Effects of different drying processes on the quality of sweet potato leaf tea fermented by Eurotium cristatum
In order to optimize the drying process with respect to the maximal sensory quality of the product,contents of sensory relat-ed chemical constituents and free amino acids,along with sensory evaluation and volatile profiles were analyzed for dehydrated sweet potato leaf tea treated by hot air drying(HAD)with drying temperature of 60,70,and 80 ℃,heat pump drying(HPD),and vacuum freeze drying(FD).The results showed that for the HAD treatment,with the increase in the drying temperature,both total polyphenol content and total flavonoids content decreased whereas the content of soluble sugar increased.No significant differences on tannins content were found between tea samples.In the HAD 80 ℃ tea sample,content of phenolic substances and flavonoids that cause astringency in the tea soup was low,the sensory evaluation of the tea soup color and aroma was high,and the aroma components were the most and the overall quality was the best;HAD 60 ℃ tea sample had high content of total phenols,total flavonoids,and bitter amino acids,with a strong bitter taste;FD tea sample has the best appearance evaluation and the lowest tannin content,but it had the highest total phenols and flavonoids,and a strong grassy aroma,which was related to the high content of guaiacol in its volatile substances,resulting in a lower sensory score.In the volatile profiles of all tea samples,the OAV values of 1-octen-3-ol,2-methoxy-phenol,and β-ionone were higher than 100.It re-vealed that 1-octen-3-ol,2-methoxy-phenol,and[3-ionone were the key aroma compounds that were responsible for the aroma characteris-tics formation in the dehydrated sweet potato leaf tea.Taken together,these findings provided the useful information for understanding the formation mechanisms of the taste and aroma characteristic in sweet potato leaf tea fermented by Eurotium cristatum.This research also pro-vided theoretical basis for the optimization of the drying process with respect to the maximal sensory quality of sweet potato leaf tea for the industrial production.
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