Valorization of Underutilized Mandarin Juice Byproduct Through Encapsulation of Flavonoids Using Freeze-Drying Technique

Featured Application

Encapsulation may be beneficial for citrus byproducts phenolics, according to low levels of bioactivity because of (i) unfavorable processing and storage conditions in food production and (ii) unfavorable conditions during transit through the gastrointestinal tract.

Abstract

This study evaluated Maltodextrin (MD), Gum Arabic (GA), and Carboxymethylcellulose (CMC) in different ratios as coating materials to encapsulate citrus pomace phenolic compounds. Citrus encapsulates were obtained by ultrasound-assisted extraction followed by the freeze-drying process and were characterized regarding the microencapsulation efficiency, physical, and chemical properties. Carrier material choice reflected a significant effect on encapsulation efficiency, phenolic compounds retention, and reconstitution properties of encapsulated extract. The encapsulation efficiency of prepared encapsulates ranked from 50.909% to 84.000%, and it was strongly dependent upon CMC addition. A wide range of reconstitution parameters (water absorption index-WAI and water solubility index-WSI) suggested possible release mechanism modifications. HPLC analysis revealed the presence of three main phenolic compounds, namely Hesperidin, Naringin, and Rutin. A wall material mixture of MD, GA, and CMC in the same proportions was optimal for freeze-drying. This combination resulted in encapsulates with a low moisture content (1.936 ± 0.012%) and a low water activity (0.110 ± 0.001), indicating prolonged stability. Based on the obtained results, freeze-drying as an encapsulation technique should be considered as a promising solution to recover compounds from industry byproducts and protect them from environmental and gastrointestinal circumstances.

1. Introduction

Polyphenols are a diverse group of naturally occurring compounds found in fruits, but in other parts of plants, they are widely known for their antioxidant, anti-inflammatory, antimicrobial, and other bioactivities. As bioactive compounds, polyphenols have gained significant attention due to their potential health benefits and protective effects against noncommunicable chronic diseases [1,2]. Citrus fruit is a rich source of polyphenols (phenolic acids, flavanones, flavanol, and flavones) [3]. Citrus fruit processing generates a significant number of byproducts, including peels, pulp, and rag, which are usually discarded. Despite the processing conditions, these byproducts are rich in polyphenols, which present an opportunity for their utilization. Transforming these byproducts into new products or materials both addresses environmental issues and produces new economic value [4,5]. Stability and bioavailability are recognized as one of the main challenges in utilizing polyphenols delivered from industry byproducts. Some phenolic compounds can easily degrade when exposed to elevated temperature, light, oxygen, and other non-desirable environmental conditions [6,7]. An increased number of authors recognized encapsulation as a possible solution to enhance the stability and preserve the bioactivity of polyphenol compounds [5,8,9,10]. Moreover, different combinations and modifications of encapsulating agents (coating) enable controlled, targeted, or postponed release of polyphenols from microcapsules or mask the unpleasant bitter and astringent taste [11,12,13]. On top of that, our previous results [12] showed that encapsulation using spray or freeze-drying can enhance the solubility and stability of phenolic compounds (hesperidin) and therefore broaden applications of phenolic compounds in food, food supplements, or pharmaceuticals. Many well-known techniques can serve as encapsulation techniques including spray drying, particle from gas-saturated solution processes, fluidized bed coating, coacervation, and freeze-drying [13,14,15]. Between various encapsulation techniques, freeze-drying has been recognized for effectively preserving heat-sensitive compounds [16]. Freeze-drying is an encapsulation technique based on the dehydration by sublimation of a liquid and semi-liquid mixture of core and carrier material. Carrier material (encapsulant) may be selected among various natural or synthetic materials, like Maltodextrins, dextrins, other polysaccharides, and gums. There are several requirements for compounds to be suitable for carrier material. Some of them are the ability to form films, desirable viscosity, safety, availability, low price, biocompatibility, and biodegradability [17,18]. The key feature of freeze-drying as an encapsulation technique is its performance at low temperatures where encapsulated compounds are not exposed to high temperatures, unlike spray-drying [19]. Despite the potential benefits, there is a lack of data on the encapsulation of polyphenols derived from mandarin juice byproducts using freeze-drying. Hu et al. [20] used a nanoencapsulation process to encapsulate mandarin peel polyphenols into whey protein coatings, while Mahdi et al. [21] used the same process for the encapsulation of mandarin essential oil. In an earlier study, Hu et al. [22] proved that during the encapsulation process, a synergistic effect between citrus peel extract and coating material (pectin) can occur and increase the bioaccessibility of phenolic compounds.

