Post-Harvest Problems of Strawberry and Their Solutions

Abstract

Strawberry is a fruit with a short season of harvest. Strawberry is well-known among people all over the world for its distinct flavour, nutritional value, and delicacy. While on the other hand, preserving strawberry and shelf life extension has been a huge difficulty due to their perishable nature. Making effective and sustainable use of already available food processing and preservation technology needs time. Researchers must use advanced techniques like a cool store, modified atmospheric packaging (MAP), cool store, controlled atmospheric storage (CA), various packaging methods, and a variety of chemical and physical treatments to retain commodities for a longer period due to strategic market sales following harvest. Except for the preserving techniques, there is some polysaccharide-based edible coating which has a crucial role in delaying fruit softening, fruit decay, maintaining the increased levels of ascorbic acid and phenols, enhancing the activities of antioxidant enzymes, and reducing membrane damage. During the postharvest stages, there are numerous threats to keep in view regarding the safety and quality of strawberries. In this chapter, we will discuss the benefits and drawbacks of some of the various preservation technologies, as well as how they might be utilised to preserve and a prolonged period of freshly harvested strawberries.

1. Introduction

The strawberry (Fragaria ananassa) belongs to the Rosaceae (flowering plant). It is among the most well-known non-climacteric fruits because of its nutritional and organoleptic characteristics [1]. The fleshy component is formed not from the plant’s ovary but from the receptacle that stores the ovaries, making it an aggregate accessory fruit. Each “seed” (achene) outside the fruit is one of the flower’s ovaries, which contains seeds. The genetic makeup of the currently grown strawberry fruit is an octoploid hybrid (8n), with 56 chromosomes. It’s eaten in huge volumes, both freshly and in ready food like juice, pies, jam, ice cream, chocolates, milkshakes etc. Strawberries are commercially grown for sustenance as well as can be eaten fresh or processed into frozen, canned, or preserved fruit or juice.

Strawberry fruit slices are high in flavonoids, fibre, vitamins, potassium, and a wide range of phenolic acids, including hydroxycinnamic and hydroxybenzoic acids [2]. They are quite beneficial to one’s health. They’re high in vitamin C and manganese, and they also have a considerable quantity of folate (vitamin B₉) and potassium. Fruit antioxidants such as kaempferol, quercetin, and anthocyanins help to prevent the creation of deadly blood clots that are linked to strokes. The antioxidants work by neutralising free radicals in the body, preventing tumour formation, and reducing inflammation. Because of their nutritious content, strawberries had been recommended to those with high blood pressure and sugar. Strawberries have a low glycemic index (40) as compared to other fruits, making them a good choice for diabetic patients.

Table 1 shows the nutritional values per 100 g of strawberry:

Nutritional components	Quantity	Nutritional components	Quantity
Energy	136 kJ	Choline	5.7 mg
Water	90.95 g	Vitamin C	58.8 mg
Carbohydrates	7.68 g	Vitamin E	0.29 mg
Sugars	4.89 g	Vitamin K	2.2 μg
Dietary fibre	2 g	Calcium	16 mg
Fat	0.3 g	Iron	0.41 mg
Protein	0.67 g	Magnesium	13 mg
Thiamine (B1)	0.024 mg	Manganese	0.386 mg
Riboflavin (B2)	0.022 mg	Phosphorous	24 mg
Niacin (B3)	0.386 mg	Potassium	154 mg
Pantothenic acid (B5)	0.125 mg	Sodium	1 mg
Vitamin B6	0.047 mg	Zinc	0.14 mg
Folate B9	24 μg	—	—

Table 1.

The nutritional values per 100 g of strawberry.

Strawberry production is getting importance by the consumers due to its nutritional facts. In 2019, global strawberry output totalled 8.9 million tons, with China accounting for 40% of the entire and the United States and Mexico rounding out the top three producers. China is the largest producer with 3.9 million tons of production annually in 2019. Table 2 shows the top producers of strawberries in 2019.

Countries	Production (million tons)
China	3.2
United States	1.0
Mexico	0.9
Egypt	0.5
Turkey	0.5
Spain	0.4
World	8.9

Table 2.

Countries wise the production (million tons).

