Changes in the Amino Acid Composition of Bee-Collected Pollen During 15 Months of Storage in Fresh-Frozen and Dried Forms

Abstract

Bee pollen (BP) is a nutritionally valuable natural product whose biological activity is strongly influenced by its amino acid profile. This study evaluated qualitative and quantitative changes in free amino acids in Lithuanian BP subjected to freezing (−20 °C and −80 °C) or low-temperature drying and stored for 15 months. Seventeen amino acids, including all nine essential amino acids, were identified using UHPLC-ESI-MS/MS, accounting for 47–48% of the total amino acid content (TAAC). Arginine, proline, and aspartic acid were the predominant free amino acids. Both frozen and dried samples showed a statistically significant decrease in TAAC after nine months of storage (p < 0.05), resulting in a 1.5–1.7-fold reduction after prolonged storage. Frozen storage at −20 °C and −80 °C better preserved free amino acids, particularly alanine, glutamic acid, and proline, whereas dried BP stored at room temperature exhibited accelerated degradation. Sulfur-containing amino acids, especially cysteine and methionine, were highly unstable under all storage conditions. These results provide practical guidance for selecting storage strategies that minimize amino acid losses and help maintain the nutritional quality of bee pollen during long-term storage.