Protein Hydrolysates Supplement in the Nutrient Solution of Soilless Grown Fresh Peppermint and Spearmint as a Tool for Improving Product Quality

Abstract

The present study investigated the potential of fresh peppermint (Mentha × piperita L.) and spearmint (Mentha spicata L.) production on a floating raft system combined with a commercial protein hydrolysate supplement (Amino16®) in a nutrient solution aiming to improve plant product quality. Three levels of the protein hydrolysate solution (0, 0.25 and 0.50%) were added in the nutrient solution, and the plants were harvested after twenty-four days. Plant growth characteristics were recorded, and nutritional, essential oil and polyphenolic composition were determined in fresh tissue. The addition of protein hydrolysates did not affect the fresh or dry weight but reduced plant height. Nitrate content significantly decreased, while total chlorophyll and essential oil content increased in both species. Moreover, the protein hydrolysate solution further increased total antioxidant capacity, total soluble phenol and carotenoid contents in spearmint plants, while it did not affect the essential oil and polyphenolic composition in both species. In conclusion, protein hydrolysates solution may be added in the nutrient solution, to improve the quality of peppermint and spearmint grown in a floating system, without adverse effects on crop yield or the essential oil and polyphenolic profile.

Responses of Peppermint and Spearmint Crops to Excessive Biostimulant Application and Increased Salinity in a Closed Soilless Production System

“…The protein hydrolysate supplement of the solutions has already been reported to affect both the plant nutritional composition as well as eventually the growth of the plant harvested at the vegetative herbaceous stage [5]. Fresh weight, plant height, and root length in the plants near the flowering stage were significantly affected by the amino acid concentrations, according to the analysis of variance (Table 1).…”

“…Any change that occurs during plant growth leads to alterations in EC values of the nutrient solution. The water and nutrient absorption by plants during cultivation and the high water and nutrient use efficiency leads to an increase in electrical conductivity in the solutions [5]. Simultaneously, electrical conductivity is also an indication of osmotic pressure in the NS.…”

“…According to Aktsoglou et al [5], both peppermint and spearmint crops are suitable for hydroponic cultivation, particularly in a floating raft system. This soilless hydroponic system may be subjected to customized modification in order to enhance the produce quality while employing sustainable agricultural practices [6].…”

“…Protein hydrolysates (PHs) are a mixture of amino acids and peptides deriving from the chemical or enzymatic hydrolysis of animal or plant origin by-products [6]. According to the published literature, it has been confirmed that the biostimulant activity of PHs results in improved quality of leafy vegetables [5,8] and induces protection in plants against several abiotic stressful conditions [9][10][11]. Moreover, even the application of PHs either as a supplement in nutrient solutions or as a foliar spray solution can serve as alternative nitrogen sources for plant growth and development [12].…”

“…Moreover, given that there is a linear regression between the salt concentrations and EC values, high EC levels increase the osmotic pressure of the NS and induce osmotic stress in plants and in turn, adverse growing conditions. Apart from the modification of the EC in the nutrient solutions, the addition of protein hydrolysates has been associated with ammonium toxicity, which is induced by the concentrated nitrogen presence in amino acid solutions [5]. Indeed, this situation may often be encountered in commercial hydroponic production because apart from their biostimulant activity, the amino acids included in the PH solutions are considered as important alternative nitrogen sources for plants [12] and there is always a high risk of excessive application, similar to fertilizer use during crop production on soil.…”