**5.1 Chitosan**

*Modern Fruit Industry*

**6**

**Common name**

**MRL (ppm)**

> EU [17]

> > **Avocado**

> > > Cyprodinil

Carbendazim

Thiabendazole Pyraclostrobin Trifloxystrobin

Fludioxonil

Iprodione

Prochloraz

Difenoconazole

**Table 1.**

—

0.1

0.6 *Common name, chemical group, mode and target site as well as its MRL in some fruits for consumption [23].*

0.6

0.07

0.2

Triazoles

—

—

—

—

5

2

1

Imidazoles

Sterol biosynthesis in

membranes

—

—

10

10

10

Dicarboximides

5

5

5

5

5

5

Phenylpyrroles

Signal transduction

MAP/Histidine-Kinase in osmotic

signal transduction

C14-demethylase in sterol

biosynthesis

—

0.7

0.7

—

0.7

—

Oximino-acetates

0.6

0.6

0.6

—

0.05

0.2

Methoxycarbamates

Respiration

Complex III: cytochrome bc1 (ubiquinol oxidase) at Qo site

10

10

5

3

3

10

—

—

—

3

2

3

Benzimidazoles

Cytoskeleton and motor

ß-tubulin assembly in mitosis

proteins

1.2

1.2

1.2

1

1

1

Anilinopyrimidines

Amino acids and protein synthesis

Methionine biosynthesis (proposed)

**Mango**

**Papaya**

**Avocado**

**Mango**

**Papaya**

US [16]

**Chemical group**

**Mode action**

**Target site**

The excessive use of agrochemicals in tropical and in subtropical fruit has leaded the search for new natural products, eco-friendly, and nontoxic to humans. In several investigations, chitosan has proved their efficacy for controlling several postharvest diseases. Several mechanisms of action have been proposed for chitosan:


The induction of defense systems has been reported by the application of chitosan at post-harvest stage, preventing the development and dispersion of important pathogens such as *Colletotrichum gloeosporioides*, *Alternaria alternata*, *Rhizopus stolonifer*, and *Fusarium oxysporum* [26–28]. Enzymatic activity is also affected by the curative application of chitosan, and it increases the activity of polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine amino-lyase (PAL) that induce the expression genes of β-1,3-glucanase and chitinase, involved in the defense against pathogens [29, 30]. The physiological mechanisms of the fruit are positively affected by the application of chitosan at post-harvest management under biotic and abiotic stress, that is why the post-harvest shelf-life and quality (firmness, appearance, color) of fruit can be maintained during the storage time, besides the respiration rate and ethylene production of fruits decrease [31]. Some studies reported an enhanced content of total soluble solids, ascorbic acid, the nutritional value, and acceptability [30, 32, 33]. Chitosan is compatible with other substances like organic salts, gums, or essential oils, and this alternative can improve their efficacy against pathogens due to a synergistic effect [34, 35]. Even when important information has been generated on the use of chitosan in post-harvest tropical and subtropical fruits, it is still necessary to generate information on the regulation (activation and suppression) of genes that participate in both systems of acquired resistance and those that control the processes physiological, enzymatic, and physicochemical factors of maturation in post-harvest.
