Submit to Foods Review for Foods Propose a Special Issue

Journal Menu

Journal Browser

Frontiers on Sustainable Food Packaging

Special Issue Editors
Special Issue Information
Keywords
Benefits of Publishing in a Special Issue
Published Papers

A special issue of Foods (ISSN 2304-8158). This special issue belongs to the section "Food Security and Sustainability".

Deadline for manuscript submissions: closed (10 December 2022) | Viewed by 99952

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special issue Frontiers on Sustainable Food Packaging book cover image

Share This Special Issue

Special Issue Editors

Prof. Dr. Theodoros Varzakas

E-Mail
Guest Editor

Department of Food Science and Technology, University of Peloponnese, 24100 Antikalamos, Kalamata, Greece
Interests: food technology; food engineering; food safety; food quality; extra virgin olive oil; mycotoxins; fermented foods
Special Issues, Collections and Topics in MDPI journals

Dr. Rui M.S. Cruz

E-Mail Website
Guest Editor

1. Department of Food Engineering, Institute of Engineering, Universidade do Algarve, Campus da Penha, 8005-139 Faro, Portugal
2. MED-Mediterranean Institute for Agriculture, Environment and Development and CHANGE-Global Change and Sustainability Institute, Faculty of Sciences and Technology, Campus de Gambelas, Universidade do Algarve, 8005-139 Faro, Portugal
Interests: food packaging; food processing; emerging technologies; biomaterials; sustainability; mathematical modeling; shelf-life; food preservation; food waste recovery
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The implementation of sustainable food packaging solutions within future circular food supply chains is essential today to protect customers and ensure food quality, safety, and optimal shelf-life. This will be improved by new innovative packaging materials and the reduction of food waste. In this direction, it is important to employ lifecycle assessment (LCA) to define food supply chain impacts, taking into consideration food waste, global food industry environmental impacts, and shipping distances with the final target to achieve consumer satisfaction.

The purpose of this Special Issue is to attract papers in the new era of sustainability and food packaging addressing all major sectors of food from cereals and confectionery to fruits and vegetables, meat, and dairy products.

It is important to share data on the (i) consequences of specific food product–package interactions, (ii) consideration of the utilization of novel packaging biomaterials, and (iii) overall consumer behavior and satisfaction as a critical focus.

This implementation will be facilitated by the interaction of all scientists in the field from food packaging experts to consumer scientists and policy experts.

Prof. Dr. Theodoros Varzakas
Prof. Dr. Rui M.S. Cruz
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Foods is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

consumers
food packaging systems
LCA (life cycle assessment)
novel biomaterials
quality
safety
security
shelf-life
sustainability

Benefits of Publishing in a Special Issue

Ease of navigation: Grouping papers by topic helps scholars navigate broad scope journals more efficiently.
Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
Expansion of research network: Special Issues facilitate connections among authors, fostering scientific collaborations.
External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
e-Book format: Special Issues with more than 10 articles can be published as dedicated e-books, ensuring wide and rapid dissemination.

Further information on MDPI's Special Issue polices can be found here.

Published Papers (13 papers)

Download All Papers

Order results

Result details

Show export options Show export options

Select all

Export citation of selected articles as:

Editorial

Jump to: Research, Review

3 pages, 180 KiB

Open AccessEditorial

Frontiers on Sustainable Food Packaging

by Rui M. S. Cruz and Theodoros Varzakas

Foods 2023, 12(2), 349; https://doi.org/10.3390/foods12020349 - 11 Jan 2023

Cited by 1 | Viewed by 2199

Abstract

The implementation of sustainable food packaging solutions within future circular food supply chains is essential to protect customers and ensure food quality, safety, and optimal shelf-life [...] Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

Research

Jump to: Editorial, Review

20 pages, 13955 KiB

Open AccessArticle

(Not) Communicating the Environmental Friendliness of Food Packaging to Consumers—An Attribute- and Cue-Based Concept and Its Application

by Krisztina Rita Dörnyei, Anna-Sophia Bauer, Victoria Krauter and Carsten Herbes

