Published: 2021-07-29

Investigation of the antibacterial activity against Cutibacterium acnes of lysozyme pu-rified from “Co Co” duck egg whites

Khoa Nguyen Tran, Van Song Toan Vo
Abstract | PDF
Lysozyme has been applied in various fields such as food technology, medicine, and diagnostics because it can resist many types of bacteria. In this research, lysozyme from duck egg whites was studied to evaluate the antibacterial activity against Cutibacterium acnes (C. acnes) often causing acne on human skin. Lysozyme was purified from duck egg whites by ion-exchange chromatography and gel-filtration chromatography. After that, this enzyme was used to investigate the resistance to C. acnes at different pH, temperature, concentration, and storage conditions. The results presented that lysozyme exhibited the best resistance to C. acnes at pH 6.0 and 6.5 on trypticase - yeast extract - heart extract - glycerol agar (TYEG) medium, at 30°C and 35°C. Additionally, these conditions had the least effect on lysozyme antibacterial activity. The minimal inhibitory concentration (MIC80) and minimum bactericidal concentration (MBC) of lysozyme to C. acnes were 0.55 mg/mL and 1.11 mg/mL, respectively. Lysozyme could keep up the best antimicrobial activity when stored at -20oC and -10oC; After 30 days, it still kept nearly 80% of its activity. These findings will offer a basis for larger-scale production of lysozyme powder for further research and commercial purposes, especially skin-care products.

Evaluation of the purification process of phosvitin extracted from chicken egg yolk using liquid chromatography

Vo Van Song Toan, Thi Bao Tran Le, Khoa Nguyen Tran, Thanh Nam Huynh, Hoang Thinh Nhan, Viet Ha Tao
Abstract | PDF
Phosvitin from chicken egg yolk, known as a phosphoglycoprotein, owns a very strong metal chelating property due to its polyanionic character. This study aimed to evaluate the factors affecting the purification process and suitable conditions to increase phosvitin’s purity. Phosvitin was separated from yolk granules by using 10% of NaCl solution in 0.05 M NaOH solution and heat treatment which removes lipoprotein from the extracted solution. The highest phosphorus content (58.14 mg) and phosphorus recovery rate (32.4%) were obtained at thermal treatment of 30℃ for 30 minutes. In addition, phosvitin was purified using anion-exchange chromatography (AEC) and gel-filtration chromatography (GFC). The fraction 1 (F1) obtained from AEC using UNO-Sphere Q at pH 8 had the recovery rate of phosvitin approximately 72.73%. Furthermore, fraction F1 was separated on GFC to obtain two main sub-fractions (F1 and F2). Sub-fraction F1 from gel filtration was composed mostly of β-phosvitin with a high recovery rate (81.93%) while F2 was dominant with α-phosvitin in a lower phosvitin recovery rate (16.89%). These findings will provide useful information for further researches on other properties of phosvitin so that it can be applied widely in human needs.

Study on corporate culture of vietnamese enterprises: An approach of denison’s model

Thach Keo Sa Rate, Chau Thi Le Duyen, Nguyen Quang Tuong, Thi Ngoc Hoa Nguyen, Pham Tuyet Anh Nguyen
Abstract | PDF
This study was conducted to identify the elements that constitute corporate culture, applying Denison’s organisational culture (DOC) model. The study uses the following data analysis methods: descriptive statistics methods were used to determine the enterprise culture's strengths and weaknesses and the DOC model to assess corporate culture. The results show that the corporate culture scale of the studied business is made up of 12 factors: empowerment, team orientation, capacity development, core values, agreement, coordination and integration, creating change, customer focus, organizational learning, strategic direction and intent, goals and objectives, and vision. The results show that the studied enterprises achieve consistency when building a long-term vision and mission, and stable objectives. According to the DOC model's calculation formula, core values, agreement, coordination and integration are also significantly promoted in the studied enterprises' corporate culture.

