Effect of Various Fertilizers on Stable Isotope Ratios and Relative Amino Acid Content in Apple Seeds

Abstract

A modern, healthy diet relies on ever greater consumption of fruits, vegetables and other plant-based foods, with apples being some of the most affordable and readily available fruits that in most cases can be produced locally. With the higher interest of consumers in certified organic food products, methods for testing the food authenticity are becoming of key interest. For a food product to be labelled “organic”, it must be grown in certain conditions, without the use of pesticides, herbicides and synthetic fertilizers to elevate the yield. In this study the effect of different fertilizers on the nitrogen isotope ratios and amino acid composition in apples has been evaluated. Different parts of an apple were analyzed, and it was determined that only seeds contained enough nitrogen to give reliable results on δ15NAIR values and total nitrogen content. The results of apple seed analysis with stable isotope ratio mass spectrometry (SIRMS) showed that in three out of four apple varieties, the heavier nitrogen isotope (15N) content was higher in nitrogen-fertilized apples than in non-fertilized ones. Our research did not find any statistically significant correlation between the nitrogen and carbon content in apple seeds and the fertilization regime. The relative amino acid content in apple seeds was determined by gas chromatography and it was found that there is a moderate correlation between the stable nitrogen isotope ratios in apple seeds and the relative content of alanine and tryptophan.