**Kamil Wilczy ´nski 1, Zbigniew Kobus 2,\* and Dariusz Dziki <sup>3</sup>**


Received: 31 May 2019; Accepted: 28 June 2019; Published: 2 July 2019

**Abstract:** The paper presents the possibility of applying different press constructions for juice extraction in small farms. The research was carried out with three different varieties of apples, namely, Rubin, Mutsu, and Jonaprince. Two types of presses were tested: a basket press and a screw press. Generally, application of the screw press makes it possible to obtain a higher yield of extraction compared to the basket press. In our study, the differences in the pressing yield among press machines also depended on the apple variety used. The juices obtained on the screw press were found to be of a higher quality characterized by a higher content of soluble solids, higher viscosity, higher total content of polyphenols, higher antioxidant activity, and lower acidity. Thus, the selection of an appropriate press is the key to producing high-quality apple juice with health-promoting properties for manufacturers of apple juice at the local marketplace.

**Keywords:** sustainable production; screw press; basket press; polyphenols; antioxidant activity; texture properties

#### **1. Introduction**

Apples (*Malus domestica*) are the most commonly used fruit for juice extraction in the European Union (EU). They are a rich source of nutrients and polyphenols and possess antioxidant properties that have beneficial effects on human health [1,2]. The yield of apples is estimated to be 12.59 million tons per year in Europe and 3.6 million tons in Poland [3].

Apples are mainly processed into concentrates, which contributes to the reduction of volume and facilitates storage. Poland is the largest producer and exporter of concentrated juices extracted from fruits grown in the temperate zone of the EU [4]. The European share of the juice yield was estimated to account for 66% in 2016.

Currently, there is a growing trend towards healthy eating and an increased interest in ecological produced food. This in turn contributes to the increasing interest of scientists in functional foods and new methods of production to preserve their quality and high level of bioactive compounds [5]. Some examples of these kinds of foods include juices that are not obtained from concentrate (NFC) and freshly squeezed non-pasteurized juices (FS). These juices are obtained from the fruit tissue by pressing and centrifugation of the pulp. Cloudy juices are classified as products obtained with a low degree of processing. They contain higher amounts of bioactive compounds, such as polyphenols or flavonoids, than clarified ones due to the omission of enzymatic and clarifying treatments. They are also richer in dietary fibre, which is necessary for the proper functioning of the digestive system, and several mineral compounds [6]. In their studies, Paepe et al. [7] and Markowski et al. [8] showed that cloudy juices contain substantially higher amounts of beneficial compounds such as polyphenols and also exhibit considerably higher antioxidant activity than clarified juices. Additionally, apple pomace obtained

after low-degree processing can be used as animal feed after drying or pickling. The natural nutrients contained in the pomace can serve as a valuable source of nutrition for animals in organic farms [9].

Fruit juices are extracted on an industrial scale using different devices, depending on the type of operation (periodic or continuous) and raw material [10]. Many different press construction solutions are used in the industry for obtaining apple juice. Among them, belt press, water press [11], decanter, rack-and-frame press, hydraulic press [12], basket press [13], and screw press [14] are the most distinguished.

A basket press ensures high pressing yields of up to 60%, but it is less often used on an industrial scale. In one study, Nadulski [15] confirmed the usefulness of the basket press in juice extraction from Jonagold apples. In another study, the same author and his group [10] showed that not all apple cultivars are suitable for juice pressing under farm conditions. This suggests that the use of a suitable fruit variety for juice pressing may reduce the cost of pressing and increase the quality parameters of the juice produced.

A screw press is mainly used for oil extraction from oilseeds such as rape [16,17], flax [18], sunflower [19], cumin [20], tobacco seeds [21], and pistachio nuts [22]. Currently, screw presses are becoming increasingly popular, especially on small farms, among local entrepreneurs and for domestic applications. Based on the construction solution, screw presses are classified as single- and double-screw type. These presses are characterized by several extracting processes, where the pulp is subjected to energetic grinding and mixing. The main advantage of a screw press is that the juice obtained has a much higher amount of soluble solids and bioactive compounds [23,24].

The programmes implemented by the EU such as 'Agricultural and rural development 2014–2020 and 'Promotion of farm products' help producers develop new products based on the policy of sustainable agriculture [25,26]. These programmes allow appropriate usage of resources (raw material, energy) and increase the effectiveness of production without affecting the environment [27]. The protection and promotion of regional and traditional products is one of the most important factors supporting the sustainable development of rural areas (as it increases the income of agricultural producers, prevents depopulation and enhances the attractiveness of rural areas). In addition, this may be considered as potentially influencing the development of agricultural products. In the context of sustainable agriculture, the use of a new press construction may allow the farmers to obtain juices with higher quality and a large amount of bioactive compounds. Moreover, fresh pressing of apple juice may help open new markets.

