Introduction: Strawberry is one of the native and small fruits of moderate regions, which its cultivation has been increased in all over the world including Iran. Due to the abundance of vitamin C and mineral materials, it is very useful for some diseaseses. Lack of the knowledge in production management, harvesting, cooling, transportion, storage, marketing and processing equipments and connection between these different parts are the main problems throgh industrial production of strawberry fruit (Salami et al., 2010). According to the various studies, the parameters such as color, shape, size and mass are not sufficient for the consumer to purchase the fruit (Abbot, 1991). They would like to have more information about the fruit which is supposed to be purchased (Voca et al., 2008). Several researchers have been investigated physical and chemical properties of different varieties of strawberry fruit (Wojdylo et al., 2009; Salamat, 2011; Nemzer et al., 2018). According to the litrature, any international standard classification for Parus strawberry (which is mostly cultivated in Iran) based on physical and chemical was not found. In this study, some physical, mechanical and chemical properties of strawberry fruit Parus variety, as well as the relationship between them, were investigated. The classification was performed based on the appearance features including color and size with the opinion of the expert in six classes.
Materials and methods: In Kurdistan province strawberry fruit is often grown in open area and cultivated areas of Parus variety due to many reasons are increasing. To classify the strawberries, six classes were considered. Physical and mechanical properties such as dimensions, density, porosity, stiffness and biological yield point were measured at least at five replications. The porosity of the strawberries was also calculated through the division of the difference between actual and apparent density to actual density. Also, the stiffness and biological yield point were measured using Universal Instron Testing Machine (Zwick/Roll). Chemical properties of Parus strawberry including vitamin C, acidity, total soluble solids and flavor index were investigated at five replications.
Results and discussions: The analysis of variance showed that all chemical properties including ascorbic acid, acidity, total soluble solids, and flavor index, were strongly influenced by the class. The LSD mean comparison showed that the highest levels of vitamin C were related to the ripe fruits which had a direct relationship with fruit size. The acidity values between the classes varied from 0.55 to 1.08, and the lowest value was related to the first, second and third classes, respectively. The total soluble solid material (TSS) was affected by some factors: sugar (as main part), organic acid and organic pectins and was increased by growing strawberries and increasing the amount of sugar. For the first, second and third classes, TSS was higher than those of the fourth, fifth and sixth clases. The flavor index value for the lower classes (first, second and third) is higher than the higher classes (almost 2 times). The analysis of variance for all physical and mechanical properties indicated that all parameters are affected by the classes. Due to its more soluble materials, the maximum value for actual density was related to the third and second classes, respectively. The apparent density of agricultural products depends on various factors such as geometric shape, size, surface properties, moisture content and measurement method. The apparent density for the first and fourth classes were 561.743 and 498.408 gr.mm-3, respectively. The maximum and minimum value of stiffness was related to first (about 5.2 N.mm-2) and fourth (about 28.2 N.mm-2), respectively. For biological yield the maximumvalue was related to the fourth class, as well.
Conclusion: In this study, the classification of strawberry, variety of Parus was investigated based on physical, mechanical and chemical properties. All properties were affected by changing the classes. The results of this research can be used to design and construct post-harvest and sorting mechanisms of agricultural products which require comprehensive information about physical, mechanical, chemical properties.