Research Progress on Physical Preservation Technology of Fresh-Cut Fruits and Vegetables

Abstract

Fresh-cut fruits and vegetables have become more popular among consumers because of their nutritional value and convenience. However, the lower shelf life of fresh-cut fruits and vegetables due to processing and mechanical damage is a critical factor affecting their market expansion, and advances in preservation technology are needed to prolong their shelf life. Some traditional chemical preservatives are disliked by health-seeking consumers because of worries about toxicity. Chemical preservation is inexpensive and highly efficient, but sometimes it carries risks for human health. Biological preservation methods are safer and more appealing, but they are not applicable to large-scale production. Physical fresh-keeping methods have been used for the storage and transportation of fresh-cut fruits and vegetables due to the ease of application. This review discusses current research in fresh-keeping technology for the preservation of fresh-cut fruits and vegetables. Preservation methods include low temperature, modified atmosphere packaging, cold plasma, pulsed light, ultrasonics, ultraviolet light, and ozonated water. As promising alternatives to chemical methods, these novel processes have been evaluated singly or combined with natural preservatives or other methods to extend the shelf life of fresh-cut fruits and vegetables and to provide references and assessments for further development and application of fresh-cut fruit and vegetable preservation technology.

1. Introduction

Nowadays, fresh-cut fruits and vegetables are available worldwide, and they are chiefly represented by salads, crudités, ready-to-cook vegetables and fruits. A greater consumption of fruits and vegetables has been recommended by the World Health Organization (WHO) and others, as they contain beneficial dietary fiber, vitamins, minerals, and phytochemicals and have fewer calories [1]. Fruits and vegetables have long been an indispensable part of human diets, and in recent years, the global fruit and vegetable market has been thriving and developing. The global market for minimally processed fruits and vegetables in 2021 was USD 310 billion and is forecast to increase to USD 530 billion by 2028 [2]. Eating fruits and vegetables is held to be a sign of good nutrition and a health-conscious approach to living that has been linked to a lower incidence of cardiovascular problems, cancers, stroke, diabetes, Alzheimer’s, cataracts and cognitive decline [3]. With the improvement of people’s living standards, the demand for more healthful food and greater convenience has steadily increased, which makes fresh-cut fruits and vegetables more attractive to busy consumers.

Following the guidelines of the European Community, healthful fresh-cut fruits and vegetables are defined as minimally processed, ready-to-eat products, requiring less technology and handling for immediate consumption [2]. Fresh-cut product refers to a raw food product that was graded, cleaned, peeled, cut, preserved and packaged. It is popular among consumers because of its nutrition and convenience.

However, fresh-cut fruit and vegetables are susceptible to oxidation and deterioration after peeling and cutting, leading to shorter shelf life. Fresh cutting results in the loss of microbial resistance and antioxidant defenses resulting in the typical enzymatic browning seen on an apple, for example [4]. Fifty percent of all fresh-cut fruit is discarded because of this browning reaction, which is catalyzed by polyphenol oxidase (PPO) [5]. Fresh-cut fruits and vegetables are also vulnerable to contamination with foodborne pathogens because of the lack of bactericidal treatments such as pasteurization [6]. Potentially harmful microbes include Escherichia coli, Salmonella enterica, Staphylococcus aureus, Shigella flexneri and Listeria monocytogenes [7]. Short shelf life and susceptibility to microbial contamination are the main disadvantages of fresh-cut fruits and vegetables, and they are the most important factors limiting their market expansion. Some effective physical methods for prolonging the shelf life of fresh-cut fruits and vegetables have been developed over the past few decades, but they all have some disadvantages [8]. Acidulants and anti-browning chemicals, firming agents, stabilizers, antioxidants and antimicrobials are useful in preventing physical breakdown and decay [9], but more and more consumers are rejecting some foods laced with traditional chemical preservatives because of concern over their toxicity [10]. The chemical preservatives used in the food industry include oxidative substances containing chlorine or peroxyacetic acid and non-oxidizing quaternary ammonium compounds. Some chlorinated preservatives have been widely adopted for washing fresh-cut produce because they are inexpensive and effective at killing a wide range of microbes. However, the continued use of chlorine for washing can result in the formation of carcinogens like trihalomethane [10].

As substitutes for harmful agents like these, plant extracts and essential oils with preservative and antimicrobial properties have been tested, often combined with reactive packaging and edible coatings that preserve the freshness, color, and texture of fresh-cut fruits and vegetables [11,12]. The pasteurization of fresh-cut products is rarely possible because of the effects of the heat on texture and appearance [13], but non-thermal treatments such as ultrasonics, cold plasma, high pressure, ultraviolet irradiation, and pulsed electric fields have proven effective in some cases [14]. These techniques have been tested together with natural anti-browning, antifungal, and antibacterial additives to extend the shelf life of premium quality fresh-cut fruits and vegetables, including cucumber [15], apples [16], lettuce [17], banana [18], asparagus [19], papaya [20], pears [21], pitayas [22], Chinese cabbage [23], tomatoes [24], carrots [25], apricots [26], and broccoli [27]. In this review, we evaluated the effectiveness of the principal methods for preserving the characteristic qualities of fresh-cut fruits and vegetables with the goal of assisting food scientists in developing the best strategy for ensuring that their fresh-cut products retain their pristine condition and nutritional value.

2. Different Methods and Their Effects

Physical preservation methods are mainly used to prevent spoilage by inhibiting the growth of bacteria and fungi on the surface of fresh-cut fruits and vegetables and to prolong shelf life by inhibiting oxidation and respiration (Figure 1). The main preservation technologies include low temperature, modified atmosphere packaging, cold plasma, pulsed light, ultrasonics, ultraviolet light and ozonated water. Physical fresh-keeping methods have been frequently employed in the storage and transportation of fresh-cut fruits and vegetables because of the relatively low threshold of use.

2.1. The Preservative Effect of Low-Temperature Treatment on Fresh-Cut Fruits and Vegetables

Low temperature has been commonly used for the storage and preservation of perishable fruits and vegetables because of the decreased temperature reduced respiration and ethylene production. Cold storage also decreases bacterial growth in the products [28]. Efficient cooling systems must be in use for all minimal processing steps of fresh-cut fruits and vegetables [29].

