage, and W_f is the weight at each storage period.

2.6. Firmness

The firmness (N) was measured in four fruits by recording the force necessary to penetrate 5 mm of the fruit with a probe of 3.5 mm diameter using a fruit hardness tester, model GY-2 (Zhejiang, China).

2.7. Color Parameters

The L* (luminosity, white to black), a* (red to green), and b* (yellow to blue) color parameters of the CIELAB color space were superficially evaluated in four plums using a Precise Color Reader model TCR 2000 (Beijing, China). Total color change (ΔE) was calculated using Equation (2).

(2)$∆E=\sqrt{{\left(L*-L_0^{*}\right)}^2+{\left(a*-a_0^{*}\right)}^2+{\left(b*-b_0^{*}\right)}^2}$

where $L_0^{*}$, $a_0^{*}$, and $b_0^{*}$ are the color parameters of the plums at the beginning of the storage, and L*, a*, and b* are the color parameters at each storage period.

2.8. Plum Puree

To evaluate the physicochemical characteristics, bioactive compounds, and antioxidant capacity of plums, six samples were blended for 30 s using a domestic food processor (Black and Decker, Towson, MD, USA). Plum puree was immediately used to conduct the analysis mentioned before.

2.9. Physicochemical Characteristics

Total soluble solids (%) and titratable acidity (% malic acid) were determined following the 932.12 and 942.15 methods of the AOAC [25], respectively. The maturity index was determined by the relation of the total soluble solids and the titratable acidity.

2.10. Total Anthocyanins

Total anthocyanins were evaluated using the differential pH method [26] with some modifications. Five g of puree were mixed with 25 mL of acidified methanol (1% hydrochloric acid) at 300 rpm for 3 h in the dark. Then, 10 mL of cotton-filtered extract were mixed with HCl (1 M) or NaOH (1 N) to reach pH values of 1 or 4.5, respectively. The absorbance was measured at 520 and 700 nm using a UV-Vis spectrophotometer (Jenway model 6405, Staffordshire, UK). Total anthocyanin content was expressed as milligrams of cyanidin-3-glucoside equivalents per 100 g of fresh weight using Equations (3) and (4).

(3)$Total anthocyanin\left(\mathrm{m}\mathrm{g}/100 \mathrm{g}\right)={\displaystyle \frac{A\times MW\times DF\times 1000}{ϵ\times L}}$

(4)$A={\left({Abs}_{520}-{Abs}_{700}\right)}_{pH=1}-{\left({Abs}_{520}-{Abs}_{700}\right)}_{pH=4.5}$

where A is the difference in absorbance, MW is the molecular weight of cyanidin-3-glucoside (g/mol), DF is the dilution factor, L is the quartz cell pathway (1 cm), and ε is the molar extinction coefficient (26, 900 M⁻¹ cm⁻¹).

2.11. Phenolic Compounds

The phenolic compounds and antioxidant capacity were determined following the methodology proposed by Hernández-Carranza et al. [27]. Ten g of plum puree were mixed with 100 mL of absolute ethanol. Then, one mL of cotton-filtered extract was mixed with 1 mL of Folin–Ciocalteu reagent (0.1 N) in an amber glass tube. After 3 min of reaction, 1 mL of NaCO₃ (0.05%) was added, mixed, and kept in a dark environment at room temperature for 30 min. Absorbance was measured at 765 nm using a UV-Vis spectrophotometer. The phenolic compounds content was calculated as milligrams of gallic acid per 100 g of fresh weight (mg GAE/100 g) using Equation (5).

(5)$Phenolic compounds\left(\mathrm{m}\mathrm{g}/100 \mathrm{g}\right)={\displaystyle \frac{abs-b}{m}}\times 100$

where abs is the absorbance, b (0.0234) is the intercept, and m (0.0229 L/100 g) is the slope of the linear regression of the Gallic acid standard curve (R² = 0.997).

2.12. Antioxidant Capacity

For determining the antioxidant capacity, 1 mL of plum filtered extract was mixed with 1 mL of DPPH radical (0.004%) and stored in a dark environment at room temperature for 30 min. Then, the absorbance was measured at 517 nm using a UV-Vis spectrophotometer. Antioxidant capacity was reported as milligrams of Trolox equivalent per 100 g of fresh weight (mg TE/100 g) using Equation (6).

