Acta agriculturae Slovenica, 118/2, 1–12, Ljubljana 2022 doi:10.14720/aas.2022.118.2.2404 Original research article / izvirni znanstveni članek Studies of the impact of environmental conditions and varietal features of sweet cherry on the accumulation of vitamin C in fruits by using the regression analysis method Іryna IVANOVA 1, Мarina SERDYUK 2, Vira MALKINA 3, Tetiana TYMOSHCHUK 4, 5, Marharyta VOROVKA 6, Ivan MRYNSKYI 7, Anastasiia ADAMOVYCH 8 Received November 02, 2021; accepted April 03, 2022. Delo je prispelo 2. novembra 2021, sprejeto 3. aprila 2022 1 Department of Horticulture, Viticulture and Biochemistry, Faculty of Agrotechnology and Ecology, Dmytro Motornyi Tavria State Agrotechnological University, Melitopol, Ukraine 2 Department of Food Technology and Hotel and Restaurant Business, Faculty of Agrotechnology and Ecology, Dmytro Motornyi Tavria State Agrotechnological University, Melitopol, Ukraine 3 Department of Higher Mathematics and Physics, Faculty of Energy and Computer Technology, Dmytro Motornyi Tavria State Agrotechnological University, Melitopol, Ukraine 4 Department of Plant Protection, Faculty of Agronomy, Polissia National University, Zhytomyr, Ukraine 5 Corresponding author, e-mail: tat-niktim@ukr.net 6 Department of Pedagogy and Pedagogical Mastership, Bogdan Khmelnitsky Melitopol State Pedagogical University, Melitopol, Ukraine 7 Department of Botany and Plant Protection, Faculty of Agronomy, Kherson State Agrarian and Economic University, Kherson, Ukraine 8 Department of Social Sciences and Humanities, Dmytro Motornyi Tavria State Agrotechnological University, Melitopol, Ukraine Studies of the impact of environmental conditions and vari- etal features of sweet cherry on the accumulation of vitamin C in fruits by using the regression analysis method Abstract: The accumulation of vitamin C in sweet cher- ry fruits depends on the variety and environmental condi- tions. The aim of our research was to substantiate the rate of impact of weather factors as well as of varietal features on vitamin C accumulation in sweet cherry fruits. The variet- ies ʹKazkaʹ and ʹZabutaʹ, ʹKordiaʹ and ʹMirazhʹ were chosen as the best ones from among 33 varieties of early, medium and late term of ripening (7.31–10.67 mg 100 g-1) according to the average content of vitamin C in sweet cherry fruits. The stud- ies found that the environmental conditions of the research years had the largest impact on the vitamin C content in the fruits of late and early ripening varieties, and in the fruits of medium ripening variety the vitamin C amount depended on the varietal features. The practicability of forecasting of vitamin C content in sweet cherry fruits on the average in- dices for a group of early and late maturity varieties, but not separately for every pomological variety, has been proven. For the medium ripening variety this index can be forecasted within each pomological variety. The models of dependence of vitamins C accumulation on the impact of meteorological parameters were evaluated on the basis of the principle com- ponents analysis and the least square method. Key words: antioxidants; variety; terms of fruit ripening; vitamin C; weather conditions; principle components analysis Preučevanje vpliva vremenskih dejavnikov in lastnosti sort na vsebnost vitamin C v plodovih češenj z metodo regresij- ske analize Izvleček: Količina vitamin C v plodovih češenj je od- visna od sorte in okoljskih razmer. Namen te raziskave je bil ovrednotiti vpliv vremenskih dejavnikov in lastnosti sort na količino vitamina C v plodovih češenj. Izmed 33 zgodnjih, srednjih in poznih sort so bile izbrane najboljše sorte kot so ʹKazkaʹ,ʹZabutaʹ, ʹKordiaʹ in ʹMirazhʹ glede na poprečno vseb- nost vitamin C (7,31–10,67 mg 100 g-1) v plodovih. Raziskava je odkrila, da so imele na vsebnost vitamina C v plodovih zgo- dnjih in poznih sort češenj največji vpliv vremenske razmere posamezne rastne sezone, pri srednje dozorevajočih sortah pa so imele največji vpliv na vsebnost vitamina lastnosti sort. Dokazana je bila možnost napovedovanja vsebnosti vitamina C v plodovih zgodnjih in poznih sort na osnovi povprečnih indeksov, vendar ne za vsako sorto posebej. Za srednje do- zorevajoče sorte bi lahko uporabili ta indeks za vsako sorto posebej. Model za ugotavljanje odvisnosti kopičenja vitamina C v odvisnosti od vremenskih dejavnikov je bil ovrednoten na osnovi analize glavnih komponent in metode najmanjšega kvadrata. Ključne besede: antioksidanti; sorte; čas dozorevanja; vitamin C; vremenske razmere; analiza glavnih komponent Acta agriculturae Slovenica, 118/2 – 20222 I. IVANOVA et al. 1 INTRODUCTION Sensible nutrition of people is one of the main pri- orities of the state policy of most countries. The fruits are considered as an essential element of good nutri- tion, as they are the source of a vitamin complex. Vi- tamins belong to a group of indispensable nutrients of organic nature, which facilitate metabolism. They are scarcely synthesized in an organism, so they should be in taken