**1. Introduction**

Nowadays, the agro-food industry generates a huge amount of waste, which constitutes one of the main environmental problems due to the high organic charge [1], but it could represent a potential source of valuable bioactive compounds, suitable for food, pharmaceutical, and textile industries [1,2]. Recently, the search for new and renewable sources of bioactive compounds has been encouraged by the European Commission, which targeted the achievement of a fully circular economy by 2050, also through the farm to fork strategy. This program represents the heart of the European green deal, which aims to achieve healthier and more environmentally friendly food systems [3].

Therefore, great effort has been made by scientists and companies in order to investigate and characterize the potential applications of agro-food by-product bioactive compounds or metabolites in food, pharmaceutical, and cosmetic industries [1,2]. These natural compounds can be used as both nutraceutical ingredients and additives thanks to their strong antioxidant capacities, and are thus potentially useful for the development of products with enhanced nutritional value, potential health benefits, and long shelf-lives [1].

Among agro-food wastes, corn cobs are the main by-products generated during corn processing, and purple corn cobs are still lacking added-value applications [4]. Purple corns (*Zea mays* L.) are pigmented corn varieties from South America, mainly Peru and Bolivia, which have strong antioxidant properties thanks to their high anthocyanin content [5].

**Citation:** Ferron, L.; Milanese, C.; Colombo, R.; Pugliese, R.; Papetti, A. A New Polysaccharide Carrier Isolated from Camelina Cake: Structural Characterization, Rheological Behavior, and Its Influence on Purple Corn Cob Extract's Bioaccessibility. *Foods* **2022**, *11*, 1736. https://doi.org/10.3390/ foods11121736

Academic Editors: Jianhua Xie, Yanjun Zhang and Hansong Yu

Received: 23 May 2022 Accepted: 10 June 2022 Published: 14 June 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/).

Several studies have investigated the anthocyanin contents in purple corn extracts obtained from different tissues, i.e., kernel, cob, husk, and silk, and tested their bioprotective effects [6,7]. Husk and cob extracts are richer in anthocyanins than kernel extracts. Contents range from 0.49 to 4.6% and from 1.25 to 13.18% (*w*/*w* dry material) for cob and husk, respectively [7]; moreover, the husk and cob differ from the kernel by the presence of perlagonidin in their phytocomplex [8]. Moradyn is a new Italian purple corn variety obtained from a Peruvian corn line (Morado), and it is characterized by highly pigmented cobs. The extract obtained from Moradyn cob (MCE) is characterized by a phytocomplex rich in antioxidant compounds, such as anthocyanins, quercetin, and kaempferol derivatives, but a preliminary study highlighted that the bioaccessibility of these MCE polyphenols was markedly affected by digestion, leading to a decrease in bioactivity [8], as already reported for other natural extracts [9]; this behavior limits polyphenols bioavailability and their subsequent efficacy.

During the last five years, there has been growing interest in the application of encapsulation technology in order to entrap antioxidant compounds, protect them against environmental conditions during storage, extend their shelf lives, and enhance their bioavailability [10,11]. Different carriers have been employed, depending on the type and nature of core materials and on the targeted applications of the microencapsulated ingredients [10]. Several authors reported that vegetable polysaccharides such as Arabic gum, maltodextrins, inulin, and other purified native gums are carriers more stable, biocompatible, biodegradable, and versatile than proteins (which might be melted or denatured), since they better resist high temperatures (>40 ◦C) and pH changes [12]. In fact, their functional groups make them extremely versatile, as they can interact with a wide range of both hydrophilic and hydrophobic bioactive compounds. Examples are anthocyanin and quercetin derivatives which are consistent with water-based gel formulations, including gum, maltodextrin, and starch [13]. Moreover, polysaccharides are efficient at entrapping bioactives due to their high molecular weights and the presence of numerous functional groups in their structures [12]. In addition, among natural polysaccharides, gums have remarkable and specific rheological features, which have been strictly related to their biological properties and technological applications [5,14].

