Introduction

Orange and apple flavours are dominant in European countries where fruit juice consumption is greater than the consumption of fruit nectars, while in Turkey the reverse situation is valid and because the consumption of about 66% fruit nectar, flavors peaches, cherries and apricots are more preferred (Anonymous 2011).

Sour cherry (Prunus cerasus L.) homeland is a region which in possibly extending between the Caspian Sea and the North Anatolian Mountains. Today the economic life of cultures form grown in many countries in the world is 15–20 years. Cherry fruits have significant economic value due to their nutritive and commercial properties (Pérez-Sánchez et al. 2010).

In recent years Turkey has an important place in world rankings with increased production of cherries. Sour cherry cultivation has spread to all regions of Turkey, although limited commercial farming are maintained in areas with appropriate climatic conditions (Önal 2002). Because of its compatible with a wide variety of continental climate conditions, sour cherry (Prunus cerasus L.) is profitable and therefore widely used in the industry (Lezzoni et al. 1990; Aslantaş et al. 2016).

Sour cherry production in Turkey plays an important economic role. In contrast to production value of the early 1990s, Turkey has become a major producer and exporter of sour cherries (Aslantaş et al. 2016). Sour cherry harvest is still largely done by hand in Turkey and in the world. Therefore, the harvest comes at the beginning of the fruit of labor requirements per unit area and harvested by hand constitute from 30 to 60% of total production costs (Moser 1989; Gezer 2001; Brzozowski 2005). In our country, a ‘Kutahya’ cherry variety which produces widely has passed through several stages as harvesting, storage and packaging. Fruit harvesting operation has emerged cost of production is the most important determinants (Kocabıyık et al. 2009).

Gezer (2001) stated that basic research should be done in the study of mechanical harvesting for each fruit varieties to be used as data indicated. The studies are required to reduce costs and yield losses and sour cherry losses that occur during harvesting.

Biological properties as well as the physico-mechanical properties of cherries must be known to mechanical harvesting, to minimize cherries loss and grain damages. Product properties are change according to harvesting time. Effect of harvesting time on product characteristics has been studied by Daniels (2009). Depending on his analysis results, coffee fruits harvested at different days have differences in the quality.

In recent years, physical properties have been studied for various crops including fruits, grains and seeds, such as; faba beans, pumpkin seeds, lentil seeds, pearl millet i.e. Pennisetum gambiense white lupin, sunflower seeds, bambara groundnuts, sea buckthorn, blueberry, hackberry, sweet cherry, apricot pit, chickpea seeds, hemp seed, groundnut kernel, lentil seed, edible squash seed, oranges, Juniperus drupacea fruits, garlic and funnel seed, almond, grape, pistachio, coffee, olives (Aslantaş et al. 2016; Hamdani et al. 2014).

In this study, some physico-mechanical properties were determined for mechanical harvesting of two cherries (‘Kutahya’ and ‘Hungarian Cherry’) in four different harvesting times. This work is aimed to assess the variability of physico-mechanical properties of the sour cherry fruits in terms of four harvesting times. These properties are such as dimensions, projection area, fruit hardness, picking force of fruit stalk, picking force of fruit from stalk. To determine these parameters, an apparatus consisting of a load cell, and slot was used. The knowledge on these parameters is important for the development of new technological equipment and for reducing the losses occurred in sour cherry production.

Materials and Method

In this study, sour cherry used in all the experiments was grown and gathered from markets in Isparta. ‘Kutahya’ variety is a crown structure and its tree is so strong. Fruit of ‘Kutahya’ is quite large, tasty hard, dark purple, wine colored, roundish and very high quality ‘Hungarian Cherry’ matures from ‘Kutahya’ variety two weeks before. The fruit is heart-shaped, dark red color, soft flesh, tart and juicy. Harvesting of sour cherry was performed in the July to the end of August.

In this study, two sour cherry varieties were harvested at four different times, 10 July (H1), 17 July (H2), 24 July (H3) and 31 July (H4).

Some physical properties of fruit of ‘Kutahya’ and ‘Hungarian Cherry’ varieties which are harvested with branches were determined in four different harvesting times. Such physical properties is must be examined for the design of equipment for the handling, harvesting, transport, collection, processing, sorting, conveying and transport of these products (Hamdani et al. 2014; Davies 2009). These fruit properties of cherries varieties are length, width, thickness, geometric mean diameter, sphericity, weight and projection area. Length L, width W and thickness T, of each of the fruits were measured with a digital calliper compass reading to 0.01 mm (Fig. 1). The geometric mean diameter (Dg) and sphericity of fruits were calculated by using the following equations:

$$Dg=(LWT)1/3$$
(1)
$$\phi =Dg/L(2)$$
(2)
Fig. 1
figure 1

Axis dimension of sour cherry fruit

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A balance reading to 0.001 g was used to obtain the weight of fruits. The projection area of sour cherry fruit was calculated by Global Lab Image software.

The picking force is one of the most important criteria in fruit of mechanically harvested (Erdoğan et al. 1992, 2003). A universal testing machine with a load cell was used to measure picking force of the fruit from sour cherry stalk, picking force of stalk from brunches and hardness of fruit (Fig. 2). To picking force of the fruit from sour cherry stalk, picking force of stalk from brunches, fruit or stalk was connected jaw of the universal testing machine and then stalk or brunch attached to a jaw with load cell of machine was pulled upward to determine the picking force of the fruit and stalk (Fig. 3).

