酸奶制品的酸度控制

对于凝固型酸奶的评价,既要有浓郁芳香的乳酸风味和良好的凝固状态,还要有酸甜适口的口感.酸度过高的产品,其风味和口感往往不佳,很难被消费者接受和喜爱.在生产和贮藏过程中产生过多的酸而导致强烈的酸味是酸奶常见的问题,合理控制酸奶的酸度,就显得尤为重要.本文研究了酸奶在生产和冷藏温度(7℃)条件下其滴定酸度变化的情况.结果表明,在7℃条件下,第一天,酸度升高最快,平均可达26.4°T,而随后的7d,酸度升高相对缓慢,平均每天上升3.6°T.贮藏8天后的酸度在112122°T范围内波动.终止酸度在6672°T凝固良好,表面光滑,组织紧密,有微量的乳清析出;90110°T范围的酸奶,风味最好,顾客满意度高.本研究对酸奶产品酸度质量控制具有十分重要的意义.     

葡萄酿酒的酸度控制

2001年9月,我应国务院侨办邀请,作为“西部行”的海外百名博士之一,去新疆开展葡萄酒方面的咨询,发现有关葡萄酒企业在葡萄酒生产中特别强调用滴定酸值表示总酸值。对葡萄酒酸度的控制,主要以总酸值的变化为标准,pH值仅作为一个辅助参考值来考虑。当我问为什么,负责的技术人员告诉我,因为相关的     

Kinetics of mass transfer-limited bacterial growth on solid PAHs

The importance of mass transfer relative to the intrinsic microbial activity was examined in a laboratory system using Mycobacterium sp. LB501T and poorly soluble anthracene as sole carbon source. M. sp. LB501T was grown on various amounts of solid anthracene in batch cultures, and microbial biomass formation was compared to independently determined dissolution fluxes. Provision of only a few anthracene crystals (< or = 2 g L(-1)) resulted in pseudolinear growth due to low dissolution fluxes, whereas exponential growth was only obtained when high amounts of solid anthracene (30 g L(-1)) were provided. The influence of substrate bioavailability on microbial growth was predicted successfully by a dynamic, flux-based approach (Best-Equation), which combines substrate dissolution from crystals into solution, substrate uptake by microorganisms from solution, and concurrent biomass formation.     

Transverse mixing enhancement due to bacterial random motility in porous microfluidic devices

Bacterial swimming in groundwater may create flow disturbances in the surrounding microenvironment thereby enhancing contaminant mixing. Porous microfluidic devices (MFDs) were fabricated in three different pore geometry designs: uniform grain size with large pore throats (MFD-I), nonuniform grain size with restricted pore space (MFD-II), and uniform grain size with small pore throats (MFD-III). Escherichia coli HCB33 was used to assess the effect of bacterial random motility on transverse mixing of a tracer, fluorescent labeled dextran, under three experimental conditions in which motile bacteria, nonmotile bacteria, and plain buffer suspensions were flown through the MFDs at four different flow rates. Mixing was quantified in terms of the best-fit effective transverse dispersion coefficient ((D(cy))(eff)). A mixing enhancement index (MEI) was defined as the ratio of the (D(cy))(eff) of tracer in experiments with motile bacteria and without bacteria. Motile bacteria caused a maximum 5-6 fold increase in MEI in MFD-II, a nearly 4-fold increase in MFD-I, and very little observed change in MFD-III. The apparent transverse dispersivities (α(app)) of MFD-II and MFD-I increased by 3 and 2.3 times, respectively, with no change in MFD-III. These observations indicate that both pore throat size and pore arrangement are critical factors for contaminant mixing in porous media.     

