Research And Practice: Quantification Of Raw And Heat-Treated Cow Milk in Sheep Milk, Cheese And Bryndza By ELISA Method

Lucia Zeleňáková,Peter Zajác,Margita Čanigová,Radoslav Židek,Jana Žiarovská,Lenka Maršálková,Martina Fikselová,Jozef Golian

doi:10.5219/566

Abstract

The aim of this study was to test the reliability of commercial ELISA tests (RC-bovino) within raw and heat treated cow milk detection in sheep milk and cheese in order to obtain a high-quality, reliable and economically beneficial method suitable for routine application in practice. These tests were subsequently used for quantification of cow milk in commercial "Bryndza". Raw sheep milk, cow milk and heat-treated cow milk (pasteurisation at 72 °C for 15 sec or at 85 °C for 3 sec) were mixed in precisely defined proportions (0 - 100% cow milk in sheep milk). The milk mixtures were sampled to detect adulteration and subsequently cheese was made. By ELISA tests was possible to determine these amounts of raw cow milk in sheep milk: 0.5% (0.2%), 5 % (4.81%), 50% (42.08%) and 75% (56.52%). The pasteurized samples in different combinations gave lower optical density responses than those prepared from raw milk (by approximately 60%). In context with the above mentioned, the relationship between the real and detected amount of cow milk (%) in different production stages (milk, cheese) using a regression analysis was examined. However, a lower reliability of the detection was indicated by R2 values, which ranged from 0.4058 (cheese) to 0.5175 (milk). In practice this means that although individual percentage (%) of cow milk in the sample can be detected, but in the unknown sample it can not be clearly confirm whether the cow milk was raw or heat-treated. In this context, the results can be inaccurate and may not correspond to the real situation. Within monitoring phase of this research, 9 samples of bryndza were analysed with the results of detected cow milk ranged from 11.56% to 14.3%. The obtained results confirm that the appropriate selection of ELISA tests can become an important factor in the setting of analytical capabilities for the detection of milk and cheese adulteration.

Highlights

Consumption of fresh dairy products is the important motive factor for their production in European Union (Habánová et al, 2010)
Accurate evaluation of the milk species used in dairy products is needed, especially for high-grade cheeses made exclusively with sheep or goat milk, many of which are registered by European law with a Protected Designation of Origin (PDO) (Zeleňáková et al, 2008)
As the basis for the evaluation, calibration curves were made by plotting % of cow milk in standard samples in a Y-axis and absorbance values in the X-axis

Summary

Introduction

Consumption of fresh dairy products is the important motive factor for their production in European Union (Habánová et al, 2010). The unknown mixture of milk from different species is a common fraud in dairy sector. Milk with high economic value is commonly adulterated with milk from species of lower cost. This adulteration is especially important for cheese makers, due to unknown milk mixtures produce changes in the final sensory properties and reduce the product quality. Accurate evaluation of the milk species used in dairy products is needed, especially for high-grade cheeses made exclusively with sheep or goat milk, many of which are registered by European law with a Protected Designation of Origin (PDO) (Zeleňáková et al, 2008)

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