Determination of optimum humidity for air-curing of cigar tobacco leaves during the browning period

Hainan is a natural air-curing barn for cigar leaves. Humidity has a marked influence on the air-curing of cigar leaves. The browning stage is a key period, which determines the degree and quality of cigar tobacco leaf browning. To understand the effects of humidity in the browning stage on tobacco leaf quality, we examined the malondialdehyde and polyphenol contents, polyphenol oxidase activity, moisture, chemical composition, and appearance of tobacco leaves that were air cured at humidities of 60%, 70%, and 80% during the browning stage. High humidity (80%) during curing led to a high moisture content and polyphenol oxidase activity in leaves. With regard to malondialdehyde content, a minute differences between moderate-humidity (70%) and high-humidity (80%) air-curing were observed. During the browning stage, the chlorogenic acid content was reduced by 85.32% when tobacco leaves were air-cured at 80% humidity, which means that it underwent a more comprehensive oxidized process compared to the other two treatments, whereas rutin and scopoletin experienced a more thorough oxidation at 60% humidity. 70% Humidity was found to be the most suitable humidity for the appearance of air-cured leaves than others, producing the optimum appearance of the cigar leaves. At the end of air-curing, the treatment with 70% curing humidity had a more coordinated chemical composition compared to the other treatments, for instance, it had a starch content of 1.14% and a potassium-chloride ratio of 7.65, which indicated a much better quality of cigar tobacco leaves. In summary, these findings indicate that air-curing at 70% humidity during the browning stage was the most favorable choice for improving tobacco leaf quality for cigar production.