Apple is one of the most important fruit in international trade.
The current annual worldwide apple production of commodity is
estimated at over 80 million tons (FAO-STAT 2013). Over the years,
consumers' attention to fruit quality is not limited to external
attributes including color, size and shape (Zhang et al., 2014), but
further extends to internal attributes such as the soluble solids
content (SSC) and the nutritional content (Mendoza et al., 2014;
Kumar et al., 2015). SSC is the most important internal quality
index of apple, and also relates to fruit maturity and harvest time
(Drogoudi and Pantelidis, 2011). Knowledge of the SSC may
enhance the competiveness and profitability of the industry and
assure consumer acceptance and satisfaction. To face this
challenge, a recent trend in agribusiness is a declining reliance
on subjective assessments of quality and increasing adoption of
objective and innovative techniques for sensing and measuring the