A review about water loss as postharvest quality marker in apple

Apple fruit can be stored for long periods of time, especially with the use of controlled atmosphere storage, but like many fruits and vegetables are susceptible to water loss.

Water loss can result in compromised appearance such as skin shriveling, as well as loss of firmness, and reduced saleable weight, which in turn affect the income of growers and other industry stakeholders.

Preharvest factors that can influence water loss in apples during the postharvest period include climate, cultivar, fruit size, tree age, orchard practices, and harvest maturity.

Postharvest factors such as the storage temperature, relative humidity, storage type, and duration can also affect water loss in apple fruit during storage.

The mechanisms of cuticle biosynthesis in water permeance, the role of stomata and lenticels, microcracking, crosstalk with mechanical injuries, storage disorders, and decay incidence during the storage of apples are reviewed.

Additionally, the review summarizes: preharvest and postharvest factors influencing water loss; recent management strategies including pre-cooling, cold storage, controlled atmospheres, packaging, and anti-senescence chemicals; the use of edible coatings, as well as other non-chemical approaches for modulating water loss and maintaining storage quality.

The review also provides direction for the industry to manage this destructive problem in the postharvest supply chain of apple fruit.

Introduction

Apple (Malus × domestica Borkh.) belongs to the Rosaceae family and is known as a pome fruit composed of two to five carpels covered with crunchy flesh.

 It is one of the leading fruit crops grown in more than 63 countries with diverse climatic zones including temperate and subtropical regions of the world; however, commercial production comes under 25° to 52° latitude limits (Musacchi & Serra, 2018). According to FAOSTAT (2020), it is grown on 6.5 million hectares of land with global production of 126 million tonnes. In total worldwide production, China is the leading producer of apples with 81.0 million tonnes of production followed by the United States of America (USA), Turkey, Poland, India, and Italy, Iran, and Russia.

It is one of the major fruit crops grown all over the world, and very popular among consumers due to their pleasant taste, attractive colour, unique aroma, crispness, and promising nutritional profile.

A promising nutritional profile

Apples are consumed fresh due to a wide array of health-promoting compounds such as polyphenols, flavonoids, and enzymatic and non-enzymatic antioxidants that provides aid against chronic diseases in humans (Oyenihi et al., 2022; Watkins & Liu, 2011). 

In addition, apple fruit also contains a variety of macronutrients including sugars (glucose, fructose, sucrose, and sorbitol), protein, fat, and, vitamins such as B6, C, and E; organic acids (malic acid, fumaric acid, succinic acid, citric acid, and tartaric acid); minerals (nitrogen, potassium, calcium, magnesium), fibre, and trace elements (copper, iron, manganese, zinc) which help in boosting the immune system of the human body (Skinner et al., 2018).

The bioactive compounds in fresh apple fruit reported significant pharmacological effects for curing different chronic diseases (Oyenihi et al., 2022).

The apple fruit contained higher polyphenol antioxidants representing up to 25% of total polyphenols from fruit intake on a daily basis diet in the USA (Musacchi & Serra, 2018). Further, apple fruits have a wide range of individual phenolic acids such as quercetins, phloretin, epi-catechin, procyanidins, and chlorogenic acids, which vary with maturity stage, cultivar, agroclimatic conditions, and postharvest storage conditions and period (Pissard et al., 2013; Tokala et al., 2022).

Long storage potential

Apples, depending on cultivar, can be stored for long time periods in air or under controlled atmosphere (CA) conditions, and shipped worldwide from temperate production zones. A large number of cultivars are grown, specific ones often associated with a given production region. Storage periods employed by the growing region are a function of cultivar and availability of storage technology.

While apple fruits exhibit climacteric peaks of ethylene and respiration during their ripening period, they show great storage potential when compared to other climacteric fruits.

Nevertheless, this temperate fruit experiences varied recurrent postharvest quality issues, including water loss and susceptibility to physiological disorders and pathogenic diseases, as well as mechanical and storage injuries that could be due to different pre- and postharvest factors, resulting in lower storage life and earlier senescence (Singh et al., 2022).

Control of the water loss, key to mantain the quality

Therefore, the apple industry is very keen to address postharvest handling issues, particularly towards reducing water loss and maintaining the quality of the fruit when stored for long-term periods.

Water loss, also known as weight loss, or moisture loss, has been regarded as a quality indicator during the postharvest period (Lufu et al., 2020).

 Apple fruit depending on the cultivar, is prone to water loss, considered one of the major constraints in long-term storage, which in turn reduces saleable weight, downgrades overall quality, limits their storability, and consequently lowers grower income (Singh et al., 2022).

