Juhi Ranjan
PhD Research Scholar, ICAR-IARI, New Delhi

Vegetables and fruits are an important part of the human diet because they are high in minerals, vitamins, micronutrients, fiber, diverse flavors, and taste, and they provide not only food security but also nutritional security. It provides essential vitamins, minerals, phytochemical compounds, dietary fibre and other nutrients such as antioxidants, flavonoids,making them beneficial to human health. India is known as the "basket of fruits and vegetables" as it is the world's largest fruits producer and the world's second largest vegetables producer.Horticulture production is expected to reach 326.58 million tonnes in 2020-21, representing a 5.81 million tonne (1.81%) increase over 2019-20. Horticulture production increased by approximately 49.86% from 2007-08 to 2019-20. Fruit production is expected to be 103.23 million tonnes, up from 102.03 million tonnes in 2019-20. Vegetable production is expected to be 197.61 million tonnes, up from 188.91 million tonnes in 2019-20 (Anonymous, 2021). In fact, vegetables account for approximately 59.2% of horticulture production in India, while they account for nearly 14% of global horticulture. In India, nearly 76% of vegetables are consumed fresh, while only 2% are processed (Anonymous, 2017).

Fruits and vegetables have a short shelf life. Due to the highly perishable nature of fruits and vegetables, total losses range between 20 and 30% (Rajapaksha et al., 2021). Horticultural produce waste is a major concern for the nation's economy. Every year, approximately one-third of the world's food produce (1.4 billion tons) fit for human consumption is wasted. Annually, an estimated $1 trillion is lost due to post-harvest operations and treatments. In fact, the amount of perishable food lost, particularly fruits and vegetables, has been alarming. These perishables are easily damaged and have a very short shelf life, especially in the hot weather that prevails in most of the country.

Massive post-harvest losses of fruits and vegetables are also a major concern for India's agricultural sector. Massive post-harvest losses occur due to a lack of adequate and efficient cold chain infrastructure. It is estimated to cost INR 92,561 crore (US$12.1 billion) per year, and many existing resources are inefficiently allocated (NITI Aayog, 2018). According to ICAR-CIPHET, Ludhiana, approximately 16% of the country's fruit and vegetables, worth an estimated INR 133 billion, are wasted each year due to a lack of cold storage facilities. Fruit and vegetables suffer the highest post-harvest losses than any food product in India, owing primarily to insufficient cold storage and inefficient handling.

Importance of good storage facilities
Proper storage facilities help to reduce post-harvest losses by extending the shelf life of fruits and vegetables. Proper storage entails controlling abiotic factors such as keeping the storage area at a low temperature and high relative humidity, which drastically reduces the rate of decay of agricultural commodities during storage. Temperature and relative humidity are the two most important abiotic factors influencing vegetable longevity (Liberty et al., 2013). Contaminations can begin during harvest and continue until the product is consumed. At higher temperatures, the rate of respiration increases, resulting in moisture loss and weight loss of vegetables, as well as a loss of quality and nutritive value. According to Liberty et al. (2014), every 10°C increase in temperature causes a 2-3 times increase in the rate of deterioration.

According to ASHRAE (1997), the best storage temperature for vegetables of tropical and subtropical origin is between 5-10°C. Even after harvest, vital tissue activities such as respiration and ripening continue. The horticulture commodity's high moisture content accelerates these reaction rates, making it highly perishable. When compared to those exposed to ambient high temperature and low humidity conditions, storage structures with low temperature and high humidity maintain the quality of fruits and vegetables by reducing the reaction rate of tissues. As a result, to obtain high-quality produce, proper temperature and humidity should be maintained beginning with harvest. As a result, proper storage is critical in maintaining the quality of fresh produce.

Different types of storage structures
There are several storage structures which helps in increasing shelf life of fruits and vegetables. Below are some of the major structures:

Cold storage facilities
Cold storage is a widely adopted method for preserving fruits and vegetables in India. These facilities are equipped with temperature and humidity control systems, allowing produce to be stored at specific conditions that inhibit microbial growth and slow down the ripening process. Cold storage helps to extend the shelf life of perishable commodities, prevent quality deterioration, and maintain freshness. Farmers and traders can store large quantities of fruits and vegetables, ensuring a consistent supply throughout the year and reducing post-harvest losses.

1. Evaporative cooling storage
Evaporative cooling is a process that reduces the temperature of a substance by using the cooling effect of water evaporation. When water evaporates, it converts sensible heat to latent heat, which results in a decrease in ambient temperature and provides effective cooling. This cooling effect can be applied on many different scales, ranging from small-scale space cooling to large-scale industrial applications. Unlike typical air conditioning and refrigeration systems, evaporative cooling can deliver adequate cooling without the need for an external energy source. Simply wetting a surface and allowing the water to evaporate can offer excellent cooling. In humans, this effect is most visible when the body is cooled by sweat evaporation from the skin during physical exercise.

It is the foundation for more elaborate and automated evaporative cooling systems. This process works by evaporating water from the surface of a structure to cool it down. The cooling of this device also results in a high relative humidity of the air in the cooling chamber, where evaporation occurs in comparison to ambient air. This makes the environment in the chamber more favourable to the preservation of fruits and vegetables. When dry air travels over a wet surface, evaporative cooling occurs. The higher the evaporation rate, the greater the cooling effect. The effectiveness of an evaporative cooler is affected by the humidity of the surrounding air. Dry air cools faster because it can absorb more moisture. In the extreme scenario of totally saturated air, there is no evaporation and no cooling. A basic evaporative cooling structure is comprised of a porous substance that is filled with water. Hot, dry air is sprayed on the material. Water evaporates into the atmosphere, increasing humidity while lowering temperature.It has many advantages over refrigeration systems because it does not use refrigerant and thus is environmentally friendly (reduces CO2). It makes no noise because there is no moving part. It does not require electricity, thus saving energy. It does not necessitate a large initial investment, and the operational costs are minimal. Because of its simple design, it can be quickly and easily installed. Its maintenance is simple. It can be built in remote areas using locally available materials and, most importantly, it is eco-friendly because it does not require chlorofluorocarbons (Banyat and Bunjerd, 2013).

