Review Article

In the past decade much effort has been devoted to the development of new expression systems and novel techniques for the surface display of heterologous proteins in yeast in order to improve their applications in biotechnology, food technology, pharmacology and medicine. Heterologous protein-encoding genes are generally fused with genes coding for yeast cell wall proteins or their fragments required for anchoring. The variety of reactions by which a protein can be displayed at the cell surface enables finding the appropriate one for each individual protein. However, it is still challenging how to improve the efficiency of display of protein complexes and increase the quantity of protein displayed on the yeast surface. Recently, synthetic protein chimeras that self-assemble into the scaffolds on the yeast surface displaying different proteins have been constructed. This review focuses on systems and techniques for display of recombinant proteins on the yeast cell surfaces and applications afforded by this technology.

Original Article

Low grade grape juice concentrate was used as carbon source for xanthan production. Significant factors affecting xanthan concentration, productivity and viscosity were investigated using Plackett-Burman Design. Based on the obtained results, carbon and nitrogen concentrations, inoculum size and agitation rate, were assumed as significant factors. Broth culture viscosity and xanthan concentration were optimized using Response Surface Methodology with four independent variables: carbon source (30, 40, 50 g l-1), ammonium sulfate as nitrogen source (0.5, 1.25, 2 g l-1), agitation (150, 200, 250 rpm) and inoculum size (5, 10, 15% v v-1). Optimum level for each factor was obtained by desirability function approach. The average of xanthan gum production and its viscosity under optimized conditions were recorded as 14.35 g l-1 and 1268 cP, respectively. The average yield of production and productivity of xanthan within 72 h under optimized conditions were 35% and 0.19 g l-1 h-1, respectively. The current study showed the potential of low-grade grape juice concentrate as an economic carbon source for xanthan gum production.

Optimization of Phospholipase A1 Immobilization on Plasma Surface Modified Chitosan Nanofibrous Mat

Zahra Beig Mohammadi, Zohreh Hamidi-Esfahani, Mohammad Ali Sahari, Kianoush Khosravi-Darani

Applied Food Biotechnology, Vol. 3 No. 1 (2016), , Page 25-34

Phospholipase A1 is known as an effective catalyst for hydrolysis of various phospholipids in enzymatic vegetable oil degumming. Immobilization is one of the most efficient strategies to improve its activity, recovery and functional properties. In this study, chitosan-co-polyethylene oxide (90:10) nanofibrous mat was successfully fabricated and modified with atmospheric plasma at different times (2, 6 and 10 min) to interact with enzyme molecules. Scanning electron microscopy images revealed that the membranes retained uniform nanofibrous and open porous structures before and after the treatment. PLA1 was successfully immobilized onto the membrane surfaces via covalent bonds with the functional groups of chitosan nanofibrous mat. Response surface methodology was used to optimize the immobilization conditions for reaching the maximum immobilization efficiency. Enzyme concentration, pH, and immobilization time were found to be significant key factors. Under optimum conditions (5.03 h, pH 5.63, and enzyme dosage 654.36 UI), the atmospheric plasma surface modified chitosan nanofibers reached the highest immobilization efficiency (78.50%). Fourier transform infrared spectroscopy of the control and plasma surface-modified chitosan nanofibers revealed the functional groups of nanofibers and their reaction with the enzyme. The results indicated that surface modification by atmospheric plasma induced an increase in PLA1 loading on the membrane surfaces.

The effect of different carbon sources on bacterial cellulose production by Gluconacetobacter xylinus (PTCC 1734) and two newly isolated strains (from vinegar) under static culture conditions was studied. The production of bacterial cellulose was examined in modified Hestrin-Shramm medium by replacing D-glucose with other carbon sources. The results showed that the yield and characteristics of bacterial cellulose were influenced by the type of carbon source. Glycerol gave the highest yield in all of the studied strains (6%, 9.7% and 3.8% for S, A2 strain and Gluconacetobacter xylinus (PTCC 1734), respectively). The maximum dry bacterial cellulose weight in the glycerol containing medium is due to A2 strain (1.9 g l-1) in comparison to Gluconacetobacter xylinus as reference strain (0.76 g l-1). Although all of the studied strains were in Gluconacetobacter family, each used different sugars for maximum production after glycerol (mannitol and fructose for two newly isolated strains and glucose for Gluconacetobacter xylinus). The maximum moisture content was observed when sucrose and food-grade sucrose were used as carbon source. Contrary to expectations, while the maximum thickness of bacterial cellulose membrane was attained when glycerol was used, bacterial cellulose from glycerol had less moisture content than the others. The oxidized cellulose showed antibacterial activities, which makes it as a good candidate for food-preservatives.