Foods 2022, 11(9), 1371; https://doi.org/10.3390/foods11091371 - 9 May 2022

Cited by 13 | Viewed by 6020

Abstract

While consumer understanding of and preferences for environmentally friendly packaging options have been well investigated, little is known about the environmentally friendly packaging attributes communicated to consumers by suppliers via packaging cues. We thus propose a literature-based attribute-cue matrix as a tool for analyzing packaging solutions. Using a 2021 snapshot of the wafer market in nine European countries, we demonstrate the tool’s utility by analyzing the cues found that signal environmentally friendly packaging attributes. While the literature suggests that environmentally friendly packaging is increasingly used by manufacturers, our analysis of 164 wafer packages shows that communication is very limited except for information related to recyclability and disposal. This is frequently communicated via labels (e.g., recycling codes, Green Dot) and structural cues that implicitly signal reduced material use (e.g., less headspace and few packaging levels). Our attribute–cue matrix enables researchers, companies, and policymakers to analyze and improve packaging solutions across countries and product categories. Our finding that environmentally friendly packaging attributes are not being communicated to consumers underscores a pressing need for better communication strategies. Both direct on-pack and implicit communication should help consumers choose more environmentally friendly packaging. Governments are encouraged to apply our tool to identify communication gaps and adopt labeling regulations where needed. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

18 pages, 18841 KiB

Open AccessArticle

Design of a Blockchain-Enabled Traceability System Framework for Food Supply Chains

by Lixing Wang, Yulin He and Zhenning Wu

Foods 2022, 11(5), 744; https://doi.org/10.3390/foods11050744 - 3 Mar 2022

Cited by 64 | Viewed by 8092

Abstract

Tracing food products along the entire supply chain is important for achieving better management of food products. Traditionally, centralized traceability systems have been developed for such purposes. One major drawback of this approach is that different users of the supply chain have their own systems with their own complexities and distinct features; thus, the interaction among them creates challenges when implementing a single centralized system. Therefore, a decentralized traceability system is favorable for tracing food products along the supply chain. In this study, we develop a supply chain traceability system framework based on blockchain and radio frequency identification (RFID) technology. The system consists of a decentralized blockchain-enabled data storage platform for data management and an RFID system at the packaging level for data collection and storage. We applied a consortium blockchain to the application. Fabric 2.0 in Hyperledger was chosen as the development platform. The proposed blockchain-enabled platform can provide decentralized data management and its underlying algorithm can guarantee data security. The system includes a creatively designed blockchain-enabled data structure in the RFID tag. When people scan the tag, the relevant information is written in the tag as a block linked to the previous blocks; simultaneously, the information is transmitted to the blockchain platform and recorded on the platform. No battery is required and the system works when there is an RFID reader nearby. The usage conditions included shipment, stocking, and storage. The RFID tag can be directly attached to paper packaging. This approach embeds the blockchain technique into the RFID tag and develops a corresponding system. The new traceability system has the potential to simplify the tracking of products and can be scaled for industrial use. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

12 pages, 1239 KiB

Open AccessArticle

Effects of Chitosan and Duck Fat-Based Emulsion Coatings on the Quality Characteristics of Chicken Meat during Storage

by Dong-Min Shin, Yea-Ji Kim, Jong-Hyeok Yune, Do-Hyun Kim, Hyuk-Cheol Kwon, Hyejin Sohn, Seo-Gu Han, Jong-Hyeon Han, Su-Jin Lim and Sung-Gu Han

Foods 2022, 11(2), 245; https://doi.org/10.3390/foods11020245 - 17 Jan 2022

Cited by 14 | Viewed by 2736

Abstract

Chicken meat is a popular food commodity that is widely consumed worldwide. However, the shelf-life or quality maintenance of chicken meat is a major concern for industries because of spoilage by microbial growth. The aim of this study was to evaluate the effects of chitosan and duck fat-based emulsion coatings on the quality characteristics and microbial stability of chicken meat during refrigerated storage. The coated chicken meat samples were as follows: control (non-coated), DFC0 (coated with duck fat), DFC0.5 (coated with duck fat and 0.5% chitosan), DFC1 (coated with duck fat and 1% chitosan), DFC2 (coated with duck fat and 2% chitosan), and SOC2 (coated with soybean oil and 2% chitosan). The results showed that the apparent viscosity and coating rate were higher in DFC2 than in other groups. Physicochemical parameters (pH, color, and Warner–Bratzler shear force) were better in DFC2 than those in other groups during 15 days of storage. Moreover, DFC2 delayed lipid oxidation, protein deterioration, and growth of microorganisms during storage. These data suggest that chitosan-supplemented duck fat-based emulsion coating could be used to maintain the quality of raw chicken meat during refrigerated storage. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

14 pages, 980 KiB

Open AccessArticle

Biofilm Formation Reduction by Eugenol and Thymol on Biodegradable Food Packaging Material

by Pavel Pleva, Lucie Bartošová, Daniela Máčalová, Ludmila Zálešáková, Jana Sedlaříková and Magda Janalíková