2. Zero energy cool chambers
In rural areas with limited access to electricity, zero energy cool chambers offer an innovative solution for post-harvest storage. These chambers are designed to utilize natural cooling mechanisms, such as evaporative cooling or underground insulation, to maintain low temperatures. Zero energy cool chambers (ZECCs) are cost-effective and environmentally friendly, providing a viable storage option for small-scale farmers and local communities. Evaporative cooling is a process that lowers the temperature and increases the humidity of the air by passing it through a saturated surface. This process is based on the principle of adiabatic exchange of heat. This is beneficial for extending the storage life of fruits and vegetables (Das and Chandra 2001). Small capacity, low cost, on-farm scientific storage structures based on this principle, such as ZECC (Roy and Pal, 1989), have a greater opportunity for adoption in rural areas where there is a severe energy shortage. Horticultural products should be stored in a cool place.

Horticultural produce stored in a cold chamber showed reduced physiological weight loss, optimal colour, improved firmness, and a shelf life of 1-2 weeks. Cool chambers are useful for maintaining fruit acceptability and reducing weight loss during storage (Bhatnagar et al., 1990). Many studies have found that fruits and vegetables lose less weight when exposed to evaporative coolers than when exposed to room temperature. Sandooja et al. (1987) observed the least decline in quality measures such as TSS, acidity, and ascorbic acid concentration when tomatoes were stored in a ZECC. The basic concept is a storage pot inside a bigger water-holding pot. The inner pot contains food that has been kept chilled. A storage pot is placed in a pottery bowl filled with water. Then, the pot is covered with a moist towel dipped in the water reservoir. The water absorbed by the cloth evaporates, keeping the storage pot cold. The bowl is also set on damp sand to prevent the pot from touching the ground.

3. Farm sun fridge
The Farm Sun Fridge (FSF) is a cold storage facility that uses a integrate solar refrigeration and evaporative cooling techniques to store harvested farm products. It is an innovative, off-grid, battery-free facility, constructed using locally available materials, provides small holder farmers with low-cost cold storage, even without using electricity. FSF uses wetted fabric over iron mesh walls for passive, evaporative cooling, autoclaved aerated concrete blocks and styrofoam panels for insulation, a solar-powered mini split inverter air-conditioning unit for refrigeration, water-based thermal storage instead of batteries for night time cooling, and a novel solar sensor that better balances refrigeration demand with available solar energy.Farmers can construct the evaporative cooling chamber with locally available materials in the first stage, which provides modest cooling. Solar refrigeration is installed in the second stage with minimal additional investment and no major structural modifications. Figure 2 depicts the FSF built at Pusa Fair Ground, IARI Delhi. The PusaFSF is able to maintain an inside temperature of 3-4°C during the day and 8-10°C during the night with high relative humidity around 85-100%.

4. Controlled atmosphere storage
Controlled Atmospheric (CA) storage is a method of preserving fruits and vegetables by manipulating the atmospheric composition surrounding them. The primary factors regulated during CA storage are temperature, humidity, oxygen, carbon dioxide, and ethylene levels. These parameters are adjusted to create an optimal environment that slows down the aging process, retards microbial growth, and minimizes physiological changes in the stored produce.

The journey from farm to table often involves several stages, and one critical aspect of this process is the storage of fruits and vegetables. CA storage is a modern technique that helps preserve the freshness, nutritional value, and overall quality of perishable produce. By carefully managing the composition of gases within storage environments, CA storage offers extended shelf life, reduced spoilage, and improved marketability for a wide range of fruits and vegetables. CAstorage is gaining popularity in India, especially for apples, pomegranates, and other sensitive fruits. CA storage involves modifying the composition of the storage environment by controlling oxygen, carbon dioxide, and ethylene levels. This technique helps to delay the ripening process and maintain the quality and freshness of fruits and vegetables.

5. Modified atmospheric storage
In the quest to maintain the freshness and quality of fruits and vegetables, modified atmospheric storage (MAS) has emerged as an effective technique. By manipulating the composition of gases surrounding perishable produce, MAS creates an optimized storage environment that extends shelf life, reduces spoilage, and enhances overall product quality. MAS involves adjusting the atmospheric composition within storage facilities to slow down the natural aging process and maintain the quality of fruits and vegetables. The primary gases controlled in MAS are oxygen (O2), carbon dioxide (CO2), and sometimes nitrogen (N2). The specific gas ratios and levels are determined by the respiratory behaviour of the stored produce and their individual sensitivity to different gas compositions. Several benefits of MAS incudes extended shelf life, delayed senescence, preservation of nutritional quality and reduction in post-harvest losses.

Post-harvest storage structures are critical in India for reducing losses and ensuring the availability of high-quality fruits and vegetables. The use of advanced storage technologies and practices, such as controlled atmosphere storage, refrigeration, and modified atmosphere packaging, can increase the shelf life of produce while preserving its nutritional value. These technologies can help farmers access better market opportunities and higher returns by significantly reducing spoilage and maintaining product quality. By addressing the challenges in this area, India can increase farmers' incomes and contribute to the overall development of the agricultural sector.


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