The aim of this study is to address this gap by conducting the encapsulation freeze-drying process to maximize polyphenol retention and evaluate the efficiency of encapsulation. For the first time, three encapsulating agents were compared and evaluated for valorization of underutilized byproducts. By exploring this approach, the study contributes to sustainable practices within the food industry, offering a novel method to enhance the value of mandarin juice byproducts.

2. Materials and Methods

2.1. Materials

Mandarin juice processing byproducts comprised of peel (flavedo and albedo), pulp (juice sac residue), and rag (membranes and cores) were obtained from Regius Company, Čapljina, Bosnia and Herzegovina immediately after processing (juice pressing). Samples were freeze-dried and stored in a dark place at 4 °C.

Carrier materials (Maltodextrin, DE:16-19; Gum Arabic, Carboxymethylcellulose) were obtained from Sigma-Aldrich, Saint Louis, MO, USA. Ethanol was obtained from JT Baker, Phillipsburg, NJ, USA. Standards used for HPLC analysis were obtained from Sigma-Aldrich and were of HPLC grade. All other chemicals were of analytical grade.

2.2. Citrus Pomace Extract: Obtaining and Characterization

Extraction of citrus polyphenols was performed using ultrasound-assisted extraction with optimal conditions defined by the study Montero-Calderon et al. [23] with a power of 400 W, temperature maximum of 40 °C using 50% aqueous ethanol solution (V/V) as a solvent, with 10 mL/g solvent solid ratio during 30 min of treatment. After the extraction procedure, the extract was filtered using vacuum filtration and concentrated using a rotary evaporator to remove ethanol. The concentration of the final extract was 74.72 mg/mL. The extract was characterized using UV-VIS spectrophotometer and HPLC.

2.3. Preparation for Encapsulation

Carrier materials were dissolved in the extract to achieve a concentration of 30% (w/V) according to the procedure described in Papoutsis et al. [24]. The prepared solution was homogenized for 60 min in a magnetic stirrer to achieve complete dissolution of carrier material. Three different carrier materials and a combination of them were used for the encapsulation of mandarin byproduct extract, as shown by the experimental plan in

Table 1. Experimental plan for encapsulating bioactive compounds from mandarin byproducts.

	Maltodextrin (MD)	Gum Arabic (GA)	Carboxymethylcellulose (CMC)	Abbreviation
1.	6	0	0	MD6
2.	0	6	0	GA6
3.	0	0	6	CMC6
4.	2	2	2	MD2GA2CMC2
5.	4	2	0	MD4GA2
6.	4	0	2	MD4CMC2
7.	0	4	2	GA4CMC2
8.	2	4	0	MD2GA4
9.	2	0	4	MD2CMC4
10.	0	2	4	GA2CMC4

. Prepared mixtures were frozen in the laboratory freezer FORMA™ 88,000 Series (Thermo Scientific, Waltham, MA, USA) at a temperature of −80 °C for 24 h.

2.4. Encapsulation Using Freeze-Dryer

Following the preparation procedure, the feed was placed in a freeze-dryer (the Alpha LCS Plus system, Christ, Osterode am Harz, Germany) for 48 h. Vacuum during the main drying was set for 0.250 mbar. The maximum shelf temperature reached was 18 °C. Afterward, prepared encapsulates were collected and stored in a desiccator until further analysis.

