Aroma Volatile Profiles from Ripe Tomatoes are Influenced by Physiological Maturity at Harvest: An Application for Electronic Nose Technology

Abstract

The effect of physiological maturity at harvest on ripe tomato (Lycopersicon esculentum Mill.) volatile profiles was studied using ripening response time (in days) to 100 μL·L-1 exogenous ethylene treatment as a tool to separate immature-green from mature-green fruit. Electronic nose (EN) sensor array and gas chromatography (GC) analyses were used to document volatile profile changes in tomatoes that required a 1-, 3-, or 5-day ethylene treatment to reach the breaker stage. EN output analysis using multivariate discriminant and canonical analyses classified intact tomato and whole tomato homogenate samples that required 3 or 5 days of ethylene treatment as significantly different (P < 0.01) from those that required only 1 day. The GC aroma profiles from whole tomato homogenate showed that 1-day fruit had significantly higher levels (P < 0.05) of 1-penten-3-one, cis-3-hexenal, 6-methyl-5-hepten-2-one, 2-isobutylthiazole, and geranylacetone when compared to 5-day fruit. Analysis of excised tomato tissues showed that pericarp (including columnella) produced an average 219% greater concentration of the 16 aroma volatiles quantified by GC when compared to locular gel (442 and 203 μL·L-1, respectively). EN analysis concurred with GC by showing greater average Mahalanobis distance between pericarp tissue groupings when compared to locular gel groupings (78.25 and 12.33 units, respectively). Pericarp tissue from the 5-day ethylene treatment showed significantly lower levels of 1-penten-3-one, trans-2-heptenal, 6-methyl-5-hepten-2-one, 2-isobutylthiazole, geranylacetone, and β-ionone compared to the 1- and 3-day treatments, Similarly, locular gel from the 3- and 5-day ethylene treatments had significantly lower levels of 1-penten-3-one, 2-isobutylthiazole, and 1-nitro-2-phenylethane compared to 1-day samples. cis-3-Hexenol in locular gel was the only volatile compound that showed significantly higher levels with increasing ethylene treatment. EN analysis showed greater Mahalanobis distances between 1- and 3-day ethylene samples than between 3- and 5-day ethylene samples (32.09 and 12.90, 24.14 and 6.52, 116.31 and 65.04, and 15.74 and 13.28 units, for intact tomato, whole tomato, pericarp, and locular gel homogenate, respectively).