**2. Green and novel postharvest treatments and traditional postharvest techniques**

Novel postharvest treatments are postharvest treatments other than conventional or already known postharvest treatments whereas green postharvest treatments are those that are environmentally friendly and socially acceptable [6, 12].

Some of the latest novel postharvest treatments include the application of nitric oxide, ozone, salicylic acid, oxalic acid, methyl jasmonates, calcium, and heat [6]. Notwithstanding, various compounds, including AVG (Aminoethoxyvinylglycine), 1MCP (1-Methylcyclopropene), and PAs (Polyamines) and other postharvest treatments have been previously used to regulate postharvest quality in some FFVs at different degrees of effectiveness. The aforementioned chemicals had limitations, such as uneven ripening, post-ripening disorders, and non-viability for commercial use. Conventional postharvest harvest techniques that are used to prolong the shelf life of fruits and vegetables include cold storage, modified and controlled atmosphere storage, suppression of ethylene biosynthesis or ethylene inaction by PAs, AVG, and 1-MCP application [6].

Green and novel postharvest treatments extend the shelf life of freshly harvested produce by maintaining their quality [6]. We focused on the latest applications of

*Alternative Green and Novel Postharvest Treatments for Minimally Processed Fruits… DOI: http://dx.doi.org/10.5772/intechopen.111978*

nitric oxide, ozone, methyl jasmonate, salicylic acid, oxalic acid, calcium, and heat treatments on FFVs, with emphasis on quality and shelf life under storage. The seven were chosen because of their extensive use on FFVs [6, 8].

#### **2.1 Nitric oxide (NO)**

Nitric oxide (NO) is an important signalling molecule mediating several pre- and postharvest developmental and physiological activities in horticultural crops [6, 14].

NO is a bioactive, mobile gaseous molecule that also mediates various abiotic and biotic stress responses [15]. NO can protect against various stressful impacts, scavenge free oxygen radicals, counteract oxidative damage, inhibit, or suppress ethylene biosynthesis, delay ripening and senescence, and enhance the resistance to diseases [6, 14–17]. NO has a more profound effect on non-climacteric horticultural crops (especially fruits) than climacteric crops. Consequently, the climacteric phase (i.e., the surge in ethylene production and an increased respiration rate) of many horticultural crops can be impeded by endogenous NO production. Also, endogenous NO reduces yellowing, chlorophyll degradation and extends the shelf life of fruits and vegetables [6]. Notwithstanding, NO is volatile and exhibits reactive oxygen species toxicity. Hence, super-optimal concentrations can be harmful. Thus, it is necessary that the correct threshold levels are employed to obtain the desirable ripening modulation and extension of shelf life in FFVs [6]. It is worth noting that NO is more effective in its gaseous or donor form in suppressing ethylene production and respiration rate, reducing softness, retarding colour development and metabolism, reducing chlorophyll degradation, and delaying senescence [6].

#### *2.1.1 NO treatments of fresh fruits and vegetables*

NO is a good alternative for extending the shelf life of fresh horticultural produce. The application of optimum levels of NO has been shown to impede senescence and ripening processes in many horticultural crops, including FFVs. Donor compounds (e.g., sodium nitroprusside (SNP)) can also be incorporated into biological systems to release NO gas under controlled environmental conditions [6]. Due to the highly diffusible nature of NO, NO was earlier considered an environmental pollutant as it caused, among other things the reduction of ozone in the stratosphere [6, 14]. Also, the emission of NO is related to the greenhouse effect [6, 14, 18]. Moreover, NO gas has a short lifetime, such that in the presence of oxygen (O2), it can be converted to the noxious gas nitrogen dioxide (NO2), which can degrade the quality of FFVs. Consequently, NO gas should be placed in airtight containers to minimize contact with oxygen. Further, NO must be diluted by flushing with nitrogen (N2) after fumigation to avoid damage to FFVs [17].