Substantial water loss in apple fruit results in higher skin shriveling, changes in wax composition, and enhanced fruit softening, as well as deteriorated cosmetic and eating quality during the postharvest period (Atkinson et al., 2012; Harker et al., 2019; Veraverbeke et al., 2001, 2003b) (Fig. 1).

Studies have reported that fresh fruit and vegetables become unmarketable when they lose 5 to 10% of water content, which ends up in quality loss that includes wilting or skin shriveling during storage (Ben-Yehoshua & Rodov, 2002).

Water loss in the postharvest phase depends on several factors related to production, harvest, postharvest handling, storage, and marketing (Lufu et al., 2020).

Index of the open access paper

Morphology and Physiology of Apple Fruits that Affect Water Loss

• Cuticle Biosynthesis and Water Permeance
• Stomata and Lenticels
• Microcracking in Apple

Preharvest Factors Affecting Water Loss and Fruit Quality

• Maturity Stage
• Cultivar
• Fruit Size
• Tree Age
• Orchard Practices

Postharvest Factors Affecting Water Loss and Fruit Quality

• Temperature
• Relative Humidity
• Storage Type

Crosstalk with Water Loss and Fruit Quality

• Mechanical Injuries
• Storage Disorders
• Microbial Decay

Postharvest Water Loss and Quality Management

• Pre-Cooling
• Cold Storage
• Intermittent Warming
• Controlled Atmospheres
• CA Storage
• DCA Storage
• Packaging
• Edible Coatings

Chemical Treatments

• 1-Methylcyclopropene (1-MCP)
• 1H-Cyclopropabenzene and 1H-cyclopropa[b]naphthalene
• Nitric Oxide (NO)
• Salicylic Acid (SA)
• Calcium Chloride (CaCl2)
• Melatonin (MT)

Non-chemical Treatments

• Heat Treatments
• Irradiation
• Ozone
• Molecular Aspects

Conclusion and Prospects

Based on a review of the literature, water loss has been established as a complex quality marker associated with different metabolic responses and is greatly influenced by multiple preharvest and postharvest factors during the value chain, from farmgate to consumption.

Cultiva characteristics

As discussed in detail, a waxy layer of polymeric cutin plays an important role in retaining water content, providing protection against environmental stresses, injuries, and cracking during storage in apple fruit.

However, susceptibility to water loss varies with cultivar. Apple fruit containing many lenticels with variable size, colour, and positioning on fruit skin expressively contributed to water loss and quality during storage.

Similarly, microcracking on apple fruit surface also contributed to earlier or delayed desiccation along progression during the postharvest period.

Influence of pre and postharvest factors

Preharvest factors including climate change, cultivar, maturity stage, fruit size, tree age, nutritional schedule, and irrigation aid in reducing water loss in apple fruit.

The postharvest variables that include temperature, RH, humidification system, and storage type depicted significant changes in postharvest water loss and fruit quality.

Tools to reduce water loss and aspects to be further investigated

Postharvest implications of packaging and cold storage coupled with CA, ULO, DCA, pre-storage 1-MCP application, and edible coatings could be the possible solution in reducing water loss, though the response to technology might be not suitable for different cultivars at commercial scale.

This review article provides the information with a multiscale approach for reducing water loss along the postharvest value chain.

Future apple breeding programmes should focus on modulation of wax composition in fruit peel, as evidence suggests that this might help in lessening water loss during the postharvest period.

The preharvest application of plant growth regulators and other factors may also be beneficial in reducing water loss during storage, but is yet to be investigated in detail, while the traditional humidification systems used usually produce water droplets in storage rooms which may substantially increase skin moisture and microcracking provides a favourable condition for higher water loss and intrusion of fungal pathogens consequently results in accelerated decay.

Improved humidification systems?

This humidification system in storage may be modified to overcome these constraints. DCA-CF technology could be a better alternative for CA storage for reducing water loss and maintaining higher internal quality attributes by alleviating physiological changes during storage.

Picture is Fig. 1 of the paper - The signs of water loss expressed as shriveling in ‘Cripps Pink’ apple during the postharvest period

Source

Water Loss: A Postharvest Quality Marker in Apple Storage
Mahmood Ul Hasan, Zora Singh, Hafiz Muhammad Shoaib Shah, Jashanpreet Kaur & Andrew Woodward 
Food and Bioprocess Technology, Volume 17, pages 2155–2180, (2024)
https://link.springer.com/article/10.1007/s11947-023-03305-9?fromPaywallRec=true