Introduction Lactobacilli have found tremendous applications in both food industries and medicine 1, 2. The members of this family are gram-positive, non-spore forming and lack catalase activity. One of the most important species is Lactobacillus plantarum which has drawn the attention of researchers. Its widespread niches accompanying safety approval and probiotic effects, have made it as a suitable lactic acid bacterium 3. One of the basic drawbacks of lactic acid bacteria utilization is their sensitivity to stresses such as low pH which results in their decreased viability. It has been mentioned that at least 106 CFU/ml should be contained in a probiotic product 4. Henceforth, numerous methods have proposed to maintain cell viability during processes.
Among them, entrapment and high-density condition (HD) are two of the most effective and modern techniques. Entrapment techniques benefit from the formation of beads loaded with bacteria. The beads have two main parts; core and coating 5. The most widely used matrix material is sodium alginate. This polysaccharide can form strong interaction with divalent ions e.g. calcium ions and form hydrogels 6.
These hydrogels entrap cells in the matrix so that they will not be free as in spray drying and fluidized bed drying 7. Although some authors indicated a positive effect of calcium-alginate hydrogel loaded with lactic acid bacteria 8, 9, sodium alginate hydrogels have some disadvantages. Their structure can disrupt in lactate presence 10 and as sodium alginate is a porous gel, the harsh condition can have a partial effect on the entrapped cells 11. To overcome the mentioned downfalls, using the second protective material has been suggested. The range of materials from proteins and polysaccharides can be used. One of the recently used material is plant gums 12. The gums can be used in different manners and with different techniques13 14-16.
Considering our research, there is a considerable gap for Iranian gums.Tragacanth gum is one that is obtained from Astragalus sp. 17. It has the safety code from FDA under title 21 section 184.
1351 18. This gum has been applied in the food industry as stabilizing agent 19. High acidity tolerance and long shelf time of this gum, facilitated its use as dressing in desserts 20. Salep gum is another Iranian gum that is obtained from Orchis sp. This gum can improve the aroma and flavor of a product and can also act as a stabilizing agent. It also contains glucomannose 21.
To develop the efficiency of entrapment, utilizing high-density structures instead of planktonic ones has proposed. Among lactic acid bacteria, Lactobacillus can adhere to mucosal layer. This natural trait can be used in biotechnology 22.
Formation of high-density bacteria can increase their tolerance to thermal stress and freeze drying 23. In order to achieve a high-quality product which agrees with customer’s taste, the beads should be in the powder form. One way to achieve this is using freeze-drying. As the hydrogel contains water as one main component 24, freeze-drying can result in removal of the water and formation of stable powder.
The combination of these two methods has mentioned in some papers with positive outcomes 16, 25. Regarding the given introduction, we used Lactobacillus plantarum and entrapped it in the gum-alginate matrix and its ability to form high-density condition was analyzed. Based on our knowledge, there is no paper indicating tragacanth gum lactic acid bacteria capsules. We also could not retrieve any study regarding using salep gum and the combination of these two gums as a matrix.
Hence, as using endemic gums can decrease the costs of production, we chose these two gums. On the other hand, as we followed commercial goals, we decided to form powder from the encapsulated bacterium by freeze-drying as an available method. At the end, storage time periods were assigned to evaluate of our beads.