Application Note | CoaguSens™ Flex
How to measure yogurt formation in real time - animal and plant-based
by Noémie Deloire, CPE,
Application Scientist, Rheolution Inc.
Summary of findings
- The optimization of yogurt texture is imperative for ensuring product quality, consumer appeal, and satisfaction.
- Commonly employed in the industry, rheometers, viscometers, and texture analyzers each possess distinct limitations.
- In this study, the CoaguSens™ Flex was used to continuously monitor the viscoelastic properties of yogurt gels. Analyzing the viscoelasticity of yogurt gels facilitates the precise timing of production processes and the effective adjustment of ingredient dosages.
- The findings illustrate that viscoelasticity measurements, when used alongside pH assessments, provide a comprehensive evaluation of the textural properties of the product.
Case Study: Measuring yogurt texture with the CoaguSens™ Flex
The viscoelastic properties of yogurt significantly influences the overall sensory experience of the consumer. A smooth, creamy consistency enhances mouthfeel and consumer satisfaction, serving as a key differentiator among brands. Viscoelasticity affects flavor perception, with variations in thickness and creaminess potentially altering the taste experience, making texture crucial for yogurt appeal and enjoyment.
Rheometers, viscometers, and texture analyzers are commonly used to assess the texture of yogurts; however, each of these instruments has inherent limitations. Rheometers, which require substantial expertise in rheology, are complex instruments that may not be suitable for use in a production environment due to their operational complexity. Viscometers, while useful, perform destructively and are unable to evaluate the viscoelastic properties of yogurt gel during the fermentation process. Texture analyzers, on the other hand, lack the sensitivity required to accurately measure gel formation and are typically utilized for evaluating the final texture of set yogurts.
In this study, we introduce the use of the CoaguSens™ Flex to precisely measure, in real time, the viscoelastic properties of milk gels during the fermentation process and after cooling. Leveraging a modern testing technology (CoaguSens™ Flex is already successfully applied to monitor enzymatic milk coagulation in cheese production) we introduce an innovative approach to measure the kinetics of animal and vegan milk gel formation during acid fermentation and cooling phases to produce yogurt. The rich and precise data provided by the instrument can serve to develop new products or to control the quality and consistency of yogurt production.
Easy-to-use tool for yogurt gelation and fermentation monitoring
Materials and Methods
A precise methodology was implemented to capture a comprehensive view of fermentation dynamics, comparing real-time monitoring of viscoelasticity with traditional monitoring of pH, and closely analyzing the impact of bacterial cultures on the formation of yogurt gels during the production process.
Inoculation process and sample collection
The collected milk was inoculated with a specific blend of bacterial cultures essential to the fermentation process. The bacteria used for the cow’s milk used in this study were Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, while those employed for the coconut milk included Bifidobacterium species, Lactobacillus acidophilus, Lactobacillus delbrueckii subsp. Bulgaricus, Lactobacillus paracasei, and Streptococcus thermophilus.
The inoculation took place immediately after pasteurization (10 minutes at 90°C). Subsequently, the milk was cooled to 4°C before bacterial seeding. A 1-liter sample of pasteurized and inoculated milk was collected during the production process in the production plant, just before the packaging of the product.
Sampling for testing
To monitor the fermentation process on the CoaguSens™ Flex, 7 mL of milk were pipetted in the instrument’s sample holder for analysis.
Temperature profiles
For the cow’s milk, the temperature of the instrument’s thermal chamber was first set at 42.5°C during 280 minutes (approximately 4.5 hours). The temperature was then decreased to 4°C during 220 minutes (approximately 3.5 hours) to simulate the cooling phase of the product.
For the coconut milk, the temperature of the instrument’s thermal chamber was first set at 42.5°C during 300 minutes (approximately 5 hours). The temperature was then decreased to 4°C during 100 minutes (approximately 1.5 hours) to simulate the cooling phase of the product.
Control samples in the lab incubator
In parallel with the sample placed in the CoaguSens™ Flex, additional samples were placed in a lab incubator under identical conditions. The samples in this parallel setup served as control samples, allowing to evaluate the effectiveness of real-time monitoring of the gel firmness with the CoaguSens™ Flex compared to traditional yogurt-making conditions. The control samples were specifically used to monitor pH and temperature changes during the fermentation process. The control samples went through the same temperature history as the samples tested on the CoaguSens™ Flex.
