Investigating the Qualitative Changes of Golden Delicious Apple Variety during Storage Using X-ray Imaging

Introduction Isfahan province is considered to be one of the top ten producing provinces of apple orchards with an area of 17,274 hectares and a production of 120,000 tons of apple. Determining the quality parameters of agricultural products requires the use of various methods, which are different according to the nature and characteristics of each product. The two main categories for dividing these methods include analytical (objective) methods and sensory (intrinsic) methods. Both qualitative assessment methods can be used in destructive and non-destructive ways. Apple is one of the fruits that can be stored for a relatively long time. Physiological changes during the storage period are inevitable and cause  change to some quality characteristics of the fruit, such as firmness, moisture content, density, pH, and soluble solids. Using the methods of determining and extracting the quality characteristics of fruit during storage and monitoring the changes created, provides a suitable criterion for selecting and preparing the necessary conditions for storage and storage at the disposal of users and producers. X-ray imaging technique is among the methods used and computed tomography, which is now well-known in evaluation of various agricultural commodities and food quality. X-rays are electromagnetic waves with a short wavelength (0.01 to 10 nm) and high energy (from 120 electron volts to 120 kilo electron volts) that can penetrate many materials.   Materials and Methods In order to determine the relationship between the physicochemical properties and the CT number of Golden Delicious apples, 280 Golden Delicious apples were collected from an orchard located in Semirom city of Isfahan province and stored in a cold room at 0 and 4 ºC and a humidity of 85±5%. These apples were harvested and collected from several trees after the fruit ripened completely. The weight and volume of apples were randomly selected based on the apples on the trees. The samples of stored apples were examined in 4 stages and based on the duration of storage on zero (the beginning of storage), 45, 90 and 135 days.. These tests included non-destructive tests of CT scan imaging and destructive tests to extract the physicochemical properties of apples, including CT number, pH, firmness, moisture, density, and soluble solids. In order to prepare CT scan images of apple samples (non-destructive X-ray test), a GE Healthcare multi-slice CT scan machine model 5122080-12 with 80 kV and 10 mA was used in the CT scan center of Al-Zahra Hospital in Isfahan. Moisture content was determined by weighing the samples and recording their moisture changes before and after drying in the oven at 105 ºC s for 24 hours. Total soluble solids were measured by refractometer device and reported as Brix degree. In order to measure the density of fruits, the weight and volume of each fruit was recorded. A digital pH meter was used to measure the pH of fruit. Penetrometer device was used to measure the firmness of apples. At the end, with the specified values, Pearson correlation coefficients between CT number and other physicochemical properties were determined. Also, by plotting the mentioned values, the most suitable regression equations with the highest coefficients of determination were obtained.   Results and Discussion Based on the results, the average value of CT number, pH, firmness, moisture, density and total soluble solid of apple at two temperatures of zero and 4 ºC were -115.02 and -166.86, 3.85 and 3.86, 76 37.36 and 33.36 N, 0.82 and 0.80%, 0.76 and 0.72 g/cm3  and 15.30 and 15.79% Brix, respectively. The results showed that the CT number has a negative linear correlation with pH and total soluble solid and a positive linear correlation with the properties of apple firmness, moisture and fruit density. Based on the results, at two storage temperatures of 0 and 4 ºC, the coefficients of determination (R2) obtained from the linear regression model of CT number with pH levels of 0.75 and 0.55, apple firmness 0.32 and 0.57, moisture content 0.78 and 0.85, fruit density 0.82 and 0.84 and total soluble solid 0.85 and 0.62 were obtained.   Conclusion These results shown that the non-destructive test of X-ray imaging can be used with a suitable approximation to determine some quality properties of apple products.