Maturity indexing, pharmacological properties and postharvest performance of pomegranate fruit grown in South Africa

[摘要] ENGLISH ABSTRACT: The development and application of science-based tools for determining optimum fruitmaturity and postharvest handling protocols to maintain quality and reduce losses duringpostharvest handling and marketing is essential to maintain the competitiveness of the emergingpomegranate industry in South Africa. Currently, there are no quality standards for the SouthAfrican pomegranate industry, neither is there a general consensus on the optimal harvestmaturity indices for fruit cultivars. These information are important to ensure the delivery ofgood quality fruit to consumers, particularly for long supply chains. The overall aims of thisstudy were (a) to develop science-based management tools for determining optimum maturityindices and storage performance of pomegranate fruit cultivars grown in South Africa, and (b) tocharacterise the physico-chemical and pharmacological properties of selected cultivars relevantto postharvest handling and industrial applications.In Section II, seasonal studies on pomegranate ('Baghwa' and 'Ruby') fruit growth andthe evolution of maturity indices during development were conducted. Significant increases intotal soluble solids (TSS), sugars (glucose and fructose) and anthocyanin composition, coupledwith significant decline in titratable acidity (TA), organic acids and total phenolics (TP) occurredwith advancing fruit maturity. Fruit at advanced maturity stages were characterized by intensepigmentation of peel and aril, which coincided with maximum accumulation of anthocyanins.Among all the major maturity indices investigated, TSS, BrimA and anthocyanins did not showsignificant (p<0.05) seasonal variability, and strong correlations were found among the indices.In combination, these indices accounted for fruit juice sugar content, acidity and colour andcould serve as reliable markers to determine optimal maturity for both pomegranate cultivars.The studies in Section III focused on characterization of postharvest quality includingnutritional, medicinal and antioxidant properties of fruit parts. Quality attributes of eightcommercial cultivars were analysed by cluster analysis, which enabled the cultivars to beseparated into two clusters (cluster 1 = 'Ruby', 'Arakta' and 'Ganesh'; cluster 2 = 'Bhagwa','Acco' and 'Herskawitz') and two ungrouped cultivars ('Molla de Elche' and 'Wonderful')based on important quality attributes (size, texture, colour, soluble solids, acidity, juiciness andphenolics). Furthermore, pomegranate fruit peel extracts were studied to highlight their potentialfor value-adding in pharmaceutical and other industrial applications. The results showed that fruit peels of the investigated cultivars possess strong antibacterial, antioxidant and antityrosinaseactivities, and hence could be exploited as potential sources of natural antimicrobialand antioxidant agents, as well as a potential tyrosinase inhibitor.The research reported in Section IV investigated the effects of harvest maturity andstorage conditions on postharvest quality and nutritional value of 'Bhagwa' and 'Ruby' cultivars.Fruit harvested at commercial maturity were stored at 5±0.3°C, 7±0.5°C and 10±0.4°C with92±3% RH and at room temperature (20±2.2°C, 65±5.5% RH) for 16 weeks. Fruit physiologicalresponses and quality were affected by storage condition, with the maximum levels of respirationoccurring at higher temperature and extended storage duration. Fruit colour and antioxidantcapacity varied slightly among storage temperatures, with total soluble solids and titratableacidity decreasing gradually over time at different temperatures. Considering that fruit stored at5°C and 92% RH had significantly reduced weight loss, low incidence of physiological disordersand best results in maintaining flavour attributes (TSS and TA, TSS:TA ratio), the investigatedcultivars may be stored at 5°C and >92% RH for 8 - 12 weeks.In paper 9 (Section IV), the research investigated the relationships between instrumentaland sensory measurements of pomegranate fruit at different harvest maturities during storage andshelf life. Mature 'Bhagwa' fruit harvested at different times could not be discriminated bysensory attributes assessed by a trained panel. However, TSS (R2 = 0.677) and juice content (R2= 0.512) were the two most decisive quality attributes at shelf life related to harvest maturitystatus. For 'Ruby', however, a combination of instrumental and sensory attributes appeared to beinfluential in discriminating mature fruit harvested at different times, with TSS:TA ratio beingthe most decisive (R2 = 0.654) in distinguishing different fruit harvests, followed by sweet taste(R2 = 0.474) and hue angle (R2 = 0.431). The results showed that to ensure the best post-storagequality of 'Bhagwa', the optimum harvest maturity was between 167 - 175 DAFB (H2 and H3)when fruit reached maximum TSS level (>16°Brix; H3) and juice content (>65 mL/100 g aril;H2). However, for 'Ruby', this study indicated that the optimum harvest date was at 143 DAFB(H2) when TSS:TA ratio was >55, which coincided with significantly higher sensory rating forsweet taste after shelf life of fruit at H2 than H1 and H3, respectively.The results from this thesis provide new understanding and better insights on fruitcharacteristics of major pomegranate cultivars grown in South Africa. Overall, the studyprovides new knowledge on science-based tools for assessing fruit readiness for harvest as well as storage conditions to maintain fruit postharvest quality and reduce losses. It also providesscientific information on phytochemical contents and antioxidant compounds in fruit to promotevalue-adding of pomegranate as a good raw material with potential applications in health foodproducts and other industrial applications such as pharmaceuticals and cosmetics.

[发布机构] Stellenbosch University