Effects of ultraviolet light and ultrasound on microbial quality and aroma-active components of milk

Heat treatment is the most common way to extend the shelf life of milk. However, alternative technologies such as ultraviolet (UV) light and ultrasound (US), which are non-thermal methods for processing milk, have been developed to replace heat treatment. These technologies do not have any adverse effects on the quality of milk. The major purpose of this study was to investigate the effects of UV and US on different micro-organism groups and aroma compounds in milk.

Heat pasteurisation at 65 °C for 30 min was used as thermal control treatment. The growth of total coliform group bacteria, Escherichia coli and Staphylococcus spp. was completely reduced by UV treatment. Application of US was not sufficient to reduce the numbers of yeasts and moulds. In neutral/basic fractions, 3-methylthiophene (plastic), hexanal (grass) and 1-hexen-3-one (floral) were major volatiles in milk samples.

UV had a major effect on total coliforms, E. coli and Staphylococcus spp., but US was not as effective as UV and heat treatment in reducing certain groups of micro-organisms. No major differences were observed in terms of aroma-active compounds and flavour of milk following the different treatments. However, some new volatiles and change in rheological properties were generated by UV and US treatments.