Studying the Effect of Chitosan on the Growth and Productivity of Lactic-Acid Producing Bacteria with GC-MS

The influence of chitosan's physicochemical characteristics on the functionality of lactic acid bacteria and the production of lactic acid remains contradictory to date. While some studies have shown a stimulatory effect of oligochitosans on the growth of Lactobacillus spp, other studies show a bactericidal effect of chitosan. This prompted researchers to study the effect of chitosan on the growth and productivity of L. bulgaricus in the presence of chitosan and its derivatives, with gas chromatography-mass spectrometry (GC-MS) used to examine fermented dairy products. The resulting article was published in Frontiers in Nutrition (1).

Fermented dairy products are one of the most common groups of functional food products and recognized as the most popular and extensively produced and consumed dairy products worldwide (2,3). Cultured buttermilk, sour cream, and yogurt are among the most common fermented dairy products in the Western world. Other lesser-known products include kefir, koumiss, acidophilus milk, and new yogurts containing Bifidobacteria. Cultured dairy foods provide numerous potential health benefits to the diet, as they are excellent sources of calcium and protein, as well as help to establish and maintain beneficial intestinal bacterial flora and reduce lactose intolerance (4). The production of lactic acid by bacteria of the genera Lactobacillus is commonly used in the making of fermented dairy products, along with Bifidobacterium genera (5).

Reconstituted skim milk (100 mL) was mixed with a fixed amount (0.0025, 0.005, 0.075, and 0.01 g) of chitosan stock solution, and the mixture was pasteurized at 85°C for 5 min. After cooling to 43–45 °C, 3 g of the commercial freeze-dried starter culture of L. bulgaricus was added to achieve a viable count of 105 CFU/mL in the sample. The sample was thoroughly mixed and incubated at 43–45 °C for 17 days, until the maximum titratable acidity was reached. Subsequently, the sample was stored at 4 °C before being analyzed (1).

After 17 days of storage, a 10 mL sample of the fermented dairy product was centrifuged at 6,000 rpm for 30 min, followed by lyophilization. The residual solid product (1 g) was then extracted twice with 70% ethanol (1:10 wt/v). The resulting extracts were combined and filtered through 0.25 μm PVDF membranes. Secondary metabolites were separated and analyzed using a gas chromatograph equipped with a mass selective detector. The separation of secondary metabolites was performed using a capillary column DB-5MS (5% phenyl methyl siloxane). Comparative semi-quantitative analysis of secondary metabolites was performed based on peak areas without using correction factors. The semi-quantitative content of secondary metabolites was calculated from the peak area without considering the peak of lactic acid and without using correction factors (1).

The results of this study indicate different mechanisms of action of oligochitosans and chitosan on the synthesis of lactic acid. With increasing concentrations of oligochitosans, a slowdown in the synthesis of lactic acid is observed. At the same time, its content remained higher than in the control sample. During the 17-day storage period of the dairy product fermented with oligochitosan, further accumulation of lactic acid, decrease in pH, and L. bulgaricus content occurred. The results obtained confirm that oligochitosans can be used as stimulators of lactic acid synthesis based on lactose containing substrates industrial fermentation using L. bulgaricus starter cultures. Furthermore, the concentrations of chitosan used did not give astringent taste to the fermented dairy product (1).

Cold fermented yogurt drink. © Ms Vectorplus- stock.adobe.com

References

1. Kurchenko, V.; Halavach, T.; Yantsevich, A.; Shramko, M.; Alieva, L.; Evdokimov, I.; Lodygin, A.; Tikhonov, V.; Nagdalian, A.; Ali Zainy, F. M.; Al-Farga, A.; ALFaris, N. A.; Shariati, M. A. Chitosan and its Derivatives Regulate Lactic Acid Synthesis During Milk Fermentation. Front Nutr. 2024, 16 (11), 1441355. DOI:10.3389/fnut.2024.1441355.

2. Marco, M. L.; Sanders, M. E.; Gänzle, M.; Arrieta, M. C.; Cotter, P. D.; De Vuyst, L, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) Consensus Statement on Fermented Foods. Nat. Rev. Gastroenterol. Hepatol. 2021, 18, 196–208. DOI: 10.1038/s41575-020-00390-5

3. Abdullah Thaidi, N. I.; Rios-Solis, L.; Halim, M. Fermented Milk: The Most Famous Probiotic, Prebiotic, and Synbiotic Food Carrier. Probiot. Prebiot. Foods 2021, 4, 135–151. DOI: 10.1016/B978-0-12-819662-5.00012-4

4. Cultured dairy foods. Brittanica website. https://www.britannica.com/topic/dairy-product/Cultured-dairy-foods (accessed 2024-10-01)

5. Ahansaz, N.; Tarrah, A.; Pakroo, S.; Corich, V.; Giacomini A. Lactic Acid Bacteria in Dairy Foods: Prime Sources of Antimicrobial Compounds. Fermentation 2023, 9, 964. DOI: 10.3390/fermentation9110964