The widely studied low-temperature preservation method has been used to preserve fresh-cut fruits and vegetables (

Table 1. Low-temperature methods to maintain the quality of fresh-cut fruits and vegetables.

Species	Shape	Processing Condition	Fresh-Keeping Effect	Reference
Welsh onion	Slices, pieces, and shreds	Stored at 4 and 20 °C.	High storage temperature reduces quality and shelf life.	[30]
Onion	Slices and cubes	Stored at different temperatures (0, 5, 10 and 15 °C) with 85–90% relative humidity (RH) for 15 d.	0 °C storage resulted in lower pungency and respiration and fewer changes in total phenolics, anthocyanin and quercetin levels. Physicochemical properties and appearance were maintained at 0 °C.	[31]
Honeydew melon, cantaloupe, watermelon, pitaya, mango, papaya, and pineapple	Slices or wedges	Stored at 5 °C, 13 °C, and 25 °C after inoculation with pathogens.	Pathogens grew on fresh-cut fruits (except pineapple) at 13 °C and 25 °C.	[32]
Cucumber	0.5 cm cubes	Stored at 5, 10, 15, 20, 25, 30, and 35 °C.	The conservation of fresh-cut cucumbers at temperatures below 5 °C to guarantee product safety.	[33]
Radish	Slices and shreds	Three storage temperatures (1, 5 and 10 °C).	Fresh-cut radish cubes stored at 5 °C and 1 °C had lower respiration rates and nutrient content.	[34]
Apple	Slices	Packaged in tannin-loaded chitosan+gelatin films and stored at 4 °C.	Decreased weight loss, browning, lipid oxidase activity, and malondialdehyde (MDA) during 10 d storage < 4 °C.	[36]
Pineapple	Wedges 1 cm thick	Stored at 0 °C and 10 °C.	The shelf life at 10 °C ranges from 4 to 10 d, and the shelf life at 0 °C exceeds 14 d.	[37]
Potato	2 cm cubes	SHOP (80% O2, 4 °C), SC (21% O2, −2 °C), and SHOP + SC (80% O2, −2 °C).	The browning and softening of fresh-cut potato were delayed by inhibiting the activity of related enzymes.	[38]
Potato	3 mm slices	Dipped in chlorine dioxide solution (100 mg L−1), citric acid solution (1.5%) and potassium sorbate solution (0.1%), stored at 0 °C, 4 °C, 7 °C and 10 °C.	The weight loss rate, polyphenol oxidase (PPO) activity and total number of colonies decreased significantly, and 0 °C was the best.	[39]

Note: SHOP means short-term hyperoxic pre-stimulation and SC means supercooling.

). Han et al. indicated that a higher storage temperature of onions increased the respiration and pungency, soluble-solids content and vitamin C. Phenylalanine ammonia lyase activity, phenolic compounds and antioxidant capacity were enhanced by higher storage temperature [30]. In contrast, onions stored at 0 °C were less pungent, had a lower respiratory rate, and had lower variation in total phenolics, anthocyanin and quercetin. The physicochemical features and appearance of onions stored at 0 °C were improved [31]. The study showed that both Salmonella spp. and Escherichia coli O157:H7 pathogens were able to grow on fresh-cut honeydew melons, cantaloupes, watermelons, pitayas, mangos and papayas (except fresh-cut pineapples) at 13 °C and 25 °C but not at 5 °C [32]. The preservation of fresh-cut cucumbers at temperatures < 5 °C ensured safety [33]. The loss of soluble solids in fresh-cut radishes increased with longer storage times and higher temperatures. A temperature between 1 and 5 °C is recommended for retaining the color, texture and flavor of fresh-cut radishes [34]. However, the inhibitory effect of low-temperature storage on the growth of L. monocytogenes is not stable [35].

Because of the universality of low-temperature storage, this treatment is generally used in conjunction with other preservation methods. Apple slices packaged with tannic acid-impregnated chitosan–gelatin films stored at 4 °C were excellent materials for preservation [36]. Modified atmosphere packaging combined with storage at 5 °C or lower can preserve fresh-cut pineapple for more than 14 d without adverse effects on quality parameters [37]. Short-term hyperoxic pre-stimulation (SHOP) combined with supercooling (SC) provided storage below the freezing temperature but above the nucleation temperature to inhibit potato oxidation and delay the browning and softening of fresh-cut potatoes [38]. Fresh-cut potatoes treated with chlorine dioxide, citric acid and potassium sorbate solutions had lower PPO activity and fewer total colonies when stored at 0 °C [39].

Low-temperature preservation is currently the most effective low-threshold preservation method. It has been widely used in food preservation and is often combined with other preservation methods.

2.2. Preservation of Fresh-Cut Fruits and Vegetables by Modified Atmosphere Packaging

Modified atmosphere packaging (MAP) is a commonly applied method to preserve minimally processed products and prolong their shelf life [40]. MAP creates an atmosphere with low oxygen and high carbon dioxide levels that reduces the metabolic and respiratory rate, oxidant levels, tissue aging, and ethylene formation. Currently, MAP has been developed mainly for maintaining product qualities with little emphasis on safety or cost. Some deterioration still happens, and further improvements are necessary [41].

Several studies have focused on MAP technology for prolonging the shelf life of fresh-cut fruits and vegetables (Table 2). Relative to air packaging, the growth of E. coli O157:H7 on fresh-cut cucumbers was significantly lower under eight days of MAP (2% oxygen, 7% carbon dioxide, 91% nitrogen), and the shape, color, texture and smell were maintained. Under MAP, the expressions of fliC, eaeA, sodB and ropS genes of E. coli O157:H7 reduced its adherence and stress response [42]. Chitosan, a deacetylated derivative of the natural polysaccharide chitin, was also shown to preserve the quality, nutrition and sensory appeal of minimally processed table grapes, delaying spoilage when stored under high carbon dioxide [43]. Likewise, the quality indicators of fresh-cut pears under MAP remained stable throughout the storage period [44]. Lanzhou lily bulbs stored in an atmosphere of 10% O₂ + 5% CO₂ + 85% N₂ showed less lipid peroxidation than bulbs stored in air, and the cell-membrane structures remained stable [45]. High-oxygen-modified atmospheric packaging (HOMAP) sustained the integrity of fresh-cut broccoli cell membranes during storage [46].

