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Highlights: [•] Anthocyanins bind to human serum albumin. [•] Binding constants for anthocyanins ranged from 1.08×105 to 13.16×105 M−1. [•] The effect of anthocyanin structure on the strength of binding to HSA was pH dependent. [Copyright &y& Elsevier]

Abstract: β-Casein and α-casein showed radical-scavenging activities in aqueous solution, whereas bovine serum albumin (BSA), α-lactalbumin and β-lactoglobulin showed much weaker antioxidant activity, when assessed by the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical-scavenging assay. However, β-casein and α-casein showed reduced antioxidant activity after storage at 30°C. An increase in radical-scavenging activity and a fall in fluorescence of the protein component were evident after 6h, when BSA, β-lactoglobulin or casein were mixed with EGCG, and excess EGCG was removed, indicating the formation of a complex with this protein on mixing. Storage of all the proteins with EGCG at 30°C caused an increase in the antioxidant activity of the isolated protein component after separation from excess EGCG. This showed that EGCG was reacting with the proteins and that the protein-bound catechin had antioxidant properties. The reaction of EGCG with BSA, casein and β-lactoglobulin was confirmed by the loss of fluorescence of the protein on storage, and the increase in UV absorbance between 250 and 400nm. The increase in antioxidant activity of BSA after storage with EGCG was confirmed by the ferric reducing antioxidant potential (FRAP) and the oxygen radical antioxidant capacity (ORAC) assays. [Copyright &y& Elsevier]

Whey is a by-product of cheese manufacturing and therefore investigating new applications of whey proteins will contribute towards the valorisation of whey and hence waste reduction. This study shows for the first time a detailed comparison of the effectiveness of gelatin and β-lactoglobulin (β-LG) as fining agents. Gelatin was more reactive than whey proteins to tannic acid as shown by both the astringency method (with ovalbumin as a precipitant) and the tannins determination method (with methylcellulose as a precipitant). The two proteins showed similar selectivity for polyphenols but β-LG did not remove as much catechin. The fining agent was removed completely or to a trace level after centrifugation followed by filtration which minimises its potential allergenicity. In addition, improved understanding of protein–tannin interactions was obtained by fluorescence, size measurement and isothermal titration calorimetry (ITC). Overall this study demonstrates that whey proteins have the potential of reducing astringency in red wine and can find a place in enology. [ABSTRACT FROM AUTHOR]