Effects of 1-Methylcyclopropene Fumigant on Texture and Nutritional Quality of ‘Yanshu 25’ Sweet Potato During Shelf-Life and Long-Term Storage at Room Temperature

Abstract

Sweet potatoes are highly susceptible to postharvest losses, primarily due to texture softening and nutrient degradation during room-temperature storage. This study investigated the effects of various concentrations of 1-Methylcyclopropene (1-MCP) fumigation (0.5, 1, 2, 4, and 8 μL·L⁻¹) on the textural and nutritional quality of the ‘Yanshu 25’ sweet potato variety stored at room temperature (25 ± 1 °C) for 120 days. Results showed that 1-MCP treatment significantly delayed texture softening and nutrient loss, with concentrations of 1–2 μL·L⁻¹ demonstrating the most balanced effects for long-term storage. The highest concentration (8 μL·L⁻¹) exhibited favourable effects during the first 22 days of storage. Principal Component Analysis (PCA) revealed that texture properties (firmness and chewiness) and bioactive compounds (total polyphenols) were the main quality markers. This study provides the first evidence for optimising 1-MCP concentration to enhance storage quality of sweet potato, offering tailored solutions for supply chain management.

1. Introduction

Sweet potato (Ipomoea batatas L.) is not only a globally significant crop for food security, but it is also a nutritional powerhouse that plays an important role in combating malnutrition worldwide [1]. “Yanshu 25” is an orange-fleshed, smooth-skinned sweet potato cultivar developed by the Yantai Academy of Agricultural Sciences. It offers moderate disease resistance and a pleasant taste, making it ideal for both consumption and processing. Rich in essential nutrients carbohydrate, dietary fibre, beta-carotene (a vitamin A precursor), and vitamins and minerals such as vitamin C, potassium, and iron, Yanshu 25 supports overall health, especially in regions with limited access to nutrient-dense foods [2]. However, the perishability and storage challenges remain significant obstacles that affect both the cultivation and utilisation of sweet potatoes [3]. During storage, they are susceptible to texture softening, starch degradation, and nutrient loss, especially of heat-sensitive compounds like vitamin C [4]. Postharvest losses significantly reduce the profitability of sweet potato production in many parts of the world. In China, for instance, sweet potatoes can lose between 20% and 30% of their value during storage after harvest [5,6]. These losses not only threaten food security and nutritional health but also have detrimental financial consequences for both consumers and farmers. Therefore, extending the dormancy period of the roots, reducing damage and decay, and preserving their nutritional qualities are the key factors in the utilisation, storage, processing, and marketing of sweet potatoes.

Several postharvest management strategies are available within the commercial industry for handling sweet potatoes. Managing the physical environment typically involves controlling storage temperature and relative humidity. Ideal conditions for sweet potato storage are temperatures between 13 °C and 16 °C [7], with relative humidity levels ranging from 80% to 95% [8]. However, sweet potatoes are susceptible to cold damage, and refrigeration facilities are often impractical due to their high energy consumption and the substantial financial costs for growers. On the other hand, fungicides are commonly used in industrial postharvest applications to preserve root quality. These fungicides are typically applied by immersing roots in chemical suspensions, utilising waterfall applications, or spraying them individually or in wax solutions as sweet potatoes pass through brush roller conveyors. Although synthetic bud inhibitors and fungicides, such as prochloraz, are effective in maintaining quality during storage, the use of chemicals can result in environmental pollution and pose potential risks to human health due to chemical residues [9,10].

Ethylene (C₂H₄) is a crucial endogenous phytohormone involved in plant development, maturation, and senescence. During postharvest storage, the accumulation of ethylene typically accelerates physiological ageing and deterioration, negatively affecting the storage quality of plant products [11]. Sweet potatoes naturally produce ethylene during storage, and factors such as pathogen attacks, cold stress, and physical damage can exacerbate its production in affected storage roots [12,13,14,15,16]. 1-Methylcyclopropene (1-MCP) is an innovative ethylene inhibitor that irreversibly binds to ethylene receptors, thereby blocking the ethylene signalling pathway and delaying the ripening and ageing processes of fruits and vegetables [17,18]. Widely regarded as a safe and non-toxic agent, 1-Methylcyclopropene (1-MCP) has been approved for use in food in numerous countries, including the United States and European Union, for a variety of fruits and vegetables to delay ripening and extend shelf life [19,20]. It effectively protects a variety of vegetables and fruits from the adverse effects of self-produced ethylene at room temperature, thereby enhancing their storage quality [21]. Its action is characterised by a significant reduction in respiration rate and ethylene release, as well as a delay in the decline of firmness and the preservation of nutrient stability. In recent years, the significant role of 1-MCP as a safe and non-toxic green preservative in sweet potato storage has gained recognition. Compared to conventional methods, 1-MCP offers several advantages, including non-toxicity, excellent chemical stability, ease of synthesis, minimal residue, and the ability to be used at low concentrations for postharvest treatment of sweet potatoes [6]. 1-MCP treatment effectively inhibits root sprouting during wound healing and throughout subsequent long-term storage [22,23]. Phenolic compounds and dry matter were higher in the skin than in the flesh, with accumulation increasing over time. This accumulation was more pronounced in the proximal slices of 1-MCP-treated roots [24]. Heat treatment combined with 1-MCP effectively reduced chilling injury in purple sweet potatoes stored at 4 °C, enhancing antioxidant levels and maintaining reactive oxygen species balance [25]. 1-MCP reduced storage root weight loss and decay without affecting respiration rate or non-structural carbohydrates. It temporarily hindered phenolic accumulation, particularly in middle and distal segments, making proximal dominance more pronounced [26].

