Influence of ripening container on the lactic acid bacteria population in Tulum cheese

The objective of the present study was to investigate the influence of container material (plastic or goat-skin bag) on the growth of lactic acid bacteria in Tulum cheese during 9 months of ripening. The lactic acid bacteria in Tulum cheeses were periodically counted on MRS and M17 agars throughout ripening. Results showed that the highest counts of lactic acid bacteria on MRS or M17 were observed at the beginning of ripening and their counts decreased during later stages of ripening. The cheese samples ripened in plastic bags exhibited higher numbers of LAB on MRS and M-17 agars than those ripened in goat-skin bags. A total of 112 strains of lactic acid bacteria were isolated from Tulum cheeses ripened in plastic or goat-skin bags during ripening. The lactic acid bacteria present in the cheese were classified by Microbial Identification System (MIS) based on a comparison of the fatty acid methyl ester profiles. Different species including Enteroccocus, Lactobacillus, Streptococcus, Lactococcus and Pediococcus genera were found in unripened cheese. As ripening proceeded, the species Streptococcus and Lactococcus disappeared and the percentages of the species Enterococcus was unchanged in both containers. There were slight differences between the cheeses ripened in plastic or goat-skin bags in terms of the profiles of lactic acid bacteria isolated. Some species including L. brevis, L. mesenteroides subsp. dextranicum, P. damnosus and E. mundtii were isolated only in the cheeses ripened in plastic bags; however, L. coryniformis and L. malafermentans were isolated only in the cheeses ripened in goat-skin bags at 6 or 9 months of ripening. Also the numbers of E. faecalis isolates were higher in the cheeses ripened in plastic containers than cheeses ripened goat-skin bags at the 6 or 9 months of ripening. The results showed that Lactobacillus and Enterococcus were the predominant species in matured Tulum cheeses in both ripening containers. It seemed possible to produce Tulum cheese with similar characteristics from both the containers used.     

白三叶草生长期西花蓟马的空间分布型变化

利用聚集度指标检验和比较频次法对白三叶草Trifolium repens生长期间西花蓟马Frankliniella occidentalis的空间分布型变化进行研究,结果如下：聚集度指标检验分析表明西花蓟马在白三叶草上的空间分布为聚集分布;利用频次拟合分析表明白三叶草上大部分生长期内其分布型为负二项分布,其聚集程度与虫口密度有关系,其空间分布不会因为一些人为干扰而改变。     

The role of lactic acid bacteria in accelerated cheese ripening

Abstract: The ripening of cheese is a slow and consequently an expensive process. The economic advantage of rapid development of more intense cheese flavour in shorter periods of time would be substantial. Lactic acid bacteria play a key role during ripening and can therefore be used as accelerating agents. This review describes the different strategies where lactic acid bacteria or their enzymes were used to reduce the ripening time of cheese. The advantages, limitations and technical feasibility as well as the commercial potential of the different approaches are also considered.     

The temporal and spatial distribution of nematodes in percolating filters

The spatial and temporal distribution of nematodes in two low rate percolating filter bed sewage treatment plants at Carnforth and Caton, Lancashire, were investigated. Nematodes were abundant reaching densities up to 900 cm⁻² of media surface. Numbers decreased down the bed and species composition displayed spatial differences with bed depth. Eight orders of nematode were represented, members of the sub-family Diplogasterinae and Rhabditinae were particularly common. A seasonal pattern of abundance was clearly apparent; two peaks occurred, one in May and a second during the winter months. Lowest numbers corresponded with periods of highest temperature. The demise of the nematodes in the spring was related to the sloughing of the surface film on the media.     

松突圆蚧空间分布型的研究

应用聚集度指标和回归分析,对松突圆蚧空间分布型进行测定,结果表明：松突圆蚧的若虫在松林中呈聚集分布,聚集度随虫口密度增大而增强;而成虫在松林中呈均匀分布,从而确定出不同种群密度下最适抽样数。通过林间调查和数理统计分析,结果表明：松突圆蚧在松树枝条的东、南、西、北不同方位,以及松树树冠的上、中、下不同层次和幼林、中龄林、成林不同树龄的松林之间的虫口数量差异不显;但在郁闭度不同的松林中虫口数量存在着显差异。     

Seasonal and spatial distribution pattern of nitrogen fixing bacteria in fish ponds under different management systems

Enumeration of nitrogen fixing bacterial population in water and sediment samples of six fish farming ponds (polyculture, monoculture and traditional systems) over a period of two and a half years revealed significant differences between the culture systems with maximal and lowest counts in the monoculture and traditional systems, respectively. Polynomial equations of the 2nd to 4th degree were used to represent the observed seasonal data in these ponds. The bacterial populations peaked in summer, while the lowest count was observed in winter. The environmental factors such as pH, different species of nitrogen, dissolved organic carbon were responsible for the seasonal changes in nitrogen fixing bacteria.     

