Interactive effect of maturity stages and fruit accessions on primary and secondary metabolites profile of Mimusops zeyheri sond

Abstract

Mimusops zeyheri Sond is a member of the Sapotaceae Family and it is an undervalued or unappreciated indigenous fruit tree consumed raw as a healthful snack in rural communities across Sub-Saharan Africa. It is known for its predominantly high vitamin C content. The objectives of this study were to investigate whether the interaction between different accessions and fruit maturity stages has effect on post-harvest quality, physicochemical attributes, primary and secondary metabolites in M. zeyheri. To achieve the objectives of this study, fruits of M. zeyheri were harvested from trees of five accessions namely, 6E, M7, 3E, HY, and 3L at four different maturity stages: dark green (T1), breaker (T2), pale yellow (T3), and yellow (T4). A 5 × 4 factorial experiment was established as an interaction between five accessions and four fruit maturity stages. The experiment was laid in a randomised complete design with four replication per accession and maturity stage. The mean separation was done using a Duncan’s Multiple Range Test at the significance level of 5% using the GenStat 18th version. Five accessions and four fruit maturity stages demonstrated significant variation (p< 0.05) on quality and physicochemical attributes. Accession 6E had the highest fruit length at T1 to T4 maturity stage (25.85-27.63 mm). The other accessions including 3E, HY, and 3L had similar moderate length however, these were higher than that of accession M7 which exhibited the least, irrespective of maturity stage. Fruit firmness declined as fruits ripened with the highest values recorded at T1 and lowest values at T4 fruit maturity stages, for all five accessions. Fruits of accession HY had the highest total soluble solids (32.80%) at T4 maturity stage while that of accession 3L had lowest total soluble solids (2.40%) at T1 maturity stage. Accession M7 had the highest total titratable acid (3.20%) at T1 maturity stage, whilst accession 6E had the lowest total titratable acidity (0.22%) at T4 maturity stage. The highest TSS/TA ratio values were reported in accession M7 (32.20%) at T4 maturity stage than all accessions. All the accessions at T1 to T4 stages demonstrated different values of colour change on Hunter a*. The Hunter L* values were lower at T1 and highest at T4 maturity stages. The H˚ angle were high at T1 and lowest at T4 maturity stages as fruit reached ripening period. On the nutritional compositions, accession HY recorded highest values of moisture content at T1 to T4 maturity stages (93-97%) and protein content at T2 to T4 maturity stages (0.41-0.40%), whilst accession HY recorded at T4 maturity stage (0.43%). The moisture content was highest in accession 6E at T1 and T3 maturity stages (92 and 89%) and ash content (4.20-3.75%) at T1 to T3 maturity stages. The dry matter, ash and protein content were reduced from T1 to T4 maturity stages, while moisture content enhanced with advanced of fruit maturity stages. The mineral such as calcium, potassium, iron, magnesium, manganese, sodium, zinc and phosphorus were assessed. Accession M7 had highest values of calcium at T1 maturity stage (27.73 mg/L), magnesium (5.96 and 4.37 mg/L) at T1 and T2 maturity stages and sodium (5.63-3.64 mg/L) at T1 to T4 maturity stages. Accession 3E had highest values of potassium at T2 maturity stage (8.70 mg/L) and Manganese at T1 and T2 maturity stages (0.07 and 0.06 mg/L). Furthermore, accession HY had highest values of calcium at T2 to T4 maturity stages ranged from (21.50-17.17 mg/L), T1 to T3 maturity stages were recorded in iron (1.57-0.37 mg/L) and potassium (50.83-44.93 mg/L). Accession 3E had highest values of phosphorus at T1 to T3 maturity stages ranged from (9.39-6.83 mg/L), zinc ranged from (1.73-0.60 mg/L). The mineral compositions decreased with advanced of fruit maturity stages in all accessions. This study demonstrated that fruits of five accessions of M. zeyheri at T1 maturity stage should be used for the food fortification program due to high amount of mineral compositions and fruits at T4 maturity stage should be consumed as raw fruits for snacking, dried fruits and can also be processed to generate fermented juices, jellies and dried fruits to reduce the malnutrition and food insecurity. Secondary metabolites, such polyphenolic and flavonoids were identified and quantified in five accessions of M. zeyheri at two different fruit maturity stages, which were T1 and T4. For untargeted secondary metabolites, methanol extracts were analysed using ultra-performance liquid chromatography mass spectrometer. In five accessions of M. zeyheri, exploratory principal component analysis plot revealed five major clusters based on the heterogeneity of metabolites. The highest value of 3,4-bis(acetyloxy)-5-acetamido-6-(3-nitrophenoxy)oxan-2-yl]methyl acetate was recorded in accession 3L at the T1 fruit maturity stage (719.90 mg/kg) including paeonoside (48.98 mg/kg) and T4 fruit maturity stage of 7-oxo-8,9-dihydroxy-4'-N-demethyl staurosporine (122.48 mg/kg). The highest value in accession HY was recorded at the T4 fruit maturity stage (646.70 mg/kg). The three flavonoid metabolites found in M. zeyheri that were most abundant were quercetin, quercetin galactoside, and quercetin glucoside. The results discovered that M. zeyheri fruit possesses a high level of concentration at T1 and T4 fruit maturity stages which could contribute and serve as a food source, especially for vulnerable rural communities that need food security, and prevent chronic non-communicable diseases.