Although research highlights 1-MCP’s potential in fruit and vegetable preservation, significant gaps remain in studying its effects on long-term storage (>1 month) and shelf-life quality of edible sweet potatoes at room temperature. Most studies focus on low temperatures as 4 or 15 °C, while the dynamic effects of 1-MCP on sweet potato texture and nutritional quality at room temperature (20–30 °C, shelf-life and stocking temperature in many markets and supermarkets) have not been thoroughly examined. This study aims to investigate the effects of various concentrations of 1-MCP fumigation (0, 0.5, 1, 2, 4, and 8 μL·L⁻¹) on the texture properties (hardness, chewiness, etc.), nutritional quality (amylose, glucose content, etc.). The edible sweet potatoes (famous orange-flesh variety Yanshu 25) stored at room temperature (25 ± 1 °C) for 120 days, along with shelf-life (simulated sales for 0–30 days) and long-term storage (30–120 days). The goal is to determine the optimal 1-MCP concentration for both shelf-life and long-term storage at room temperature. This research will provide a theoretical foundation for developing green preservation technologies for postharvest sweet potatoes and offer technical support for expanding the use of 1-MCP in the storage and transportation of root vegetables at room temperature.

2. Materials and Methods

2.1. Plant Materials and Experiment Design

The edible sweet potato variety Yanshu 25 was used in this study. They were carried out in May and harvested in October 2023 and 2024 at Zhejiang A&F University, Hangzhou, Zhejiang, China. The spindle-shaped tuberous root without pests and diseases, mechanical damage and medium size (weighing between 200 and 250 g) was selected. The 1-MCP used in the experiment was provided by Shandong Ovite Biotechnology Co., Ltd. (Jinan, China), with an effective content of 0.03 g/100 g. The crisper size was 8.5 L (38 cm × 26 cm × 13 cm). Sweet potato samples were treated with 1-MCP fumigation at concentrations of 0 μL·L⁻¹ (Control, CK), 0.5, 1, 2, 4, and 8 μL·L⁻¹. The fumigation reagent was placed in the crisper, with three replicates for each treatment. Tubers with undamaged skin and an average diameter of about 4 ± 1 cm were selected. The tubers were placed in crisper containing test tubes with different concentrations of 1-MCP solution. The control group was placed with distilled water of the same mass. After joint treatment of wound healing at 30 °C and 1-MCP fumigation for 12 h, the healing methods was modified from the protocol described by Wu [3] et al. The storage design includes two phases: Shelf-life phase and long-term storage phase. In this study, shelf-life is defined as the period from 0 to 30 days after storage (DAS), and long-term storage refers to the period from 30 to 120 DAS. During the shelf-life phase, the tuberous roots were placed in a climate chamber at 25 ± 1 °C (representing the shelf-life temperature in the fresh area of a supermarket) with a relative humidity of 85% for 30 days. Samples were collected once a week with three replicates (at 0, 7, 15, 21, and 30 DAS). During the long-term storage phase, the tuberous roots were placed in a warehouse at 25 ± 1 °C with 85% relative humidity to simulate long-term room temperature conditions. Samples were collected once a month with three replicates (at 60, 90, and 120 DAS). The samples were completely tuberous roots. They were washed and dried. Part of the samples was cut into small cubes, mixed in a ziplock plastic bag, and stored in the fridge at −80 °C. Another part was immediately used for tests on flesh colour, texture properties, and dry matter content.

2.2. Flesh Colour

There were five sweet potato tubers were randomly selected and sliced equatorially into 1.0 cm thick sections with three replicates of three slices for each treatment. The colour of the sweet potato flesh was quantified with a chroma metre CR 400 (Konica Minolta Sensing Inc., Osaka, Japan), operating within the Commission International de l’Eclairage (CIE) framework, and represented by lightness (L), a and b values.

2.3. Texture Properties

Texture properties was measured according Xu [27]’s and Dong [28]’s study. Texture profile analysis (TPA) was conducted using a texture analyser. A cylindrical probe (P/5) with a 5 mm diameter was used. The TPA parameters were set as follows: pre-test speed at 30 mm/min, test speed at 60 mm/min, post-test speed at 90 mm/min, 50% compression ratio, a 5 s pause between cycles, and a trigger force of 0.2 N. Firmness was defined as the maximum strength peak observed during the first extrusion cycle. This measurement reflects the force required to deform the sweet potato root when external pressure exceeds the biological yield point. It was indicative of the sample’s resistance to deformation and was expressed in Newtons (N). Cohesion was calculated as the ratio of the positive peak area during the second extrusion cycle to that during the first extrusion cycle. It provides insight into the root’s resistance to breakage and its ability to maintain structural integrity during chewing, thus ensuring the root tuber remains intact. Springiness refers to the extent to which the sample recovers after the first compression before the second compression cycle. It was quantified as the ratio of the height of the second compression to the height of the first compression, measured in millimetres. Gumminess was the force required to break the sweet potato root before it can be swallowed. This value was also measured in Newtons (N). Chewiness was a descriptor of the characteristics of solid test samples, specifically the force required by teeth to break down the sweet potato root to a swallowable state. It was the product of hardness, springiness, and cohesiveness, offering a comprehensive assessment of the root’s resistance to chewing. The unit of measurement for chewiness was Newtons (N). Each sample had three replicates.

