食品加工业对农业的影响

现在我们吃的食物大部分是多少经过了加工的。现在欧洲和北美的食物依靠于食品加工业的程度和它们依靠于农业的一样重要。粗略估算这两个产业部门在国民生产总值中占的分量是一样大的。人们在饮食习惯上的这种变化的社会经济原因已经一再阐述,不需要再在这里重复了。

Numerical simulation of freezing effect and tool change of shield machine with a frozen cutterhead

A shield machine with freezing function is proposed in order to realize tool change operation at atmospheric pressure. Furthermore, the transformation project of freezing cutterhead and tool change maintenance method are put forward. Taking the shield construction of Huanxi Power Tunnel as an example, a numerical analysis of the freezing cutter head of the project was carried out. The results show that when the brine temperature is-25 °C, after 30 d of freezing, the thickness of the frozen wall can reach 0.67 m and the average temperature drops to-9.9 °C. When the brine temperature is-30 °C, after 50 d of freezing, the thickness of the frozen wall can reach 1.01 m and the average temperature drops to-12.4 °C. If the thickness of the frozen wall is 0.5 m and the average temperature is-10 °C, as the design index of the frozen wall, the brine temperature should be lower than-28 °C to meet the excavation requirements in 30 d. Analyzing the frozen wall stress under 0.5 m thickness and-10 °C average temperature condition, the tensile safety factor and compressive safety factor are both greater than 2 at the most dangerous position, which can meet the tool change requirements for shield construction.

Ice Crystal Sizes and Their Impact on Microwave Assisted Freeze Drying

Freeze drying of an aqueous solution would result in the non-uniform distribution of solute concentration.Because ice is almost transparent to microwave, therefore such a non-uniform distribution may affect the microwave assisted freeze drying. The direct observation of the ice crystals formed under microscope reveals that the ice crystal sizes formed from de-ionized water depend on the cooling rate with fast cooling rate giving smaller ice crystals as expected. Once there is a sufficient amount of solute mixed with the de-ionized water, for example the reactive red,the size and its distribution are not very much dependent on either cooling rate or the final temperature provided there is sufficient time of cooling and the final temperature is not too low. The size of ice crystals formed within the solution of reactive red is usually below 100μm with a freezing rate of 1℃·min-1 for a droplet of the size of less than 1 mm. A simplified simulation indicates that such a small ice crystal would not cause a significant non-uniform distribution of temperature for microwave assisted freeze drying. When the ice crystal size is larger than 5 mm, heat conduction from the solute concentrated region to the ice region may need to be considered.

Chilled Semen of Captive Collared Peccaries （Pecari tajacu）： Effects of Preservation at 17 ℃ on Semen Quality

The trade creation and conservation of wild species in Amazon, including collared peccaries （Pecari tajacu）, may be favored by artificial insemination, but the time of semen storage may lead to reduced fertility in sperm of some wild animals. Thus, the aim of this research was to evaluate the influence of semen storage at 17 ℃ over time on seminal features of peccaries in captivity. Eight adult males were sedated and underwent electroejaculation. The ejaculates （n = 65） were evaluated for volume, concentration, pH, sperm motility, vigor, and cell with intact plasma membrane intact （IPM） and sperm morphology. Selected ejaculates （n = 21） were diluted （1：1） in Beltsville Thawing Solution and kept during 48 hours under controlled temperature （17 ℃）. Assessments were made after dilution （TO）, after 24 hours （T24）, and 48 hours after the onset of cooling （T48）. The storage impacted on sperm survival （P 〈 0.05）. Semen characteristics changed throughout the storage period studied and after 48 hours storage. The decline of sperm motility was of 55.2% for 10.9%, vigor was 2.3 for 0.5 and IPM cells were of 59.0% for 15.8%. Primary defects sperm increased of 19.8% for 32.2%, secondary defects of 9.8% for 10.4% and total defects of 29.4% for 42.7%. However, within 24 hours of preservation, chilled semen peccaries presented sperm motility average rate and IMP cells levels indicative to use in assisted reproductive events. These results indicate chilled semen for 24 hours could be used in experimentally artificial insemination of peccaries, technology that still has not been performed before.

Changes of Pectin Quantity in Fresh and Frozen Apple Products

Recently more and more innovations enter the manufacture of food products and one of them is food hydrocolloids. Food colloids open a lot of different possibilities in dessert production, which are used to perform certain functions. Pectin is a traditional agent for jams and jellies, but its application extends to fruit products for the food industry. In food product technology pectin is added as gelling agent and stabilizer. The three apple varieties ＂Antonovka＂, ＂Baltais Dzidrais＂ and ＂Zarja Alatau＂ harvested in Latvia State Institute of Fruit Growing were used for the experiment. Photometric measurement was used to determine the composition of pectin. Pectin was isolated from the apple mass by leaching with ethanol, and from the residues by extracting with diluted sodium hydroxide solution. By adding carbasol and sulphuric acid to the extract, through different intermediate stages carroty condensation product formed, which was photometrically measured at 525 nm. Pectin, pH and soluble dry matter were determined in fresh and frozen apple mass from apples of three ripeness stages. On the basis of worked out functional analysis of colloids, it is possible to optimize regulation of heat processes for different ripeness stages of apples. It is established that ripeness stage influences pectin quantity in fruits, but there are no data about pectin quantity changes in frozen fruits. By fruit ripening under the impact of enzyme protopectinase, protopectin hydrolyzes and transforms into pectin, which flows from the intercellular spaces into protoplasm of cells. Therefore ripe as well as heat treated fruits are soft and loose. It is important to measure pectin in frozen apple mass, in order to determine its potential jellying power. For each kind of product appropriate conditions have to be chosen for freezing, as well as the condition of products before freezing has to be taken into consideration in order to reduce the harmful influence on their quality to the minimum. The results of the research indicate that pectin quantity in frozen apple mass has decreased substantially. This susceptibility of sugar containing products to temperature fluctuations possibly is due to their high concentration of unfrozen water and lower melting temperature. It is possible to calculate the mass fraction of ice depending on temperature and moisture content in product which is very important for prognosticating the product quality. The aim of the research is to compare changes of pectin quantity in fresh and frozen apple products depending on storage time. The research is related to application possibilities of the current colloids, which are used in food industry at present.