Food waste is a serious problem with negative environmental and economic consequences. Unused food (either as waste or by-products and referred to as food residues in the present work) is a source of carbohydrates, lipids, proteins, vitamins, minerals and bioactive compounds that could be used in an alternate or secondary life cycle to avoid discarding it. The present work reviews the potential use of food residues for the bioengineering of single-cell protein (SCP), addressing aspects of production, nutrition and safety, as well as the main challenges and perspectives. SCP is obtained from various microorganisms, including fungi, bacteria, yeasts and algae, in pure or mixed form. SCP generally contains a higher percentage of protein (30–80%) compared to soy (38.6%), fish (17.8%), meat (21.2%) and whole milk (3.28%). SCP is a source of essential amino acids, including methionine, threonine and lysine. The use of food residues as substrates for the production of SCP would reduce production costs (35–75%); however, optimization and industrial scaling are some of the main challenges to its sustainable production. The use food waste and agro by-products from the food industry could be a promising alternative to obtain protein according to a circular production scheme.

The ability of phenolic compounds to cross the blood–brain barrier and reach the central nervous system is discussed. There are knowledge gaps that require additional experimentation, such as inconclusive transport mechanisms and lack of human data.

One of the biggest problems faced by food industries is the generation of large amounts of agro-industrial byproducts, such as those derived from fruit processing, as well as the negative effects of their inadequate management. Approximately 1/3 of the food produced worldwide is unused or is otherwise wasted along the chain, which represents a burden on the environment and an inefficiency of the system. Thus, there is growing interest in reintroducing agro-industrial byproducts (both from fruits and other sources) into the processing chain, either by adding them as such or utilizing them as sources of health-promoting bioactive compounds. The present work discusses recent scientific studies on the nutritional and bioactive composition of some agro-industrial byproducts derived from fruit processing, their applications as ingredients to supplement baked foods, and their main biological activities on the consumer’s health. Research shows that agro-industrial fruit byproducts can be incorporated into various baked foods, increasing their fiber content, bioactive profile, and antioxidant capacity, in addition to other positive effects such as reducing their glycemic impact and inducing satiety, all while maintaining good sensory acceptance. Using agro-industrial fruit byproducts as food ingredients avoids discarding them; it can promote some bioactivities and maintain or even improve sensory acceptance. This contributes to incorporating edible material back into the processing chain as part of a circular bioeconomy, which can significantly benefit primary producers, processing industries (particularly smaller ones), and the final consumer.

The importance of bioactive compounds in agro-industrial by-products of plant origin lies in their direct impacts on human health. These compounds have been shown to possess antioxidant, anti-inflammatory, and antimicrobial properties, contributing to disease prevention and strengthening the immune system. In particular, the antimicrobial action of these compounds emerges as an important tool in food preservation, providing natural alternatives to synthetic preservatives and contributing to combating antimicrobial resistance. Using agro-industrial by-products of plant origin not only addresses the need to reduce waste and promote sustainability but also inaugurates a new era in the formulation of functional foods. From fruit peels to pulps and seeds, these by-products are emerging as essential ingredients in the creation of products that can promote health. Continued research in this area will unveil new applications and properties of these by-products and open doors to a food paradigm in which health and sustainability converge, paving the way to a healthier and more equitable future. The present review presents an overview of our knowledge of agro-industrial by-products and some of their more relevant health-promoting bioactivities.

El presente trabajo describe los nutrientes y compuestos fenólicos contenidos en diversos residuos agroindustriales (RAI). Los RAI pueden derivar en problemas que comprometen la alimentación y salud de las poblaciones más vulnerables si no son aprovechados adecuadamente. Por ello es importante crear alternativas que contribuyan a contrarrestar el problema, desde la producción de alimentos hasta la mesa del consumidor. Los RAI de frutas, verduras, cereales y oleaginosas contienen nutrientes y compuestos fenólicos que pueden ser benéficos a la salud debido a sus efectos antioxidantes, antiinflamatorios, antidiabéticos, entre otros. Los RAI podrían también ser aplicados en el desarrollo de alimentos, debido a sus características tecnofuncionales como la capacidad de actuar como agentes gelificantes, emulsificantes, estabilizantes y espesantes. De acuerdo con lo anterior, el empleo de RAI para un segundo uso es prometedor, sin embargo, aún quedan algunos retos por resolver, tales como el escalamiento y la optimización de su extracción.