with food. The amount of vitamin C in fruits (Bastos et al., 2015; Hayaloglu & Demir, 2015) is an im- portant characteristic of fruits for their consumption in raw condition, for processing and storing (Vasylyshy- na, 2018). One of the directions of solving the defined problem is to provide the population with fruits with a high amount of biologically active substances which are essential for people (Dhandevi & Jeewon, 2015). The sweet cherry fruits (Prunus avium L.) belong to the food stuff which contains digestible sugars, phe- nolic acids with a predominant amount of anthocya- nins, mineral substances and vitamins (Leong & Oey, 2012; Pissard et al., 2016; Ivanova et al., 2021a, 2021b, 2021c). Biologically active substances represented by phyto-nutrients and antioxidants provide antioxidant, anti-cancerogenic and anti-phlogogenic action on human organism (Ballistreri et al., 2013; Popescu et al., 2014; Legua et al., 2017). Due to this, sweet cherry fruits reveal some preventive effect against cardiovascular diseases, di- abetes, cancer, which is connected with an oxidative stress (He et al., 2007; Faniadis et al., 2008; Schmitz-Eiberger & Blanke, 2012). Sweet cherry fruits are characterized by a high amount of dietary medicative substances, which promote to organism functioning. Sweet cherry fruits contain water soluble (C, B) and fat soluble (A, E, K) vi- tamins (Antognoni et al., 2020). Vitamins take part in oxidation-reductions, respiration, nucleic acids forma- tion and amino-acids exchange, protein secretion as well as improve carbohydrate digestion. Besides, they control cholesterol metabolism, prevent the accumulation of harmful free radicals in body tissues, improve the resist- ance to infectious diseases as well as to unfavorable en- vironmental factors which cause overheating, excessive heat loss, hypoxia and improve person’s performance (Bastos et al., 2015). Vitamin C or L-ascorbic acid is one of the most important phyto-nutrients, which determines the biological value of sweet cherry fruits. Vitamin C be- longs to a group of water soluble vitamins (Antognoni et al., 2020). Vitamin C amount in sweet cherry fruits equals 7.26–10.78 mg 100 g-1 on the average. In living organ- isms, the ascorbic acid is an antioxidant, as it protects the organism against the oxidative stress and is a co-factor in essential vital enzyme reactions (Nowak et al., 2018; An- tognoni et al., 2020). The immunity protection and the maintaining of psychical processes in a proper condition are the most important functions of vitamin C. Vitamin C is one of the regulators of reductive-oxidative processes in living cells. Vitamin C scarcity results in metabolic disor- der in the whole organism (Prior, 2003). For a human an every-day need for vitamin C equals 50–100 mg. Vitamin C scarcity in a human diet can cause hypoavitaminosis and avitaminosis C, as this vitamin is not synthesized in an organism (Acero et al., 2019). Fresh fruits are the main source of vitamin C. This fact testifies to the expediency of prolonging the term of fruits consuming. Thus, it is im- portant to retain this valuable nutritive constituent under sweet cherry fruits keeping and processing (Correia et al., 2017). Palatability traits and biochemical composition of sweet cherry fruits depend on the genetic traits of the variety (Serrano et al., 2005; Faniadis et al., 2008; Cor- reia et al., 2020). The researchers have produced the va- rieties of stone fruits which meet modern requirements, but there are still some problems which are very topical (Correia et al., 2017; Grandi et al., 2017). The chemical composition of the fruits of any harvest, except varietal features, depend on the meteorological conditions of the growing period as well as of the zone of fruit growing (Hayaloglu & Demir, 2015; Luna-Vázquez et al., 2016). The researchers of the subtropical regions of Brazil estimated the chemical composition, identificated the biologically active compounds and estimated the antioxi- dant activity of berries and fruits including sweet cherries. It was established that the amount of ascorbic acid in the fruits of the subtropical regions of Brazil is much higher than in the zone with moderate climate (Rios de Souza et al., 2014). The formation of the biochemical composition of sweet cherry fruits as well as of their consumption value depend on the temperature, light intensity, fruit ripeness (Martini et al., 2017; Acero et al., 2019). The dependence of vitamin C amount on the meteorological indicators within the period from blooming to stone fruit ripening was studied by many scientists. A higher concentration of vitamin C in fruits was registered in the years with suf- ficient water availability (Lakatos et al., 2010, 2014). The level of ascorbic acid content in fruits is formed geneti- cally. But the weather factors during the growing period have great impact on the accumulation of vitamin C fund (Bieniek et al., 2011). The greatest amount of vitamin C is formed during the years with moderately warm