Isothermal Calorimetry applied to Food Science

Overview

Calorimetry is a useful tool for any chemical, biological or physical reaction that releases or absorbs heat. Thermal power is measured continuously, thereby providing information about the rate of a reaction and giving an understanding that most traditional physical testing cannot provide. Many times, calorimetry proves to be an invaluable complementary tool to other test methods, providing the missing information on how, and how quickly, a given process evolves over time.

Calmetrix offers isothermal conduction calorimeters for Food Science, where the temperature is kept constant around the sample for the duration of the experiment. One significant advantage of Calmetrix instruments is the wide choice of sample sizes, from less than 1 ml and up to 450 ml, which is much larger than most other calorimeters in the market. This opens the possibility to study the properties and response to different processes of a wide variety of food items, such as whole pieces of fruits and vegetables, meat, fish, dairy products, chocolate, as well as fruit juices, nuts and grains, etc. 

There are many applications of isothermal calorimetry in Food Science. The most common can be summarized in three categories:

Spoilage and shelf life (microbial activity)

• Compare the efficiency of different conserving methods (thermal, chemical, etc.)
• Determine the optimum dosage of a preservative
• Detect degradation in fresh food when not visible through other observations
• Quality control of packaged foods (microbial activity check)
• Sensitivity of preserved food to contaminants

Metabolic response

• Detect deterioration of quality due to wound respiration
• Study aging of sliced fruit and vegetables
• Response to blanching or parboiling (determine the temperature at which cells are killed)

Fermentation studies

• Assess the effectiveness of different cultures (measure doubling time)
• Assess the influence of additives (e.g. enzymes) on the effectiveness of fermentation
• Understand fermentation reaction kinetics, in conjunction e.g. with pH measurements

Three samples of a fresh carrot juice were tested at 25 °C in this example. The blue curve corresponds to a sample with a high dose of contaminant, and shows an increase in thermal power after about 7 hours, indicating an increase in microbial activity and beginning of spoilage. The red curve shows the same fresh juice and equal quantity of contaminant, but with a preservative (Formulation A). We observe a delay of approximately 4 hours before thermal power increases, showing some moderate efficiency of this formulation on extending shelf life. The green curve shows again the same fresh juice and contaminant, but with a different preservative (Formulation B). No thermal activity, hence no microbial growth appears for a period of time beyond 15 hours, showing that this formulation is much more effective at extending shelf life.

Conclusion: isothermal calorimetry clearly shows at what time microbiological spoilage starts to occur, and with how much intensity. Sample preparation and data interpretation only take minutes, making it easy, for example,  to compare the efficiency of different preservatives, formulations or dosages.