F.A. Payne

On-line sensing techniques for coagulum setting in renneted milks

Abstract In cheesemaking, the on-line measurement of clotting time, coagulum firmness and cutting point is useful for process monitoring but has proven difficult to carry out. This work presents a comparison of on-line sensors, more or less capable of allowing the determination of these data. An experiment was undertaken in which six on-line sensors, comprising of optical systems (NIR transmission X2 wavelengths and NIR reflectance), hot-wire, and vibrational systems (torsional and transverse), were used simultaneously to monitor milk coagulation in trials where protein levels and enzyme concentrations were varied and the sensor response characteristics were compared with oscillatory shear measurements. It was found that protein level mainly influenced curd firming rate, while rennet level mainly influenced gel time. Up to three coagulation parameters were derived using each sensor. While all sensors were able to detect the effect of rennet level, which is mainly seen in the gelation (or clotting) time, the sensors varied in their sensitivity to changes in protein level, which mainly affects the curd-firming time. For some sensors, a combination of response parameters was shown by multiple linear regression to be advantageous for predicting coagulum-firming time. By combining response parameters in this way the standard errors of prediction of coagulum cutting point (using oscillatory shear measurements as the reference) were better than 100 s for NIR reflectance, NIR transmission and low-frequency vibration systems as compared with ca.300 s for the hot-wire or torsional vibration systems.

Textural and viscoelastic properties of pork frankfurters containing canola-olive oils, rice bran, and walnut.

Textural, rheological and microstructural properties of frankfurters made with 20% pork backfat, 20% canola or 20% canola-olive (3:1) oils, including rice bran (RB) and walnut extract (WE) as macronutrients (2.5%) were investigated. Textural parameters, including hardness, gumminess and rupture-force, were highly (P<0.05) influenced by the fat-oil composition. Addition of RB or WE in vegetable oil emulsions improved textural consistency (P<0.05). However, RB addition reduced gelling capacity, suggesting antagonistic interactions between fiber and oil droplets. Vegetable oil addition favored gel network formation, and, when combined with WE, showed the highest improvement of gel elasticity. These textural and gelling properties were corroborated by frankfurter micrographs, which revealed interactions between vegetable oils, RB, or WE with protein matrix and fat globules affecting these parameters. The results suggest that functional plant-derived ingredients can be valuable to the modification of frankfurter formulations for improved nutrition and as well as textural quality.

Antioxidant and emulsifying properties of alcalase-hydrolyzed potato proteins in meat emulsions with different fat concentrations

The effect of hydrolyzed potato protein (HPP), a natural antioxidant, on emulsion quality was investigated using a factorial design with two Fat (15%, 30%) and two HPP (0%, 2.5%) levels, with three replications. The colour of the raw emulsions as well as cooking losses, textural properties and TBARS of cooked frankfurters were measured. Increasing the Fat proportion significantly (P<0.05) increased L(∗), H(ab)(0) and decreased a(∗), b(∗), C(ab)(∗) and hardness. Meat emulsions with added HPP were darker (lower L(∗)) than those made without HPP and also had lower values of a(∗) and b(∗). The addition of HPP (2.5%) significantly (P<0.05) decreased cooking losses and fracture force, and had a significant (P<0.05) inhibitory effect on lipid oxidation in cooked frankfurters. These results suggest that HPP has both antioxidant and emulsifying properties which may be of potential use in meat emulsion manufacturing.

A review of puffing processes for expansion of biological products

Abstract A research objective to develop a puffing process which would improve the rehydration characteristics of air-dried fruits and vegetables led to a review of puffing processes described in the US patent and published literature. The puffing processes found were classified into four categories based on the method responsible for gas evolution: phase change, absorption, adsorption, and chemical reaction. An explosive expansion rate E was calculated for different puffing processes in each category. It appears that E must be in the range 0·05–12 m 3 /s kg to puff biological products.

Fiber Optic Sensor for Predicting the Cutting Time of Coagulating Milk for Cheese Production

A fiber optic sensor was developed to measure the changes in diffuse reflectance of coagulating milk using infrared light at a wavelength of 950 nm. Reflectance profiles were measured during tests in which the coagulating temperature, pH, enzyme concentration, and milk fat content were controlled. All reflectance profiles showed an induction, sigmoidal, and logarithmic period. The diffuse reflectance was found to be a function of milk fat content and affected by milk pH, temperature, and enzyme concentration.

