Plants of Genus Mentha: From Farm to Food Factory

Genus Mentha, a member of Lamiaceae family, encompasses a series of species used on an industrial scale and with a well-described and developed culture process. Extracts of this genus are traditionally used as foods and are highly valued due to the presence of significant amounts of antioxidant phenolic compounds. Many essential oil chemotypes show distinct aromatic flavor conferred by different terpene proportions. Mint extracts and their derived essential oils exert notable effects against a broad spectrum of bacteria, fungi or yeasts, tested both in vitro or in various food matrices. Their chemical compositions are well-known, which suggest and even prompt their safe use. In this review, genus Mentha plant cultivation, phytochemical analysis and even antimicrobial activity are carefully described. Also, in consideration of its natural origin, antioxidant and antimicrobial properties, a special emphasis was given to mint-derived products as an interesting alternative to artificial preservatives towards establishing a wide range of applications for shelf-life extension of food ingredients and even foodstuffs. Mentha cultivation techniques markedly influence its phytochemical composition. Both extracts and essential oils display a broad spectrum of activity, closely related to its phytochemical composition. Therefore, industrial implementation of genus Mentha depends on its efficacy, safety and neutral taste.


AP
On the other hand, M. arvensis essential oil was found to contain a lower number of chemical constituents (from 7 to 26) than the other members of Mentha genus. In the study carried out by Hussain et al. [135], menthol and isomenthone were the most abundant compounds.
Studies on M. canadensis essential oil, collected in China, Brazil and India and extracted using hydrodistillation, identified menthol as the main constituent [96,98,99]. Still, in the study performed in China, it was observed that salt stress can reduce menthol concentration at the same time increase menthone and pulegone contents in M. canadensis essential oil.
Regarding M. cervina essential oil, pulegone and isomenthone were the main constituents identified in all studies performed [85,101,102]. Rodrigues et al. [85] found that cultivated populations belonging to the same chemotype were characterized by the presence of pulegone as the most abundant constituent. Therefore, the studied essential oils contained in their chemical composition oxygenated monoterpenes, with pulegone being the main compound (52-75%), followed by isomenthone, limonene and menthone. These findings allowed authors to classify the obtained oils into two categories: (1) pulegone-rich with low isomenthone content; and (2) pulegone-and isomenthone-rich oils.
Chowdhury et al. [136] investigated the essential oil chemical profile of different M. spicata varieties from Bangladesh, and found (−)-carvone and limonene as major constituents, with these data having been recently confirmed by Dwivedy et al. [100]. For Mentha diemenica essential oil, collected in Queensland (Australia), menthone, neomenthyl acetate and pulegone were found to be the main compounds present, while essential oil of the same species from Canada had significantly higher amounts of pulegone, clearly supporting it as the main compound, followed by menthone and isomenthone, with neomenthyl acetate not being found [103].
There are a number of studies dealing with the chemical composition of M. longifolia essential oils from different geographical origins, showing a great degree of chemical variation, which is not surprising, bearing in mind the very high morphological diversity of this species, resulting in a high number (n = 276) of subspecies, varieties and forms. The main constituents of M. longifolia essential oil belong to oxygenated monoterpenes group, which include pulegone [108], piperitenone oxide [107] and 1,8-cineole [105]. Beyond these, carvone, isomenthone, borneol, menthol, menthone, piperitenone, dihydrocarvone, limonene, sabinene, α-pinene, eucalyptol, γ-terpineol, β-caryophyllene, isopulegone, cadinene and β-pinene were also recorded as meaningful compounds from M. longifolia essential oil.
For M. spicata subsp. condensata (Briq.) Greuter and Burdet there is only one study assessing their chemical composition, in which pulegone, piperitenone oxide and piperitenone were identified as the most abundant ones [123].
Mentha × rotundifolia (L.) Huds. is a species originating from M. longifolia and M. suaveolens hybridization. Twenty-three compounds were identified by Lorenzo et al. [112] in the essential oil of an Uruguayan population, where the main constituent (80.8%) was piperitenone oxide.
Considering M. × piperita essential oil, studies showed a very high variability derived from the existence of numerous chemotypes. Barrosa et al. [96] studied two different M. × piperita varieties (chocolate mint and grapefruit mint varieties) and identified menthofuran, menthone d-neoisomenthol and pulegone as the main compounds in a chocolate mint variety, while linalyl acetate with linalool were those prevailing in a grapefruit mint variety. A commercial essential oil purchased in New Delhi (India) presented, in its chemical composition, menthol (19.1%), isomenthone (14.8%) and limonene (10.6%) as major components [127]. M. × piperita essential oil collected in Serbia presented a similar composition to that collected in Morocco, with menthol, menthyl acetate and menthone as the main constituents [120,128]. Menthol was also found to be the main compound present in M. × piperita essential oils isolated from plant material collected in Iran, China, Taiwan, Saudi Arabia and Brazil [129][130][131][132][133]. However, beyond menthol (up to 59.7%), high amounts of menthone, isomenthone, menthyl acetate and menthofuran were also reported. Another chemotype identified from this species is characterized by its high amount of (−)-carvone, accompanied by limonene as the second main constituent [134].