and wet growing period. A sufficient fruits lightning is a very im- portant factor which affects the process of ascorbic acid synthesis (Kevers et al., 2011). On the basis of literature sources it can be stated that there is a strong correlation between vitamin C amount and the environmental con- ditions of the region of fruit growing. Under conditions of climate changes, stress abiotic factors have negative im- pact on the formation of vitamin C fund in sweet cherry Acta agriculturae Slovenica, 118/2 – 2022 3 Studies of the impact of environmental conditions and varietal features of sweet cherry on the accumulation of vitamin C in fruits ... fruits under conditions of a Southern Steppe sub-zone of Ukraine. Therefore, there is a necessity to study the pecu- liarities of vitamin C accumulation in sweet cherry fruits of different terms of ripening under the influence of stress weather factors in order to single out the most suitable varieties for fruit storing and processing. The aim of the study was to develop a model for vitamin C content forecasting in the fruits of early, me- dium and late terms of ripening depending on the envi- ronmental conditions. The received mathematic model is the basis for the forecasting of a test parameter of fruits quality in the regions with similar environmental conditions. The task of the research was to recommend the fruits of early, medium and late maturity varieties with a high amount of vitamin C for consuming fresh as well for fruit storing and processing. To achieve the aim, it is necessary to: - analyze the environmental conditions during the period of phenological stages of sweet cherry fruits growing and developing; - estimate the vitamin C amount in fruits on the stage of their economic maturity and choose the best varieties; - study the correlations between the accumulation of vitamin C and weather factors and to develop the mathematical models of their dependence; - estimate the rate of impact of each weather factor on the formation of vitamin C fund in test varieties of three groups. 2 MATERIALS AND METHODS The research was conducted during 2008–2019 in sweet cherry fruiteries in the Southern Steppe sub-zone of Ukraine. The region is characterized by insufficient wa- ter availability as to the amount of rainfalls. The climate is Atlantic-continental, dry with a high temperature regime. The dry winds are of Northeastern direction. According to the complex of climatic parameters, the test region is favorable for sweet cherry fruits growing (Table 1). The data of Melitopol meteorological station of the South of Ukraine (46° 49’N, 35° 22’E) were used for the calculation of the model of forecasting of vitamin C amount in sweet cherry fruits The research areas have black southern loamy soil, which was formed on the loesses. The agrochemical characteristic of soil is given in Table 2. The technology of sweet cherry growing in the ex- periment was standard for a given region. The scheme of trees planting in 2001 was – 5 × 3 m. The space between rows on the fruit plantation was kept under autumn fallow. All sweet cherry varieties on ‚Magaleb- ska‘ cherry rootstock were divided into three groups according to the term of ripening (early, medium and late): early term of ripening 7 varieties, medium term of ripening 13 varieties, late term of ripening 13 variet- ies. The fruits of an early ripening term were harvested in the third decade of June and in the first decade of July. The fruits of a medium ripening term were har- vested in the second decade of July. The fruits of a late ripening term were harvested in the third decade of July. To study the vitamin C amount, 100 fruits were chosen from 6 trees of each sweet cherry variety of the same age on the stage of heavy bearing with average intensity. There was a threefold frequency of variants in the experiment. The fruits of each variety were picked by hand from four different sides of the tree crown on Depth of arable layer, cm Humus content, % pH kCl Nutrient content, mg g-1 100 of soil N P2O5 K2O 40.0 1.38 6.9 27.0 90.0 154.0 Table 2: Agrochemical characteristics of topsoil of tested soil Readings Value Average annual air temperatures, °С 9.1–9.9 Average monthly air temperatures in the warmest months, С 20.5–23.1 Sum of active temperatures higher than 10 C from April to October, С 3316 Average amount of rainfalls per year, mm 475 Average annual relative air humidity, % 73 Average annual air velocity, m s–1 3 Hydrothermic coefficient 0.22–0.77 Table 1: Meteorological conditions of Southern Steppe sub-zone of Ukraine Acta agriculturae Slovenica, 118/2 – 20224 I. IVANOVA et al. the stage of economic maturity. After harvesting the fruits, they were weighed and counted (Serdyuk et al., 2020). The sweet cherry fruits were transported to the laboratory for 2–3 hours after their harvesting to esti- mate the tested parameter. During the period of sweet cherry fruits harvesting, their economic maturity was estimated by visual and organoleptic examination. The fruit pulp was