(6)$Antioxidant capacity\left(\mathrm{m}\mathrm{g}/100 \mathrm{g}\right)={\displaystyle \frac{abs-b}{m}}\times 100$

where abs is the absorbance, b (4.5113) is the intercept, and m (4.809 L/100 g) is the slope of the linear regression of the Trolox standard curve (R² = 0.997).

2.13. Microbial Counts

Ten g of plums were combined with 90 mL of sterile peptone water (0.1% w/v) in a sterile plastic bag. The sample was homogenized using a stomacher (model 400, Seward, West Sussex, UK) at 300 rpm for 3 min. Then, 1 mL of the sample was serially diluted using peptone water until an appropriate dilution in the range of 30–300 colony-forming units (CFU)/g was obtained. Samples were plated on nutritive and potato dextrose (acidified with tartaric acid) agars for counting mesophiles and molds plus yeasts, respectively. Petri dishes were incubated at 37 ± 2 °C for 24–48 h for mesophiles and at 27 ± 2 °C for 4–5 days for molds plus yeasts. Microorganisms were reported as CFU/g.

2.14. Sensory Acceptance

To evaluate the sensory attributes of plums at a selected storage condition, a 7-point hedonic scale was used [28]. In the scale, number 7 being “I like very much” and number 1 being “I dislike very much”. Plums (each by judges) were given to 20 untrained judges to evaluate their color, aroma, texture, flavor, and overall acceptability. Sensory analysis was performed every 10 days during the storage time.

2.15. Statistical Analysis

All determinations were conducted in duplicate, and each experiment was performed twice. The results were analyzed by a one-way analysis of variance (ANOVA) using Minitab 15 software (Minitab Inc., PA, USA, 2008). A p-value of 0.05 was used for deciding statistical differences among the averages (Tukey’s test).

3. Results and Discussion

3.1. Effect of UV-C Light on Bioactive Compounds and Antioxidant Capacity of Plums

Plums are considered fruits rich in bioactive compounds due to their carotenoid and anthocyanin content, which provides them with a high antioxidant capacity [10]. Figure 2 shows the effect of UV-C light treatment on the bioactive compounds and the antioxidant capacity of plums. Untreated plums present phenolic compounds, total anthocyanins, and antioxidant capacity of 87.84 ± 3.4 mg GAE/100 g, 14.73 ± 0.08 mg of cyanidin-3-glucoside per 100 g, and 215.23 ± 6.54 mg TE/100 g, respectively. These values are very similar to those obtained by Zhang et al. [29]. They informed values of 88–219 mg GAE/100 g, non-detected to 58.54 mg/100 g, and 50–75 mg Trolox/100 g for the phenolic compounds, total anthocyanins, and antioxidant capacity, respectively. However, they also pointed out that the plum variety considerably affects the bioactive compounds and antioxidant capacity.

On the other hand, the UV-C light treatment significantly enhanced (p < 0.05) the bioactive compounds and antioxidant capacity in a dose-dependent manner, showing increases in the range of 3–10%, 22–39%, and 8–15% for the phenolic compounds, total anthocyanins, and antioxidant capacity, respectively. According to the available literature, UV-C light has not been assessed in plums as an abiotic stress to increase bioactive compounds. However, Fang et al. [30] evaluated the effect of abiotic factors (temperature and light) on anthocyanin accumulation in plums. They indicated that 20 °C and LED light (400–800 nm) induce the anthocyanin synthesis through the upregulation of phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumaroyl: CoA-ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT), and glutathione S-transferase (GST) enzymes. This phenomenon is known as hormesis [31]. In addition, the Pearson analysis indicates a strong correlation between phenolic compounds, particularly anthocyanins, and antioxidant capacity, showing values higher than 0.93. Based on these results, UV-C light treatment at a dose of 0.356 kJ/m² was chosen to assess the impact of the storage conditions on the quality attributes of the plums.