In addition, the use of inert gases such as helium, argon and xenon in MAP have been shown to inhibit bacterial and fungal growth and retain the quality of fresh produce [47,48,49], as well as under cold storage conditions [50,51]. Compared with N₂ MAP, fresh-cut red beet leaves stored under helium retained a greater total chlorophyll content and sensory quality throughout their shelf life [52]. The loss of moisture, VC, color and hardness of fresh-cut potatoes was delayed by argon treatment under pressure, and the respiration and cell membrane oxidation of fresh-cut potatoes were significantly inhibited [53]. In addition, pressurized argon treatments on cucumber prevented the loss of soluble solids. Treated cucumbers showed significantly lower numbers of bacteria [51].

Combining MAP with other treatments like anti-browning agents is an effective way of extending the shelf life of fresh-cut produce [39]. The initial gas concentration, the type of film, the storage temperature, and the metabolic state of the fresh-cut produce should be determined to retain the nutrient value, visual appeal and safe storage.

Table 2. Modified atmosphere packaging to maintain the desirable qualities of fresh-cut fruits and vegetables under storage.

Species	Shape	Processing Conditions	Fresh-Keeping Effects	Reference Literature
Cucumber	Slices	Inoculated with Escherichia coli O157:H7, packaged in atmospheres with different gas compositions.	E. coli O157:H7 in fresh-cut cucumbers was efficiently inhibited under MAP (atmosphere = 2% O2, 7% CO2, 91% N2); visual appeal also maintained.	[42]
Grape	Clusters	Modified passive atmosphere (air), used as control. Modified active atmosphere (10 kPa CO2 and 20 kPa O2) plus chitosan. Stored at 5 °C for 14 d.	High-CO2-MAP plus chitosan was best for preservation of quality, nutrients, and sensorial parameters, and delayed spoilage of minimally processed table grapes.	[43]
Pear	Slice	Modified atmospheric packaging (MAP) in combination with 2% NatureSeal®.	Inhibited microbial growth and nutrient loss.	[44]
Lily	Bulbs	MAP1: 5% O2 + 5% CO2 + 90% N2; MAP2: 10% O2 + 5% CO2 + 85% N2; MAP3: 5% O2 + 10%CO2 + 85% N2; MAP4: 10% O2 + 10% CO2 + 80% N2.	Lipid peroxidation was inhibited, and the membrane integrity of Lanzhou lily bulbs was maintained.	[45]
Broccoli	Single-florets	HOMAP storage boxes were filled with 100% O2 and sealed, and control boxes contained normal air.	HOMAP lowered the content of substances with undesirable odors in fresh-cut broccoli by inhibiting the expression of specific enzymes.	[46]
Cucumber	Cubes	0.5 MPa Ar, 1.0 MPa Ar, 1.5 MPa Ar and 1.5 MPa air for 1 h at 20 °C. (control without pressure), and then stored at 4 °C and 90% RH for 12 d.	Pressurized Ar treatments inhibited respiration, water loss, softening, chlorophyll degradation, and color change, and also prevented a decrease in ascorbic acid and soluble solids. Treated cucumbers had lower bacterial load.	[51]
Red chard leaves	Leaves	O2, He, N2 or N2O MAP.	MAP with He and O2 inhibited bacterial growth and decreased chlorophyll and vitamin C (VC) contents.	[52]
Potato	Slices	After 60 min of pressure at 4 MPa, 4% O2 + 2% CO2 + 94% N2 was applied.	Argon treatment successfully delayed the loss of moisture, VC, color and hardness, and microbial growth.	[53]

Note: HOMAP means high-oxygen-modified atmospheric packaging.

Table 2. Modified atmosphere packaging to maintain the desirable qualities of fresh-cut fruits and vegetables under storage.

Species	Shape	Processing Conditions	Fresh-Keeping Effects	Reference Literature
Cucumber	Slices	Inoculated with Escherichia coli O157:H7, packaged in atmospheres with different gas compositions.	E. coli O157:H7 in fresh-cut cucumbers was efficiently inhibited under MAP (atmosphere = 2% O2, 7% CO2, 91% N2); visual appeal also maintained.	[42]
Grape	Clusters	Modified passive atmosphere (air), used as control. Modified active atmosphere (10 kPa CO2 and 20 kPa O2) plus chitosan. Stored at 5 °C for 14 d.	High-CO2-MAP plus chitosan was best for preservation of quality, nutrients, and sensorial parameters, and delayed spoilage of minimally processed table grapes.	[43]
Pear	Slice	Modified atmospheric packaging (MAP) in combination with 2% NatureSeal®.	Inhibited microbial growth and nutrient loss.	[44]
Lily	Bulbs	MAP1: 5% O2 + 5% CO2 + 90% N2; MAP2: 10% O2 + 5% CO2 + 85% N2; MAP3: 5% O2 + 10%CO2 + 85% N2; MAP4: 10% O2 + 10% CO2 + 80% N2.	Lipid peroxidation was inhibited, and the membrane integrity of Lanzhou lily bulbs was maintained.	[45]
Broccoli	Single-florets	HOMAP storage boxes were filled with 100% O2 and sealed, and control boxes contained normal air.	HOMAP lowered the content of substances with undesirable odors in fresh-cut broccoli by inhibiting the expression of specific enzymes.	[46]
Cucumber	Cubes	0.5 MPa Ar, 1.0 MPa Ar, 1.5 MPa Ar and 1.5 MPa air for 1 h at 20 °C. (control without pressure), and then stored at 4 °C and 90% RH for 12 d.	Pressurized Ar treatments inhibited respiration, water loss, softening, chlorophyll degradation, and color change, and also prevented a decrease in ascorbic acid and soluble solids. Treated cucumbers had lower bacterial load.	[51]
Red chard leaves	Leaves	O2, He, N2 or N2O MAP.	MAP with He and O2 inhibited bacterial growth and decreased chlorophyll and vitamin C (VC) contents.	[52]
Potato	Slices	After 60 min of pressure at 4 MPa, 4% O2 + 2% CO2 + 94% N2 was applied.	Argon treatment successfully delayed the loss of moisture, VC, color and hardness, and microbial growth.	[53]

Note: HOMAP means high-oxygen-modified atmospheric packaging.