Adoption of TBLT at a primary school in Vietnam: A case study

Le Diem Trang Bui
Abstract | PDF
This case study provides an account of how a Vietnamese primary school teacher carried out the task-based versions of the presentation, practice and production (PPP) speaking lessons in an authentic primary school classroom. Data were collected from digital recordings of the lessons, semi-structured interviews, and field notes. Detailed descriptions were made of each of the phases of the videoed lesson and then compared with the field notes. The interview data were analysed manually following an inductive approach to data analysis. The results indicated that the teacher and her students successfully carried out the two redesigned PPP speaking lessons in her normally scheduled classroom. The results point to the feasibility of redesigning the PPP lessons to reflect task-based language teaching (TBLT) principles and of implementing the task-based versions of the PPP speaking lessons in real classrooms.

Effect of different salinities on the susceptibility of striped catfish (Pangasianodon hy-pophthalmus) to Aeromonas hydrophila bacteria causing hemorrhagic disease

Thi Hoang Oanh Dang, Truong Quoc Phu
Abstract | PDF
This study was conducted to determine the effect of different salinities on striped catfish (Pangasianodon hypophthalmus) susceptibility to hemorrhagic disease causing by Aeromonas hydrophila bacteria. The experiment was set up in plastic tanks at various salinities (0, 3, 5, 8, 11 and 14‰). Experimental fish (about 25 ± 0.8g/fish) were challenged with A. hydrophila bacteria by intramuscular injection. After infection, the mortality and disease signs were recorded for 14 days. At the same time, bacteria re-isolation and re-identification were carried out with infected fish samples that displayed signs of lethargy, disorientation, hemorrhagic in anal, peritoneal sinus and spleen. Recorded cumulative mortality after 14 days was 86.7% at salinity 0‰ and 8.3% and 11.7% at salinities 11 and 14‰, respectively. At higher salinity, striped catfish is less susceptible to A. hydrophila bacteria than at lower salinities.

Status of using rope in purse seine fisheries in Viet Nam

Nguyen Phan Phuoc Long, Dinh Xuan Hung, Tran Xuan Lam
Abstract | PDF
This study is to investigate the status of using rope in purse seine fisheries in Viet Nam based on surveyed data from 13 provinces/cities across country. Statistic data were taken randomly from 30 purse seine samples per each region of North, Middle, and South by pre-designed questionnaire with direct survey method of fishing gears combined with interview with the owners/captains. The results indicated that the initial constructing and annual replacing ropes of purse seine is mainly concentrated in the group of diameters from 10 - 20 mm. Up to 98% of Polypropylene (PP) material is used in Vietnamese purse seine. Float line and lead line are used the most ropes in purse seine. In purse seine fisheries, the annual additional rope is one quarter of the original amount of rope fitted. Purse seine in the Middle and the South is larger than that in the North of Viet Nam. The ratio of lengths between the float line and the lead line among the regions is different. The ratio of the main purse line with the lead line ranges from 1.1 to 1.75. Average life expectancy of main purse line is lowest in rope types of the purse seiners. The characteristics of the fishing grounds are different in these three regions, so the rope of purse seine is also different.

Antimicrobial activity of herbal extracts against Vibrio spp. bacteria isolated from white feces syndrome on white leg shrimp (Litopenaeus vannamei) in some provinces in the mekong delta

Minh Ut Truong , Thi Tu Uyen Dao, Tu Thanh Dung
Abstract | PDF
The study was conducted to determine the antibacterial activity of three herbal extracts: guava (Psidium guajava), leafflower (Phyllanthus urinaria L), beach daisy (Wedelia biflora (L.) DC ) against Vibrio spp. isolated from white feces syndrome infected shrimp in some provinces in the Mekong Delta. The antibacterial activity of the three herbal extracts was evaluated by the well diffusion method, Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). The results indicated that there were 102 isolates in total of 378 shrimp samples which were clarified into 7 groups. Among these group, Vibrio alginolyticus group were the most abundant species with the percentage of 50 %, followed by Vibrio cholerae group with the percentage of 17.7%. The herbal extracts of P. guajava and P. urinaria L showed a broad - spectrum antibacterial activity against ten isolates which were selected for MIC and MBC test. The extract of P. urinaria L had the strongest antibacterial activity against V. harveyi CM3HPA2 and V. alginolyticus CM3IB2 (MIC of 0.2 mg/ml, MBC of 0.39 mg/ml). The obtained results indicated that the herbal extract of P. urinaria L will be a good candidate for reducing opportunistic pathogens Vibrio spp. abundant in gastrointestinal tract of shrimp.

