Seasonal and Environmental Influences on Free Sugar and Amino Acid Profiles of Lycium barbarum Berries Cultivated in Southern Tuscany

Lycium barbarum L. (Goji) berries are highly valued for their nutritional and nutraceutical properties, largely due to their sugar and amino acid content. This study analyzed organically cultivated berries from southern Tuscany (Italy), sampled across four ripening stages (July–November). Free sugars were measured over 3 years (2018–2020), and amino acids over two (2019–2020). Fully ripe berries (S4) exhibited high levels of glucose (80.2 ± 19.3 mg/g FW), fructose (75.5 ± 18.1 mg/g FW), and pectins (46.3 ± 16.1 mg/g FW), while sucrose remained low. Seasonal and interannual trends revealed progressive increases in glucose, fructose, pectins, and ethanol (up to 15.9 mg/g FW), positively correlated with precipitation and negatively with temperature. Total free amino acids averaged 3.21 mg/g FW, with non-essential amino acids representing 55.4%. Proline was most abundant (1.05 mg/g FW), and its accumulation increased with rainfall and decreased with higher temperatures. Other compounds influenced by climatic stress included β-aminobutyric acid (BABA) and ornithine. These findings highlight the strong impact of environmental variables on berry metabolism, particularly in sugar and amino acid biosynthesis. The optimal harvest window lies between version and full ripeness, when metabolic profiles peak. This work underscores the importance of climate-driven strategies to optimize goji berry quality through informed cultivation practices.