مجله میکروبیولوژی کاربردی در صنایع غذایی
سال پنجم شماره 4 (زمستان 1398)

Lactic acid bacteria are the most common type of bacteria known as probiotics and are commonly found in dairy products. Probiotics are living microorganisms that, when consumed in adequate amounts, provide health to the host. In this research, 15 Pousti cheese samples were collected from cold regions of Jiroft city. Lactobacillus bacteria were isolated using MRS agar medium. The isolates were subjected to biochemical tests and growth ability at different concentrations of sodium chloride (1 to 9 percent w/v). According to the results of biochemical tests, four isolates (L1, L3, L4 and L5) were compatible with Lactobacillus. The highest salt tolerance at 3percent concentration was related to L1 and L3 isolates, so lactic cheese production was performed by L1 and L3 strains. Cheese samples containing Lactobacillus isolates showed lower bacterial, mold and yeast counts than control samples during storage. At the end of the storage period, the highest bacterial count was observed in the control treatment (without Lactobacillus isolates) and the lowest bacterial count was in the samples containing L3 isolate and no mold growth was observed in the samples containing this isolate. Finally, L3 isolate was selected for molecular identification. Based on the results of sequencing blast and phylogenetic tree, the studied isolate was Lactobacillus brevis. In the present study, a potentially probiotic bacteria were isolated from local (Pousti) cheese of Jiroft city. It had good probiotic properties and can be used in the dairy industry.

The object of this study was to investigate the possibility of using xanthan gum and flaxseedmucilage as edible coatings for Cheddar cheese and the effect of these coatings on the qualitative properties of Cheddar cheese during ripening. Samples were prepared triplicate as follows: Coated with polyvinyl acetate as control (C), coated with 0.5% xanthan gum (XG), coated with 0.75%, 1%, and 1.25% flaxseed mucilage (FM1, FM2, and FM3 respectively). All samples were kept at 8±2°C in a cold room for 90 days. Edible coatings did not significantly affect the growth of total mesophilic aerobic bacteria, Pseudomonas bacteria, and Coliform bacteria (P>0.01). In contrast, a xanthan gum coating significantly increased the population of Mold and Yeast (P<0.01). The type of coating had a significant effect on acidity and pH(P<0.01); so that the highest pH and acidity rates were observed in the FM1 and XG samples respectively after 90 days of ripening. The highest amount of weight loss at the end of the ripening period was observed significantly in FM3 (P<0.05). In all frequencies, G/ and ƞ* in FM1 and G// in FM2 showed the highest value, while the lowest values of these parameters were observed in the control sample. Sensory evaluation revealed that coating have no significant effect on sensory properties of cheese. Therefore, in order to achieve the desired qualitative and organoleptic properties, the coating of Cheddar cheese is recommended by using Xanthan gum (0.5%) or Flaxseed mucilage (1.25%).

Doogh is a fermented drink and consist of healthful as well as sensorial traits. In this study, chemical composition and sensorial properties of heated non-carbonated probiotic doogh were explored. treatments were prepared as follows: T1 as a control sample without probiotic strain and maltodextrin, T2 and T3 containing 1 and 2percent of maltodextrin respectively and 108 cfu/ml Lactobacillus acidophilus. Results showed that treatments containing higher concentrations of maltodextrin had more survival rate during storage. Acidity (dornic) was increased during storage, parallel to acidity, pH of all sample decreased. The percentage of dry matter of all samples with due attention to higher concentration of maltodextrin were increased. The percentage of fat did not affect by maltodextrin during storage. Sensory evaluation showed control sample had highest score among all treatments, however, T2 was the highest similarity to control sample and was the best among other treatments.

