Determination of the composition of carbohydrate fraction in secondary plant raw materials

U kontekstu rastućeg trenda iskorištavanja otpadne biljne biomase, u novije vrijeme se, posebice u industriji funkcionalne hrane, ističe potencijal složenih ugljikohidrata iz sekundarnih biljnih sirovina za proizvodnju funkcionalnih ugljikohidratnih frakcija, kao što su oligosaharidi s prebiotičkim svojstvima. Stoga je cilj ovoga rada bio odrediti sastav ugljikohidratne frakcije šest sekundarnih biljnih sirovina - pulpe šećerne repe, ljuske oraha, ljuske kakaovog zrna, ljuske crvenog luka, kore krumpira te mahune graška. Razvojem odgovarajuće analitičke metodologije u sekundarnim biljnim sirovinama određen je udjel sirove ugljikohidratne frakcije te udjel i sastav strukturnih polisaharida na temelju provedene karakterizacije sirove ugljikohidratne frakcije. Analiza makrokomponenata pokazala je dominantan udjel ugljikohidratne frakcije u suhoj tvari svih sirovina. Nestrukturni ugljikohidrati (glukoza, fruktoza, saharoza) određeni su u rasponu udjela suhe tvari od 0,12% (ljuska kakaovog zrna) do 10,38% (mahuna graška). Strukturni ugljikohidrati činili su većinu ugljikohidratne frakcije te su određeni kao topljiva i netopljiva vlakna. Korekcijom istih za udjel lignina određen je udjel strukturnih polisaharida, koji je iznosio 41,89 - 66,17% s.tv., ovisno o sirovini. HPLC analizom hidrolizata strukturnih ugljikohidrata, uz prethodnu PMP derivatizaciju, definiran je profil monosaharida za svaku sirovinu. Predložena metodologija i dobiveni rezultati ovoga rada omogućit će bolje planiranje daljnjih postupaka s ciljem izdvajanja i ponovnog korištenja ugljikohidratnih frakcija iz različitih sekundarnih biljnih sirovina.In recent years, within the context of the growing trend of waste plant biomass reutilization, the potential of complex carbohydrates from secondary raw materials stands out, proposing the latter as novel ingredients, such as functional prebiotic oligosaccharides, for the functional food industry. Therefore, the aim of this study was to determine the composition of the carbohydrate fraction of the six secondary plant raw materials - sugar beet pulp, walnut shell, cocoa bean husk, onion peel, potato peel and pea pod. With the development of a reliable analytical methodology it was possible to determine content of carbohydrates in the dry matter of all samples and also content and composition of structural polysaccharides of all samples based on the characterization of the carbohydrate fraction. Analysis of macrocomponents reveiled dominant content of carbohydrates in the dry matter of all samples. Non-structural carbohydrates (glucose, fructose, sucrose) were determined in the range of 0.12% (cocoa husk) to 10.38% (pea pod). Structural carbohydrates, which were determined by means of soluble and insoluble dietary fiber content, accounted for most of the carbohydrate fraction. Correction of the latter for lignin content enabled determination of the content of structural polysaccharides, which ranged from 41,89 to 66,17% on dry matter basis, depending on the material. HPLC analysis of the hydrolysates of structural polysaccharides, with pre-column PMP derivatization, resulted in distinguishing monomeric profiles for each raw material. The proposed methodology as well as the results of this work will allow better planning of further activities aimed at recovery and reutilisation of carbohydrate fractions of different secondary plant raw materials