3.2. Effect of Storage on the Quality of Plums

3.2.1. Physicochemical Characteristics of Plums

At the beginning of the storage, total soluble solids, titratable acidity, and maturity index of the plums were 10.3 ± 0.6%, 0.5 ± 0.1% (malic acid), and 20.6 ± 2.7, respectively. Similar values were reported by Álvarez-Herrera et al. [32]. They analyzed the effect of maturity stage and storage temperature on the physicochemical characteristics of Horvin plums. At the beginning of storage, the total soluble solids, titratable acidity, and maturity index ranged from 9.14 to 13.68%, 0.75 to 1.22% (no majoritarian acid was indicated), and 9.38 to 17.91, respectively. In storage, the conditions did not affect the total soluble solids (p > 0.05). However, the titratable acidity decreased during the first 15 days of storage before remaining constant. In this context, during the respiration process, both sugar and organic acids are metabolized, causing their reduction. However, as will be discussed later, weight loss during storage may maintain the values of these physicochemical parameters. In addition, it is well-known that titratable acidity is the sum of volatile and non-volatile organic acids, but the latter compounds may be lost during storage [33]. Vangdal et al. [34] stated that, after 2 weeks of storage, the titratable acidity of plums was reduced in the range of 15–20% (a similar result was obtained in this study) due to the maturation and senescence (organic acids degradation) processes.

3.2.2. Weight Loss and Firmness of Plums

Dehydration is one of the main factors that affect the quality of fruits and vegetables during storage [23]. Figure 3A shows the weight loss of plums stored under different conditions. Non-packed plums (T1, T6, and T8) and packed with perforations (T3, T5, and T7) showed higher weight loss, while plums stored in closed packed (T2, T4, and T9) exhibited lower weight loss. Both storage temperature and packaging significantly affect the weight loss of plums during storage (p < 0.05). This phenomenon can be seen by comparing treatments T4 and T6. In this sense, T6 (non-packed and stored at 20 °C) showed the highest weight loss (27.24 ± 5.29%), whereas T4 (packed and stored at 5 °C) presented the lowest weight loss (6%) after 40 days of storage. Higher storage temperatures increase the respiration rate, leading to oxidative reactions of sugars and organic acids, and producing H₂O that can be easily lost due to the absence of packaging [32,35]. In general, the factors that most affect the weight loss of fruit and vegetables during storage are atmospheric composition, temperature, and relative humidity [36,37]. Figure 3B shows the firmness of plums (resistance to penetration) during storage under different conditions. As is observed, the firmness of the plum cv. Moscatel did not change along with the storage (p > 0.05), which is a significant advantage since firmness is a key quality parameter for plum consumption [38]. These findings align with those reported by Steffens et al. [8], who reported values of 1.1 N for plum cv. Laetitia was stored for 60 d at 0.5 °C. This suggests that low temperatures may inhibit pectolytic enzymes, maintaining the firmness of the plums [39]. Although fruits and vegetables lose firmness during storage (increasing as the temperature increases), the water loss may compact their structure, leading to shrinkage and potentially enhancing firmness [38].

3.2.3. Color Parameters and Total Color Change of Plums

Color is a key quality attribute that can enhance the value and acceptance of fruit and vegetables [40]. At the beginning of storage, plums showed values of 26.83 ± 3.9, 25.00 ± 3.90, and 4.61 ± 0.70 for L*, a*, and b* color parameters, respectively, indicating a medium dark shade of pink–red color according to the Hex color code (#632f39). Figure 4 shows the a* and b* color parameters and the total color change of plums during storage under different conditions. Notably, the L* (luminosity) color parameter did not change (p > 0.05) during the storage time. At the end of the storage, in all conditions, the values of a* significantly (p < 0.05) decreased, and the values of b* were slightly reduced. It is interesting to note that, despite the different shelf life of plums, 15 days for T2, T3, T6, and T8, 20 days for T5 and T9, 30 days for T1 and T7, and 40 days for T4, all fruits showed the same characteristic color at the end of their storage period. This information is presented in Figure 4B, showing a similar total color change for all samples at the end of the storage time, regardless of the treatment applied. The color of plums is primarily associated with two types of pigments: carotenoids (such as β-carotene and cryptoxanthin) and anthocyanins (including cyanidin-3-rutinoside, cyanidin-3-glucoside, and peonidin-3-rutinoside), which are found in both the peel and pulp. However, anthocyanins are mainly responsible for the external color of plums [1]. The color transitions from bright red to purple are due to the accumulation of anthocyanins (see Figure 5B) that occur during the ripening and senescence processes [40]. A similar finding was reported by Kodagoda et al. [41], who studied the color changes in Queen Garnet plum. They indicated that the Hue angle [tan⁻¹(b*/a*] did not change during storage time (a similar value is obtained in this study, Figure 4A). However, the Chroma color parameter (saturation of color) was significantly reduced during storage at 23 °C, comparable to those results obtained in this study, as appreciated when comparing the color parameters at the beginning and end of storage.

