ISOLATION AND CHARACTERIZATION OF BACTERIOCIN-PRODUCING MICROORGANISMS FROM AGOS-OS

Agos-os, a fermented meat and sweetpotato mixture, was produced and analyzed for its microbial characteristics. pH decreased during fermentation. Mold and anaerobic bacterial counts increased while yeasts and aerobic bacterial counts decreased during the third and seventh day of fermentation. Six isolates with the widest zones of inhibition on the indicator lawn were selected for bacteriocin production. These isolates had exactly the same morphological, physiological and biochemical characteristics. The ribosomal RNA sequence was 99.5% identical with Enterococcus faecalis VRE 1492. The identification was confirmed through DNA homology test by the EMBL Genbank, Canada. This bacterium produced the L-isomer lactic acid. The amount of bacteriocin produced by the bacterium was optimized by growing the bacterium at different growth media, initial pH and fermentation time. Maximum production of bacteriocin was achieved in MRS (De Man Rugosa and Sharpe) medium (with glucose) at pH 7.50. The crude bacteriocin inhibited the growth of gram-positive bacteria such as Lactobacillus sake 15521 and Listeria innocua. The gram-negative bacteria such as Escherichia coli DH 5-alpha (with plasmid, PUC) , Salmonella typhii and Staphylococcus aureus were weakly inhibited. Other microorganisms such as Lactobacillus curvatus D31685 , Lactobacillus confusius M23036 , Lactococcus lactis MG1363 , Leuconostoc paramesenteroides S67831 , Pediococcus pentosaceus M58834 , Saccharomyces cerevisiae SS553 (wild type) and Escherichia coli JM109 (no plasmid) were not inhibited.     

ISOLATION AND CHARACTERIZATION OF PECTINESTERASE FROM VALENCIA ORANGE1

Thermolabile (TL) and thermostable (TS) pectinesterases (PE) were extracted from the pulp of fresh Valencia oranges by enzyme hydrolysis using a native pH and high ionic strength buffer system. Each form was separated individually by CM-Sephadex C-50, Phenyl Sepharose CL-4B and CM-Bio-Gel A chromatography. TLPE and TSPE exist as multiple forms which were shown to differ in their stability and effects on cloud loss in single strength orange juice.     

ISOLATION AND PHYSICOCHEMICAL CHARACTERIZATION OF STARCHES FROM DIFFERENT BANANA VARIETIES

The physicochemical properties of the starches extracted from three varieties of banana indigenous to Thailand were investigated. The Thai names of these varieties are Hak Muk, Nam Wa Kom, and Ta Nee. Starch from all three varieties were found to contain 30.9% to 32.0% amylose. Other components were moisture (11.47 to 11.76%), protein (0.22 to 0.93% dry weight basis dwb), lipid (0.07to 0.11 % dwb) and ash (0.07to 0.17% dwb). X‐ray diflraction patterns showed Hak Muk and Nam Wa Kom were of B type whereas Ta Nee was of C type. All three varieties showed strong paste stability to both thermal heating and mechanical shearing but high retrogradation. The banana starch paste stability in digerent pH slurries pH 7 to 4.5) indicated that they are suitable for food application that require high amylose and high retrogradation afer processing.     

ISOLATION AND CHARACTERIZATION OF TRYPSIN INHIBITORS FROM SOME THAI LEGUME SEEDS

Trypsin inhibitors from cultivars of cowpea (Vigna unguiculata (L.) Wasp.), pigeon pea (Cajanus cajan (L.) Millsp.) and bambara groundnuts (Voandzeia subterranea (L.) Thou) grown in Thailand were isolated and characterized. Extraction of seeds with NaCl rendered a higher recovery of trypsin inhibitor than other solvents tested (P<0.05). The extraction time affected the inhibitor recovery (P<0.05). The extraction time of 3 h was optimum for the recovery of trypsin inhibitor from pigeon and bambara groundnuts, whereas 1 h was optimum for cowpea. Based cn inhibitor activity of zones separated by electrophoresis, the molecular mass of the inhibitor from bambara groundnuts was 13 kDa. Two inhibitory bands were observed for cowpea (10 and 18 kDa) and pigeon pea (15 and 25 kDa). Partial purification of inhibitors was achieved by heat‐treatment at 90C for 10 min, followed by ammonium sulfate precipitation with 30–65% saturation. The partially purified inhibitors from four seeds were heat stable up to 30 min at 90C at pH 7.0. The activities were also retained over a wide pH range at 25C but were lost when samples were treated with β‐mercaptoethanol prior to electrophoresis.     

ISOLATION AND CHARACTERIZATION OF THE 11S GLOBULIN FROM AMARANTH SEEDS

Globulins of Amaranthus hypochondriacus were extracted with two different buffer systems which varied in ionic strength. SDS-PAGE analysis demonstrated that subunit patterns were different between the two extracting systems. Amarantin, the native 11S globulin of amaranth, and its subunits were purified by gel filtration chromatography and preparative electrophoresis. The native amarantin exhibited two heterogeneous forms of MW 330 and 400 kDa, which yielded the same subunit composition after reduction. SDS-PAGE analysis showed that prior to reduction, the 50–52 kDa subunit was the major band, and that after reduction, two new bands of 32–34 kDa and 22–24 kDa appeared. This is a typical characteristic of 11S proteins whose subunits consist of an acidic polypeptide (27–37 kDa) and a basic polypeptide (20–24 kDa) linked by a disulfide bond. Ultracentrification analysis showed that amarantin has a 11.9S sedimentation coefficient whereas DSC demonstrated that the denaturation temperatures in the presence of H₂O, Tris-HCl and K₂HPO₄-KH₂PO₄ are 99C, 99.8C and 103C, respectively.     

