Vol. 14 No. 7 (2016): Tạp chí Khoa học Nông nghiệp Việt Nam

Bacillus subtilis is usually found in foods such as dry cured sausages, cheeses, traditional fermented milks, etc., in which they cooperate with other microorganisms during fermentation, release amylases, lipases and proteases… B. subtilis not only play with probiotic role but also produce antimicrobial substance. Muong Khuong chilli sauce is a naturally fermented product derived from Muong Khuong special peppers without heat treatment and is able to be preserved in ambient conditions for 1.5-2 years. Amongst 512 types of colonies, 48 Bacillus sp. strains were isolated from 80 chilli samples. Their ability against pathogenic bacteria was determined using the agar-well diffusion method through measuring the inhibition zone diameter. The four pathogenic bacteria strains tested were Escherichia coli RG1.1, Salmonella typhi GT4.3, Listeria monocytogenes MI2.6, and Staphylococcus aureus TS1.9. The results of 16S rRNA genotype sequencing for the two strains, TO43.13 and TO53.2, that had broad-range antimicrobial activity indicated that the TO43.13 sequence was homologous up to 95% with B. subtilis BcX1 (JX504009.1) and B. subtilis EPP2 2 (JQ308548.1). The TO53.2 strain sequence was homologous up to 94% with the two strains B. subtilis Pe-Lg-1 (FR687210.1) and B. subtilis YT2 (HQ143571.1). The optimal conditions for the growth and development of these two strains were with a 0.6% concentrations of NaCl, a pH of 7, and a temperature of 35°C.

Quá trình tách chiết piceatannol từ hạt chanh leo - Passiflora edulis có hỗ trợ của siêu âm được nghiên cứu. Ảnh hưởng của nồng độ ethanol, nhiệt độ và thời gian siêu âm đến hàm lượng picetannol tách chiết được khảo sát. Điều kiện tốt nhất cho sự tách chiết như sau: nồng độ ethanol, 80% (v/v); nhiệt độ 70oC; thời gian tách chiết, 30 phút. Với điều kiện này, hiệu suất thu hồi piceatannol là 4.5 ± 0.17 mg từ 1 g chất khô hạt. Bột đông khô dịch chiết piceatannol thể hiện khả năng kháng hai dòng tế bào ung thư bao gồm HeLa và MCF7. Nghiên cứu này có thể coi như bước đầu cho việc sản xuất sản phẩm giàu piceatannol sử dụng như sản phẩm hỗ trợ sức khỏe từ hạt chanh leo, một phụ phẩm của quá trình chế biến nước quả.

In this work, we investigated the developmental changes in cell-wall polysaccharides associated with the physiological properties of pericarp and mesocarp tissues of grape berries during ripening, and aimed to clarify the mechanisms involved in the softening process. The firmness of fruits, ethanol insoluble solids content, changes in pectins content, and hemicellulose and cellulose content were studied. The results showed that the changes in pectic fractions occurred dramatically in the sub-epidermal layer (pericarp), and the amount of water soluble pectin (WSP) increased greatly during berry ripening in the three cultivars tested, while the changes were not significant in mesocarp and/or other pectic polysaccharide fractions. Moreover, the hemicellulose content did not change markedly from stage 1 to stage 3, and decreased significantly to stage 4 in all cultivars, while the cellulose content decreased markedly during ripening in all cultivars analyzed, both in pericarp and mesocarp tissues.

White cabbage (Brassica oleracea var. capitata f. alba) has high nutritional value and is considered “the magic drug for the poor.” As a member of the Brassica family, white cabbage contains glucosinolates that prevent the growth of some types of cancer, enhance immunity of cells, and are capable of producing antibiotics and preventing disease. The present study aimed to extract glucosinolates from by-products of the white cabbage industry to apply in the preservation of agricultural products and foodstuff, and the prevention of postharvest losses caused by microorganisms. The study focused on understanding the impact of materials, solvents, and extraction parameters to glucosinolates extraction from by-products of cabbage. Plant material particles sized 0.5 mm to 1 mm in diameter were considered the best plant material sizes to extract glucosinolates. The aqueous solution of methanol (60%), the ratio of material to solvent (g/ml) 1:10, the extraction temperature of 50°C, and the extraction time of 1 hour were the most efficient for extractions of glucosinolates from the by-products of cabbage.

