1. Distributed Ledger Technologies - Brief Description and Definition

Distributed Ledger Technology (DLT) is a term used to represent a digital network of distributed models, consisting of blockchain-based ledgers, and collaborating on shared tasks and activities. Blockchain technology is a data structure, composed of “blocks”, that are cryptographically linked together in a chained sequence using cryptographic hashes, secured against manipulations ^[1][2]. Due to wider functionality, DLT is a commonly used term for a computer-based system consisting of distributed ledger-based data structures, which can provide increased levels of trust, service availability, resiliency, and security of digital systems, as well as distributed storage, computation, and control ^[2].

Integration of blockchain technology in Internet of Things (IoT) systems can potentially improve system and cyber security, safety ^[3][4][5], data confidentiality ^[6] and data integrity ^[4]. For instance, blockchains can help prevent food fraud by retaining trustworthy product information on biological and geographic origin ^[3][7]. The combination of blockchains with IoT can potentially improve FSCs transparency, efficiency, and sustainability ^[4][8] save costs and time ^[7][5][4], reduce information asymmetry, paperwork, fraud risks, and increase trust among supply chain stakeholders and end consumers ^[4][8]. Integration of DLTs across organizations and infrastructures can potentially enhance stability, resilience, and security of systems ^[2][5], enabling distributed solutions for industries and societies.

2. Scalability Challenges

The moDist frequent and prominent challenge, which was identified in the selected literature, was the scalability issue of blockchain and IoT implementation in FSCs, i.e., the ability to maintain transactions of a network at scale without business process interruption ^[9]. The consensus algoriibuted Ledger Technology (DLT) is a term used to representhms of blockchains, such as Proof-of-Work and Proof-of-Stake, require competition for computational resources, hence achieving scalability and stability in blockchain and IoT-based systems is still a challenge ^[10].

Cua digital network of distrrent existing blockchain platforms, such as Hyperledger Sawtooth, are not capable to handle high amount of data arriving simultaneously, including sensory data and IoT data, due to the low maturity of the solution. ^[11] highlighted the buted models, consiscalability issue of Hyperledger Sawtooth and suggested to dedicate research efforts towards improvement of ing of blockchain scalability ^[11]. Another -basolution of the Hyperd ledger Fabric Composer was investigated by ^[12], whs, and co implemented an experimental study with RFID and IoT for traceability of a halal FSC.

Alaboratinotherg blockchain platform, Ethereum, was compared with Hyperledger Sawtooth with respect to performance by ^[13]. They presenteon shared tasks and a fully decentralized IoT-integrated btivities. Blockchain-based traceability solution for agri-food supply chains. From a performance perspective, the Hyperledger Sawtooth performed better than Ethereum with respect to CPU load, latency, and network traffic. Ethereum had better scalability performance and reliability with increased number of participants, as well as better software maturity ^[13].

Another way to address the sca technology is a data structure, composed of “blability issue of blockchains was the implementation of various mechanisms, one of which being the “sharding” mechanism integrated by ^[14]. Tcks”, that are cryptographey introduced a permissioned 3-tier blockchain framework, with integrated Hazard Control and Critical Control Point (HACCP), permissioned blockchain, and IoT infrastructure. The “sharding” mechanism used a set of parallel blockchains, called “shards”, to scale the network with large number of transactions in multiple shards in parallel. The task of verifying transactions was divided across multiple shards, and each shard maintained its own synchronized ledger, allocating the shards according to geographic zones. The network performance was evaluated in a simcally linked together in a chained sequence using cryptographic hashes, secured against manipulation, and resulteds in^[1][2]. a qDuery time of just a few milliseconds even when the data was gathered from multiple shards ^[9][14] also me to wider functioned the “sharding” mechanism to improve scalability by dividing blockchain data into several nodes or shards, thereby spreading computational power among the nodes simultaneously. In their review, private and consortium blockchain solutions were considered more scalable comparing to public ones, since in public blockchains all nodes share identical responsibilities, e.g., an establishment of a consensus, interaction with user and ledger management ^[9]. Consortality, DLT is a commonly used term for a computer-based system consistium blockchains are shared among a consortium of multiple institutions, which have access to the blockchain ^[15]. Pg of distributed ledgerivate -blockchains, on the other hand, allocate tasks to different nodes, which improves performance of the network. Public Ethereum blockchain is able to support 15 transactions per second, while private blockchains, such as Hyperledger Fabric, caased data structures, which can provide 3500 transactions per second ^[9]. Efficient “lightweight” stincrategies of consensus mechanisms were suggested to address the issues of scalability, data integrity and privacy by performing any expensive high-computational tasks off-chainased levels of ^[9].

