بررسی ویژگی‌های پروبیوتیکی و تکنولوژیکی باکتری‌های اسید لاکتیک جدا شده از دوغ بومی بهبهان

زمینه مطالعاتی: باکتری‌های اسید لاکتیک می‌توانند علاوه بر اثرات مفیدی که بر سلامتی مصرف‌کنندگان ایجاد میکنند، خصوصیات متعدد تکنولوژیکی و ضدمیکروبی در ارتباط با استفاده‌های غذایی نیز داشته باشند. هدف: هدف از این پژوهش بررسی پتانسیل پروبیوتیکی، تکنولوژیکی و ضدمیکروبی سویه‌های اسید لاکتیک جداشده از دوغ محلی شهرستان بهبهان می‌باشد. روش کار: در این مطالعه ابتدا ویژگی‌های پروبیوتیکی باکتری‌های اسید لاکتیک از قبیل زنده‌مانی تحت شرایط اسیدی، زنده‌مانی در محیط شبیه سازی شده معده و روده، هیدروفوبیسیتی، خود و همتجمعی مورد بررسی قرار گرفت. سپس پتانسیل تکنولوژیکی آن‌ها با آزمون‌های قابلیت تولید اسید، فعالیت اتولیتیکی و مقاومت در برابر حرارت تعیین شد. در نهایت فعالیت ضدمیکروبی سویه‌هایی که ویژگی‌های پروبیوتیکی و تکنولوژیکی بهتری داشتند علیه 5 پاتوژن شاخص غذایی مورد بررسی قرار گرفت. نتایج: سویه‌های لاکتوباسیلوس پلانتاروم و لاکتوباسیلوس دلبروکی زمانی‌که در معرض شرایط اسیدی و همینطور، شرایط شبیه‌سازی شده معده و روده قرار گرفتند کمترین کاهش در تعداد را نشان دادند. هیدروفوبیسیتی سویه‌ها 585.3/17 درصد گزارش شد که بیشترین درصد مربوط به لاکتوباسیلوس پلانتاروم بود. خود تجمعی باکتری‌های اسید لاکتیک در محدود 483.2/25 درصد محاسبه گردید و بیشترین میزان خود تجمعی مربوط به پدیوکوکوس پنتوزاسئوس بود. همچنین تمامی سویه‌ها فعالیت هم‌تجمعی علیه اشرشیاکلی از خود بروز دادند که بیشترین مقدار مربوط به لاکتوباسیلوس پلانتاروم با 46.3 درصد بود. در ارتباط با ویژگی‌های تکنولوژیکی، باکتری‌های لاکتوباسیلوس دلبروکی و پدیوکوکوس پنتوزاسئوس بهترین پاسخ را در تمامی آزمون‌ها از خود نشان دادند. همچنین فعالیت ضدمیکروبی باکتری‌های لاکتوباسیلوس پلانتاروم، لاکتوباسیلوس دلبروکی و پدیوکوکوس پنتوزاسئوس علیه پاتوژن‌های اشرشیا کلی، سودوموناس آئروژینوزا، سالمونلا تایفی‌موریوم، میکروکوکوس لوتئوس و استافیلوکوکوس اورئوس مورد بررسی قرار گرفت که بیشترین حساسیت در باکتری‌های میکروکوکوس لوتئوس و استافیلوکوکوس اورئوس و بیشترین مقاومت نیز توسط باکتری اشرشیا ‌کلی مشاهده شد. نتیجه‌گیری نهایی: با توجه به نتایج به دست آمده باکتری‌های لاکتوباسیلوس دلبروکی و پدیوکوکوس پنتوزاسئوس خصوصیات مناسبی جهت استفاده به‌عنوان کشت الحاقی برای تولید محصولات تخمیری لبنی از خود نشان دادند.

Investigation of probiotic and technological characteristics of lactic acid bacteria isolated from native Doogh of Behbahan