白底辐肛参酸性黏多糖的分离及特性研究

以K2CO3和木瓜蛋白酶从白底辐肛参中提取粗多糖，再以H2O2除色素，乙酸钾蛋白，柱层析后得到精制的酸性黏多糖，琼脂糖凝胶电泳表明其为单一成分。凝胶渗透色谱法测得分子量为71098u，多糖组成中硫酸基、葡萄糖醛酸、氨基半乳糖、岩藻糖含量分别为30．6％、15．46％、17．75％、13．56％。     

甘薯糖蛋白的分离纯化及其性质研究

采用二乙基氨基52离子交换和葡聚糖凝胶G100柱层析法,从甘薯中分离纯化甘薯糖蛋白,并对其理化性质进行了研究.通过高效凝胶过滤色谱和SDS-聚丙烯酰胺凝胶电泳表明糖蛋白的纯度为97%;测得其分子量为58575u.采用DSC技术对甘薯水溶性糖蛋白热力学性质进行了研究,结果表明甘薯水溶性糖蛋白的热变性温度为106.67℃,而去糖基后的热变性温度为66.84℃,说明糖蛋白上的寡糖链有很好的稳定作用,具有增强糖蛋白抗变性功能.     

ISOLATION AND CHARACTERIZATION OF NONTYPHOID SALMONELLA FROM HOSPITAL FOOD HANDLERS IN BEIJING, CHINA

Salmonella enterica isolates recovered from stool samples of healthy food handlers in two hospital dining halls in Beijing, China were characterized by serotyping, susceptibility to 15 antimicrobials and pulsed field gel electrophoresis (PFGE). Our data showed that 9.5% (29/305) of food handlers in these two dining halls were Salmonella carriers. Twenty-nine isolates were grouped into five serotypes including Agona, Derby, Enteritidis, Infantis and Senftenberg. All six Enteritidis isolates were resistant to chloramphenicol, nalidixic acid and tetracycline. Identical PFGE patterns were identified from food handlers in the same dining hall that indicated the possible transmission of Salmonella among food handlers and to customers. Our findings underscore the importance of food hygiene education and regular health examination among food handlers in dining halls in China.

PRACTICAL APPLICATIONS

Food handlers in dining halls should be considered as a high-risk group for Salmonella carrier state in China. Food hygiene education and regular health examination among food handlers in dining halls should be carried out.     

ISOLATION, PURIFICATION AND CHARACTERIZATION OF THE SEED STORAGE GLOBULIN AND ITS POLYMERIZED FORM FROM TRITICUM AESTIVUM

The salt-soluble globulin and its polymerized counterpart from wheat (Triticum aestivum) seed were isolated and purified to homogeneity employing both gel filtration and anion exchange chromatography. The two globulins were purified free of any purothionin (an oxidation-reduction protein) contamination. Some of the physico-chemical properties of purothionin are also reported. Both globulins were found to be oligomers composed of two polypeptide chains, i.e., 35,000 and 49,000 Da, with no apparent evidence of any covalent inter-chain disulfide linkages between these major subunits. The molecular weights for the globulin and its polymerized (i.e., polymerized via interchain disulfide bonds between various subunits of differing molecular weights, excluding any interchain disulfide bonds between the 35,000 and 49,000 Da subunits) counterpart were determined to be 474,000 and 567,000 Da, respectively, by gel chromatography. Surface charge profiles of fractions 2 and 3 were determined using electrophoretic isoelectric focusing, electrophoretic titration and zeta potential analysis and indicated pIs of 6.90 and 6.55, respectively. The nonpolymerized globulin was found to be more positively charged below its isoelectric point and less negatively charged above it than its polymerized counterpart. Microcalorimetric studies indicated that the two globulins had similar T_m values.     

ISOLATION AND PARTIAL CHARACTERIZATION OF THE DIMETHYL SULPHIDE PRECURSOR IN GREEN MALT,AND ITS EFFECT ON BEER DIMETHYL SULPHIDE LEVELS

The component from which dimethyl sulphide (DMS) is produced when green malt worts are heated has been purified and its effects on wort and beer DMS levels studied. The green malt precursor can be split into S-methylmethionine and an as-yet uncharacterized ninhydrin-positive component. When the purified precursor is added to worts derived from kilned malts, it is rapidly taken up by yeast, but there is no resulting increase in DMS production. DMS production during fermentation occurs with worts made from kilned malts but not with worts from green malt; however, this difference is not due to an inhibitor being present in green malt worts. The evidence suggests that malt kilning affects the nature as well as the amount of DMS precursor in malts.     

PURIFICATION AND PARTIAL CHARACTERIZATION OF AN ENDO-β1,3-GLUCANASE FROM GREEN MALT

An endo-β1,3-glucanase from a green malt extract was purified by DEAE- and CM-cellulose ion exchange chromatography followed by molecular sieve chromatography on BioGel P-100. A final enzyme preparation had two protein components on disc electrophoresis, one of which was in-active. The enzyme had a pH optimum of 5·0 for activity on laminarin and 5·8 on carboxymethyl pachyman. The activity was stable up to 60°C and was stimulated by NaCl. The isoelectric point of the enzyme was 9·8.