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Valorization of brewers’ spent grain and spent yeast through protein hydrolysates with antioxidant properties

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Abstract

Brewers’ spent grain (BSG) and spent yeast (BSY) are the main by-products of the brewing industry, with currently limited valuable applications. However, BSG protein fraction can be a valuable substrate for enzymatic hydrolysis to produce hydrolysates with biological properties and BSY contains numerous vacuole proteases, which can be used to obtain these hydrolysates. Thus, the objective of this work was to explore the valorization of these two brewing by-products, based on the production of BSG protein hydrolysates that present antioxidant properties. Response surface methodology was employed to optimize the hydrolysis of BSG proteins using BSY proteases, based on degree of hydrolysis (DH %), total phenolic content (TPC) and antioxidant activity (FRAP assay). Reversed-phase chromatography was also used to monitor the hydrolysis rate (HR %), and the potential presence of endogenous and other inhibitors of BSY proteases was also investigated. BSG protein hydrolysate prepared at 50 °C, pH 6, for 6 h and using an enzyme/substrate ratio of 0.29:1 U/mg presented maximum bioactivity with DH % of 17.10 %, TPC of 1.65 mg GAE/mL and FRAP value of 1.88 mg Trolox equivalent/mL. A good correlation was obtained between HR (%) and DH (%) (R 2 = 0.928). The experimental values agreed with the predicted values (p < 0.05), suggesting a good fit between the models and the experimental data. BSY proteases involved in the hydrolysis of BSG proteins are serine peptidases and metallopeptidases.

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Acknowledgments

This work received financial support from project UID/QUI/50006/2013-POCI/01/0145/FEDER/007265 with financial support from FCT/MEC through national funds and co-financed by FEDER, under the Partnership Agreement PT2020. One of the authors (E. F. Vieira) wishes to thank the FCT Grant SFRH/BD/81845/2011. To all financing sources, the authors are greatly indebted.

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    Authors and Affiliations

    1. LAQV/REQUIMTE, Laboratório de Bromatologia e Hidrologia, Departamento de Ciências Químicas, Faculdade de Farmácia, Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal

      Elsa Vieira, Juliana Teixeira & Isabel M. P. L. V. O. Ferreira

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    1. Elsa Vieira
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    2. Juliana Teixeira
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    3. Isabel M. P. L. V. O. Ferreira
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    Correspondence to Isabel M. P. L. V. O. Ferreira.

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    This article does not contain any studies with human or animal subjects.

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    Elsa Vieira and Juliana Teixeira have contributed equally to this experimental work.

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    Vieira, E., Teixeira, J. & Ferreira, I.M.P.L.V.O. Valorization of brewers’ spent grain and spent yeast through protein hydrolysates with antioxidant properties. Eur Food Res Technol 242, 1975–1984 (2016). https://doi.org/10.1007/s00217-016-2696-y

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    • DOI: https://doi.org/10.1007/s00217-016-2696-y

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