A study on carbothermal reduction of sulfur dioxide to elemental sulfur using oilsands fluid coke

Experiments and reaction equilibrium calculations were carried out for the SO2 gas and oilsands fluid coke system. The goal was to develop a coke-based sulfur-producing flue gas desulfurization (SP-FGD) process that removes SO2 from flue gases and converts it into elemental sulfur. The conversion of SO2 to elemental sulfur proceeded efficiently at temperatures higher than 600 degrees C, and the sulfur yield reached a maximum (> 95%) at about 700 degrees C. An increase of temperature beyond 700 degrees C enhanced the reduction of product elemental sulfur, resulting in the formation of reduced sulfur species (COS and CS2), which lowered the sulfur yield at 900 degrees C to 90%. Although equilibrium calculations suggest that a lower temperature favors the conversion of SO2 as well as the yield of elemental sulfur, experiments showed no formation of elemental sulfur at 600 degrees C and below, likely due to hindered kinetics. Faster reduction of SO2 was observed at a higher temperature in the range of 700-1000 degrees C. A complete conversion of SO2 was achieved in about 8 s at 700 degrees C. Prolonging the product gas--coke contact, the yield of elemental sulfur decreased due to the formation of COS and CS2 while the SO2 conversion remained complete. Equilibrium calculations suggest that the ultimate yield of elemental sulfur maximizes at the C/SO2 ratio of 1, which represents the stoichiometry of SO2 + C-->CO2 + S. For the C/SO2 ratio < 1, equilibrium calculations predict elemental sulfur and CO2 being major products, suggesting that SO2 + C-->CO2 + S is the predominant reaction if SO2 is in excess. Experiments revealed that elemental sulfur and CO2 were only major products if the conversion of SO2 was incomplete, which is in agreement with the result of the equilibrium modeling.     

大曲降酸的探讨

采用低中温制曲与添加适量的降酸药剂—青霉素的新工艺与传统的中温制曲工艺培制大曲 ,然后将两工艺培制的大曲进行感官和理化检测 ,验证方案的可行性     

Effect of harvesting time and fruit size on titratable acidity, soluble solid and distribution of limonin in Thai tangerine juice

The effect of fruit size and harvesting of Thai tangerine fruit ( Citrus reticulata , Blanco) at different growth stages, 8–12 months after fruit set, on the distribution of limonin in whole fruit as well as in the individual fruit parts and extracted juice was investigated. The highest limonin concentration was observed in seed, followed by albedo, flavedo, segment membrane and juice sacs in decreasing order. The limonin concentration in juice as well as in whole fruit was decreased when fruit was harvested 8–12 months of fruit set. Increasing harvesting time from 8 to 12 months showed corresponding decreases in the amount of limonin in flavedo, albedo and seed. There was a decrease in titrable acidity and increase in total soluble solid and total soluble solid/titrable acidity ratio of juice with a later than normal harvesting time. However, fruit size showed no effect on limonin content and other properties of juice extracted from tangerine.     

混合菌种固态发酵大豆粕生产大豆肽研究

大豆肽系由大豆蛋白经水解所得由3～6个氨基酸残基组成低分子肽混合物,分子量以低于1000Da为主。以大豆粕为原料,采用黑曲霉、米曲霉混合菌种固态发酵法生产大豆肽,所得大豆肽具有较好理化特性和生理活性,克服酶解法产品苦味重、口感差等缺点,可在很多领域得以广泛应用。     

Assessment of color development due to twin-screw extrusion of rice-glucose-lysine blend using image analysis

An image analysis method was developed to determine the color change of rice-glucose-lysine blend during extrusion. The color of extrudates was analysed and compared by using different extrusion conditions. Extrusion process variables included moisture content, screw speed, barrel temperature, and screw geometry. The influence of specific mechanical energy input (SME) and product temperature on the color of extrudates was significant. The color parameters were related to product temperature and SME by a 4th degree polynomial. Product temperature and color were modeled and tested using rice-glucose-lysine blend at various screw configurations and extrusion conditions with reasonable accuracy. Validations of product temperature and color models were done using different screw geometries and other processing variables with reasonable accuracy. Extrusion tests indicated that the developed predictive models can be of use for extrusion processing. The results also showed that the image analysis method developed provides an objective and efficient approach for assessing the color development of extrudates.     

