添加柠檬酸促进粘质沙雷氏菌发酵产过氧化氢酶

在优化1株粘质沙雷氏菌发酵产过氧化氢酶(CAT)的培养基成分时发现,柠檬酸可以显著提高该菌胞内CAT的活力。结合先前报道,探究了柠檬酸促进粘质沙雷氏菌合成胞内CAT的原因。以等摩尔碳含量的柠檬酸、葡萄糖、柠檬酸与葡萄糖的混合物分别作为碳源,测定了在不同碳源发酵产CAT时粘质沙雷氏菌胞内抗氧化的相关数据。结果显示:添加柠檬酸(20g/L)后,该菌细胞内H_2O_2和羟自由基含量均比对照组(葡萄糖)高,说明柠檬酸代谢物对其产生了活性氧胁迫,进而诱导更多CAT的合成。考察了甲萘醌和百草枯(活性氧O~(2-)·的来源物)对该菌合成CAT的影响,实验结果验证了适量的活性氧能够诱导该菌合成CAT的结论。     

金黄色葡萄球菌在蘑菇罐头中生长繁殖与产毒规律的研究

本试验通过对临床分离的金黄色葡萄球菌，经培养筛选出产毒菌株，接种于蘑菇罐中，研究其生长和产毒规律。试验结果表明：金黄色葡萄球菌在蘑菇罐头中生长良好，培养１２小时后即进入对数生长期，培养３０小时后达到生长繁殖高峰，然后进入衰老和死亡期。当菌数达到１０＾７／ｍｌ时即可检测出肠毒素，随后大量积累，培养１８小时及以后各阶段肠毒素检测结果均为强阳性，说明随着金黄色葡萄球菌的不断生长和繁殖，不断产生肠毒素。     

粘质沙雷氏菌的分离鉴定及产红色素培养基的优化

为确定KMR-3菌株的分类地位,对其进行了分类鉴定;为了提高其红色素产量,对发酵培养基进行了优化。以分离到的KMR-3菌株为供试材料,通过形态学、生理生化特征和16S rRNA基因序列分析对其进行了生物学分类鉴定。以LB液体培养基作为基础培养基,通过优化其不同组分(蛋白胨,酵母膏和NaCl)及含量以提高红色素产量。结果表明:KMR-3菌株归属为粘质沙雷氏菌,该菌株产红色素的最佳培养基为5g/L胰蛋白胨和1%甘油,pH5.0,温度28℃;该条件下,色素产量是基础培养基的13.4倍。该培养基蛋白用量少,促进粘质沙雷氏菌产生大量红色素,为其大规模生产提供依据。     

金黄色葡萄球菌在蘑菇罐头中生长繁殖与产毒规律的研究

通过对临床分离的金黄色葡萄球菌培养，筛选出产毒菌株，接种于蘑菇罐头中。全黄色葡萄球菌在蘑菇罐头中生长良好，培养１２ｈ即进入对数生长期，培养３０ｈ达到生长繁殖高峰，当菌数达到１７＾７个／ｍ１时即可检测出肠毒素，培养１８ｈ及以后各阶段肠毒素测均为强阳性。     

玉米浆粉预处理对粘质沙雷氏菌发酵产2-酮基-D-葡萄糖酸的影响

通过比较不同预处理方法获得的玉米浆粉在粘质沙雷氏菌SD136作用下产2-酮基-D-葡萄糖酸的影响,组合复配玉米浆粉,结果表明:最佳玉米浆粉复配比为玉米原浆粉和酶解玉米浆粉3∶1,2-酮基-D-葡萄糖酸产量达到(171.39±4.5) g/L,发酵时间由40 h缩短至37 h,对糖转化率达到95.22%。玉米原浆粉和酶解玉米浆粉的组合复配能够提高粘质沙雷氏菌SD136的发酵效率和2-酮基-D-葡萄糖酸的产量。     

