Título da Tese:Produção e caracterização de xilooligossacarídeos antioxidantes obtidos de resíduos de pupunheira

Orientadora: Profa. Dra. Rosane Marina Peralta

Data da Defesa:01/03/2021


INTRODUCTION AND AIMS: Antioxidants are natural or synthetic substances that can prevent or delay, on a substrate, oxidative cell damage caused by physiological oxidants. Research carried out recently in the field of natural antioxidants has considerably expanded the knowledge on naturally occurring compounds with beneficial health effects in foods, among which oligosaccharides can be highlighted. These are of considerable interest due to their physicochemical and biological properties, especially as antioxidants, antimicrobials and prebiotics. Oligosaccharides can be found naturally in some foods or produced from the depolymerization of polysaccharides, such as xylans, from which xylooligosaccharides (XOS) are produced via hydrolysis. Xylans can be extracted from lignocellulosic materials through several kinds of pre-treatments. In Brazil, the production and consumption of palm heart (palmito), especially from the Bactris gasipaes Kunth species, generate a large amount of lignocellulosic by-products. It is known that approximately 37% of the volume of all the plant matter that arrives at the industry ends as waste generated during the processing of palm hearts. Taking into account these informations, this work has two main purposes. The first one is based on published research and aims at providing an up-to-date, broad and critical review on the topic of antioxidant oligosaccharides. The second purpose is of experimental nature and consists in a study aiming at adding value to the peach palm residues through the production of xylooligosaccharides. Besides determining its structural features, the production of the xylooligosaccharides will be accompanied by an investigation of its antioxidant properties, which can be regarded as indicators of its possible health beneficial properties.
MATERIAL AND METHODS: For the review article, a search, using the words oligosaccharides and antioxidants, was conducted for recent studies trying to establish, whenever possible, correlations between chemical structure and antioxidant activity. Consideration was given to both in vitro and in vivo methods in animals and humans. For the experimental study, peach palm wastes (inner sheath and peel) were used, kindly donated by Embrapa Florestas, Colombo - PR. An alkaline extraction (NaOH, 8%) was performed to obtain xylans, which were characterized by techniques of Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy.
From the extracted xylans, xylooligosaccharides were produced via enzymatic hydrolysis, using a commercially available endoxylanase (1.25 U.mL-1) from Aspergillus oryzae. In parallel, XOS were produced from commercial xylans (beechwood, birchwood, oat spelt), for comparative purposes. The XOS yield was measured using the gravimetric method and evaluation of reducing sugar contents by the DNS method, in addition to their detection by thin layer chromatography. The antioxidant potential of the XOS were evaluated employing in vitro assays: TPC, FRAP, ORAC, scavenging of hydroxyl radicals and DPPH. Finally, the XOS were characterized by mass spectrometry (ESI-MS). All data were submitted to ANOVA with a Student-Newman-Keuls post hoc test, using the GraphPad Prism software (version 8.0).
RESULTS AND DISCUSSION: According to the survey conducted, it was noted that the oligosaccharides most studied to date include chitooligosaccharides, xylooligosaccharides, and their derivatives. The avaliable data reveal that the antioxidant activities of oligosaccharides depend on several factors, such as degree of polymerization, the method used for depolymerization, solubility, monosaccharide composition, the type of glycosidic bonds of the side chains, molecular weight, the content of reducing sugar, and the presence of phenolic groups such as ferulic acid and uronic acid, among others. Besides, the addition of organic groups to the structures of oligosaccharides allows to modify the antioxidant capacity of these compounds, increasing the spectrum of potentially useful molecules. For the experimental study, xylans from peach palm inner sheath and peel were extracted using an alkaline treatment and yields of 82% and 80% were achieved, respectively. The XOS obtained through enzymatic hydrolysis showed yields of 50.1% and 48.8%, for the inner sheath and peel xylans, respectively. The antioxidant potentials of XOS were evaluated by five in vitro assays and, in overall terms, the XOS of the xylans from the peach palm wastes, peel especially, showed higher antioxidant potential when compared to the XOS obtained from commercial xylans. The ESI-MS spectra suggest XOS with grouped xylose or arabinose units ranging from 2 to 5 (differing by 132 Da) and as sodium adduct ions [M + Na]+ in the range of 100-1000 m/z.
CONCLUSIONS: From the literature review it can be concluded that the large-scale production of antioxidant oligosaccharides is still a challenge for food science and technology. However, several methods have recently been developed, modified, and adapted to optimize the production of different oligosaccharides. Besides, a great amount of high-quality evidence has been accumulated during the last decade in support of meaningful antioxidant activity of oligosaccharides and derivatives. This suggests that the ingestion of antioxidant oligosaccharides can be viewed as beneficial to human and animal health. Regarding the capacity of free radical scavenging, in general, the XOS obtained from the xylans of the peach palm wastes showed higher antioxidant capacity than the XOS obtained from the three commercial xylans. These results suggest that the peach palm wastes can be explored for the production of XOS, which could be applied as natural antioxidants in functional foods and pharmaceutical preparations. It is worth to emphasize that this application, by being linked to the bio-based economy, will certainly fit well into the biocircular economy concept.
Key words: antioxidant, oligosaccharides, Bactris gasipaes Kunth, waste recovery, circular economy.  

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