Spectrophotometric Method for Determination of Heat-Activated Sulfhydryl Groups of Skimmilk

Koka, M.; Mikolajcik, E.M.; Gould, I.A.

doi:10.3168/jds.s0022-0302(68)86956-5

Cited by 31 publications

(16 citation statements)

References 8 publications

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“…Overall, calculated SH levels were slightly higher than the published values (Aboshama & Hansen, 1977;Cosio, Mannino, & Buratti, 2000;Owusu-Apenten, 2005), probably due to the use of WPI instead of skim milk fractions, and to different analytical and quantification techniques being employed. Nevertheless, the results obtained indicate unmasking and activation of SH groups in whey proteins upon extended heat treatment, as observed and reported in previous studies at temperatures above 70 o C (Koka, Mikolajcik, & Gould, 1968;Owusu-Apenten, 2005;Owusu-Apenten & Chee, 2004).…”

Section: Unfolding Of Whey Proteinssupporting

confidence: 89%

Influence of moderate electric fields on gelation of whey protein isolate

et al. 2015

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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

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Section: Unfolding Of Whey Proteinssupporting

confidence: 89%

Influence of moderate electric fields on gelation of whey protein isolate

et al. 2015

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“…SH group reactions and their mechanisms have been discussed extensively by Owusu‐Apenten (2005). In contrast to our findings, Koka et al. (1968) reported that free sulphydryl group formation in skim milk followed first order reaction kinetics at 70–90 °C.…”

Section: Resultscontrasting

confidence: 88%

Formation kinetics of hydroxymethylfurfural and brown coloured compounds in goat milk during heating

Güneşer

Toklucu²,

Karagül‐Yüceer

2012

Int J of Dairy Tech

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The formation of hydroxymethylfurfural, nonenzymatic brown coloured compounds and free sulphydryl groups in goat milk was studied during heating at 75-95°C. Analysis of kinetic data suggested that formation of hydroxymethylfurfural and nonenzymatic brown coloured compounds followed zero order reaction kinetics, while formation of free sulphydryl groups during heating varied depending on heating time. A good linear correlation (r = 0.839) was found between brown coloured compounds and hydroxymethylfurfural content in milk samples during heating. Activation energies (E a ) for the formation of hydroxymethylfurfural and nonenzymatic brown coloured compounds were 96.31 and 69.79 kJ ⁄ mol, respectively.

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“…Next to the amount of free sulphidryl groups, also the quantity of total SH-groups was determined by performing the method of Koka et al (13) in the presence of urea. After reaction of the protein samples with 5,5'-dithiobis (2-nitrobenzoic acid), DTNB, proteins were removed by filtration after precipitation with ammoniumsulphate.…”

Section: Analysis Of the Gels Formedmentioning

confidence: 99%