In this study, 170 strains isolated from 22 samples of fermented foods were identified as lactic acid bacteria by biochemical and morphological methods. Of which, fifty two isolated strains had antibacterial activity when tested using the agar well-diffusion method. Two strains, CS3.7 and FME1.7, expressed high antimicrobial activity against all of the four indicator bacteria: E. coli, Bacillus cereus, Listeria monocytogenes, and Salmonella spp., and were selected for further studies. The results showed that both strains had antimicrobial activity against the indicator strains 2 hours before the bacteria reached the stationary phase. The antimicrobial activity of the cell free supernatants was completely lost when incubated with papain enzyme for 2 hours at room temperature. This result led us to conclude that antimicrobial substances of the free cell supernatants were peptides. Characterization of the peptides demonstrated that they were highly stable at 68oC, in which residual activity of FME1.7 and CS3.7 was above 90% and 75% for 20 min, respectively. At 100oC for 10 min, the antimicrobial activity of the two strains remained around 40%. The study also indicated that the peptides were stable at pH 5. However, antimicrobial activity was significantly reduced when incubated in other pHs. The results showed that peptides of CS3.7 and FME1.7 are quite promising to be used as biopreservatives because of their high range of antimicrobial activity and thermostability.

This study examined the effects of perilla essential oil treatments on pH, NH3, and thiobarbituric acid (TBA), and microbiological indices, including total aerobic counts, E. coli, and Staphylococcus aureus, on the shelf-life of fresh pork. Fresh sirloin pork was sprayed with perilla oil at two concentrations of 1% (v/v) and 2% (v/v) and stored at 5°C. Results revealed that compared to the control samples stored in the same refrigerated cold condition, the shelf-life of the treated sirloin pork was extended to 6 and 9 days, respectively to the two concentrations of perilla oil applied. This indicates that perrila essential oil might play an important role as antioxidant and antibacterial agent in prolonging the shelf-life of refrigerated fresh pork. The treatment with 1% perilla oil had less effect on color and flavor of the fresh pork sample compared to concentration of 2%.

Tea polyphenol extracts (TPE) (94.08% dry mater (DM) total polyphenols, 71.14% DM total catechins) at three concentrations (100 ppm, 200 ppm, and 400 ppm) were examined in soybean oil in accelerated oxidation conditions at 600C. A sample without antioxidants and a sample with 100 ppm butylated hydroxyanisole (BHA) + 100 ppm butylated hydroxytoluene (BHT) were used as the negative and positive controls, respectively. The results showed that TPE was more effective than BHA+BHT for the stability of soybean oil at the same concentration (200 ppm). TPE was capable of the maintenance of the sensorial properties, and reductions of diene and peroxide formations as well as the secondary oxidative compounds (p-anisidine). Concerning the TPE concentration, 200 ppm of TPE was suitable to stabilize the soybean oil quality during storage.

Fresh green peas are rich in vitamin C, a powerful natural water-soluble anti-oxidant. Green peas are normally consumed after thermal processing, mostly canning or cooking, which causes vitamin C degradation and chlorophyll breakdown. This study aimed to determine the changes of vitamin C and chlorophyll during thermal processing through analyzing their contents in peas during typical thermal processing stages, including blanching, boiling, and pasteurizing. The results revealed that the vitamin C content was reduced significantly when the blanching temperature increased by 10oC. The vitamin C in green peas blanched at 70oC, 80oC, and 90oC for 3 minutes were 32.68, 12.60 and 13.02 mg%, respectively. A high loss of chlorophyll was recorded when the peas were blanched at 90oC. The experiment’s results also showed that the vitamin C and chlorophyll losses were higher in the peas put in water of 22oC than those put in water of 100oC prior to boiling. Pasteurizing at 95oC for 8 or 11 minutes gave lower vitamin C content in the peas than at 100oC for 5 minutes. For retention of vitamin C and chlorophyll, it is recommended that green peas be put in initial water of 100oC during boiling, blanching, and pasteurization as fast as possible in the canning process.

The objective of this study was to evaluate the effect of temperature on physiological changes of ‘Savior’ tomatoes during postharvest ripening. Tomatoes grown in the winter season and summer season were harvested at two maturity stages, mature green and breaker, and ripened at two temperatures, 22°C and 35°C. At the time of harvesting, ethylene production and respiration rate were measuredand then again every two days during the 14 day postharvest ripening process. The results showed that temperature has a great effect on the physiological attributes of tomatoes during postharvest ripening. Ethylene production and respiration rate in tomatoes ripened at 22°C were higher than those ripened at 35°C. Ethylene production was slightly higher in fruits grown in the summer season than those grown in the winter season. Postharvest ripening was inhibited at 35°C.

