The effect of mechanical deformation on the movement of water in foods.
This study has shown the importance of relating NMR spectroscopic information on the water in model food structures to the mechanical properties of those structures. Analysis of the NMR relaxation data can be used to examine the distribution of water domain sizes, and this has been related to the mechanical properties of the samples. A novel NMR probe-head has been designed, which allows both the NMR and the mechanical data to be simultaneously measured during compression of the sample. This probe-head allows compressive stress/strain data to be obtained directly from the NMR sample, allowing changes in the distribution of the water to be directly correlated to changes in mechanical properties.
Applications of NMR to Food and Model Systems in Process Engineering
The overall objective of the present work is to elucidate the possibilities to monitor and quantify transport phenomena and to characterise the structure of heterogeneous disperse media, which are non-matched and thus inaccessible to many optical techniques by means of Nuclear Magnetic Resonance (NMR). NMR offers the possibility to perform measurements non-invasively and non-destructively in order to study the structure or to trace structural changes or transport processes inside the sample without preparations or unpredictable modifications caused by the measurement. Thus it is not only possible to detect and quantify the static structure, but also to monitor dynamic structural changes and processes during production, storage, transportation and even consumption of food-products with temporal, spatial and chemical resolution (multi-dimensional). NMR enables, therefore, repetitive testing of dynamic processes including enzymic and non-enzymic chemical reactions. Samples may be studied several times under identical or changed conditions, which is a great advantage compared to other imaging preparative methods like optical or electron microscopy-methods. The following topics have proved to be promising applications of NMR in food technology and process engineering: (a) structure and structural changes of disperse media, (b) convective transport processes, (c) diffusive transport processes and (d) spectroscopic material characterisation.
SOME RHEOLOGICAL PROPERTIES OF A CHEESE‐LIKE PRODUCT PREPARED BY DIRECT ACIDIFICATION
A processed, nonfermented cheese-like product was prepared by direct acidification of milk and heat coagulation of the curd. Modification of the textural properties was done by the incorporation of carrageenan. Textural evaluation was done by uniaxial compression. The parameters analyzed were true stress-true (Hencky's) strain relationships obtained at two deformation histories, residual stresses after relaxation and true stresses and strains at failure. Results showed that with respect to all these parameters the experimental nonfermented product resembled commercial processed American cheese though at generally smaller strength levels. Introduction of carrageenan contributed solid properties to the experimental processed cheese. At 1% level of carrageenan the product had mechanical properties similar to those of commercial cheese.