Changes of the bacterial and fungal populations present in organic dark leafy green vegetable juices during refrigerated storage

Dark leafy green vegetable juices (DLGVJs), prepared with vegetables such as kale and chard, have shown substantial market growth in the past decade due to its profound health benefits. Unfortunately, as an innovative product, there was limited research focusing on DLGVJs. This study aimed to bridge key critical knowledge gaps associated with the microbial quality and shelf life of DLGVJs and elucidate the changes in both physicochemical and microbial properties of different organic DLGVJs during refrigerated storage. Culture-dependent and culture-independent analytical methods were applied to profile the bacterial and fungal populations in three organic DLGVJs (kale, chard, and collard greens) during refrigeration. Plate count results showed that the initial total aerobic plate counts (APC) ranged from 6.49 ± 0.03 to 6.74 ± 0.08 Log CFU/mL, and the initial total fungal counts ranged from 5.19 ± 0.06 to 6.75 ± 0.04 Log CFU/mL in fresh DLGVJs. During refrigerated storage the pH of DLGVJs decreased as the storage time increased and the redness of the juices increased as well. The culture-dependent analysis revealed bacterial counts initially increased and then declined, while fungal counts showed an initial decrease followed by an increase. By the end of the storage, the highest APC and fungal population were observed in kale juice and chard juice (7.03 ± 0.05 and 6.70 ± 0.03 Log CFU/mL) respectively. 16S rRNA sequencing results showed that the dominant bacterial genera of spoiled DLGVJs at the end of storage included Serratia, Leuconostoc, and Hafnia-obesumbacterium, and the major spoilage fungal were composed of Mrakia, Filobasidium, and Vishniacozyma. Results of this study provide insights into the microbial populations present in DLGVJs and the dominant spoilage genera during refrigerated storage, laying the foundation for the development of intervention strategies in the future.