Impacts Of Different Postharvest Physico-Chemical Treatments On Aromatic Volatile Development In 'FL 47' Tomato Fruits

Aroma,a complex mixture of volatile compounds,is one of the most appreciated tomato characteristics,and plays a key role in the perception and acceptability of tomato products by consumers.Of more than 400 volatile compounds identified in tomato,the changes of some compounds are studied during ripening;however,our information of expression patterns of most compounds is limited.Besides a large emphasis of commercial breeding programs on disease resistance,productivity,and firmness,which has resulted in cheaper,year-round produce availability which runs at the expense of aroma quality,inappropriate postharvest handling practice could impact aroma quality in tomato fruit as well.Furthermore,pre-chilling treatment/fumigation with heat,methyl salicylate(MeSA),or methyl jasmonate(MeJA)shows a potential to alleviate visible chilling injury(CI)symptoms of tomato fruit,although little is studied on their impacts on tomato aroma quality.On the other hand,the impacts of consumer handling practices of tomatoes such as refrigeration and heating on aroma quality are less reported.In this study,we firstly determined the expression patterns of volatile compounds during 'FL 47' tomato ripening,and then assayed the impacts of different postharvest handling practices at different ripening stages on aromatic volatile development in 'FL 47'tomato fruits.The results of our study were as follow:1.Based on headspace,solid phase micro-extraction,and gas chromatography-mass spectrometry system(HS-SPME-GC-MS)analysis,the changes of different volatile compounds were investigate as 'FL 47' tomato ripened.Totally,50 total compounds,belonging to ten chemical classes,were identified with the major compounds being aldehydes,ketones and alcohols.In agreement with the expression pattern of total volatile concentration,a burst at red-ripe stage was also observed for aldehydes,alcohols,ketones,hydrocarbons,and nitrogen compounds.Meanwhile,there are six expression patterns(?-?)for volatile compounds during tomato ripening process.50%volatile compounds fluctuated or accumulated at early ripening stages with a burst at red-ripe stage(Pattern ?);12%gradually increased during ripening(Pattern?);8%fluctuated or accumulated at early ripening stages with a burst at pink stage(Pattern?);12%volatiles fluctuated during ripening with the highest level at turning stage(Pattern IV);10%fluctuated during ripening with the highest level in pink fruits(Pattern?);and others remained stable as fruits ripened(Pattern VI).Red-ripe fruits possessed the highest volatile concentration in comparison with fruits at other stages,and both e-nose and PCA&Cluster analysis could discriminate the volatile profile in red-ripe fruits from those at other stages.2.A combination of HS-SPME-GC-MS and sensory panel was conducted to study the impact of 4-day exposure of 'FL 47' tomato fruit to 5?at mature green stage on aroma quality(internal CI)after ripening at 20?,and if a pre-chilling heat treatment(5?for 4 days)could alleviate the internal CI.The results showed that chilling treatment generally suppressed production of hydrocarbons,aldehydes,phenols,alcohols,esters,ketones,acids and sulfur-and nitrogen-containing heterocyclic compounds,including the following abundant and/or important volatiles:hexanal,trans-2-hexenal,6-methyl-5-hepten-2-one,?-ionone,2-methylbutanal,2-phenylethanol,guaiacol and 2-isobutylthiazole.Heat treatment alone did not affect most volatile levels after ripening;however,heat treatment prior to chilling exposure alleviated the reduction of some key volatile compounds(6-methyl-5-hepten-2-one,?-ionone,2-methylbutanal,and 2-phenylethanol)caused by chilling exposure,which was in agreement with sensory panel results in that panelists perceived more tomato flavor in "heating + chilling" treated fruit than fruit that were chilled only.3.'FL 47' tomatoes at breaker stage were treated with 0.05 mM DI water,MeSA or MeJA vapor for 24 h prior to ripening at 20?or exposure to 5?for 9 d before ripening at 20?.Fruits were sampled at red-ripe stage to study the impact of MeSA/MeJA on the development of volatile compounds,and their effects on alleviation of aroma loss after chilling exposure.The results showed that 9-day chilling treatment at 5?did not result in any visual CI;however,for internal CI it generally suppressed production of oxygen-containing heterocyclic compounds,ketones,sulfur-and nitrogen-containing heterocyclic compounds,alcohols and aldehydes,in association with 9 important aroma contributors to tomato fruit:1-penten-3-one,6-methyl-5-hepten-2-one,geranyl acetone,2-phenylethanol,2-phenylacetaldehyde,2-methylbutanal,3-methylbutanal,3-methylbutanol and 2-isobutylthiazole.Compared with chilling alone and MeJA + chilling treatment,MeSA treatment alleviated the loss of some key aroma volatiles contributed to tomato aroma,including geranyl acetone and methyl salicylate.In agreement with this,panelists perceived a higher overall tomato aroma in MeSA + chilling treated tomatoes than that in chilled tomatoes.The pre-chilling MeJA treatment,although mitigating some volatile reduction such as 2-isobutylthiazole and 6-methyl-5-hepten-2-one,had little impact on mitigating overall perceived aroma loss.Furthermore,MeJA/MeSA treatments alone at the breaker stage,although reduced the abundances of 1-penten-3-one,geranyl acetone,2-methylbutanal,3-methylbutanal,3-methylbutanol,and 6-methyl-5-hepten-2-one,had little effect on tomato aroma quality as perceived by a sensory panel.4.'FL 47' tomatoes at red stage were dipped in 50?hot water for 5 min or exposed to 5?for 4 days(refrigeration)to simulate consumer handling of tomato in food service or home kitchens,respectively.The result showed that of the 42 volatile compounds detected,refrigeration generally suppressed production of aldehydes,alcohols,oxygen-containing heterocyclic compounds and nitrogen-and oxygen-containing compounds,including the following abundant and/or important volatiles:3-methylbutanal,2-methylbutanal,hexanal,cis-3-hexenal,trans-2-hexenal,2-phenylacetaldehyde,3-methylbutanol,2-phenylethanol,1-penten-3-one,and geranyl acetone.On the other hand,the production of aldehydes,alcohols,hydrocarbons,oxygen-containing heterocyclic compounds,and nitrogen-and oxygen-containing compounds were reduced by heating,associated with low concentrations of 2-methylbutanal,cis-3-hexenal,trans-2-hexenal,2-phenylacetaldehyde and 2-phenylethanol.Both e-nose and PC A&Cluster analysis could discriminate three treatments based on volatile profile in tomato fruits.These results indicate that a short heating or refrigeration of tomatoes substantially impacts tomato aroma quality,and are not recommended.