Ultrasound tests in a stirred vessel to evaluate the reconstitution ability of dairy powders

Insolubility in milk protein concentrates: potential causes and strategies to minimize its occurrence

Milk protein concentrates (MPCs), which are produced from skim milk following a series of manufacturing steps including pasteurization, membrane filtration, evaporation and spray drying, represent a relatively new category of dairy ingredients. MPC powders mainly comprise caseins and whey proteins in the same ratio of occurrence as in milk. While bovine MPCs have applications as an ingredient in several protein enriched food products, technofunctional concerns, e.g., reduced solubility and emulsification properties, especially after long-term storage, limit their widespread and consistent utilization in many food products. Changes in the surface and internal structure of MPC powder particles during manufacture and storage occur via casein-casein and casein-whey protein interactions and also via the formation of casein crosslinks in the presence of calcium ions which are associated with diminishment of MPCs functional properties. The aggregation of micellar caseins as a result of these interactions has been considered as the main cause of insolubility in MPCs. In addition, the occurrence of lactose-protein interactions as a result of the promotion of the Maillard reaction mainly during storage of MPC may lead to greater insolubility. This review focuses on the solubility of MPC with an emphasis on understanding the factors involved in its insolubility along with approaches which may be employed to overcome MPC insolubility. Several strategies have been developed based on manipulation of the manufacturing process, along with composition, physical, chemical and enzymatic modifications to overcome MPC insolubility. Despite many advances, dairy ingredient manufacturers are still investigating technical solutions to resolve the insolubility issues associated with the large-scale manufacture of MPC.

Monitoring Viscosity and Total Solids Content of Milk Protein Concentrate Using an Inline Acoustic Flowmeter at Laboratory Scale

Control of milk concentrate viscosity and total solids (TS) content prior to spray drying can improve dairy ingredient manufacture. However, the availability of hygienic and appropriately pressure rated process viscometers for inline monitoring of viscosity is limited. An acoustic flowmeter (FLOWave) is an inline process analytical technology (PAT) tool that measures changes in acoustic signals in response to changes in liquid properties (i.e., acoustic transmission (AT), acoustic impedance (AI), temperature and volume flowrate). In this study, an acoustic flowmeter is evaluated as an inline PAT tool for monitoring viscosity of milk protein concentrate (MPC85), protein and TS content of (MPC85), and standardised MPC (sMPC). Laboratory scale experiments were carried out at 45 °C for five different concentrations (4–21%) of MPC85 and sMPC. Results showed that AT decreased with an increase in MPC85 viscosity (e.g., AT was 98.79 ± 0.04% and 86.65 ± 0.17% for 4% and 21% TS content, respectively). Non-linear regression was carried out to develop a relationship between AT and offline viscosity (R² (coefficient of determination) value = 0.97 and standard error of prediction = 1.86 mPa·s). AI was observed to increase at higher protein and TS content which was dependent on protein to total solid ratio (P_TSR). Multiple linear regression was carried out to develop the relationship between AI, protein content, TS content and P_TSR. Results demonstrated that AI could be used to monitor the protein and TS content of milk protein concentrate (R² > 0.96). Overall this study demonstrated the potential of an inline acoustic flowmeter for monitoring process viscosity, protein and TS during dairy concentrate processing.

Using ultrasound to characterize the tongue-food interface: An in vitro study examining the impact of surface roughness and lubrication

We measured the apparent reflection coefficient of a 1-MHz ultrasound compressional wave at the interface between rough and lubricated tongue mimicking surfaces and various food gels, composed of agar or gelatin. For the smoothest mimicking surface, when a lubricating layer was present, the apparent reflection coefficient was fairly similar for the different food gels (33.6% on average). The apparent reflection coefficient was significantly larger in the following situations: (i) tongue asperities were high and dense; (ii) lubrication levels were low; and (iii) gels were less rigid (range for the different gels-45.9-84.3%). The apparent reflection coefficient conveys the ability of food gels to mold themselves to surface asperities or to form a coupling film of liquid at the interface. This study demonstrates that ultrasound methods can and should be used to explore the physical phenomena that underlie the texture perceptions resulting from tongue-palate interactions.

Application of front-face fluorescence spectroscopy as a tool for monitoring changes in milk protein concentrate powders during storage

This study investigated the feasibility of front-face fluorescence spectroscopy (FFFS) to predict the solubility index and relative dissolution index (RDI) of milk protein concentrate (MPC) powders during storage. Twenty MPC powders with varying protein contents from 4 different commercial manufacturers were used in this study. The MPC powders were stored at 2 temperatures (25 and 40°C) for 0, 1, 2, 4, 8, and 12 wk. The front-face fluorescence spectra of tryptophan and Maillard products were recorded and analyzed with chemometrics to predict solubility of MPC powders. The similarity maps showed clear discrimination of the MPC samples stored at 25 and 40°C. Partial least squares regression models were developed using the fluorescence spectra of tryptophan and Maillard products to predict the solubility index and RDI measurements of MPC powders, and the prediction models were validated using an independent test set. Coefficients of determination (R²) of 0.76, 0.84, and 0.68 were obtained between fluorescence spectra (tryptophan emission, Maillard emission, and Maillard excitation, respectively) and solubility index. The R² values for the RDI predictions were 0.58 and 0.60 for the data set of tryptophan emission and Maillard emission, respectively. The ratio of prediction error to standard deviation was >2 for Maillard emission fluorescence spectra and solubility index measurements, indicating good practical utility of the partial least squares regression prediction models. The results indicated that the solubility and dissolution behavior of MPC powders were related to their protein content and storage conditions that could be measured using FFFS. Hence, FFFS can be used as a rapid nondestructive analytical technique to predict the solubility and dissolution characteristics of MPC powders.

Milk protein concentrates: opportunities and challenges

Poor solubility of milk protein concentrates (MPCs) is a key deterrent factor in their wider applications in the food industry as compared to other protein-rich dried products such as casein, caseinates and whey protein concentrates and isolates. Apart from the processing factors, the protein content of a MPC also decides its solubility. Solubility is a pre-requisite property of MPCs on which its other functional properties are majorly depended. Further, there is a confusion about the term MPC itself in the literature. An attempt has been made to describe MPC and provide an understanding on the manufacture of MPCs. Further, mechanisms of insolubility, factors affecting solubility of MPCs and an insight into the recently evolved strategies for overcoming the challenges related to their poor heat stability and solubility have been reviewed. Potential applications of MPC to be utilized as a novel ingredient in food industry are also outlined.