Effect of bleaching with different agents on protein hydrolysate characteristics

Abstract

High temperatures can reduce the phenolic content of grapes, especially anthocyanins and copigments involved in colour stabilisation of red wines [1]. This could make it difficult to maintain stable colour during storage [2]. To address this, protein hydrolysates added to red wines during the stabilisation process could preserve colour by forming a protective protein-phenolic complex [3]. However, protein hydrolysates exhibit a brown tonality, which may not be ideal as a colour stabiliser in wine due to the possible undesirable coloration. This study evaluates the effect of different bleaching agents on protein hydrolysate characteristics. The colour has been determined by CIELAB colorimetric parameters (L*, C*_ab, h_ab), the antioxidant activity by DPPH and ABTS, and the protein content by Kjeldahl. First, the defatted grape seed meal was dephenolised to remove phenolic compounds and discard their influence on the colour of the hydrolysates. The hydrolysate from enzymatic hydrolysis was subjected to bleaching using activated carbon (1 g/L, 5 g/L), PVPP (30 g/hL, 150 g/hL), and resin (25%, 50%). It was observed that protein hydrolysates submitted to a higher concentration of each bleaching agent presented a higher colour reduction. In terms of colour, all samples exhibited brown tonalities (h_ab, 62-78), except those treated with the combination of 50% resin:5 g/L activated carbon, which displayed the yellowish one (h_ab, 84). The lightest samples were those treated with 50% resin (L*, 63), while the use of 150 g/hL PVPP led to darkest samples (L*, 30), even more than the control (without bleaching). Additionally, the samples treated with the combination of 50% resin:5 g/L activated carbon, exhibited the lowest chroma value (C*_ab, 12), resulting in a more greyish appearance, which makes it more suitable for not imparting colour to the wine. In addition, protein percentage did not show a significantly (p > 0.05) reduction in the treated samples, except for 50% resin and the combination of 50% resin:5 g/L activated carbon, which showed around 20% of reduction. However, the antioxidant activity, by both DPPH and ABTS methods, of almost all samples displayed a significant (p < 0.05) decrease, even more for the combination of 50% resin:5 g/L activated carbon and 50% resin. In conclusion, the 50 % resin and its combination with 5 g/L activated carbon proved to be the most effective in terms of colour reduction, and although the antioxidant activity and protein percentage decrease, the values are considered acceptable compared to the loss of colour involved.

Acknowledgement

Alvinesa Natural Ingredients, S.A. (Daimiel, Ciudad Real, España), and Agrovin (Alcázar de San Juan, Ciudad Real, España).

Funding

PID2021-127126OB-C22 y PID2021-124964OB-C22 del Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033 y “ERDF A way of making Europe”.

References

[1] Boulton, R. (2001). AJEV, 52, 67-87.

[2] Cejudo-Bastante, M. J., Rivero Granados, F. J., & Heredia, F. J. (2017). Eur. Food Res. Technol. 243, 575-582.

[3] Mora-Garrido, A. B., Escudero-Gilete, M. L., Heredia, F. J., & Cejudo-Bastante, M. J. (2024). Cogent Food Agric. 10, 2314231.