Review on the Impact of Gamma Irradiation on the Phytochemical and Proximate Composition of Different Food Products: Mechanisms, Dose–Response Dynamics, and Nutritional Implications

Gamma irradiation is a widely accepted non-thermal preservation technique that reduces post-harvest losses, delays spoilage, prevents sprouting, and enhances microbial safety. Its impact on nutritional and phytochemical integrity, however, is still subject to scientific assessment, despite its well-established microbiological efficacy. This review critically summarises research on the effects of gamma irradiation on phytochemicals (phenolics, flavonoids, carotenoids, vitamins, and antioxidant capacity) and proximate composition (moisture, protein, lipid, ash, fibre, and carbohydrate) in cereals, legumes, fruits, vegetables, spices, and oilseeds from 2015 to 2025. It reveals that proximate macronutrients are generally stable at doses below 10 kGy, but at higher exposures, lipid oxidation and mild protein denaturation may occur. Phytochemicals exhibit dose-dependent dual behaviour: moderate doses (1–5 kGy) frequently increase extractable phenolics and antioxidant activity due to cell wall disruption, while higher doses (>10 kGy) may degrade vitamin C, carotenoids, and some flavonoids by radiolytic oxidation. The food matrix, moisture content, oxygen availability, packaging environment, and storage conditions all have a significant impact on the outcome. Gamma irradiation is generally safe for nutrition at recommended dosages; however, product-specific optimisation is required to protect sensitive bioactive materials.