Fig. 2
figure 2

Test device

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Fig. 3
figure 3

Picking force of fruit or stalk

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To determine the fruit hardness, a curve-ended cylindrical probe, 6 mm in diameter, was used to compress sour cherry fruit at 100 mm min−1 defined as penetration speed (ASABE 1993). The force was measured by using a strain-gage load cell. A force time record was obtained up to the failure of the specimen. With the use of a computer software program, force as a function of deformation was graphically recorded during the experiments (Fig. 4).

Fig. 4
figure 4

Fruit hardness

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Results and Discussion

Some physico-mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties were given in Table 1 in different harvesting time. The results of this study showed that harvesting time has an impact upon the physical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties. Physico-mechanical properties of sour cherry rapidly changed by maturity stage and harvesting time (Aslantaş et al. 2016).

Table 1 Some physical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties
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Average value of dimensions, projection area, weight of ‘Kutahya’ and ‘Hungarian Cherry’ varieties were increased with harvesting time from H1 to H4 for two sour cherry varieties. Otherwise, average value of sphericity and fruit hardness were decreased with harvesting time from H1 to H4. The effects of harvesting time on some physical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties was found to be statistically significant (p < 0.05). All average values of these varieties are different between and average physical properties values of ‘Kutahya’ variety are greater than ‘Hungarian Cherry’ varieties. This may be due the fact that genotype of these varieties are different from each other.

Some mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties to separated stalk from brunches in different harvesting time were given in Table 2. Average maximum force values were decreased with increasing harvesting time. Average maximum force values were determined in H1 harvesting time for two sour cherry varieties as 8.87 and 7.60 N, respectively. Average bioyield values were found to be like average maximum force values for two sour cherry varieties. The effects of harvesting time on some mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties to separated stalk from brunches was found to be statistically significant (p < 0.05). Picking force for separated stalk to brunch of sour cherry is so important parameters for design the harvesting machine. If the harvesting with machine want to be design, weight/picking force rate must be bigger than (Gezer 2001). For ‘Kutahya’ cherry variety, mechanical harvesting is suitable after the H1 harvesting time. On the other hand, harvesting by machine must be used after H3 harvesting time.

Table 2 Some mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties to separated stalk from brunches in different harvesting time
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Stress in maximum force and picking force were decreased with increasing the harvesting time. Average values of ‘Hungarian Cherry’ were higher than ‘Kutahya’. Works to maximum force were found as not different each other. Minimum deformations to maximum force were determined in H4 in ‘Kutahya’. Deformation was decreased with increasing matures.

Some mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties to separated fruit from stalk in different harvesting time are given in Table 3. Maximum force to separate from fruit to stalk for ‘Kutahya’ variety were determined as 5.85, 3.73, 3.60, 2.58 N, for H1, H2, H3, and H4 harvesting time, respectively. This decreasing trend is similar to those reported by Aslantas et al. (2016) for sour cherry varieties. These properties for ‘Hungarian Cherry’ were found to be 2.01, 1.87, 1.81 and 1.80 N, respectively. Maximum force values in ‘Kutahya’ variety were higher than values of ‘Hungarian Cherry’. The effects of harvesting time on some mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ to separated fruit from stalk was found to be statistically significant (p < 0.05). For two cherry varieties, the highest maximum force values were determined in H1 harvesting time, while the minimum force values were found in H4 harvesting time. Bioyield force values have changed as a function of the maximum force in four different harvesting times. Picking force must be known for separation fruit from stalk. If the properties want to design a shaker, weight/picking force of fruit rate must be higher than 1. Because of this, this rate was found bigger than in H1 harvesting time for two sour cherry varieties. When the harvesting is started by machine, H1 harvesting time should be used.

Table 3 Some mechanical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties to separated fruit from stalk in different harvesting time
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Average stress in maximum force values of ‘Kutahya’ cheery variety were determined 7.11, 4.54, 4.29 and 4.07 MPa for different harvesting time, respectively. For ‘Hungarian Cherry’ variety, these values were 2.80, 2.53, 2.45 and 2.45 MPa at different harvesting time, respectively.

The highest stress in picking force was measured in H1 harvesting time for two sour cherry varieties while the lowest stress in picking force was measured in H4 harvesting time for two sour cherry varieties. Works to maximum force values for ‘Kutahya’ cheery variety were 0.013 and 0.006 J in four different harvesting times. Deformation to maximum force for ‘Kutahya’ ‘Hungarian Cherry’ varieties varied from 6–10%, respectively. The highest and lowest values for ‘Kutahya’ and ‘Hungarian Cherry’ variety were determined as 28.73 and 25.79%; 34.49 and 29.57%, respectively.

Conclusions

In this study, effect of the harvesting time on some physical-mechanical properties of two cherries (‘Kutahya’ and ‘Hungarian Cherry’) which will be applied for the design of harvesting machines used in mechanization applications was investigated. Dimensions, projection area, fruit hardness, picking force of fruit stalk, picking force of fruit from stalk were determined at four different harvesting times. The following conclusions can be drawn from this study:

Harvesting time has an impact upon the physical properties of ‘Kutahya’ and ‘Hungarian Cherry’ varieties. The fruit hardness varies 4.34 and 3.01 N/m. These dates should be considered for design the separation, harvesting and storage machine. The weight/picking force separated stalk to brunch rate must be bigger than 1 for mechanical harvesting. For ‘Kutahya’ cherry variety, mechanical harvesting is suitable after the H1 harvesting time. On the other hand, harvesting by machine must be used after H3 harvesting time. Maximum force to separate from fruit to stalk of sour cherry should be considered for not only pneumatic but also for mechanical harvest of sour cherry. The harvest of sour cherry is very demanding. Hence, mechanical harvest of sour cherry employing automatic control systems should be investigated.