Lipid maturity trend in crops as characterized by alfa linolenic acid decay and by NIRS study

The present work investigates the trend and characteristics of lipids, and considers the feasibility of Near Infrared spectroscopic (NIRS) prediction, in twelve crops (borage, chia, false flax, flax, galega, hemp, niger, perilla, quinoa, ravizzone, safflower and sunflower). A total of 143 samples, harvested at different growth stages, were collected and processed as freeze-dried or oven-dried specimens. As plants grow, a proportional increase in linoleic, stearic, oleic, palmitic, arachidic and palmitoleic acid and a relative decrease in the total lipids and in other four fatty acids (FAs) were observed, but only the α-linolenic acid (ALA) decreased significantly. The ALA mobilization over a 20 day term was almost -15% of its mean value. In order to express the dynamics of the lipid trend, two maturity indices were calculated: a quantitative indices, i.e. total lipid maturity indices (TLMI) and a qualitative indices, i.e. fatty acid maturity indices (FAMI). Both indices were calculated as the sum of the standardized deviates of the total lipid content and of the twelve FA percentage contents, respectively, which were weighted with +1 or –1 on the basis of whether the regression coefficient increased or decreased over time, respectively. As a result, the twelve species were more differentiated in FAMI (6 levels, with borage being the most mature and sunflower the least mature) than in TLMI (3 levels, with false flax being the most mature and ravizzone, hemp and quinoa being the least mature). Application of the maturity indices formulae to the results of published experiments has shown that it can be a meaningful and simple way of interpreting the experimental effects concerning the anabolism of lipids in the pre-reproductive phase of the crops. Overall, the prediction of the lipid composition of the crops, by means of NIRS, has proved to be equally efficient for the two preparation methods (ratio performance deviation, RPD =2.11 for the freeze-dried samples and 2.03 for the oven dried ones, respectively). However, although FAMI was not well predicted in the oven-dried samples (R-square in cross-validation 1-VR =0.51), it was predicted slightly better in the freeze-dried samples (0.68). The species (0.90 and 0.92), the days after seeding (1-VR =0.78 and 0.73) and the ALA content (0.77 and 0.76) were predicted well in both kinds of samples. It has been concluded that the lipid trend maturity may be summarized by means of simple indices in any kind of experiment that attempts to modify the ontogeny of crops. The driver FA is ALA, whose prediction may be obtained through a rapid NIRS examination of conventional crop samples.