2.3. Effects of Cold Plasma Treatment on Preservation of Fresh-Cut Fruits and Vegetables

Cold plasma (CP), which is an ionized gas consisting of active particles such as electrons, ions, free radicals, and atoms, is generated through the energetic stimulation of a gas or mixture of gases [54]. CP has been shown to prolong the shelf life and safety of fruits and vegetables by preventing the growth of harmful microorganisms, such as Escherichia coli, Salmonella enterica and Listeria monocytogenes [55,56]. The fresh-keeping effects of CP on fresh-cut fruits and vegetables have been the subject of numerous studies (

Table 3. Use of cold plasma to improve quality of fresh-cut fruits and vegetables.

Species	Shape	Processing Condition	Fresh-Keeping Effect	Reference Literature
Cucumbers	Slices	E. coli was inoculated and then treated with atmospheric low-temperature plasma.	Inhibited bacterial growth, retained moisture, sugar, acidity, VC and color, and improved the aroma of fresh-cut cucumbers.	[57]
Melon	Trapezoidal	Gas plasma for 30 or 60 min.	The 30-min treatment group showed better antibacterial and antioxidant capacity.	[58]
Hami melon	Long strips	Voltage 120 kV, frequency 130 Hz, distance 60 mm, time 150 s.	Inhibited oxidation, reduced microbial contamination, and extended the shelf life of fresh-cut cantaloupes.	[59]
Kiwifruit	Slices	Voltages of 15, 25 and 35 kV, discharge times of 90 s (45 s each side), 110 s (55 s each side) and 130 s (65 s each side).	Significantly decreased bacterial level in fresh-cut kiwi fruit.	[60]
Kiwifruit	cubes	1 mL of plasma-activated water (PAW) and 1 mL of sterile water as control sample were separately sprayed on fresh-cut kiwifruit (FCK) and stored at 4 °C for 8 d.	PAW reduced the microbial population of FCK by 1.8 log CFU/g. The activities of superoxide dismutase, peroxidase, and catalase in PAW-treated FCK samples were higher.	[61]
Lettuce	Slices	Rinse 30 s with plasma-functionalized water.	The effective removal of microorganisms did not affect the organelles of lettuce tissue.	[62]
Potato	Cubes	PAW was prepared using a frequency of 200 Hz (200 Hz-PAW). Its efficacy was compared with that of PAW prepared using 10 kHz.	PAW inactivated the browning-related enzymes PPO and POD, lowering the browning index and inhibiting browning. The fewest aerobic mesophilic, mold, and yeast counts during storage were measured with 200 Hz-PAW treatment.	[63]
Cantaloupe	Circular sections	Treatment with cold plasma at 40 kV for 90 s.	Microbial growth was significantly inhibited and the surface color, soluble solid content (SSC), VC content and pulp firmness were maintained.	[64]

). For example, CP was found to eliminate E. coli from fresh-cut cucumber slices under normal pressure, but the treatment showed no significant improvement of the physicochemical attributes and positive sensorial qualities of fresh-cut cucumbers [57]. Also, CP treatment significantly decreased the bacterial level in fresh-cut melons and sustained the desirable qualities better than in controls [58]. Short duration CP treatment at high voltage prolonged the shelf life of fresh-cut Hami melons by inhibiting oxidative reactions and limiting the growth of microorganisms with no adverse effects on flavor, color, odor, etc. [59]. CP also helped to retard bacterial growth in fresh-cut kiwi fruit [60].

Recently, evidence has shown that plasma-activated water (PAW), which is produced by the reaction of cold plasma with water, has outstanding antimicrobial activity on kiwifruit [61]. During the rinsing step of fresh-cut lettuce, the use of another type of aqueous CP, called plasma-functionalized water, effectively reduced the microbial content and maintained color and texture without affecting food quality [62]. Fresh-cut potatoes treated with plasma-activated water had the fewest aerobic mesophilic, mold, and yeast counts during storage [63]. Zhou et al. found that CP could prevent the loss of color, VC, soluble solid contents and firmness in fresh-cut cantaloupe held at 4 °C for ten days [64]. However, some research has indicated that CP treatment can cause a decrease in up to 10% in antioxidant level and total antioxidant capacity in fresh-cut apples. This may result from the modification of some bioactive substances in food by reaction with active components of CP [65].

The food atmosphere is used to produce reactive plasma species (RPSs), such as peroxides, nitrites, nitrates, and ozone [66]. These RPS are rapidly formed from collisions among the electrons, atoms, and molecules of the gas. The gases used affect RPS generation in cold-plasma systems, and air is most often used to generate reactive oxygen species (ROS) and reactive nitrogen species (RNS). ROS and RNS damage DNA, oxidize lipids, and disrupt the secondary structure in protein. CP also causes electrostatic disruption, electroporation, apoptosis, and death from the strong energies applied [67]. So far, the authors have not found any literature on the cost of CP technology. CP is highly effective in killing foodborne pathogens, and scaling up to industrial level may be implemented soon.

2.4. Effects of Pulsed-Light Treatment on Preservation of Fresh-Cut Fruits and Vegetables

Pulsed light (PL), sometimes called pulsed white light, lighting pulses, high-intensity PL and intense PL, is a recently developed method for disinfecting the surface of fruits and vegetables [68]. The effectiveness of PL depends on the fluence, the distance from lamp to sample, the medium through which the light propagates and the wavelength [69]. PL-activated sterilization is mainly due to the wavelength selected and the interaction between the light and the food microbiome [68].