rather firm, color and flavor were typical for each pomological variety. The sweet cherry fruits were harvested with a fruit-stalk. The fruits transpor- tation and storing were conducted under condition of preserving of the external appearance and flavor typi- cal for a variety. The restoring of Tilman’s reagent (2.6-dichlorphe- nol-indophenol) was taken as the basis of the technique on the evaluation of a mass fraction of vitamin C. The amount of ascorbic acid in the extracts (Serdyuk et al., 2020) was evaluated in terms of the amount of the reagent which was used for titration. The model of dependence of vitamin C amount in sweet cherry fruits on the weather factors was developed according to the schedule (Ivanova et al., 2021a, 2021b): 1. Evaluation of a mass fraction of ascorbic acid (AA). 2. Analysis of the weather factor during the years of the research. 3. Choosing the weather factor which show the cor- relation with vitamin C amount in fruits. 4. Developing the regression model of dependence of vitamin C amount in the fruits of sweet cherry varieties on the weather factor. 5. Evaluation and ranging of the rate of impact of each weather factor on the tested parameter of fruits quality. The statistical analysis was made using modern computer technologies DataMining – software environ- ment RStudio. 3 RESULTS AND DISCUSSION For the sweet cherry fruits of three groups of ripen- ing the average content of vitamin C equaled 8.17 mg 100 g-1 (Tables 3–5). The accumulation of vitamin C in the fruits of seven cultivars grown in Turkey was analyzed by Demir T. The average content of vitamin C in sweet cherry fruits varied between 4 and 7 g kg-1 of fresh mass (Demir, 2013). The ascorbate levels for 22 sweet cherry cultivars grown in southern of Italy was considerably lower – 0.034–0.260 g kg-1 of fresh mass (Matteo et al., 2016). The rate of accumulation of vitamin C fund in sweet cherry fruits of an early term of ripening equaled 7.10 mg 100 g-1, which is by 13.1 % lower as compared with the average index for three groups. In a group of an early term of ripening the varieties, ʹKazkaʹ (7.36 ± 1.40 %) and ́ Zabutaʹ (7.31 ± 1.49 %) had the largest vitamin C content on the average during the years of studies. In the fruits of ʹBigaro Burlatʹ variety vitamin C content was the lowest (6.84 ± 1.22 %). The fruits of ʹBigaro Burlatʹ (the early term ripening group) had the lowest content of vitamin C in 2018 – 5.02 mg 100 g–1, which is for 26.6 % lower than the average va- rietal parameters. The fruits of ʹMerchantʹ variety had a maximal accumulation of vitamin C (11.29 mg 100 g–1) in 2019, which is for 63.6 % higher as compared with the average varietal parameters. The highest content of vitamin C during the years of research was in ʹKazkaʹ and ʹZabutaʹ varieties, and the lowest – in ʹBigaro Burlatʹ variety (Table 3). The average content of vitamin C in sweet cherry Variety Vitamin C content, % Variation according to years, Vр, %average min max ʹBigaro Burlatʹ 6.84 ± 1.22 5.02 9.83 17.9 ʹZabutaʹ 7.31 ± 1.49 5.16 10.27 20.4 ʹKazkaʹ 7.36 ± 1.40 6.08 10.12 19.1 ʹMerchantʹ 6.90 ± 1.84 5.18 11.29 26.7 ʹRubinova Ranniaʹ 6.92 ± 1.28 5.12 9.03 18.5 ʹSweet Erlizʹ 7.26 ± 1.68 5.17 11.00 23.1 ʹValeriy Chkalovʹ 7.13 ± 1.54 5.19 10.12 21.5 Average value 7.10 ± 1.46 5.26 10.23 21.02 LSD05 0.579 – – – Таble 3: The accumulation of vitamin C in sweet cherry fruits of early term ripening varieties, mg 100 g-1 (2008–2019), x sx± , n = 5 Acta agriculturae Slovenica, 118/2 – 2022 5 Studies of the impact of environmental conditions and varietal features of sweet cherry on the accumulation of vitamin C in fruits ... fruits of two varieties (medium and late terms of ripen- ing) equals 8.93 ± 2.27 % and 8.48 ± 1.74 % respectively (Table 4, 5). The rate of formation of vitamin C fund in sweet cherry fruits of medium term of ripening ex- ceeds the average varietal parameters by 3.8 % and in the fruits of late term of ripening by 9.3 %. It has been established that the fruits of a medium term of ripening had the maximal content of vitamin C. In a medium term ripening group a minimal amount of vitamin C had the fruits of ʹDachnytsiaʹ, Variety Vitamin C content, % Variation according to years, Vр, %average min max ʹChervneva Ranniaʹ 5.95 ± 1.06 4.12 7.67 17.9 ʹDachnytsiaʹ 6.32 ± 1.11 5.01 7.88 17.5 ʹDilemaʹ 10.94 ± 2.20 8.19 14.51 20.1 ʹKordiaʹ 10.63 ± 1.81 8.01 13.85 17.1 ʹOktaviaʹ 10.11 ± 1.74 7.40 12.08 17.2 ʹOktaviaʹ 9.25 ± 2.25 5.12 12.47 24.3 ʹOrionʹ 10.46 ±1.83 7.51 12.82 17.8 ʹPervystokʹ 9.05 ± 1.59 6.34 11.18 17.5 ʹProstirʹ 7.73 ± 1.19 5.19 9.27 15.4 ʹTalismanʹ 10.48 ± 2.46 7.23 14.11 23.4 ʹTempʹ 8.07 ± 1.49 5.89 9.85 18.5 ʹUliublenytsia Turovtsevaʹ 9.02 ± 1.60 6.11 11.91 17.7 ʹVynkaʹ 8.08 ± 1.51 6.23 10.14 18.7 Average value 8.93 ± 2.27 6.33 11.36 18.7 LSD05 0.645 – – – Таble 4: Vitamin C content in sweet cherry fruits of medium term ripening varieties, mg 100 g–1 (2008–2019), x sx± , n=5 Variety Vitamin C content, % Variation according to years, Vр, %average min max ʹАnonsʹ 8.20 ± 1.59 5.71 11.81 19.3 ʹКarinaʹ 8.33 ± 1.48 5.78 10.28 17.7 ʹKolhoznytsiaʹ 7.85 ± 1.24 5.79 10.92 15.8 ʹКоsmichnaʹ 8.95 ± 1.60 6.69 12.03 17.9 ʹKrupnoplidnaʹ 7.74 ± 1.16 5.79 10.23 14.9 ʹMeotydaʹ 8.03 ± 1.45 5.61 10.72 18.1 ʹMirazhʹ 10.67 ± 1.49 8.28 14.14 14.0 ʹPrazdnichnaʹ 10.25 ± 2.02 7.61 13.08 19.7 ʹReginaʹ 7.29 ± 1.01 6.03 10.54 13.8 ʹSurpryzʹ 8.10 ± 1.47 5.65 11.01 18.2 ʹТemporionʹ 7.72 ± 1.44 5.01 9.76 18.7 ʹUdivitelnaʹ 7.58 ± 1.31 5.41 9.23 17.3 ʹZodiakʹ 9.60 ± 1.46 7.79 11.19 15.2 Average value 8.93 ± 2.27 6.33 11.36 18.7 LSD05 0.645 – – – Таble 5: Vitamin C content in sweet cherry fruits of late ripening varieties, mg 100 g-1 (2008–2019), x sx± , n = 5 Acta agriculturae Slovenica, 118/2 – 20226 I. IVANOVA et al. ʹTempʹ and ʹChervneva Ranniaʹ varieties of 2008. Vi- tamin C content was lower than the average varietal parameter by 20.7 %, 27.0 % and 30.7 % respectively. A maximal amount of vitamin C was registered in the fruits of ʹTalismanʹ (14.11 %) and ʹDilemaʹ (14.51 %) of 2010 that is by 34.6 and 32.6 % higher than the average varietal parameter. The highest accumulation of an av- erage content of vitamin C was registered in the fruits of ʹDilemaʹ (10.94 ± 2.20 %) and ʹKordiaʹ (10.63 ± 1.81 %) varieties. In a late term ripening group a minimal amount of vitamin C had the fruits of ʹTemporionʹ variety (5.01 %) of 2008 (Table 5). The content of vitamin C was by 9.8 % lower than the average varietal param- eter. The fruits of ʹMirazhʹ (14.14 %) and ʹPrazdnichnaʹ (13.08 %) of 2014 had a maximal amount of vitamin C that is by 34.9 and 27.6 % higher as compared with an average varietal parameter. A maximal accumulation of an average vitamin C content was registered in the fruits of ʹMirazhʹ (10.67 ± 1.49 %) and ʹPrazdnichnaʹ (10.25 ± 2.02 %). Especially valuable are the varieties whose fruits are characterized by a high and stable amount of vitamin C content (Leong & Oey, 2012). Their variation parameter Vр can be used as an indicator of stability – of a variety in reference to the meteorological conditions of different years of fruits growing. The variation of sampling can be considered insignificant or low under the Vp lower than 10 %, aver- age – under 10 – 20 % and high under 20 % and more. Therefore, the varieties whose fruits have a high and stable vitamin C content are of special value. The variability of vitamin C content during the years of research in the sweet cherry fruits of an early and medium terms of ripening was in the range from 15,4 tо 26,7 %. For a group of early ripening varieties (ʹValeriy Chkalovʹ, ́ Svit Earlizʹ, ́ Merchantʹ and ́ Zabutaʹ) the variation parameter equaled 20.4–26.7 %, for a group of medium terms ripening varieties (ʹTalismanʹ, ʹDilemaʹ, ʹOktaviaʹ) Vp equaled 20.1–24.3 %. It testifies to a maximal impact of weather factors on vitamin C content in the sweet cherry fruits of these groups. The variation parameter for ʹProstirʹ and ʹBigaro Burlatʹ va- rieties equals 15.4 % and 17.9 % respectively that testi- fies to their resistance to stress factors. The Vp range for the sweet cherry fruits of the late term of ripening varied within the average values 13.8–19.7 %. The lowest values of the variation param- eter were registered in ʹReginaʹ and ʹMirazhʹ varieties (Vр = 13.8–14.0 %). The highest vitamin C stability in a group of an early term of ripening is in ʹBigaro Burlatʹ variety (Vр = 17.9 %). The varieties ʹKazkaʹ and ʹZabutaʹ have the highest rate of vitamin C accumula- tion (7.36 ± 1.40 %) and (7.31 ± 1.49 %) respectively. The most perspective from the point of view of fruits storing and processing are ʹKordiaʹ (Vр = 17.1 %) of the medium term and ʹMirazhʹ (Vр = 14.0 %) of the late term of ripening. These varieties are characterized by a high and nearly high content of vitamin C as well as by minimal variability as compared with other va- rieties. The received results of the research have been confirmed by literature data (Bieniek et al., 2011). The chemical composition analysis of fruit revealed sig- nificant differences both between the cultivars and be- tween the years of the research. Environmental conditions, Factor A (Table 6) had the greatest impact on vitamin C content in the fruits of Source of variation Sum of squares Degree of freedom Dispersion Ffact Ftable095 Impact, % Group 1, early ripening sweet cherry varieties Factor A (year) 448.5 11 40.7 321.5 1.8 80.2 Factor В (cultivar) 9.9 6 1.6 13.0 2.2 1.7 Interaction АВ 79.6 66 1.2 9.5 1.4 1.2 Group 2, medium term sweet cherry varieties Factor A (year) 998.05 11 90.7 577.7 1.8 39.1 Factor В (cultivar) 1266.13 12 105.5 671.9 1.8 49.6 Interaction АВ 237.68 132 1.8 11.4 1.3 9.3 Group 3, late ripening sweet cherry varieties Factor A (year) 640.38 11 58.2 244.3 1.8 43.5 Factor В (cultivar) 513.89 12 42.8 179.7 1.8 34.9 Interaction АВ 241.40 132 1.8 7.67 1.3 16.4 Таble 6: The results of two factors dispersion analysis under the accumulation of vitamin C in sweet cherry fruits of different terms of ripening Acta agriculturae Slovenica, 118/2 – 2022 7 