2.5. Physical Properties of Prepared Encapsulates

Physical properties (color changes, water solubility index, water absorption index, moisture, and water activity) were determined by established procedures described previously [12].

The color measurements of the encapsulates were determined using a colorimeter (CS-10 portable 8 mm, Smart Color Solutions, Haryana, India). The equipment was previously calibrated using white and black calibration plates. The samples were placed in Petri dishes and measured in three parallels to obtain L* (lightness), a* (redness/greenness), b* (yellowness/blueness), C* (chroma), and hue angle (°h) parameters.

AACC Method 88–04 was used to determine the water absorption index (WAI) and water solubility index (WSI) with minimal modifications reported previously [12]. A total of 0.8 g of encapsulates were mixed with 10 mL of water, left standing for 30 min with periodic mixing and centrifuged for 15 min at 5000 rpm. Separated supernatant was dried at 105 °C until a constant mass was reached. WAI and WSI experiments were done in duplicates, calculated using Equations (1) and (2) expressed as % for WSI and grams of water per gram of encapsulates for WAI.

$$WAI[g/g]={\displaystyle \frac{gell mass}{dry matter mass of the initial sample}}$$

(1)

$$WSI[\%]={\displaystyle \frac{weight of dry solids in supernatant}{dry weight of sample}} \times 100$$

(2)

The dry matter of the encapsulates was determined using a halogen moisture analyzer (Mettler Toledo HR73, Columbus, OH, USA). A total of 0.13 g of encapsulates was weighed on an aluminum plate and dried at 105 °C with switch-off criteria 5 (mass loss less than 1 mg in 140 s interval).

Water activity (a_w) was measured using a HygroPalm (Rotronic, Switzerland) at room temperature (22 °C). Approximately 10 g of the encapsulates was weighed into a special measuring cup and thermostated at room temperature (22 °C) under a cover for 10 min. Measurements were done in triplicate.

2.6. Encapsulation Efficiency Evaluation

Samples for calculating encapsulation efficiency were prepared following a previously established procedure by Tolun et al. [25]. Briefly, 15 mg of encapsulates was diluted with 3 mL of a 50:8:42, V/V/V ethanol/acetic acid solution, vortex mixed, and filtered through a 0.45 μm PTFE filter. Folin–Ciocalteu method was then applied to calculate the total phenolic content (TPC). 100 µL of Folin–Ciocalteu reagent, 40 µL of prepared solution, and 3160 µL of distilled water were combined. After 4 min of incubation, 300 µL of 20% (w/V) sodium carbonate was added and the mixture was incubated at 40 °C for 30 min. Gallic acid solutions (50–1000 mg/L) were used as a standard for establishing the calibration curve. The absorbance was measured at 765 nm in triplicates, and results are expressed as gallic acid equivalents. For the determination of surface phenol (SPC) content, 24 mg of encapsulates were washed for 5 min using 3 mL of ethanol/methanol (1:1, V/V) solution. The solution was filtered through a 0.45 μm PTFE filter and measured using the previously described Folin–Ciocalteu method.

Encapsulation efficiency (EE) was calculated using the following equation: Equation (3):

$$EE[\%]={\displaystyle \frac{TPC-SPC}{TPC}}$$

(3)