Non-Volatile Compounds
A wide range of other chemical constituents, mostly phenolic compounds, are also present in mint tissues [144], as briefly shown in Table 2. Interestingly, it should be highlighted that rosmarinic acid, luteolin-7-O-glucoside, salvianolic acid, eriocitrin and hesperidin have been found to be the major non-volatile constituents in Mentha species [145].

Food Preservative Applications of Genus Mentha Essential Oils
Food manufacturers, regulatory agencies and, finally, consumers have been increasingly concerned about microbiological food safety and the growing number of foodborne illnesses caused by pathogens [146]. According to the World Health Organization's (WHO) global estimates of foodborne diseases, 600 million people fall ill after consuming contaminated food, of which 420,000 die. In European countries alone, more than 23 million people fall ill every year from unsafe food, and this results in 5,000 deaths [147]. Over 90% of all cases of food poisoning are caused by Bacillus cereus, Campylobacter jejuni, Clostridium botulinum, Clostridium perfringens, Escherichia coli pathogenic strains, Listeria monocytogenes, Salmonella spp., Shigella spp., Staphylococcus aureus, Yersinia enterocolitica, as well as Vibrio cholerae [148]. These microorganisms are responsible for foodborne outbreaks in different food branches, such as drinking water, beverages, dairy products, fruits, vegetables and even meat and fish products [149]. For decades, in the food industry, a wide variety of synthetic compounds has been used for preservative and antimicrobial purposes with the aim of inhibiting microorganism growth and spoiling. Sodium benzoate, sodium and calcium propionate, sorbic acid, ethyl formate, and sulfur dioxide are examples of chemical substances commercially used to inhibit the growth of microorganisms in foods [150]. Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylated hydroquinone (TBHQ), propyl gallate, ascorbic acid (vitamin C) and tocopherols (vitamin E) are antioxidants used as food preservatives [150]. However, it has also been stated that the widespread use of synthetic preservatives has led to huge ecological and medical problems, which, in addition to economic considerations, have triggered the search for new/safer strategies against microbiota spoilage [151,152]. Due to the growing consumer demand for safe, high-quality and healthy food with reduced quantity of synthetic preservatives or antimicrobials, an increasing interest has been stated on natural antimicrobials from plants [153]. It has long been known that plant phytochemicals protect against viruses, bacteria, fungi and herbivores, but it has only recently been learned that they can be also used for food spoilage microorganism protection.
One of the most popular and representative plant groups is the Lamiaceae family. Nowadays, it is used both in traditional and modern medicine, as well as in the pharmaceutical and food industries. The use of mint is not strictly limited to essential oils, which are widely recognized for their strong aromatic properties. Indeed, essential oils and their derived extracts can be effectively used as natural food preservatives. As a result, they can fulfill several important tasks: prolong shelf-life, eliminate synthetic preservatives and food flavors, as well as forming part of a healthy food trend that influences market sales. Due to the overall popularity and occurrence, mint appear to be relatively well tested in terms of antibacterial activity against a wide spectrum of bacteria, such as E. coli pathogenic strains, L. monocytogenes, Salmonella spp., S. aureus, and many others (Table 3). Curiously, the vast majority of studies on Mentha spp. antimicrobial effects have been linked to essential oils and plant extracts.