2.4. Amylose Content

Amylose content was measured according Xu ’s study [29]. Quantification of amylose (AM) content was performed using the Megazyme Amylose Assay Kit (K-AMYL, Megazyme International, Bray, Ireland). This methodology leverages the specific binding affinity of concanavalin A (Con A) for selective polysaccharide precipitation. Precisely weighed samples (25.0 ± 0.1 mg) were processed in strict adherence to the manufacturer’s protocol. Amylose levels were determined colorimetrically by enzymatic oxidation with glucose oxidase-peroxidase (GOPOD) reagent, with absorbance measured at 510 nm. Each sample had three replicates.

2.5. Glucose Content

Glucose content determination followed Li [30] et al. The 0.2 g of sweet potato freeze-dried powder was weighed and mixed it thoroughly with 4 mL of ultrapure water. The mixture was centrifuged at 4000 r/min for 10 min. There was 0.5 mL of the supernatant collected and 3.5 mL of 70% acetonitrile was added to prepare the test solution. An appropriate amount of the test solution was filtered through a 0.22 μm organic microporous membrane. Transfer the filtered solution to a sample vial for high-performance liquid chromatography with refractive index detector (HPLC-RID, Waters Corporation, Milford, MA, USA) analysis. Chromatography Column was XB-NH₂ column (4.6 × 250 mm, 5 μm, Waters Corporation, USA). The column temperature and detector temperature was 35 °C. The flow rate was 1.0 mL/min. The mobile phase was acetonitrile and water. The injection volume was 10.0 µL. Each sample had three replicates.

2.6. Dry Matter Content

Dry matter content determination followed Xu [27] et al. Three intact storage roots were washed, air-dried (30 min), and sectioned into 0.5 cm slices using a precision slicer. Sweet potato slices (10.00 g) were placed in pre-dried crucibles (135 °C preconditioned, desiccator-cooled, room-temperature equilibrated). Samples underwent forced-air oven drying at 135 °C for 2 h. After desiccation cooling and thermal re-equilibration, the crucibles were reweighed. Tuberous root moisture content was determined gravimetrically. Each sample had three replicates.

Dry matter content (%) = (Dry mass/Fresh mass) × 100%

(1)

2.7. Total Polyphenols Content

Total polyphenols content was quantified following Shi’s [31] methodology. Reaction mixtures containing SPLEs (0.5 mL), 10% Folin–Ciocalteu reagent (2.5 mL), and 7.5% sodium carbonate (2 mL) underwent chromogenic reaction at 50 °C for 5 min. Absorbance was recorded at 760 nm against reagent blanks. Results were expressed as chlorogenic acid equivalents per gram dry weight (mg CAE/g DW). Each sample had three replicates.

2.8. Crude Protein Content

The crude protein content was measured following the AOAC method 984.13 [32]. The crude protein content was determined via micro-Kjeldahl nitrogen analysis using a Foss Kjeltec 2300 system. Each sample had three replicates. Protein quantification employed the standard conversion formula:

Protein (%) = Total nitrogen (%) × 6.25

(2)

2.9. Crude Fibre Content

Crude fibre content quantification was performed following AOAC method 978.10 [33]. Tuberous root’s powder samples were subjected to sequential digestion in 0.255 M sulphuric acid (30 minutes’ boiling), followed by filtration and washing. The residue was subsequently refluxed in 0.313 M sodium hydroxide. After secondary filtration and washing, samples were oven-dried at 130± °C for 2 h, then ashed at 350 ± 25 °C. Crude fibre content was calculated as a percentage of dry matter (% DM). Each sample had three replicates.

2.10. Statistical Analysis

Statistical analyses were conducted in SPSS 23.0 (IBM, Armonk, YK, USA), employing one-way ANOVA with post hoc Duncan’s multiple range tests, and Principle Components Analysis (PCA) in SPSS 23.0 (IBM, USA). Principal component analysis (PCA) was performed, during which the quality attributes of different sweet potato varieties were normalised. The eigenvalues and their corresponding contribution rates were established, and the composite scores of the sweet potatoes were determined. Tabular data were generated using Microsoft Excel 2018 (Microsoft Corp., Redmond, WA, USA), while graphical representations were plotted in Origin 9.0 Professional (OriginLab Corp., Northampton, MA, USA).

3. Results

3.1. Effects of 1-MCP on Flesh Colour

The appearance of sweet potato flesh is a critical quality attribute that significantly determines market value, particularly in terms of colour uniformity, textural integrity, and the absence of physiological disorders. As evidenced in Figure 1, chromatic parameters (L, a, b*) of flesh was changed after 1-MCP treatments at 0 DAS, especially L* value of1-MCP treatments (except 2 μL·L⁻¹) was significantly higher than CK (p < 0.05). Then, L, a, and b* value exhibited progressive declines throughout shelf-life (0–30 days after storage, DAS). Minimum values for all colorimetric indices were recorded at 22 DAS, indicating peak quality deterioration. The L* value of CK remained significantly higher than all 1-MCP treatments throughout the long-term storage (p < 0.05). Partial L* value recovery in all treatments, except 8 μL·L⁻¹ showing accelerated decline. The treatments of 1 μL·L⁻¹ was exhibited less substantial L* value decreases in shelf-life, and the treatments of 0.5 and 2 μL·L⁻¹ exhibited less substantial L* value decreases in long-term storage. The overall trend of the a* value in flesh across all 1-MCP treatments showed a decreasing pattern over the shelf-life. The a* value of 1,2 and 8 μL·L⁻¹ 1-MCP treatments was higher than CK in shelf-life (p < 0.05). The a* value of all 1-MCP treatments was higher than CK in long-term storage. It indicated that the flesh exhibited a notable red coloration after treatment with 1-MCP. The b* value of all 1-MCP treatments was higher than CK in shelf-life and long-term storage in this study. The b* value of 2 μL·L⁻¹ 1-MCP treatment was highest at 7, 22, 30 and 60 DAS, 1 μL·L⁻¹ 1-MCP treatment was highest at 90 and 120 DAS. No significant differences in ΔH value were observed between 1-MCP treatments and CK at p < 0.05 level in shelf-life and long-term storage. These results suggest that 1-MCP influences flesh colour, significantly altering the L*, a*, and b* values during shelf-life and long-term storage, with the 0.5, 1, and 2 μL·L⁻¹ 1-MCP treatments having a more pronounced effect.

