Detection of Alicyclobacillus spp. in the NAB area.
All cloudy, non-filterable non-alcoholic beverages and raw material samples.
The representatives of the genus Alicyclobacillus spp. are acidophilic and thermophilic, spore-forming bacteria that can spoil juices, nectars, drinks containing juice, sports drinks, iced tea and even flavoured waters by forming an off-flavour (guaiacol; 2,6-di-bromophenol; 2,6-di-chlorophenol). The beverage itself remains visually flawless. There is no gas formation, discolouration, clarification or sedimentation. Even slight contamination can lead to sensory issues for the product.
The ubiquitous soil inhabitant is usually introduced into the production process of e.g. juices (e.g. NFC) or fruit juice concentrates during the fruit harvest. Other sources of contamination include raw materials such as sugar, stabilisers and binding agents (pectin, starch, etc.) or special additives (cereals, herbs, protein powder, seeds, etc.), usually with pH values that differ from the juice.
The spores of the bacteria can survive common pasteurisation conditions and then germinate again under favourable conditions (presence of oxygen, warm temperatures, low pH value). To date, only Alicyclobacillus acidoterrestris, A. acidophilus, A. acidocaldarius and A. herbarius have the potential to form off-flavours. Therefore, the sole detection of Alicyclobacilli is not a clear indication of the risk of beverage damage, but must be verified in a second step using a suitable test, e.g. the enzymatic guaiacol detection kit, to determine the risk potential of off-flavour formation.
Internationally, detection in 10 g samples is recommended, see also IFU method MM12 (International Fruit and Vegetable Juice Association) [1].
There are three different methods of analysis:
Quantitative detection from non-filterable samples using the pour-plate method
Quantitative detection from filterable samples using membrane filtration
Qualitative detection (presence/absence test) by means of pre-enrichment (higher sensitivity)