Review Article

Overview of Catalytic Properties of Fungal Xylose Reductases and Molecular Engineering Approaches for Improved Xylose Utilisation in Yeast

Sk Amir Hossain, Danijel Švec, Vladimir Mrša, Renata Teparic

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 47-58

Background and Objective: Xylose reductases belong to the aldo-keto reductase family of enzymes, which catalyse the conversion of xylose to xylitol. Yeast xylose reductases have been intensively studied in the last two decades due to their significance in biotechnological production of ethanol and xylitol from xylose. Due to its GRAS status and pronounced tolerance to harsh conditions, Saccharomyces cerevisiae is the ideal organism for industrial production of both xylitol and ethanol. However, Saccharomyces cerevisiae is unable to use xylose as the sole carbon source due to the lack of xylose specific transporters and insufficient activity of metabolic pathways for xylose utilisation. The aim of this paper is to give an overview of attempts in increasing biotechnological potential of xylose reductases and to highlight the prospective of this application.

Results and Conclusion: In order to create strains with improved xylose utilization, different approaches were attempted including simultaneous overexpression of xylitol dehydrogenase, xylose reductase and pentose phosphate pathway enzymes, heterologous expression of putative xylose transporters or heterologous expression of genes coding for enzymes included in the xylose metabolism, respectively. Furthermore, number of attempts to genetically modify different xylose reductases is increasing. This review presents current knowledge about yeast xylose reductases and the different approaches applied in order to improve xylose metabolism in yeast.

Conflict of interest: The authors declare no conflict of interest.

Original Article

Development of Synbiotic Milk Chocolate Enriched with Lactobacillus paracasei, D-tagatose and Galactooligosaccharide

Aziz Homayouni Rad, Aslan Azizi, Roghayeh Darghahi, Omid Bakhtiari, Mina Javadi, Maryam Jafarzadeh Moghaddam, Hamideh Homayouni Rad, Seyed Bagher Mirtajeddini, Noushin Mobaraki Asl, Maryam Tayebali, Haniyeh Rasouli Pirouzian

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 59-68

Background and Objective: Prebiotics are food ingredients that induce the growth or activity of beneficial bacteria (Bifidobacteria and Lactobacilli). Galactooligosaccharide and tagatose are two main prebiotic compounds which are used in the food industry. Chocolate is widely consumed all over the world and could be used as an excellent vehicle for delivery of prebiotics. Furthermore, the incorporation of probiotics into chocolate, allows broadening the health claims of chocolate. The aim of the current study was to investigate the effect of tagatose and galactooligosaccharide on the physicochemical and sensory properties of milk chocolate and the survivability of Lactobacillus paracasei in the optimized formulation.

Material and Methods: Probiotic milk chocolate containing Lactobacillus paracasei were formulated by replacing a portion of the sucrose with the galactooligosaccharide powder and tagatose. For this purpose various concentrations of galactooligosaccharide and tagatose (2.5, 5 and 7.5% w w-1) along with stevia were used in chocolate formulation. Nine formulations were examined to determine some physicochemical, mechanical and sensory properties in order to find the optimum concentrations of these components. The lyophilized Lactobacillus paracasei were incorporated in the optimal formulation of prebiotic milk chocolate. The viability of probiotic bacteria in milk chocolate was carried out during storage at 22°C for up to 6 months.

Results and Conclusion: In general, chocolate formulations with high levels of galactooligosaccharide, achieved the highest plastic viscosity and yield stress. The lowest viscosity and yield stress were observed for the samples containing high concentrations of tagatose and in control. In addition, galactooligosaccharide at higher ratios induced the least desirable sensorial effects, whereas tagatose improved the overall acceptability. It can be concluded that the overall acceptability of milk chocolate samples were with (7.5), tagatose: galactooligosaccharide ratios of 2.5%-2.5%, presenting the optimal applicable range as prebiotic compounds. Numbers of live Lactobacillus paracasei cells remained above 8.0 log CFU g-1 until 6 months under ambient conditions. Milk chocolate was shown to be an excellent vehicle for the delivery of Lactobacillus paracasei, and the prebiotic ingredients galactooligosaccharide and tagatose did not interfere in its viability.

Conflict of interest: The authors declare no conflict of interest.

Preparation and Characterizations of Chitosan/Citral Nanoemulsions and their Antimicrobial Activity

Gehan I. Kh. Marei, Entsar I. Rabea, Mohamed E. I. Badawy

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 69-78

Background and Objective: The antimicrobial activity of essential oils has been long recognized, however, they easily evaporate and/or decompose during preparation, owing to direct exposure to heat, pressure and light. The current study deals with the formulation and characterization of bio-based oil in water nanoemulsions and their antimicrobial activity against plant pathogens.

