Characterization of the composition of selected secondary plant raw materials: Implementation of bioactive banana peel extract in edible film formulations

Budući da se agro-industrijski otpad sve više pokušava iskoristiti kao izvor bioaktivnih sastojaka za funkcionalne prehrambene proizvode, cilj ovoga rada bio je analizirati osnovni kemijski i bioaktivni sastav šest sekundarnih biljnih sirovina (kore banane i cikle, ljuske kakaovog zrna, crvenog luka i oraha te mahuna graška), a s korom banane je provedena detaljnija karakterizacija i bioaktivni ekstrakt je primijenjen u formuliranju funkcionanih jestivih filmova, uz alginat i pektin kao nosače. Ekstrakcije sirovina provedene su sa 70 %-tnim etanolom, dok je za koru banane pripremljen i vodeni ekstrakt. Karakterizacija osnovnog sastava (udjel proteina, masti, mineralnih tvari, prirodnog i ukupnog inverta te ukupnih vlakana) provedena je primjenom standardne analitičke metodologije, dok je bioaktivni sastav (ukupni polifenoli, flavonoidi i neflavonoidi, flavoni i flavonoli, flavan-3-oli, hidroksicimetne kiseline, proantocijaidini, antioksidacijski kapacitet, antocijani, karotenoidi, klorofili) određen spektrofotometrijskim metodama. Među analiziranim sirovinama, kora banane se istaknula višim udjelom prirodnog inverta, saharoze i makroelemenata, ljuska oraha udjelom prehrambenih vlakana i proantocijanidina, ljuska crvenog luka udjelom mikroelemenata, ukupnih polifenola, flavona i flavonola, hidroksicimetnih kiselina i višim antioksidacijskim kapacitetom, dok je ljuska kakaovog zrna imala viši udjel flavan-3-ola. Od pigmenata u svim sirovinama najzastupljeniji je bio klorofil b. U odnosu na kontrolni jestivi film, pripremljen s vodom, filmovi pripremljeni s vodenim ekstraktom kore banane bili su deblji i tamniji, s jačim intenzitetom žute boje. Među pripremljenim filmovima, najveći udjel ukupnih polifenola, antioksidacijki kapacitet te profil otpuštanja istih, pokazao je funkcionalni jestivi film pripremljen lijevanjem ekstrakta kore banane s pektinom preko sloja s aginatom. Prema dobivenim rezultatima sve ispitivane sirovine predstavljaju vrijedne izvore nutritivnih i bioaktivnih sastojaka otvarajući brojne mogućnosti njihove implementacije u razvoju različitih prehrambenih proizvoda s dodanom vrijednošću.Since agro-industrial waste is increasingly tried to be used as a source of bioactive ingredients for functional food products, the aim of this paper was to analyze the basic chemical and bioactive composition of six secondary plant raw materials (banana and beetroot peels, cocoa and walnut shells, red onion skin and pea pod), with a more detailed characterization of the banana peel and its bioactive extract was applied in the formulation of functional edible films, with alginate and pectin as carriers. Raw material extractions were carried out with 70 % ethanol, while an aqueous extract was prepared for the banana peel. Characterization of the basic composition (content of proteins, fats, minerals, natural and total invert and total fibers) was performed using standard analytical methodology, while the bioactive composition (total polyphenols, flavonoids and neflavonoids, flavones and flavonols, flavan-3-ols, hydroxycinnamic acids, proanthocyanidins, antioxidant capacity, anthocyanins, carotenoids, chlorophyll) determined by spectrophotometric methods. Among the analyzed raw materials, the banana peel was distinguished by a higher content of natural invert, sucrose and macroelements, walnut shells by dietary fiber and proanthocyanidins, red onion skin by microelements, total polyphenols, flavones and flavonols, hydroxycinnamic acids and higher antioxidation while cocoa shells had a higher content of flavan-3-ol. Of the pigments in all raw materials, the most prevalent was chlorophyll b. Compared to the control edible film, prepared with water, the films prepared with aqueous banana peel were thicker and darker, with a stronger intensity of yellow. Among the prepared films, the highest proportion of total polyphenols, antioxidant capacity and release profile of these were shown by a functional edible film prepared by solvent casting a banana peel extract with pectin over an aginate layer. According to the obtained results, all tested raw materials represent valuable sources of nutritional and bioactive ingredients, opening up numerous possibilities for their implementation in the development of various value-added food products