3.2. Effects of 1-MCP on Flesh Texture Properties

Texture properties quantified the compressive resistance of sweet potato flesh tissue [28]. As shown in Figure 2, the texture properties of flesh were changed after 1-MCP treatments at 0 DAS, which is significantly higher than CK (p < 0.05). Elevated firmness values correlated with enhanced structural integrity against compressive deformation. The flesh firmness in all treatments exhibited a decreasing trend over time during both shelf-life and long-term storage (Figure 2a). Compared to the control (CK), all 1-MCP treatments significantly slowed the decline in hardness. At both shelf-life and long-term storage stages, all 1-MCP concentrations maintained significantly higher firmness than the control (p < 0.05). However, during the initial 0–30 days after storage (DAS), the 8 μL·L⁻¹ treatment resulted in significantly lower firmness compared to the other 1-MCP concentrations.

Cohesiveness across all treatments exhibited a biphasic response: an initial decline followed by a gradual recovery, reaching its nadir at 60 DAS (Figure 2b). Throughout the shelf-life and long-term storage, all samples treated with 1-MCP at all concentrations demonstrated significantly higher cohesiveness than CK (p < 0.05). The cohesiveness of 2 and 8 μL·L⁻¹ 1-MCP treatments was significantly higher than other treatments during 0–7 DAS (p < 0.05). Notably, the 1 and 8 μL·L⁻¹ 1-MCP treatments showed the most pronounced enhancement in tissue integrity, exceeding both the CK and other 1-MCP concentration treatments during 30–120 DAS (p < 0.05). This suggests that the optimal concentration of 1-MCP for long-term storage may not necessarily be the highest, but the highest concentration can still maintain cohesiveness.

All treatments exhibited springiness decline during shelf-life (0–30 DAS), reaching a critical minimum at 30 DAS (2.5–3.5 mm, Figure 2c). This was followed by gradual recovery during long-term storage (30–120 DAS), suggesting activation of cell wall repair mechanisms. The springiness of 1-MCP treatments remained above 4.0 mm throughout the 0–7 DAS, except 4.0 µL·L⁻¹ treatment. Notably, the springiness of 1–2 μL·L⁻¹ 1-MCP treatments still remained above 4.0 mm in shelf-life and long-term storage, and the springiness of 1 μL·L⁻¹ 1-MCP treatments was 4.72 mm at 30 DAS, which is significantly higher than other treatments. The springiness of other 1-MCP treatments was decreased. The high-concentration 8.0 µL·L⁻¹ treatment inhibited recovery (+0.4 mm), underperforming even the control group’s minimal recovery (+0.3 mm) at 30–60 DAS. The 1 and 2 μL·L⁻¹ 1-MCP treatments exhibited significantly higher springiness than the CK and other 1-MCP concentration treatments during 30–120 DAS (p < 0.05). However, in terms of springiness, the effectiveness of other 1-MCP treatments is also significantly higher than that of CK during 30–120 DAS (p < 0.05).

Chewiness reflected the solidity of sweet potato storage root, generally decreased during long-term storage, as shown in Figure 2d. All 1-MCP treatments effectively delayed the decrease in chewiness. Throughout shelf-life and long-term storage, the 1-MCP treatments were significantly higher than the CK (p < 0.05), with the 2 μL·L⁻¹ treatment showing the most obvious effect. The chewiness of the 2 μL·L⁻¹ treatment reached its maximum value of 89.67 N at 30 days after storage (DAS), which was higher than that of other treatments. It remained the highest throughout the 30–120 DAS (long-term storage). Maybe 1-MCP preserves chewiness via dose-dependent ethylene signalling suppression. Moderate concentrations (1–2 μL·L⁻¹) provide the most balanced protection across storage phases, while high doses (8 μL·L⁻¹) offer transient benefits at the cost of accelerated later degradation.

Gumminess reflected the status and stability of pectin and soluble sugars in flesh of sweet potato. As shown in Figure 2e, the trends fibre the similar with springiness and chewiness, gumminess of all 1-MCP treatments was significantly higher than CK (p < 0.05). The 8 µL·L⁻¹ 1-MCP treatment maintained peak gumminess levels (near upper range of 19–20 N), significantly outperforming lower concentrations and CK. This indicates high-concentration 1-MCP effectively preserves structural integrity during 0–15 DAS. All treatments showed accelerated gumminess decline, but 2 µL·L⁻¹ 1-MCP demonstrated superior retention (approximately 16–18 N) compared to steeper drops in CK and higher concentrations (8 µL·L⁻¹) during 15–22 DAS. The 2 µL·L⁻¹ treatment stabilised at the highest level (12–14 N), confirming its optimal efficacy for preserving chewiness/texture as produce approaches during 22–30 DAS. All treatments exhibited rapid gumminess deterioration, but 1 and 4 µL·L⁻¹ treatments maintained relative superiority (8–10 N) over CK (which dropped to ≤8 N). The 8 µL·L⁻¹ 1-MCP treatment maintained peak gumminess levels during 30–120 DAS (long-term storage). Although the other concentration (0.5–4 µL·L⁻¹) consistently under performed relative to 8 µL·L⁻¹ 1-MCP treatments, it remained superior to the CK. The gumminess of CK exhibited the most rapid degradation, underscoring 1-MCP’s essential role in texture preservation.

