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DSC melting profile of cold-pressed hemp seed oil as an authenticity fingerprint influenced by scanning rate
Among the variety of edible cold-pressed oils on the market, hemp seed oil is becoming increasingly popular among scientists and consumers due to its plethora of nutritional compounds. In this study, the goal was to examine the thermal characteristics of cold-pressed hemp seed oil pressed from seeds of the Henola cultivar procured by five different suppliers in two different seasons. This aim of this research was to establish how various scanning rates can affect the unique thermal profile of cold-pressed hemp seed oil in terms of an authenticity assessment. The melting transition was manifested by curves with four peaks for all hemp seed oils; however, they differed for each scanning rate in terms of the shape and peak intensity. Comparing the curves obtained at heating rates of 1 and 2 °C/min, noticeable differences were observed in the melting transition parameters between hemp seed oils, showing that small differences in fatty acid composition can cause changes in DSC profiles. In contrast, at a scanning rate 5 °C/min, the melting curves were similar for all hemp seed oils. It was also observed that for all the scanning rates, there was a strong negative correlation between the total content of polyunsaturated fatty acids (ƩPUFAs) and the peak temperature of the three peaks (Tm2, Tm3, and Tm4). The most abundant fatty acids were PUFAs, i.e., linoleic acid (C18:2), with contents ranging from 47 to 55%; and α-linolenic acid (C 18:3 n–3), with contents ranging from 17 to 25%. The application of linear discriminant analysis (LDA) enabled a discriminant model to be built based on the DSC data obtained for differentiation of oils pressed from fresh and stored seeds.
DSC phase transition profiles analyzed by control charts to determine markers for the authenticity and deterioration of flaxseed oil during storage
An approach of implementing X-bar and R control charts as a statistical control tool to monitor the changes in the melting profile of fresh and stored flaxseed oils by differential scanning calorimetry (DSC) was used. Phase transition melting profiles were collected after 0, 2, 4, and 6 months of storing flaxseed oils, originating from five different cultivars. Four peaks at around −36, −30, −25, and −12 °C were identified using the deconvolution analysis procedure, which enabled the data to be collected at peak temperature (T), peak height (h), the peak area (A), and the percentages of the area (P A), as well as the ratio calculated from these parameters. Control charts obtained for the second peak of the melting profile showed a significant decrease of peak height (h2) from 0.50 to 0.39 W/g and the percentage of the area (P A2) from 50 to 38%, within the storage time (p ≤ 0.05); thus, they were considered to be indicators of oil deterioration. Strong negative correlations of the unstable parameters of DSC with chemical indicators of the oils’ oxidative stability (PV, p-AV, TOTOX) were found. For DSC parameters, related to the first peak (h1, A1) and the third peak (h3, A3), changes were statistically not significant within storage (p > 0.05); thus, they can be used as markers of flaxseed oil authenticity. The study demonstrated that X-bar and R control charts could effectively monitor changes in the specific peaks and calculated ratios from the DSC melting profile of fresh and stored flaxseed oils, serving as reliable indicators of oil deterioration.
DSC Phase Transition Profiles Analysed by Control Charts to Determine Markers for the Authenticity and Deterioration of Flaxseed Oil during Storage
An approach of implementing X-bar and R control charts as a statistical control tool to monitor changes in the melting profile of fresh and stored flaxseed oils by differential scanning calorimetry (DSC) was used. Phase transition melting profiles were collected after 0, 2, 4, 6 months of storing flaxseed oils, originated from five different cultivars. Four peaks at around -36, -30, -25, -12 °C were identified using the deconvolution analysis procedure, which enabled data to be collected on peak temperature (T), peak height (h) and the peak area (A), as well as the ratio calculated from these parameters. Control charts of DSC parameters, linked to the second peak (h2, A2) and calculated ratios of those parameters showed an increasing or decreasing trend within the storage time, thus were considered to be indicators of oil deterioration. Since DSC parameters related to the first peak (h1, A1) and third peak (h3, A3) remained unchanged within storage, they were established as the markers of flaxseed oil authenticity.