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The evolution of volatile compounds in three Vitis uinifera varieties (Monastrell, Cabernet Sauvignon and Tempranillo) was followed during maturation to determine whether they could be used as a maturation index. The volatile compounds were extracted and analysed by gas chromatography and gas chromatography-mass spectrometry. The volatile compounds of these nonaromatic varieties generally occurred in very low concentrations and only the C, compounds appeared in sufficiently high concentrations for their evolution to be followed and used to determine optimum maturity.

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°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=β0T2 min (1+γ% Protein) was found to predict cutting time with a SEP of 2·42 min and an R2 of 0·98. γ was considered constant (γ=−0·0674, goats' milk) representing the protein effect on β0. 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 κ-casein hydrolysis was calculated based on changes in reflectance profile parameters and was found to be in the range 63–72 kJ mol−1.

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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°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 (τ2) and curd firming processes (τ1) were found when temperature decreased or protein increased. Theoretical asymptotic value of reflectance ratio, R∞, increased with increasing level of protein and temperature (P<0·05). The parameter β1, which represented the fraction of diffuse reflectance ratio attributed to aggregation, decreased with increasing temperature and decreasing protein.