3.3. Effects of 1-MCP on Chemical and Nutritional Properties

Dry matter content reflects the total nutrient reserves in storage roots of sweet potato [34]. It showed notable fluctuations across the different treatments (Figure 3a). In general, the levels tended to decline during the first 60 days of storage, followed by a subsequent increase. All 1-MCP-treated groups exhibited significantly higher dry matter content compared to CK from 30 DAS (p < 0.05). The treatments with 0.5 μL·L⁻¹ and 4 μL·L⁻¹ concentrations outperformed all other treatments during 60–120 DAS (p < 0.05), with the 4 μL·L⁻¹ treatment reaching the highest value of 41.09%. The increase in dry matter content of sweet potatoes during storage is primarily attributed to the relative increase caused by the gradual reduction in water content. This is accompanied by reprogramming of carbon metabolism and an increase in the proportion of structural carbon compounds, such as fibre. This phenomenon is more pronounced following treatment with 1-MCP.

Higher amylose content tends to produce firmer, drier flesh in sweet potatoes. This is because amylose molecules form a more crystalline structure that is less prone to breaking down during cooking [35,36]. In this study, 1-MCP treatment was found to slow down the degradation of amylose during storage. The amylose content of 1-MCP treatments was still lower than CK from 0 to 15 DAS and long-term storage (30–120 DAS, Figure 3b). The CK reached peak amylose content at 15 DAS, while all 1-MCP treatments peaked at 22 DAS. After 22 DAS, amylose levels in all 1-MCP treatments were significantly lower than CK (p < 0.05. Starch is composed of amylose and amylopectin. Assuming that starch metabolism is the dominant mechanism during storage, branched starch is more readily hydrolysed compared to linear starch. This is due to the dense and complex structure of amylose versus the loose and clustered structure of amylopectin. Particularly, short-chain branched starch is more easily broken down into soluble sugars by amylase during storage. In this study, we found that the amylose content of the control (CK) was higher than that of all 1-MCP treatments during the shelf-life stage, except at 22 days after storage (DAS). During long-term storage, the amylose content of the CK treatment was significantly higher than that of all 1-MCP treatments, with the lowest amylose content observed in the 0.5 μL·L⁻¹ treatment.

Glucose is a key indicator for consumption and processing quality [37], generally followed by an initial increase followed by a decrease starting from 7 DAS (Figure 3c). Glucose content increased significantly across all treatments during the shelf-life. This rise is common and is associated with starch degradation into simpler sugars like glucose due to postharvest metabolic activity. In untreated (control) samples, glucose content continued to increase or remained high, which can be linked to over-ripening or senescence. Glucose peaked at 60 DAS in CK, while treatment groups peaked at DAS: 30 DAS (0.5 and 2.0 μL·L⁻¹), 15 DAS (1.0 and 4.0 μL·L⁻¹), and 7 DAS (8.0 μL·L⁻¹), followed by gradual declines. Notably, the 2.0 μL·L⁻¹ treatment reached the highest observed glucose level of 455.95 mg/g at 30 DAS. In 1-MCP treatments, particularly at moderate concentrations (1–2 μL·L⁻¹), glucose accumulation was moderated over time. This suggests that 1-MCP slowed down starch degradation and reduced respiration rates, thereby helping to maintain the nutritional and textural quality of sweet potatoes. However, at higher concentrations (4–8 μL·L⁻¹), while 1-MCP further reduced glucose accumulation, it also coincided with some undesirable effects on texture and germination in the long term. This indicates that excessive inhibition of metabolic activity may impair physiological balance.

Total polyphenols are valued for their antioxidant, antimicrobial, and chronic disease prevention properties, exhibiting a slow overall increasing trend during storage [38]. Total polyphenol content was consistently higher in all treatments compared to the CK throughout shelf-life and long-term storage, increasing with treatment concentration (Figure 3d). At 120 DAS, the 8.0 μL·L⁻¹ treatment yielded significantly higher polyphenol content (peak: 9.91 mg/g) than other groups (p < 0.05), demonstrating the best enhancement effect.

Crude fibre was beneficial for intestinal motility, metabolism, gastrointestinal function, and blood sugar regulation, which generally increased in all groups (Figure 3e). Treatment groups consistently maintained higher crude fibre content than the control during storage. By day 120, nearly all treatments peaked, with the 1 μL·L⁻¹ treatment achieving the highest level (5.09%), which is significantly greater than the control (p < 0.05).

Crude protein was generally decreased across all treatments (Figure 3f). Most treatments peaked around 7 DAS, with the 2 μL·L⁻¹ group reaching the highest crude protein content (4.89%), significantly exceeding the control (p < 0.05). By 30 DAS, all treatments reached their minima; the control showed the lowest level (2.45%) and subsequently remained significantly lower than all treatment groups (p < 0.05).

