Instrumental measurements of juiciness and freshness to sell apples with a premium value

Juiciness and freshness play a critical role in consumers' choice of apples, and objective measurements of the traits are essential for adding a premium to fruits with high consumer demand. Juiciness and freshness were sensory evaluated by four apple-breeding experts. The score of sensory juiciness decreased with decreased instrumental measurements of water content (WC), firmness, and apoplastic solution (AS). The influence of firmness on sensory juiciness was not linear, and perception of juiciness rapidly decreased when firmness decreased below 60 N. The sensory freshness score was related to titratable acidity (TA), firmness, and the AS. A nonlinear regression model for freshness indicated that freshness was less likely to be perceived as the AS in flesh tissue decreased, and the perception of freshness rapidly decreased when firmness decreased below 60 N or TA decreased below 0.25 g 100 ml−1. The firmness of fruit treated with 1-MCP hardly decreased during storage. The titratable acidity of fruit treated with 1-MCP decreased; however, the degree of the decrease was significantly lower than that of non-treated fruit. The AS immediately decreased just after harvest and was not significantly different in most cases between 1-MCP-treated and non-treated fruit during storage. Therefore, measurements of firmness and TA were useful for distinguishing 1-MCP-treated fruit from non-treated fruit and the AS is necessary to distinguish between stored fruit and that just after harvest. The performance of calibration models developed by NIR spectroscopy for TA, firmness, and AS was lower than that for soluble solids content (SSC), which is used to grade apples by NIR spectroscopy in Japanese packing houses. Therefore, it is impractical to grade fruit by freshness using calibration models. However, high correlation coefficients were obtained in the calibration model for WC. The correlation coefficient of WC was about as high as that of SSC. Therefore, apples could be graded by juiciness using the calibration model for WC with the auxiliary use of calibration models for firmness and AS.