Low-field nuclear magnetic resonance for online determination of water content during sausage fermentation

Abstract

Traditional fermented sausages containing 0%, 25%, 50%, and 75% fat are produced by natural fermentation. Water in sausages was investigated by low-field nuclear magnetic resonance (LF-NMR). T1-weighted phantom magnetic resonance images visually showed spatial inhomogeneity in water content. Center of intensity was brighter than its edges, indicating that water distribution in sausages was inhomogeneous because of vaporization. Low-fat samples showed remarkable spatial inhomogeneity in water content. T2 populations, which were referred to as free water (T23) and immobilized water (T22), shifted toward short relaxation times and gradually merged into one population during fermentation. Relative area percentage of immobilized water (M22) increased, whereas that of free water (M23) decreased. Approximately 95% of water was present as free water and immobilized water. Water content of sausages showed the strongest linear correlation (R2 > 0.92) with T2 area. The linear model showed good accuracy and precision but overestimated water content. Reliability of model decreased as fat content increased because of inhomogeneity in water content of low-fat samples. Therefore, water content can be measured based on sample weight, fat content, and T2 area in a nondestructive manner and regardless of sample size.