Due to the ever-increasing demand for strawberries, several issues arise during the cultivation, production and harvesting phases. Strawberry is regarded as among the most problematic fresh food to preserve due to the difficulties in maintaining fruit freshness [3]. After production, the berries are harvested by hands and placed in trays for further operations. Moreover, it is highly perishable and has a limited postharvest life, owing to its fast metabolism and sensitivity to mechanical damage as well as infection by plant pathogens bacteria, fungi, and viruses [4].

Various operations like cooling at low temperature, edible films coating, UV radiations, fruit sanitization and many more are carried out for lowering the respiration rate and loss of water, maintaining fruit firmness, and restricting microbial spread are all objectives of postharvest operations to extend its life span. Cooling at low temperatures is one of the most efficient procedures for increasing fruit longevity [5]. In recent years, there has been a surge in interest in edible films coating. Edible films are effective as they provide a physical border around the fruit, shielding it from moisture, fumes, and microorganisms that could compromise its quality [5]. Aside from that, starch-based films are edible, translucent, odourless, tasteless, and colourless, all of which are desirable qualities for food packaging [6]. The use of C ultraviolet (UV-C) entails eradicating microorganisms from vegetative tissues through the antibacterial effect generated by radiation, which is one of the strategies that has been gaining traction to extend post-harvest fruit lifespan [7]. Chlorine, mostly in the form of sodium hypochlorite, is commonly employed in fruit sanitization. It works by removing harmful organisms, resulting in a longer fruit lifespan [8]. A need to produce healthier foodstuff while reducing the usage of fungicides and other elevated toxic treatments emphasise the significance of investigating and presenting sustainable fruit conservation approaches in detail. The goal of the study is to assemble and discuss in detail the procedures that must be followed during harvest and postharvest activities of strawberries to minimise losses.

2. Factors involve in post-harvest handling of strawberries and their issues

2.1 Harvesting of strawberry

Strawberry fruit is non-climacteric, meaning it ripens while still attached to the parent plant. The fruit should be harvested after it has reached the desired shape and size, as determined by varietal characteristics. The berries should be harvested with care because ripe one’s bruise readily. Strawberry fruit is carefully collected with its calyx by manually pinching the stem (0.5–1.0 cm above calyx) instead of pressing the fruit’s fleshy section.

Three main factors affect the harvesting and postharvest strategies of strawberries.

• Phases of fruit ripening: Strawberries should not ripen after they have been picked. They should be harvested when they are ripe, red, and firm. Harvesting time is determined by the fruit’s ripeness and market demand. Plant nutrients can help the fruit to retain its firmness and freshness.

• Cleanliness: Keep the fruits clean as much as possible. Keep watering the roads to avoid the dust and vulnerability to soil-born pathogens. Instruct labourers on the causes of contamination, the consequences (health issues, reputational damage, financial loss, etc.), and a detailed study to prevent contamination.

• Harvesting time: The harvesting time has a significant impact on the fruit’s shelf life. Try to keep the fruit at its optimal temperature. Before the temperature rises, pluck the fruits early in the morning before 10 am to avoid heat injury and sunburn. Before transferring the fruit to the cold storage, keep it in the shade. Usage of the forced air-cooling system to reduce the temperature of the fruit to an acceptable level is important. At 0°C–2°C, the life span is extended.

• Other factors: Place the berries in suitable containers, reduce vibration damage during transportation, reduce the exposure duration to unfavourable conditions, storage etc.

Though manual harvesting is the most common way of strawberry harvesting, various investigations on mechanical and intelligent robotic harvesting systems have been conducted. Han et al. [9] created a computer vision-assisted robot system to recognise and handle mature strawberries planted in a bench-type farming system. The fruit detection algorithms were programmed utilising real-time position tracking methods in natural light. Strawberry harvesting [10], cucumber harvesting [11], aubergine harvesting [12], and de-leafing [13] are only a few of the studies that have used robotic technology in greenhouses.

