Alcoholic Off-Flavor Disorders in Fresh Fruits

The off-flavor disorder is one of the most quality deteriorating and undesirable postharvest physiological disorders in fresh fruits. Over-biosynthesis and accumulation of ethanol metabolism-related metabolites such as acetaldehyde and ethanol have been associated with an alcoholic off-flavor disorder in various fresh fruits at both pre- and postharvest stages. Correspondingly, many studies have reported the association of such off-flavor disorders with several inducing factors, including anaerobic respiration, low O2 stress, high CO2 stress, and storage temperature stress, that upregulate ethanol metabolism in fruits. Furthermore, numerous metabolic and physiological mechanisms that govern ethanol metabolism under such factors are subsequently addressed. These mechanisms include the γ-aminobutyric acid (GABA) shunt pathway, mitochondrial energy metabolism, glycolysis, Krebs or TCA cycle, cytosolic malate metabolism, and starch and sugar metabolism. To summarize the relevant findings, the current paper reviews the literature on alcoholic off-flavor disorder, focusing on the role of significant underlying causes and key metabolic and physiological mechanisms in boosting ethanol metabolism in fresh fruits. In addition, recent measures that have been already taken or are in progress to control the higher activity of ethanol metabolism that may eventually result in limiting the alcoholic off-flavor disorder in harvested fresh fruits have also been discussed. Moreover, functions of metabolic mechanisms, including respiratory mechanisms, and other factors such as fruit genetic makeup, degree of maturity, and postharvest handling and storage conditions, are needed to be investigated in future work at both physiological and transcriptomics levels to reveal the additional relation to alcoholic off-flavor disorders in fresh fruits during ripening and storage.