Orientadora: Profª Drª Paula Toshimi Matumoto Pintro

Data da Defesa: 30/03/2022


Barley straw is an agroindustrial residue of low added value, being the focus of studies that seek to reuse this material through chemical pretreatments to increase the availability of structural carbohydrates for the production of bioethanol or animal feed. However, these pretreatments are expensive and generate chemical residues. Barley straw is a lignocellulosic material consisting mainly of cellulose, hemicellulose and lignin, with lignin being a barrier that influences the access of enzymes to structural carbohydrates, hindering the release of reducing sugars to be fermented and transformed into alcohol. Beer adjuncts are increasingly used to partially replace malt, aiming to reduce the production cost and incorporate different characteristics to beer, seeking more accessible ingredients that add functional value to the final product.
AIMS. The objective of this study was to evaluate the influence of two methods of lignin inhibitor application in barley field, being via soil or foliar, aiming the use of pretreated straw as a brewing adjunct. The effects of treatments on the structure and application of this straw were analyzed when inserted into the wort with the addition of xylanase and cellulase, in order to increase the release of fermentable sugars and bioactive compounds in beer.
MATERIAL AND METHODS. Two methods (soil and foliar) of field application of the lignin inhibitor in barley cultivation were realized, verifying the parameters of harvest productivity and also analysis of the pretreated barley straw, determining the straw chemical composition, quantification of lignin and enzymatic saccharification with the enzymes xylanase and cellulase. To observe changes in the collected straw structure more specifically, FTIR (Fourier Transform Infrared) and SEM (Scanning Electron Microscopy) experiments were performed. Worts were produced with 2.5%, 5% and 10% proportions of partial malt replacement by barley straw and with different concentrations of xylanase and cellulase enzymes, determining the best concentrations of straw and enzymes in wort through the method of reducing sugars quantification (DNS). Selected worts were analyzed considering parameters of proteins, total polyphenols (TPC), antioxidant activity (DPPH and ABTS), color and pH, being selected those that obtained the best parameters for beer production and evaluation of the total polyphenols and antioxidant activity behavior during storage for 28 days at 4 °C.
RESULTS AND DISCUSSION. Lignin inhibitor applications via soil and foliar in the field did not influence barley productivity, making this pretreatment viable. SEM, FTIR and enzymatic saccharification analyzes showed that treatments with the lignin inhibitor caused structural alterations and changes in the chemical composition of barley straw, resulting in greater enzymatic accessibility to structural carbohydrates, with higher release of reducing sugars using cellulase. Straws obtained with the two application methods showed increases in fermentable sugars release when inserted in wort with 2.5% of barley straw, using cellulase isolated or a xylanase and cellulase mixture in 1:2 proportion, maintaining the final enzyme concentration of 16 U mL-1. Worts with these concentrations of pretreated straw and enzymes had increases mainly in the quantification of total polyphenols and antioxidant activity. After fermentation of worts, beer showed stability of these bioactive compounds during storage analysis, demonstrating that barley straw pretreated with lignin inhibitor combined with enzymes is capable of increasing the functional value of the beer produced from these worts.
CONCLUSIONS. Barley straw pretreated with lignin inhibitor applied via soil or foliar is capable of being used as a brewing adjunct combined with cell wall hydrolytic enzymes to partially replace malt, acting mainly in increasing the release of fermentable sugars and bioactive compounds in brewer's wort.
Key words: piperonylic acid; fermentable sugars; functional beer; bioactive compounds; cellulase; cell wall

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