2.2 Pre-cooling

Pre-cooling fresh fruits before storage and marketing have a big impact on their quality [14]. The respiration rate and all metabolic responses in newly harvested produce are reduced when field heat is removed. Pre-cooling is the elimination of heat from the field from the freshly harvested commodity. Strawberry precooling (rapid reduction of field heat) is required within 1 hour following harvest. Strawberry has a high rate of metabolism, so its marketability is reduced by 20%, 37%, 50%, or 70% with cooling delays of 2, 4, 6, or 8 hours, respectively. There are different methods involved in pre-cooling such as forced air cooling, hydro cooling contact icing, room cooling, vacuum cooling. All these techniques vary in their ability to remove field heat. Forced-air cooling is the most popular approach for precooling berries. The containers are forced to circulate cold air quickly, enabling the cold air to come into interact directly with the warm berries. Strawberry pallets are arranged in such a way that cooler air must penetrate through the package opening as well as around each berry to reach the low-pressure area. Heat removal is a very important process to the low temperature (0°C–1°C) and relative humidity (90%–95%) because it extends the shelf life of produce, lessens physiological decline and reduces the occurrence of pathological degradation [15, 16].

A few elements influence the system’s cooling rate and performance:

1. the difference in temperature between the cool air and the fruit,

2. the rate at which air flows,

3. the fruit’s ability to be exposed to cool air,

4. the width and length of the air channel.

Although hydro-cooling is a faster form of precooling, strawberries are not commercially hydro-cooled due to deterioration concern by the water left on strawberries after hydro cooling [17]. As a result, the most frequent strategy for preserving strawberry fruit quality after harvest is to cool the fruits immediately after harvesting and then store them at a low temperature (0°C–4°C) [18].

2.3 Modified atmosphere packaging

Mmodified atmospheric packaging (MAP) is a technique of packaging that involves altering the gaseous atmosphere surrounding a food product within a package by using packing materials and layouts that have enough level of gas barriers to keep the altered environment at a safe level for food preservation. MAP methods preserve fresh food by reducing oxygen exposure and raising carbon dioxide content. The use of CO₂ as part of a modified environment has been found to help preserve strawberry sensory attributes [19]. The oxygen content should be kept low because oxidation is caused by the presence of oxygen and can result in discolouration, rotting, and off-flavours and textures. The model incorporates respiration, transpiration, and diffusional movement of O₂, CO₂, N₂, and H₂O in a microperforated pack.

For strawberries, the optimal MAP composition is O₂ (5%–10%), CO₂ (15%–20%), and N₂ (70%–80%) [20]. Maintaining a reasonably low temperature is required for MAP storage since the temperature has a greater influence on the rate of respiration than gaseous concentration, with a 72%–82% drop in respiration rate for various O₂ and CO₂ combinations when the temperature was reduced from 23°C to 10°C [21]. Short exposure to increased levels of carbon dioxide has been shown to reduce the chemical and physical concepts affiliated with fruit decay, lowering tissue ATP levels and producing a low ethanol metabolism, in contrast to when the fruit is stored in the presence of air, which causes an increase in ATP and an explosion of fermentation processes in the tissue, leading to putrefaction [22]. Similarly, when strawberries are processed for 3 hours at 3°C with % CO₂, then packaged in MAP film, stored at 1°C for a day, transported at 1°C for 10 days, and lastly distributed at 4°C for 3 days [23]. When paired with MAP, CO₂ treatment preserved the quality of fruit (strawberry) by lowering weight loss, tissue softening index, as well as duration.

Polypropylene with different perforation sizes is used as a packaging material in modified atmosphere packaging and develop a gas combination with proportions that are like those employed in MAP [24]. Strawberries were stored at 2°C in polypropylene packets with various holes [25]. This perforated packing was suggested because there was minimal loss of marketable fruits, no symptoms of Botrytis-related decay, and a little fall in sugar content. The use of carbon dioxide has an influence on the spread of bacteria like Botrytis cinerea, which causes strawberry quality to deteriorate. According to the studies, using CO₂ concentrations of 5%–10% helps to limit Botrytis multiplication while preserving a uniform and appealing colour for the consumer [26, 27].

Before using strawberries in modified atmosphere packaging, they were treated with various gases and coated, and the overall impact of MAP was found to be increased. In comparison to simply MAP, which increased shelf life by 4–6 days, MAP (2.5% O₂ and 15% CO₂) coupled with an edible film coating and ozone treatments prolonged life span up to 8–10 days. The handling of ethylene presence in MAP is the most important technique to for managing the ripening process in fruits and vegetables. As in case of the strawberry, some research has been done in this approach, with the goal of clarifying the molecular pathways accountable for the tissue’s response to this gas [28]. In terms of changed atmospheres, packages have been devised that directly regulate the quantities of various gases throughout the shipping and storage of the product, extending the useful life of strawberries by around 10 days compared to ordinary packages [29, 30].