3.3. Bioactive Compounds and Antioxidant Capacity of Plums

Figure 5 shows the phenolic compounds (Figure 5A), total anthocyanins (Figure 5B), and antioxidant capacity (Figure 5C) of plums stored under different conditions. The phenolic compounds presented different tendencies based on the storage conditions. Generally, the phenolic compounds decreased (6–7%) in plums stored at higher temperatures. In contrast, plums stored at low temperature showed an increase of 12–24%. This enhancement can be attributed to the increased activity of PAL, C4H, and 4CL induced by low temperatures, which leads to a greater synthesis of phenolic compounds, such as anthocyanins, which serve as a defense mechanism against chilling stress [41,42]. Similar outcomes were reported by Singh and Singh [43]. In their study, plums (Prunus salicina Lindl. cv Amber Jewel) stored for 4–5 weeks at temperatures between 0 and 1 °C showed an increase in their content of phenolic compounds.

The total anthocyanins increased (100–340%) as the storage time increased, presenting higher values in fruits with the highest total color change and the shortest shelf life (T2, T3, and T6), indicating a higher anthocyanin biosynthesis associated with the overripening and senescence processes of plums [44]. It is well-known that anthocyanins are compounds that significantly contribute to the antioxidant capacity of plums [12]. This study corroborates this information, showing that the antioxidant capacity correlates well with the total anthocyanins under various storage conditions. During the ripening of plums, several biochemical processes occur, leading to the color changes associated with the synthesis of anthocyanins, which involve multiple biochemical pathways [40,41,44]. Table 1 shows the Pearson correlation between the color parameters, bioactive compounds, and antioxidant capacity of plums during storage. A negative correlation between a* and b* color parameters and total anthocyanins accumulation and their antioxidant capacity was observed. Usenik et al. [45] found negative correlations between the a* and b* color parameters and the anthocyanins presented in different varieties of plums. Interestingly, plums with a purple color are the most demanded by the consumers [41].

3.4. Microbial Counts of Plums

Plums before the UV-C light treatment showed low microbial loads (<1000 CFU/g). However, no microbial growth was detected (<10 CFU/g) after UV-C light treatment at 0.356 kJ/m². Several reports indicated that UV-C light treatment affects microorganisms at the DNA level, forming pyrimidine dimers that block the replication and transcription processes [46]. During storage, the microbial load (mesophiles and molds plus yeasts) remains constant (<100 CFU/g), regardless of the storage conditions. Pérez-Ambrocio et al. [19] highlighted that UV-C light can be effectively used to disinfect both whole and fresh-cut fruits and vegetables. The results from this study are similar to those reported by D’Hallewin et al. [47]; they pointed out that UV-C light (6 and 12 kJ/m²) reduced the microbial load in plums inoculated with Penicillium expansum L. and Botrytis cinerea. Moreover, the microbial load remained constant for 4 weeks in plums treated with a combination of UV-C light and sodium bicarbonate (2%).

3.5. Sensory Attributes of Plums Stored at Selected Conditions

According to the previous results, plums stored at 5 °C with closed packaging (T4) presented the lowest weight loss, total color change, and an adequate appearance for 40 days. Therefore, these plums were sensory evaluated (Table 2). The texture and overall acceptability of plums remained constant during 20 days of storage (I like much—I like very much). Then, consumer preferences decreased to I like much—I like moderately. The aroma and flavor scored between five and six (I like moderately—I like much). However, a slight decrease in flavor was noted at the end of the storage. These results match the tendency observed in the physicochemical characteristics, particularly regarding acidity. Crisosto et al. [4] observed that acidity, astringency, and firmness of plums decrease during the ripening and storage processes. This decline is associated with the development of flavor compounds, which enhance consumer acceptance. Additionally, color is a key sensory characteristic of fruits and vegetables [48]. In this respect, judges did not perceive any change during storage, showing an acceptance between I like much and I like very much during all of the storage times. However, at the beginning of the storage, 45% of the judges indicated that the color was liked very much. After 40 days of storage, 60% of the judges pointed out the same acceptance value of color plums. The results showed that judges recognized the change in the plums’ color, starting from light red at the beginning and transitioning to a red-to-purple hue after 40 days of storage. This observation aligns with the color measurements taken with the colorimeter (see Figure 4A).

