Production of whey protein-based aggregates under ohmic heating

Formation of whey protein isolate protein aggregates under the influence of moderate electric fields upon ohmic heating (OH) has been monitored through evaluation of molecular protein unfolding, loss of its solubility, and aggregation. To shed more light on the microstructure of the protein aggregates produced by OH, samples were assayed by transmission electron microscopy (TEM). Results show that during early steps of an OH thermal treatment, aggregation of whey proteins can be reduced with a concomitant reduction of the heating chargeby reducing the come-up time (CUT) needed to reach a target temperatureand increase of the electric field applied (from 6 to 12 V cm1). Exposure of reactive free thiol groups involved in molecular unfolding of -lactoglobulin (-lg) can be reduced from 10 to 20 %, when a CUT of 10 s is combined with an electric field of 12 V cm1. Kinetic and multivariate analysis evidenced that the presence of an electric field during heating contributes to a change in the amplitude of aggregation, as well as in the shape of the produced aggregates. TEM discloses the appearance of small fibrillar aggregates upon the influence of OH, which have recognized potential in the functionalization of food protein networks. This study demonstrated that OH technology can be used to tailor denaturation and aggregation behavior of whey proteins due to the presence of a constant electric field together with the ability to provide a very fast heating, thus overcoming heat transfer limitations that naturally occur during conventional thermal treatments.

The authors thank the Portuguese Foundation for Science and Technology (FCT) strategic project UID/BIO/04469/2013 unit, the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124FEDER-027462), and the project BBioInd - Biotechnology and Bioengineering for improved Industrial and Agro-Food processes^ REF. NORTE-07-0124-FEDER-000028 co-funded by the Programa Operacional Regional do Norte(ON.2–O Novo Norte), QREN, FEDER. The authors would like to acknowledge Rui Fernandes from the Institute for Molecular and Cell Biology (IBMC), University of Porto, for the assistance in taking the TEM pictures. The authors Ricardo N. Pereira and Oscar L. Ramos also acknowledge FCT for their post-doctoral grants with references SFRH/BPD/81887/2011 and SFRH/BPD/80766/2011, respectively.