Many studies show that the application of 1-methylcyclopropene in strawberry during MAP lower the senescence rate, with beneficial benefits without impairing quality at doses ranging from 0.5 to 5 μL⁻¹, while the effects of deterioration intensified at larger doses.

2.4 Controlled atmosphere storage

A continuously controlled gas environment is referred to as controlled atmospheric storage (CA). A controlled situation is an agrarian store system, manages the percentages of O₂, CO₂, and N, as well as the humidity and temperature of the storage room. CA suppresses some taste development while slowing ripeness and maintaining firmness. Fruit respiration can be minimised by lowering the oxygen concentration and fruit viability can be maintained by reducing the oxygen in an enclosed storage area. The CO₂ content is usually permitted to increase as well, which helps to maintain quality. Fruit emit carbon dioxide during respiration, which piles up in an enclosed environment and slows ripening. Several research has concluded that CO₂ levels of 15%–20% and O₂ concentrations of 5%–10% are the acceptable atmospheric composition for effective strawberry storage [31].

Castellanos et al. [32] found that investigating the impact of respiratory gases on fruit physiology is critical for developing optimal packaging to improve post-harvest shelf life. Alamar et al. [33] investigated the CA effect at the early and middle stages of strawberries. The results showed that applying CA for 2.5 days midway through storage at 5°C (2.5 days; 15 kPa CO₂ + 5 kPa O₂ after 2 days in the air) extended life span by 3 days (depending on the prevalence of disease). CA also inhibited inner ethylene synthesis, resulting in fruit that was lighter, vibrant, as well as firmer, implying a lessening in ripening.

Almenar et al. [19] experimented by storing the wild strawberry for 3 weeks at 3°C in different atmospheric conditions. The study claimed that the combination of 10% CO₂ and 11% O₂ can efficiently enhance the fruit shelf life by keeping quality criteria within a reasonable range and preventing the spread of Botrytis cinerea, without affecting consumer approval greatly.

Strawberry fruits maintained in CA storage retain their freshness too long than those kept in the refrigerator, and decaying loss is minimised in storage having high CO₂ concentration. Strawberries held in a controlled atmosphere of 12% CO₂ and 2% O₂ had higher fruit texture, total soluble solids, titratable acidity, and ascorbic acid concentration than strawberries stored in the open air [34]. This research also finds that the CA retain the maximum level of volatile compounds like esters and furanone during storing strawberry. Total terpenes, total alcohols, total acids, and cold stress resistance were all higher in CA-stored strawberries in comparison to air-stored strawberries.

The strawberry when stored in CA and MAP with high CO₂ content increases the quality attributes and decreases the incidence of microbes. Nakata and Izumi [35] experimented by storing strawberries at high concentrations of CO₂ (20%, 30% and 40%) for 10 days at 5°C, using CA and active MAP. The CA of 20%–40% CO₂ was efficient in limiting the exterior production of mould mycelia and inhibiting the increase in the fungus population. However, because of CO₂ injury, a CA of >30% CO₂ caused black staining over the berry skin. Strawberry fruit when placed in a MAP had consistent fungal levels throughout the days of storage. External development of mould mycelia characterised as Botrytis cinerea and surface black staining were produced in strawberry fruit in MAP flushed with 30% and 40% CO₂ after transfer to ambient conditions for 6 days at 10 8C.

2.5 Losses due to mechanical injury

Mechanical damage is a sort of stress that happens throughout the harvesting and manipulation of fruits after they have been harvested. Physiological and morphological changes accompany this stress, affecting the fruit quality. Soft fruits, such as strawberries, are especially subject to severe harm during and after harvesting due to their thin epidermis. Strawberry fruits may be crushed, impacted, punctured, or damaged during postharvest handling, resulting in a shortened shelf life and deterioration. Strawberry fruits soften quickly after harvest at the ripening stage due to pectin solubilisation and hemicellulose and cellulose hydrolysis, which causes the central lamella to degrade [36].