3.4. PCA

The principal component analysis was performed on 14 quality and texture properties index based on the initial data, extracting four principal components from the feature values. The contribution rates of these components were 36.978%, 20.527%, and 12.257%, with a cumulative contribution rate of 77.749% (

Table 1. Principal component analysis of variance.

Components	Initial Eigenvalue			Extracting Square SUM and Loading
	Total	Variance/%	Accumulate/%	Total	Variance/%	Accumulate/%
PC1	5.177	36.978	36.978	5.177	36.978	36.978
PC2	2.874	20.527	57.505	2.874	20.527	57.505
PC3	1.716	12.259	69.764	1.716	12.259	69.764
PC4	1.080	7.715	77.479	1.080	7.715	77.479
PC5	0.796	5.683	83.163
PC6	0.598	4.268	87.431
PC7	0.448	3.202	90.632
PC8	0.430	3.070	93.702
PC9	0.338	2.411	96.114
PC10	0.225	1.609	97.723
PC11	0.119	0.847	98.570
PC12	0.104	0.744	99.314
PC13	0.058	0.412	99.726
PC14	0.038	0.274	100.000

). Only PCs 1–4 were retained as their cumulative variance exceeds 77%, while components 5–14 were excluded due to their individual variance being less than 6%.

As

Table 2. The load values of principal components.

Indexs	PC1 (Y1)	PC2 (Y2)	PC3 (Y3)	PC4 (Y4)
Dry matter content (X1)	0.310	0.328	0.485	−0.631
L* value (X2)	−0.040	0.617	−0.636	−0.090
a* value (X3)	0.635	0.419	−0.343	−0.036
b* value (X4)	0.533	0.613	−0.542	0.050
Amylose content (X5)	−0.578	−0.334	0.065	0.467
Glucose content (X6)	0.731	−0.138	−0.073	0.286
Crude fibre content (X7)	−0.019	0.666	0.482	0.342
Crude protein content (X8)	0.617	−0.344	−0.284	0.170
Total Polyphenols content (X9)	0.128	0.704	0.384	0.407
Firmness (X10)	0.726	−0.561	0.106	−0.135
Cohesiveness (X11)	0.653	0.388	0.241	−0.061
Springiness (X12)	0.903	−0.078	0.153	0.136
Gumminess (X13)	0.833	−0.085	0.308	0.007
Chewiness (X14)	0.815	−0.407	−0.088	0.133

shown, PC1 (the first principal component) has the highest loadings for 9 sweet potato storage characteristic indicators: springiness, gumminess, chewiness, glucose content, hardness, cohesiveness, a* value, crude protein and amylose content. This means PC1 mainly reflects these nine indicators’ information. Amylose has a high negative loading, while the other eight have high positive loadings. Their contribution rates to PC1 are ordered as springiness (0.903) > gumminess (0.833) > chewiness (0.815) > glucose content (0.731) > firmness (0.726) > cohesiveness (0.653) > a* value (0.635) > crude protein content (0.617) > amylose content (−0.578). Higher amylose content may weaken texture properties in this study.

PC2 has high loadings for total polyphenols content, crude fibre content, L* value, and b* value, meaning that PC2 mainly represents these four indicators. Their contribution rates to PC2 are ordered as total polyphenols content (0.704) > crude fibre content (0.666) > b* value (0.613) > L* value (0.617). PC3 mainly has a high negative loading for the L* value (−0.636), indicating it primarily reflects the L* value’s information with a significant contribution from it. PC4 mainly has a high negative loading for dry matter content (−0.631), showing it mainly reflects the dry matter content’s information. Except for dry matter content, other indicators have small contribution rates to PC4. The inverse relationship between dry matter content and glucose content in PC4 suggests that sugar metabolism may reduce the solid content.

Principal component coefficients (eigenvectors) were calculated by scaling the factor loadings of the 14 variables by the reciprocal of their eigenvalues’ square roots (

Table 3. Principal component eigenvectors.

Indexs	PC1	PC2	PC3	PC4
X1	0.136	0.193	0.370	−0.607
X2	−0.018	0.364	−0.486	−0.087
X3	0.279	0.247	−0.262	−0.035
X4	0.234	0.362	−0.414	0.048
X5	−0.254	−0.197	0.050	0.449
X6	0.321	−0.081	−0.056	0.275
X7	−0.008	0.393	0.368	0.329
X8	0.271	−0.203	−0.217	0.164
X9	0.056	0.415	0.293	0.392
X10	0.319	−0.331	0.081	−0.130
X11	0.287	0.229	0.184	−0.059
X12	0.397	−0.046	0.117	0.131
X13	0.366	−0.050	0.235	0.007
X14	0.358	−0.240	−0.067	0.128

). The principal components were then formulated as linear combinations using these coefficients:

PC1(Y₁) = 0.136 × X₁ − 0.018 × X₂ + 0.279 × X₃ + 0.234 × X₄ − 0.254 × X₅ + 0.321 × X₆ − 0.008 × X₇ + 0.271 × X₈ +
0.056 × X₉ + 0.319 × X₁₀ + 0.287 × X₁₁ + 0.397 × X₁₂ + 0.366 × X₁₃ + 0.358 × X₁₄

(3)

PC2(Y₂) = 0.193 × X₁ + 0.364 × X₂ + 0.247 × X₃ + 0.362 × X₄ − 0.197 × X₅ − 0.081 × X₆ + 0.393 × X₇ − 0.203 × X₈ +
0.415 × X₉ − 0.331 × X₁₀ + 0.229 × X₁₁ − 0.046 × X₁₂ − 0.050 × X₁₃ − 0.240 × X₁₄