Material and Methods: Citral oil and low molecular weight chitosan were used for preparation of nanoemulsions in the presence of sodium tripolyphosphate. Nanoemulsions were prepared by adding dropwise citral at different ratios into an aqueous solution containing chitosan, sodium tripolyphosphate and surfactant with continuous stirring and then ultrasonication. The success of formulation was confirmed by dynamic light scattering and scanning electron microscopy techniques. Physical stability and viscosity were investigated in details. The antimicrobial activity was evaluated against Erwinia carotovora, Aspergillus niger and Rhizopus stolonifer.

Results and Conclusion: The nanoemulsions had a polydispersity index ranged from 0.508 to 0.614 and particle size from 27 to 1283 nm. The highest antimicrobial activity was observed with F1 formulation (EC50 = 23, 278 and 221 mg L-1, against Erwinia carotovora, Aspergillus niger and Rhizopus stolonifer, respectively). Based on the antimicrobial activity, the prepared chitosan/citral nanoemulsions can be a cost-effective way to protect crops from microbial pathogens. Because such formulations contain bioactive products, the development of resistant pathogens can be delayed.

Conflict of Interest: The authors declare no conflict of interest.


Physicochemical Properties of Probiotic Soy milk Chocolate Mousse During Refrigerated Storage

Golnoush Taghizadeh, Mahshid Jahadi, Hajar Abbasi

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 79-86

Background and Objective: Recently, several researchers have shown the benefits deriving from probiotic products containing lactobacilli and bifidobacteria in their formulation. The purpose of this study was to develop a probiotic chocolate mousse using milk and soy milk in formulation with regard to survival of probiotic bacteria and sensorial acceptance during 21 days.

Material and Methods: Nine functional probiotic chocolate mousse formulations were produced by milk, milk/soy milk and soy milk and 3 probiotic strains (Lactobacillus acidophilus; Lactobacillus paracasei; Bifidobacteriumlactis). ThepH, acidity, survival of microbial strains, rheological and sensory properties of all treatments were monitored during 21 days refrigerated storage (4°C).

Results and Conclusion: The pH drop rate and acidity increase rate of all samples were significant during 21 days of storage (p≤0.05). There was a significant increase in the probiotic bacteria of all samples during 21 days of storage at 4°C (p≤0.05). However, the rate of probiotics growth was accelerated in formulation prepared with soy milk and milk/soy milk (1:1) in the chocolate mousse at day 7 and 14. Rheological experiment demonstrated that all samples known as viscoelastic solid dessert had shear-thinning behavior. In conclusion, chocolate dessert including soy milk as well as milk was shown to be more effective vehicle for delivery of probiotics, including Lactobacillus acidophilus, Lactobacillus paracasei, Bifidobacteriumlactis.

Conflict of interest: The authors declare no conflict of interest.

Statistical Optimization of Medium Compositions for High Cell Mass and Exopolysaccharide Production by Lactobacillus plantarum ATCC 8014

Nor Zalina Othman, Abdul Rahman Jabir Mohd Din, Zahida Mohamad Azam, Mohamad Azuan Rosli, Mohamad Roji Sarmidi

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 87-96

Background and Objective: Lactobacillus plantarum ATCC 8014 is known as a good producer of water soluble exopolysaccharide. Therefore, the aim of this study is to optimize the medium composition concurrently for high cell mass and exopolysaccharide production by Lactobacillus plantarum ATCC 8014. Since both are useful for food and pharmaceutical application and where most studies typically focus on one outcome only, the optimization process was carried out by using molasses as cheaper carbon source.

Material and Methods: The main medium component which is known significantly give high effect on the cell mass and EPS production was selected as variables and statistically optimized based on Box-Behnken design in shake flask levels. The optimal medium for cell mass and exopolysaccharide production was composed of (in g l -1): molasses, 40; yeast extract, 16.8; phosphate, 2.72; sodium acetate, 3.98. The model was found to be significant and subsequently validated through the growth kinetics studies in un-optimized and optimized medium in the shake flask cultivation.

Results and Conclusion: The maximum cell mass and exopolysaccharide in the new optimized medium was 4.40 g l-1 and 4.37 g l-1 respectively after 44 h of the cultivation. As a result, cell mass and exopolysaccharide production increased up to 4.5 and 16.5 times respectively, and the maximal exopolysaccharide yield of 1.19 per gram of cells was obtained when molasses was used as the carbon source. In conclusion, molasses has the potential to be a cheap carbon source for the cultivation of Lactobacillus plantarum ATCC 8014 concurrently for high cell mass and exopolysaccharide production.

Conflict of interest: The authors declare no conflict of interest.

