A Rapid Electrophoresis Method on Agarose Gel to Characterise Dairy Protein Aggregates

Heat treatment of milk may cause whey proteins and caseins to form aggregates. These soluble and micellar aggregates and their other properties (size, composition, shape, etc.) can affect the techno-functionalities to the milk, conferring interesting or negative features depending on the application in dairy industries. In this study, we propose a new approach to characterise those protein aggregates. SDS-agarose electrophoresis is followed by the calculation of a retention factor (Rf) for each protein spot. Rf allows milk aggregates to be compared qualitatively under the same conditions. This method could be transposed to the dairy industry for a better knowledge of the milk subsequent to heat treatment.

Utilisation of a Portable Electronic Nose, NeOse Pro, to Follow the Microbial Fermentation of a Yoghurt

Yoghurt is fermented milk which results from the exclusive action of Lactobacillus delbrueckii subsp bulgaricus and Streptococcus thermophilus. However, a disruption of the bacterial growth can lead to significant industrial losses. Currents monitoring methods, based on the checking of the pH during the fermentation step are not always satisfactory. The NeOse Pro system, a portable electronic nose, is a mean to obtain immediately aromatic profiles. In this work, we applied this technology to the yoghurt ecosystem, a highly hydrated product. The profiles obtained allowed us to discriminate yoghurts before and after fermentation. In detail, the discrepancy between the two bacteria cultured alone was slight. It was also the case when we compared different initial bacterial ratios. However, two different mixes of bacteria led to clearly distinguishable profiles. A GC/MS analysis performed on products fermented 7 h allowed us to explain the detection of acetaldehyde by the stimulation of some captors of the apparatus. NeOse Pro is so convenient to study the fermentation of yogurt.