Quantification of Casein Fractions and of Some of Their Genetic Variants in Phosphate Buffer by near Infrared Spectroscopy

Abstract

Milk casein and casein fraction contents have a great influence on milk rennet properties and cheese yield so that the selection of dairy cattle with genetic characteristics suitable for milk transformation is of great interest to dairy farms and firms. The possibility of a rapid and accurate determination of these parameters would be very useful to predict milk aptitude to cheese making. This work aimed to determine casein fractions and their genetic variants content using near infrared (NIR) spectroscopy in reconstituted casein samples by comparing the performance of different NIR equipment (a monochromator instrument and a Fourier transform instrument) and different modes of measurement (reflectance and transflectance) in order to evaluate the best operative conditions for this application. Fifty-eight raw milk samples, collected from different farms in the Asturias region, Spain, were analysed for protein (TP%) and non caseinic nitrogen (NCN%) content using the Kjeldahl method. Casein content was calculated as the difference between TP and NCN content. Casein fractions (a s0 -, a s1 -, a s2 -, k-casein) and genetic variants of b-casein (bB-bA1-, bA2-casein) were determined by a capillary electrophoresis system. Samples were ultra-centrifuged to obtain native casein and then reconstituted in phosphate buffer (pH = 6.8) at the same original milk concentration, previously determined by the Kjeldahl method. Spectra were collected at 37°C with a FT-NIR instrument in transflectance mode and a monochrometer in both transflectance and reflectance mode. Partial least square (PLS) analyses performed on transflectance spectra showed good prediction ability for all variables-(min R 2 = 0.80 for k-casein; max R 2 = 0.94 for bA2-casein), with the exception of a s2 -casein. NIR spectroscopy has the ability to determine and quantify casein genetic variants and could be used to select milk for its final purpose and to predict the aptitude of milk to cheese-making.

Review of near-infrared spectroscopy as a process analytical technology for real-time product monitoring in dairy processing

“…Validation of the sensor at industrial level is currently under investigation. Another application of NIR spectroscopy in terms of cheese manufacturing was quantification of casein fractions and their genetic variants in reconstituted casein samples (Marinoni, Monti, Barzaghi, & de la Roza-Delgado, 2013).…”

New Applications of near Infrared Spectroscopy on Dairy Products

“…Marinoni et al 12 contributed to this special issue with a paper focused on the ability of NIR spectroscopy to determine casein fractions and genetic variants. They compared the performance of different NIR instruments and sample presentation modes.…”

Amaltheys: A fluorescence-based analyzer to assess cheese milk denatured whey proteins

“…The 1-anilino-8-naphtalene sulfonate technique provides a relative but quick estimation of DWP by measuring surface hydrophobicity of the proteins (Bonomi et al, 1988;Saulnier et al, 1991). For 15 yr, very few NIR-based prediction models have been developed for assessment of specific protein fractions in milk; some calibrations over casein content have been successful on cow raw milks (Laporte and Paquin, 1999;Jankovska and Sustova, 2003), goat raw milks (Drackova et al, 2008), or reconstituted casein solutions (Marinoni et al, 2013). Overall, they do not seem to provide reliable assessment in milk samples of different compositions (Pouliot et al, 1997) and thermally processed.…”