Vatrious decentralized storage solutions were investigated to improve the scat, service availability of blockchain solutions. The Interplanetary File System (IPFS) a, resiliend Ethereum blockchain were integrated for decentralized storage of IoT data in an automated FSC traceability model ^[16], y, and security of din agri-food prototypicital ^[17], and system design solutions, as ^[18][19]. Manufacturwerll data and various quality inspections details were stored in a centralized server, while IoT data was stored in a so-called table of content (TOC) located both on a central server and on a decentralizedas distributed storage, computation, and control database of ^[2].

IPFS. This menthod allowed a faster transaction process and backward traceability, tracking each product by the TOC identifier from each supply chain member ^[16]. egration of blockchain technology in In addition to the IPFS, different hybrid storage solutions were proposed, including lightweight data structures and a Delegate Proof-of-Stake consensus mechanism, which restricts the number of validators toernet of Things (IoT) systems can potentially improve the scalability of the blockchainsystem and ^[20]. Hcyberid on-chain and off-chain data storage solutions security, safety were described ^[213][224], such as DoubleChain ^[205], das well as smart contract filtering algorithms, such as a Distributed Time-based Consensus algorithm,ta confidentiality to^[6] reduce on-chain datand ^[20]. Additionally, grouping nodes into clusters in the Blockchain of Things infrastructure was suggested to improve blockchain scalabilita integrity ^[204].

In ^[23], a decentralized stForage solution for blockchain in the FSC domain was also integrated to enhance throughput, latency, and capacity, introducing the BigchainDB. The real-time IoT sensor data and HACCP were integrated for real-time food tracing. Throughput and latency issues were addressed with the BigchainDB for distributed database, which could increase throughput and data storage in a positive linear correlation, while maintaining blockchain properties, such as immutability, transparency, peer-to-peer network, chronoinstance, blockchains can help prevent food fraud by retaining trustworthy product information on biological order of transactions, and decentralized user governance with a consensus and geographic origin mechanism ^[238].

Moreover, ^[243]. proposed using a lightning network technologyThe combination of blockchains with edge computing in a blockhain-based food safety management system to IoT can potentially improve transaction and performanceFSCs transparency, efficiency. Real-time transactions were carried out in an off-chain channel without, and sustainability ^[4][7] uplosading data on to the blockchain. A dynamic programming algorithm was appliedve costs and time to^[8][5][4], reduce lightning network fees ^[24].

Annfother approach was the introduction of a new consensus algorithm, proposed by ^[10], mation asymmetry, paperwho addressed the issue of blockchain scalability by integrating IoT, IBM cloud and blockchain in a scalable traceability system. A system prototype was presented with an integrated consensus mechanism, called the proof of suprk, fraud risks, and increase trust among supply chain share, as well as fuzzy logic to perform shelf-life management for perishable food traceability. The feasibility of the proposed model was evaluated with a case study in a retail e-commerce sector takeholders and end consumers ^[4][107]. A Intwo-level blockchain solution was additionally proposed by ^[25], who peegration of DLTs acrformed a case study-based pilot project, combining a permissionless (public) ledger, shared externally, with a permissioned ledger, available only to licensed stakeholders ^[25].

The major concern oss organizations and inf recent blockchain developments is the technological immaturity ^[21], and many approachastructures highlighted the lack of solid scalable blockchain solutions. Most blockchain initiatives stay in a small implementation or proof-of-concept phase through small pilot studies, while large scale implementations and integration to normal operations are usually initiated by companiesan potentially enhance stability, resilience, and security of systems ^[2][5], and are not widely represented in research publications ^[26]. Blockchain technolonablingy is still perceived by organizadistributed solutions as an emerging technology and an “experimental tool” for achieving a potential competitive advantage in future ^[26]for industries and societies.