Lemongrass (Cymbopogon citratus (DC.) Stapf, Poaceae) has been known for demonstrating antimicrobial activity against food spoilage bacteria. These antimicrobial properties can be further utilized for the development of natural food preservatives. In this study, the compounds present in water extract and essential oil of lemongrass were analyzed and their potential as tofu preservatives was evaluated. The water extract was prepared by the infusion method, while the essential oil was made by steam and water distillation. The phytochemicals composition of the water extract and essential oil was analyzed by qualitative colorimetric phytochemical screening and Gas Chromatography-Mass Spectroscopy (GC-MS) technique, respectively. Their preservative activity on tofu was evaluated by observing their ability to inhibit the growth of bacteria on the tofu and the physical changes of tofu during 10 days of preservation at room temperature. The results showed that lemongrass water extract contained terpenoids, tannins, and saponins. The GC-MS analysis identified 13 compounds in the essential oil. Neral, geranial, β-myrcene, juniper camphor, and viridiflorol were found as the major compounds. At concentration of 20%, lemongrass water extract demonstrated inhibition of bacterial growth during 10 day storage of tofu and improved the shelf life by 4 days longer from those of the negative control. In contrast, lemongrass essential oil did not show inhibitory activity in bacterial growth in tofu but it was capable of maintaining the color, odor, and texture of tofu as well as delaying the slime formation up to 4 days.

This study evaluated the profile of microbial growth inhibition on tofu treated by the essential oil of the selected spices. The microbial growth on the tofu was visually observed by the pour plate method, while their number was enumerated by the indirect optical density (OD) method. All the tested essential oils were visually reduced the microbial growth on tofu during storage. Each spices oil showed a different inhibition pattern, with bay leaf, galangal, and ginger oils exerting favorable effects for the most prolonged period. The day-bay-day comparison demonstrated that the best inhibition effect was on day-6 and -8, with bay leaf and galangal oils showing the most promising activity. The best profile of both essential oils might play a vital role in the tofu preservation process by natural products.