Nutrition, Sensory, Quality and Safety Evaluation of A New Specialty Produce: Microgreens
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Microgreens are new emerging food products, which are young seedlings of vegetables and herbs, having two fully developed cotyledons with the first pair of true leaves emerging or partially expanded. They have gained popularity in upscale restaurants and grocery stores in recent years. However, little relevant scientific data is currently available on microgreens. The present research project was dedicated to explore the nutritional value, sensory attributes, consumer acceptance, postharvest quality and microbial safety of microgreens.
In the first part of this project, phytonutrients were determined in 25 commercially available microgreens. Results showed that different microgreens provided extremely varying amounts of phytonutrients. Among the 25 microgreens assayed, red cabbage (Brassica oleracea L.), cilantro (Coriandrum sativum L.), garnet amaranth (Amaranthus hypochondriacus L.) and green daikon radish (Raphanus sativus L.) had the highest concentrations of ascorbic acids, carotenoids, phylloquinone, and tocopherols, respectively. Compared with the nutrient concentrations in mature leaves recorded in USDA National Nutrient Database, microgreen possessed higher nutrient density.
Although microgrees are nutrient-dense, there is little information and data on the consumer acceptability of microgreens; therefore, consumer acceptance test were carried out. Six microgreens were first selected out of 25 varieties of microgreens in the prelimanry test and subsquently evaluated by 80 consumer panelists for sensory attributes. Chemical compositions and nutritional values of the taste-panel tested microgreens were also investigated for correlations with sensory attributes. All microgreens evaluated demonstrated "good" to "excellent" consumer acceptance and nutritional profil and overall acceptability of microgreens was significantly correlated with flavor acceptability.
Generally, microgreens are very tender, and thus have a short shelf life. To optimize the postharvest handling conditions, the effects of temperature, modified atmosphere packaging (MAP) and chlorine wash on postharvest quality and shelf life of radish microgreens (Raphanus sativus L. var. longipinnatus) were studied. The impacts of light exposure during storage on sensorial quality and bioactive compounds were also investigated. Results showed that 1) one degree Celsius was the optimal temperature for radish microgreens storage; 2) MAP did not significantly affect quality attributes during 28 days of storage at 1°C; 3) chlorine wash treatment reduced microbial populations initially, however, it rebounded to pre chlorine wash levels within 7 days; and 4) light exposure accelerated quality deterioration and increased the amount of ascorbic acid, while dark storage may be profound for quality and carotenoid retention.
The final part of this project was a comparative microbiological study between radish sprouts and radish microgreens producd from artificially contaminated radish seeds. Starting from seeds with same contamination levels, E. coli O157: H7 and E. coli O104: H4 populations on harvested radish microgreens were 3-4 logs lower than that on radish sprouts. These results demonstrated that the microbial growth on sprouts were much faster than that on microgreens, which poses great risk of microbiological hazard to sprout-consumers. In contrast, microgreens seem to bear a relatively low food safety risk.