Plant organs, such as leaves, roots, stems, and flowers, contain high concentrations of essential oils. Volatile oils, also known as ethereal oils, obtain their names from their ability to evaporate quickly when exposed to air at room temperature. Secondary metabolites, such as sesquiterpenes and phenylpropanoids, make up most of these oils. They are well-known for their antimicrobial and sprout-inhibiting properties
[18][41]. Both
S-carvone, 2-methyl-5-(1-methylethenyl)-2-cyclohexene-1-one, and its enantiomer,
R-carvone, are volatile monoterpenes in the essential oils of caraway (
Carum carvi L.), mint (
Mentha spicata L.), and dill (
Anethum graveolens L.), which have potent inhibitory bioactivities on the sprouting of potato tubers at continuous low headspace concentrations
[19][20][21][8,42,43]. In addition to its sprout suppression bioactivities,
S-carvone inhibits bacterial and fungal growth, thereby presenting secondary benefits, such as suppressing storage pathogens such as
Fusarium and
Rhizoctonia species
[21][22][43,44]. Other notable advantages of
S-carvone over CIPC include its strong odor, which is transmitted to foods when used as a flavoring agent, it is non-toxic and safe for humans, and it contributes less to ozone depletion compared to CIPC
[22][23][44,45]. Some European nations have commercialized
S-carvone and market it under tradenames such as Talent
TM [24][27].
3.1. Mode of Action of S-carvone
The precise mechanism of sprout suppression employed by
S-carvone is yet to be fully resolved. However,
S-carvone is believed to influence potato tuber sprouting by interfering with isoprenoid metabolism. The mevalonate pathway, which employs the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), is implicated in the process that prevents sprouts from growing
[25][20].
S-carvone interferes with sprouting by inhibiting HMGR activity
[26][46] through repression at the post-translational level
[27][47]. Another model proposes the inhibition of the 2-
C-methyl-
D-erythritol 4-phosphate (MEP) isoprenoid pathway, which affects the mevalonate pathway downstream and isoprenoid metabolism by blocking protein isoprenylation. Here,
S-carvone blocks an MEP pathway-dependent protein geranylgeranylation that is required for signaling
[28][48]. The mevalonate pathway partakes mainly is the provision of metabolites for the biosynthesis of hormones that are important for plant growth.
3.2. Evaluation of S-carvone as a Sprout Inhibitor
Sprout growth inhibition was achievable for the Bintje cultivar only for 15 days compared to CIPC and the Agria cultivar, 0 days compared to CIPC. Sprout suppression for treated Russet Burbank cultivar was achievable for 70 days with a dosage of 0.080 mL/kg
[8][4]. An in vitro study demonstrated the effectiveness of the essential oils and clearly showed that sprout growth and extension of shelf-life were achievable
[29][50]. Using mint (
M. spicata) essential oil, which contains a significant amount of carvones (51–73%)
[19][30][8,21], and synthetic
R-carvone, Teper-Bamnolker et al.
[19][8] noted a significant decrease in sprouting and weight loss in tubers of eight different potato cultivars that were stored for six months. However, these studies were not shelf-life extension studies as they only demonstrated the effectiveness of the essential oil at reducing sprout growth.
With a dosage application of 0.6 mL/kg, sprout suppression for the Monalisa cultivar compared to the control was achieved 21 days
[31][51]. Dosage application of 155 mL/kg extended tuber shelf-life by 25 days compared to the control for both Agria and Kennebec cultivars
[25][20]. Using the Agria cultivar,
[24][27] demonstrated that the tuber shelf-life extension at different temperatures was achieved with a dosage application of 0.6 mL/kg. Compared to the control and CIPC, different results were achieved with
S-carvone. CIPC performed better than
S-carvone at shelf-life extension. At 5 °C, they noted 60 days of the shelf-life extension was achieved compared to the control, whereas 0 days compared to CIPC. At 10 °C, 75 days extension was noted compared to the control, whereas 0 days was achieved compared to CIPC and at 15 °C, 90 days compared to the control and 15 days compared to CIPC.