乳生物合成的研究进展

乳腺在动物机体中有着很重要的地位,它可以将营养物质循环转化为成乳成分。本文汇集了人们很感兴趣的发展了近25年的关于乳生物合成的4个领域,而且有了新的理解或揭示了新的机会。首先,对乳分泌机制的研究已经使我们对细胞内脂滴的起源和特性以及乳脂肪分泌时乳脂球膜蛋白功能的了解有了质的增加。第二,目前我们对乳脂的营养调节的研究有了突破性进展,阐明了日粮组成、瘤胃的消化处理以及乳腺合成乳脂的调节机理之间的关系。第三,由于消费者已经意识到饮食和健康的关系,营养价值在食物选择中日趋重要。人们普遍承认的奶和奶产品有很高的营养价值,而且最近发现奶中存在许多对人体健康有益的活性物质。最后,利用基因工程、使动物作为生物反应器在奶中形成药性蛋白,这些先进技术的发展必将促进乳产业的进一步发展。

Influences of operating conditions on biocatalytic activity and reusability of Novozym 435 for esterification of free fatty acids with short-chain alcohols:A case study of palm fatty acid distillate

In the present study, the effects of operating conditions on biocatalytic activity and stability of Novozym 435 for repeated-batch biodiesel production from free fatty acid （FFA） were investigated. Thermal deactivation caused by increased operating temperature from 45 to 50 ℃ could seriously affect the reusability of Novozym 435. The deactivation of Novozym 435 during the esterification of oleic acid with ethanol tended to be stronger than that in the system with methanol. Under the optimal conditions, considering both biocatalytic activity and stability of the enzyme, Novozym 435 could be reused for 13 cycles for biodiesel productions from oleic acid and absolute alcohols （methanol and ethanol） with FFA conversions of at least 90%. The presence of 4%-5% water in ethanol significantly affected the reusability of Novozym 435. Changes in the surface morphology of Novozym 435 during the esterification with various conditions were observed. It was revealed that the reduction in catalytic activity was related to the swelling degree of the catalyst surface, Additionally, biodiesel production from low cost renewable feedstocks, such as palm fatty acid distillate （PFAD） and 95% ethanol was examined, The esterification of PFAD with 95% ethanol catalyzed by Novozym 435 in 10-repeated batch operation showed the similar results in FFA conversion as compared to those using oleic acid. Novozym 435 remained active and could maintain 97.6% of its initial conversion after being used for 10 hatches.

Quality Characteristics and Microbiology Status in Kundi, an Intermediate Moisture Meat （IMM） Product

Meat and meat products are extremely perishable, so special care and handling must be exercised during slaughtering operation. Moreover, due to its high nutritive value, deterioration set in immediately after slaughtered, therefore it is necessary to preserved meat, using simple techniques. One of such method of preservation is drying method to produced Intermediate Moisture Meat （IMM）. The quality attributes and microbiological status of Kundi, a West African dried meat product （IMM） were studied over three months of storage period by comparing commercial products and laboratory Kundi products. Chemical and minerals composition and microbiological counts were reported. Moisture and water activity results indicated that the experimental Kundi was sufficiently dried to minimize microbial growth. Fat oxidation levels measured by free fatty acids （FFA, %） on extracted fats were unacceptably high for the commercial Kundi （2.64%）, which may be a reflection of the oil used in spraying the products. Processing of Kundi, appears to have relative higher amounts of minerals than fresh meat but their relative solubility were lower. Aflatoxin levels far exceeded established safe limits for commercial samples while laboratory samples fell under the safe limits, resulting from the mould growth in each product, with laboratory samples having lower growth than commercial samples.

Distribution of microbial fatty acids and fatty alcohols in soils from an altitude transect of Mt. Jianfengling in Hainan, China: Implication for paleoaltimetry and paleotemperature reconstruction

The temperature gradient along the altitude transect of Mt. Jianfengling provides a good opportunity to establish and evaluate the microbial lipid-based environmental proxies. The soils collected from 14 different altitudes of Mt. Jianfengling contain abundant microbial fatty acids and fatty alcohols, including iso/anteiso fatty acids （i/aC12：0-i[aCl9：0）, 10-Me-C16：0 fatty acid, iso/anteiso fatty alcohols （i/aC13-iC26）, 10-Me-C16：0 fatty alcohol and unsaturated fatty alcohols, which can indicate a strong microbial activity in the Jianfengling soils. The branched and unsaturated fatty alcohols can be only detected when saponifica- tion is performed, implying that these lipids are present as the constituents of bacterial wax esters in the soils. The ratio of aC15/iC15 fatty acids is positively correlated with altitude, suggesting that the decrease in temperature can induce the increase in the relative abundance of anteiso C^5 fatty acid. In contrast, the ratio of aCJiC15 fatty alcohols and of aCjs/nC15 fatty alco- hols both decrease with increased altitude or decreased temperature. Similarly, the ratio of nC18：l/nCi8：0 fatty alcohols also de- creases with decreased temperature, which is opposite to the previous observation that unsaturation of fatty acids in microor- ganism increases in response to decreased temperature. Besides, the average chain length （ACL） of long chain fatty alcohols （C22-C30） from leaf waxes and carbon preference index （CPI） of all n-fatty alcohols are also significantly correlated with alti- tude or mean annual temperature, demonstrating their potential for paleoclimate reconstruction. The correlation of microbial fatty acids and alcohols as well as ACL and CPI of plant wax-derived fatty alcohols with altitude may provide novel ways to reconstruct paleotemperature and paleoaltimetry.