COMPARATIVE REFERENCE VALUES OF SOMATIC CELLS, ENZYMES AND SOME BIOCHEMICAL CONSTITUENTS IN THE MILK FROM UNINFECTED MAMMARY GLANDS OF NILI-RAVI BUFFALOES, SAHIWAL AND CROSS-BRED COWS.

Abstract

Pakistan is among the top milk producing countries of the world. However, the quality control standards for milk have not as yet been established. The present study was conducted to establish the normal reference values of milk somatic cell counts (SCC), different milk enzymes and other important milk constituents in non-infected milk of Nili-Ravi buffaloes, Sahiwal and cross-bred cows. The milk samples from 30 animals (in the first two months of first to 5th lactation) of each group were collected from Livestock Experimental Station, University of Agriculture, Faisalabad and commercial dairy farms and tested for mastitis using Surf Field Mastitis test and microbiological examination and negative samples were used to establish the reference values. Milk samples were analyzed for different parameters like pH, electrical conductivity (EC), SCC, milk enzymes i.e. lacto-peroxidase (LPO), superoxide dismutase (SOD), guaiacol peroxidase (GPO), catalase (CAT), protease, amylase, α-esterase, NAGase, total phenolic contents (TPC), proteins and malondialdehyde (MDA) content and reference values were established. Total protein (81.6±2.0 mg mL-1), casein (71.4±1.2 mg mL-1), TPC (2381.6±71.85 μM mL-1), total oxidant status (TOS) (61.25±0.59 μM mL-1), protease (81.3±3.35 U/mL), CAT (97.45±4.8 U/mL), LPO (1.75±0.06 U/mL), NAGase (56.07±2.33 U/mL) and SCC (178645.83±2324.0 mL-1) were the highest in milk of crossbred cows. Whey protein (28.8±1.25 mg mL-1), GPO (110.74±8.64 U/mL), SOD (17.15±0.56 U/mL), amylase (89.44±2.51U/mL), EC (5.7±0.04) and MDA (2.27±0.07 μM mL-1) was the highest in Sahiwal cow’s milk. Total antioxidant capacity (TAC) (3.296±0.005 mM L-1) and α-esterase (361.19±13.63 U/mL) activity were the highest in milk of Nili-Ravi buffaloes. The SCC negatively correlated with TOS, TAC, Lacto-serum protein and α-esterase activity while NAGase with lacto-serum protein and amylase, therefore, their higher values can be used as indicators of good milk quality. SCC and NAGase positively correlated with TPC, CAT and LPO. As such their lower values seem to be associated with better udder health and good milk quality. GPO and SOD negatively correlated with TOS, TAC, total protein, casein and α-esterase activity but positively correlated with amylase, EC, SCC, MDA and lacto-serum protein therefore, their lower values in milk may be desirable. Milk quality of Nili-Ravi was comparatively superior based on lower values of SCC, EC, NAGase, CAT, GPO, SOD, TPC, protease and higher TAC. Protein profiling through SDS-PAGE clearly resolved the major milk peptides. In high molecular weight (M. wt.) zone, proteins of ~208 kDa and ~190 kDa were detected in all tested samples. In medium M. wt. zone, three peptides i.e. lactoferrin (78.2kDa), serum albumin (66.2kDa) and heavy chain of immunoglobulin (IgG) (54 kDa) were detected in all samples while a prominent band of ovalbumin (45kDa) was also detected mainly in cow milk samples. In low M. wt. zone, clear bands of milk caseins were detected. All four casein (CN) bands i.e. αS2 – CN (29 kDa), αS1 – CN (27 kDa), β - CN (24 kDa) and κ- CN (22 kDa) were detected in Sahiwal and cross-bred cows. However, in milk of Nili-Ravi buffaloes, three casein protein i.e. αS2 – CN (29 kDa), β - CN (25 kDa) and κ- CN (22 kDa) were detected. In milk of Nili-Ravi buffaloes, αS1 – CN (27 kDa) was not detected. Moreover, a band of β-lactoglobulin (~18 kDa) was detected in milk of cross-bred cows and not in other samples especially those of Nili-Ravi buffaloes. As the αS1-casein and β-lactoglobulin are the major allergens, milk of Nili- Ravi buffaloes that lacks these peptides can be used for development of hypoallergenic or non-allergic dairy products. Deferential peptides may also help to differentiate the milk from different tested dairy species/cow types.