(4)

PC3(Y₃) = 0.370 × X₁ − 0.486 × X₂ + 0.262 × X₃ − 0.414 × X₄ + 0.050 × X₅ − 0.056 × X₆ + 0.368 × X₇ − 0.217 × X₈ +
0.293 × X₉ + 0.081 × X₁₀ + 0.184 × X₁₁ + 0.117 × X₁₂ + 0.235 × X₁₃ − 0.067 × X₁₄

(5)

PC4(Y₄) = −0.607 × X₁ − 0.087 × X₂ − 0.035 × X₃ + 0.048 × X₄ + 0.449 × X₅ + 0.275 × X₆ +
0.329 × X₇ + 0.164 × X₈ + 0.392 × X₉ − 0.130 × X₁₀ − 0.059 × X₁₁ + 0.131 × X₁₂ + 0.007 × X₁₃ + 0.128 × X₁₄

(6)

PC_Total (Y_Total) = 0.370 × Y₁ + 0.205 × Y₂ + 0.123 × Y₃ + 0.077 × Y₄

(7)

We calculated composite scores for 1-MCP treatments and CK (Figure 4) and visualised how treatments preserve “fresh-like” quality at shelf-life and long-term storage. Composite scores for all 1-MCP treatments were significantly higher than the control (CK) during both shelf-life (0–30 days after storage, DAS) and long-term storage (30–120 DAS). All treatment groups exhibited rapid declines in composite scores starting at 22 DAS. The quality loss of sweet potato occurred rapidly in shelf-life. During the shelf-life period (0–30 DAS at 25 °C), the 8 μL·L⁻¹ 1-MCP treatment maintained the highest composite scores from 0 to 15 DAS, while the 2 μL·L⁻¹ treatment showed superior scores during 22–30 DAS. This indicates that both concentrations effectively preserved sweet potato quality during room-temperature storage. For long-term storage (30–120 DAS at 25 °C), the 1 μL·L⁻¹ 1-MCP treatments yielded the highest composite scores, demonstrating its efficacy for extended storage quality. PCA objectively quantifies that texture (PC1) and bioactive compounds (PC2) are the core quality indicators.

4. Discussion

Sweet potatoes were nutritionally and economically valuable for growers and consumers worldwide. The storage challenges have hampered the advancement of sweet potato production. In this study, we discovered that not only does 1-MCP treatment improve sweet potato quality during shelf-life and long-term storage, but it also alters the flesh colour, texture properties, and chemical and nutritional composition following fumigation treatment at 0 DAS. All 1-MCP treatments delayed texture softening (Figure 2) and nutrient loss (Figure 3), results aligning with the hypothesis that blocking ethylene receptors with 1-MCP could extend shelf-life. The 1 μL·L⁻¹ 1-MCP concentration has been proven effective for sweet potato storage, as previously found by researchers [39,40].

Previous studies have suggested that higher concentrations of 1-MCP may lead to greater durability during storage in fruits [41,42,43]. However, in our study, we observed that while higher concentrations of 1-MCP (such as 8 μL·L⁻¹) enhanced short-term texture preservation, they also caused a reduction in key quality indicators, such as the germination rate, germination index, and malondialdehyde content, after prolonged storage. This suggests that although high 1-MCP concentrations may provide initial benefits, they can negatively affect long-term quality, which aligns with the dose-dependent nature of 1-MCP’s effects. In this study, we found colour and texture properties of sweet potato flesh were nonlinearly correlated with 1-MCP concentration. The flesh colour indicators (L*, a*, and b* value) after high concentration 1-MCP treated (8 μL·L⁻¹) was not significantly higher than other low 1-MCP treatments in shelf-life and long-term storage. The high concentration (8 μL·L⁻¹) enhances short-term (≤15 days) hardness, gumminess, and other texture properties, but causes degradation overdue 30 days, like inhibiting springiness recovery. Low concentrations (1–2 μL·L⁻¹) are better for long-term storage, with 1 μL·L⁻¹ offering the highest firmness retention rate.

The 2 μL·L⁻¹ 1-MCP treatment accelerated sugar transformation, causing the glucose peak to occur earlier at 30 DAS (455.95 mg/g) compared to the control group’s 60 DAS peak. Amylose content was significantly reduced in all treated groups compared to the control (p < 0.05), with a delayed peak (Figure 3), suggesting that 1-MCP may suppresses the consume of amylopectin. The decrease in amylose is typically associated with texture softening [35], but in this study, the 1-MCP treatments with the lowest amylose content actually maintained the highest firmness (15–18 N). 1-MCP may repress polygalacturonase transcription by blocking ethylene signalling while simultaneously stimulating cellulose synthase [28], thereby diverting glucose flux toward fibre synthesis instead of storage (Figure 3). This suggests that cell wall metabolism may have a greater influence on texture than starch.

For total polyphenols content, higher 1-MCP concentrations led to greater accumulation, with the 8 μL·L⁻¹ treatment reaching 9.91 mg/g by 120 DAS, indicating enhanced antioxidant potential. Exposure to 8 μL·L⁻¹ 1-MCP appears to enhance polyphenol production by up-regulating the phenylpropanoid pathway-evidenced by elevated phenylalanine ammonia-lyase activity, thereby sustaining reactive oxygen species homeostasis [25]. This metabolic shift aligns with the marked positive loading of total polyphenols on PC2 (0.704).