View of the 7 mL sample holder of the CoaguSens™ Flex containing yogurt sample after fermentation.
Analysis of pH
Measurement of pH was conducted at fixed time intervals during the fermentation kinetics and cooling phase. This involved taking measurements on the control samples. pH values were systematically recorded to capture the evolution of acidity over time.
Phase analysis of yogurt fermentation and texturing: Elasticity and acidity dynamics
Results and discussion
Figure 1: Time kinetics of the shear elastic modulus (firmness) and pH of the cow milk during the fermentation and cooling phases.
Figure 2: Time kinetics of tan(δ) (G”/G’) and pH of the cow milk during the fermentation and cooling phases.
The fermentation process of cow milk reveals a distinct curve characterized by various phases:
- Initiation of Gelation (pH 4.9). Tan(δ) is maximum.
- A noticeable rise in the curve of G’ marks the onset of gelation, occurring at a pH of 5.15. Gelling increases at a rate of 0.1Pa/s, up to a pH of 4.6 (target pH). Tan(δ) decreases as the elastic nature of the gel increases.
- Cooling Phase: The sample was programmed to cool to 4°C, and the gel firmness exhibited a noticeable increase during this phase. Tan(δ) remains relatively stable at 0.30 during the cooling phase.
The plateau was observed in the curve one hour after the initiation of the cooling phase, indicating a stabilization of the gel firmness at a value of 7,700 Pa. Tan(δ) remains stable at 0.30.
Figure 3: Time kinetics of the shear elastic modulus (firmness) and pH of the plant-based milk during the fermentation and cooling phases.
Figure 4: Time kinetics of tan(δ) (G”/G’) and pH of the plant-based milk during the fermentation and cooling phases.
The fermentation process of the coconut milk exhibited its own unique characteristics:
- Initiation of Gelation : the pH is at 5.50 and Tan(δ) is maximum.
- Gelling increases at a rate of 0.08Pa/s. The pH decreases down to 4.6 (target pH) during 2h.
- After 5 hours the pH stabilizes at a value of 4.5. The firmness reached a significant level of 1,500 Pa but was not yet fully stabilized. Tan(δ) decreased as the elasticity of the gel increased and stabilized at a value of 0.25.
- Cooling Phase: the sample was programmed to cool to 4°C and the gel firmness increased from 1,500 Pa to 3,500 Pa in 1 hour before reaching a plateau. The cooling phase had an effect on Tan(δ) that rapidly stabilized at a value of 0.30.
CoaguSens™ Flex: Precision texture analysis for milk-based and fermented dairy products
This study illustrates the capability of the CoaguSens™ Flex in measuring the gelation process of animal or vegan milk during acid fermentation. Its non-destructive nature makes it suitable for high throughput analysis in labs. Indeed, the sample holder of the CoaguSens™ Flex is detachable and can be stored in an incubator between tests making the instrument available to test additional samples.
In production environment, the CoaguSens™ Flex can be used to accurately measure the viscoelastic properties of yogurt gels in order to:
- Control the quality of production using an easy-to-use and high throughput testing technology;
- Modify production parameters to achieve batch-to-batch consistency in terms of yogurt texture;
- Adjust recipe formulations to ingredient substitutions caused by the fluctuating market prices of ingredients;
- Optimize production time and cycles by monitoring viscoelasticity in addition to pH during the fermentation process and the texturization phase (cooling phase).
In R&D and product development, the CoaguSens™ Flex may be used to:
- Precisely formulate new products;
- Evaluate and optimize the long-term texture stability to maintain the gel quality throughout its shelf life.
CoaguSens™ Flex, with its ease of use and cost-effectiveness, is especially suitable for quality control and analysis laboratories within yogurt manufacturing facilities. Its non-destructive measurement approach, coupled with the use of detachable sample holders, facilitates efficient, high-throughput assessments of slowly forming gels without the need for numerous devices or immobilizing the instrument for extended periods.
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