PL treatment was effective in reducing microbial contamination and maintaining the VC and carotenoid content as well as the antioxidant capacity in fresh-cut fruits and vegetables (

Table 4. Pulsed light used to improve qualities of fresh-cut fruits and vegetables.

Species	Shape	Processing Condition	Fresh-Keeping Effect	Reference Literature
Apple	Wedges	Rinsed with 1% w/v N-acetylcysteine and 0.5% w/v CaCl2 and pulsed with broad-spectrum light at an overall radiant exposure of 4, 8, 12 and 16 J cm−2.	Inhibited microbial growth and maintained antioxidant capacity.	[70]
Apple	Slices	1% (w/v) VC plus 0.1% (w/v) CaCl2 and 2.4, 11.9, 23.9, 71.6 and 119.4 J cm−2 PL.	Inhibited microbial growth and prevented decline of soluble solids and hardness.	[71]
Red bell pepper	Pieces	4 and 32 J cm−2 PL treatments with exposure times varying between 3.5 and 26.5 min.	Inhibited microbial growth and retained content of VC, phenols and carotenoids.	[72]
Cantaloupe	Cuboid, triangular prism and spherical	Number of pulses were 9, 26, 39 and 52 with corresponding fluences of 2.7, 7.8, 11.7 and 15.6 J cm−2.	The spherical samples treated with 7.8 J cm−1 PL had lower microbial count and higher VC content.	[73]
Mangos	Cubes	Control (0 P), 1 pulse (1 P; 0.7 J cm−2), 4 successive pulses (4 P; 2.80 J cm−2) and 1 pulse per day for 4 d (1 P 4 D; 2.80 J cm−2) before storage for 7 d at 6 °C.	Treatment with four continuous pulses (4 P; 2.80 J cm−2) resulted in higher VC and carotenoid content as well as antioxidant activity.	[74]
Cantaloupe	Spherical	A fluence of 0.9 J cm−2 was applied every 48 h during storage until day 26.	Sensory quality was maintained effectively with no change in the contents of sugar and organic acids, and minimal loss of total aroma compound concentration.	[75]
Mango	Cubes	Xenon gas, 190 mm width, lateral position, with a capacity of one pulse every 15 s and 0.3 × 104 J m−2 per pulse power (100% lamp potency).	PL irradiation maintained the integrity of the cell wall and inhibited the decrease in VC content and the color change during storage.	[76]

). Llano et al. reported that flashing fresh-cut apple slices with PL fluences of 4 and 8 J cm⁻² resulted in a reduction of 0.75–1.55 logs in psychrophilic bacteria and 2.3 logs in mold and yeast counts [70]. PL combined with VC and calcium chloride (CaCl₂) solution (AD) effectively inhibited browning and reduced microbial counts in fresh-cut apple slices [71]. The PL treatment of fresh-cut red bell pepper inhibited microbial content and preserved the concentrations of VC, phenolic substances and carotenoids [72]. Koh et al. (2016) showed that PL exposure reduced microbial growth and increased the shelf life of fresh-cut cantaloupes by eight days compared with the control [73]. PL-treated fresh-cut mangoes showed significantly higher VC and carotenoid content than controls on the 7th day [74]. Repeated flashing with pulsed light together with alginate coating was effective in maintaining the sensory qualities of fresh-cut cantaloupe [75]. Non-thermal pulsed light (PL) irradiation maintained the integrity of the cell wall of fresh-cut mango and inhibited the decrease in VC content and color change during storage [76].

The mechanism of microbial killing by PL has been attributed to photochemical damage to the genetic material and localized heating [77]. The FDA approved using PL technology in food applications in 1996, but the fluence cannot surpass 12 J cm² [78]. PL is a non-thermal method for the inactivation of vegetative organisms and spores in fruits and vegetables. With the PL technique, microbial inactivation is rapid, and it requires only low energy, few residual compounds, and no toxic chemicals or environmental pollutants [79]. PL treatments are a promising technology for the food processing industry because they are cost-effective, have low energy requirements and reduced treatment time.

2.5. Effects of Ultrasound Treatment on Preservation of Fresh-Cut Fruits and Vegetables

Ultrasound (US) is considered a safe, non-toxic, and environmentally friendly decontamination technology, which works with pressure waves at frequencies ranging from 20 to 100 kHz in a liquid media [80]. The high-pressure waves induce acoustic cavitation, liberating high amounts of energy that destroy the microbial cell walls and damage the DNA via free radical production [81]. Ultrasound offers many advantages such as a decrease in the use of fossil fuels for energy during food processing (e.g., drying and heating); decreases in the amount of water consumed; enhanced productivity; and retention of product nutrients [82]. US treatment kills pathogenic microorganisms through cavitation and is often used in food processing and preservation [83]. US can also inactivate oxidation-related enzymes, improve antioxidant capacity [84], lower PPO activity, improve visual appeal, reduce spoiling and offensive odors, enhance vitamin C, antioxidant capacity and total phenolics [85], maintain food color and restrict the microbial growth (bacteria, yeast and mold) [86], which increases the shelf life of food.

Several authors have reported the main effects of US alone or combined with other methods on various fresh-cut fruits and vegetables (

Table 5. Use of ultrasound to preserve the desirable qualities of fresh-cut fruits and vegetables.