唐菖蒲伯克霍尔德菌椰毒致病变种污染调查及其生长与产毒特性分析

唐菖蒲伯克霍尔德菌椰毒致病种（Burkholderia gladioli pathovar cocovenenans,BGC）是迄今我国发现的发病率和死亡率最高的食源性致病菌。为调查广州市市售湿米面制品、银耳及木耳中BGC的污染状况,同时掌握在不同培养条件下BGC的生长与产毒规律,依据GB 4789.29-2020对100份食品样品进行定性分析;通过测定BGC菌株在各培养条件下菌液的OD600值和毒素含量,分析了不同的温度、时间、pH及NaCl浓度下BGC的生长状况与产毒能力。结果表明,100份食品样品中共检出1份（湿木耳）BGC阳性样品,污染率为1%（1/100）;BGC的生长与产毒受培养基的影响较大,碱性（pH值为9.5~10.5）与一定渗透压（NaCl质量浓度为0.02~0.04 g/mL）环境下,BGC在马铃薯葡萄糖水中能生长,而在脑心浸液肉汤中几乎不生长,BGC在马铃薯半固体琼脂中的产毒量（231.24 μg/mL）远大于BHI半固体琼脂和LB半固体琼脂;BGC适宜生长和产毒的温度为20~37 ℃、适宜pH值为4~8.5,其中最适生长温度与pH值分别为37 ℃、6.0,最佳产毒温度与pH值为30 ℃、7.0;BGC在低温（4~15 ℃）下仍能存活,且有少量的毒素产生（2.11 μg/mL）;当NaCl质量浓度为0.005 g/mL时,产毒量从未添加前的139.80降至52.27 μg/mL,达到0.04 g/mL时,产毒为0。结果提示,广州市市售木耳中存在BGC污染的风险,在食品加工或贮存过程中添加一定浓度的NaCl可减少由BGC引起的食物中毒。     

一株温敏型产红色素粘质沙雷氏菌的分离及其培养条件研究

从土壤中分离纯化得到1株产红色素细菌,对该菌进行生理生化和16S rDNA鉴定,并对菌株色素产量的培养特性进行了研究.结果表明,该菌为粘质沙雷氏菌(Serratia marcescens),有机氮和乳糖能促进其色素产生;K+、Ca2+、Cu2+ 和Mn2+ 能显著提高色素产量;25℃条件下培养红色素产量最高,37℃培养不产色素,该菌株是温敏型红色素产生菌.     

植物乳杆菌SCB2505代谢物对液化沙雷氏菌的抑菌机理

液化沙雷氏菌是畜产食品在低温贮藏中的一种常见致腐菌和食源性病原菌。该实验通过最小抑菌浓度(minimum inhibitory concentration, MIC)和生长曲线分析植物乳杆菌SCB2505代谢物对液化沙雷氏菌的抑菌活性,并通过高温、过氧化氢酶及蛋白酶、pH处理和乳酸排除实验分析抑菌物质组成,再通过生物被膜抑制率、细胞壁和细胞膜完整性、菌体形态变化的研究来分析其抑菌机理。结果表明,植物乳杆菌SCB2505代谢物对液化沙雷氏菌的MIC为8 mg/mL,其抑菌物质的高温耐受性较好,pH越低其抑菌效果越好,但相同pH的乳酸溶液不具有抑菌活性,过氧化氢酶和蛋白酶对其抑菌圈大小有显著影响,推测抑菌物质可能为乳酸盐、细菌素与过氧化氢的复合物。植物乳杆菌SCB2505代谢物能明显抑制液化沙雷氏菌生物被膜合成,破坏细胞壁和细胞膜的完整性,使得菌体皱缩凹陷,甚至裂解死亡。该研究结果说明植物乳杆菌SCB2505代谢物作为天然防腐剂在动物食品防腐领域具有较好的应用前景。     

