RVA 4800 - Small-scale food ingredients analysis in high-temperature condition

Modern food processing methods require temperatures above 100°C to cook, pasteurize, sterilize, or add texture to the product. The Rapid Visco Analyser (RVA) 4800 offers an increased maximum test temperature of 140°C, which now allows pasting and viscosity analysis of ingredients at temperatures beyond the boiling point of water. The RVA 4800 can help gather information on the magnitude and the specific effect of high temperature conditions on the functionality and rheology of different ingredients.

Rheological devices, such as viscometers, are used to observe the changes in viscosity in response to temperature, shear, and time. These analytical instruments have a wide range of applications such as quality analysis, pilot-scale tests, optimizing formulation, observing effect of starch modifications, or determining ingredient process suitability. Analyzing the characteristics of an ingredient at temperatures above 100°C has generally been limited to calorimetry techniques. Calorimetry however does not analyze the series of changes that occur during cooking and the effect of shear on the viscosity of the sample. Such information is useful in predicting ingredient behavior in high temperature processes such as extrusion, pasteurization, sterilization, jet cooking, and retort. The aim is to provide results that better reflect the rheology of ingredients in modern high-temperature food processes.

Perten Instruments launched an extension to the RVA series, named the RVA 4800, that enables testing up to 140°C. The RVA 4800 allows researchers, formulators, and manufacturers to better mimic high temperature conditions with the advantage of operating at a small-scale level. Researchers can expand their study on difficult-to-cook resistant starches. Food manufacturers can make better informed decisions when optimizing formulations. Ingredient manufacturers can support their claims of process resistance and further expand their product range. The RVA 4800 offers improved robustness and a wider range of applications that can be executed from a single instrument.

RVA 4800 users can customize profile analyses to show variable shear rates, staggered temperature curves, or extended cook or cool holds. A custom profile called the “shear loops” (Figure 1) was used in the examples below. This profile shows the effect of high temperatures and varying shear rates on the viscosity of the sample. Figure 1 shows three separate profiles with maximum temperatures of 95°C (to represent the standard profile), 121°C (to represent the ‘botulinum’ cook used in retorting), and 140°C (to represent the maximum temperature of the RVA). During the hot and cool hold periods, the stirring speed is varied to obtain more information on the Newtonian (or non-Newtonian) fluid behavior of various samples.

RVA 4800 Figure 1
Figure 1. RVA test conditions - “Shear Loops” profile.

Thermal Resistance and Viscosity Recovery
The thermal resistance of an ingredient, or its ability to resist viscosity loss during heating at temperatures above 100°C, can now be observed. Knowledge of the ingredient’s thermal resistance will allow manufacturers to confidently choose ingredients that can better retain functionality during the most extreme phases of food processes.

The ability of an ingredient to recover its viscosity during cooling can be compared in the RVA 4800 against the previous standard of the 95°C analysis. The cooling viscosity can be translated as the product viscosity or relative texture of the food after cooling, during storage, or prior to consumption.
Figure 2 shows a high process tolerant starch under the “shear loops” pasting profile at 95, 121, and 140°C. This starch exhibited excellent thermal resistance (with little to no breakdown in viscosity at the hot stage), and good viscosity recovery (ability to recover viscosity following extended period at high temperatures) across all maximum cooking temperatures. This starch could be confidently used in processing temperatures of up to 140°C with minimal degradation, functional or rheological change.

RVA 4800 Figure 2
Figure 2. RVA curves of a high process tolerant starch, tested with “shear loops” at 95, 121, and 140°C.

Gelling agents and thickeners can also be analyzed in the RVA 4800. Some ingredients can withstand high temperatures up to a certain point. The hydrocolloid in Figure 3 was able to resist major degradation at 121°C but not at 140°C. Further investigation by changing the maximum temperature of the profile can show which temperature will cause the ingredient to lose most of its functionality. In food processes, this information would be useful when balancing temperature-time efficiency calculations.

RVA 4800 Figure 3
Figure 3. RVA curves of a hydrocolloid, tested with “shear loops” at 95, 121, and 140°C.

Structural variants of the same hydrocolloid can also be discriminated at temperatures up to 140°C. Figure 4 shows three variants of one hydrocolloid analyzed with the “shear loops” profile at 140°C. The RVA curves show that this hydrocolloid has a general behavior of low hot viscosity with high cooling viscosity. An ingredient with this behavior is particularly useful for increasing heating efficiency or reducing back pressure issues in processing systems but must still be able to contribute texture by gelling or thickening when cooled. Choosing the wrong variant may cause disastrous effects on the quality and consistency of the final product. 

RVA 4800 Figure 4
Figure 4. RVA curves of three variants of a hydrocolloid, tested with “shear loops” at 140°C.

The high temperature capability of the RVA 4800 allows the assessment of the pasting behavior of resistant starches (i.e. high-amylose starches) (Figure 5). Difficult-to-cook resistant starches require high temperatures in order to sufficiently gelatinize, cook, or paste. For the high-amylose starch in Figure 5, 140°C was the most effective temperature to cause significant changes in the granules (i.e. gelatinization and retrogradation). This valuable information can help determine which process temperature must be used to access the functional properties of high-resistant starches (i.e. enhancing crispiness). The RVA 4800 could be used as a tool to predict how well the starch can resist extreme conditions (i.e. digestion).

RVA 4800 Figure 5
Figure 5. RVA curves of a high-amylose starch, tested with “shear loops” at 95, 121, and 140°C.

The RVA 4800 can distinguish starches with varying degrees of modification. Three degrees (low, medium, and high) of starch modification were analyzed with the “shear loops” profile at 140°C. From the RVA curves (Figure 6), the starch with low modification exhibited poor thermal resistance due to its low overall viscosity. On the other hand, the highly modified starch showed minimal thermal degradation and a significant viscosity recovery. The highly modified starch would be the most stable and the ideal starch to use in high temperature processing conditions. These RVA curves (Figure 6) demonstrate the magnitude and effect of increasing the degree of modification on the thermal and process resistance of starches. The RVA 4800 can also be used to help determine which type of modification is most suited to a specific process.

RVA 4800 Figure
Figure 6.  RVA curves of a starch with varying degrees of modification, tested with “shear loops” at 140°C.

Effect of batch variation
Several factors (such as biological origin and process/manufacture/preparation conditions) can drastically affect the rheological behavior of a hydrocolloid and its process suitability. Figure 7 shows the importance and power of the RVA 4800 in differentiating between batches of the same hydrocolloid. The RVA 4800 is a handy tool in assuring quality of ingredients prior to homogenizing batch formulations, and thereby crucial in reducing costs and maintaining process efficiency.

RVA 4800 Figure 7
Figure 7. RVA curves of two different batches of the same hydrocolloid, tested with “shear loops” at 121°C.

The RVA 4800 provides a tool to researchers, and food and ingredient manufacturers, to further understand and better utilize food ingredients. It can offer manufacturers a sense of confidence in optimizing formulations or processes, while helping ingredient manufacturers to confirm claims of temperature resistance in their products.

Read more about the RVA 4800