# Phytochemical and Functional Properties of Fruit and Vegetable Processing By-Products
## 1 Introduction  
In recent decades, global food production and dietary patterns have undergone notable changes. Actual models of production, whilst they encourage growth, higher yields, and food security, are damaging the environment, increasing global greenhouse gas emissions, and driving biodiversity loss, water scarcity, the overuse of pesticides, nutrient pollution, climate change, and the excessive use of antibiotics [1; 2; 3; 4; 5]. Malnutrition is a widespread phenomenon in many areas of the planet. In fact, it is estimated that people from a lot of countries (77%) show a calorie deficit, 2 billion people exhibit a micronutrient deficiency, and an additional 2.2 billion people are considered overweight or obese [6]. Unhealthy, high-calory, and low-micronutrient diets, based on highly processed saturated fats and animal-based foods, increase the over-weight and obese global population [5]. Malnutrition can also cause diet-related non-communicable diseases [5]. In this context, the global food system cannot meet the food needs of 10 billion people by 2050 without impacts on water, land use, and gas emissions, and irreversibly damaging the planet. Agriculture accounts for 70% of freshwater consumption, the occupation of half the world's habitable land, and 78% of the global eutrophication of oceans andfreshwater [7]. Furthermore, 26.0% of anthropogenic greenhouse gas emissions are caused by agriculture and 14.5% by livestock production, especially beef and lamb [7]. Specifically, a comparison between plant food production and animal food production showed that, on average, producing animal protein (meat and dairy) requires 11 times more fossil fuel energy than grain-based protein [8]. For all these reasons, a transition to healthy, environmentally sustainable diets is necessary. The promotion of healthy and safe diets can be a starting point to guarantee food security, to provide sufficient affordable and nutritious foods, and to preserve biodiversity and the environment [9]. The Planetary Health Diet (PHD), based on the recommendations proposed by the EAT-Lancet Commission, can be considered a reference diet because it establishes scientific targets for healthy diets that will optimize human health. According to dietary requirements, personal preferences, and cultural traditions, healthy and sustainable diets encourage (1) an appropriate caloric intake, especially from fruits and vegetables, legumes, nuts, and whole grains; (2) low amounts of animal-sourced foods, such as red meat, and unsaturated rather than saturated fats; and (3) small amounts of refined grains, highly processed foods, and added sugars [5]. At the same time, the presence of adequate macronutrients and essential micronutrients in healthy diets must be ensured [10]. In recent years, an important ongoing field of research concerns the use of waste and by-products to provide healthy foods with a high content of nutrients and antioxidants and from plant-based resources, from the perspective of sustainability and circularity. According to the Food and Agriculture Organization (FAO), one-third of the global food production is lost or wasted along food supply chains. Food losses and waste have exponentially increased over the last few decades, with high negative effects on the environment and economic losses due to waste disposal [11; 12]. Vegetables (24% of total losses and waste), fruits (22%), cereals (12%), oil crops (10%), potatoes (7%), and sugar beets (4%) constitute massive amounts of residues [12; 13]. Specifically, it is estimated that the pre- and post-harvesting process and fruit and vegetable processing produce high amounts of by-products such as peels, seeds, shells, pods, pomace, etc., every year [14].