Species	Shape	Processing Condition	Fresh-Keeping Effect	Reference Literature
Cucumber	Slices	The power intensity was 226 W cm−2, the frequency was 20 kHz, and the treatment lasted for 10 min.	Bacterial growth was inhibited significantly, the minimum respiration rate, the weight, and the SSC content were maintained, and the MDA concentration of fresh-cut cucumber was low.	[87]
Quince	Slices	Slices were treated in ultrasonic bath with frequency of 28 kHz, intensity of 100 kWm−3, power of 50 W and time of 15 min.	Inactivated browning enzymes to prevent enzymatic browning.	[88]
Cucumber	Slices	Cucumber was treated with ultrasound (20 kHz) at different times (5, 10 and 15 min) and then stored in the modified atmospheric packaged at 4 °C for 15 d.	US treatment inhibited the growth of mold and yeast in MAP fresh-cut cucumber.	[89]
Mango	Slices	Immerse in 0.5% (w/w) anti-browning preservative for 3 min and ultrasonic water bath for 4 min.	The browning enzyme activity was effectively inhibited, and the color and bioactive substance content were maintained.	[90]
Cucumber	Slices	US for 5 min, 10 min, and 15 min plus rinsing with 50, 75, 100 ppm NaOCl.	Inhibited microbial contamination, maintained the integrity of cell membranes and tissue hardness, and reduced water loss.	[91]
Carrot	Cubes	US plus citral nanoemulsion (CLON): combined treatment with CLON (0.10, 0.15 mg mL−1) and US (115, 230 and 345 W cm−2).	0.15 mg mL−1 of CLON combined with US (20 kHz, 345 W cm−2) for 9 min significantly improved the bactericidal effect against Sh. flexneri.	[92]

). US treatment combined with a coating of carbon dots (CDs) significantly inhibited bacterial growth in fresh-cut cucumbers and maintained a low respiratory rate, minimal loss of SSC and weight, and low malondialdehyde (MDA) content [87]. The enzymatic browning of fresh-cut quince was significantly inhibited by US treatment, and fresh-cut papaya treated with US was superior to ascorbic acid treatment and heating at 65 °C for inhibiting decay and odor [88]. Fan et al. showed that US treatment inhibited microbial load and improved the quality of stored cucumbers [89]. Yildiz, G. and Aadil, R.M. treated fresh-cut mangoes with high-intensity ultrasound (HIU), anti-browning agents (VC and CaCl₂), and heating at 65 °C. HIU treatment resulted in low PPO activity during storage at 4 °C, improved sensory parameters by reducing decay and odor, and enhanced the content of bioactive compounds including VC and total phenolics as well as antioxidant capacity [90]. Treatment with US and sodium hypochlorite (US-NaClO) inhibited microbial growth during the storage of fresh-cut cucumber and maintained cell membrane integrity [91]. US plus citral nanoemulsion (CLON) treatment significantly improved the bactericidal effect against Clostridium flexneri on fresh-cut carrots [92].

Excessive US treatment can be damaging to fresh-cut fruit and vegetable cells and accelerate oxidation-mediated deterioration. However, the activities of non-enzymatic antioxidants, total antioxidant activity, superoxide dismutase and catalase were not affected by US [93]. Published reports have shown that the intensity of US treatment could influence the firmness and color of fresh fruits and vegetables, possibly from acoustic cavitation and the inactivation of phenol oxidase and polyphenol oxidase [81].

2.6. Effect of UV Treatment on Preservation of Fresh-Cut Fruits and Vegetables

UV treatment can effectively preserve fresh-cut fruit by killing microorganisms on the surface. Short-wavelength ultraviolet (UV-C) treatment is applicable for the preservation of fresh-cut organic produce, and it can replace the non-permissible chlorine added to the washing water [94]. UV radiation damages microbial membranes and nucleic acids, and it activates defense pathways [95]. This method has the advantage of ease of use and low cost of installation and maintenance. It has no legal limitations, is lethal to a wide range of pathogens and decay organisms, has no food residues, and has minimal loss in sensory quality or thermosensitive nutrients [96]. As a food preservation treatment, UV-C irradiation is limited by low surface penetration and packaging, allowing microbes to escape its killing activity [96]. Despite this drawback, the application of UV irradiation to minimize microbial contamination on fresh-cut fruits and vegetables is growing [95], primarily in the disinfection step after cutting [96,97].

Numerous studies have shown that UV sterilization can help to maintain the desirable qualities of fresh-cut horticultural products (

Table 6. Ultraviolet irradiation preserves the desirable qualities of fresh-cut fruits and vegetables.

Species	Shape	Processing Condition	Fresh-Keeping Effect	Reference Literature
Strawberries	Wedges	Brief UV-C treatments with different combinations of radiation intensity (0, 9, or 36 W m−2) and dose (0, 2, or 4 kJ m−2).	UV-C irradiation with 4 kJ m−2 at an intensity of 36 W m−2 reduced decay, juice leakage, dehydration softening, and yeast/mold spores. Freshness, color, and shelf life were maintained.	[98]
Strawberries	Slices	UV-C treatment (5.8 kJ m−2) alone and combined with the addition of orange juice for 12 d at 0 °C.	Both UV-C treatments alone and combined with juice immersion reduced microbial load; UV-C applied alone allowed obtaining the highest microbial reductions.	[99]
Watermelon	Cylinders	Fruit cylinders irradiated with UV-C at a dose of 2.4 (exposure time of 60 s), 4.8 (120 s) and 7.2 kJ m−2 (190 s).	The growth of microorganisms was significantly inhibited, and phenolic content was maintained.	[100]
Stem lettuce	Slices	Treated with different doses (0, 1, 4, 8 or 12 kJ m−2) of UV-C, then stored at 4 °C for 6 d.	UV-C treatment decreased the degradation of chlorophyll, the loss of VC and the accumulation of phenolic compounds. UV-C treatment did not affect PPO or POD activity, but it did inhibit PAL.	[101]
Rocket leaves	Slices	Separate application of UV-C (25 kJ m−2, 380 s) and O3 gaseous (2.5 mg L−1 for 10 min) treatments and of their combination were studied to evaluate the effect of combined treatments on microbial counts.	The UV-C treatment was better at reducing microorganisms present, and non-significant differences were found regarding the combined treatment.	[102]
Strawberries	Wedges	The dose of UV-C used in this experiment was 4.0 kJ m−2.	Inhibited microbial growth, promoted the production of ROS, and increased the content of total phenols, total anthocyanins and individual phenolic compounds.	[103]
Lettuce and cherry tomatoes	Pieces	US-free chlorine (FC)/peracetic acid (PAA) (5 min), US-FC/PAA-UV (3 min; 1.71 kJ m−2).	US-FC/PAA-UV was more effective in reducing microbial colonization on products with smooth surfaces, such as cherry tomatoes.	[104]
Mango	Spear	A UV-C dose of 6 kJ m−2 established.	The microbiological safety and surface color of fresh-cut mango were maintained, and the total carotenoid content was increased.	[105]

). Strawberries treated with high-intensity UV-C showed less decay as well as reduced water loss, softening, and levels of yeast and mold, resulting in higher scores in consumer surveys of freshness, color, and overall appeal. The acidity, soluble solids, and phenolic content were unchanged [98], while the microbial load was significantly reduced [99].

