Effect of protein and temperature on cutting time prediction in goats' milk using an optical reflectance sensor

An objective method for determining the coagulum cutting time is needed to improve consistency and processing efficiency of goats' cheese. A fibre optic sensor was used to measure the backscatter of near-infrared radiation at 880 nm during the coagulation of skimmed goats' milk for the purpose of predicting coagulum cutting time. A randomised block design, replicated three times, was used to test the effect of three protein concentrations (3, 5 and 7% (w/w)) on diffuse reflectance parameters for cutting time prediction of milk coagulated at five different temperatures (20, 25, 30, 35 and 40 degrees C) to assure a wide range of coagulation rates. The inclusion of a protein term in the existing algorithms was essential to reduce the standard error of prediction to under 6.2 min. An algorithm including a time-based parameter and a protein term, Tcut=beta0 T2min (1 + gamma% Protein) was found to predict cutting time with a SEP of 2.42 min and an R2 of 0.98. Gamma was considered constant (gamma=-0.0674, goats' milk) representing the protein effect on beta0. Algorithms using response-based parameters (such as change in reflectance ratio) and the composition parameter protein required additional regression parameters such as temperature and an intercept term to predict the cutting time with the same precision as algorithms using only time-based parameters. Time-based parameters were found to decrease proportionally with increasing temperature and decreasing protein concentration. Response-based and mixed-based parameters were found to decrease with decreasing temperature. Reflectance ratio at cutting time did not significantly change with protein concentration for skimmed goats' milk. The activation energy of kappa-casein hydrolysis was calculated based on changes in reflectance profile parameters and was found to be in the range 63-72 kJ mol(-1).     

Plasma-enhanced chemical vapor deposition of zinc oxide at atmospheric pressure and low temperature

The plasma-enhanced chemical vapor deposition of aluminum-doped zinc oxide has been demonstrated for the first time at 800 Torr and under 250 °C. A film resistivity of and a transparency of 95% from 375 to 2500 nm was obtained for deposition at 20-mTorr diethylzinc, 1.0 Torr CO₂, 799 Torr He, a TMAl/DEZn ratio of 1:100, RF power, and 225 °C. The average aluminum concentration in the ZnO film was . It was found that, while the growth rate did not change with substrate temperature, both the resistivity and optical absorption coefficient declined with increasing temperature.     

Spatial power combining for two-dimensional structures

The two-dimensional (2-D) hybrid dielectric slab-beam open and closed waveguide systems are suitable for the design of planar quasi-optical integrated circuits and devices. An open system consisting of an active E-plane amplifier array consisting of Vivaldi-type antennas with MESFET and monolithic microwave integrated circuit (MMIC) devices was investigated. The 4×1 MESFET amplifier array generated 11 and 4.5 dB of amplifier and system gain, respectively, at 7.12 GHz, and the cascade MMTC Vivaldi-type antenna produced 24 dB of amplifier gain at 8.4 GHz. Also, experiments on a new 2-D H-plane parallel-plate closed system with a stripline slot antenna is introduced, and the wavebeam-mode theory is presented. The new system minimizes scattering and isolation losses associated with open structures. The amplifier gain of the closed system based on slot antennas is compared to the open system based on Vivaldi antennas     

Oils and fats

Journal of the American Oil Chemists' Society -     

Fatigue crack growth analysis of 2024 T3 aluminium specimens under aircraft service spectra

The fatigue crack growth behaviour of 2024 T3 aluminium was investigated experimentally. The fatigue experiments were performed under constant stress amplitude, constant amplitude with single and multiple overloads and aircraft service spectra. The fatigue spectra used correspond to the air-to-air, air-to-ground and instrumentation and navigation flight phases. They were applied for different stress levels. In total 11 different random flight service spectra were examined. The retardation effects caused by the overloads on the fatigue crack growth behaviour and the fatigue crack growth under aircraft service spectra were predicted using an in-house-developed code. The code makes use of the strip plastic zone approximation to account for material hardening effects along the path of prospective crack growth. Crack growth is treated incrementally and corresponds to failure of material elements ahead of an existing crack after a certain critical number of fatigue cycles. For the simulation of irregular service spectra by equivalent sequences of distinguished stress cycles a modified rainflow counting method is utilized. Spectrum simulation accounts also for non-linearity in fatigue damage accumulation and load sequence effects. The computed fatigue curves fit well with the experimental results.     

Modelling casein aggregation and curd firming in goats' milk from backscatter of infrared light

A kinetic model was proposed for describing the curd assembly of skimmed goats' milk during enzymic coagulation. The enzymic coagulation of milk was monitored using an optical sensor that measured diffuse reflectance (light backscatter) at 880 nm. The appearance of a shoulder, at low temperatures and protein concentrations, in the diffuse reflectance ratio profile after the inflection point of the curve (Tmax) appeared to separate the aggregation and curd firming steps. The diffuse reflectance ratio profile after Tmax was attributed to the overlapping of casein micelles aggregation and curd firming reactions. The developed kinetic model combined a second order reaction model to describe aggregation reactions and a first order reaction model to describe firming processes reactions. A completely randomised block design with three replications was used to determine the effect of protein concentration and temperature on kinetic constants. Milk was adjusted to three levels of protein (30, 50 and 70 g/kg), and coagulated at five temperatures (20, 25, 30, 35 and 40 degrees C) to test a wide range of processing conditions. Data points from each profile after Tmax were fitted to the proposed model using non-linear regression. The average R2 and standard error of prediction (SEP) for 45 tests conducted were in the range of 0.9975 +/- 0.0027 and 0.0081 +/- 0.0037, respectively. A significant increase in characteristic times for aggregation (tau2) and curd firming processes (tau1) were found when temperature decreased or protein increased. Theoretical asymptotic value of reflectance ratio, R(infinity), increased with increasing level of protein and temperature (P < 0.05). The parameter beta1, which represented the fraction of diffuse reflectance ratio attributed to aggregation, decreased with increasing temperature and decreasing protein.