Ice structuring proteins (ISPs) naturally exist in many foods consumed as part of the human diet including plants or fish. ISPs from winter wheat grass have gained interest in the pharmaceutical and food industries as a non-toxic, natural and cost-effective product, which is easy to prepare as a crude extract. However, they have not been purified reproducibly and studied in detail to elucidate their structures, mechanism of actions and difference(s). ISPs from the apoplast region of cold acclimated winter wheat leaves were extracted through vacuum infiltration and purified using heat and ethanol precipitations, size exclusion and anionic exchange fast protein liquid chromatography techniques. The ISPs showed both significant inhibition of ice growth and thermal hysteresis activities. The non-acclimated apoplastic extracts from winter wheat leaves contained similar proteins without any abovementioned activities. The ISPs contained disulfide bridges, similar to thaumatin-like proteins (TLPs) and partially similar to ISPs from winter rye leaves and carrot. ISPs remained active after thermal treatment (i.e., pasteurization conditions) and over a wide range of pH (3-12). There are very few quantitative assays to measure the activity of antifreeze proteins (AFPs, or Ice Structuring Proteins, ISPs), which often suffer from various inaccuracies and inconsistencies. Some methods rely only on unassisted visual assessment. When microscopy is used to measure ice crystal size, it is critical that standardized procedures be adopted, especially when image analysis software is used to quantify sizes. Differential Scanning Calorimetry (DSC) has been used to measure the thermal hysteresis activity (TH) of AFPs. In this study, DSC was used isothermally to measure enthalpic changes associated with structural rearrangements as a function of time. Differences in slopes of thermograms between winter wheat ISP or AFP type I containing samples, and those without ISP or AFP type I were demonstrated. ISP or AFP type I containing samples had much higher slopes compared to those without ISP or AFP type I. Samples with higher concentration of ISP or AFP type I showed higher slope values. The proteinaceous activity of ISPs or AFP type I was confirmed by demonstrating changes in samples with and without proteases. A proposed mechanism of this method is discussed.