DHA功能及其在固体饮料中的开发现状

DHA,二十二碳六烯酸,俗称"脑黄金",是一种非常重要的多不饱和脂肪酸,属于Omega-3脂肪酸家族,对人体有着重要的功能。随着人们对DHA认知度的不断提升,对其重视及需求程度也日益增加。在食品和保健品行业,DHA被广泛应用。近来,将DHA添加于固体饮料中成为一种新的应用趋势。本文综述了DHA功能及其在固体饮料中的开发现状。     

Effects of variation of dietary sulfur on movement of sulfur in sheep rumen

Effects of variations in dietary sulfur on rumen sulfur dynamics were studied under steady state conditions. In the first experimental period, three sheep were given 33.3 g of a pelleted diet hourly containing 1.59 g sulfur/kg (low) and in the second period the sulfur content was increased to 3.21 g/kg (high) by the addition of sodium sulfate. The daily sulfur intake was 1.158 g on the low sulfur diet and .545 g of this passed from the rumen in protein, .614 g was calculated to be absorbed from the rumen as sulfide, and .052 g was estimated to be recycled to the rumen. For sheep with daily intakes of 2.317 g sulfur, 1.212 g passed from the rumen in protein, 1.078 g was absorbed from the rumen, and .093 g was estimated to be recycled. It was estimated that 127 and 165 g microbial protein were synthesized/kg organic matter "truly digested" in the rumen for low and high sulfur diets, respectively. A simple model using simultaneous equations was proposed to describe rumen sulfur metabolism.     

混合菌种固态发酵法发酵豆粕生产大豆肽的研究

大豆肽是由大豆蛋白经水解所得到的由3～6个氨基酸残基组成的低分子肽混合物,分子量以低于1000Da的为主。以豆粕为原料,采用黑曲霉、米曲霉混合菌种固态发酵法生产大豆肽,制得的大豆肽具有较好的理化特性和生理活性,克服了酶解法产品苦味大和口感差等缺点,在很多领域得到了广泛应用。     

Effect of lactococcus lactis var. lactis biovar diacetylactis on bacterial counts, pH and total acidity of minced goat meat during refrigerated storage

The mesophillic aerobic and psychrotrophic plate counts, pH and total acidity were determined in minced goat meat treated with Lactococcus lactis var. lactis biovar diacetylactis and stored at 4 °C. The inhibitory effect was pronounced when the initial contamination of the meat, particularly with psychrotrophs was low. Of pH and total acidity, pH was better correlated with microbial inhibition. There was development of odour (non-putrefactive) from the 4th day of storage reducing acceptability.     

The effect of lipoxygenase action on the mechanical development of wheat flour doughs

The mechanical development of dough has been followed by measurement of the relaxation time of dough samples after mixing to various levels of work input. Parallel determinations of free and bound lipid have also been made. When doughs were mixed in air, addition of full-fat, enzyme-active soya bean flour (subsequently referred to as “soya flour”) resulted in an increase in relaxation time, particularly at higher work levels. The magnitude of this improvement increased with increasing work input and was dependent on the rate of work input. Addition of soya flour also enabled a higher level of mechanical work to be introduced before dough breakdown occurred. When doughs were mixed under nitrogen, or when the soya flour was heat denatured, no change in the rheological properties compared with the respective control doughs was found. The release of bound lipid, which occurred during dough development in air in the presence of soya flour, could also be induced by adding purified lipoxygenase to the dough, together with linoleic acid as a substrate. This resulted in rheological changes similar to those observed using soya flour. However addition of enzymically pre-peroxidised lipid to doughs mixed in nitrogen was without effect on relaxation times. These findings suggest that lipid release is linked with structural changes in dough protein and provide further support for a mechanism of coupled oxidation of protein -SH groups by lipoxygenase.     