Considering the above, it appears viable that local farms can use small presses for juice production. In this view, the aim of the present study is to compare the efficiency of screw and basket presses in the extraction of apple juice. This includes the determination of parameters affecting the juice quality such as the content of soluble solids, pH, viscosity, total phenolic content (TPC) and antioxidant activity.

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

The research material included three varieties of apples, namely Rubin, Mutsu, and Jonaprince, all obtained from the 2017 harvest. The fruits were delivered by Groups of Fruit Producers, which is related to the company Rylex Sp. z o.o with office registered in the village of Bł ˛edów (near Grójec, Poland; GPS coordinates: 51◦47 N, 20◦42 E), to the local Auchan store in Lublin, Poland.

The experimental flowchart is presented in Figure 1.

**Figure 1.** Experimental flowchart.

#### *2.1. Washing and Blotting*

The apples were washed in tap water and blotted dry using laboratory tissue paper.

#### *2.2. Grinding*

The apples were crushed using a shredding machine (MKJ250; Spomasz Nakło, Poland) equipped with a standard grating disc with 8 mm holes. The rotational speed of the disc was set at 170 rpm. The obtained mash was divided into portions weighing 300 g and placed in plastic containers.

#### *2.3. Determination of Moisture Content*

The moisture content of the apple mash was measured before pressing by drying 3 g of mash at a temperature of 105 ◦C for 3 hours [28]. The measurements were carried out in five replicates.

#### *2.4. Analysis of Texture Properties*

The texture of the apples was examined using a texture analyser (model TA.XT Plus Texture Analyzer) equipped with a measuring head that has a working range of up to 0.5 kN. A double-compression test and a cutting test were performed. The speed of the measuring head was set at 0.83 mm·s−<sup>1</sup> for the double-compression test (TPA) and 1 mm·s−<sup>1</sup> for the cutting test. For TPA, the apple samples with skin were cut into cylinders of 15 mm diameter and 10 mm height and were then placed with their diameter dimension parallel to the device base. Hardness was defined as the maximum force recorded during the first compression cycle (Fh). For the cutting test, a Warner–Bratzler blade was used. The samples with skin were cut into cylinders of 20 mm diameter and 20 mm height. The maximum value of the cutting force (Fc) was determined. The texture analysis was repeated ten times.

#### *2.5. Pressing*

Two kinds of presses were used to extract apple juices: basket press and screw press.

#### 2.5.1. Types of Presses

The basket press (Figure 2) consisted of a perforated cylinder with holes of 3 mm diameter, piston, construction frame, and hydraulic system (UHJG 20/C/2; Hydrotech, Lublin, Poland), which allowed for maintaining a pressure of 4.5 MPa. The press was equipped with a tensometric sensor system for measuring pressure (EMS50; WObit, Poznan, Poland) combined with a digital recorder (MG-TAE1; WObit, Poznan, Poland).

**Figure 2.** Construction and principle underlying the operation of the hydraulic press: 1 – hydraulic ram, 2 – measurement system, 3 – frame, 4 – tensometer, 5 – piston, 6 – cylinder and 7 – base.

The screw press used was a twin-screw type (Green Star Elite 5000; Tribest), which had a rated power of 260 W and was equipped with a sieve with holes of 0.4/0.5 mm. The press has two rotating gears. The dual stainless steel gears contain magnets and utilize bioceramic technologies that pull more nutrients into the juice. The press gears at a low 110 rpm and generates minimal heat while juicing.

#### 2.5.2. Extraction Procedure

The sample materials weighed 300 g. They were pressed in ten replicates in each type of press. In the case of the basket press, the material was put in a special bag made of pressing cloth, placed in the cylinder of the press, and subjected to the force applied by the piston. Once a pressure of 4.0 ± 0.1 MPa was reached, the extraction process was stopped.

In the case of the screw press, the material was directly put into the press chamber.

The extracted juice was collected in plastic containers, filtered using a Whatman No. 1 filter and stored in a refrigerator at a temperature of 4 ◦C.

#### 2.5.3. Pressing Yield

The efficiency of pressing was calculated using the formula:

$$\mathbf{W}\_{\mathbf{j}}(\%) = \frac{\mathbf{M}\_{\mathbf{j}}}{\mathbf{M}\_{\mathbf{i}}} \cdot 100 \tag{1}$$

where

Wj is the efficiency of pressing (%), Mj is the mass of juice after pressing (kg), and Mi is the mass of input material (kg). The calculation was performed for all ten replicated samples.