Plant Species Bacterial Strain References
Mentha × piperita L.

Gram negative:
Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.

Gram negative:
Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none).  [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.

Plant Species Bacterial Strain References
Mentha × piperita L.  [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.

Plant Species Bacterial Strain References
Mentha × piperita L.  [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none).

Plant Species Bacterial Strain References
Mentha arvensis L.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and S. aureus) and Gram-negative Salmonella and E. coli species. Soković et al. [181] found that M. × piperita and M. spicata essential oils were more active against pathogenic bacteria B. subtilis, E. coli, Pseudomonas (P. mirabilis, P. aeruginosa), Salmonella (S. enteritidis, S. typhimurium) and S. aureus spp. than essential oils from sweet basil (Ocimum basilicum L.), lavender (Lavandula angustifolia Mill.), bitter orange (Citrus × aurantium L.), sage (Salvia officinalis L.) and chamomile (Matricaria chamomilla L.). The authors also noted that menthol was more active than linalyl acetate, limonene, β-pinene, α-pinene, camphor, linalool and 1,8-cineole.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and S. aureus) and Gram-negative Salmonella and E. coli species. Soković et al. [181] found that M. × piperita and M. spicata essential oils were more active against pathogenic bacteria B. subtilis, E. coli, Pseudomonas (P. mirabilis, P. aeruginosa), Salmonella (S. enteritidis, S. typhimurium) and S. aureus spp. than essential oils from sweet basil (Ocimum basilicum L.), lavender (Lavandula angustifolia Mill.), bitter orange (Citrus × aurantium L.), sage (Salvia officinalis L.) and chamomile (Matricaria chamomilla L.). The authors also noted that menthol was more active than linalyl acetate, limonene, β-pinene, α-pinene, camphor, linalool and 1,8-cineole.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and S. aureus) and Gram-negative Salmonella and E. coli species. Soković et al. [181] found that M. × piperita and M. spicata essential oils were more active against pathogenic bacteria B. subtilis, E. coli, Pseudomonas (P. mirabilis, P. aeruginosa), Salmonella (S. enteritidis, S. typhimurium) and S. aureus spp. than essential oils from sweet basil (Ocimum basilicum L.), lavender (Lavandula angustifolia Mill.), bitter orange (Citrus × aurantium L.), sage (Salvia officinalis L.) and chamomile (Matricaria chamomilla L.). The authors also noted that menthol was more active than linalyl acetate, limonene, β-pinene, α-pinene, camphor, linalool and 1,8-cineole.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none).  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and S. aureus) and Gram-negative Salmonella and E. coli species. Soković et al. [181] found that M. × piperita and M. spicata essential oils were more active against pathogenic bacteria B. subtilis, E. coli, Pseudomonas (P. mirabilis, P. aeruginosa), Salmonella (S. enteritidis, S. typhimurium) and S. aureus spp. than essential oils from sweet basil (Ocimum basilicum L.), lavender (Lavandula angustifolia Mill.), bitter orange (Citrus × aurantium L.), sage (Salvia officinalis L.) and chamomile (Matricaria chamomilla L.). The authors also noted that menthol was more active than linalyl acetate, limonene, β-pinene, α-pinene, camphor, linalool and 1,8-cineole.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade Staphylococcus aureus [173] Mentha longifolia L.