Foods 2022, 11(1), 2; https://doi.org/10.3390/foods11010002 - 21 Dec 2021

Cited by 13 | Viewed by 4833

Abstract

Biofilm is a structured community of microorganisms adhering to surfaces of various polymeric materials used in food packaging. Microbes in the biofilm may affect food quality. However, the presence of biofilm can ensure biodegradation of discarded packaging. This work aims to evaluate a biofilm formation on the selected biodegradable polymer films: poly (lactic acid) (PLA), poly (butylene adipate-co-terephthalate) (PBAT), and poly (butylene succinate) (PBS) by selected bacterial strains; collection strains of Escherichiacoli, Staphylococcusaureus; and Bacillus pumilus, Bacillussubtilis, Bacillustequilensis, and Stenotrophomonasmaltophilia isolated from dairy products. Three different methods for biofilm evaluation were performed: the Christensen method, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and fluorescence microscopy. High biofilm formation was confirmed on the control PBS film, whereas low biofilm formation ability was observed on the PLA polymer sample. Furthermore, the films with incorporated antimicrobial compounds (thymol or eugenol) were also prepared. Antimicrobial activity and also reduction in biofilm formation on enriched polymer films were determined. Therefore, they were all proved to be antimicrobial and effective in reducing biofilm formation. These films can be used to prepare novel active food packaging for the dairy industry to prevent biofilm formation and enhance food quality and safety in the future. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

9 pages, 2107 KiB

Open AccessArticle

Developing Edible Starch Film Used for Packaging Seasonings in Instant Noodles

by Hui Chen, Mahafooj Alee, Ying Chen, Yinglin Zhou, Mao Yang, Amjad Ali, Hongsheng Liu, Ling Chen and Long Yu

Foods 2021, 10(12), 3105; https://doi.org/10.3390/foods10123105 - 14 Dec 2021

Cited by 13 | Viewed by 4989

Abstract

Edible starch-based film was developed for packaging seasoning applied in instant noodles. The edible film can quickly dissolve into hot water so that the seasoning bag can mix in the soup of instant noodles during preparation. To meet the specific requirements of the packaging, such as reasonable high tensile properties, ductility under arid conditions, and low gas permeability, hydroxypropyl cornstarch with various edible additives from food-grade ingredients were applied to enhance the functionality of starch film. In this work, xylose was used as a plasticizer, cellulose crystals were used as a reinforcing agent, and laver was used to decrease gas permeability. The microstructures, interface, and compatibility of various components and film performance were investigated using an optical microscope under polarized light, scanning electron microscope, gas permeability, and tensile testing. The relationship was established between processing methodologies, microstructures, and performances. The results showed that the developed starch-based film have a modulus of 960 MPa, tensile strength of 36 Mpa with 14% elongation, and water vapor permeability less than 5.8 g/m².h under 20% RH condition at room temperature (25 °C), which meets the general requirements of the flavor bag packaging used in instant noodles. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

17 pages, 1775 KiB

Open AccessArticle

Reusable Plastic Crates (RPCs) for Fresh Produce (Case Study on Cauliflowers): Sustainable Packaging but Potential Salmonella Survival and Risk of Cross-Contamination

by Francisco López-Gálvez, Laura Rasines, Encarnación Conesa, Perla A. Gómez, Francisco Artés-Hernández and Encarna Aguayo

Foods 2021, 10(6), 1254; https://doi.org/10.3390/foods10061254 - 1 Jun 2021

Cited by 21 | Viewed by 5742

Abstract

The handling of fresh fruits and vegetables in reusable plastic crates (RPCs) has the potential to increase the sustainability of packaging in the fresh produce supply chain. However, the utilization of multiple-use containers can have consequences related to the microbial safety of this type of food. The present study assessed the potential cross-contamination of fresh cauliflowers with Salmonella enterica via different contact materials (polypropylene from RPCs, corrugated cardboard, and medium-density fiberboard (MDF) from wooden boxes). Additionally, the survival of the pathogenic microorganism was studied in cauliflowers and the contact materials during storage. The life cycle assessment (LCA) approach was used to evaluate the environmental impact of produce handling containers made from the different food-contact materials tested. The results show a higher risk of cross-contamination via polypropylene compared with cardboard and MDF. Another outcome of the study is the potential of Salmonella for surviving both in cross-contaminated produce and in contact materials under supply chain conditions. Regarding environmental sustainability, RPCs have a lower environmental impact than single-use containers (cardboard and wooden boxes). To exploit the potential environmental benefits of RPCs while ensuring food safety, it is necessary to guarantee the hygiene of this type of container. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Graphical abstract

