Masters Degrees (Food Science)

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Browsing Masters Degrees (Food Science) by Author "Atukuri, Julian"

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    Application of postharvest chemical treatments to enhance storage and shelf life of pomegranate fruit (cv. Wonderful)
    (Stellenbosch : Stellenbosch University, 2017-03) Atukuri, Julian; Opara, Umezuruike Linus; Olaniyi, Amos Fawole; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Pomegranate fruit is susceptible to a number of postharvest quality problems such as external and internal decay, weight loss, internal browning, chilling injury and husk scald. Postharvest treatments offer the possibility of alleviating these challenges and maintain fruit quality. The aim of the study was to investigate the potential of exogenous application of chemical treatments (putrescine (PUT) and fludioxonil (FLU)) in reducing the incidence of postharvest physiological disorders of pomegranate fruit (cv. Wonderful). Fruit were treated at three concentrations (putrescine – 1, 2 and 3 mM; fludioxonil – 150, 300 and 600 mg/L) and stored for 4 months at 5 °C plus an additional 4 days at 20 °C (shelf life). The effects of the chemical treatments and storage duration on fruit physiological response and quality were investigated. The results showed that treating pomegranate fruit with putrescine at different concentrations (1, 2 and 3 mM) reduced incidence of physiological disorders such as external fruit decay, chilling injury and husk scald during the first 3 months of storage. However, putrescine had no effect on internal disorders such as internal decay and aril browning. Physico-chemical attributes such as peel colour, aril colour, TSS, TA and pH were not significantly (p > 0.05) affected by putrescine application. After four months of storage, treated samples had firmer fruit and arils while the control had softer fruit with lower firmness (10.12 ± 0.40 N) and aril hardness (143.20 ± 3.84 N). Fruit treated with 2 mM PUT had the best sensory quality (crispness, sweet taste, juiciness) after 3 months of storage. Although 3 mM PUT effectively reduced physiological disorders, 2 mM PUT had the advantage of both reducing the external disorders and maintaining fruit sensory quality during storage up to 3 months. Fludioxonil was very effective in reducing decay incidence among treated fruit, with 600 mg/L as the most effective FLU concentration having 15.7 % lower decay than control. However, other physiological disorders such as aril browning, chilling injury and husk scald were more pronounced in treated fruit. Fruit firmness was maintained among treated fruit while aril texture was not significantly (p > 0.05) affected. Control fruit had higher aril redness (a*) and intensity (C*) compared to fruit treated with FLU. The chemical attributes TA, TSS and BrimA generally decreased with storage for all FLU concentrations. Fruit treated with 600 mg/L were related to eating attributes for crisp, juicy and sweet fruits. Fruit were successfully stored up to 3 months without adversely affecting quality and 600 mg/L was the most effective FLU concentration. A further study on the effects of the PUT and FLU treatments on phytochemical and volatile composition of fruit revealed that fruit juice ascorbic acid content decreased slightly while total phenolic content (TPC) significantly decreased during storage for both chemicals. Fruit treated with FLU had higher TPC for the first 3 months while fruit treated with PUT only showed high TPC after month 2 of storage. Total anthocyanin content (TAC) of fruit initially increased to values above harvest regardless of FLU concentration. However, TAC decreased as storage progressed with no significant difference (p > 0.05) between FLU concentration at the end of the storage duration. On the other hand, TAC of PUT treated fruit significantly reduced throughout storage (except at month 2), with no significant differences observed among PUT concentrations at the end of storage. In contrast, the antioxidant capacity of both FLU and PUT treated fruit increased throughout the storage duration. Furthermore, a total of 31 and 32 volatile compounds were identified in fruit treated with FLU and PUT, respectively. Six chemical groups (alcohols, aldehydes, acids, ketones, esters and terpenes) were identified among fruit treated with FLU, while five (alcohols, aldehydes, acids, esters and terpenes) were detected in fruit treated with PUT. Volatile compounds evolved with prolonged storage, with new compounds, especially terpenes, detected at later storage durations. Accumulation of terpenes had adverse effects on fruit sensory quality and therefore storage for long duration may result in lower fruit flavour. Overall, the study provided insightful information on the potential of putrescine and fludioxonil treatments in reducing pomegranate fruit postharvest disorders and their effects on fruit edible and nutritional quality attributes. The application of FLU greatly reduced fruit decay but not chilling injury, husk scald and aril browning while PUT alleviated all these physiological disorders. However, PUT and FLU did not effectively reduce weight loss, and therefore, future studies may focus on combining chemical treatments together with physical treatments such as film wrapping and waxing so as to benefit from the hurdle effect. In addition, combination of FLU and PUT may be explored to harness the full potential of the two chemical treatments.