UV treatment not only helps with the preservation of fresh-cut fruits by killing microbes but also decreases oxidant levels and extends shelf life. Compared with untreated samples, the total antioxidant capacity of UV-C-irradiated fresh-cut watermelon samples increased by 2–14 times during the storage period, which may be due to the antioxidative response caused by UV stress on the samples [100]. Han demonstrated that UV-C treatment reduced the loss of chlorophyll and vitamin C while raising the content of phenolics in fresh-cut stem lettuce. The treatment had little effect on PPO and POD activity but did reduce PAL [101]. Additionally, UV-C significantly reduced microbial counts on fresh-cut rocket leaves that was not enhanced by ozone pre-treatment [102]. Li et al. showed that UV-C preserved the quality, phenolics level, and antioxidative protection by inducing the phenylpropanoid pathway in fresh-cut strawberries [103]. The combination of US, free chlorine (FC), peracetic acid (PAA), and UV was more effective in reducing microbial contamination on products with smooth surfaces, such as cherry tomatoes [104]. UV-C treatment increased the safety of eating stored fresh-cut mango by reducing microbial colonization, enhanced the carotenoid content, and preserved the color [105].

2.7. Effect of Ozone Treatment on Preservation of Fresh-Cut Fruits and Vegetables

Traditional fruit and vegetable preservation methods generally have a lower technical threshold and cost and are, therefore, still widely used. Ozone (O₃) is a highly effective antibacterial agent that can ensure food safety by rapidly killing foodborne pathogens. Ozone dissolved in deionized water has powerful bactericidal activity. In tens of seconds or even only a few seconds, ozone can oxidize bacterial proteins, killing them. Because ozone has unique antimicrobial properties against bacteria, fungi and viruses, ozone disinfection technology has attracted much attention in the food industry in recent years [106].

Many researchers have investigated ozone for the sterilization of fresh cut fruits and vegetables and the preservation of their quality (

Table 7. Use of ozone to preserve the quality of fresh-cut fruits and vegetables.

Species	Shape	Processing Condition	Fresh-Keeping Effect	Reference Literature
Lettuce and bell peppers	Slices	Dipped in continuously ozonated (0.5 mg L−1) water.	Approx. 2-log reduction in microbial load after 15 min and 3.5-log after 30 min of exposure.	[106]
Papaya	Cubes	Treated with 9.2 pl L−1 ozone for 10, 20, and 30 min.	Microbial population of fresh-cut papaya was significantly reduced, and the total phenolics content was somewhat increased.	[107]
Durian	Peeled flesh	Ozone at 500 and 900 mg L−1 was selected to reduce microbial contamination in vivo.	Significantly reduced microbial counts with 900 mg L−1 being the most effective.	[108]
Potato	Slices	Soak in acidic dip with aqueous ozone and stir for 5 min.	Reduced enzymatic browning of fresh-cut potatoes.	[109]
Cabbage	Slices	Wash for 1, 5, and 10 min with ozone concentration of 1.4 mg L−1.	Inhibited aerobic bacteria, coliform bacteria and yeast and removed some pesticide residues.	[110]
Iceberg lettuce	Pieces	Soak in ozonated water at 20 °C for 2 min.	Controlled the growth of Enterobacteriaceae, thermophilic and psychrophilic bacteria.	[111]
Water fennel	Slices	Treated with 18.52, 37.04, 55.56 and 74.07 mg m−3 ozone for 15 min.	Maintained ascorbic acid content, inhibited polyphenol oxidase activity, lowered content of reduced glutathione, and increased peroxidase, catalase, ascorbate peroxidase and superoxide dismutase.	[112]
Kiwi fruit	Pieces	One group was fumigated with 1 mg L−1 of gaseous ozone for 10 min, while the other group was unfumigated.	Inhibited activity of polysaccharide-degrading enzymes and electrolyte leakage, reduced MDA and hydrogen peroxide content, and maintained the original pectin and cellulose levels, thus preventing the softening of fresh-cut kiwi fruit.	[113]
Kiwi fruit	Pieces	Subjected to fumigation with gaseous ozone (1 mg L−1) for 10 min.	Ozone treatment maintained AsA/dehydroascorbic acid content and reduced the total soluble solids/titratable acidity.	[114]
Red pitaya	Strips	Fumigated with 10 μL L−1 ozone in enclosed chamber; control treated with air.	The activity of antioxidant enzymes was increased, the ascorbate–glutathione cycle was activated, and the loss of hardness and total soluble solids/titratable acids was delayed.	[115]
Honey pineapple, banana and guava	Cubes	Exposure to ozone for 0, 10, 20 and 30 min.	Levels of total phenols and flavonoids in pineapples and bananas were increased; vitamin C levels in pineapples, bananas and guava were significantly reduced.	[116]
Apple	Slices	Ozone (1.4 mg L−1) treatment for 1, 5, and 10 min.	Activities of polyphenol oxidase and peroxidase were reduced as well as total phenols and MDA concentration; antioxidant capacity was enhanced.	[117]