Fig juice Fortified with Inulin and Lactobacillus Delbrueckii: A Promising Functional Food

Sima Khezri, Razzagh Mahmoudi, Parvin Dehghan

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 97-106

Background and Objective: Nowadays, consumption of functional foods is favored because of their health promoting characteristics. Also there is an increasing demand for nondairy products because of lactose intolerance in dairies. Fig juice as a source of dietary fiber and other nutrients would be a functional food. Adding probiotics and prebiotics makes it more functional for daily use. No study has yet been done on synbiotic fig juice. Accordingly, the aim of this study was to characterize synbiotic fig juice prepared by Lactobacillus delbrueckii and inulin.

Material and Methods: Samples consisted of control fig juice; fig juice fermented by Lactobacillus delbrueckii (probiotic) and fig juice containing inulin fermented by Lactobacillus delbrueckii (synbiotic) were produced. Physico-chemical parameters, total phenolic content, antioxidant capacity and microbial survival aspects were analyzed during the fermentation period. Aforementioned parameters were also evaluated in 4 weeks with one-week time intervals. Sensory characteristics of fig juices were assessed in the second week of storage.

Results and Conclusion: The results showed significant differences among treatments (p≤0.05) in physico-chemical indices during incubation and storage time. Total phenolic content and antioxidant capacity of fermented fig juices were significantly increased in comparison to the control samples (p≤0.05). Viability of Lactobacillus delbrueckii was increased in both probiotic and synbiotic treatments during incubation; but a significant reduction was observed during storage time. Sensory analysis revealed that there were significant differences in terms of odor, taste and overall acceptance between the fermented fig juices and control (p≤0.05) and the highest scores were obtained for control. Considering viable counts of Lactobacillus delbrueckii depicted that fermented fig juice could be a suitable medium for survival and proliferation of Lactobacillus delbrueckii in adequate amount for health promotion. So this research showed that fig juice can be a potential product for manufacture of a new functional food.

Conflict of interest: The authors declare no conflict of interest.

Production of Vitamins B3, B6 and B9 by Lactobacillus Isolated from Traditional Yogurt Samples from 3 Cities in Iran, Winter 2016

Pegah Hamzehlou, Abbas Akhavan Sepahy, Sedigheh Mehrabian, Farzaneh Hosseini

Applied Food Biotechnology, Vol. 5 No. 2 (2018), 23 March 2018, Page 107-120

Background and Objective: B-group vitamins have important roles in many aspects of cellular metabolism and humans cannot synthesize them. So, they should be obtained from external resources. This project provides a new insight into assessing the production of vitamins B3, B6 and B9 by Lactobacillus, isolated from traditional yogurt samples from 3 different cities of Iran; Golpayegan, Sanandaj and Tehran (Damavand).

Material and Methods: Following 72 h of anaerobic culture of the Lactic acid bacteria at 37°C in 5% CO2, some Lactobacillus species from traditional yogurt samples were isolated and characterized both morphologically and biochemically. Isolates were identified following 16S rRNA PCR-amplification and sequencing. Including Lactobacillus (L.) ozensis strain Gon2-7, L. acidophilus strain KU, L. helveticus strain D76, L. helveticus strain Dpc 4571, L. fermentum strain 1, L. rossiae strain DSM15814T, L. casei strain NCDO, L. delbrueckii strain ATCC 11842, L. crispatus strain MRS 54.4, L. delbrueckii strain SB3 and L. paracasei subsp. tolerans JCM1171 (T). The sequence of L. paracasei subsp. tolerans JCM1171 (T) was submitted to the NCBI. The ability to produce B-group vitamins was evaluated by high performance liquid chromatography. Lactobacillus strains and amount of vitamin B3, B6 and B9 production were analyzed by Analysis of Variance test.

Results and Conclusion: Eleven isolates of Lactobacillus species from traditional yogurt samples were identified. Optimal conditions for Lactobacillus growth were pH 5-6 and temperatures 37-40°C. The isolates produced vitamins B3, B6 and B9. L. paracasei subsp. tolerance JCM 1171 (T) showed the highest amount of produced vitamins (p≤0.01) consist of vitamin B6 (1566.17 µg ml-1) and B9 (1279.72 µg ml-1). L. acidophilus strain KU showed the highest production of vitamin B3 (522.7 µg ml-1). L. fermentum produced the highest amount of vitamin B2. These strains are a natural and cost efficient source of vitamin. The Lactobacillus strains isolated in this research particularly, L. paracasei, could be applied in improving new fermented products, fortified with B-group vitamin that could be applied as substitution for enriching and supplementation with the controversial synthetic vitamins.

Conflict of interest: The authors declare that there is no conflict of interest.