مجله میکروبیولوژی کاربردی در صنایع غذایی
سال هفتم شماره 1 (بهار 1400)

Dairy-based traditional fermented foods have rich sources of native lactic flora which isolation. The aim of this study was to identify and investigate the technological and antimicrobial properties of Lactobacillus casei and Lactobacillus acidophilus isolated from local yogurt in Behbahan. After isolation, Gram and catalase tests was done and identification was performed by 16S rRNA gene analysis method. Then, their technological properties such as acidification, proteolytic, lipolytic and autolytic activity, resistance to acid and heat, and finally their antimicrobial activity against foodborne pathogens were examined. The results of the sequencing showed that the two isolates belonged to Lactobacillus casei strain CE28.26 and Lactobacillus acidophilus strain BCRC106955. The proteolytic activity of isolates was investigated by agar test and o-phthaldialdehyde method and the results showed that both isolates have the ability to hydrolyze casein. Also, no lipolytic activity was observed for any of the bacteria but isolates had high acidification activity. Studies of autolytic activity have shown that both sides have relatively good levels of this feature. The results showed the resistance of the strains decreased when the acidity production increased. So that the isolates could not grow in pH 3. Also, the study of temperature resistance showed with increasing the temperature and time, the resistance of isolates decreased. The results showed that L. acidophilus had more antimicrobial activity. The highest resistance and sensitivity were belonged to Pseudomonas aeruginosa and Staphylococcus aureus respectively. Due to the appropriate technological properties of Lactobacillus casei and Lactobacillus acidophilusisolates, they can be used as adjuncts culture in target industries such as dairy.

Lactones are widely used in the food industry due to their special flavor. Gamma-decalactone has a very distinctive peach aroma and is the most important lactone in the food industry. The wild-type strains of yeast Yarrowia lipolytica is capable of converting castor oil and ricinoleic acid (the main constituent of castor oil) into gamma-decalactone. The present study aims to optimize the production of gammadecalactone via the Taguchi method by Y. lipolytica mutant strain U6 which this strain can produce lipase up to ten times more than the wild-type strain. The Taguchi method of experimental design for four factors of carbon source, peptone, yeast extract, and pH included 16 experimental arrays. The optimal values for castor oil, peptone, yeast extract and pH were 40, 9, 6, and 6, respectively. In these conditions, the amount of produced gamma-decalactone is on average 100 mg /L which shows a 15% increase in production compared to non-optimal conditions. Based on the obtained results, the Taguchi method of experimental design can optimize gamma-decalactone production by Y. lipolytica mutant strain U6. The results of this study revealed the appropriate potential of this strain for further studies and industrial-scale production of gamma-decalactone.

Strawberries are very short shelf life due to the high sensitivity to fungal growth factors. The use of artificial antifungal chemical compounds has been a source of concern for increasing the shelf life of this fruit. For this reason, it is necessary to use safe methods to control the damage and maintain the quality of strawberry fruit when stored in storage. In this study, strawberry treatments were packaged in polyethylene film containing different percentages of carbon dioxide / nitrogen gas (35/65, 25/75, 15/85). The control sample was a modified strawberry-packed strawberry treatment without atmosphere. After packing, all strawberry treatments were stored at 0 and 15 °C. Tests including mold-counting tests, measuring solids content, texture firmness, ascorbic acid content, anthocyanin content and sensory evaluation for packaged strawberries were performed on the treatments during nine days of storage. The results showed that the amount of anthocyanin, ascorbic acid and tissue stiffness decreased significantly (P≤ 0.05) in all treatments during 9 days of storage, but the trend was reduced in treatments that were modified in the atmosphere with higher concentrations of carbon dioxide They were gentler and kept at a lower temperature. Due to the fact that the highest levels of anthocyanins, ascorbic acid and texture firmness were observed in strawberry samples stored in a controlled atmosphere with 85% carbon dioxide and 15% nitrogen and a temperature of 0 °C, so the treatment was treated. It was selected as superior in terms of quality and nutritional properties of strawberries after 9 days of storage.

