How to Increase the Nutritional Quality of Stinging Nettle Through Controlled Plant Nutrition§

Abstract

Research background. As food production faces major challenges, modern agricultural practices are increasingly focused on conserving resources, reducing negative environmental impacts and sustainably producing food with a high content of health-promoting phytochemicals. During production, many factors can affect the quality and chemical composition of a final food product. Proper selection of cultivating conditions, especially a balanced nutrition, can significantly increase nutritional value and result in foods with strong biological and functional properties. Stinging nettle is a rich source of minerals, vitamins, pigments, phenols and other bioactive compounds and can be consumed as a green leafy vegetable with beneficial effects on human health. Therefore, the aim of this study is to determine the nutritional quality and antioxidant capacity of stinging nettle leaves under the influence of different nutrient solution (NS) treatments and three harvest cycles. Experimental approach. The experiment was conducted in a floating hydroponic system in which treatments with different nutrient solutions were applied and three harvest cycles were carried out. After each harvest, the following treatments were applied: treatment 1 – depletion of nutrient solution by adding water, treatment 2 – supplementation of nutrient solution by adding initial nutrient solution and treatment 3 – correction of nutrient solution by adding nutrients. Among the bioactive compounds, minerals, ascorbic acid, phenols and photosynthetic pigments content, as well as antioxidant capacity were analysed spectrophotometrically, while individual phenols were determined by liquid chromatography. Results and conclusions. Different nutrition solution treatments and the number of harvest cycles had a significant effect on the content of the analysed bioactive compounds. The highest mass fraction (on fresh mass basis) of total phenols expressed as gallic acid equivalents (377.04 mg/100 g), total flavonoids expressed as catechol equivalents (279.54 mg/100 g), ascorbic acid (112.37 mg/100 g) and pigments (total chlorophylls 1.84, and total carotenoids 0.36 mg/g) as well as the highest antioxidant capacity expressed as Trolox equivalents (35.47 µmol/g) were recorded in the samples supplemented with nutrient solution (treatment NS2) and analysed after the third harvest. Novelty and scientific contribution. This is the first time that stinging nettle leaves have been produced in a floating hydroponic system by controlled plant nutrition. We have set this type of nutritional manipulation with multiple harvest cycles as an innovative technique for the production of novel food with improved nutritional value that can be consumed as green leafy vegetables.

Alternate abstract:

Pozadina istraživanja. Budući da se proizvodnja hrane suočava s velikim izazovima, suvremene poljoprivredne prakse sve su više usmjerene na očuvanje resursa, smanjenje negativnog učinka na okoliš i održivu proizvodnju hrane s velikim udjelom fitokemikalija koje pozitivno utječu na ljudsko zdravlje. Tijekom uzgoja, brojni čimbenici mogu utjecati na kakvoću i kemijski sastav konačnog proizvoda. Pravilnim odabirom uvjeta uzgoja, posebice uravnoteženom ishranom (gnojidbom), može se znatno povećati nutritivna kakvoća sirovine te pozitivno utjecati na njezina biološka i funkcionalna svojstva. Kopriva je bogat izvor mineralnih tvari, vitamina, pigmenata, fenola i drugih bioaktivnih spojeva, a može se konzumirati kao zeleno lisnato povrće blagotvornog učinka na zdravlje ljudi. Stoga je svrha ovog istraživanja bila odrediti nutritivnu kakvoću i antioksidacijski kapacitet lista koprive tretirane različitim hranjivim otopinama tijekom tri ciklusa berbe. Eksperimentalni pristup. Pokus je proveden u plutajućem hidroponskom sustavu u kojem su biljke tretirane različitim hranjivim otopinama tijekom tri ciklusa berbe. Korišteni su sljedeći postupci: tretman 1 – iscrpljivanje hranjive otopine vodom, tretman 2 – prihrana standardnom hranjivom otopinom i tretman 3 – korekcija sastava hranjive otopine dodatkom nutrijenata. Od bioaktivnih spojeva ispitani su maseni udjeli mineralnih tvari, askorbinske kiseline, ukupnih fenola i fotosintetskih pigmenata, te je utvrđen antioksidacijski kapacitet pomoću spektrofotometrije, dok su udjeli pojedinih fenola određeni tekućinskom kromatografijom. Rezultati i zaključci. Različiti tretmani hranjivim otopinama i broj ciklusa berbe bitno su utjecali na udjele ispitanih bioaktivnih spojeva u listu koprive. Najveći udjel (u svježoj masi lista) ukupnih fenola izražen kao ekvivalent galne kiseline (377,04 mg/100 g), ukupnih flavonoida izražen kao ekvivalent katehola (279,54 mg/100 g), askorbinske kiseline (112,37 mg/100 g) i pigmenata (ukupni klorofili 1,84, ukupni karotenoidi 0,36 mg/g), te najveći antioksidacijski kapacitet izražen kao ekvivalent Troloxa (35,47 µmol/g) zabilježeni su u uzorcima prihranjenim standardnom hranjivom otopinom, ispitanim nakon treće berbe. Novina i znanstveni doprinos. Kopriva je prvi put uzgojena u plutajućem hidroponskom sustavu s kontroliranom ishranom biljaka. Ovaj način uzgoja uz višestruke cikluse berbe je postavljen kao inovativna tehnika proizvodnje nove hrane, poboljšane nutritivne vrijednosti, koja se može konzumirati kao zeleno lisnato povrće.