The Japanese mint (Mentha arvensis L.) is known as a culinary and medicinal herb widely cultivated in several countries. The mint essential oil is considered as one main source of menthol. In this study, the Japanese mint collected from the Central Highlands of Lam Dong Province (Vietnam) was extracted the essential oil by hydro-distillation (HD) and microwave-assisted extraction (MAE). Different extraction parameters were investigated, involving mint leaf drying periods (30, 60, and 90 mins) at 50 °C, material to water ratios (1:4, 1:6, 1:8, and 1:10 for HD and 1:1, 1:1.5, 1:2, and 1:2.5 for MAE), extraction durations (60-180 for HD and 10-25 mins for MAE), and microwave energy (230, 380, 540, and 700 W) in order to discover the conditions with the highest yields for both HD and MAE. The GC-MS was used to determine the oil chemical constituents. For dried mint leaves (nearly 40 % moisture), the highest oil yield of 0.0832 mL g−1 (dried weight) was recorded, and the content of menthol was up to 70.60 % extracted by MAE whilst 0.0510 mL g−1 of yield (dried weight) and lower menthol (62.80 %) were obtained from HD. Besides, menthol, trans- and cis-menthone were found at relatively high concentrations for both HD and MAE (20.19-16.30 and 4.62-5.01 %, respectively). Compared to HD, MAE exhibited higher oil yields and menthol contents, but lower distillation time, resulting in more effective extraction performance of MAE.
Fermentation of cocoa beans is the most important process contributing to the flavor in chocolate and other related products. The present study aimed to investigate the fermentation at a laboratory scale of cocoa beans with and without 10% w/w mucilage removal (whole beans). The physicochemical properties and microorganism development were monitored for six days of continuous fermentation (sampling was conducted every 24 hours). The results indicated the effects of partial mucilage removal of cocoa beans before the fermentation, in which the temperature, pH, and mucilage content (with/without mucilage removal) were recorded as 36.5 oC/38.6 oC, 3.44/3.31, and 18.41%/21.84%, respectively at the final day. Besides, the density of microorganisms (yeast-mold, lactic acid bacteria, and acetic acid bacteria) of cocoa beans with partial mucilage removal was higher than whole cocoa beans due to the increased aeration of the beans with mucilage removal, creating favorable conditions for the growth of microorganisms. After the fermentation, several physicochemical properties of the two cocoa bean types were compared, which demonstrated the more favorable quality of the cocoa beans with partial mucilage removal compared to the whole cocoa beans for the fermentation, e.g., lower seed shell content (14.1% vs. 17.8%), lower total acid (1.67% vs. 2.77%), and pH of around 5.0.
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