nutrients Review Cereal Processing By-Products as Rich Sources of Phenolic Compounds and Their Potential Bioactivities Anca Fărcas , , Georgiana Dret , canu , Teodora Daria Pop, Bianca Enaru, Sonia Socaci and Zorit , a Diaconeasa *   Citation: F˘ arcas , , A.; Dret , canu, G.; Pop, T.D.; Enaru, B.; Socaci, S.; Diaconeasa, Z. Cereal Processing By-Products as Rich Sources of Phenolic Compounds and Their Potential Bioactivities. Nutrients 2021, 13, 3934. https://doi.org/10.3390/ nu13113934 Academic Editors: Alessandra Napolitano and Begoña Bartolomé Received: 6 October 2021 Accepted: 1 November 2021 Published: 3 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Food Science, Faculty of Food Science and Technology, University of Agricultural Science and Veterinary Medicine, 400372 Cluj-Napoca, Romania; anca.farcas@usamvcluj.ro (A.F.); georgiana.dretcanu@stud.ubbcluj.ro (G.D.); teodora-daria.pop@student.usamvcluj.ro (T.D.P.); bianca.enaru@stud.ubbcluj.ro (B.E.); sonia.socaci@usamvcluj.ro (S.S.) * Correspondence: zorita.sconta@usamvcluj.ro; Tel.: +40-751-033-871 Abstract: In today’s society, we can see a progressive paradigm shift that tends towards a healthy and sustainable lifestyle. The proof is represented by the growing interest in food loss and waste of different sectors, from the political to the academic, or even to the private sector. In order to reduce food waste and to increase sustainability, the European Union (EU) has planned a circular bioeconomy. This action plan includes an approach based on reducing, reusing, recovering, and recycling materials and energy. Every year, there are high amounts of waste and by-products resulting from agricultural producing and agro-industrial processing, impacting the environment and the socio-economic sector. Cereal food products cover over 20% of daily diet, so it can be assumed that cereal production and processing are one of the most important sectors of agri-food industries. It is estimated that the waste generated from cereal processing and manufacturing is up to 13%, a percentage that can be decreased by converting the by-products in raw materials for biofuels, biodegradable plastics, alcohols, antioxidants, food additives, or pharmaceutic ingredients due to their content in macro- and micro-nutrients or bioactive compounds. Based on the fact that diet plays a crucial role in maintaining the integrity of our body, it is important to capitalize on any source of bioactive compounds to which we have access. This review aims to highlight the need to recirculate by-products for the purpose of extraction and use of their key compounds, polyphenols, which have not only antioxidant effects, but also preventive and therapeutic effects against cancer. For these, it is necessary to understand the biotechnologies needed for processing the most consumed cereals, the methods of extraction of phenolic compounds, and the main effects that these compounds have, summarizing the most relevant in vitro and in vivo studies performed so far. Keywords: cereals; grains; by-product; brewers spent grain; polyphenols; bran; antioxidant; anti- cancer 1. Introduction One of the biggest challenges for humanity is to live in a society without hunger but with high quality and safe food. In order to achieve this, we have to assume that worldwide food loss has to be drastically reduced [1]. Every year, approximately 1.3 billion tons of food loss and waste are generated from the whole food chain, including manufacturing, production, and consumption, representing close to one-third of the food produced [2]. Food loss and waste represent also a substantial consumption of important resources such as water, land, energy, and labor. These losses go hand-in-hand with the environmental deteriorations caused by the ineffective management of this waste. In order to reduce these insufficiencies, a viable solution is represented by the concept of circular bioeconomy, which have as prime goals the achievement of sustainability and economic viability for bio-stream production, a reduction in costs, the enhancement of competitiveness, and a reduction in poverty and hunger [3,4]. This paradigm shift from a linear towards a circular bioeconomy implies public awareness and acceptance, systems thinking, sustainable production and Nutrients 2021, 13, 3934. https://doi.org/10.3390/nu13113934 https://www.mdpi.com/journal/nutrients