Gram negative:
Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1)  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make Streptococcus pyogenes [171,174] Mentha pulegium L.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade of excrete antimicrobial agents; and (3) cell wall/membrane interaction leading to increased uptake of other antimicrobials [183]. For example, in yeasts, the results obtained by Ferreira et al. [184] indicated that M. × piperita essential oil was able to induce cell death in Saccharomyces cerevisiae due to pro-oxidant effects, both in cytosol and mitochondria.
Synergy can not only be observed between different constituents of one essential oil or extract but also in a mixture of them. For example, the combination of Lippia multiflora Moldenke and M. × piperita essential oils showed synergetic effects against E. coli, Enterococcus faecalis, Enterobacter aerogenes, L. monocytogenes, P. aeruginosa, Shigella dysenteriae, S. aureus and Salmonella (S. enterica and S. typhimurium) species [185]. Soković et al. [181] and Riahi et al. [172] indicated that, in general, essential oils show stronger action against Gram-positive than Gram-negative bacteria. In fact, it has been shown that the lower susceptibility of Gram-negative bacteria results from the presence of hydrophobic lipopolysaccharide in their outer cell membrane, which confers protection against different active agents [170]. This bacterial structure prevents depolarization and pore formation, while at the same time increasing membrane permeability or fluidifying effect [183].
There are some crucial factors affecting antimicrobial activity, including essential oil composition, active substances concentration and type of microorganisms tested. First of all, essential oil composition may be determined by some plant cultivation factors, such as environmental conditions, harvesting period, drying method, storage conditions as well as extraction methods [186]. Although the different mint varieties from which plant extracts and essential oils are derived are characterized by strong and multifaceted in vitro activities against bacteria, yeasts and molds, it should be clearly emphasized that their biological activity may vary considerably in industrial conditions for specific food matrices. Table 4 lists in vitro Mentha species activities against fungi and yeasts. Results from in vitro studies for M. × piperita essential oils against several Aspergillus (A. flavus, A. fumigatus, A. oryzae, A. clavatus), Candida (C. albicans, C. glabrata, C. tropicalis, C. krusei, C. dubliniensis, C. parapsilosis) and Cryptococcus neoformans species showed prominent effects at relatively low concentrations, ranging from 0.5 to 4 µL/mL [187]. According Pandey et al. [188], M. arvensis essential oil displayed a high toxicity on Penicillium italicum than lemon grass (Cymbopogon citratus) and sweet basil (O. basilicum) essential oils. Mentha spp. essential oils used for Aspergillus parasiticus control inhibited aflatoxin synthesis [189]. In the work performed by Kumar et al. [190], M. arvensis essential oil was tested against 9 postharvest fungi and exhibited absolute inhibition of Aspergillus species (A. flavus, A. fumigatus, A. ochraceus, A. niger, A. terreus), Helminthosporium oryzae and Sclerotium rolfsii. Still, essential oil significantly exhibited growth in all tested fungi at a concentration of 500 ppm, with the observed activity being similar to basil (Ocimum americanum L.) essential oil [191]. Soković et al. [120] investigated M. spicata, M. × piperita and thymes (Thymus vulgaris L. and T. sibthorpii Benth.) activity against 17 plant, animal and human pathogens. Results showed that M. spicata essential oil had a greater fungistatic activity than M. × piperita, but a weaker one than T. vulgaris. In addition, the authors found that all tested essential oils showed stronger antimicrobial activities than bifonazole against A. alternata, Aspergillus (A. niger, A. ochraceus, A. versicolor, A. flavus, A. terreus), Cladosporium cladosporioides, Fusarium tricinctum, Penicillium (P. ochrochloron, P. funiculosum), Phomopsis helianthi, Trichoderma viride, and Trichophyton (T. mentagrophytes, T. rubrum, T. tonsurans) species.

