|Image source: Wikimedia Commons|
The aim of this study was to evaluate the effect of encapsulating a malolactic bacteria starter culture in two different gels to improve its activity and stability under stressful winemaking conditions. The two different encapsulation methods: a normal alginate gel as well as a silica-alginate gel, were also compared to a “free” version of the bacteria. The bacteria used in the trial was Lalvin VP 41 MBR from Lallemand. Bacteria was inoculated into de-alcoholised wine with adjusted concentrations of alcohol, pH, YAN and malic acid. Malolactic fermentation was also conducted at various temperatures ranging from 13 – 22°C.
- The malolactic activity of the Si-Al capsules was significantly higher than the alginate capsules and the free bacteria, in high alcohol conditions. At 16% alcohol free bacteria decreased the malic acid concentration only 1% 72 hours after inoculation. The alginate capsules consumed 55% of the malic acid and the Si-Al capsules 88% of the malic acid.
- At the lowest fermentation temperature of 13°C the best results were obtained with the Si-Al gels. Improving the efficiency of MLF bacteria at low temperatures can significantly reduce energy costs in cellars that usually have to warm up tanks towards the end of the season to stimulate MLF.
- At pH 3.0 the best results were obtained with the Si-Al gels followed by the alginate gels and the free bacteria performing the worst. At pH 3.2 however the alginate gels performed the worst with Si-Al still the best. At pH 4 all bacteria versions performed equally well with almost 100% of malic acid degraded after 72 hours.
- At the different YAN levels the Si-Al gels did not always perform the best, with the free bacteria performing the best after 72 hours at the lowest YAN of 52 mg/l. At 250 mg/l YAN the different bacteria versions performed similarly.
- At 2g/l malic acid concentration the free bacteria and the Si-Al gels performed equally well consuming about 92% of the malic acid after 72 hours in contrast with the alginate gels that only consumed 66% of the malic acid. Performance of all bacteria types increased with higher malic acid concentrations. At 5 g/l however the performance of the Si-Al gels decreased.
Significance of the study
Encapsulating MLF starter cultures in a Si-Al gel can significantly improve the efficiency of MLF in winemaking, especially under stressful conditions often encountered in warm wine producing areas. According to this publication alginates are “generally regarded as safe” for human consumption. Silica precursors are used in the biomedical field also indicating that they are safe for humans. It might therefore be possible for Si-Al coated alginate MLF bacteria gels to become commercially available in the future.