Effect of Moist Cooking Blanching on Colour, Phenolic Metabolites and Glucosinolate Content in Chinese Cabbage (Brassica rapa L. subsp. chinensis)

Abstract

Non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis) is a widely consumed leafy vegetable by the rural people in South Africa. Traditional blanching methods (5%, 10% or 20% lemon juice solutions in steam, microwave treatments and hot water bath at 95 °C) on the changes of colour properties, phenolic metabolites, glucosinolates and antioxidant properties were investigated in this study. Blanching at 95 °C in 5% lemon juice solution maintained the chlorophyll content, reduced the difference in colour change ∆E, and increased the total phenolic content and the antioxidant activities (ferric reducing-antioxidant power assay (FRAP) and Trolox equivalent antioxidant capacity (TEAC) assay). The highest concentration of kaempferol-dihexoside, kaempferol-sophoroside, kaempferol hexoside, and ferulic acid was noted in samples blanched in 5% lemon juice, at 95 °C. However, concentrations of kaempferol O-sophoroside-O-hexoside was highest in raw leaf samples. Supervised Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) and the UPLC-MS and chemometric approach showed the acid protocatechuoyl hexose unique marker identified responsible for the separation of the blanching treatments (5% lemon juice at 95° C) and raw leaves. However, other unidentified markers are also responsible for the separation of the two groups (the raw leaves and the hot water moist blanched samples) and these need to be identified. Blanching at 95 °C in 10% lemon solution significantly increased the glucosinolate sinigrin content. Overall blanching at 95 °C in 5% lemon juice solution can be recommended to preserve the functional compounds in Nightshade leaves.

Comparison of Phenolic Compounds, Carotenoids, Amino Acid Composition, In Vitro Antioxidant and Anti-Diabetic Activities in the Leaves of Seven Cowpea (Vigna unguiculata) Cultivars

“…Phenolic compounds were extracted from cowpea leaves using the method described by Ndou et al [14] and Managa et al [15]. Cowpea snap frozen leaf samples (50 mg) were extracted in ethanol/water solution (70:30, v/v), ultrasonicated for 30 min then centrifuged (Hermle Z326k, Hermle Labortechnik GmbH, Wehingen, Germany) at 1000× g for 20 min at 4 • C. The supernatants were collected and filtered through a 0.22-µm polytetrafluorethylene filter prior to UPLC-QTOF/MS analysis.…”

“…Peak identities and quantification of predominant polyphenol metabolites were carried out using an UPLC-QTOF/MS system (Waters, Milford, MA, USA) equipped with a Quadrupole 120 time-of-flight (QTOF) mass spectrometer. The chromatographic conditions were performed as per Ndou et al [14] and Managa et al [15]. Due to the unavailability of commercial standards, these were semi-quantitatively measured against calibration curves prepared using chlorogenic acid, catechin, luteolin, epicatechin and rutin.…”

“…Due to the unavailability of commercial standards, these were semi-quantitatively measured against calibration curves prepared using chlorogenic acid, catechin, luteolin, epicatechin and rutin. Data processing using TargetLynx software was conducted as described previously [14,15]. The differences between the phenolic metabolic profiles of the different cowpea cultivars were analysed using an unsupervised Principal Component Analysis (PCA) approach using the data generated by the UPLC-Q-TOF/MS analysis.…”

Enrichment of Mango Fruit Leathers with Natal Plum (Carissa macrocarpa) Improves Their Phytochemical Content and Antioxidant Properties

“…Colour properties of mango, Natal plum, and the mango-Nata plum mixed leathers were objectively measured at three points of the fruit leathers (two each on the opposite side and bottom) using a colour meter, Minolta CR-400 chromameter (Minolta, Osaka, Japan) [16]. A standard white tile was used to calibrate the chromameter.…”

“…Furthermore, the h • values, known as a colour wheel, consist of red-purple angled at 0 • , yellow at 90 • , bluish-green at 180 • , and blue colour at 270 • . The total colour difference ∆E = [(∆L*) 2 + (∆a*) 2 + (∆b*) 2 ] 1 2 was calculated according to which ∆L = colour difference is calculated as the sample L* value minus standard, ∆a* = colour difference is calculated as the sample a* value minus standard, ∆b* = Colour difference is calculated as the sample b* value minus standard [16].…”