蔗渣碱法制浆蒸煮黑液增浓过程中的相变化

利用DSC的热分析法探讨了蔗渣浆黑液在蒸发浓缩中的相转变过程。当蔗渣黑液中固形物含量接近40%时，黑液聚合物由水的连续相转变为聚合物（由有机物和无机物组成）的连续相。此时，黑液由凝固点（冰点）温度过渡到玻璃化转变点温度，相应地，黑液的物化性能如粘度等变化很大。     

草莓玻璃化转变温度的DSC测量

在测量溶液的部分玻璃化转变温度时,往往无法直接测得溶液在最大冻结浓缩状态下的部分玻璃化转变温度(Tg’),而是测得部分结晶玻璃化转变温度(Tgf)。本文用差示扫描量热仪,采用不经过退火处理的连续扫描法、分步扫描法对草莓打浆液、榨汁草莓经抽滤的草莓汁液和浓缩掉三分之一水分的浓缩草莓汁进行了玻璃化转变温度的测量。研究发现,用同一种方法测得的三者的玻璃化转变温度相差不大。在-48℃以下退火,玻璃化转变温度随着退火温度的增大而增大,在-48℃以上退火,玻璃化转变温度随着退火温度的增大而减小,并有很好的线性关系,从Tgf确定Tg’的新方法是两侧Tgf的交点对应的温度为Tg’。得到草莓的Tg’为-52.8℃。     

Kinetics of non-enzymatic browning in amorphous solid systems: distinguishing the effects of water activity and the glass transition

Debates have emerged recently on whether water activity or the state of the system as dictated by the glass transition temperature (T_g) impacts the rates of chemical reactions in reduced-moisture solid systems. The objective of this study was to evaluate the kinetics of brown pigment formation in polyvinylpyrrolidone model systems of different molecular weights so that the effects of water activity and the glass transition could be distinguished. Browning rates at different T_gs, but constant water activity, were significantly different except when all were in the glassy state. As the system changed from a glassy state to a rubbery state, the rate of browning increased 7-fold. The rate of browning also increased as water activity increased from 0.33 to 0.54, but then appeared to plateau with further increases in water activity. Thus, the rate of brown pigment formation is influenced significantly by the glass transition temperature of the system and less by the water activity. In addition, the concentration of reactants in the aqueous microenvironment had a significant impact on the rate of brown pigment formation.     

Determining the effects of annealing time on the glass transition temperature of Pueraria lobata (Willd.) Ohwi starch

To probe the effects of annealing time on the glass transition temperature (T_g) and digestibility of Pueraria lobata (Willd.) Ohwi starch, the starch crystal structure and moisture distribution through the components of P. lobata (Willd.) Ohwi starch were investigated. Annealing times of 0, 1, 3, 6, 12 and 24 h were employed to determine the effect of starch T_g using differential scanning calorimetry (DSC) with the support of ¹H low‐field NMR, polarised light microscopy and ¹³C CP/MAS NMR. The T_g values of the starch increased with longer annealing times. The ¹H low‐field NMR results showed that the T₂ relaxation time decreased and starch–water interactions increased as the annealing time increased. Compared with native starch, annealed starch had higher contents of slowly digested starch (SDS) and resistant starch (RS). The starch crystal structure was not destroyed after annealing, but the relative crystallinity percentage increased slightly.     

Indicators of resilience during the transition period in dairy cows: A case study

The transition period is a demanding phase in the life of dairy cows. Metabolic and infectious disorders frequently occur in the first weeks after calving. To identify cows that are less able to cope with the transition period, physiologic or behavioral signals acquired with sensors might be useful. However, it is not yet clear which signals or combination of signals and which signal properties are most informative with respect to disease severity after calving. Sensor data on activity and behavior measurements as well as rumen and ear temperature data from 22 dairy cows were collected during a period starting 2 wk before expected parturition until 6 wk after parturition. During this period, the health status of each cow was clinically scored daily. A total deficit score (TDS) was calculated based on the clinical assessment, summarizing disease length and intensity for each cow. Different sensor data properties recorded during the period before calving as well as the period after calving were tested as a predictor for TDS using univariate analysis of covariance. To select the model with the best combination of signals and signal properties, we quantified the prediction accuracy for TDS in a multivariate model. Prediction accuracy for TDS increased when sensors were combined, using static and dynamic signal properties. Statistically, the most optimal linear combination of predictors consisted of average eating time, variance of daily ear temperature, and regularity of daily behavior patterns in the dry period. Our research indicates that a combination of static and dynamic sensor data properties could be used as indicators of cow resilience.     

The glassy state phenomenon in applications for the food industry: Application of the food polymer science approach to structure–function relationships of sucrose in cookie and cracker systems

This review of the glassy state phenomenon in applications for the food industry comprises two main parts. The first is a broad but brief overview of the so-called ‘food polymer science’ approach and its importance to food R&D studies of glassy solid and rubbery liquid states and glass transitions in food products and processes. The following elements of this approach are discussed: (i) the glass transition temperature (T_g) and methods for its measurement in foods; (ii) plasticization by water and its effect on T_g; (iii) the concepts of ‘water dynamics’ and ‘glass dynamics’ in non-equilibrium food systems; (iv) Williams–Landel–Ferry kinetics in the rubbery state above T_g, (v) state diagrams; and (vi) the effect of molecular weight on T_g. A comprehensive and up-to-date listing of more than 400 literature references on the glassy state phenomenon and glass transitions in food materials and systems is featured in that part of the paper, and these references are also compiled and tabulated according to specific subject headings. The second part of this review highlights the application of the food polymer science approach in recently reported studies on the structure–function relationships of sucrose in cookie and cracker systems. This part describes (i) the sucrose–water state diagram as a tool in understanding cookie and cracker baking; (ii) shortcomings of the traditional AACC sugar-snap cookie method as a test-baking system, in contrast to a new test system based on a model commercial-type wire-cut cookie formula; and (iii) a revealing illustration of sucrose functionality in cookie baking. The review concludes with a word about future prospects.