青杨脊虎天牛幼虫空间分布格局

20 0 3年 4～ 6月 ,在黑龙江省大庆市红旗林场对青杨脊虎天牛XylotechusrusticusL .幼虫空间分布格局进行了调查研究 ,结果表明该天牛幼虫在杨树人工林内呈负二项分布 ;采用 6种不同聚集指标测定结果均表明为聚集分布。对青杨脊虎天牛幼虫在树干高度上垂直分布研究表明 ,该天牛幼虫在树干上危害部位主要集中在 1～ 4m范围内 ;对该幼虫垂直分布与树干高度进行曲线拟合 ,符合立方曲线 ,曲线方程为y =0 0 68+0 41 7x -0 1 3 6x2 +0 0 1 1x3 ,由相关系数方值R2 =0 83 6验证     

桃一点斑叶蝉种群消长动态和空间分布型研究

研究探明了桃一点斑叶蝉Erythroneurasudra种群消长动态和空间分布型 ,结果表明 :该虫在桃园全年共出现 3个为害高峰 ,分别发生于 4月下旬、5月下旬和 8月上旬 ;该害虫在桃园中呈聚集型的负二项分布。讨论了适宜取样调查方法。     

拉缘蝽空间格局及抽样技术的研究

拉缘蝽空间格局测定结果表明,拉缘蝽的1—3龄若虫、4—5龄若虫和成虫等各虫态的空间格局均属于聚集分布,拉缘蝽1—3龄若虫聚集度最高,4—5龄若虫聚集度下降,成虫聚集度更低。在拉缘蝽空间格局的基础上,确定了Kuno风险决策序贯抽样表和1wao—Kuno（1968）理论抽样数。     

长江口浮游甲壳动物空间分布特征

2010年研究了长江口南、北支浮游甲壳动物的空间分布特征。共采集到浮游甲壳动物50种,其中桡足类39种,枝角类11种。种类数南支高于北支;平均密度北支高于南支,南、北支分别为1.7 ind./L和61.8 ind./L。基于群落相似性矩阵的CLUSTER聚类和MDS分析显示,在群落相似性为40%时,长江口区域浮游甲壳动物群落可分为北支组、南支组1和南支组2共3组。3组的优势种有差异。浮游甲壳动物的平均密度变化趋势为北支组（61.8±22.11 ind./L）〉南支组1（3.07±2.06 ind./L）〉南支组2（0.72±0.45 ind./L）。盐度、潮汐和径流量是影响长江口南北支浮游甲壳动物种类组成、密度和空间分布差异的重要环境因素。     

荔枝蝽田间种群消长动态及空间分布型研究

对海南省儋州地区荔枝园中荔枝蝽Tessaratoma papillosa(Drury)种群动态及空间分布进行了系统调查与分析。结果表明,在2005—2006与2008—2009年期间,荔枝蝽的产卵高峰期分别为4月与2月,若虫高峰期为3月,成虫高峰期分别为4月及7月;分析表明荔枝蝽各虫态在荔枝园中均为聚集分布,且成虫个体间相互排斥。     

甘肃省苹果蠹蛾卵的空间分布格局

为准确掌握苹果蠹蛾Cydia pomonella(L.)的田间发生动态,本文对苹果园中苹果蠹蛾卵的空间分布格局和抽样技术进行了研究。结果表明:在第2代卵发生高峰期,苹果叶片上的苹果蠹蛾卵量显著高于果实上的卵量(叶片上着卵量占总卵量的58.2%,P<0.05),叶片上的卵主要分布于叶片正面(正面着卵量占叶片上总卵量的69.6%,P<0.05);在树冠不同方位上,东、南两面的着卵量最大,但在不同空间层次上分布的卵量没有差异。卵在叶片和果实上均呈聚集分布,且聚集强度随种群密度的升高而增加,其聚集是由环境因素造成的。文中还根据Taylor幂法则参数建立了苹果蠹蛾卵的理论抽样数模型。     

北京地区红脂大小蠹空间分布型与抽样技术研究

对北京地区红脂大小蠹Dendroctonus valens LeConte空间分布型进行了研究。结果表明红脂大小蠹成聚集分布,其聚集原因是由红脂大小蠹本身的聚集行为或聚集行为与环境的异质性共同作用引起。同时,应用Iwao统计方法,提出了最适理论抽样数和最佳序贯抽样模型。     

