Metabolomics Combined with Standard Quality Measures of ‘Honeycrisp' Apple Fruit Reveals Aspects of Metabolism Related to Flavor, Crispness, Maturity, and Storability

‘Honeycrisp’ is popular dessert apple.  As acreage of planted ‘Honeycrisp’ increases, reliably assessing optimum storage duration is becoming increasingly important.  Apple fruit quality is typically assessed by measuring titratible acidity, internal ethylene concentration, firmness, soluble solids, and starch index.  These evaluations are commonly used both in commercial and research settings to analyze storage potential to decide whether fruit is ready to harvest and how long it will be expected to store.  In research, metabolomic techniques can be used to attribute metabolic events to the progression of quality data measurements.  The current study evaluates changes in levels of peel metabolites including volatiles, amino acids, organic acids, carbohydrates, cell wall, and membrane components and relates them to standard quality measures associated with ripening, flavor development, and storage potential.  Volatile compounds characteristic of ripeness to overripeness tend to increase with storage, concomitant with increases in internal ethylene and starch clearing.  Certain amino acids and organic acids exhibited variable patterns of response that may suggest metabolic shifts such as the response to initial chilling and the transition from ripeness to senescence.  While metabolic indication of senescence corresponds to changes quality parameters such as the loss of firmness, the fruit response to chilling is not consistently captured by quality measurements.  Results suggest that the divergence from a healthy metabolome following storage disorder onset, which includes changes cell membrane and cell wall components, is not consistently captured or predicted using standard apple maturity and quality measurements.  Monitoring metabolites may provide a more reliable indication of not only fruit quality, but also susceptibility to disorders.