الملخص الإنجليزي
The state diagram offreeze-dried broccoli is useful for determining the stability during storage and selecting the optimum processing conditions.
The concept of water mobility would be more interesting to provide a complete picture of food stability and is a food stability indicator. Low Frequency Nuclear Magnetic Resonance (LF-NMR) was used to identify different pools of proton and their mobility in freeze-dried broccoli (moisture: 0.01 to 0.25 g/g sample and temperature: -80 to 170°C) containing un-freezable water. Three pools of protons were determined from transversal T2 (i.e. spin-spin) relaxation times. These were T2b (i.e. tightly pools of protons associated with macromolecules), T21 (i.e. protons in the strongly bound water with the solids) and T22 (i.e. protons in the weakly bound or capillary water). Two critical temperatures and one peak temperature from the plot of T2b, T21 and T22versus temperature were identified and related to the moisture content. The critical temperatures determined from T26 and Tzı increased with the increase of moisture up to BET-monolayer followed by an exponential decrease.
However, the first critical temperature from T22 increased and reached to a plateau, while the second and third critical temperatures increased linearly with the increase of moisture. The critical temperature from Tzb were determined from the intersection of the first and second segments and compared with the onset glass as measured by Differential Scanning Calorimetry (DSC). At moisture 0.01 g/g sample, this critical temperature showed lower than the thermal glass transition temperature. The opposite trend was observed at or above moisture 0.05 g/g sample and the difference between critical temperature and glass transition temperature increased with the increase of moisture content. It was also observed that peak temperatures were closed to the solids-melting temperature as measured by differential scanning calorimetry,
The stability of vitamin C in fresh broccoli stored at chiller, room, cooking, and roasting or baking temperature(5-120°C) was investigated. The vitamin C decay was modeled by first order reaction kinetics and the reaction rate constants were observed as 9,03x10-8 and 5.65x10-3 sl within the temperature 5-120°C, respectively. The activation energy was estimated as 74.2 kJ/mole.
In conclusion, this study was able to assess the anti-diabetic effects of broccoli extract and its capacity to reduce oxidative damage; developed the macro-micro regions in the state diagram and proton mobility of freeze-dried broccoli. The macro micro region and proton mobility could be used to determine the stability or reactivity of functional components as a function of moisture and temperature. In addition, vitamin C stability in the rubbery state of broccoli was experimentally measured and modelled. However, chemical reactions in different micro-regions need to be measured experimentally to validate the concept in the future work.