Postharvest immersion of FFVs such as plum, longan, apple, and broccoli in NO or SNP impeded internal browning. Also, exogenous application of NO via fumigation (In an O2-free environment or NO-releasing agents such as "N-tertbutyl-α-phenylnitrone" and "3-morpholino sydnonimine") remarkedly delayed maturation and ripening, controlled postharvest pest and prolonged the shelf life of FFVs such as apples, bananas, peaches, strawberries, and some other vegetables [6, 16]. Additionally, NO maintained the levels of polyphenols, soluble solids ascorbic acid in sliced apples, longan, fresh-cut apples, litchi, peach, lettuce, and broccoli and generally improved the quality and postharvest shelf life of some stored fruits and vegetables [6, 17, 19].

A significant reduction of chlorophyll degradation, delayed postharvest yellowing, accumulation of malondialdehyde, and reduced lipid peroxidation were observed in broccoli florets [6]. Treatment of cucumber with 25 microlitres per litre NO also reduced deterioration and exhibited radical scavenging activities compared to the control during storage. Furthermore, NO significantly increased the antioxidative process in cucumber fruits. Browning on the cut surfaces of leafy vegetables was effectively inhibited by NO treatments [6]. **Tables 1** and **2** present treatments of some fruits and vegetables with NO or NO donors, respectively.

#### **2.2 Ozone treatments**

Ozone is a highly reactive form of oxygen that decomposes easily into diatomic oxygen. Ozone can function as a potential oxidant and disinfectant when it reacts with targeted organic matter and microorganisms. Historically, it has been used as a water disinfectant. Ozone attained "GRAS" (generally regarded as safe) status and was approved as an antimicrobial additive by the United States Food and Drug Administration (FDA) in 2001 [1, 6, 21].

The influence of ozone on postharvest disease control and storage has been investigated in some fruits and vegetables for shelf life extension and preservation [1, 6, 13, 21–26]. Ozonated water/aqueous ozone has been used for disinfecting vegetables, while gaseous ozone is used for the sanitization and preservation of vegetables during storage. Gaseous ozone is a less effective antimicrobial agent than aqueous ozone [1, 21]. Moreover, ozone can be potentially used for the decontamination of surfaces of freshly harvested produce, degradation of ethylene, odour elimination in mixed storage, spore elimination in storage rooms, and reduction of pesticide levels over the fresh produce [1, 6, 13, 21, 25, 26]. Nevertheless, ozone should be properly used to avoid negative effects such as loss of sensory quality although ozone application is an eco-friendly technology [1, 21]. Consequently, ozone treatments are mostly specific for various fresh produce due to the intrinsic characteristics of fresh produce and the extrinsic factors that affect ozone efficiency [1, 21]. **Table 3** provides information on the ozone treatment of some fresh fruits and vegetables.

### **2.3 Salicylic acid treatments**

Salicylic acid (SA) is a plant hormone that acts as a signalling molecule against environmental and pathogenic stress. SA influences various physiological events in plants [6, 34–36]. SA plays a key role in the retardation of fruit ripening, and the inhibition of ethylene biosynthesis, promoting pathogen resistance, activating antioxidant systems, consequently, maintaining postharvest quality and prolonging the shelf life of fruits and vegetables. Moreover, SA is an effective enhancer of biocontrol agents like antagonist yeast in controlling rot and decay [6, 34]. SA and its derivatives (particularly Methyl salicylate; MeSA) have been generally recognized as safe (GRAS) for fruits and vegetables and are environmentally friendly [34, 35, 37].

Several studies have demonstrated the effect of postharvest SA application (exogenous) in fruits and vegetables [3, 6, 34, 38]. The dose of SA for exogenous postharvest application is varied for various fruits and vegetables, however a general non-toxic range for fruits and vegetables is 0.5–2.0 mM. Higher concentrations can damage fruit skin and cause fungal attacks [37]. **Table 4** presents information on some current applications of SA on some fruits and vegetables.


*Alternative Green and Novel Postharvest Treatments for Minimally Processed Fruits… DOI: http://dx.doi.org/10.5772/intechopen.111978*

**Table 1.** *Nitric oxide (NO) treatments on some fresh fruits.*


**Table 2.** *Nitric oxide (NO) treatments on some fresh vegetables (FVs).*


## *Alternative Green and Novel Postharvest Treatments for Minimally Processed Fruits… DOI: http://dx.doi.org/10.5772/intechopen.111978*