Review

Jump to: Editorial, Research

20 pages, 1460 KiB

Open AccessReview

Latest Trends in Sustainable Polymeric Food Packaging Films

by Edilson G. S. Silva, Sara Cardoso, Ana F. Bettencourt and Isabel A. C. Ribeiro

Foods 2023, 12(1), 168; https://doi.org/10.3390/foods12010168 - 29 Dec 2022

Cited by 17 | Viewed by 4748

Abstract

Food packaging is the best way to protect food while it moves along the entire supply chain to the consumer. However, conventional food packaging poses some problems related to food wastage and excessive plastic production. Considering this, the aim of this work was to examine recent findings related to bio-based alternative food packaging films by means of conventional methodologies and additive manufacturing technologies, such as 3D printing (3D-P), with potential to replace conventional petroleum-based food packaging. Based on the findings, progress in the development of bio-based packaging films, biopolymer-based feedstocks for 3D-P, and innovative food packaging materials produced by this technology was identified. However, the lack of studies suggests that 3D-P has not been well-explored in this field. Nonetheless, it is probable that in the future this technology will be more widely employed in the food packaging field, which could lead to a reduction in plastic production as well as safer food consumption. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Graphical abstract

39 pages, 1183 KiB

Open AccessEditor’s ChoiceReview

Bioplastics for Food Packaging: Environmental Impact, Trends and Regulatory Aspects

by Rui M. S. Cruz, Victoria Krauter, Simon Krauter, Sofia Agriopoulou, Ramona Weinrich, Carsten Herbes, Philip B. V. Scholten, Ilke Uysal-Unalan, Ece Sogut, Samir Kopacic, Johanna Lahti, Ramune Rutkaite and Theodoros Varzakas

Foods 2022, 11(19), 3087; https://doi.org/10.3390/foods11193087 - 5 Oct 2022

Cited by 60 | Viewed by 22514

Abstract

The demand to develop and produce eco-friendly alternatives for food packaging is increasing. The huge negative impact that the disposal of so-called “single-use plastics” has on the environment is propelling the market to search for new solutions, and requires initiatives to drive faster responses from the scientific community, the industry, and governmental bodies for the adoption and implementation of new materials. Bioplastics are an alternative group of materials that are partly or entirely produced from renewable sources. Some bioplastics are biodegradable or even compostable under the right conditions. This review presents the different properties of these materials, mechanisms of biodegradation, and their environmental impact, but also presents a holistic overview of the most important bioplastics available in the market and their potential application for food packaging, consumer perception of the bioplastics, regulatory aspects, and future challenges. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

38 pages, 3140 KiB

Open AccessReview

Physical, Chemical and Biochemical Modification Approaches of Potato (Peel) Constituents for Bio-Based Food Packaging Concepts: A Review

by Katharina Miller, Corina L. Reichert, Markus Schmid and Myriam Loeffler

Foods 2022, 11(18), 2927; https://doi.org/10.3390/foods11182927 - 19 Sep 2022

Cited by 10 | Viewed by 5239

Abstract

Potatoes are grown in large quantities and are mainly used as food or animal feed. Potato processing generates a large amount of side streams, which are currently low value by-products of the potato processing industry. The utilization of the potato peel side stream and other potato residues is also becoming increasingly important from a sustainability point of view. Individual constituents of potato peel or complete potato tubers can for instance be used for application in other products such as bio-based food packaging. Prior using constituents for specific applications, their properties and characteristics need to be known and understood. This article extensively reviews the scientific literature about physical, chemical, and biochemical modification of potato constituents. Besides short explanations about the modification techniques, extensive summaries of the results from scientific articles are outlined focusing on the main constituents of potatoes, namely potato starch and potato protein. The effects of the different modification techniques are qualitatively interpreted in tables to obtain a condensed overview about the influence of different modification techniques on the potato constituents. Overall, this article provides an up-to-date and comprehensive overview of the possibilities and implications of modifying potato components for potential further valorization in, e.g., bio-based food packaging. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

42 pages, 1003 KiB

Open AccessReview

Cereal and Confectionary Packaging: Assessment of Sustainability and Environmental Impact with a Special Focus on Greenhouse Gas Emissions

by Victoria Krauter, Anna-Sophia Bauer, Maria Milousi, Krisztina Rita Dörnyei, Greg Ganczewski, Kärt Leppik, Jan Krepil and Theodoros Varzakas

