Organic milk: understanding intrinsic characteristics and their origin, and development of novel means of detection

Organic milk has been receiving more and more attention in recent years. However, it is also susceptible to fraud considering its high retail price and the strict requirements of organic production. Since the quality of milk is affected by many factors, such as seasons, environment, lactation stage, feed, cow breed, etc., it is challenging to distinguish organic milk from conventional milk. To ensure fair competition and consumer confidence, there is a strong need to confirm the identity of organic products including milk. Therefore, this study was carried out to elucidate the differences in characteristics, in terms of fatty acid (FA) and volatile organic compound (VOC) profiles, of organic milk and other milks, and to study their underlying causes.

In Chapter 2 and Chapter 4, the FA profiles of different farm (raw) milks and retail milks were investigated by gas chromatography (GC). Both the types of silages and grazing management strategies in different dairy production systems impacted on the FA profiles of milks, where the impact of the latter one was more significant. Corresponding to this result for farm (raw) milks, the differences of the FA profiles of different milks have also been observed among retail milks. Hence, industrial processing and milk pooling did not erase all the characteristics of organic milks. However, due to the relatively flexible regulations of pasture milk, the differences between pasture retail milk and conventional retail milk were less significant than the differences between pasture raw milk and conventional raw milk.

Similarly, the VOC profiles of raw milks and retail milks were analysed in Chapter 3 and Chapter 6. By using proton transfer reaction quadrupole mass spectrometry (PTR-(Quad)MS) and proton transfer reaction time of flight mass spectrometry (PTR-(ToF)MS), the characteristics of different milks in winter and summer were investigated. Similar to the results of FA analysis, the grazing management had a greater impact on VOC profiles than the type of silages. This is not only due to the VOCs resulting from the feedstuff consumed by the cows, but relates also to the FA composition of the milks. Moreover, the characteristics of the VOC profiles of retail milks were investigated as well, which revealed that the differences between milks from organic and other production systems in summer and winter could still be observed.

In general, pasture milk was closer to conventional milk in winter and closer to organic milk in summer, in terms of its FA profile and VOC profile, whereas the differences between organic milk and conventional milk were significant both in summer and winter.

Subsequently, different analysis approaches were compared for various stakeholders. PTR-(ToF)/(Quad)MS and GC told the differences between organic milk and milks from other production system (including conventional and pasture systems). They provide options for the authorities to confirm the authenticity of organic milk. Fourier transform near-infrared spectroscopy (FT-NIR) and micro near infrared spectroscopy (Micro-NIR) could distinguish organic milk from conventional retail milk but not from pasture milk. They can provide a first, on site check of the identity of organic milk. The novel handheld near-infrared spectroscopy, SCIO, can be easily operated by consumers and generate some relevant information of the products.

The results of this study could contribute to the authenticity of organic milk and help protect the rights of stakeholders.