The feasibility of determining of optimal harvest time of edamame using a handheld and portable colorimeter in the field

Dajun Yu,  Ph.D. student of Water INTERface IGEP, Department of Food Science and Technology

Advisor: Haibo Huang

Edamame is a trending soy food due to its high nutritional value and its potential use as functional foods to reduce the risk of different diseases like heart diseases, cancer, and diabetes. The demand for edamame in the US market keeps increasing while most of the edamame is still imported from other countries. To promote the domestic production of edamame, it is important to ensure the quality of harvested edamame and appropriate harvest time is crucial. However, the current harvest is highly dependent on farmers’ experiences and might lead to variations of quality.

In this study, edamame pods were harvested at six different time points named R5-1, R5-2, R6-1, R6-2, R7-1, and R7-2. Pod dimensions (pod length, pod thickness and pod width), pod weight, 20-bean weight, sugar content and chemical compositions (e.g. protein, fat, fiber, undesired sugars) were determined on these edamame samples to divide them into 3 groups labeled “too early to harvest’, “ready to harvest” and “too late to harvest” respectively. Meanwhile, the pod color (lightness, red/green, blue/yellow, and reflection under different wavelengths) was also measured by a hand-held, portable colorimeter. The correlation was analyzed between the pod color and the sample groups to see if the color could help identify “ready to harvest” samples.

Taken all physical properties and chemical compositions change into consideration, stage R6-1 was the best harvest window to harvest edamame with high quality (highest pods weight and thickness, highest sweetness and starch content, and relatively low oligosaccharides and fat content). To have a longer harvest window, R6-2 could also be an acceptable harvest window because no big difference was found between samples harvested at R6-1 and R6-2. Additionally, from our data, the portable spectrometer, which is convenient and easy to use, can assist farmers in determining the right time to harvest the best quality edamame.

Images of hand-held colorimeter/spectrophotometer and edamame samples.

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