1株唐菖蒲伯克霍尔德氏菌在湿米粉中的产毒规律分析

目的:了解防腐剂(脱氢乙酸、ε-聚赖氨酸盐酸盐)和培养温度对唐菖蒲伯克霍尔德氏菌在湿米粉培养基上生长及产毒的影响。方法:以1株自食物中毒事件样品中分离得到的唐菖蒲伯克霍尔德氏菌(椰毒假单胞菌酵米面亚种)菌株为研究对象，分别接种至添加脱氢乙酸(1.0 g/kg)、添加ε-聚赖氨酸盐酸盐(0.25 g/kg)以及未添加防腐剂的湿米粉培养基中，置于10，26，36 ℃条件下培养，研究其在湿米粉中生长及产毒情况。采用修正的 Gompertz 模型构建初级生长模型。结果:在10 ℃条件下该菌生长缓慢且未产生米酵菌酸；在26 ℃条件下培养至96 h，该菌对照组和各试验组产生的毒素均超过500 μg/kg，在添加脱氢乙酸的样品中最早产生米酵菌酸，其最高质量浓度(1 484 μg/kg)略低于对照组(2 561 μg/kg)和ε-聚赖氨酸盐酸盐组(2 762 μg/kg)；在36 ℃条件下该菌生长最为快速，各组产毒量均低于350 μg/kg。结论:湿米粉在10 ℃贮存可有效降低产生米酵菌酸的风险，脱氢乙酸、ε-聚赖氨酸盐酸盐均未能阻止唐菖蒲伯克霍尔德氏菌的生长和产毒，需进一步探索能起作用的防腐剂，制定多手段结合的控制措施。     

粘质沙雷氏菌高产发酵灵菌红素的工艺优化及抗病毒活性

为提高粘质沙雷氏菌S3菌株的灵菌红素产率,本研究对粘质沙雷氏菌S3发酵过程中重要的发酵条件参数和关键组分进行逐项优化,并验证了发酵液灵菌红素提取物对本氏烟草病毒的抑制效果。结果表明,最佳培养基配方为：丙三醇0.5%,蛋白胨1.5%,氯化钠0.5%,氯化钾0.25%;最佳发酵条件为：接种量为10%,装液量为60%~70%,pH恒定为6.0,培养温度为28℃,振摇速度160r/min,发酵周期为60h。在该发酵条件下,既有利于粘质沙雷氏菌菌体生长,又能够使灵菌红素的产量达到最大化。按照该优化条件进行发酵后,其灵菌红素提取物溶液喷施于接种TMV、CMV和PVY的本氏烟,烟叶中TMV、CMV和PVY病毒量分别为空白对照的12.61%、29.41%和17.69%,对病毒的抑制效果优于氨基寡糖素。试验所得的发酵制备条件能够提高灵菌红素产量,提取物具备显著抗病毒特性,具有产业化开发潜力和经济应用价值。     

Staphylococcus aureus Growth and Enterotoxin Production in Mushrooms

An enterotoxin A (SEA) producing strain of Staphylococcus aureus was inoculated onto mushrooms and incubated under simulated pre-and post-canning conditions. S. aureus grew and produced SEA in mushrooms incubated at 25°C in 10% to 20% NaCl. Growth and SEA production occurred when mushrooms were stored in plastic bags at 37°C, but not at 25°C. Mushrooms heat-processed at 121.1°C supported S. aureus growth and SEA production. No SEA was recovered from mushrooms inoculated with 1 or 10 ng SEA/g and heated at 121.1°C for 4.5 min. At higher inoculated SEA levels (100 and 1,000 ng/g), SEA was detectable after 10 min of heating. Staphylococcal enterotoxin could be present in canned mushrooms as a result of pre-, but more likely post-processing contamination.     