2.7. HPLC Analyses

The identification of individual phenolic compounds in encapsulates was performed by the high-performance liquid chromatography (HPLC) method with an injection volume of 20 μL. Samples were analyzed by HPLC (Agilent 1260 Infinity II (Agilent Technologies, Santa Clara, CA, USA), using a PLA detector (Maharashtra, India) (at 270 and 280 nm). Before analysis, encapsulates were extracted using a 50:8:42, V/V/V ethanol/acetic acid solution, vortex mixed, and filtered through a 0.45 μm PTFE filter. Separation was performed in an InfinityLab Inertsil ODS-3V (Noida, India) (250 × 4.6 mm inner diameter, 5 μm) column. The mobile phase was composed of solvent A (formic acid 0.1%) and solvent B (formic acid 0.1% in methanol). The elution was as follows: elution gradient started with 90% solvent A and 10% solvent B; solvent B is to reach 25% at 8 min, 45% at 25 min, and 80% at 45 min and then returned to the initial conditions by 10 min. The main phenolic compounds from encapsulates were identified by comparison against the retention times of the standards, their spectra, and the peak area of maximum absorption wavelength. OpenLab CDS software v. 2.5 (Agilent Technologies) was employed to process the chromatograms and spectra. Phenolic compounds were identified and quantified by measuring their absorption at characteristic wavelengths. All analyses were performed in triplicate.

2.8. Statistical Analysis

Data are presented as mean value ± SD of triplicate. Variances of mean values were statistically analyzed with a 95% confidence interval by one-way ANOVA followed by Tukey multiple comparisons HSD test using XLSTAT software 2014 1.04.

3. Results and Discussion

A total of 10 encapsulation experiments were carried out using three different coatings (MD, GA, and CMC) in varying proportions according to the experimental design described in Table 1. Visually, all obtained encapsulates were in the form of light yellowish-white free-flowing powder without agglomerate formation. Encapsulates quality is greatly affected by moisture content and water activity, significantly affecting shelf life. Water activity (a_w) refers to the availability of free water in a food system, and it is responsible for biochemical reactions. In contrast, moisture content refers to the water composition of the food system. In the present study, the moisture content in the obtained encapsulates varied from 1.854 to 4.027%.

The highest moisture level was recorded for encapsulates encapsulated using pure CMC. Even the CMC is well-known for its hygroscopic properties [26]. A combination of CMC and GA gave very low moisture content (2.036 and 1.854%), while in combination with MD the moisture values were something higher (2.532 and 3.394%). Papoutsis et al. [24] reported moisture values between 1.150% and 2.105% for encapsulates delivered from lemon byproducts and encapsulated using Maltodextrin, soybean protein isolate, and ι-carrageenan. Water activity values varied between 0.110 and 0.240. According to a_w values, all obtained encapsulates could be considered microbiologically and enzymatically stable since their water activity did not exceed 0.60 [27,28]. Functional rehydration properties of prepared encapsulated can be described by two properties, WAI and WSI, which are inversely proportional. In this study, both parameters were significantly affected by the addition of CMC to the carrier material, where the highest WAI values were obtained for pure CMC (11.316 g/g) and carriers with high levels of CMC (MD2CMC4 and GA2CMC4) (

Table 2. The physical properties of prepared citrus byproduct encapsulates.

Sample	Moisture Content (%)	Aw Value	WAI (g/g)	WSI (%)
MD6	2.410 ± 0.029 cde	0.170 ± 0.002 c	0.884 ± 0.042 f	77.233 ± 0.042 c
GA6	3.615 ± 0.281 ab	0.203 ± 0.006 b	0.354 ± 0.003 g	88.530 ± 0.003 b
CMC6	4.027 ± 0.000 a	0.207 ± 0.012 b	11.316 ± 0.104 a	7.113 ± 0.104 f
MD2GA2CMC2	1.936 ± 0.012 de	0.110 ± 0.001 e	6.580 ± 0.06 c	30.152 ± 0.06 e
MD4GA2	3.474 ± 0.009 ab	0.240 ± 0.001 a	1.302 ± 0.012 e	60.535 ± 0.012 d
MD4CMC2	2.532 ± 0.032 cd	0.180 ± 0.010 c	5.371 ± 0.049 d	32.093 ± 0.049 e
GA4CMC2	2.036 ± 0.016 de	0.180 ± 0.001 c	8.107 ± 0.074 b	8.169 ± 0.074 f
MD2GA4	2.695 ± 0.064 c	0.193 ± 0.006 bc	0.363 ± 0.003 g	98.257 ± 0.003 a
MD2CMC4	3.394 ± 0.189 b	0.203 ± 0.006 b	11.282 ± 0.102 a	8.935 ± 0.102 f
GA2CMC4	1.854 ± 0.057 e	0.140 ± 0.001 d	11.499 ± 0.100 a	6.267 ± 0.100 f