Studies of the impact of environmental conditions and varietal features of sweet cherry on the accumulation of vitamin C in fruits ... early and late terms of ripening. The rate of impact of the environmental conditions of the years of research (Factor A) for early ripening varieties equaled 80.2 %, for late ripening varieties only 43.5 %. The rate of im- pact on varietal features (Factor B) was significantly lower for these two groups of varieties in terms of ripe- ness rate. For early ripening varieties, it equaled 1.7 %, for late ripening varieties 34.9 %. It was established that the formation of vitamin C fund in the sweet cherry fruits of medium term of ripening depended on the varietal features (Factor B, 49.6 %). The impact of envi- ronmental conditions of the research years (Factor A) for this group of varieties equaled 39.1 %. The research shows the practicability of forecast- ing of vitamin C accumulation in fruits of early and late ripening sweet cherry varieties in terms of aver- age variety values but not for each pomological variety. The forecasting of accumulation of vitamin C fund in the fruits of medium ripening varieties is expedient to make in terms of average varietal parameters and rate of content for each pomological variety. To establish the correlation relationships between vitamin C content in fruits of early (Y1), medium (Y2), late (Y3) terms of ripening and the climatic factors, the following analysis was made. On the basis of the es- tablished matching coefficients of correlation rY1Xi, rY2Xi , rY3Xi were chosen the most significant factors. The signif- icance of these correlation coefficients was established by checking a statistical hypothesis H0: p = 0 (where p - is a correlation coefficient of general population) under the alternative hypothesis H1: p ≠ 0 under the reliability level α = 0,05. Student’s criteria was used to check the statistical hypothesis. It was established that significant correlation coefficients, under the significance level of 0.05 and the number of degrees of freedom k = 10, were within an interval [–0.55; 0.55]. Further experiments were conducted according to the schedule: First step. On the basis of the principle com- ponents analysis we build a set of the princi- pal components iPC ( 1 )i n= … represent- ed by a liniar combination of weather factors: 1 m i ij j j PC p X = =∑ , 1i n= … (1) where jX – weather factors parameters, 1..j m= iPC - principal components, 1i n= … ijp - coefficients, 1i n= … , 1..j m= . We choose first five principal components ( ), 1 ..5iPC i = , which provide more than 93,5 % of cumu- lative proportion of variance. Second step. The development of the regres- sion models of dependence of vitamin C value on the weather factors for each group of varie- ties from the principal components was as follows: 5 0 1 ˆ i i i Y b b PC = = + ⋅∑ (2) where Ŷ – vitamin C content, mg 100 g-1 iPC - principal components, 1 5i = … ib - regression coefficients, 1 5i = … . The regression equation for early ripening varie- ties is as follows: 1 1 2 3 4 5 ˆ 7.10762 0.41631 0.13542 0.61543 0.13960 0.25401Y PC PC PC PC PC= − + + + − The regression equation for medium ripening varieties is as follows: 2 1 2 3 4 58.9078 0.4252 0.1872 0.0064 0.7698 0.ˆ 1628Y PC PC PC PC PC= − + − + + The regression equation for late ripening varieties is as follows: 3 1 2 3 4 58.4881 0.3533 0.3044 0.0150 0.1113 0.ˆ 0869Y PC PC PC PC PC= − + − − − The value of the determination coefficient (R- squared) for early ripening varieties equals 0.9239, for medium –ripening, 0.7273, for late ripening varieties, 0.7069, it indicates that there is a strong impact of inde- pendent variables on the dependent variables. The p-value is < 0.05 for F-statistic value for all regression models, it testifies to the adequacy of the models according to Fisher’s criterion under the level of significance -0.05. Third step. We proceed from the principal com- ponents to the initial factors by applying formula 1. We carry on the standardization process of variable mod- els. We receive a regression model which characterizes the dependence of vitamin C value (for 1 2 3 ˆ ˆ, ˆ ,Y Y Y ) from weather factors. 1 ˆ n j j j Y a X = = ⋅∑  (3) where j j j j X X X X σ − = – values of weather Acta agriculturae Slovenica, 118/2 – 20228 I. IVANOVA et al. and environmental factors in a standardized form 1j n= … jX - arithmetic mean of factors jX , 1j n= … jX σ - standard deviation of factors jX , 1j n= … ja - model coefficients, 1j n= … Ŷ - vitamin C content, mg 100 g-1. Table 7 presents the coefficients of model (3) for vitamin C content in sweet cherry fruits of early 1( ˆ )Y , medium ( 2̂Y ) and late ( 3̂ )Y terms of ripening. The coefficients ( ) , 1 ..12i i∆ = were estimated by formula for each factor on the basis of the developed models: 2 ii yx i a r R ⋅ ∆ =  (4) where ia - coefficients of a regression model (3) iyx r - matching coefficients correlation 2R − determination coefficients. Twelve parameters of the climatic factors ( iX ) which in a particular