Shelf-Life Prolongation
Despite Mentha spp. plant extracts and essential oils having shown great in vitro antimicrobial effects against bacteria, yeasts and molds, their action can be quite different in complex environments, such as food matrices. Indeed, essential oils' biological activity is markedly influenced by food components (e.g., fats, carbohydrates, proteins, water, salt, preservatives), temperature, pH, water activity and packaging methods [193]. The negative impact of high protein content on essential oil activity was reported by Tassou et al. [163], who studied the effect of mint essential oils on S. enteritidis and S. aureus growth. The authors attributed antimicrobial activity reduction to protein content, suggesting that the phenolic group monoterpenes could bind to proteins, thereby lowering the number of antimicrobial compounds available. Cava et al. [194] tested the antimicrobial activity of mint essential oils against L. monocytogenes in milk, and found that essential oils bioactivity was reduced by fats. Diverse studies reported that essential oils exhibited highest activity at low pH levels [195,196]. However, other parameters also affect essential oil activity, like temperature and sodium chloride. Combination of carvacrol and p-cymene with sodium chloride (1.3 g/L) showed an antagonistic effect. On the other hand, it is well known that high sodium chloride concentration contributes to cell lysis. Going further, essential oils show better antimicrobial activity in vapor than in liquid phase [197].
Both extracts and essential oils derived from different mint species may extend food products shelf-life (Table 5).
M. longifolia leaf extract (6.0%) application shows better antioxidant and antimicrobial activities than cumin (Cuminum cyminum L.) seed extract. Wild mint extracts significantly affected fresh rainbow trout shelf-life, extending it by up to 12-18 days during storage in a refrigerator, which suggests that they can be effectively applied as natural preservatives in fish products shelf-life extension. Sensory analysis showed that rainbow trout treatment with M. longifolia extract improved overall quality and sensory properties [204].
Results obtained by Tassou et al. [210] showed that M. × piperita essential oil at concentrations ranging from 0.5 to 2.0% completely reduced S. enteritidis number in tzatziki, and markedly decreased its number in taramosalata. In the same study, L. monocytogenes populations showed a declining trend in a one-week storage period. However, this effect was not observed for pâté. The authors speculated that mint essential oils' antibacterial action depends not only on essential oil concentration, but also on food product (type, pH, storage temperature) and type of spoilage microbiota. Klūga et al. [198], reported that M. × piperita leaf extract protected fish from spoilage. Also, mint extract treatment suppressed total Enterobacteriaceae and Pseudomonas spp. bacteria growth in mackerel. Moreover, in these food matrices, mint extract inhibited lipid oxidation, and then enhanced stability storage and extended shelf life by 2 to 5 days [201]. Nonetheless, mint essential oils and extracts can also be successfully used in other food products. The study of Choi et al. [199] demonstrated peppermint oil antibacterial activities against Acidovorax citrulli, a bacteria responsible for watermelon blotch. These results suggested the possibility of using peppermint oil as an antibacterial agent to treat contaminated seeds. In addition to that, a mint-supplemented cereal biscuit (in different forms) enriched in natural antioxidants, maintained acceptable for consumption over 5 months storage period. Polyphenols' antioxidant efficiency prevented biscuit rancidity onset during storage; therefore, mint may be conceived of as a key substitute for synthetic antioxidants in baked food product preservation [203]. Table 5. Mentha spp. essential oil or extract application and food shelf-life prolongation.

Plant Species Spoiling Microorganisms Food Matrix Reference
Mentha × piperita L.

Bacteria
Gram negative: Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.

Bacteria Gram negative:
Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.

Bacteria Gram negative:
Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none).  [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none).  [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none).

Listeria monocytogenes
White cheese [205]  development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade  [133]. M. × piperita essential oil, with (−)-carvone (35%), pulegone (15%), methyl petroselinate (16%) as main compounds, demonstrated antimicrobial activity against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria [134]. Essential oils from M. aquatica, M. longifolia or M. × piperita aerial parts were markedly active against pathogenic fungi, like C. albicans, Epidermophyton floccosum, Microsporum canis and Trichophyton spp. (T. mentagrophytes, T. rubrum and T. tonsurans) [138,177]. M. × piperita essential oil showed significant antifungal activity against A. alternata, Fusarium tabacinum, Penicillum spp., Fusarium oxyporum and Aspergillus fumigatus [133]. Studies conducted by Mahboubi and Haghi [178] reported that M. pulegium essential oil exhibited antimicrobial activity against S. aureus, L. monocytogenes, B. cereus, E. coli and yeast C. albicans. The data obtained by the authors pointed out that M. pulegium essential oil activity was comparable to well-known antibiotics vancomycin, erythromycin or gentamycin. In a similar way, Ait-Ouazzou et al. [179] highlighted that M. pulegium essential oil antibacterial activity against S. aureus, L. monocytogenes, S. enteritidis and E. coli was higher than galingale (Cyperus longus) and juniper (Juniperus phoenicea). Dhifi et al. [180] also reported that M. spicata essential oil showed high activity against Gram-positive Staphylococcus (S. epidermidis and S. aureus) and Gram-negative Salmonella and E. coli species. Soković et al. [181] found that M. × piperita and M. spicata essential oils were more active against pathogenic bacteria B. subtilis, E. coli, Pseudomonas (P. mirabilis, P. aeruginosa), Salmonella (S. enteritidis, S. typhimurium) and S. aureus spp. than essential oils from sweet basil (Ocimum basilicum L.), lavender (Lavandula angustifolia Mill.), bitter orange (Citrus × aurantium L.), sage (Salvia officinalis L.) and chamomile (Matricaria chamomilla L.). The authors also noted that menthol was more active than linalyl acetate, limonene, β-pinene, α-pinene, camphor, linalool and 1,8-cineole.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak antibacterial activity, with it being suggested that the benzene ring is of huge importance to promoting strong effects. Indeed, menthol molecules have a cyclohexane ring, which seems to make this compound less active. Nonetheless, compounds present in essential oils and extracts show multiple actions and even synergistic effects. Consequently, mixtures can be more effective as food preservatives than pure substances. The main mechanisms of antimicrobial synergy include: (1) sequential steps inhibition in specific biochemical pathways; (2) inhibition of enzymes that degrade