In our previous work, the polysaccharide fraction isolated from camelina cake (*Camelina sativa* L. Krantz) was selected as potential carrier for MCE, based on the high encapsulation efficiency values registered at 1:1 and 1:3 core/wall material ratios. Camelina sativa is an important seed oil crop belonging to the Brassicaceae family. It is cultivated worldwide, and its oil is a valuable and well-characterized source of unsaturated fatty acids, mainly linolenic and α-linoleic acids [15].

To the best of our knowledge, the potential application in the food industry of Camelina sativa's by-product has never been investigated, so the use of camelina cake polysaccharide fraction (CCP) as a carrier for MCE could represent a valuable technological innovation. Preliminary spectroscopic analysis performed both on CCP and on MCE encapsulated with CCP indicated that CCP is mainly characterized by mannose, arabinose, and rhanmose residues, and by the presence of a protein component with a random coil conformation, suggesting a gum-like composition [16] maintained after MCE addition. CCP also increased MCE shelf-life when used as a carrier at 50 and 75% *w*/*w* [17].

Therefore, considering these preliminary results, the aim of the present work was to determine the CCP's average molecular weight and rheological properties, since these physico-chemical and structural parameters are strictly related to the biological behavior of natural polysaccharides [16,18,19]. The relationship between the CPP's physico-chemical features and its stabilizing properties was evaluated by submitting a MCE-based ingredient to simulated gastrointestinal conditions (applying a slightly modified INFOGEST protocol) [20] and monitoring the MCE bioaccessibility index for thirteen selected markers. CCP hypocholesterolemic activity was assessed by testing its bile salt binding activity [21].

#### **2. Materials and Methods**

#### *2.1. Chemicals*

Ethanol (96% *v*/*v*), methanol, HPLC-grade acetonitrile, phosphoric acid (85% *w*/*v*), and sodium chloride were obtained from Carlo Erba (Milan, Italy). HPLC-grade formic acid, hydrochloric acid (37% *w*/*v*), Type VI-porcine pancreatic α-amylase, pepsin from porcine gastric mucosa (≥400 U mg−1), bile extract porcine, pancreatin (8 × USP) from porcine pancreas, sodium taurocholate (NaTC), sodium glycocholate (NaGC), sodium taurodeoxycholate (NaTCDC), sodium glycochenoxycholate (NaGCDC), protease from Streptomyces griseus type XIV (≥3.5 U mg−1), viscozyme L cellulolytic enzyme mixture, sodium azide, and cholesterolamine were provided by Merck KGaA (Darmstadt, Germany).

Water was obtained from a Millipore Direct-QTM system (Merck-Millipore, Milan, Italy).

Pullulan gel filtration chromatography standard kit was purchased from Waters Corporation (Milford, MA, USA).

#### *2.2. Camelina Cake Polysaccharide (CCP) Extraction*

Camelina cake was kindly provided by FlaNat Research Italia S.r.l. (Milan, Italy).

A CCP dried extract was prepared following the procedure previously optimized [17]. Briefly, the cake obtained from cold-press oil production was immediately soaked with water (1:10 solvent/raw material ratio) and extracted at 115 ◦C for 15 min. After filtration of the supernatant, CCP was precipitated by adding a 96% ethanol solution (1:2.5, *v*/*v*) at 4 ◦C overnight. Finally, the polysaccharide fraction was separated by centrifugation at 5000 rpm (Neya 8 ZFKN-39276, Remi Eletrotechnik LTD, Mumbai, India) for 10 min at 25 ◦C, freeze dried (Modulyo freeze-drier s/n 5101, 5 Pascal, Trezzano sul Naviglio, Italy), and then used in the experiments.

#### *2.3. Moradyn Cob Extract (MCE) Preparation*

Moradyn chopped cobs were kindly provided by FlaNat Research Italia S.r.l. (Milan, Italy) and extracted with 50% aqueous ethanol for 3 h at 50 ◦C. The extract (MCE) was filtered through 0.45 μm membrane filters (Merck-Millipore, Milan, Italy) and the organic solvent removed under reduced pressure at 40 ◦C (Buchi R-II, Büchi Labortechnik AG, Flawil, Switzerland) [8]. Finally, MCE was freeze-dried (Modulyo freeze-drier s/n 5101, 5 Pascal, Trezzano sul Naviglio, Italy) and used in the experiments.
