Impact of Heat Stress at Flowering Stages on Nutraceutical Traits and Allergen Expression in Tomato Fruits

Tomato (Solanum lycopersicum L.) is a key source of bioactive compounds and essential minerals, but it also contains clinically relevant allergens. Despite growing concern about the effects of climate change on crop quality, the impact of heat stress during specific reproductive stages on fruit allergen accumulation remains poorly understood. This study aimed to investigate how the timing of heat stress affects tomato fruit quality, antioxidant traits, and the expression of major pan-allergens. Plants of the cultivar Micro-Tom were exposed to heat stress (40 °C for 8 h) at three flowering stages: pre-anthesis, anthesis, and post-anthesis. Ripe fruits were evaluated for morphological parameters, mineral composition, nutraceutical properties, antioxidant responses, and the expression of profilin and cyclophilin. Heat stress applied at post-anthesis significantly reduced fruit weight and diameter, while earlier treatments had limited morphological effects. Mineral composition was largely unchanged across treatments. In contrast, total phenolic content increased progressively with later stress application, whereas flavonoid content and antioxidant capacity (FRAP) remained relatively stable. Antioxidant enzyme activity showed only minor stage-dependent variation, suggesting a controlled oxidative response. Notably, allergen-related proteins exhibited distinct patterns: profilin accumulation increased progressively under heat stress, while cyclophilin showed a transient peak at anthesis. These findings demonstrate that the timing of reproductive heat stress differentially affects tomato fruit quality and allergen accumulation. This study provides novel insights into the stage-specific modulation of food allergens under heat stress, contributing to a better understanding of crop nutritional and allergenic properties in the context of climate change.