Shrinkage in canned mushrooms treated with xanthan gum as a pre-blanch soak treatment

Vacuum treating freshly harvested mushrooms with a 1% xanthan gum solution (XVT) containing 0.25% sodium metabisulphite (SMBS) prior to blanching and canning gave a lower shrinkage value than for corresponding samples vacuum treated with water, or those canned by conventional means or the 3S process. A combination of chill storage (2-4°C) for 1-3 days coupled with 1% XVT was found best and gave even lower total canning losses (chill storage loss + blanch loss + retort loss); these were 6% lower than in the 3S process and 11.5% lower than for mushrooms canned by the conventional procedure. These data suggest that xanthan gum has considerable potential for reducing shrinkage in canned mushrooms. The XVT canned samples had an excellent colour and an acceptable texture. Further storage tests over a 9 month period with xanthan treated canned mushrooms showed than an SMBS level of 0.1% in the pre-blanch soak solution maintained an excellent colour in the canned product. No in-can mushroom shrinkage took place during the 9 month storage test.     

INFLUENCE OF PRETREATMENTS AND BLANCHING TREATMENTS ON THE YIELD AND COLOR OF CANNED MUSHROOMS

Three factors in PSU-3S and SSV processes, i.e. soaking, cold storage, soaking again or vacuum hydration, which might increase the yield of canned mushrooms, were investigated. The results of experiments revealed that only cold storage time in these processes significantly affected the yield of canned mushrooms. The undesirable effect of PSU-3S or SSV processes on the color of canned mushrooms may be significantly remedied by acid blanching.     

The influence of Lactobacillus plantarum culture inoculation on the fate of Staphylococcus aureus and Salmonella typhimurium in Montasio cheese.

The growth and survival of Staphylococcus aureus and Salmonella typhimurium were investigated during the manufacturing and ripening of raw milk Montasio cheese. Initial inoculated populations in the cheese milk were about 10(5) cfu/ml for S. aureus and 10(6) cfu/ml for S. typhimurium. Samples of curds and cheeses were taken during manufacturing and storage and analysed for pH and microbial populations. S. aureus increased slightly in number during the early period of ripening and attained a population of about 10(6) cfu/ml during the remaining period of storage. S. typhimurium decreased during cheesemaking and storage but persisted through 90 days. The addition of Lactobacillus plantarum culture (0.2% v/v) produced a marked reduction in populations of the test strains in 10 days of storage. Enterotoxin A was not detected in Montasio cheese even with a S. aureus population of 1.1 X 10(7) cfu/ml. L. plantarum strains were also tested by the spot method and the associative growth approach for their antagonistic activity against S. aureus and S. typhimurium. The compound excreted by L. plantarum was active only toward S. aureus. Furthermore, its activity was destroyed by protease treatment. These results indicated that while the growth of S. typhimurium is reduced by the acid production, S. aureus inhibition can be ascribed to bacteriocin production.     

Effect of Lactococcus garvieae, Lactococcus lactis and Enterococcus faecalis on the behaviour of Staphylococcus aureus in microfiltered milk

The effect of four strains of Lactococcus garvieae, three strains of Lactococcus lactis and one strain of Enterococcus faecalis on Staphylococcus aureus SA15 growth in microfiltered milk was evaluated. Lactococcus and Enterococcus strains were co-cultured with S. aureus in microfiltered milk and in medium buffered at pH 6.8. All Lactococcus and Enterococcus strains were able to inhibit S. aureus growth after 6h of incubation. Inhibition by L. lactis and E. faecalis strains could be partially attributed to the decrease in pH below 6.0 as it has been observed in medium buffered at pH 6.8. L. garvieae strains were the most effective to inhibit S. aureus growth without acidification. Inhibition of S. aureus could not be attributed neither to production of lactate, acetate or nor to antistaphylococcal substance. Amino acids competition was not involved in the inhibition by L. garvieae as addition of valine, isoleucine, threonine, methionine and phenylalanine did not suppress the inhibition of S. aureus.     

致病菌在四川泡菜发酵过程中生长规律的研究

通过在四川泡菜中分别接种志贺氏菌、沙门氏菌和金黄色葡萄球菌等致病菌,经过乳酸菌发酵,对3种致病菌在发酵期间的菌落数及pH值进行检测分析.结果表明:随着发酵时间的延长,pH值逐渐下降,3种致病菌生长均受到抑制,在pH值为3.4～3.6时,志贺氏菌不能存活,在pH值为3.56～3.7时,沙门氏菌不能存活,在pH值为3.6时,金黄色葡萄球菌仍然存在.故将金黄色葡萄球菌作为目标致病菌,根据金黄色葡萄球菌生理特性,进而从生产上控制和灭杀金黄色葡萄球菌.     

