Food Engineering and Physical Properties Study of Caking in Powdered Foods Using Nuclear Magnetic Resonance Spectroscopy

ABSTRACT: Twenty-three powdered foods and ingredients were subjected to 2 treatments: temperature scan from – 20 to 110 °C within 2 hours, and storage at 37 °C and 55 °C for 60 d. During temperature scans, the spin-spin relax-ation time T2 values of individual samples were determined using a nuclear magnetic resonance (NMR) technique, resulting in a temperature-T2 curve for each sample. Four typical temperature-T2 curve patterns were identified and were found to be closely related to the physical changes in the samples, including agglomeration, water vaporiza-tion, and caking observed during temperature scans. Based on the temperature-T2 curve patterns, the samples were classified into 4 groups each having distinguished caking behavior. In the storage tests, the samples were removed from the incubators every half an hour during first 2 d of storage period and every day afterwards. The storage test also suggests a strong relationship between molecular mobility and caking. Monitoring changes in T 2 as a function of temperature provides information useful for predicting whether and when caking would occur. Key Words: caking, molecular mobility, NMR, powder, relaxation, T2 cizers (usually water) to mobilize the powder particles, and the contact time between particles becomes very long. In this case, caking may not happen within the shelf life time. On the other hand, if the system is stored at a temperature above its Tg (or in the rubbery state), the dramatic decrease in viscosity and in-crease in polymer segmental mobility greatly reduces the con-tact time and promotes sticking and caking. The decrease in viscosity will also favor diffusion of solvent and solutes, thus, facilitating chemical and microbiological reactions. Tg has therefore become a very important and practical variable in the control of caking and chemical and microbiological reactivity. The rate of caking (Rcaking) is believed to be mainly governe