Values are expressed as mean ± standard deviation where different letters within the same column represent significant differences at p < 0.05. MD—Maltodextrin, GA—Gum Arabic, CMC—Carboxymethylcellulose, A_w—water activity, WAI—water absorption index, WSI—water solubility index.

). An increase in WAI (g/g) led conversely to a decrease in WSI (%) (Table 2). Aside from CMC content, the decrease in WSI can be attributed to moisture content. However, in this case, moisture level was shown to be highly dependent on CMC content. Namely, CMC has a unique chemical structure where -CH₂-COOH groups are attached to several hydroxyl groups of the cellulose units, which makes CMC soluble in water in contrast to insoluble cellulose [29]. High WSI values are especially desirable for application in the food and pharmaceutical industries, enabling even distribution and simple incorporation into the final product. On the opposite end, WAI values indicate immobilized water content and are more related to product microbial stability because with the increase in WAI values, the possibility of microbiological instability increases [30]. However, too high solubility can lead to undesirable fast release of core material. In general, formulations produced by freeze-drying have a more porous structure [31], which is the main reason for its high solubility properties. Nonetheless, solubility data presented in Table 2 indicate that with a careful selection of carriers, even encapsulates produced with freeze-drying can achieve a wide range of solubility, which could be suitable for controlled release. In our previous study [12], solubility of hesperidin encapsulates (pure or delivered from citrus peel) were between 88 and 99%. Lower-solubility parameters obtained in this study could be justified with CMC addition and higher WAI values. A similar trend was observed by Stabrauskiene et al. [19] for citrus paradisi extract encapsulated with different carriers with the addition of CMC.

Color coordinates of encapsulates are shown in

Table 3. CIELab colour parameters of the citrus byproduct encapsulates.

Sample	L	a*	b*	C*	°h	ΔE
MD6	80.073 ± 0.27 b	6.007 ± 0.43 ab	22.723 ± 0.404 cd	23.720 ± 0.468 cde	75.180 ± 0.865 e	17.875 ± 0.45 c
GA6	75.433 ± 1.032 cd	5.497 ± 0.403 bcd	24.557 ± 0.543 ab	25.033 ± 0.545 ab	77.377 ± 0.756 cd	21.867 ± 0.114 ab
CMC6	78.943 ± 0.105 b	3.743 ± 0.045 g	22.453 ± 0.215 d	22.837 ± 0.315 e	81.650 ± 1.897 a	18.025 ± 0.193 c
MIX2:2:2	83.253 ± 0.430 a	3.787 ± 0.012 g	19.170 ± 0.06 e	19.570 ± 0.108 f	78.443 ± 0.653 bc	12.842 ± 0.190 d
MD4GA2	73.107 ± 0.528 d	6.197 ± 0.042 a	24.960 ± 0.592 a	25.400 ± 0.06 a	75.863 ± 0.093 de	24.101 ± 0.100 a
MD4CMC2	77.703 ± 0.528 bc	4.917 ± 0.071 de	23.873 ± 0.07 abc	24.010 ± 0.265 bcde	78.173 ± 0.274 bc	20.022 ± 0.848 bc
GA4CMC2	74.900 ± 1.975 d	5.207 ± 0.284 cde	23.607 ± 0.823 bcd	24.200 ± 0.884 abcd	77.850 ± 0.238 bcd	21.750 ± 1.939 ab
MD2GA4	77.810 ± 0.626 bc	5.593 ± 0.099 abc	24.187 ± 0.482 ab	24.827 ± 0.475 abc	76.967 ± 0.333 cde	20.294 ± 0.742 bc
MD2CMC4	79.113 ± 0.641 b	4.103 ± 0.093 fg	22.727 ± 0.239 cd	23.097 ± 0.246 de	79.757 ± 0.172 ab	18.163 ± 0.515 c
GA2CMC4	78.387 ± 0.798 b	4.687 ± 0.257 ef	24.253 ± 0.551 ab	24.700 ± 0.589 abc	79.077 ± 0.359 bc	19.868 ± 0.551 bc

