Restricted (Penn State Only)
Caliskan Aydogan, Oznur
Graduate Program:
Agricultural and Biological Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 15, 2018
Committee Members:
  • Virendra M. Puri, Thesis Advisor
  • Daeun Dana Choi, Committee Member
  • James Schupp, Committee Member
  • Paul Heinemann, Committee Member
  • Hojae Yi, Committee Member
  • thermal conductivity
  • DNHP
  • Malus x domestica (Borkh.)
  • fruit maturity
  • harvest time
Apple is one of the most widely cultivated fruit worldwide and processed into many products. The maturity of apple fruit at harvest is a factor that significantly impacts quality and storage. An early or late picked apple is more sensitive to physiological disorders and has shorter storage life than fruit harvested at the proper maturity time. To determine the harvest time, many physical, biochemical, and physiological properties have been assessed by destructive and nondestructive methods. However, no study on the measurement of thermal properties, which are a set of physical properties to predict the apple harvest time has been reported in the literature. Therefore, the objective of this study was to measure thermal properties, i.e., thermal conductivity, thermal diffusivity, and specific heat, of ‘Gala’ apple cultivar from the Fruit Research and Extension Center, Biglerville, PA during the 2017 growing season using the dual needle heated probe (DNHP), which is simple, rapid, and portable method. The measured weekly average of thermal conductivity, thermal diffusivity, and specific heat values of apple samples during the growing season in the laboratory (18-23°C) were between 0.441 ± 0.015 and 0.445 ± 0.014 W/m-K, 0.137 ± 0.004 and 0.152 ± 0.006 mm2/s, and 3.93 ± 0.20 and 4.23 ± 0.25 kJ/kg-K, respectively, with mean temperature of apple from 19.1 to 22.6°C. Average thermal conductivity and thermal diffusivity values of apple decreased significantly as apple ripened (p < 0.05) while specific heat values did not change significantly (p > 0.05) during the growing season. Overall, the most noticeable changes in thermal conductivity occurred during the last two weeks of the growing season, which corresponds to the time when major biochemical changes are known to occur. Subsequently, the apple’s thermal property changes during the growing season were examined for their prospective relationships with physical properties (size, density, and moisture content) and harvest fruit quality and maturity indices (firmness, soluble solid content, starch index, and Streif Index). Based on the Pearson correlation coefficient (r) among thermal properties and the physical properties and the harvest fruit quality and maturity indices, thermal conductivity had moderate correlation with thermal diffusivity (0.44), moisture content (0.45), firmness (0.44), soluble solid content (-0.62), starch index (-0.53), flesh stain % (0.44), and Streif Index (0.46) during the growing season. Hence, thermal conductivity can detect the quality changes during the growing season and determine the harvest time of apple but not as the sole predictor.