A Comparative Review of Phytochemical Composition, Bioactivity, and Health Implications of Single- and Multiple-Clove Garlic

Single-clove garlic (SCG) and multiple-clove garlic (MCG) exhibit notable differences in their phytochemical composition, bioactivity, and therapeutic potential. The major organosulfur compounds originate and undergo their enzymatic and chemical formation pathways from the precursor alliin. SCG displays a distinct structural morphology and consistently higher concentrations of key bioactive compounds, including allicin and phenolic constituents, contributing to enhanced antioxidant capacity. Consequently, SCG extracts demonstrate superior acute antibacterial effectiveness against Escherichia coli and Staphylococcus aureus, along with stronger antibiofilm activity. In contrast, MCG shows more sustained effects in lipid modulation and broader antifungal spectra. Preharvesting factors (genotype, growing conditions, fertilization, and harvesting stage) along with post-harvesting conditions (e.g., processing, storage, and curing) significantly influence the chemical components of garlic, particularly its organosulfur compounds and phenolic constituents. The stability and bioavailability of critical compounds, for instance, allicin and S-allyl cysteine (SAC), are significantly affected by processing methods (e.g., crushing, heating, and aging). The principal therapeutic mechanisms of garlic include Nuclear Factor kappa-light-chain enhancer of activated B cells (NF-κB) pathway inhibition (anti-inflammatory), thiol–disulfide bond disruption (antimicrobial), and Nuclear factor erythroid 2-related factor 2 (Nrf2) activation leading to apoptosis induction in cancer cells (anticancer). Garlic modulates cardiovascular risk factors through 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibition, hydrogen sulfide-mediated vasodilation, and antiplatelet activity. However, major challenges remain due to experimental variability, inconsistencies in garlic sourcing and preparation, and the chemical instability of allicin. Future research should emphasize the standardization of processing protocols, development of stabilization strategies (e.g., nanoencapsulation, high-pressure processing), and rigorous clinical validation of SCG-specific benefits. Overall, SCG exhibits enhanced acute bioactivity, while MCG confers more sustained therapeutic effects, underscoring the importance of morphology-specific applications in maximizing garlic’s pharmacological potential.