Effect of using propionic acid bacteria as an adjunct culture in yogurt production.

Researchers F.Y. Ekinci and M. Gurel thought so and tested the concept in their research published in the paper: Effect of using propionic acid bacteria as an adjunct culture in yogurt production. The paper was published in The Journal of Dairy Science, Volume 91, pages 892-899.

The advantage of yogurt is that it contains many beneficial microflora from lactic acid fermentation which offers the consumer more than just conventional nutrients. In recent years researchers have been experimenting with different starter cultures to exploit further possibilities, such as introducing more functional (eg health enhancement) properties and flavours. One of the bacterial species investigated is propionibacteria which add characteristic flavours, but more importantly have potential as probiotics with several beneficial attributes to human health. Some of the propionic bacterial strains may also contribute to controlling undesired micro-organisms with the added advantage of prolonging shelf life. A potent coculture on the market in this regard contains Lactobacillus rhamnosus LC705 (DSM 7061) and Propionibacterium freudenreichii spp. shermanii JS (DSM 7067). In this study the promising strains Propionibacterium jensenii B1264 and Propionibacterium thoenii (jensenii) P126 were used as adjunct starter cultures in yogurt, to investigate their potential beneficial properties.

These cultures were compared with the standard commercial YC-380 starter culture as Control. The results showed that there were no significant differences between Control and the adjunct starter cultures in total solids and protein contents of the yogurts. Titratable acid in the Control was lower because of more lactic acid being produced compared to more propionic acid by the test cultures, but the difference did not result in poorer storage over the 15-day test. The yogurts produced by YC-380 + P126 cultures had the firmest structure; otherwise there were no meaningful differences in physical and chemical properties. The highest acetaldehyde content was obtained with yogurt made with YC-380 + P126 + B1264 cultures. Acetaldehyde provides an indication of flavour. Microbiological analyses revealed no formation of coliforms, yeasts or molds at the end of the storage period and the addition of propionibacteria did not have a negative effect on the counts of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, suggesting that the activities of propionibacteria did not interfere with those of the lactic starters. What is of significance to the objectives of the study is that during the first week of storage, propionibacteria counts remained high, suggesting that the yogurt provided a good environment for these bacteria.

In conclusion the results suggest that the addition of propionibacteria will not only provide beneficial health effects, but will also provide the opportunity for development of alternative products to plain set-type yogurt.