**1. Introduction**

During the process of obtaining vegetable oils, considerable amounts of waste and byproducts are generated. These byproducts from the vegetable oil industry are important due to their high value-added substances, and they represent an excellent source of bioactive components, such as antioxidants. Byproducts such as flour, meals, and groats

**Citation:** Multescu, M.; Marinas, I.C.; Susman, I.E.; Belc, N. Byproducts (Flour, Meals, and Groats) from the Vegetable Oil Industry as a Potential Source of Antioxidants. *Foods* **2022**, *11*, 253. https://doi.org/10.3390/ foods11030253

Academic Editors: Marco Poiana, Francesco Caponio and Antonio Piga

Received: 9 December 2021 Accepted: 13 January 2022 Published: 18 January 2022

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**Copyright:** © 2022 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/).

resulting from the vegetable oil industry are considered economic resources due to the antioxidant compounds, which have attracted interest in making functional products with a higher nutritional value, satisfying consumer demand for such products [1].

Sea buckthorn berries are rich in substances with biological activity [2]. Sea buckthorn is rich in nutrients and antioxidants, so it is used as a dietary supplement [3]. Ghendov-Mosanu et al. [2] have determined the characteristics of sea buckthorn flour and investigated its effects on sensory, physicochemical, and antioxidant properties. The results obtained showed that sea buckthorn flour is a good source of ascorbic acid, polyphenols, and flavonoids. This byproduct added in different concentrations in wheat bread has extended the shelf life to 72 h and has improved antioxidant activity. Increasing the concentration of sea buckthorn flour in wheat bread was directly proportional to its benefits. Hemp is rich in protein, fat, carbohydrates, and fiber. It contains significant amounts of macroelements, such as P, K, Mg, Na, and Ca. Hemp flour is a good source of bioactive compounds, especially polyphenols [4]. Rusu et al. [4] have nutritionally characterized the bread with the addition of hemp flour in different concentrations. Studies have shown that the addition of hemp flour to bread improves the nutritional properties.

Walnuts are a significant source of vegetable protein and amino acids. They contain over 50% oil rich in polyunsaturated fatty acids. Walnuts are an excellent source of phytochemicals, such as phenolic compounds, carotenoids, and tocopherols [5]. Almoraie et al. [6] determined the possibility of using walnut flour in the production of wheat bread. Bread samples with different concentrations of walnut flour have been shown to have a higher nutritional value than bread samples made from 100% wheat flour. Grape seed flour contains a significant number of polyphenols and presents high antioxidant capacity [7]. This byproduct can be an alternative in the production of various foods due to a high content of dietary fiber. Previous studies have shown that grape seed flour has been used in many products, such as cookies, pancakes, butter biscuits, and bread [8].

Sunflower has many nutritional components. Examples are sunflower flour, meal, groats, etc. [9]. Sunflower meal can be used in a wide range of bakery products due to the high concentration of antioxidants. Byproducts such as sunflower meal represent an excellent source of protein, essential amino acids, and fiber. It contains essential amino acids, vitamin B, and minerals, and has a high antioxidant property [10]. Grasso et al. [11] observed that sunflower meal could be used for the nutritional improvement of muffins. Rapeseed's meal is rich in phenolic compounds, tocopherols, vitamins B, calcium, magnesium, and presents high antioxidant activity [12]. Along with rapeseed meal, black sesame meal is a potential source of polyphenolics with high antioxidant status [13]. Flax seeds contain a high level of oil and are rich in polyunsaturated fatty acids. They are also an important source of soluble and insoluble fiber [14]. Numerous phytochemical compounds with antioxidant activity are found in flax seeds, including phenolic acids, flavonoids, and lignins [15]. Pourabedin et al. [16] observed that adding flaxseed flour to toast bread increases phenolic compounds. Milk thistle is known for its high content of bioactive compounds, mainly flavonoids with a powerful antioxidant character [17]. Milk thistle seeds contain the largest number of active substances, about 70–80% of silymarin flavonolignans and about 20–30% of substances with polyphenolic structures [18].

The byproducts (meal) obtained in the vegetable oils industry contain phenolic compounds with different chemical structures, such as tocopherols, carotenoids, flavonoids, lignins, phenolic acids, and tannins with high values of antioxidant capacity [19]. These are natural and cheap sources of antioxidants that could replace synthetic additives (BHT or BHA) [19]. It is known that antioxidants play an important role in preventing many diseases, such as cancer and cardiovascular disease [20]. The main biologically active compounds of the byproducts obtained from the vegetable oil industry are polyphenols and flavonoids. Phenolic compounds are a broad group of secondary metabolites that are spread throughout the plant. Polyphenolics have special properties for human health, including anti-inflammatory activity, enzyme inhibition, antimicrobial, antiallergic, reducing the risk of cardiovascular disease, and cytotoxic antitumor activity [21]. Antioxidants such

as polyphenols are considered possible protective agents, reducing the oxidative damage caused by reactive oxygen species in the human body and delaying the progression of many chronic diseases, as well as the oxidation of low-density lipoproteins (LDL), which play an important role in atherosclerosis [22]. One of the major causes of atherosclerosis is the high cholesterol. Flavonoids represent a class of phenolic compounds, which are found naturally in plants. These bioactive compounds are also found in a variety of nutraceutical, pharmaceutical, medicinal, and cosmetic applications. This is attributed to their antioxidant, anti-inflammatory, antimutagenic, and anticarcinogenic properties, along with their ability to modulate the key function of cellular enzymes. Research on flavonoids has received an additional boost with the discovery of a low rate of cardiovascular mortality and the prevention of cardiovascular disease [23].

The aim of this study was to determine the total polyphenolic and flavonoid content, as well as to evaluate the antioxidant activity by different methods (DPPH, FRAP, CUPRAC, ABTS) and the antioxidant capacity by PCL-ACL of various byproducts obtained from the vegetable oil industry. It is necessary to find alternative strategies for the use of these byproducts in order to avoid their impact on the environment and to increase the profitability of plant resources. The main attraction of these byproducts obtained in the vegetable oil industry is the possibility to use them in the production of food products with high nutritional value.