Listeria innocua
Yogurt drink (ayran) [206] Mint extract Total count Tomato juice [207] Bacteria Gram negative: Plants 2018, 7, x FOR PEER REVIEW 20 of 35 development [160,161]. The final concentration of the extracts in the wells was 1 mg/mL, while ciprofloxacin at a concentration of 2,5 μg/mL and amphotericin B at 5 μg/mL were used as the positive controls for P. aeruginosa and C. albicans, respectively [160]; for the other microorganisms, the control samples were the same culture media but without M. × piperita [161]. Panda et al. [162] showed that M. arvensis aqueous extract at 0.8 mg/mL inhibited citrinin production by P. citrinum up to 73% (positive control: none). Table 3. Mentha spp. activity against bacterial pathogens tested in vitro.
On the other hand, Ben Arfa et al. [182] compared the antimicrobial activity of carvacrol with that of carvacrol methyl ether, carvacrol acetate, eugenol, and menthol. Menthol showed very weak

Mint powder
Standard plate count Yeast/mould count Chicken slices [209] Finally, essential oil synergy is also an interesting point [31]. M. × piperita essential oil and silver ions (Ag + ) combination acted synergistically against E. coli, S. aureus and C. albicans cultures [211]. Also, M. × piperita essential oil (0.5%) and bacteriocin (1000 AU/g) combination delayed microorganism spoilage proliferation in stored minced beef meat. Thus, biopreservative effect in combination can be considered a promising tool for upcoming application in meat products preservation [212].

Conclusions and Future Perspectives
Among Lamiaceae family, the Mentha genus encompasses several species already used at industrial scale and with well-developed cultivation. Extracts are traditionally used as food, and contain remarkable antioxidant phenolic compounds. Many essential oil chemotypes show distinct aromatic flavor conferred by different terpenes proportions. Both extracts and essential oils show activities on a broad spectrum of microorganisms tested in vitro as well as using various food matrices. Due to its natural origin, antioxidant and antimicrobial activities, mint-derived products could become a great alternative to artificial preservatives, and to find a wide range of applications for shelf-life extension of fruits and vegetables, beverages, dairy products, baking or meat and fish products. Nevertheless, industrial implementation depends on efficacy, ease of use and profitability of such natural additive over synthetic preservatives.
Extracts could be obtained as essential oil by-products, allowing a higher profitability, and where its moderate activity can be compensated by their safety. Besides that, essential oil taste is not neutral, and therefore its wide aroma should be carefully adapted to the matrices used in order to minimize the aromatic impact, and might also be used for food ingredient preservation before processing. Not least important to emphasize is that the finished products could also be marketed with the explicit mention of such natural preservatives to facilitate overall acceptance and demand. Further organoleptic studies should be performed, along with antimicrobial studies to assess the relevance of such ingredient in finished food products.