Relationship between optical properties and soluble sugar contents of apple flesh during storage
Kangli Wei, Chen Ma, Ke Sun, Qiang Liu, Nan Zhao, Ye Sun, Kang Tu and Leiqing Pan
Postharvest Biology and Technology, Volume 159, January 2020, 111021
2020
บทคัดย่อ
Soluble solids (SS) in fruit are mainly composed of soluble sugars. This research aims to further the understanding of the detection mechanism of soluble solid content (SSC) based on optical technology by exploring the relationship between optical properties and soluble sugar contents. The total reflectance and total transmittance at 400–1050โ€ฏnm of Fuji apple flesh stored at 25 °C for 50 d and 0 °C for 150 d were collected by an automatic integrating sphere system. The absorption coefficient (µa) and reduced scattering coefficient (µ's) were obtained by iteratively solving the radiative transfer equation using the inverse adding doubling algorithm. The relationship of µa and µ's with the contents of SS, total soluble sugars, fructose, glucose and sucrose were quantitatively analyzed at different wavelengths, and prediction models were established by partial least squares regression (PLSR). The results showed that the changes in µa, µ's, SSC and soluble sugar content presented similar trends during storage at the two test temperatures. As the storage time increased, the decreases in µa and µ's were accompanied by declines in SSC and soluble sugar content. In addition, µa and µ's at 550–1050โ€ฏnm were both positively correlated with SSC and soluble sugar content, with correlation coefficients (r) of 0.834-0.992 and 0.737-0.981, respectively. Compared with the correlations at 550–780โ€ฏnm, the correlations at 780–1050โ€ฏnm between µa and SSC and soluble sugar content were enhanced, while the corresponding correlations with µ's were gradually weakened. In addition, SS was most strongly correlated with sucrose among the three types of soluble sugars. SS and sucrose had closer relationship with µa and µ's than fructose and glucose with µa and µ's. Moreover, their prediction models also performed better than the models for fructose and glucose, with Rp2 values of 0.731-0.804. Thus, the prediction of SSC based on Vis-NIR optical technology may be related to the high correlations between the absorption and scattering properties and the sucrose content.