Foods 2022, 11(9), 1347; https://doi.org/10.3390/foods11091347 - 6 May 2022

Cited by 10 | Viewed by 6624

Abstract

The usefulness of food packaging is often questioned in the public debate about (ecological) sustainability. While worldwide packaging-related CO₂ emissions are accountable for approximately 5% of emissions, specific packaging solutions can reach significantly higher values depending on use case and product group. Unlike other groups, greenhouse gas (GHG) emissions and life cycle assessment (LCA) of cereal and confectionary products have not been the focus of comprehensive reviews so far. Consequently, the present review first contextualizes packaging, sustainability and related LCA methods and then depicts how cereal and confectionary packaging has been presented in different LCA studies. The results reveal that only a few studies sufficiently include (primary, secondary and tertiary) packaging in LCAs and when they do, the focus is mainly on the direct (e.g., material used) rather than indirect environmental impacts (e.g., food losses and waste) of the like. In addition, it is shown that the packaging of cereals and confectionary contributes on average 9.18% to GHG emissions of the entire food packaging system. Finally, recommendations on how to improve packaging sustainability, how to better include packaging in LCAs and how to reflect this in management-related activities are displayed. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

28 pages, 986 KiB

Open AccessReview

Cereal and Confectionary Packaging: Background, Application and Shelf-Life Extension

by Anna-Sophia Bauer, Kärt Leppik, Kata Galić, Ioannis Anestopoulos, Mihalis I. Panayiotidis, Sofia Agriopoulou, Maria Milousi, Ilke Uysal-Unalan, Theodoros Varzakas and Victoria Krauter

Foods 2022, 11(5), 697; https://doi.org/10.3390/foods11050697 - 26 Feb 2022

Cited by 20 | Viewed by 11041

Abstract

In both public and private sectors, one can notice a strong interest in the topic of sustainable food and packaging. For a long time, the spotlight for optimization was placed on well-known examples of high environmental impacts, whether regarding indirect resource use (e.g., meat, dairy) or problems in waste management. Staple and hedonistic foods such as cereals and confectionary have gained less attention. However, these products and their packaging solutions are likewise of worldwide ecologic and economic relevance, accounting for high resource input, production amounts, as well as food losses and waste. This review provides a profound elaboration of the status quo in cereal and confectionary packaging, essential for practitioners to improve sustainability in the sector. Here, we present packaging functions and properties along with related product characteristics and decay mechanisms in the subcategories of cereals and cereal products, confectionary and bakery wares alongside ready-to-eat savories and snacks. Moreover, we offer an overview to formerly and recently used packaging concepts as well as established and modern shelf-life extending technologies, expanding upon our knowledge to thoroughly understand the packaging’s purpose; we conclude that a comparison of the environmental burden share between product and packaging is necessary to properly derive the need for action(s), such as packaging redesign. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Figure 1

17 pages, 847 KiB

Open AccessReview

Recyclability and Redesign Challenges in Multilayer Flexible Food Packaging—A Review

by Anna-Sophia Bauer, Manfred Tacker, Ilke Uysal-Unalan, Rui M. S. Cruz, Theo Varzakas and Victoria Krauter

Foods 2021, 10(11), 2702; https://doi.org/10.3390/foods10112702 - 5 Nov 2021

Cited by 52 | Viewed by 11289

Abstract

Multilayer flexible food packaging is under pressure to redesign for recyclability. Most multilayer films are not sorted and recycled with the currently available infrastructure, which is based on mechanical recycling in most countries. Up to now, multilayer flexible food packaging was highly customizable. Diverse polymers and non-polymeric layers allowed a long product shelf-life and an optimized material efficiency. The need for more recyclable solutions asks for a reduction in the choice of material. Prospectively, there is a strong tendency that multilayer flexible barrier packaging should be based on polyolefins and a few recyclable barrier layers, such as aluminium oxide (AlOx) and silicon oxide (SiOx). The use of ethylene vinyl alcohol (EVOH) and metallization could be more restricted in the future, as popular Design for Recycling Guidelines have recently reduced the maximum tolerable content of barrier materials in polyolefin packaging. The substitution of non-recyclable flexible barrier packaging is challenging because only a limited number of barriers are available. In the worst case, the restriction on material choice could result in a higher environmental burden through a shortened food shelf-life and increased packaging weights. Full article

(This article belongs to the Special Issue Frontiers on Sustainable Food Packaging)

► Show Figures

Journal Menu

Journal Browser

Frontiers on Sustainable Food Packaging

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Benefits of Publishing in a Special Issue

Published Papers (13 papers)

Editorial

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI