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Article

Technology for Apple Pomace Utilization within a Sustainable Development Policy Framework

by
Paweł Sobczak
1,
Rafał Nadulski
1,*,
Zbigniew Kobus
2 and
Kazimierz Zawiślak
1
1
Department of Food Engineering and Machines, University of Life Sciences, Głęboka 28, 20-612 Lublin, Poland
2
Department of Technology Fundamentals, University of Life Sciences, Głęboka 28, 20-612 Lublin, Poland
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(9), 5470; https://doi.org/10.3390/su14095470
Submission received: 7 March 2022 / Revised: 27 April 2022 / Accepted: 29 April 2022 / Published: 2 May 2022
(This article belongs to the Special Issue Emerging Trends and Sustainable Production in Agricultural Engineering)
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Abstract

:
The aim of this study was to develop a concept, within the framework of sustainable agriculture, for utilizing apple pomace as a valuable raw material in food production. The proposal includes a description of the production technology of four food products together with the characteristics of their chemical composition, wholesome compounds, and physical properties. These new products were developed on the basis of apple pomace and wheat bran. In the developed technology, heat treatment in a convection oven, treatment with infrared radiation, and two types of barothermic treatments, i.e., extrusion and granulation, were implemented as the principal methods. All of the proposed technologies allow for the use of pomace for the production of food products to be made directly in the home plant and are relatively easy to implement in small processing facilities. It was found that the product consisting of fragmented apple pomace (mass fraction: 75%) and wheat bran (mass fraction: 25%), obtained using infrared radiation treatment, had the greatest value in terms of wholesome characteristics among the products obtained. This product had high contents of fiber and simple sugars, the highest content of polyphenols among the obtained products, and the ability to scavenge free radicals. It was also the only one with partially preserved vitamin C. The proposed method for processing pomace for food is in line with the sustainable agriculture movement.

1. Introduction

Poland, as a top producer of apples, is the first in the European Union and fourth in the world, after China, the USA, and Turkey [1]. Apples are a source of many valuable compounds with proven antioxidant, antibacterial, antiviral, anti-inflammatory, anti-allergic, and even anticancer properties [2,3,4]. Apples (Malus domestica) contain, on average, 85% water, 12–14% carbohydrates, approximately 0.3% proteins, a small amount of fats (< 0.1%), and also minerals and vitamins [5,6,7]. The chemical composition of apples depends on their variety, ripeness at the time of the harvest, conditions and place of cultivation, and environmental conditions [8,9].
The main aim of apple processing is the production of juice and its concentrate. The process of juice production can be supported by the use of various forms of pretreatment [10]. The waste produced after pressing apple juice is called pomace. Its quantity depends primarily on the technical and technological conditions of the processing as well as the characteristics of the fruit variety, which may vary from 10% to 40% of the input material [11,12]. The estimated quantities of apple pomace production in the top countries are as follows: China, 1,000,000 tons [13]; USA, 27,000 tons [14]; Poland, 240,000 tons [15]. The use of enzymatic treatment and an appropriate pressing machine can increase the process efficiency rate close to 90% and, thereby, reduce the amount of generated pomace. However, the use of enzymes for pulp liquefaction results in partial degradation of the anthocyanins and other polyphenols [16,17]. Therefore, the use of enzymatic treatment in the production of juices raises consumer concerns, and contemporary trends indicate an increase in the production of juices pressed without this form of treatment. Currently, the processing of apples for juices is also carried out by local processing plants run by producer groups of farmers. This is consistent with the modern concept of sustainable agriculture. In small processing facilities, press cake obtained after pressing is characterized by, among others, higher moisture content as compared with the pomace obtained under industrial conditions after initial enzymatic treatment and pressed using a basket press with drainage tubing.
In general, pomace is an unstable material with a relatively high water content and, thus, is susceptible to the development of microflora. Pomace is problematic for processing plants but, at the same time, is a cheap raw material suitable for further processing. Apple pomace is a heterogeneous mixture composed of various fractions such as fragmented peel and pulp (95%), seeds (2–4%), and stems (1%) [18,19]. The share of individual fractions in the pomace depends on the biological (morphological) characteristics and technological conditions [20]. Apple pomace contains many valuable ingredients, such as saccharides, proteins, minerals, pectin, dietary fiber, polyphenols, organic acids, and vitamins (including vitamin C) [21]. According to Antonic et al., the nutrient composition of dried apple pomace is as follows: moisture 3.97–9.75 g/100 g; fat 0.26–8.49 g/100 g; protein 1.2–6.91 g/100 g; fructose 11.5–49 g/100 g; glucose 2.5–22.7 g/100 g; TDFs (total dietary fibers) 26.8–82.0 g/100 g; pectin 3.5–14.32 g/100 g; total polyphenolics 0.17–0.99 g/100 g; malic acid 0.05–3.28 g/100 g; sodium 2–200 mg/100 g; potassium 449 mg/100 g; calcium 50–150 mg/ 100 g; ash 0.5–4.29 g/100 g; phosphorus 50–950 mg/100 g; magnesium 20–45 mg/ 100 g; iron 2.4–23 mg/100 g; zinc 0.22–1.5 mg/100 g; copper 0.11–0.22 mg/100 g; manganese 0.61–0.9 mg/100 g [22].
Due to the chemical composition, apple pomace has found widespread use in the food processing industry [23]. Utilization of pomace for food purposes includes the production of jams and marmalades, alcoholic drinks, vinegar, lactic acid, citric acid, pectin and pectin preparations, fiber preparations, dyes, fruit teas, filling preparations used in baking, confectionery and meat industries, enzymes (on the pomace substrate), as well as polyphenols [23,24,25]. In addition, pomace is used for fodder purposes (fresh or as silage and, after drying, as a component of compound feed) [26,27] and to produce energy in the form of biogas or ethanol, i.e., a component of biofuels [28,29]. Pressed pomace can also be used for the production of consumer products or energy [30]. Despite many initiatives undertaken in the field of pomace management, a significant part of it still goes to waste landfills and, thus, to soil and groundwater [31]. Composting causes secondary environmental pollution through the production of greenhouse gases. The development of micro-organisms, including pathogenic ones, and uncontrolled fermentation, pose a threat to public health. Undeveloped and perishable pomace, due to the need for its quick disposal, is a major problem for processing companies. Apple pomace has a high nutritional value; therefore, it is advisable to process it for food purposes.
Due to the high water content, pomace requires preservation by drying or, less often, by freezing. Dried or frozen apple pomace is a raw material used for the production of other products, often in another plant. The high energy demand (drying or freezing), as well as the additional transport and storage costs, make this an uneconomical method. It is, therefore, necessary to develop methods of in situ utilization of pomace. Proper management of pomace is one of the methods of reducing environmental pollution and, at the same time, fits into the concept of sustainable agriculture.
The research aim was to develop the concept of apple pomace utilization as a valuable raw material in food production. The concept includes a description of the production process of four products intended for food production together with the characteristics of the chemical composition, wholesome compounds, and physical properties of the obtained products.

2. Materials and Methods

2.1. Preparation of apple pomace samples for testing

The study was conducted on pomace obtained from five varieties of apples: Szampion, Idared, Ligol, Red Jonaprince, and Redchief. The apples were purchased from Zrzeszenie Producentów Owoców Stryjno-Sad (English: the Association of Fruit Producers Stryjno-Sad) based in Kawęczyn near Piaski (GPS coordinates: 51°9′56.0″ N, 22°50′49.1″ E), which brings together fruit growers specialized in the production of apples and pears. The tests were performed on raw material after two months of storage in a controlled atmosphere cold storage (temperature 1.6–2.2 °C; oxygen 1.6%; carbon dioxide 2.2%; 96.2% nitrogen). As recommended, the study was conducted using raw materials close to consumer maturity [32]. Healthy apples with no mechanical damage were washed and then dried. Fruits were fragmented with a machine shredder MKJ250 (Spomasz Nakło, Poland) using a standard shredding disc with 8 mm holes. The resulting mash, divided into portions weighing 300 g, was placed in cloth bags. The pressing process was carried out on the pulp and was not subjected to enzymatic treatment. Juice extraction was carried out using a laboratory self-constructed basket press with a capacity of approximately 1000 mL [10]. The press allowed for a process efficiency of between 60% and 70%, i.e., within the range typical of small-scale processing plants run by producer groups of farmers. The pulp was subjected to a loading force until it reached approximately 50 kN, and then the pressing process was terminated. The obtained juice was collected in bottles while the pomace was collected in plastic containers. Before further examination, the pomace was stored in a refrigerator at a temperature of approximately 4 °C for 2 days. Before the next stage of the research, the pomace originating from different apple varieties was thoroughly mixed.

2.2. Concepts of food products

As part of the experiment, four technologies were developed (proposed) for the production of foodstuffs out of pomace and wheat bran by means of thermal treatment. In the research, a mixture of pomace was used that had been obtained from the mash pressing of individual apple varieties. Table 1 shows in detail the chemical composition of the pomace mixture used in the study.
The data from Table 1 show that the chemical composition of the pomace allows for its use as a functional ingredient of food that increases the nutritional value thereof.
For the preparation of food products, apple pomace and wheat bran, produced by Sante company, were used. The basic nutrient content of 100 g of wheat bran is as follows: protein, 16 g; fat, 4.8 g; carbohydrates, 19 g; dietary fiber, 43.6 g (Sante, Warsaw, Poland).
Product PI was based on shredded apple pomace and wheat bran. It was prepared with the use of heat treatment in an oven. For the preparation of the product, pomace and wheat bran were used in the following ratio: 1 part wheat bran to 3 parts pomace. In this process, apple pomace was shredded with a model R2A knife cutter (Robot Coupe, Montceau-en-Bourgogne, France) with a bowl capacity of 3 L, mixed with bran using a Universal Mixer Caterina (Inoxpa Banyoles, Spain) with a bowl capacity of 8 L and mixer speed of 125 rpm, for 10 min until a homogeneous texture was obtained. The resulting product was heat-treated in a convection oven, model XV303G (UNOX, Cadoneghe (PD), Italy), without added steam, at the temperature of 200 °C for 15 min. Afterward, the product was cooled in ambient conditions. The resulting product could be used either directly for consumption or as an additive to mixtures of a crunchips type. A simplified flowsheet of the preparation process is shown in Figure 1.
Product PII was based on shredded apple pomace and wheat bran. It was prepared with the use of heat treatment in an infrared radiator. For the preparation of the product, pomace and wheat bran were used in the following ratio: 1 part wheat bran to 3 parts pomace. In this process, apple pomace was shredded with a model R2A knife cutter (Robot Coupe, Montceau-en-Bourgogne, France) with a bowl capacity of 3 L, mixed with bran using a Universal Mixer Caterina (Inoxpa, Banyoles, Spain) with a bowl capacity of 8 L and a mixer speed of 125 rpm for 10 min until a homogeneous texture was obtained. The heat treatment was conducted by means of a device emitting infrared radiation. The radiation source consisted of a set of two infrared lamps with 300 W each. The infrared radiation treatment was carried out at a temperature of 140 °C for 10 min. After the treatment, the product was cooled at ambient temperature. A simplified process flowsheet is shown in Figure 2.
Product PIII consisted of pellets made out of shredded apple pomace and wheat bran. In the granulation process, mixtures subjected to pressing through matrix holes must have adequate humidity; therefore, for the preparation of the final product, apple pomace and wheat bran were mixed in the following ratio: 1 part pomace to 3 parts wheat bran. Apple pomace was shredded with a model R2A knife cutter (Robot Coupe, Montceau-en-Bourgogne, France) with a bowl capacity of 3 L, mixed with bran using a Universal Mixer Caterina (Inoxpa, Banyoles, Spain) with a bowl capacity of 8 L and a mixer speed of 125 rpm for 10 min until a homogeneous texture was obtained. After conditioning, the mixture was granulated on granulation line using a pellet mill RMP 250 (MÜNCH-Edelstahl GmbH, Hilden, Germany). The pellet press had the following parameters set for the granulation: compression ratio of the matrix (length-to-diameter ratio of the hole in the die), 15; number of incisions in the roller made parallel to the axis, 48; number of rollers, 2. Steam for conditioning was produced in an LW 81 steam generator (Protocolet sp. z o.o., Konstantynów Łódzki Poland) with an output of 45 kg·h−1 and a pressure of 0.5 MPa. The obtained pellets were cooled to ambient temperature. A simplified process flowsheet is shown in Figure 3.
Product PIV consisted of food extrudate made out of shredded apple pomace and wheat bran. For the preparation of the final product, pomace and wheat bran were used in the following ratios: 1 part pomace to 3 parts wheat bran and 1 part pomace to 1 part wheat bran. Apple pomace was shredded with a model R2A knife cutter (Robot Coupe, Montceau-en-Bourgogne, France) with a bowl capacity of 3 L, mixed with bran using a Universal Mixer Caterina (Inoxpa Banyoles, Spain) with a bowl capacity of 8 L and a mixer speed of 125 rpm for 10 min until a homogeneous texture was obtained. After conditioning, both mixtures were extruded in a single-screw extruder model S-60 (Spomasz, Poland). For extruding, a die with 8 mm diameter holes was used. The temperature of the section was 70 °C, while the temperature of the head was 150 °C. The obtained pellets were cooled to ambient temperature. A simplified process flowsheet is shown in Figure 4.

2.3. Methodology of the chemical research

2.3.1. Sugar

The content of glucose, fructose, sucrose, and sorbitol was determined using HPLC with a refractive index detector [33].

2.3.2. Protein

The protein content was determined using the Kjeldahl method (Method AACC 46-08) [34].

2.3.3. Fat

The fat content was determined using the Soxhlet method (AACC 30-10) [34].

2.3.4. Dietary fiber

The total (i.e., soluble and insoluble) dietary fiber content (TDF) was measured using the enzymatic–gravimetric method (AACC 32-05 AACC 32-07) [34].

2.3.5. Vitamin C

The vitamin C content was determined using the HPLC method [35].

2.3.6. Extraction of polyphenols

Extraction was performed in a Soxhlet extractor. Ten grams of the powdered samples were extracted by 150 mL of methanol for 6 h. The collected extract was centrifuged and stored for further analyses at a temperature of 4 °C.

2.3.7. Polyphenols

The content of polyphenolic compounds was measured using a spectrophotometric determination in the presence of Folin–Ciocalteu reagent in accordance with the modified Singleton method [36] presented in the work by Wilczyński et al. [11].

2.3.8. Antioxidant activity

The antioxidant activity of the extracts obtained from apple pomace was evaluated using a free radical DPPH (2,2-diphenyl-1-picrylhydrazyl) assay according to the method presented by Wilczyński et al. [11].

2.3.9. Ash

The ash content was determined by the gravimetric method (AACC Method 08-01) [34].

2.3.10. Moisture content

The moisture content of the pomace and obtained products was measured with a moisture analyzer (MAC 210/NH Radwag, Radom, Poland). Samples weighing 5 g were dried at 105 °C, after which, the changes in the water content of the samples were not recorded by the device.
In the case of the chemical tests, each measurement was performed in three repetitions.

2.4. Methodology of testing physical characteristics of the products

Analysis of physical properties included determining the basic physical characteristics of the selected products. The angle of repose, cone angle, bulk density, tapped density, and average particle size were determined by standard methods [37], while the hardness and cutting force were determined in a compression test using a texture analyzer (TA.XT Stable Micro Systems, Godalming England).
In the case of the physical property analysis, each measurement was performed in five repetitions.

2.5. Statistical analysis of the results

Statistical analysis was performed with Statistica 12 software (StatSoft, Inc., Tulsa, OK, USA) [38] using one-way analysis of variance. The significance of differences between mean values was determined using Fisher’s test at p < 0.05. Test results are presented in tables and as graphical charts. Mean values’ standard deviations are provided.

3. Result and discussion

3.1. Physical properties of the obtained products

The photographs (Figure 5) depict the obtained products. The resulting products were characterized by varied physical properties. The obtained products were diverse in terms of their structure.
Table 2 and Table 3 summarize the basic physical characteristics of the obtained products.

3.2. Chemical composition of the obtained products

The total sugar content varied significantly for particular products (Figure 6). The highest total sugar content was measured for two of the products, viz. product PI and PII, for which the total sugar content was, respectively, 22.4 g/100 g and 22.9 g/100 g. The lowest content of total sugar was noted for product PIII (5.8 g/100 g). The highest content of simple sugars was determined for product PII (fructose, 12.5 g/100 g; glucose, 6.5 g/100 g). Products PIII and PIV were characterized by a similar amount of fructose, while their glucose content varied noticeably. In the case of product PIII, the glucose content was only 1.9 g/100 g, and it was over 6.5 times lower than in product PII. Glucose is the sugar most easily absorbed by humans, and it is used as an essential substrate for basic energy processes. A high level of sucrose in food poses a high risk of obesity and type 2 diabetes. Thus, from a dietary point of view, products with a low glycemic index should be preferred. Research by Milner et al. [39] shows that the addition of pomace and whey to sweet pastries can significantly reduce the sucrose content in the finished product while maintaining its acceptable sweetness. In our study, the sucrose content in particular products varied significantly and was within the range from 1.57 to 7.1 g/100 g (Figure 6). Product PIV was characterized by the lowest sucrose content.
Fructose, which is present in apple pomace, is a simple sugar, sweeter than sucrose, and with a lower glycemic index, thanks to which apple pomace can be used as a potential sweetener. The studies by Alongi et al. [40] show that it is possible to lower the glycemic index of sponge-cake-like products by replacing part of the wheat flour with dried apple pomace. Among the obtained products, product PII was characterized by the highest fructose content, which allows for assuming that it will be characterized by a reduced glycemic index.
According to the data presented in Figure 7, products PI and PII had a similar sorbitol content of approximately 1 g/100 g, whereas, in the case of products PIII and PIV, it was approximately 40% lower. From the nutritional point of view, the level of sorbitol present in the obtained products was not relevant.
In general, apples and apple pomace have a low protein and fat content. Hence, low levels of both protein and fat were observed in the obtained products. The data in Figure 8 indicate that the three obtained products (PI, PII, and PIV) had a similar protein content of 12.44–13.58%. Only product PIII had a significantly lower protein content (8.78%). In turn, product PIV had a fat content almost 25% higher than products PI and PII, while product PIV was characterized by the lowest fat content, lower by approximately 40%, as compared to products PI and PII. Research by Reis et al. [41] indicate that the addition of pomace reduces the protein and starch content in baked scones.
From the data presented in Figure 9, it can be seen that the dietary fiber content varies depending on the product. The highest dietary fiber content of about 35% was measured in the case of two products, viz. PI and PII. The remaining products (i.e., PIII and PIV) have more than three times lower fiber content. The dietary fiber present in apple pomace consists of well-balanced soluble and insoluble fiber fractions, represented by components of higher quality as compared to those of common cereal products [42]. Therefore, apple pomace may be a source of relatively good quality dietary fiber in final food products. This was confirmed by a study by Malik et al. [43] that indicated that the addition of pomace significantly increased dietary fiber content (TDF) in the finished product (14.2%), as compared to the control sample (0.47%). Torbica et al. [44] propose the use of an extrusion process in the production of sponge cakes based on maize flour and apple pomace. According to the researchers, from a nutritional point of view, sponge cakes made with the addition of pomace had improved characteristics thanks to their higher total dietary fiber content, as compared with the control sample of wheat sponge cake. A study by Mir et al. [45] indicated that the addition of apple pomace to gluten-free brown rice crackers resulted in a significant increase in fiber content and an increase in antioxidant activity. Obtained as part of our research, products PI and PII, made from mixtures containing three parts of pomace and one part of wheat bran, were characterized by a significantly higher content of dietary fiber, as compared to products PIII and PIV, made from mixtures containing one part pomace and three parts wheat bran.
According to research by Gorinstein et al. [46], apple pomace is characterized by a relatively high mineral content (Ca, Na, K, P, and Mg) as well as essential trace element content (Fe, Cu, Zn, and Mn). The content of minerals depends on the variety of apples from which the pomace was obtained. A higher ash content indicates a higher content of minerals in the product. Products PI and PII were made with a higher share of pomace, as compared to products PIII and PIV, hence, the higher ash content. The results of our research show that in products PI and PII, ash content was at a similar level and, at the same time, was about two and a half times higher than the ash content in products PIII and PIV (Figure 10). The lowest content of minerals characterized products PIII and PIV, viz. the products obtained through barothermic treatment (extrusion and pelletizing). In the mixture composition of these products (i.e., PII and PIV), pomace accounted for 25% of the total weight, as compared to products PI and PII, in which pomace accounted for 75% of the total weight.
Vitamin C is a thermolabile vitamin; thus, it degrades during thermal treatment. According to the study, the applied thermal treatment using infrared radiation (product PII) did not result in complete degradation of vitamin C. The content of vitamin C in product PII was 3.07 mg/100 g, while in the case of products PI, PII, and PIV, the presence of vitamin C was not detected.
The obtained products were characterized by varied polyphenol contents (Figure 10a). The results show that product PII had, unquestionably, the highest polyphenol content. In this case, the content of polyphenols was approx. four times higher compared to products PIII and PIV. At the same time, product PI had a 41.4% lower content of polyphenols when compared with product PII. Leyva-Corral et al. [47] subjected a mixture of oat flour, apple pomace, and potato starch, with varied moisture contents, to extrusion using a single screw extruder under different process temperatures. They established that, in comparison with the untreated mixture, the retention in the resulting product ranged from 79.9 to 97.1% of the total polyphenol content. Sudha et al. [48] showed that cakes made with apple pomace were characterized by a higher content of polyphenols, dietary fiber, and antioxidant activity. This is consistent with the results of our research. The results of our research and those mentioned above suggest the possibility of using an extrusion technique in processing pomace for consumption purposes.
In turn, a study by Drozd et al. [49] on extruded snacks shows that the addition of apple pomace as a partial substitute for corn porridge led to a significant increase not only in the polyphenols content but also in antioxidant activity. Our research showed that the highest antioxidant activity (69.1%) was characteristic of product PII obtained using the processing technique involving infrared radiation (Figure 10b). When compared to product PII, the antioxidant activity of product PI was 36.2% lower. For other products (i.e., PIII and PIV), the antioxidant activity was on a similar level at approximately 32%. A study by Reis et al. [34] also confirmed the beneficial effect of the addition of apple pomace on the antioxidant activity of the obtained final products, such as extruded snacks and baked scones. Our products PI and PII, containing a higher share of pomace as compared to products PIII and PIV, were characterized by higher antioxidant activity. This is consistent with the results of the studies by Singh et al. [50], who found a significant increase in antioxidant activity and fiber content in the snack containing apple pomace, skimmed soybean flour, and cornmeal made with the single-screw extrusion method.
Based on the results, it can be concluded that the products obtained by us, made with the addition of pomace, varied in terms of chemical composition. According to the studies, the manner in which particular products were manufactured largely determined their chemical composition. The proposed methods of the products’ preparation were based on thermal and barothermal treatment. The results of the research indicate that product PII, obtained with the use of infrared radiation as the heat treatment, was the most advantageous in terms of maintaining wholesome characteristics.

4. Conclusions

The research resulted in the development of four food products (components) with wholesome properties. The developed technologies allows for utilizing apple pomace for the manufacture of food products directly in the home plant. At the same time, it was shown that the processing method (technology) affected the content of the wholesome properties of the final product. Based on the obtained results, it can be concluded that, taking into account pro-health characteristics, product PII has the greatest value. This was the product consisting of shredded apple pomace (mass fraction of 75%) and wheat bran (mass fraction of 25%) obtained by heat treatment using infrared radiation. The proposed manufacturing technology for manufacturing product PII is relatively simple and feasible to implement in small processing plants operating locally, even at an agricultural farm level. In conclusion, all of the proposed solutions allow the reduction of weight of the waste generated by apple processing for juices, which may increase the financial efficiency of a processing plant. At the same time, these solutions are in line with modern trends in organic food processing.

Author Contributions

Preparation of manuscript, R.N., P.S., and Z.K.; conceptualization, R.N., P.S., K.Z., and Z.K.; methodology, R.N., P.S., and Z.K.; supervision, R.N. and K.Z.; investigation, R.N., Z.K., P.S., and K.Z.; writing—original draft, R.N. and Z.K.; writing—review and editing, P.S. and K.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Technological diagram of the production process of a food product out of pomace and wheat bran with a heat treatment in an oven (Product I).
Figure 1. Technological diagram of the production process of a food product out of pomace and wheat bran with a heat treatment in an oven (Product I).
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Figure 2. Technological diagram of the production process for making food products out of pomace and wheat bran with infrared heat treatment (Product II).
Figure 2. Technological diagram of the production process for making food products out of pomace and wheat bran with infrared heat treatment (Product II).
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Figure 3. Process flowsheet of the production process of pellets made out of wheat bran and apple pomace (Product III).
Figure 3. Process flowsheet of the production process of pellets made out of wheat bran and apple pomace (Product III).
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Figure 4. Process flowsheet of the production of an extruded food product made out of wheat bran and apple pomace (Product IV).
Figure 4. Process flowsheet of the production of an extruded food product made out of wheat bran and apple pomace (Product IV).
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Figure 5. Pictures of the obtained products: (a) product PI; (b) product PII; (c) product PIII; (d) product PIV.
Figure 5. Pictures of the obtained products: (a) product PI; (b) product PII; (c) product PIII; (d) product PIV.
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Figure 6. Sugar content in the obtained products: fructose (a); glucose (b); sucrose (c); total sugar (d). a,b,c,d Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
Figure 6. Sugar content in the obtained products: fructose (a); glucose (b); sucrose (c); total sugar (d). a,b,c,d Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
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Figure 7. The content of sorbitol in the obtained products. a,b Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
Figure 7. The content of sorbitol in the obtained products. a,b Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
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Figure 8. Protein (a) and fat (b) content in the obtained products. a,b,c Values in a column marked with the same letter are not statistically significantly different (p > 0.05).
Figure 8. Protein (a) and fat (b) content in the obtained products. a,b,c Values in a column marked with the same letter are not statistically significantly different (p > 0.05).
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Figure 9. Total dietary fiber content and ash content of the obtained products. a,b Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
Figure 9. Total dietary fiber content and ash content of the obtained products. a,b Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
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Figure 10. Total polyphenol content (a) and the ability to scavenge free radicals (b) in the obtained products. a,b,c Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
Figure 10. Total polyphenol content (a) and the ability to scavenge free radicals (b) in the obtained products. a,b,c Values in a column marked with the same letter were not statistically significantly different (p > 0.05).
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Table
Table 1. The chemical composition of the pomace mixture used in the study.
Table 1. The chemical composition of the pomace mixture used in the study.
SizeValue
Total sugars, g/100 g7.465 ± 0.32
Fructose, g/100 g5.148 ± 0.13
Sucrose, g/100g0.583 ± 0.03
Glucose, g/100 g1.733 ± 0.11
Sorbitol, g/100 g0.314 ± 0.26
Protein, %1.979 ± 0.07
Fat, %0.810 ± 0.41
Dietary fiber, %5.336 ± 0.11
Vitamin C, mg/100 g2.545 ± 0.03
Ash, %3.843 ± 0.23
Polyphenols, mg GAE/100 g45.08 ± 2.48
Antioxidant activity, %49.57 ± 2.73
Dry matter content, %18.1 ± 1.01
Table
Table 2. Physical properties of products PI and PII.
Table 2. Physical properties of products PI and PII.
ProductProduct
Moisture
Content
(%)		Angle of Repose
(°)		Cone Angle
(°)		Bulk Density (kg/m3)TAPPED Density (kg/m3)Average Particle Size
(mm)
PI8.62 ± 0.5632 ± 237.4 ± 2.8211.2 ± 16.4248.8 ± 18.12.84 ± 0.23
PII8.93 ± 0,6133 ± 338.7 ± 2.4216.1 ± 18.1253.9 ± 20.12.91 ± 0.28
Table
Table 3. Physical properties of products PIII (pellet) and PIV (extrudate).
Table 3. Physical properties of products PIII (pellet) and PIV (extrudate).
ProductProduct Moisture Content
(%)		Hardness
(N)		Cutting Force
(N)
Product PIII10.34128.3 ± 33.48.84 ± 3.3
Product PIV14.7073.53 ± 24.310.8 ± 3.8
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Sobczak, P.; Nadulski, R.; Kobus, Z.; Zawiślak, K. Technology for Apple Pomace Utilization within a Sustainable Development Policy Framework. Sustainability 2022, 14, 5470. https://doi.org/10.3390/su14095470

AMA Style

Sobczak P, Nadulski R, Kobus Z, Zawiślak K. Technology for Apple Pomace Utilization within a Sustainable Development Policy Framework. Sustainability. 2022; 14(9):5470. https://doi.org/10.3390/su14095470

Chicago/Turabian Style

Sobczak, Paweł, Rafał Nadulski, Zbigniew Kobus, and Kazimierz Zawiślak. 2022. "Technology for Apple Pomace Utilization within a Sustainable Development Policy Framework" Sustainability 14, no. 9: 5470. https://doi.org/10.3390/su14095470

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