growing period could have a significant impact on the ascorbic acid content in the sweet cherry fruits of early (Y1), medium (Y2) and late (Y3) ripening varieties were chosen (Table 8). These parameters are the following: air humid- ity; average monthly air humidity in May (Х2); aver- age monthly precipitation amount in May (Х1) and in June (Х11); average number of days with precipitation amount more than 1 mm in May (Х5), June (Х6) and July (Х7); average minimal relative air humidity in May (Х3) and in June (Х4); the amount of precipitation dur- ing the period after blooming (Х10); hydrothermal co- efficient (Х12). The parameters (Х8), the difference be- tween the average maximal and minimal temperatures in May, and in June (Х9) were chosen from among the temperature air indicators (°С). A complex of weather factors which have average and strong linear correlation dependence in terms of vitamin C content has been established for each group of varieties. The factors of impact which are expedient to study from the point of view of the importance and the logi- cality of the experiment, despite the insignificance of their correlation coefficients, have been found. The coefficients i∆ estimate the rate of each fac- tor in a total dispersion of vitamin C amount in sweet cherry fruits. On the basis of the estimated indices , 1 ..12i i∆ = we rank all the factors in terms of their impact from the most significant (rank 1) to the factor which has the lowest impact (rank 12). Table 7 repre- sents the values of index ,%i∆ and the rank of factors. For the experimental groups of sweet cherry varie- ties of three terms of ripening, i∆ varies in the range of 0.16 – 30.64 % (Table 7). According to the estimated in- dices ( ) , 1 ..12i i∆ = all the factors were divided into the ranks. An average monthly amount of precipitation in May (Х1) had a maximal impact on vitamin C content in sweet cherry fruits of early and late ripening varie- ties. An average precipitation amount in June (Х11) had impact on the formation of vitamin C fund in sweet cherry fruits of late term of ripening. This parameter got the first rank and varied in the range of i∆ indices from 14.92 % to 30.64 %. Air humidity indices had a significant impact on vitamin C content in sweet cherry fruits. The parameters of the second rank are average monthly relative air humidity in May (Х2), late term of ripening, total number of days with precipitation amount more than 1 mm in June (Х6), medium term of ripening, total number of days with precipitation amount more than 1 mm in July (Х7), early term of rip- ening. The significance of the rate of impact of these 1a 2a 3a 4a 5a 6a 1̂Y -0,529 -0,131 -0,207 -0,067 -0,234 -0,278 2̂Y -0,420 -0,164 -0,225 -0,082 -0,167 -0,263 3̂Y -0,360 -0,444 -0,478 0,070 -0,309 0,120 7a 8a 9a 10a 11a 12a 1̂Y -0,382 0,061 -0,021 -0,227 -0,183 0,101 2̂Y -0,320 0,129 0,056 -0,184 -0,090 0,056 3̂Y -0,166 0,477 0,147 0,004 0,380 0,064 Тable 7: Coefficients of a regression model in standardized factors Acta agriculturae Slovenica, 118/2 – 2022 9 Studies of the impact of environmental conditions and varietal features of sweet cherry on the accumulation of vitamin C in fruits ... factors, 6X∆ , 7X∆ , 2 ,X∆ was in the range of 11.57– 18.57 %. Weather factors which have a significant impact on vitamin C formation in sweet cherry fruits of three groups belong to the parameters of the third rank, they are: average minimal air humidity in May, % (Х3), a total number of days with precipitation amount more than 1mm in June (Х6). The rate of impact equaled 7 X∆ = 18.57 % for the varieties of an early term of ripening, and for the varieties of medium and late terms of ripening the rate of impact equaled 3X∆ 11.38 % and 14.81 % respectively. The factors of the 1–7th ranks with the rates of impact i∆ (6.09–30.64 %) had a maxi- mal impact on vitamin C content for early ripening va- rieties of sweet cherry. Relative factors term ( iX ) Factors Matching coefficients of correlation ( j iY X r ), indices of the impact rate of factors ( )i∆ and indices of the factors ranks for the varieties groups early ripening medium ripening late ripening 1 iy x r i∆ rank 2 iy x r i∆ rank 3 iy x r i∆ rank X1 Average monthly amount of precipitation in May, mm 0.889 30.64 1 0.651 23.86 1 0.535 13.45 4 X2 Average monthly relative air humidity in May, % 0.712 6.09 7 0.575 8.22 7 0.479* 14.87 2 X3 Average minimal relative air humidity in May, % 0.733 9.90 4 0.579 11.38 3 0.443* 14.81 3 X4 Average minimal relative air humidity in June, % 0.201* 0.88 11 0.348* 2.49 10 0.476* 2.34 11 X5 Total number of days with precipitation amount more than 1 mm in May, per day 0.531* 8.09 5 0.702 10.25 5 0.431* 9.29 5 X6 Total number of days with precipitation amount more than 1 mm in June, per day 0.604 10.97 3 0.503* 11.57 2 0.719 6.03 8 X7 Total number of days with precipitation amount more than 1 mm in July, per day 0.745 18.57 2 0.368* 10.28 4 0.634 7.37 7 X8 Difference between average maximal and minimal tem- peratures in May, °С –0.52* 2.07 9 –0.29* 3.35 9 –0.24* 8.24 6 X9 Difference between average maximal and minimal tem- peratures in June, °С –0.27* 0.36 12 –0.27* 1.35 12 –0.541 5.56 9 X10 Amount of precipitation in blooming period, mm 0.498* 7.37 6 0.631 10.13 6 0.528 0.16 12 X11 Average monthly amount of precipitation in June, mm 0.159* 1.90 10 0.683 5.38 8 0.563 14.92 1 X12 Hydrothermical coefficient 0.480* 3.15 8 0.452 1.74 11 0.661 2.97 10 Table 8: The table of the coefficients of matching correlation ( ) j iY X r , indices of the impact rate ( i∆ ) and their ranks, which characterize the impact of factors (Xі,) on vitamin C content in the sweet cherry fruits of three terms of ripening *some important factors which must be studied in the experiment as expedient and logical ones, though their correlation coefficients are not significant Acta agriculturae Slovenica, 118/2 – 202210 I. IVANOVA et al. Some additional impact on vitamin C content had the following parameters: average minimal relative air humidity in June (X4); the difference between average maximal and minimal temperatures in May (X8); the difference between average maximal and minimal tem- peratures in June (X9); average monthly precipitation amount in June (X11); hydrothermical coefficient (X12). The overall value of index i∆ for factors X12, X8 and X11, Х4, Х9 equaled 8.36 %. Factors of 1–8 ranks had a maximal impact on vitamin C content for medium ripening varieties. The range of i∆ for them was in the range of 5.38–23.86 %. A less significant impact on the formation of vitamin C content in sweet cherry fruits of a medium term of ripening had the climatic parameters like: average min- imal relative air humidity in June (X4), the difference between average maximal and minimal temperatures in May (X8); the difference between average maximal and minimal temperatures in June (X9); hydrothermical co- efficient (X11). The overall value of index i∆ for factors Х4, Х8, Х9, Х11, which belong to ranks 9–12 within the given group of sweet cherry varieties, equaled 8.93 %. All factors in a group of late ripening sweet cher- ry varieties ( i∆ – 5.56–14.92 %) had a largest impact on the formation of vitamin C content. The factors of 10–12 ranks (Х10, Х11, Х12) had a less significant impact on vitamin C content in sweet cherry fruits of a given group. The overall value of index i∆ for them equaled 5.47 %. The analysis of the rate of impact of weather fac- tors on vitamin C content in sweet cherry fruits of three terms of ripening testifies to the fact that the most sig- nificant climatic parameters are: humidity indices in May and June (the last months of fruits formation), the average monthly precipitation amount in May (X1) for early ripening and medium ripening varieties, and the precipitation depth in June (X11) for late ripening varie- ties respectively. 4 CONCLUSIONS 1. The varieties ʹKazkaʹ (7.36 mg 100 g–1), ʹZabutaʹ (7.31 mg 100 g–1) have been chosen in terms of vitamin C content for the group of an early term of ripening. ʹBugaro Burlatʹ variety (with a minimal variability pa- rameter Vр = 17.9 %) has been chosen in terms of min- imal variability parameter during the years of research. 2. A medium ripening variety ʹKordiaʹ (10.63 mg 100 g–1 under Vр = 17.1 %) and late ripening variety ʹMirazhʹ (10.67 mg 100 g–1 under Vр = 14.0 %) were chosen as the most perspective from the point of view of fruit storing and processing in terms of vitamin C content. The variation parameters of vitamin C content in sweet cherry fruits of three terms of ripening ranged from 13,8% to 26,7%. 3. The environmental conditions of the years of re- search (Factor A) – 43.5 % and 80.2 % respectively, had a dominating impact on vitamin C content in the fruits of late and early ripening varieties. 4. The impact of varietal features (Factor B) was dominating (49.6 %) in terms of vitamin C content in the sweet cherry fruits of medium term of ripening. 5. The models of dependence of vitamin C content on the impact of climatic conditions for three groups of varieties were developed by using the method of the principle components and the method of least squares. 6. The analysis of the rate of impact of each me- teorological parameter on vitamin C content in sweet cherry fruits was made by using the developed regres- sion models. The range of impact of the meteorological parameters in the formation of vitamin C fund has been established and their maximal values ( i ∆ 14.92 % to 30.6 %) for the groups of three-term ripening varieties have been estimated. 5 REFERENCES Acero, N., Gradillas, A., Beltran, M., García, A., Muñoz Min- garro, D. (2019). Comparison of phenolic compounds profile and antioxidant properties of different sweet cherry (Prunus avium L.) varieties. Food Chemistry, 279, 260–271. https://doi.org/10.1016/j.foodchem.2018.12.008 Antognoni, F., Potente, G., Mandrioli, R., Angeloni, C., Freschi, M., Malaguti, M., Hrelia, S., Lugli, S., Gennari, F., Muzzi, E., & Tartarini, S. (2020). 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