4. Conclusions

Ultraviolet-C light is a non-thermal technology that can improve the content of bioactive compounds and the antioxidant capacity of plums, simultaneously reducing their microbial load. Weight loss was significantly affected by the storage conditions, being lower in plums stored at low temperatures in closed packing, while firmness was not affected by the storage conditions. The color of plums ranged from light red to purple in all storage conditions, showing an inverse correlation between the a* and b* color parameters with the total anthocyanins and antioxidant capacity. The storage condition that better maintained the quality attributes of plums was in closed packaging and low temperature (5 °C). Under this condition, plums lasted 40 days in acceptable consumption conditions. Sensory attributes indicated that over 20 days of storage, flavor, texture, and aroma did not change. However, the consumers prefer the color of plums after 40 days of storage. The findings of this study are highly relevant. However, future research should explore the effects of different types of light, including UV-A, UV-B, and visible light, on the quality characteristics of plums during storage at low temperatures, utilizing various postharvest techniques.

Author Contributions

Data curation, Investigation, Methodology, P.H.-C.; Data Curation, M.N.T.-S.; Supervision, Data curation, R.A.-S.S.; Methodology, Investigation, D.M.T.-C.; Data Curation, Supervision, C.R.-L.; Conceptualization, Formal Analysis, Validation, I.I.R.-L.; Conceptualization, Formal Analysis, Funding Acquisition, Writing Original Draft, C.E.O.-V. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:

PC	Phenolic compounds
TA	Total anthocyanins
AC	Antioxidant capacity

Footnotes

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Figures and Tables

Figure 1 Schematic representation of the conducted study.

Figure 2 Effect of ultraviolet-C light on phenolic compounds (A), total anthocyanins (B), and antioxidant capacity (C) of plums. Bars in figures indicate standard deviation. Different letters a, b, and c indicate statistical differences (p < 0.05).

Figure 3 Weight loss (A) and firmness (B) of plums stored under different conditions. ■ T1, ♦ T2, ▲ T3, × T4, ● T5, □ T6, ◊ T7, ∆ T8, and ○ T9. Bars in figures indicate standard deviation.

Figure 4 Change in a* and b* color parameters (A) at the beginning and end of the storage and total color change (B) in plums during storage under different conditions. ■ T1, ♦ T2, ▲ T3, × T4, ● T5, □ T6, ◊ T7, ∆ T8, and ○ T9. Bars in (B) indicate standard deviation.

Figure 5 The phenolic compounds (A), total anthocyanins (B), and antioxidant capacity (C) of plums stored under different conditions. ■ T1, ♦ T2, ▲ T3, × T4, ● T5, □ T6, ◊ T7, ∆ T8, and ○ T9. Bars in the Figures indicate standard deviation.

Table 1

Pearson correlation between color parameters, bioactive compounds, and antioxidant capacity during the shelf life of plum.

	a*	b*	PC a	TA b	AC c
a*	--	0.84	−0.23	−0.88	−0.86
b*	--	--	−0.33	−0.74	−0.84
PC	--	--	--	0.13	0.24
TA	--	--	--	--	0.81

^a PC: Phenolic compounds; ^b TA: total anthocyanins; ^c AC: antioxidant capacity.

Table 2

Sensory acceptance of plums stored at 5 °C and closed packaging for 40 days ^a.

Time (Days)	Color	Aroma	Texture	Flavor	Overall Acceptability
0	6.25 ± 0.97 a	5.55 ± 1.15 a	6.40 ± 0.88 a	5.40 ± 1.60 a	6.40 ± 0.68 a
10	6.35 ± 0.67 a	5.70 ± 1.03 a	6.00 ± 0.92 a	5.90 ± 1.62 a	6.25 ± 0.72 a
20	6.60 ± 0.60 a	5.50 ± 1.32 a	6.35 ± 0.67 a	5.55 ± 1.15 a	6.10 ± 0.85 a
30	6.05 ± 1.36 a	5.05 ± 0.94 a	5.90 ± 1.21 a	5.30 ± 1.66 a	5.75 ± 1.12 a
40	6.20 ± 1.28 a	5.35 ± 1.09 a	5.40± 1.79 a	4.90 ± 1.68 a	5.60 ± 1.23 a

^a Average (n = 20) ± standard deviation. Different letters in the same column indicate statistical differences during the storage (p < 0.05).

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