The low concentration of 1-MCP (1 μL·L⁻¹) shows advantages in long-term storage (>30 DAS)for long-term storage at 25 °C it is basically consistent with previous studies [26,39,40,44,45]. Whereas a high concentration (8 μL·L⁻¹) is ideal for short-term shelf-life (≤15 DAS) storage. Additionally, antioxidant enzyme activity decreased as the concentration of 1-MCP increased [46]. This study provides evidence in the time dimension for the “dose-dependent effect” and makes up for the past focus on short-term experiments. This aligns with expectations for concentration optimisation in different scenarios.

PCA revealed a negative correlation between dry matter content and glucose levels (PC4 loadings: −0.631 vs. 0.275), alongside a significant increase in crude fibre (reaching 5.09% at 120 DAS after 1-MCP treatment) (Figure 3e). This study builds on previous work, such as that of Amoah and Terry [26], who suggested that 1-MCP promotes cell wall repair but did not clarify the metabolic source. This study suggests that 1-MCP fumigation may delay ethylene-mediated starch hydrolysis, as reflected by a postponed decline in amylose content and slower glucose accumulation. This temporal shift may redirect carbon skeletons toward structural carbohydrate accumulation (e.g., crude fibre) and antioxidant production (e.g., polyphenols), indicating a potential reprogramming of carbon metabolism during storage.

This active reallocation challenges the classical view of 1-MCP as a mere ‘metabolic freezer’ [12]. It explains the paradox of increasing dry matter content (Figure 3a) despite the mismatch in glucose peak timing (30 and 60 DAS in CK). This provides novel evidence for the metabolic regulatory function of ethylene inhibitors, challenging the notion of 1-MCP as a purely passive preservative. Based on the results of this study, we have summarised the following sweet potato storage scenarios in

Table 4. Guide for matching 1-MCP concentration with fumigation conditions.

Scene	Recommended Concentration	Application Scenarios
Shelves (in the market or supermarket ≤15 DAS, 20–30 °C)	High concentration (8–10 μL·L−1)	Mid-to-high-end fresh produce market and Convenience Store Supply Chain
Logistics turnover (15–30 DAS,15–30 °C)	Moderate concentration (2–4 μL·L−1)	E-commerce supply chain and Food Delivery Platform Supply Chain
Cellar storage and Large storage facilities (>30 DAS, 15 °C)	Moderate concentration (1 μL·L−1)	Off-season Supply, Feedstock Reserves, and Raw Material Stockpile

to provide guidance for 1-MCP fumigation. The 1 μL·L⁻¹ 1-MCP treatment can extend the storage times to 120 DAS. This treatment also supports the green transition by replacing chemical fungicides like prochloraz, in line with zero-residue policy requirements. Additionally, the 2–4 μL·L⁻¹ treatment results in low-starch, high-fibre characteristics, making it suitable for developing healthy food products, such as high-fibre sweet potato products.

This study focused solely on the orange-flesh edible variety ‘Yanshu 25’, without considering starch or purple-flesh varieties, and did not assess ethylene receptor binding rates, or starch synthase gene expression. Therefore, the conclusions have limitations regarding the processing adaptability and molecular mechanisms of ‘carbon reprogramming’ in high-starch varieties. Additionally, PCA incorporated secondary indicators such as colour (PC1 < 0.1), which diluted the release power. Future research should validate the 1-MCP response in high-starch varieties, such as ‘Shangshu 19’, and purple-flesh varieties, such as ‘Xuzishu 8’, and employ transcriptome analysis and ¹³C tracing to elucidate the redirection of sugars toward fibre synthesis. A PCA model should be developed using 6–8 high-loading core variables. Following Zhang’s study [17], intelligent packaging that dynamically releases 1-MCP based on storage time could be developed: an initial burst from high-dose microcapsules (8 μL·L⁻¹) confers immediate protection, followed by a low-dose sustained-release layer (1 μL·L⁻¹) that preserves quality over the long term at the industrial level. Furthermore, a variety concentration database could be established for main varieties, which would be included in the “Sweet Potato Storage Technical Specification.” This would represent a shift from “phenomenon description” to “mechanism-driven” research and provide a universal framework for the ethylene and cell wall regulation module shared by tuber crops.

In summary, the contributions of this research are as follows: 1. Verify the dose–response relationship of 1-MCP at room temperature; 2. Challenge the concentration levels of 1-MCP and examine the risk of quality deterioration under ambient temperature application; 3. Provide precise concentration solutions for different supply chain scenarios, aiming to reduce losses and increase efficiency in the sweet potato industry.

5. Conclusions

This study demonstrated that 1-MCP fumigation significantly enhanced sweet potato storage quality in a concentration- and duration-dependent manner: 8 μL·L⁻¹ optimally preserved firmness and gumminess for short-term shelf-life (≤15 DAS); 2 μL·L⁻¹ effectively delayed texture deterioration and reduced amylose content within 30 DAS, suiting logistics turnover; 1 μL·L⁻¹ maintained peak firmness and crude fibre (5.09%) during long-term storage (30–120 DAS), ideal for cellar storage. 1-MCP also boosted polyphenol accumulation (9.91 mg/g at 8 μL·L⁻¹) and revealed a novel mechanism redirecting sugar metabolism toward fibre synthesis (not accumulation) to sustain dry matter, challenging the “metabolic freezing” paradigm. This work provides tailored green preservation strategies for diverse supply chain scenarios.