**4. Vegetable extracts**

Since the origin of civilization, plants have played an essential role in the development and well-being of civilization through their varied uses (e.g., food preservatives, flavorings, and dietary supplements to maintain human health) [29]. Plant extracts have been employed as safe and efficient remedies for ailments and diseases in traditional medicine. The active constituents of many plant extracts have been characterized and are publicly available, although there is little information on their antimicrobial actions [30]. The adoption of natural antimicrobial elements as egg disinfectants opens the door to their use as a safer alternative because they are biodegradable and non-toxic, compared to chemicals that are toxic, non-degradable, and corrosive. There are several methods used for oil extraction, such as the use of liquid CO2 or microwaves, as well as low pressure distillation with boiling water or hot heat [31]. Among the most significant molecules are phenolic compounds: trans-cinnamaldehyde (an aldehyde found in cinnamon bark extract (*Cinnamomum zeylandicum*)), carvacrol extracted from oregano oil (*Origanum glandulosum*), eugenol (active ingredient of clove (*Eugenia caryophillis*)), etc. These compounds showed rapid effectiveness in reducing *Salmonella enteritidis* compared to water-washed or chlorine-challenged eggs.

Yamawaki et al. [32] used phytochemicals products of secondary metabolites produced by plants with defensive properties against predators (e.g., caproic acid, caprylic acid, linalool, and pectin-based cuminaldehyde) to reduce *Salmonella heidelberg* on eggshells at a concentration of 1.0% alone or combined at 0.5% v/v with different storage times (0, 1, 3, 5, 7, 7, 14, and 21d) at 4°C. At the end of storage (21d), the lowest *Salmonella* counts were for caproic acid and caprylic acid at 1% pectin combination (2%) from 0d to 14d, and at the end of storage compared to untreated controls [16].

Capsicum essential oil, known as allspice oil, is obtained from the leaves of *Pimenta officinalis* Lindl. The main component is antimicrobial, and its application has proved effective against *Staphylococcus epidermidis*, *Proteus hauseri*, *Micrococcus yunnanensis*, and *Corynebacterium xerosi*. *In vitro*, it acts against *Listeria monocytogenes* and *Salmonella heidelberg* in turkey skin stored over short periods at 4 and 10°C, at a concentration of 0.5 or 1.0% [16, 33]. The compound extracted from clove oil (*Eugenia caryophilis*), called eugenol, as well as trans-cinnamaldehyde, an aromatic aldehyde extracted from cinnamon bark (*Cinnamomum zeylandicum*), have shown antimicrobial effects on *Salmonella enteritidis* PT8 by interfering with several

genes associated with virulence, colonization, membrane composition, and transport ecosystems.

Ginger, garlic, oregano, and cinnamon extracts, applied in 5% aqueous solutions, showed no differences in fertility, hatchability, embryonic mortality, body weight, or viability of the chicks during 14d of brooding. Regarding the incubation variables, ginger extract was the only one effective in preventing the growth of bacterial colonies [16]. On the other hand, when comparing oregano juice at a concentration of 50% diluted in distilled water at room temperature against fumigation with 100% formaldehyde in white Akbay breeders of 48 weeks of age, no differences were observed between disinfection groups on egg characteristics, eggshell microbial load, hatchability, embryonic death, body weight, weight gain, or feed conversion rate. However, weight loss was lower in formaldehyde fumigation versus oregano juice [34].

In terms of bacterial structure and susceptibility, Positive Gram have a peptidoglycan cell wall bound to other molecules, such as proteins or teichoic acid [35], and Negative Gram have lipopolysaccharide (LPS), which forms a barrier to the hydrophobic compounds that essential oils have in their outer membrane [36]. Therefore, Negative Gram are less susceptible to the effects of essential oils than Positive Gram [37]. However, it is important to note that the hydrophobic structure of essential oils can reach the periplasm of Negative Gram through outer membrane proteins (porins), where it travels slowly, followed by leakage of potassium into the extracellular space and loss of ATP [37–41].

The use of essential oils as preservatives may be limited by changes in the organoleptic characteristics of foods. However, in the disinfection of fertile eggs, their safety has been recognized, and their use is gaining more and more practitioners every day. Therefore, it is important to carry out studies on the minimum inhibitory concentration of essential oils to allow a balance between sensory characteristics and antimicrobial efficacy.

## **5. Propolis**

Propolis is a sticky, gummy, resinous substance harvested by worker bees (*Apis Melifera*) from the buds of certain trees and shrubs. The bees use it to seal parts of the hive. At least 200 compounds have been found in different samples of propolis (e.g., esters, fatty acids, flavonoids, terpenes, β-steroids, aldehydes, aromatic alcohols, sesquiterpenes, naphthalene derivatives, and stilbenes) [42, 43]. For centuries, propolis has been used as a medicinal agent to treat infections and promote wound healing [44]. Due to its broad antimicrobial effect, it has been used as an alternative preservative agent and as a protection for various agricultural products during their storage period [45, 46]. Propolis was used to reduce microbial activity in quail eggs stored for 7 and 14d, but it reduced hatchability and increased embryo mortality between 1 and 9d of incubation.

Oliveira et al. [27] conducted an experiment to evaluate the effectiveness of an alcoholic extract of propolis (15%) as a disinfectant for hatching eggs of Japanese quail (*Coturnix coturnix* Japonica). A low eggshell conductance in the control group (egg weight loss) and a decrease in the microbial load were obtained. Likewise, no differences in hatchability and embryo mortality were observed. Therefore, alcoholic extract of propolis (15%) can be used as a safe disinfectant in fertile quail eggs [16, 47].

*Natural Products as an Alternative to Formaldehyde for Disinfection of Fertile Eggs… DOI: http://dx.doi.org/10.5772/intechopen.112568*