The most prevalent sort of mechanical injury that occurs during harvesting, handling, and transportation is bruising [37, 38]. Bruise damage occurs when an excessive amount of external force is applied to the fruit surface during interaction with a solid body or fruit versus other fruit [39, 40]. The most unfavourable damage is bruising, which serves as a portal for infections, particularly fungus [41].

Due to the strawberry’s great vulnerability to damage during the picking stage, trained people and adequate equipment are required. In addition, daily inspection of the harvested product quality and improvement of the situation can help to reduce harvest losses. Overfilling of boxes must be avoided, and the number of layers within boxes must be kept as low as feasible, to minimise package losses during handling. The use of paperboards or plastic boards between the fruit layers is useful since it prevents the fruits from moving around and thereby reduces fruit damage. It appears that good packing and regular handling methods are the most important factors in ensuring the safe delivery of a product to a market.

2.6 Edible coatings

Very fragile fruits, such as berries and tropical fruits, are good candidates for coating treatment since they are costly and have a short storability. A thin layer of edible material, often not exceeding 0.3 mm, placed to the surface of meals in addition to or as a substitute for natural coating materials is classified as an edible coating. The use of an active edible covering to enhance the longevity of fruits and vegetables is a unique and potential method [42]. Edible coverings with semipermeable film can improve post-harvest fruit life by minimising moisture, respiration, gas exchange, as well as oxidative reaction rates [43].

Li et al. [44], uses three edible coatings i.e., alginate, chitosan (CS), and pullulan (polysaccharide) during cold storage (4°C) to postharvest strawberry fruit. The experiment concluded that during 16 days of storage, polysaccharide coatings severely hampered fruit weakening and rot, as well as minimised modifications in TSS and titratable acidity content. These coatings also kept ascorbic acid and total phenolic content greater than controls from day 2 onwards, and dramatically reduced fruit deterioration and respiration after 12 days of storage. The enzymatic activities like peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) were increased by polysaccharide coatings, preventing lipid peroxidation and reducing membrane damage. Furthermore, among these coatings, CS-based coatings had the most beneficial impacts on the quality of fruit and had the highest relative antioxidant enzyme activity.

Aloe vera gel is more effective than CS. Nasrin et al. [45], performed an experiment by coating the strawberry with CS and aloe vera gel, keep in a polypropylene box and stored at 6°C ± 1°C with 50 ± 5% relative humidity. A. vera gel-coated strawberry retained their colour, wetness, firmness, fresh appearance, and general acceptability for longer than CS or uncoated ones. Furthermore, AV gel coating on strawberries slowed the emergence of microbe occurrence for approximately 15 days. While the moulds impacted control and CS (1.5% or 2%) coated strawberries on days 6 and 9 of storage, respectively.

In the sector of the food industry, the use of a CS-based antimicrobial coating to prolong the shelf life of strawberries throughout storage appears to be quite promising. Chitosan-monomethyl fumaric acid (CS-MFA) is an excellent antimicrobial coating derived from CS and its derivatives. Khan et al. [46] applied CS-MFA coating on strawberries and stored it at 10°C. The total weight loss and deterioration were considerably lower in the CS-MFA samples than in the CS and control samples. When compared to CS, CS-MFA coated fruit had a significantly lower yeast and mould load. Finally, the CS-MFA enhanced microbial properties and extended shelf life from 4 to 8 days.

The edible coating, which contains natural bioactive chemicals, could be used as a substitute for artificial additives and can help save money on cold storage. The orange peel essential peel (OPEP) and carnauba wax have been proven to decrease the damages in strawberries. Saeed et al. [47] designed an experiment to make an edible antifungal covering with different concentrations of OPEO and carnauba wax to protect strawberries against blue mould (fungus). Orange peel oil had a maximum growth constraint of 96% against fungus. Strawberry storage life was increased owing to an OPEP coating that preserved the fruit’s quality.

When strawberry was treated with polysaccharide edible coating (alginate and pectin) containing citral and eugenol showed that the fruit have higher firmness, TSS, as well as enzymatic activity, while having lesser weight loss and microbiological deterioration [4].

