Potential of Vis/NIR spectroscopy in estimating ATP content per protoplast as an indicator of freshness of spinach

The possibility of using ATP content per protoplast as an indicator of freshness was studied in spinach (Spinacia oleracea). The ATP content per protoplast of spinach was determined and compared during 3 days of storage at 25 °C. ATP content increased rapidly at the early stages of storage, reaching a peak level after 24 h. After one day (24 h) of storage, the ATP content decreased with the storage time. Overall, the ATP content changed as a quadratic polynomial function of storage time. This phenomenon, which is likely to be an expression of the loss of protoplast viability, is a useful indicator, allowing the prediction of spinach deterioration during storage. In addition, the correlation between ATP content and Vis/NIR spectra during storage was excellent (R=0.8245 for transmittance at 681 nm, and R =0.9008 for the first derivative of transmittance at 760 nm). These results demonstrate the possibility of evaluating the freshness of spinach through estimation of the ATP content per protoplast with Vis/NIR spectroscopy after approximately 30 hours of the harvested plant storage.