Effects of processing and storage on the nutrient composition of green vegetable pigeonpea

Authors: OJWANG, DAVID - University Of Nairobi; NYANKANGA, RICHAD - University Of Nairobi; IMUNGI, JASPETH - University Of Nairobi; GANGA, RAO - International Crops Research Institute For Semi-Arid Tropics (ICRISAT) - India; Olanya, Modesto; He, Zhongqi; Juneja, Vijay

Submitted to: Journal of Food Processing and Preservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2021
Publication Date: 8/15/2021
Citation: Ojwang, D.J., Nyankanga, R.O., Imungi, J., Ganga, R.N., Olanya, O.M., He, Z., Juneja, V.K. 2021. Effects of processing and post-harvest storage on nutrient content of vegetable pigeonpeas. Journal of Food Processing and Preservation. https://doi.org/10.1111/jfpp.15714.
DOI: https://doi.org/10.1111/jfpp.15714

Interpretive Summary: Pigeonpea is a tropical leguminous crop with significant food security implications in the marginal dryland regions of the world, due to its nutrient compoistion. Processing and post-harvest storage of vegetable pigeonpeas is crucial for efficient utilization of nutrients. We evaluated the post-harvest contents of zinc, iron, vitamin C, vitamin A, total sugar and proteins in processed and deep-frozen (-18C) storage vegetable pigeonpeas at 7, 14, 21 and 60 days. Pre-treatments (blanched, oven-dried, blanched+oven dried) and storage had significant (P<0.05) effects on nutrient content. Blanching reduced the content of zinc and vitamin C by 42% and 45% on a dry matter basis, respectively while dehydration positively improved most nutrients except vitamin C. All pre-treatments resulted in higher retentions of iron (7.2 mg/100g), zinc (2.8 mg/100g), total Sugars (4.3 mg/100g), vitamin A (337.2 µg/100g) and protein (23g/100g), while podded pigeonpeas had vitamin C content of 28mg/100g at 60 days following deep-frozen storage. Although it is assumed that chemical composition may not be altered with frozen-deep storage, subjecting samples to drainage (running cold water) prior to analyses may result in leaching of some soluble solids. Optimization pigeonpea of processing and storage conditions can enhance utilization subsequent to processing and storage in the dryland regions.

Technical Abstract: Vegetable pigeonpea (Cajanus cajan Milsp) is an important food crop in the dryland regions. Assessment of pigeonpea processing and storage conditions at post-harvest is important for documenting nutrient content. We evaluated the contents of zinc, iron, vitamin C, vitamin A, total sugar and protein in vegetable pigeonpeas, following pretreatments (blanched and/or oven-dried), and subsequent deep-frozen storage at -18 C (7, 14, 21 and 60 days). Pre-treatments and storage of vegetable pigeon peas had a significant influence (P<0.05) on the nutrient content quantified when samples were re-thawed and analyzed. Blanching reduced nutrient content, as zinc and vitamin C decreased (dry matter basis) by 42% and 45%, respectively. Dehydration had a positive impact on the nutrients, except vitamin C, which had a 4% reduction. Significant improvements in nutrient content were observed on iron (21%) and zinc (17%). Similarly, protein content, vitamin A and total sugars in post-harvest pigeonpeas were enhanced by 1, 6 and 2%, respectively. At 60 days of storage, blanched oven-dried pods had the highest content of iron (88%), while podded samples recorded 20% in zinc content. Overall, nutrient contents of pigeonpeas were at optimum at 14-21 days of deep-frozen storage. Ppre-treatments of oven-dried and blanched+oven dried resulted in higher retentions of iron (7.2 mg/100g), zinc (2.8 mg/100g), total Sugars (4.3 mg/100g), vitamin A (337.2 µg/100g) and protein (23g/100g), while podded pigeonpeas also showed significant increase of vitamin C content (28mg/100g) at 60 days of deep-frozen storage. Optimization of processing and storage conditions can enhance utilization of pigeonpeas in the marginal dryland regions.