About this Research Topic
Food stability determination that is based on a theoretical basis is a challenge to food scientists, technologists and engineers, and is an important component to achieving food security. Over the years, water activity and glass transition concepts are the two most successful theoretical foundations which have been developed in order to determine the stability of food.
The water activity concept is based on the binding nature of water in foods (i.e. the state of water in foods) and hypothesizes that bound water is unavailable for microorganisms and chemical and biochemical reactions, and thus provides stability to food by avoiding or reducing the deteriorative changes. This concept helped to develop generalized rules or limits for the stability of foods. When looking at the rules or limits for the stability of food, we can look – as an example- to the critical limits for bacterial growth (pathogenic bacteria cannot grow below a water activity of 0.85, whereas yeast and molds are more tolerant of reduced water activity of 0.80; spoilage bacteria are unable to grow below water activity 0.91 and no growth of bacteria is observed below water activity 0.60). This has great importance when developing microbial stable products in terms of pathogens and spoilage bacteria, as well as when beneficial bacteria are used in developing foods, such as fermented foods.
Considering that there are limitations to the water activity concept, the glass transition concept can be used as an alternative and is based on the matrix or molecular mobility as determined by the glass-rubber transition. The glass transition concept is further progressed by the developing macro-region and micro-region state diagrams which show the phases (or states) of food as a function of solids or water content and temperature. The main advantage of drawing a map is for a better understanding of the complex changes that occur when the water content and temperature of foods are varied.
These two aforementioned fundamental concepts are widely used to determine the stability of foods during processing and storage. Both concepts have their advantages and limitations when applied during the different microbial, physical and chemical changes in foods. In the literature, it has been emphasized that a combination of the two concepts- water activity and glass transition - could be a powerful tool in predicting food stability. However, the limitations of these two concepts would not invalidate the above concepts completely, but rather make it a challenge to apply universally.
Recently, other molecular mobility as measured by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR) analysis, and other spectroscopies, are being proposed as alternatives in order to explain the food stability in terms of molecular excitements and reactivity. In reality, the stability of foods requires multiple different hurdles to be applied in order to achieve. It is necessary to advance the theoretical or fundamental methods by linking different theories in combination so that different multi-hurdles can be joined together. For example, the water activity concept is based on the binding nature of water, whereas the glass transition concept is based on the mobility of water, and pH is based on the concentration of hydrogen ion.
This Research Topic aims to identify some of the theoretical links between the state of water, molecular mobility, and hydrogen ion concentration in food. It is a real challenge for food scientists and engineers to address this issue. This Research Topic aims to publish reviews on the focused theoretical aspects of food stability, and also original research papers on:
• The measurement methods of water binding and molecular mobility by moisture sorption isotherm, Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR) analysis;
• The applications of water binding, matrix or molecular mobility as measured by different spectroscopic methods;
• Innovative concepts to apply combined water binding, molecular mobility, and hydrogen ion concentration (pH) in determining food stability.
Topic Editor Professor Muthupandian Ashokkumar has the following patents registered in his name "Processing of Dairy Ingredients" (2007906986), “Processing of dairy ingredients by ultrasonication” (20090702), and " A method of generating radicals by ultrasound" (PCT/AU2018/050887). The other Topic Editors declare no competing interests with regard to the Research Topic subject.
Keywords: Food Stability, Food Security, water activity concept, glass transition concept, molecular mobility, water binding, sustainability
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