Fresh fish is highly perishable due to its high water activity, availability of nutrients, almost neutral pH (factors affecting microbial growth) and the presence of autolytic enzymes. In this regard, the use of films and edible coatings containing antimicrobial compounds in fresh fish can prevent microbial growth and prevent the formation of chemical metabolites. In this study, the effect of Althaea officinalis mucilage coating containing of 0, 0.25 and 0.5% of orange peel essential oil on preventing the growth of microbial flora of fish fillets in the refrigerator was investigated during 16 days of storage. The results showed that with increasing the orange peel essential oil, the L* index and elongation at break of the films increased and the b* and a* indices, elastic modulus and of the tensile strength decreased (p <0.05). Also, during storage, the number of aerobic mesophilic bacteria, psychrophilics, lactic acid and coliforms and pH increased significantly in all fish fillet treatments, which was less in the treatments with mucilage coating containing orange peel essential oil (p <0.05). According to the existing standards, the maximum number of aerobic mesophilic bacteria, psychrophilics, lactic acid and coliforms in rainbow trout is set at 7, 7, 6 and 4 log cfu/g, respectively. Based on this, it is possible to prevent the increase of microbial load to above the standard level by using the Althaea officinalis mucilage coating until the fourth day, with the coating containing 0.25 and 0.5% essential oil until the eighth and twelfth days, respectively.

These days, food consumers pay more attention to the quality and health of food and therefore there is a high demand for healthy and low-calorie food products, So in this study, the effect of stevia and kiwi peel extracts on the shelf life of sponge cake was investigated. Stevia extract was added to the sponge cake formulation at two levels of 0 and 0.6% and kiwi peel extract at four levels of 0, 0.5, 1 and 2%. The results showed that free fatty acid, peroxide value, and count of mold and yeast had an increasing trend over time so that different treatments on days 21 and 0 of the highest and lowest Mean free fatty acid (0.422, 0.204), peroxide value (2.48, 1.17) and logarithm of mold and yeast (6.17, 1.43) were respectively. Therefore, at the end of the period, the highest increase was observed in the control sample (T1) and the lowest increase was observed in the treatment containing 2% kiwi peel extract and 0.6% stevia extract (T8). The results of sponge cake pH showed that different treatments on days 0 and 21 had the highest and lowest mean pH, respectively. The results of organoleptic evaluation of general acceptance showed that treatments containing 1% and 2% kiwifruit peel extract (T3 and T4) had the highest score and treatments containing 0.6% stevia extract (T5) had the lowest overall acceptance score, respectively. Therefore, treatment with concentrations of 2% kiwi peel extract and 0.6% stevia extract (T8) could well increase the shelf life of sponge cake for 21 days compared to the control sample and was selected as the optimal treatment.

In the present study in order to increase the nutritional and quality values of Lavash, quinoa flour was used to prepare Lactobacillus plantarum sourdough. The quinoa and wheat sourdough samples then compared in terms of bacterial growth rate, total phenol content and antioxidant activity. The effect of 10– 40 % of quinoa sourdough on sensory properties of bread was also, evaluated. Finally, the best sample obtained from sensory evaluation (containing 25% quinoa sourdough) compared with control samples 1 and 2, prepared with Saccharomyces cerevisiae and 25% wheat sourdough, respectively, in terms of sensory and qualitative characteristics. The results showed the application of quinoa flour in sourdough preparation increased the growth rate of Lactobacillus plantarum compared to wheat flour sourdough. Evaluation of total phenol content and antioxidant activity of wheat and quinoa dough samples before and after fermentation showed quinoa dough has the higher amount of phenolic compounds and antioxidant activity and fermentation process induced to significant increase of mentioned characteristics of dough samples. The results of evaluation the effect of quinoa sourdough on sensory properties of bread showed the sample contains 25% quinoa sourdough had the highest sensory scores compared to control 1 and 2. Evaluation of hardness, staling and moisture content showed no significant difference among the bread prepared with quinoa sourdough and control 1. The results of crust color evaluation of the bread samples showed the addition of quinoa sourdough to bread formulation significantly decreased the amount of 𝐿 ∗ and 𝑏 ∗ parameters but, increased the 𝑎 ∗ value