Lactobacillus plantarum is commonly found in many fermented food products and is an ideal candidate for the development of probiotics, which have healthy benefits for the body. The starter cultures have to be prepared to maintain their activity and stability to make use of the advantages of this species. Freeze-drying is a widely used technique for the preservation and storage of heat sensitive biological materials. However, bacterial cells can suffer from dehydration stress as water is removed. Therefore, to reduce adverse effects, protective substances can be added to samples before being freeze-dried to minimize stress associated with freeze-drying and to increase survival rate. Solutions of trehalose, lactose, trehalose + lactose, skim milk, and 2X lyophilization reagent were used as protective media for Lactobacillus plantarum A17 during freeze-drying. The survival rate, moisture content, and fermentation efficiency after freeze-drying were examined. The results showed that trehalose provided the highest survival rate followed by the combination of trehalose:lactose (64% and 61%, respectively). The moisture contents at the end of the freeze-drying cycle were less than 5% for all protectants tested. The efficiency of fermentation was significantly different (P < 0.01) between freeze-dried cells with and without protectants.

The objective of this study was to isolate lactic acid bacteria (LAB) from Vietnamese fermented pork meat (nem chua) and to determine their antimicrobial activity. A total of 101 LAB isolates were screened for their inhibitory effect on the indicator organism Lactobacillus plantarum JCM 1149 in the first selection by the agar spot test. Results showed that 58 isolates had activity against Lb. plantarum JCM 1149. From the 58 LAB, the second selection by agar well diffusion method used Lb. plantarum JCM 1149, Listeria monocytogenes, Bacillus cereus, E. coli, and Salmonella typhimurium as indicator organisms, and were inhibited by 18, 17, 6, 16, and 0 isolates, respectively. There were 5 strains (NH3.6, NT1.3, NT1.6, NT2.9, and NT3.20) with wide spectrum inhibition antimicrobial activity of both pathogenic gram-positive B. cereus and L. monocytogenes, and gram-negative E. coli. Furthermore, protease K enzyme was applied to test the antimicrobial activity of the 5 LAB isolates by bacteriocin, acid, or H2O2. Results indicated the NH3.6 strain had antimicrobial activity by bacteriocin. In addition, this research characterized the bacteriocin of the NH3.6 isolate and found it was stable in temperatures at 100°C and 120°C for 10 minutes, a pH = 3, and tolerant of NaCl concentration less than 8%. 

Drought is one of the most severe environmental stress factors that affects the growth and development of plants. The effects of drought are foreseen to increase with climate change and growing water scarcity. In many parts of the world, including Vietnam, plants may frequently encounter drought stress. Plants have evolved specific mechanisms to respond to drought stresses. Studying these protective mechanisms will contribute to our knowledge of tolerance and resistance to stress. Recently, some studies indicated that the ABO3 gene coding for WRKY63 is a key gene in stress signalling pathways related to drought tolerance, of which the functions and interactions are currently unknown. Therefore, investigating its functions and interactions are considered effective strategies to control a plant’s resistance against drought. In this study, we show the results of expression and purification of the ABO3 protein coding for WRKY63 in E. coli, a solid step towards studying about the protein’s interactions and functions. The ABO3 gene was amplified from cDNA of Arabidopsis thaliana by PCR, cloned into T-Blunt vectors, and sequenced. This gene then was subcloned into the expression vector pQE-30 and expressed in E. coli strain M15. Finally, the ABO3 recombinant protein was initially purified by affinity chromatography for further studies.

Phenolic compounds are present in all plant organs and are therefore an integral part of the human diet. They have been shown to play important roles in human health. Indeed, high intakes of tea, fruits, vegetables, and whole grains, which are rich in phenolic compounds, have been linked to lowered risks of many chronic diseases, including cancer, cardiovascular diseases, chronic inflammation, and many degenerative diseases. These potential beneficial health effects of phenolic compounds are a resultof their biological properties, including antioxidant, anti-inflammatory, anti-cancer, and antimicrobial activities. In this paper, the mechanisms of the biological actions of phenolic compounds will be presented and discussed.

The aim of the present study is to identify cellulose degrading bacteria and the effects of cultural and nutritional conditions for their cellulase activity. Among the tested bacterial strains, the GT1 strain had the highest cellulase production yields. This strain was further characterized by biochemical and morphological tests and identified as Bacillus subtilis, therefore, we primarily concluded that GT1 was Bacillus sp., denoted as Bacillus sp. GT1. Different parameters: temperature, pH, nitrogen and carbon sources, and metal ions were optimized. The optimal pH and temperature for the activity of crude enzymes were 7 and 35°C, respectively. Supplementation of peptone and corn starch to the culture medium is favored for enzyme secretion. The metal profile of the enzymes indicated that the enzymes were stimulated by Mn2+, Mg2+, and Ca2+, while Fe2+, Zn2+, and Cu2+ reduced activity of cellulase from the cellulolytic bacterial strain Bacillus sp. GT1. These results open up the broad application of GT1 in many fields.