Few studies have been reported regarding probiotic properties of Lactococcus lactis strains although they are extensively used as starter cultures in the production of dairy products. In this study 8 wild isolates of Lactococcus lactis were evaluated in vitro with regard to resistance to simulated gastric and intestinal juices, adherence ability to Caco-2 cells and HT29-MTX-E12 cell lines, anti-microbial activity, hydrophobicity and antibiotic susceptibility. The results revealed that all isolates had better survival after exposure to simulated gastrointestinal tract stresses in comparison to control probiotic Lactobacillus rhamnosus GG. Regarding adherence efficiency, almost all isolates exhibited similar adherence with control. Three isolates showed antibacterial activity against Gram-positive pathogens (Staphylococcus aureus and Listeria monocytogenes) through spot-agar method. Almost all isolates (seven out of eight) showed similar hydrophobicity to control probiotic. Regarding to antibiotic resistance, all isolates were susceptible to gentamicin, ampicillin, ciprofloxacin, erythromycin, tetracycline, penicillin, kanamycin and nitrofurantoin. Although, further investigations are necessary, it was concluded that strains derived from raw milk and home-made dairy products could be a remarkable reservoir for identification of new potential probiotic strains.

Encapsulation of olive oil is an effective method to protect it against environmental deteriorative factors. In this research, olive oil microcapsules were produced by complex coacervation method. The objective was to examine the effect of gelatin and Arabic gum as shell materials, lactose as cryprotectant, and different acidification times on microencapsulation efficiency of olive oil. Arabic gum 2-5% (w/w), gelatin 2-5% (w/w), lactose 1-5% (w/w), and different acidification times (0-60 min( were given to Design-Expert software using the Response Surface Method. The surface appearance and morphology of the microcapsules were characterized by an optical microscope and scanning electron microscope. Microencapsulation efficiency ranged from 43.9 ± 0.98% to 90.5 ± 2%. The highest efficiency was obtained in gelatin 2% (w/w), Arabic gum 2% (w/w), lactose 3% (w/w) and acidification time of 60 min. The best model for describing the microencapsulation efficiency was quadratic model. The highest effect in microencapsulation efficiency was related to interaction of gelatin-Arabic gum and lactose-acidification time because they had higher coefficient estimate.

Short Communication

Effect of Refrigerated Storage on Sensory Properties and Viability of Probiotic in Grape Drink

Shirin Malganji, Sara Sohrabvandi, Mahshid Jahadi, Ameneh Nematollahi, Bahareh Sarmadi

Applied Food Biotechnology, Vol. 3 No. 1 (2016), , Page 59-62

The popularity of non-dairy probiotic products continues to persist as the consumers prefer functional foods satisfying their health needs. Among these promising foods, probiotic grape drink would have beneficial effects on modifying gastrointestinal flora and human health. In this study, the pasteurized grape drink was inoculated by three species of lactic acid bacteria (Lactobacillus delbrueckii, Lactobacillus plantarum and Lactobacillus rhamnosus) separately, and the samples were subjected to non-fermented conditions. The samples were kept in the refrigerator at 4°C for 4 weeks to determine microbial viability and sensory evaluation during cold storage. Based on the results obtained, Lactobacillus rhamnosus and Lactobacillus delbrueckii displayed greater surviving than Lactobacillus plantarum during cold storage. Sensory evaluation outcome indicated that grape juice inoculated with Lactobacillus rhamnosus showed higher overall acceptability over 4 weeks of storage. The findings revealed that sustainability and sensory properties of probiotic products are important from the consumers’ point of view; therefore, production of probiotic grape juice by Lactobacillus rhamnosus, due to its higher viability and desirable organoleptic properties, is suggested.