Abstract: In order to gain a deep understanding of the principle of an optimal method for the determination of soluble solid contents in fruits, we quantified the relationships between the contents of soluble solid, total soluble sugar, fructose, glucose and sucrose and absorption and scattering properties of apple flesh during storage (150 d at 0 ℃) using the single intergrating sphere technology. Besides, predictive models were established by partial least squares regression. The results showed that the contents of soluble solids and soluble sugars decreased during storage, and so did the absorption coefficient (μa) and reduced scattering coefficient (μ’s); highly significant positive correlations occurred between the two groups of parameters (r = 0.768–0.992). In particularly, the correlations between these soluble components and μa were higher. Among the three soluble sugars, soluble solids were the most correlated with sucrose (r = 0.961). The average correlations of soluble solids and sucrose with μa and μ’s (r = 0.890–0.963) were higher than those of fructose and glucose (r = 0.813–0.910). Furthemore, the prediction models for soluble solids and sucrose were better, with determination coefficient for prediction (Rp) of 0.886–0.893 and 0.864–0.906, respectively. The results showed that the high correlations between soluble sugars (especially sucrose) and optical properties may provide evidence that optical properties could be used to predict soluble solid contents. This study provides a theoretical rationale for optical detection of fruit quality.

Key words: apple, optical properties, integrating sphere, soluble solid, sugar, correaltion