## 2 Literature Review
Various governance model: Public chains (Ethereum) have open, community-driven governance, whereas enterprise or consortia platforms (Hyperledger) use permissioned, consortium-based control. This dichotomy affects data privacy, energy use, and regulatory alignment. Clear rules for roles and consensus are still under development. Architectural models and case studies: Recent studies propose layered frameworks to organise blockchain systems. For example, [PERSON] et al. introduced a four-layer architecture for food chains: business (supply chain actors), traceability (data services), blockchain (ledger and smart contracts), and application (user interfaces) layers. This model ensures that each layer supports traceable metrics and stakeholder needs. Other works use three-tier or IoT/blockchain layers. For cold-chain specifically, integrated IoT-blockchain prototypes (with RFID temperature tagging) allow real-time monitoring; tagged records are hashed to the ledger for auditability. Layered designs help modularise security, data storage (often using on-chain/off-chain hybrids like IPFS), and interface logic. Future directions and Digital Product Passports (DPPs): Despite pilot successes, blockchain in agriculture needs further study. Key research gaps include scalability, data privacy (e.g., zero-knowledge proofs) and governance frameworks. As one review observes, many pilot projects lack a \"comprehensive roadmap\" for broad adoption. Emerging topics include the integration of blockchain with AI for decision support and strengthening data governance across the Internet of Everything. Aligning with sustainability, Digital Product Passports (DPPs) are an EU initiative to digitally record product lifecycle data (raw materials, certifications, recycling). Blockchain underpins DPPs by ensuring immutable records and decoupling from centralised ERPs: DPPs remedy \"centralized vulnerabilities, data silos, and limited interoperability\" of traditional systems. Future work should explore blockchain-driven DPPs for agri-food, mapping traceability to environmental/social metrics. Table 1, shows implementations done, with associated technology, region and Table 2 a scientific comparative analysis of major selected papers. \begin{table}
\begin{tabular}{c c c c} \hline
**Platform** & **Technology** & **Use Case/Region** & **Notes** \\ \hline IBM Food Trust & Hyperledger Fabric & Retail produce (Walmart, & Consortium network for rapid \\  & & Albertsons, Carrefour); global pilot & farm-to-shelf traceability. \\ \hline TE-FOOD & Private Ethereum + QR & Livestock and produce in Vietnam & QR-coded IDs at each stage (pigs, eggs, poultry). \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of key blockchain platforms and their features. \begin{table}
\begin{tabular}{c c c c} \hline
**Platform** & **Technology** & **Use Case/Region** & **Notes** \\ \hline AgUnity & Blockchain/IoT app & Smallholder farmers (Africa, Asia) & Mobile app for transactions, farm data logging. \\ \hline AntChain (Alibaba) & Hyperledger & Anticounterfeit in China & Tracks origins (e.g., dairy, tea) using blockchain+IoT. \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._