Acidification of calf bedding reduces fly development and bacterial abundance

Environmental stressors, such as high fly density, can affect calf well-being. Sodium bisulfate (SBS) is an acidifier that reduces the pH of flooring and bedding, creating a medium that neither bacteria nor immature flies (also known as larvae or maggots) can thrive in. Two experiments were conducted to investigate the application of SBS to a mixture of rice hull calf bedding and calf slurry (BED) to reduce house fly (Musca domestica L.) larval density and the abundance of bacteria. In experiment 1, dish pans containing 1 L of BED and 3,000 house fly eggs were treated with SBS at concentrations of 0, 8.9, 17.7, and 26.5 g of SBS/0.05 m² of BED (CON, LOW, MED, and HIGH, respectively), with each SBS concentration applied to 4 individual pans (16 pans total). Reapplication of the same SBS concentrations in each pan occurred 3 times/wk throughout the 23-d trial. Larval house fly survival was significantly reduced in all pans with SBS relative to CON pans, with lowest survival rates in the MED and HIGH pans (99% and 100% reduction, respectively). The mean pH for each treatment was inversely related to the SBS concentration. In experiment 2, pans containing 1 L of BED and 3,000 house fly eggs were treated with either 0 g of SBS (CON), 8.9 g of SBS/0.05 m² of BED with reapplication of the acidifier 3 times/wk (SB3×), or 8.9 g of SBS/0.05 m² of BED applied only once at 48 h before the end of the 8 d-trial (SB48). Larval house fly survival and bacterial concentrations were reduced (90% larval reduction and 68% bacterial reduction) in the SB3× treatment relative to the CON. Mean pH was also reduced in SB3× pans relative to CON or SB48 pans. Overall, acidification of calf BED using the acidifier SBS resulted in a reduction of bacteria and house fly larval survival. This form of fly control might be expected to reduce adult fly production and, therefore, fly-related stress in calves.     

Effect of acidity on secondary organic aerosol formation from isoprene

The effect of particle-phase acidity on secondary organic aerosol (SOA) formation from isoprene is investigated in a laboratory chamber study, in which the acidity of the inorganic seed aerosol was controlled systematically. The observed enhancement in SOA mass concentration is closely correlated to increasing aerosol acidity (R2 = 0.979). Direct chemical evidence for acid-catalyzed particle-phase reactions was obtained from the SOA chemical analyses. Aerosol mass concentrations for the 2-methyltetrols, as well as the newly identified sulfate esters, both of which serve as tracers for isoprene SOA in ambient aerosols, increased significantly with enhanced aerosol acidity. Aerosol acidities, as measured in nmol of H+ m(-3), employed in the present study are in the same range as those observed in tropospheric aerosol collected from the eastern U.S.     

酸渍香菇的工艺研究

研究了采用冰乙酸和食盐的混合液作为汤汁的香菇酸盐渍生产工艺、产品检验等,研究表明,冰乙酸浓度2%、食盐浓度8%~12%是香菇酸盐渍的最佳生产工艺条件。     

ß-phenylethylamine as a novel nutrient treatment to reduce bacterial contamination due to Escherichia coli O157:H7 on beef meat

Bacterial infection by Escherichia coli O157:H7 through the consumption of beef meat or meat products is an ongoing problem, in part because bacteria develop resistances towards chemicals aimed at killing them. In an approach that uses bacterial nutrients to manipulate bacteria into behaviors or cellular phenotypes less harmful to humans, we screened a library of 95 carbon and 95 nitrogen sources for their effect on E. coli growth, cell division, and biofilm formation. In the initial screening experiment using the Phenotype MicroArray^TM technology from BioLog (Hayward, CA), we narrowed the 190 starting nutrients down to eight which were consecutively tested as supplements in liquid beef broth medium. Acetoacetic acid (AAA) and ß-phenylethylamine (PEA) performed best in this experiment. On beef meat pieces, PEA reduced the bacterial cell count by 90% after incubation of the PEA treated and E. coli contaminated meat pieces at 10 °C for one week.