Values are expressed as mean ± standard deviation where different letters within the same column represent significant differences at p < 0.05. MD—Maltodextrin, GA—Gum Arabic, CMC—Carboxymethylcellulose.

. The total color differences (ΔE) between the control (mixture of carrier material in 2:2:2 ratio) and encapsulates were greater than three units. Consequently, those changes are detectable by the human eye, which only detects color differences when ΔE is greater than 3 [32]. The sample MIX2:2:2 exhibited the highest lightness value (83.253), while MD4GA2 had the lowest L value (73.107), making it the darkest encapsulate. The significant differences identified by Tukey’s HSD test (Table 3) suggest that the carrier choice significantly impacts the lightness of the encapsulates. Obtained encapsulates were lighter than those obtained with spray drying and MD, GA, and sodium caseinate as carriers by Moawad et al. [33]. This could be justified by high temperatures applied during spray drying and possible non-enzymatic browning (caramelization of polysaccharide carriers), which was avoided by low temperatures during freeze-drying in the present study. The “a” parameter indicates the red/green value, with positive values towards red and negative towards green. Sample MD4GA2 had higher a and b values, which means that those encapsulated tend to be red and yellow, which could also indicate lower encapsulation efficiency where more of the core material remains non-encapsulated (on the surface of encapsulates).

The encapsulation efficiency (calculated from total phenol content and surface phenols content) is shown in Figure 1. Encapsulation efficiency could be defined as the ability of the carrier material to encapsulate bioactive compounds. Also, it can be used as a determining factor for the integrity and porosity of produced encapsulates [34]. The encapsulation efficiency is affected by various parameters including carrier concentration, carrier solubility, as well as the rate of solvent evaporation during drying. The encapsulation efficiency of prepared encapsulates in this study ranged from 50.909% to 84.000%. Differences in encapsulation efficiency could be a result of polyphenol–carrier complex formation. According to Poomkokrak et al. [35] and Mazumder and Ranganathan [36], the formation of complex structures between phenolics and carriers (polysaccharides) depends on the molecular size and solubility of the carrier material. The highest encapsulation efficiency had an encapsulate prepared with all three carriers in the same proportions (MD2GA2CMC2), while the lowest had a sample prepared with pure MD.

Additionally, a positive correlation between EE and WAI (r = 0.72, p = 0.01) and a negative between EE and WSI was observed, which could be explained by the CMC content in the carrier material. Namely, a slight positive correlation between CMC content and encapsulation efficiency was also observed (r = 0.69, p = 0.01). Surprisingly, there was no correlation between total color changes and encapsulation efficiency. However, upon comparing individual color properties a significant dependence between redness value (a) and encapsulation efficiency was observed. With an increase in the redness of the sample, a decrease in encapsulation efficiency was observed with a negative correlation of (r = −0.78, p = 0.01). This phenomenon is caused by lower encapsulation efficiency where more of the core material remains on the surface. It is evident that the increase of CMC in carrier material promotes encapsulation efficiency.

Retention of phenolic compounds was evaluated using spectrophotometric assay and HPLC analysis. Obtained encapsulates showed a high phenolic retention rate ranked from 5.641 to 12.821 mg/g. The highest retention rate had a sample encapsulated with a mixture of all three carriers in the same proportion (MD2GA2CMC2), while the lowest had a sample encapsulated with pure MD (MD6). The content of three major phenolic compounds (hesperidin, naringin, and rutin) was measured using HPLC and presented in

Table 4. Phenolic compound retention in citrus byproduct encapsulates.