Due to the high energy consumption for cooling of fermentors, isolation of thermo-tolerant Acetobacter strains to produce vinegar is necessary. On the other hand, these thermo-tolerant strains should tolerate against high percentage of ethanol, which can be used as a source of carbon. The purposes of this study were to isolate and identify thermo-resistant AAB strains from different fruits and investigation of their resistance to the high ethanol concentrations. In order to isolate the AAB strains, the extracts dilutions of fig-peach and nut-grape fruits were prepared, cultivated in Frateur culture media and incubated at 30°C for 24 hours. The individual colonies with round transparent zone were isolated and purified using same condition. The isolates for macroscopic, microscopic and biochemical evaluations were transferred to the Carr culture media. Then the resistance of the isolates against different high temperature and ethanol concentrations were measured. Finally, the molecular identification of isolates was carried out. One strain was isolated from each fruit sample. The overoxidation property in Carr medium as well as macroscopic, microscopic, biochemical and molecular characterizations showed that the isolates were related to Acetobacter spp. The isolated Acetobacter spp. were able to grow in Carr culture media with 7 percent ethanol and 38°C after 24 hours-incubation so they were considered as thermo- ethatol-resistant AAB spp. The isolated AAB from fig-peach and nut-grape were named Acetobacter pasteurianus KBMNS-IAUF-3 and Acetobacter senegalensis KBMNS-IAUF-5 and their 16s ribosomal sequences were deposited in GenBank, NCBI under the accession numbers of MG547345.1 and MG547383.1 respectively.

Herein, three semi empirical kinetic models, i.e., exponential, homographic and n-order kinetic models were established to describe the microbiological population pattern and dynamic. To prove the generalizability of these models, the Yersinia enterocolitica and Shigella dysentery population dynamics have been investigated in sausage, as a complex food system, contained four different antimicrobial Ribes rubrum extract (RRE) concentrations (0, 0.1, 0.2 and 0.4 percent) at two storage temperatures (4 and 35 °C) during 17 days. Furthermore, to test the capability of these models, the results were compared with neuro-fuzzy system. Although, all three kinetic models showed a reasonable prediction accuracy, homographic kinetic model was the best for predicting antibacterial effects of RRE against Y. enterocolitica (R2 = 0.96-0.98, R2adj = 0.95-0.97, Q-squared = 0.87-0.90, and RMSE = 0.12-0.42) and the n-order kinetic model did the best in describing the kinetic pattern of S. dysentery (R2 = 0.94-0.98, R2adj = 0.92-0.96, Q-squared = 0.88-0.90, RMSE = 0.26-0.52). Semi-empirical kinetic models had better performance for predicting microbiological population dynamic than neuro-fuzzy system. Also, it’s worth mentioning that the novel semi empirical models presented important biological parameters which provided a better understanding of the systems biological state than neuro-fuzzy system. These results could offer new perspectives in the field of microbiology

Propionibacterium, a gram-positive, anaerobic to micro-aerobic and rod-shaped bacterium, belongs to the propionic bacterial family. Propionibacteria are involved in the production of vitamin B12. The aim of this study was to evaluate the effect of physicochemical parameters (temperature and pH) as well as measurement of ascorbate peroxidase and catalase enzyme concentrations and to investigate changes in vitamin B12 production at different concentrations of folic acid in Propionibacterium freudenreichii. Propionibacterium freudenreichiiwas cultured in fermented medium containing corn and various concentrations of folic acid. The results showed that the optimum pH for the bacterial growth was 6.6 and the optimum bacterial growth at 25-40 °C. Addition of folic acid at low concentrations to the media of Propionibacterium freudenreichiiincreased UV absorption at 600 nm. High folic acid concentrations were found to decrease growth rate, indicating a negative effect of folic acid on bacterial growth. Catalase and ascorbate peroxidase activity was also determined based on H2O2 consumption at 240 and 290 nm. Due to the increase in folic acid concentration, the activity of catalase and ascorbate peroxidase was significantly reduced in this bacterium. Also in the study of vitamin B12 production, considering the bacterial dry weight, using HPLC in anaerobic and aerobic conditions, it was found that the maximum production of vitamin B12 in 750 mg/l folic acid under aerobic conditions. As the concentration of folic acid increased by up to 1000 mg/L, vitamin B12 production decreased.