Antioxidant activity of enzyme-assisted extract derived from round kumquat peel (Fortunella japonica)

Nguyen Dinh Duyen Hai, Tam Vo Dinh Le
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This study intends to apply enzyme-assisted extraction method to determine the antioxidant activity of round kumquat peel extract. Firstly, chemical composition of the kumquat peel was determined. Then, single factor test was employed to evaluate the effects of enzyme treatment conditions (enzyme amount and extraction time, ethanol concentration, material:ethanol ratio, extraction time and extraction temperature) on total phenolic content (TPC) and antioxidant activity of the kumquat peel extract. The result showed that the content of phenolic compounds in the kumquat peel achieved 1.3%. The peel extract exhibited the maximum TPC of 335.96±16.79 milligrams of gallic acid equivalents (mg GAE)/g dry matter, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) cation radical (ABTS●+) scavenging activity of 1993.26±99.66 μmol Trolox Equivalent (TE)/g dry matter and ferric reducing antioxidant power (FRAP) value of 3202.86±160.14 μmol TE/g dry matter. This extract was obtained under   enzyme treatment condition including enzyme content of 9 U/g dry matter, enzyme-treating time of 90 min and the extraction condition comprising of kumquat peel: 96% ethanol ratio of 1:40 (w/v), extraction time of 150 min and temperature of 50°C. The results revealed that the kumquat peel extract could be used as a potential natural antioxidant in food and/or pharmaceutical products.

The effect of heating factors on the properties of heat-induced surimi gel under ohmic heating

Thi Van Nguyen, Nguyen Hong Ngan, Emiko Okazaki
Abstract | PDF
Ohmic heating (OH) is a method that heat is generated within the food due to its electrical resistance, resulting in a relatively linear heating rate and uniform temperature distribution. Because surimi-based paste contains water and salts, the conductivity is sufficiently good for the ohmic effect. Gelation induced by OH greatly depends on heating conditions such as heating speed, heating time, or electrical conductivity. However, the detailed information obtained is quite limited. Therefore, in order to clarify how ohmic heating affects the physical properties of surimi gel under OH, gels from croaker surimi (SA grade) were obtained using different heating conditions (heating speed, heating time, or salt concentration - electrical conductivity). Furthermore, the gels heated by ohmic heating were compared with the gel obtained by conventional water-bath heating. The results showed that, at the same heating rates, higher salt concentration generated better surimi gels for croaker surimi. Gels cooked ohmically at a slow heating rate performed significantly better than those cooked at a fast heating rate or heated conventionally in a water bath. There was little discernible difference in protein pattern between gels heated by OH and conventional water bath heating at fast heating rates with two different salt concentrations. The results also indicated that holding time at target temperature showed no effect on the gel. These results suggested that the properties of heat-induced surimi gels by OH are affected by not only heating speed but also holding time at maximum temperature and salt content.

Synchronization in complete networks of reaction-diffusion equations of FitzHugh-Nagumo type with nonlinear coupling

Phan Van Long Em
Abstract | PDF
The synchronization in complete network consisting of  nodes is studied in this paper. Each node is connected to all other ones by nonlinear coupling and is represented by a reaction-diffusion system of FitzHugh-Nagumo type which can be obtained by simplifying the famous Hodgkin-Huxley model. From this complete network, the sufficient condition on the coupling strength to achieve the synchronization is found. The result shows that the networks with bigger in-degrees of nodes synchronize more easily. The paper also presents the numerical simulations for theoretical result and shows a compromise between the theoretical and numerical results.