Effect of Processing Methods on the Micronutrient Profile, Colour, and Anti-nutritive Components of Justicia heterocarpa (mwidu)

Abstract

Justicia heterocarpa (mwidu) is a popular indigenous leafy vegetable picked wild in rural regions of Morogoro, Tanzania, during the wet seasons. This research examined the impact of processing on micronutrients, total phenols, and anti-nutrient content. The fresh leaves (FL) underwent direct shade drying (UBLDDR), blanched shade drying (BLDR), blanched oven drying (BLDO), fermentation (FFL), and gas and microwave cooking (FLCO5, FLCO10, and FLMCO2). Vitamins, chlorophyll, minerals, phenolic compounds, and anti-nutrients were analyzed. All laboratory experiments adhered to procedures and guidelines. The pH dropped more significantly to <3.5 in a 3% salt-3% sugar brine solution with 1.328 ± 0.006 mg/100 g of lactic acid compared to its counterpart. Blanched leaves dried in 5 days, but unblanched leaves took 15 days. Fermented samples demonstrated a notable reduction in total chlorophyll concentration (0.0964 ± 0.075 mg/g) compared to other processing techniques. The nutritional and anti-nutritional composition of Justicia heterocarpa showed significant change (P < 0.05) depending on processing methods. The results indicated a significant loss of vitamin C in the fermented and ten-minute cooked samples, at 74.57% and 61.64%, respectively.Cooked FLMCO2 (107.4%, 11.29 ± 0.03 mg/100g) and FLCO5 (86.26%, 10.51 ± 0.02 mg/100g) exhibited more than a two-fold increase in beta-carotene compared to fresh leaves (3.67 mg/100g). In comparison to alternative processing procedures, samples cooked for 10 minutes exhibited significant mineral leaching, whereas unblanched direct shade drying preserved the highest mineral concentration. Fermented samples (532.83 ± 14.91 GAE/100 g) exhibited a 64.19% increase in total Phenolic compounds compared to fresh leaves (190.83 ± 14.91 GAE/100 g). Nonetheless, tannins increased by 68.1% (254.44 ± 7.45 GAE/100g) in the fermented samples. Samples exposed to extended cooking (17.8 ± 3.17 mg/100 g) and fermentation (40.28 ± 3.34 mg/100 g) exhibited the lowest levels of phytates. The oxalate concentration was significantly decreased in the cooked samples. Justicia heterocarpa may serve as a sustainable food supply in areas of Tanzania experiencing nutritional deficits.