A comparison of on-line techniques for determination of curd setting time using cheesemilks under different rates of coagulation

Abstract An experiment is described where six on-line techniques for monitoring milk coagulation (NIR diffuse reflectance, NIR transmission (two wavelengths), hot-wire, torsional vibration and tuning-fork vibration) were compared with rheological measurements of curd firming (elastic shear modulus) under a range of coagulation rates, effected by varying enzyme level in fresh whole milk. Viscous and elastic moduli were measured during renneting and were analysed to determine their usefulness for determination of a gel point. G ′ and G ′′ each gave a suitable measure of gel time as indicated by compliance with Holters Law. The correlation of gel points determined by G ′′ with those determined by G ′ showed that a sensor which detects changes in viscosity per se works in principle as a gel point detector in cheesemilk. Gel times determined from G ′′ were slightly longer than those determined from G ′ which in turn were slightly longer than those determined from tan δ , with the differences becoming larger at lower enzyme levels, i.e. longer gel times. Gel times based on G ′′ were just as good predictors of cutting time as those based on G ′ . In addition the asymptotic behaviour of tan δ showed that a viscosity sensor can determine an optimum point of curd-cutting, which is usually defined in terms of a large value of G ′ . All on-line techniques modelled rheological gel time (by rheometer) with an accuracy of ca. 1 min. and predicted curd cutting time with an accuracy of ca. 2 min.

Characterization of milk properties with a radiative transfer model

To characterize milk through light-scattering measurements, a semianalytical radiative transfer model was used to simulate the backscatter of light in milk having homogenized fat levels from 0.05 to 3.2 wt. %. The input parameters to the model include the incident wavelength, refractive index of particles and medium, and particle number densities. By varying the wavelength, we can obtain a reasonable fit between experimental data and the model for lower fat milks. Results indicate that the model is most sensitive to the particle diameter and size distribution and less sensitive to the number and index of refraction of the particles.

Effect of calcium and enzyme in cutting time prediction of coagulating goats’ milk using a light scattering sensor

An on-line fibre optic sensor measuring backscatter at 880 nm was used for predicting the cutting time of goats’ milk. A factorial design was utilised to test the kid rennet and enzyme from Mucor miehei at three levels of added CaCl2. A cutting time prediction equation using the diffuse reflectance parameter, Tmax; predicted the cutting time with a standard error of 0.55 min. Tmax and cutting time decreased with CaCl2 addition. Coagulation was faster for kid rennet. The sensor was found useful for comparing the activity of milk-clotting enzymes. r 2002 Elsevier Science Ltd. All rights reserved.

Validation of a curd-syneresis sensor over a range of milk composition and process parameters

An online visible-near-infrared sensor was used to monitor the course of syneresis during cheesemaking with the purpose of validating syneresis indices obtained using partial least squares, with cross-validation across a range of milk fat levels, gel firmness levels at cutting, curd cutting programs, stirring speeds, milk protein levels, and fat:protein ratio levels. Three series of trials were carried out in an 11-L cheese vat using recombined whole milk. Three factorial experimental designs were used, consisting of 1) 3 curd stirring speeds and 3 cutting programs; 2) 3 milk fat levels and 3 gel firmness levels at cutting; and 3) 2 milk protein levels and 3 fat:protein ratio levels, respectively. Milk was clotted under constant conditions in all experiments and the gel was cut according to the respective experimental design. Prediction models for production of whey and whey fat losses were developed in 2 of the experiments and validated in the other experiment. The best models gave standard error of prediction values of 6.6 g/100 g for yield of whey and 0.05 g/100 g for fat in whey, as compared with 4.4 and 0.013 g/100 g, respectively, for the calibration data sets. Robust models developed for predicting yield of whey and whey fat losses using a validation method have potential application in the cheese industry.

A novel fiber optic sensor to monitor beef meat emulsion stability using visible light scattering.

Accurate control of the meat emulsification process for a consistent product quality entails the development of an on-line optical sensor technology to determine the optimum chopping end-point yielding minimum cooking loss and a fine texture. Previous studies suggested that light backscatter measurements can be used to monitor physical-chemical changes during emulsification in comminuted meat products if appropriate spacing between the emitting and detecting optical fibers is used. Light backscatter intensity from beef emulsions manufactured with different fat/lean ratio (0.075, 0.250, and 0.330) and chopping duration (2, 5, and 8min) were obtained using a dedicated fiber optic prototype. Optical measurements were collected at three radial distances (2, 2.5, and 3mm) from the light source using a fiber optic spectrometer (300-1100nm). Light backscatter intensity decreased logarithmically with increasing fiber optic spacing. Light propagation through the emulsion decreased significantly with increasing chopping duration and fat concentration. Cooking loss increased with increasing fat/lean ratio and with under- or over-chopping. The maximum emulsion stability was observed at 5min of chopping. Several optically derived parameters were found to be significantly correlated with fat loss during cooking. Typically, those correlations were observed to increase with decreasing fiber distance. Based on these findings, an optical configuration is proposed that would compensate for the emulsion heterogeneity, maximizing the existing correlation between the optical signal and the emulsion quality metrics.