Immunochemical Identification and Quantification of Ovalbumin Additive in Canned Mushrooms

A method to identify and quantify additives in canned food was developed. Ninety to ninety five percent of proteins from canned mushrooms were solubilized by treatment with 0.1N NaOH for 3 days. The extracted, solubilized proteins were then detected by direct ELISA test. An ELISA test which allowed quantification of ovalbumin in canned mushrooms was developed. Immunoblotting also showed the same sensitivity and accuracy with ELISA.     

Bisphenol A (BPA) in U.S. food

Bisphenol A (BPA) is a chemical used for lining metal cans and in polycarbonate plastics, such as baby bottles. In rodents, BPA is associated with early sexual maturation, altered behavior, and effects on prostate and mammary glands. In humans, BPA is associated with cardiovascular disease, diabetes, and male sexual dysfunction in exposed workers. Food is a major exposure source. We know of no studies reporting BPA in U.S. fresh food, canned food, and food in plastic packaging in peer reviewed journals. We measured BPA levels in 105 fresh and canned foods, foods sold in plastic packaging, and in cat and dog foods in cans and plastic packaging. We detected BPA in 63 of 105 samples, including fresh turkey, canned green beans, and canned infant formula. Ninety-three of these samples were triplicates which had similar detected levels. Detected levels ranged from 0.23 to 65.0 ng/g ww and were not associated with type of food or packaging but did vary with pH. BPA levels were higher for foods of pH 5 compared to more acidic and alkaline foods. Detected levels were comparable to those found by others. Further research is indicated to determine BPA levels in U.S. food in larger, representative sampling.     

Growth of Staphylococcus aureus in fermenting tempeh made from various beans and its inhibition by Lactobacillus plantarum.

In fermenting tempeh made from non-acid-soaked horsebean, pea, and soybean Staphylococcus aureus grew rapidly to a final count of 10⁸cfu.g^-1 or more, but growth was less when chickpea was used. Inoculation of the cooked beans with Lactobacillus plantarum markedly decreased S. aureus growth rate and the final count in non-acid-soaked horsebean and pea tempeh, strongly retarded growth in chickpea-, and completely inhibited growth in soybean-tempeh. Acid-soaking the beans resulted in lower S. aureus growth, and inoculation with Lb. plantarum completely inhibited it in soybean and reduced the counts in the other products to less than 10⁴cfu.g^-1. Acidity, pH and other substances produced by Lb. plantarum are believed to inhibit S. aureus in fermenting tempeh. Inoculation of beans with Lb. plantarum may be used to control S. aureus growth and enterotoxin production during commercial scale tempeh production.     

Agaritine content in processed foods containing the cultivated mushroom (Agaricus bisporus) on the Nordic and the Czech market

The level of agaritine was measured in fresh and canned cultivated mushroom (Agaricus bisporus) as well as in other food products containing A. bisporus, by reversed phase high performance liquid chromatography. The two fresh samples were purchased on the open market and contained 212 and 229mg/kg, respectively. Of the 35 different trademarks of canned mushroom products studied, 25 were based on cut mushrooms and 10 on whole mushrooms. On average, whole mushrooms contained 14.9 ± 6.7 mg agaritine per kg product whereas cut mushrooms contained 18.1 ± 7.8mg mg/kg. There was no statistically significant difference between these two values. Agaritine levels in brine were generally slightly lower than the levels detected in canned mushrooms. Thus, the level of agaritine in A. bisporus is reduced more than 10 times during the wet canning process, resulting in low levels in canned products. On a portion basis, somewhat higher amounts of agaritine may be found in some other food products (mushroom soup and pasta sauce) containing A. bisporus.