Surface colour parameters were significantly affected by the cellulose coating. The impact of a methylcellulose edible covering on the qualitative, chemical, physical, and mechanical attributes of strawberries was studied. Nadim et al. [48] used methylcellulose on the surface of the berry and stored it for 11 days at 4°C. The edible coating inhibits weight loss and decay while also retaining a tiny quantity of fruit sugar, preserving the firmness of the strawberries and enhancing their quality and storage characteristics.

2.7 Treatment with chemicals

Strawberry is counted in the list of fruits that are perishable and is especially prone to postharvest losses (up to 50%) owing to fungal disease outbreaks. For many years’ different chemicals have been used to extend the durability of strawberries. However due to health issues now their uses are restricted. Liu et al. [49] treated the strawberry with different concentrations of melatonin for 5 min and stored it at 4°C with a relative humidity of 90% for 12 days. The results concluded that 1 mmol L⁻¹ melatonin treatment delayed the ripening of berries, extend the shelf life, improve the fruit quality and minimised the concentration of hydrogen peroxide and malondialdehyde However, the total phenolics and flavonoid levels were enhanced, leading to increased antioxidant potential. These results suggest that melatonin administration could be a viable tactic for extending strawberry fruit postharvest life and improving quality.

2.8 Combined treatments

When two or more post-harvest treatments are used together, they show a synergistic impact on the product’s standard and usable viability. Feliziani et al. [50] compares the effect of CS, laminarin, extracts of Abies spp., Polygonum spp., and Saccharomyces spp., organic acids and calcium combination, and benzothiadiazole with fungicides. These chemicals were applied to the strawberry canopy every 5 days. In comparison to water-treated controls, alternative chemical treatments reduced strawberry postharvest loss by 30%, primarily against grey mould and Rhizopus rot instead of altering the colour or firmness of the fruit.

2.9 Physical treatment

The physical treatment includes ultraviolet radiations with a focus on UV-C radiations. UV-C irradiation aids in the prevention of fruit degradation and the postponement of ripening. This sort of radiation (UV-C) is used for not only reducing fungal deterioration but also increasing fruit phytochemical content after harvesting. Several research on the application of UV-C radiation has shown that it can reduce the biological load of the fruit without compromising sensory qualities like colour, firmness, texture, and humidity, among others [51, 52, 53, 54].

However, the health risks of using pesticides on food after harvest has required research into non-chemical postharvest treatments. Non-chemical treatments such as gaseous ozone and UV-C irradiation have looked promising in the processing and preservation of certain fruits and vegetables. Gumede et al. [55] investigated the effect of ozone (gaseous form) and UV-C radiations in extending the shelf life and preserving the quality of strawberries. When compared with control treatments, fruit exposure to UV-C and continuous ozone exhibited a considerably lower deterioration rate. Furthermore, fruit mass loss was substantially reduced in ozonated atmospheres as compared to UV-C and control treatment. Fruit treated with ozone and UV-C had significantly greater antioxidant capacity. Gaseous ozone and UV-C irradiation have been demonstrated to be effective non-chemical postharvest treatments for strawberries in this study.

In several species, notably strawberry, UV-C radiation is effective in preventing disease development. UV-C radiation appears to be helpful not just because of its disinfectant properties, but also because it may boost plant defence mechanisms. Forges et al. [56] studied the effect of UV-C radiation administrated during cultivation. The UV-C-treated plants flowered earlier than the non-treated ones. Despite a modest reduction in leaf area, treated plants produced a greater amount of fruit at harvest. In reaction to UV, spontaneous infection of leaves with powdery mildew and fruit with Rhizopus was significantly reduced.

3. Conclusion

Strawberry is a non-climacteric fruit whose fruit develops and matures through a succession of physiological and molecular resulting in significant changes in fruit size, colour, texture, flavour, and fragrance and there seem to be a variety of postharvest losses after harvesting. To minimise postharvest losses various techniques, must employ to preserve the fruit quality, firmness as well as extend the shelf life. Each approach has benefits and drawbacks, and the use of one or more of these post-harvest procedures will be determined by the growing region’s economic, technological, and social considerations. Farmers could reduce the decline in fruit quality as well as keep the freshness for longer by using proper postharvest methods.