Sample	TPC (mgGAE/g)	Hesperidin (mg/g)	Naringin (mg/g)	Rutin (mg/g)
Core extract	24.808 ± 0.041	8.399 ± 0.010	8.318 ± 0.009	3.551 ± 0.004
MD6	5.641 ± 0.001 j	1.010 ± 0.000 j	1.398 ± 0.001 h	0.816 ± 0.000 e
GA6	7.846 ± 0.003 i	1.668 ± 0.002 h	2.064 ± 0.001 f	1.584 ± 0.001 b
CMC6	11.128 ± 0.002 b	2.826 ± 0.003 a	3.098 ± 0.002 a	0.250 ± 0.000 f
MD2GA2CMC2	12.821 ± 0.002 a	2.246 ± 0.003 c	2.402 ± 0.001 d	0.208 ± 0.000 g
MD4GA2	8.000 ± 0.002 h	1.444 ± 0.001 i	1.912 ± 0.001 g	1.134 ± 0.002 d
MD4CMC2	9.795 ± 0.003 e	2.246 ± 0.004 b	2.464 ± 0.002 c	0.202 ± 0.000 h
GA4CMC2	9.897 ± 0.001 d	1.816 ± 0.001 g	2.090 ± 0.002 e	1.590 ± 0.001 a
MD2GA4	9.949 ± 0.001 c	2.050 ± 0.002 e	2.592 ± 0.002 b	0.184 ± 0.000 i
MD2CMC4	9.282 ± 0.001 g	1.886 ± 0.001 f	2.091 ± 0.001 e	1.230 ± 0.002 c
GA2CMC4	9.641 ± 0.002 f	2.164 ± 0.002 d	2.406 ± 0.002 d	0.156 ± 0.001 j

Values are expressed as mean ± standard deviation where different letters within the same column represent significant differences at p < 0.05. MD—Maltodextrin, GA—Gum Arabic, CMC—Carboxymethylcellulose, TPC—total phenol content, GAE—gallic acid equivalents.

. Hesperidin was ranked from 1.010 to 2.826 mg/g, naringin from 1.398 to 2.592 mg/g, and rutin from 0.156 to 1.590 mg/g. Hesperidin and naringin are phenolic compounds well-known for their hydrophobic and low-soluble properties. Those properties limit their bioavailability and application in the food and cosmetic industry [37]. However, encapsulation with hydrophilic carriers can enable better physical properties, as proven previously. Retention of hesperidin was dependent on carrier usage (particularly, CMC content), where an increase in CMC led to higher hesperidin retention. A similar trend for naringin content and CMC as a carrier can be observed [38,39]. It was previously shown that CMC can complex with phenolic compounds, enhancing physical properties and reducing interaction with proteins (reducing astringency). Hesperidin content also positively correlated with encapsulation efficiency (r = 0.86, p = 0.01), indicating that the main encapsulated phenolic compound is hesperidin while other phenolic compounds could be distributed on the surface of the encapsulates. Although an increase in carrier material can lead to the dilution of core material, surprisingly, other authors reported an increase in encapsulation efficiency probably due to an increase in the thickness of microparticle shell walls [40].

4. Conclusions

Encapsulated polyphenols from citrus byproducts showed promising potential for use as a functional food due to their high polyphenol encapsulation efficiency, appealing color, and low water activity. The encapsulation efficiency of the prepared encapsulates was found to be strongly dependent on the addition of CMC and varied greatly between 50.909% and 84.000%. This observation suggests that CMC could potentially be used to modulate the controlled release of the encapsulated material. Further studies are required to gain a better insight into the structure of encapsulates and thermal properties. The focus of these studies should be on the stability of encapsulates in food products and simulated gastrointestinal conditions. Also, additional analyses (LC-MS) could be beneficial to confirm the presence of minor phenolic compounds, which could contribute to biochemical and physical properties of citrus byproduct encapsulates.