). Ozone disinfection is a relatively safe procedure that has been certified for food handling, storage and processing [106]. Ozone disinfection is a relatively safe procedure that has been certified for food handling, storage and processing [106]. Ozone treatment significantly reduced the microbial content of fresh-cut papaya and increased its total phenolic content [107]. For peeled durian flesh, ozone at 900 mg L⁻¹ reduced total bacterial count and coliforms by 2.72 and 1.93 log CFU g⁻¹, respectively, relative to control [108]. It has also been shown that ozone can reduce the enzymatic browning of fresh-cut potatoes, but it has no effect on the number of aerobic bacteria (APCs) and PPO activity [109]. Ozonated water is highly bactericidal and can be easily prepared by dissolving ozone gas in deionized water. Ozonated water not only kills the aerobic bacteria, coliforms, and yeast on fresh-cut cabbage but can also oxidize some pesticide residues [110]. Ozonated water moderately controlled the growth of thermophilic and psychrophilic bacteria on fresh iceberg lettuce during a 12-day storage period, but it only controlled the growth of Enterobacteriaceae for 6 d [111]. It has been reported that ozonated water (0.5 mg L⁻¹) showed better bacteriostatic effects on fresh-cut lettuce (Lactuca sativa) and sweet pepper (Capsicum annuum), and coliform and total aerobic thermophilic bacteria were more sensitive to ozone [106]. After ozone treatment, water fennel retained its appearance, texture, and high commercial value during storage [112]. Ozonation inhibited the activity of polysaccharide-degrading enzymes, electrolyte leakage and the content of MDA and H₂O₂, and it maintained the original pectin and cellulose levels, thus preventing the softening of fresh-cut kiwi fruit [113]. Ozone not only maintained AsA/dehydroascorbic acid levels and reduced the content of TSS/titratable acid in fresh-cut kiwi fruit but also changed the level of plant hormones to different degrees [114]. Ozone treatment increased the antioxidant enzyme activity of fresh-cut red pitaya during storage and delayed the decline of hardness, TSS and titratable acid content [115].

Ozone treatment also improved the antioxidant capacity of fresh-cut fruits and vegetables. It has been reported that the iron-reducing/antioxidant capacity (FRAP) and the free radical scavenging capacity of 1, 1-diphenyl-2-pyridinyl hydrazide (DPPH) in fresh-cut pineapples and bananas were maintained by ozone treatment, and the total phenolic and flavonoid contents in pineapples and bananas were significantly increased by ozone treatment for 20 min. However, ozone treatment significantly reduced VC levels in pineapples, bananas and guava [116]. The treatment of fresh-cut apples with ozonated water can also reduce ethylene production, the activities of polyphenol oxidase and peroxidase, and the contents of total phenol and MDA, enhance antioxidant capacity, and delay deterioration [117].

Ozone does not affect food quality or harm the environment, and therefore it is an ideal disinfectant for keeping fresh food safe from microbial contamination and preserving its appearance and flavor. However, ozone is unstable in aqueous solution and spontaneously breaks down at room temperature; it cannot be collected, stored or transported and it must be generated in situ as needed. Ozone is a good antioxidant because of its reactivity, and it has been approved in the food industry after being generally recognized as safe (GRAS) in the U.S. [118]. Ozone must be produced on-site, but fresh-cut fruits and vegetables can be processed in a gaseous or aqueous state. Ozone is a stronger oxidizer than chlorine against bacterial proteins, lipids, and enzymes and decomposes to oxygen, leaving no food residue [119]. Shezi et al. concluded that ozone’s bactericidal activity was a result of chemical reactions on double bonds in membrane lipids [120]. Ozonation requires a higher initial equipment cost, but otherwise it is less expensive than other preservative treatments.

3. Summary and Prospects

Fresh-cut produce has become extremely popular with consumers, and its color, texture, flavor, and nutritional value are important for marketability [121]. However, fresh-cut products deteriorate more quickly than unprocessed raw materials because of the damage from peeling, slicing, dicing, shredding, etc. necessary for processing fresh-cut fruits and vegetables. This processing can cause oxidative browning, and the exposed cut surface is also more susceptible to the growth of pathogenic microorganisms. Water loss and osmotic changes can also produce undesirable textural changes that reduce shelf life and salability [122]. These problems have been restricting the expansion of the fresh-cut food industry and are also one of the main drivers of food preservation research.

The preservation of fresh-cut fruits and vegetables generally follows two pathways: antibacterial and antioxidant, and the different fresh-keeping methods each have their advantages and disadvantages. The threshold for physical fresh keeping is low, which is suitable for large-scale storage and transportation, but some of the cost is high. The method of chemical preservation is low in price and high in efficiency, but sometimes it is harmful to human health. Biological preservation yields a product that is nutritious and healthy, but it has not yet become suitable for large-scale production. In actual production, in order to make up for the shortcomings of the various preservation techniques, the physical, chemical and biological preservation methods are often combined into a composite preservation method. The composite preservation method gives full play to the advantages of various preservation methods, and the development of multiple storage methods is likely to be the trend of future development.

Some traditional physical and chemical preservation methods have safety risks and result in poor flavor and a nutrient loss of fresh-cut foods. As consumers pay more attention to food safety, traditional preservation methods are not adequate to meet their needs, and biological preservation is receiving more and more attention. Biological preservatives are derived from animals and plants and are considered safer than some synthetic chemical preservation technologies. However, the current extraction methods of biological preservatives have unique technical requirements that make them difficult to apply for large-scale production. This problem will certainly be on the radar of biological preservation research in the future.

Different preservation methods have advantages and disadvantages, and biological preservation can better guarantee the safety of food and is also easier for consumers to accept. The main directions of future research will include studies on composite preservation methods involving natural extracts and their effectiveness in combination with novel non-thermal physical methods.

Emerging physical technologies, such as atmospheric modification, ozonation, ultraviolet irradiation, and high hydrostatic pressure, have not been fully adopted by the food industry because of inadequate safety and high cost. The future of fresh-cut food research lies in the development of customized combinations of individual preservation methods that will synergize to increase nutritiousness, sensory appeal, and safety. These composite processes need to be deployed for large-scale industrial adoption while still maintaining the nutritional, visual, flavor and keeping qualities of fresh-cut produce. Overall, the non-thermal preservation techniques including sonication, cold plasma, high-pressure, ultraviolet light, and pulsed electric fields in combination with more consumer- and environmental-friendly methods would seem to be the best strategy for the fresh-cut food industry to produce fresher-tasting, safer, more nutritious natural foods.