**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 precooling 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:


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.
