ANALySIS OF EWE’S MILK By FT NEAR INFRARED SPECTROSCOPy: MEASUREMENT OF SAMPLES ON PETRI DISHES IN REFLECTANCE MODE

ŠUSTOVá, K., KUCHTíK, j., KRáČMAR, S.: Analysis of ewe’s milk by FT Near Infrared spectroscopy: measurement of samples on Petri dishes in reflectance mode. Acta univ. agric. et silvic. Mendel. Brun., 2006, LIV, No. 2, pp. 131–138 Our work deals with a possibility of determination of basic composition (dry matter, fat, protein, casein, lactose and urea nitrogen) of ewe’s milk and colostrum by FT NIR spectroscopy. Samples of milk were warmed to 40 °C, agitated, cooled to 20 °C, transferred into Petri dishes and analysed by reference methods and by FT NIR in reflectance mode. The measured area was spaced by a metallic mirror. Statistically significant differences between the reference values and the calculated values of NIR were not found (p=0.05). Results of calibration for ewe’s milk determined the highest correlation coefficients: dry matter 0.983, fat 0.989, true protein 0.997, casein 0.977, lactose 0.980 and urea nitrogen 0.973. The study showed that NIRS method, when samples of milk are measured on Petri dishes, is a useful technique for the prediction of dry matter, fat, protein and casein in ewe’s milk. near-infrared spectroscopy, ewe’s milk, dry matter, fat, protein, lactose, chemical composition There are many factors which shape a quality of ewe’s milk. In general, the composition of milk changes significantly due to the action of many factors in the course of whole lactation, (jELíNEK et al., 1991; ŽIŽLAVSKý et al., 1989; KRáČMAR et al., 1998; ANTUNOVIČ et al., 2001; gAjDůŠEK et al., 2003). Traditional methods of the estimation of quality of milk and its major components (Kjeldahl method, gerber method) are relatively slow and rather expensive. The Milko-Scan is used as an instrumental method for cow ́s milk analysis (O’SULLIVAN et al., 1999). NIR spectroscopy of foodstuffs is one of the new analytical methods. It has numerous advantages, e.g. rapidity, non-destructive sample analysis and, especially, a great potential for on-line analysis (RU & gLATZ, 2000; ALBANELL et al., 2003). FT NIR method has been used to measure the content of various constituents in homogenised cow milk (SATO et al., 1987; RODRIgUEZ-OTERO, HERMIDA & CENTENO, 1997; RU & gLATZ, 2000; ŠAŠIČ & OZAKI, 2001). A few authors have reported analysis of non-homogenised milk samples (CHEN, IyO & KAWANO, 1999; LAPORTE & PAQUIN, 1999). TSENKOVA et al., 1999; TSENKOVA et al., 2000 and TSENKOVA, ATANASSOVA, & TOyODA, 2001) determined the highest positive coefficients for fat, lactose and crude protein in non-homogenised milk. KUKAČKOVá, ČURDA & jINDřICH, 2000 and TURZA et al., 2002 evaluated the total solids, fat and protein in raw milk using a fibre optic probe. jANKOVSKá & ŠUSTOVá, 2003 determined the major components (total solids, fat, protein, casein, urea nitrogen, lactose, and somatic cells) in non-homogenised cow milk by reflectance mode on the Petri dishes. Few applications of NIRs techniques for analysis of goat’s milk (ALBANELL et al., 2003) and ewe’s milk have been reported. 132 K. Šustová, J. Kuchtík, S. Kráčmar The objective of our experiments was to determine contents of basic components of ewe’s milk using the FT NIR method, when samples of milk are measured on Petri dishes. Our attention was paid mainly to determination of dry matter, fat, protein, casein, urea nitrogen and lactose. MATERIALS AND METHODS Materials and reference values Ewe’s milk samples were taken during the lactation. Experimental animals did not show any health problems during the whole study period. Following data were obtained by a reference method: dry matter (DM) gravimetrically method, by oven drying at 102 ± 2 °C to constant weight (ČSN ISO 6731). Total nitrogen (TN) was assessed according to Kjeldahl method using Kjeltec Auto 1031 Analyzer, Foss Tecator, Sweden (MARSHALL, 1992) and crude protein (CP) was calculated as N x factor of 6.38. True protein (TP) were determined spectrophotometrically the apparatus Pro-Milk II, Foss Electric, Denmark. Fat (F) was determined by gerber method (ČSN ISO 2446). Lactose (L) was determined polarimetrically as monohydrate (CVAK, PETERKOVá & ČERNá; 1992). Urea nitrogen (UN) was analysed by method of gAjDůŠEK, jELíNEK & HAMPL; 1996. All measurements were made in duplicate.