Background and Objectives: During thousands of years, human has unconsciously benefited from lactic acid bacteria (LAB) in the production of fermented food. This is due to the potential of these bacteria to release odor and flavor, and inhibit the growth of pathogens and foodspoilage microorganisms. LAB is Grampositive, catalasenegative, microaerophilic and nonspore forming. In addition to their healthpromoting effects, they have numerous technological and microbiological properties in food products. LAB is usually known as the microorganisms highly consumed in food products, which can be utilized as protective culture media, owing to their specific characteristics. The present study aims to examine the probiotic potential (viability in acidic and simulated gastrointestinal conditions, hydrophobicity, auto and coaggregation) of the LAB isolated from Behbahan local Doogh. Next, their technological properties (acidification and autolytic activities, and heat resistance) were determined. Finally, the antimicrobial activity of the strains was measured against some food pathogens.Materials and methods: In this study, the LAB strains of Behbahan local Doogh were identified through 16S rRNA gene replication by a polymerase chain reaction. First, 85 Grampositive and catalasenegative isolates were categorized using biochemical and sugar fermentation tests. One representative was selected from each group for the molecular identification test. In order to investigate the resistance of the bacteria to acidic conditions, their viability was examined at pH values of 2.5, 3.5 and 5. For determining the LAB viability in the gastrointestinal system, 30 µl of each bacterium was added to 270 µl of simulated gastric juice (2.5 g pepsin/l and 2 g NaCl/l) whose pH had been set at 2.75 and incubated at 37°C for 1.5 h. Then, 30 µl was mixed with 270 µl of simulated intestinal juice (1 g trypsin/l, 5 g bile salt/l, 2 g pancreatin/l, 11 g sodium bicarbonate/l and 2 g sodium chloride/l) whose pH had been adjusted to 8 and incubated at 37°C for 4 h. Afterwards, the bacteria were cultured on MRS agar at 1.5, 2, 3 and 4 h. The results were expressed as the reduction of log CFU/ml relative to time zero (time zero: 8 log CFU/ml). The other probiotic properties of the LAB, including hydrophobicity, auto and coaggregation were also investigated. Their technological potential was determined though acidification ability, autolytic activity and resistance to heat. Eventually, the antimicrobial activity of the strains with better probiotic and technological properties was examined against 5 food pathogens (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, Micrococcus luteus and Staphylococcus aureus). Oneway analysis of variance was conducted using statistical package for the social sciences (SPSS) version 22. Duncan`s multiple range test was employed for mean comparison at 95% confidence level.Results and discussion: Lactobacillus plantarum, Lactobacillus delbrueckii and Pediococcus pentosaceus were the most resistant strains to the pH values of 2.5 and 3.5, while Lactobacillus pentosus and Enterococcus faecium showed the most pronounced reduction of log CFU/ml. At the pH value of 5, all the bacteria were able to grow without being reduced. Relative to the simulated gastric juice, L. plantarum was the most resistant one with a reduction of zero log CFU/ml and E. faecium was the most sensitive one with a reduction of 3 log CFU/ml. After 3 h of digestion by the simulated intestinal juice, L. plantatum and L. delbrueckii were the most resistant strains with a reduction of 1 log CFU/ml and E. faecium was the most susceptible one with a reduction of 5 log CFU/ml. The hydrophobicity of the strains was reported to be 17.558.3%, the highest of which belonged to L. plantarum. The coaggregation of the LAB varied from 25.3 to 48.2%, the highest of which was associated with P. pentosaceus. In addition, all the strains showed coaggregation activity against E. coli, and L. plantarum had the highest value of coaggregation (46.3%). In terms of the technological properties, the results revealed that all the strains were capable of acid reduction up to 0.4 except L. pentosus. During 24 h of incubation, P. pentosaceus and L. delbrueckii caused the largest pH variations. The results of the autolytic activity of the LAB isolates indicated that all the L. pentosus, L. plantatum and L. delbrueckii could be grouped as relatively good. The highest viability and heat resistance belonged to P. pentosaceus and L. delbrueckii and the lowest viability was related to L. pentosus and E. faecium. In general, L. delbruckeii and P. pentosaceus showed the best results in all the technological tests. Moreover, the antimicrobial activity of L. plantarum, L. delbrueckii and P. pentosaceus was investigated against E. coli, P. aeruginosa, S. typhimurium, M. luteus and S. aureus. In all the samples, the acidic cellfree supernatant had a greater antimicrobial effect than the neutralized cellfree supernatant. The neutralized supernatant of L. plantarum and L. delbrueckii had no antimicrobial effect on E. coli. The shortest inhibition zone diameter of the acidic supernatants of L. plantarum, P. pentosaceus and L. delbrueckii was associated with E. coli. Furthermore, S. aureus was the most sensitive strain against the acidic supernatant of L. plantatum and S. aureus, whereas M. luteus had the longest inhibition zone diameter against the acidic supernatants of L. delbrueckii and P. pentosaceus.Conclusion: Considering the obtained results, L. delbrueckii, L. plantarum and P. pentosaceus had superlative performances and can be used as complementary strains in the production of food products. It is suggested that supplementary tests, including the adhesion ability to intestinal epithelial cells, antiadhesion ability against specific pathogens, and the lipolytic and proteolytic activity of these three strains be evaluated.