胡杨、灰叶胡杨果实空间分布及其数量特性的研究

胡杨、灰叶胡杨种间比较,果穗、种子在树冠上的垂直分布均表现为树冠上层最多,中层居中,下层最少,树冠南北侧相比较,南侧果穗量多于北侧.单果种子量在树冠各层次上差异不显著.胡杨单果重是灰叶胡杨的2.68倍,千粒重是灰叶胡杨的1.33倍,单果种子量是灰叶胡杨的2.14倍,单株种子量是灰叶胡杨的1.28倍,而单株果实量灰叶胡杨是胡杨的1.59倍.同一个种不同居群间比较,胡杨、灰叶胡杨均是单株果穗数和果穗果实数各居群间都存在差异,胡杨各居群间单果重、单果种子量差异不显著,而灰叶胡杨各居群间单果重及单果种子量差异极显著.表明胡杨在物质和能量上对后代的投资能力强于灰叶胡杨,生殖策略是通过较高的单果种子量来保证一定数量的单株种子量;而灰叶胡杨单果种子量较低,却是通过较高的单株果量来保证单株种子量,并且较小的种子占据空间生态位的潜能较胡杨占优势.     

玉米田斜纹夜蛾空间分布型及抽样技术

对秋甜玉米田的斜纹夜蛾不同发生密度田块调查 ,取得了 7组样本资料 ,运用聚集度指标法、Iwao法和Taylor法等对其空间分布型进行测定检验 ,结果表明斜纹夜蛾幼虫呈聚集分布 ,其聚集原因经Blackith种群聚集均数测定 ,当m <3 .2 60 4时 ,其聚集是由于某些环境如气侯、土壤湿度、植株生长状况等所致 ;当m >3 .2 60 4时 ,其聚集是由于害虫本身的群集行为与环境条件综合影响所致。在此基础上 ,通过几种抽样方式比较以五点式为最佳 ,并提出了最佳理论抽样数和最佳序贯抽样模型 :N =1 D2 (3 .8981 m +0 .75 0 3 ) ,To(n) =0 .5n± 2 .865n。     

柑橘全爪螨空间格局与抽样技术的研究

本应用空间分布型统计参数IwaoM-X模型中α,β及6个聚集指标分析了柑橘全爪螨的空间格局,并对抽样技术进行了探讨。结果表明,柑橘全爪螨的空间格局为聚集型;田间的抽样部位是上、中、下三部的叶片。提出了估算柑橘全爪螨在不同虫口密度下的理论抽样数。     

中国西南地区石漠化敏感性评价及其空间分析

石漠化是我国西南地区最为严重的生态环境问题之一,识别发生石漠化敏感区域,为岩溶地区石漠化防治提供科学依据显得十分必要。总体分析了目前中国石漠化和有关生态环境研究的资料,将石漠化敏感性影响因子归结为岩性、降水、坡度和植被等4项,并确定了各因素对石漠化敏感性影响等级,综合评价了我国西南五省(市)(包括黔、滇、贵、川、渝)石漠化敏感性及其空间分布格局。结果表明,敏感性评价结果基本反映石漠化现状,石漠化敏感区集中分布在贵州西部、南部,广西西部、东部以及云南东部等地。四川、重庆等地石漠化危害相对较小。     

蔬菜花期蓟马的种群动态与空间分布研究

西花蓟马是近年来在我国局部地区暴发成灾的重要外来入侵害虫,有关西花蓟马入侵对本地蓟马种群动态、空间分布及优势种影响的报道较少。对云南省昆明市近郊蔬菜花期的蓟马种群动态和空间分布研究表明,蔬菜上的蓟马种类主要是西花蓟马Frankliniella occidentalis(Pergande)、花蓟马F.intonsa(Trybom)、棕榈蓟马T.palmi(Karny)和端大蓟马Megalurothrips distalis(Karny);不同蔬菜上的蓟马优势种存在一定差异,其中辣椒和茼蒿上的蓟马优势种为西花蓟马;韭菜、茄子和四季豆上的蓟马优势种分别为花蓟马、棕榈蓟马和端大蓟马。各蔬菜上的蓟马种群数量以花期为多,盛花期达最大值,其中茄子花上的蓟马成虫平均虫口密度最高,为14.93头/朵。利用聚集度指标进行空间分布检测表明,不同蔬菜上蓟马成虫的空间分布型均为聚集分布,且聚集程度随密度的增加而增大。本研究可为深入探讨西花蓟马对本地蓟马的竞争取代机制积累资料,同时为西花蓟马的综合治理奠定理论基础。     

杨树粒肩天牛幼虫的空间格局

运用聚集度指标、回归模型、零频率等方法对福建闽北地区杨树粒肩天牛幼虫的空间格局进行测定。结果表明该天牛幼虫在杨树林中呈聚集分布,分布的基本成分为个体群,个体之间相互吸引。用零频率方法分析得出,粒肩天牛种群类型为“聚集度零频率制约型”。并确定了该天牛幼虫林间调查的最适理论抽样数和序贯抽样模型。