Influence of moderate electric fields on gelation of whey protein isolate

Abstract

Proteins are one of the food constituents most affected by heating, and some of the changes involve their unfolding, denaturation and gelation. Ohmic heating has often been claimed to improve the quality of foodstuffs due to its uniform heating and (putative) presence of a moderate electric field (MEF). However, this is still subject to discussion, so it is important to determine the effect of ohmic heating and of its MEF upon food constituents. Hence, the aim of this work was to evaluate the effects of MEF on denaturation, aggregation and viscoelastic properties of whey protein isolate (WPI), and compare them with those obtained via conventional heating under identical treatment conditions (up to 30 min at 85 o C). Results have shown that MEF interferes with whey protein unfolding and aggregation pathways at relatively high temperatures. MEF treatments have resulted in WPI solutions possessing more 8 and 10% of native Lactoglobulin and Lactalbumin, respectively, after 30 s of heating at 85 o C, when compared with a conventional heating method. Protein aggregates from MEF-treated WPI solutions presented a maximum increase in size of 78 nm, whereas conventional heating produced an increase of 86 nm. Unlike in conventional heating, aggregation of whey proteins during MEF was not sufficiently strong to form a true elastic gel network, since decreases in both storage and loss modulus were observed following MEF treatment. Our results suggest that MEF may provide a novel method for production of a whey protein matrix with distinctive gel-forming properties.2

Design of whey protein nanostructures for incorporation and release of nutraceutical compounds in food

“…Application of MEF for manufacture of WPI nanostructures has been recently reported Rodrigues et al, 2015). In agreement with these studies, MEF caused a smaller increase of whey protein's aggregate size.…”

Production of Whey Protein-Based Aggregates Under Ohmic Heating

“…In accordance with information provided by the supplier, WPI powder was essentially free of fat (max 0.2 %) and lactose (max 0.5 %). Protein composition, determined by reversed-phase highperformance liquid chromatography (RH-HPLC) as described elsewhere (Rodrigues et al 2015), was as follows: α-lactalbumin (α-lac) 22.8 %, bovine serum albumin (BSA) 1.7 %, β-lgA 44 %, β-lgB 30.7 %, and immunoglobulins (IG) 1.1 %, on a protein basis. All chemicals used were of analytical grade.…”

“…Apparent whey protein solubility was followed by means of a soluble tryptophan fluorescence value on the pH 4.6 soluble supernatant, as described before (Pereira et al 2011;Rodrigues et al 2015). Samples (1 mL) from heated and un-heated (control) solutions were adjusted to pH 4.6 to precipitate denatured whey proteins, via the addition of 1.0 mL of a 1:1 mixture of 0.83 mol L −1 acetic acid and 0.2 mol L −1 sodium acetate.…”

“…During ohmic heating, a moderate and alternating electric current passes through the product to be heated, which behaves as a resistor in an electrical circuit, allowing generation of internal heat in accordance with Joule's law (De Alwis and Fryer 1990). Ohmic heating seems to offer a great potential for modulation of WPI micro-and nano-hydrogels' properties, as well as development of water-soluble controlled delivery targeted for nutraceutical and functional food compounds (Rodrigues et al 2015). However, only a few scientific and technical reports have focused on the effects of this technology upon whey ingredients or enriched fractions of β-lg, which is the most susceptible whey protein to heat treatments during thermal pasteurization or sterilization (Rodrigues et al 2015).…”

“…Ohmic heating seems to offer a great potential for modulation of WPI micro-and nano-hydrogels' properties, as well as development of water-soluble controlled delivery targeted for nutraceutical and functional food compounds (Rodrigues et al 2015). However, only a few scientific and technical reports have focused on the effects of this technology upon whey ingredients or enriched fractions of β-lg, which is the most susceptible whey protein to heat treatments during thermal pasteurization or sterilization (Rodrigues et al 2015). The ability that ohmic heating has in providing a fast and uniform heating, together with its inherent electrical effects, should be exploited seeking processed whey protein products of high quality and distinctive technological functionalities.…”