courtesy of DataPhysics

Whey drinks area popular ready-to-drink protein beverages, owing to their excellent nutritional qualitiest and good flavor. To have a fresh and neutral taste, whey based beverages are usually prepared with fruits or vegetables. Stability issues are one of the major problems which are commonly encountered in this kind of beverages,
such as, crystallization of lactose stored in the fridge, coagulation of whey proteins amongst others. It is of great importance to study the stability of whey beverage formulations and modify them towards a better performance. With the MultiScan 20 (MS 20) (Fig. 2) dispersion stability analysis system from DataPhysics Instruments stability
changes can be detected and evalauted in a quantitative way much faster than any traditional shelflife test would permit. The stability study of four whey beverage formulations is presented throughout this application note.

 Technique and Method
The MultiScan MS 20 (Fig. 2) from DataPhysics Instruments is the measuring device for automatic optical stability and
ageing analysis of liquid dispersions and the comprehensive characterisation of time- and temperature-dependent
destabilisation mechanisms. It consists of a base unit and up to six connected ScanTowers with temperature-controlled
sample chambers. The ScanTowers of the MS 20 can be individually controlled and operated at different
temperatures (4 °C to 80 °C). With its matching software MSC, MS 20 is an ideal partner for stability analysis since even the slightest changes within dispersions can be detected and evaluated. The MS 20 enables fast and objective analysis of the dispersion stability as well as conclusions on possible destabilisation mechanisms.

 

 

Experiment

A small vial filled with the desired dispersion is placed in one of the “Scan Towers” of the MS 20. The scanning system is composed of a transmission and backscattering LED along with a detector. This system moves along the vertical side of the vial (z-axis). The obtained transmission and backscattering intensity is represented in an intensity-position diagram. The sample was scanned at regular time intervals. Changes in the detected measuring signal can provide explanations for the stability properties of the sample. 20 ml of each whey drink formulation (cassis, peach, blood orange, multifruit) were poured in a transparent glass vial and measured every 5 min for 5 h 45 min. The measured zone is between 0 mm (bottom of the glass) and 57 mm (fill level of the vial). Fig. 3 shows the samples’ vials at the end of the measurement.

Results

As the samples have a significant volume concentration, the transmission signal was too weak and exhibited very little information throughout the measurement. Therefore the backscattering signal was analysed to study the stability of whey drinks. The four samples showed similar changes in backscattering intensities over time. Figure 4 shows the plot of the backscattering intensities against the position for the whey beverage with cassis. It shows a time-dependent as well as position-dependent change of the signal, which decreased at the top between 50 mm and 55 mm, indicating a typical sedimentation process.

 

 Calculated with the respective function of the MSC software, the change in migration front can be analyzed, resulting in an average sedimentation rate of 1.038 mm/h in the first 1 h and 0.02576 mm/h in the last 4 h 45 min for cassis whey beverage (Fig. 5). The reason is that most of the particles have already sedimented during the first 1 h.

Accordingly, the other 3 samples were analyzed leading to the sedimentation rates as displayed in Fig. 6. The whey beverages with peach, cassis or blood orange were also very unstable in the first 1 h, while the multifruit containing whey beverage showed a constant sedimentation rate of only 0.1029 mm/h during the test, indicating its stability is highest. Besides, the whey beverage with peach was found

 

 to be the most unstable formulation with a sedimentation rate of 1.491 mm/h, while the drinks with cassis and blood orange showed similar stability.to be the most unstable formulation with a sedimentation rate of 1.491 mm/h, while the drinks with cassis and blood orange showed similar stability.Most notably, the MSC software can also provide an overall analysis by the stabilty index function. To directly and simply get the stability difference, the rsults of all samples can be displayed in an overlay window (Fig. 7). In consistency with the results from before also the stability index analysis supports that the beverage with multifruit is the most stable formulation, while the whey beverages with peach was the most unstable. This results underlines the excellent applicability of MS 20 to analyze and quantify stability issues of different formulations locally and globally with high reliability.

Summary
Using the MS 20 stability analysis system and its corresponding MSC software, an easy and fast way to study the stability of whey beverage formulations could be demonstrated. Changes can be detected sensitively, easily and reliably which enables the producer to anticipate and quantify stability issues and thus guarantee time and cost-optimal product development.