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In order to develop a purine-reducing functional yak yoghurt, Lactobacillus paracasei 259 and commercial starter was used as the fermentation strain in this experiment. The inoculation amount of yak yoghurt strain was optimized by single factor experiment, and the quality changes of yak yoghurt during post-ripening period and storage period were observed. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the changes of flavor substances during post-ripening period and storage period, and the purine-lowering activity of yak yoghurt was determined by high performance liquid chromatography (HPLC). The results showed that the post-ripening time of yak yoghurt was 24 h, the sensory score was the best when the inoculation amount of Lactobacillus paracasei 259 was 5%, the number of viable bacteria was 3.1x108 CFU/mL, the acidity was 96°T, and the inhibition rate of xanthine oxidase (XOD) was 51.51%. Yak yogurt with 5% inoculum of Lactobacillus paracasei 259 had a viable bacterial count higher than 107 CFU/mL during 28 d of storage, and the acidity was lower than 105.4°T. With the increase of storage time, the pH and water holding capacity decreased gradually, and the sensory quality, hardness, cohesion, viscosity, consistency and XOD inhibitory activity increased first and then decreased. The main flavor substances in yak yogurt after ripening were alcohols, esters, ketones, aromatic heterocycles and sulfur compounds. The acids increased at storage period compared to the post-ripening period. The relative content and quantity of alcohols were the highest, which gave the yogurt a fruity, floral and sweet flavor. The degradation of inosine and guanosine in yak yogurt during the storage period firstly increased and then decreased, up to 84.6% and 86.5%, respectively. It can be seen that yak yogurt fermented by Lactobacillus paracasei 259 is of better quality, inhibits xanthine oxidase activity, effectively degrades inosine guanosine, and has good potential for application in the prevention and adjunctive treatment of hyperuricemia. [ABSTRACT FROM AUTHOR]

To investigate the properties and calcium-holding capacity of yak casein phosphopeptide (CPP), this experiment was carried out using yak casein as the raw material, with trypsin being used for enzymatic hydrolysis. Static adsorption test was performed to determine the eluent, and the effects of sample amount, sample flow rate and eluent concentration on the purification process of CPP. The basic composition, functional properties, and in vitro inhibitory capacity against calcium phosphate and ferrous ion precipitation of purified CPP were examined. A low-calcium mouse model was established, and the ability of CPP to promote calcium absorption in mice was investigated using body weight, organ index, serum biochemical parameters, femur index, bone density and bone calcium as the indicators. The experimental results showed that the best purification effect on the CPP was obtained under the following conditions: 0.2 mol/L dilute hydrochloric acid as the eluent, 3 mL/min as the loading flow rate, and 100 mL as the loading volume, leading to a nitrogen to phosphorus molar ratio of 6.8, a phosphorus recovery of 95.5%, a glutamic acid content of 18.55% and a serine content of 6.01%. In vitro calcium promotion experiments showed that the purified CPP could effectively prevent the precipitation of calcium phosphate and ferrous ions. The results of animal experiments showed that after 28 d of feeding, the organ indices of all mice were within a reasonable range. After purification, CPP showed no chronic toxicity. The medium- and high-dose groups had significantly higher blood calcium and phosphorus levels than those of the model group (P<0.05), and had extremely significantly lower alkaline phosphatase (ALP) values than those in the model group (P<0.01). The femoral bone index in the high-dose group was significantly higher than that in the calcium carbonate group (P<0.05). The bone calcium and bone density of the medium- and high-dose CPP groups were significantly higher than those of the model group (P<0.05). In conclusion, this experiment can provide a theoretical basis for the development of functional yak milk foods and a reference for the subsequent research on yak milk's bioactive peptides. [ABSTRACT FROM AUTHOR]

A double roller type planetary gear drive with small tooth number difference is designed,and its meshing surface is composed by two array cylinder rollers,which is equidistributed in the internal gear and external planetary gear. The transmission principle and characteristic is analyzed,the determination and optimization method of the design parameters is discussed. According to its characteristic of discontinuous transmission,the transmission error is calculated and analyzed based on the error calculation formula. The research results reveal that this drive completely meets the error requirement of the power transmission and also has the possibility to be used in precision transmission with the optimal design.

For revealing the forming mechanism of sideband frequencies in planetary transmission, a model for modulation sideband frequencies in planetary gear system is established to analyze the effects of the basic parameters (teeth number, meshing phase and installation phase) of planetary gear system and excitation orders on the features of sideband frequencies, and a generic decision method is deduced for estimating sideband frequency features based on these parameters. Using transmission error as excitation, a simulation on five typical gear matching schemes is conducted, and the sound pressure level of a vehicle automatic transmission is measured in a semi-anechoic chamber. The results of theoretical analysis and simulation are verified by test with order ratio tracking technique. The results show that the appearing of sideband frequencies in planetary gear set is not a random phenomenon, and is rather caused by the modulation of meshing phase difference between planetary gears, and is affected by excitation order. Adjusting the basic parameters of planetary gear train can change the features of sideband frequencies, and hence effectively reduce the gear whine noise they produced. [ABSTRACT FROM AUTHOR]