Elucidating the biochemical factors governing off-flavor perception in mandarins

• Mandarin varieties showed great diversity in developing off-flavors after harvest.
• There was low correlation between ethanol levels and off-flavor perception.
• Monoterpene levels correlated negatively with off-flavor perception.
• Off-flavor evolves due to general changes in volatiles profiles and compositions.

Mandarins tend to develop off-flavors during storage, and this is attributed to induction of ethanol fermentation metabolism and accumulation of ethanol and its by-products. In order to elucidate the biochemical factors contributing to off-flavor formation in mandarins, we conducted sensory and aroma-volatile analyses of 41 different mandarin varieties within the Israeli citrus breeding collection, at harvest and after 6 weeks of cold storage at 6 °C followed by 5 days at 20 °C. Descriptive sensory analysis with the aid of a trained panel revealed great diversity among mandarin varieties, in perceived off-flavors; and gas chromatography (GC) analysis revealed only a low correlation (R = 0.14) between ethanol levels and perception of off-flavors. Gas-chromatography mass-spectrometry (GC–MS) analysis of levels and compositions of total aroma volatiles during postharvest storage revealed general increases in levels of alcohols and ethyl esters, and consequent decreases in levels of monoterpenes, sesquiterpenes, and aldehydes. Detailed volatile analysis of diverse varieties with strong and weak off-flavors revealed that the aroma volatiles compositions and the ratios between chemical classes of volatiles have completely changed during storage in varieties with strong off-flavors, but were less altered in varieties with weak off-flavors. In addition, we observed a negative correlation (R = −0.58) between monoterpene levels and off-flavor perception, i.e., most varieties with weak off-flavors had relatively high terpene levels, which might mask the perception of off-flavors. Overall, it is suggested that perception of off-flavors in mandarins does not depend solely on accumulation of specific volatile compounds, such as ethanol, but rather evolves during storage because of general changes in juice aroma-volatiles profiles and compositions which create an atypical or spoiled flavor.