Doctoral Degrees (Horticulture)

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Browsing Doctoral Degrees (Horticulture) by browse.metadata.advisor "Caleb, Oluwafemi"

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    Development of value-added dried pomegranate arils and juice powder: Effects of cultivar, harvest maturity and storage duration of whole fruit
    (Stellenbosch : Stellenbosch University, 2020-12) Adetoro, Adegoke Olusesan; Fawole, Olaniyi; Opara, Umezuruike Linus; Manley, Marena; Caleb, Oluwafemi; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: In South Africa, the increasing rate of pomegranate fruit production, processing and research has witnessed tremendous growth due to consumer interest in its high concentration of bioactive compounds. However, the edible part of the fruit (arils) has a short shelf-life of five to seven days. Agro-processing through drying reduces postharvest losses, improves the shelf-life and increases the storability of the product. Before drying, several pre-treatments, are carried out to preserve the quality attributes of the product, however, little is known about the effects of blanch-assisted drying of pomegranate arils and the prospects of developing high quality pomegranate juice powder (PJP) for formulation and/or fortification to promote product diversification within the agro-processing industry. Therefore, the overall aim of this study was to develop value-added and shelf-stable dried products from pomegranate aril with potential for multiple applications and to provide science-based tools for processing and preservation of the nutritional components. This thesis is divided into seven papers that is organised into four themes. Theme A comprised of the general introduction and comprehensive literature review. Theme B (Papers 1, 2 and 3) investigated dried arils of three pomegranate cultivars (Acco, Herskawitz and Wonderful) for optimum quality attributes. Paper 1 shows that ‘Wonderful’ had 8.1% and 22.4% higher total soluble solids (TSS) than ‘Herskawitz’ and ‘Acco’, respectively. In Paper 2, dried arils of fruit at commercial and late harvest had significantly (p<0.05) higher TSS than at early harvest. Paper 3 studied the effects of cold storage of whole fruit (cv. Wonderful) harvested at commercial maturity. This paper showed that after 12 weeks of cold storage, arils dried in hot-air had better colour retention based on total colour difference, (TCD = 3.02 vs 23.6) and retained 46% higher TSS compared with freeze-dried arils. Theme C provided information on the process optimization of dried arils. In Paper 4, blanched samples of ‘Wonderful’ (7 h) ‘Acco’ (7 h) and ‘Herskawitz’ (8 h), had shorter drying times than unblanched samples (11, 15 and 20 h), respectively. The results from Paper 5 showed that blanching at 90°C, 30s and 100°C, 60s reduced enzyme activity by 76% and 68%, respectively, compared to unblanched samples; this also indicates less browning of blanched arils. Development of value-added juice powder with multiple applications in the food industry and extended shelf-life (Theme D, Paper 6), showed that juice powder made with maltodextrin appeared 44% redder (a*) than with gum arabic. Similarly, total anthocyanin retention was 54% higher in maltodextrin than waxy starch. In Paper 7, results showed that at the end of 12 weeks storage, PJP packed in aluminium foil laminated pouches (AFLP) had lower moisture content (6.1%) and water activity (0.54) than other packaging materials, indicating better storability of PJP packed in AFLP. In conclusion, the quality of dried arils from ‘Wonderful’ at commercial harvest maturity was retained better than other cultivars and harvest maturities. Also, blanching at 90°C, 30s retained the quality of dried arils and was thus recommended as a viable aril pre-treatment condition. Finally, maltodextrin produced PJP had better quality retention compared to gum arabic and waxy starch.