Application of postharvest chemical treatments to enhance storage and shelf life of pomegranate fruit (cv. Wonderful)

Atukuri, Julian (2017-03)

Thesis (MSc Food Sc)--Stellenbosch University, 2017.

Thesis

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.

AFRIKAANSE OPSOMMING: Granate is vatbaar vir 'n aantal na-oes kwaliteit probleme soos uitwendige en inwendige verval, gewigsverlies, koueskade en dopwonde. Na-oes behandelings bied die moontlikheid van die oplossing van hierdie probleme en verbeter ook vrugkwaliteit. Die doel van hierdie studie was om die potensiaal van die uitwendige toediening van chemiese behandelings (putresien (PUT) en fludioksonil (FLU)) in die vermindering van die voorkoms van na-oes fisiologiese afwykings van granate (cv. Wonderful) te ondersoek. Die vrugte is behandel met drie konsentrasies (putresien - 1, 2 en 3 mM is; fludioksonil - 150, 300 en 600 mg/L) en gestoor vir 4 maande by 5 °Cm plus ‘n bykomende 4 dae by 20 °C (raklewe). Die gevolge van chemiese behandelings en stoortydperk op die fisiologiese vrugreaksie en gehalte is ondersoek. Resultate het getoon dat die behandeling van granate met putresien by verskillende konsentrasies (1, 2 en 3 mM) die voorkoms van fisiologiese afwykings soos uitwendige vrug verval, koueskade en dopwond gedurende die eerste 3 maande van stoor verminder. Putresien het egter geen effek op interne versteurings soos interne verval en saadhuid verbruining gehad nie. Fisiochemiese eienskappe soos die kleur van die skil en saadhuid, TSS, TA en pH was nie beduidend (p > 0.05) beïnvloed deur putresien behandeling nie. Na vier maande van stoor het kontrole vrugte verlaagde vrugfermheid (10.12 ± 0.40 N) en saadhuid hardheid (143.20 ± 3.84 N) getoon, terwyl behandelde vrugte se waardes hoër was. Vrugte wat met 2 mM PUT behandel is, het die beste sensoriese kwaliteit na `n 3 maande stoortydperk getoon. Hoewel 3 mM PUT effektief was om fisiologiese versteurings te verminder, was 2 mM PUT voordelig, deurdat dit tydend ’n 3 maansde stoortydperk uitwendige versteurings kon verminder, asook vrug sensoriese kwaliteit handhaaf. Fludioxonil was baie effektief deur dat dit die verval van behandelde vrugte kon verminder. Die mees doeltreffende FLU konsentrasie was 600 mg/L met `n 15.7 % laer verval as die by die kontrole. Maar ander fisiologiese afwykings soos saadhuid verbruining, koueskade en dopwonde was meer merkbaar in behandelde vrugte. Vrugfermheid was gehandhaaf onder behandelde vrugte, terwyl saadhuid tekstuur nie beduidend (p > 0.05) beïnvloed was nie. Hoewel rooiheid (a*) en intensiteit (C*) van die saadhuid in kontrole vrugte hoër was, het FLU-behandelde vrugte ook aanvaarbare rooi kleur vertoon. Die chemiese eienskappe TA, TSS en BrimA was oor die algemeen verlaag tydens stoor onder alle FLU konsentrasies. Vrugte wat met 600 mg/L behandel is, het verbeterde sensoriese eienskappe in terme van varsheid, sappigheid en soetigheid vertoon. Vrugte was suksesvol gestoor tot 3 maande sonder enige negatiewe invloed op gehalte en 600 mg/L was die mees doeltreffendste FLU konsentrasie. 'n Verdere studie oor die uitwerking van PUT en FLU behandelings op fitochemiese en vlugtige samestelling van vrugte, het gewys dat die askorbiensuur inhoud in vrugte effens afneem, terwyl totale fenoliese inhoud (TPC) aansienlik afneem tydens stoor vir beide chemikalieë. Vrugte onder FLU behandeling het hoër TPC gehad vir die eerste 3 maande, terwyl PUT-behandelde vrugte slegs hoë TPC na maand 2 van stoor gewys het. Algehele antosianien inhoud (TAC) van vrugte het aanvanklik gestyg bo oes, ongeag die invloed van FLU konsentrasie. Maar, TAC het afgeneem namate stoor gevorder het, met geen beduidende verskil (p > 0.05) tussen FLU konsentrasie aan die einde van die stoortydperk nie. In teenstelling het die TAC van PUT-behandelde vrugte beduidend verminder tydens stoor (behalwe op maand 2), en geen betekenisvolle verskille is waargeneem onder PUT konsentrasies aan die einde van stoor. In teenstelling hiermee het die antioksidant kapasiteit van beide FLU- en PUT-behandelde vrugte toegeneem gedurende stoor. Verder is 'n totaal van 31 en 32 vlugtige verbindings geïdentifiseer in vrugte onder FLU en PUT behandeling onderskeidelik. Ses chemiese groepe (alkohole, aldehiede, sure, ketone, esters en terpene) is geïdentifiseer in vrugte onder FLU behandeling, terwyl vyf (alkohole, aldehiede, sure, esters en terpene) opgespoor is in vrugte onder PUT behandeling. Vlugtige verbindings he met langdurige stoor ontwikkel, met nuwe verbindings, veral terpene, wat tydens latere stoortydperke opgespoor is. Ophoping van terpene het `n nadelige uitwerking op die sensoriese kwaliteit van vrugte gehad, en dus kan langtermyn stoor lei tot laer vrugsmaak. In die geheel het hierdie studie insiggewende inligting verskaf oor die potensiaal van putresien en fludioksonil behandelings in die vermindering van granaat versteurings, en die uitwerking daarvan op vrugkwaliteit-eienskappe. Die toediening van die FLU het vrug verval aansienlik verminder, maar nie koueskade, dopwonde en saadhuid verbruining nie, terwyl PUT hierdie fisiologiese versteurings insluitend vrugte verval kon verlig Nietemin kon PUT en FLU nie effektief gewigverlies verminder nie, en dus daar tydens toekomstige studies op die kombinasie van chemiese behandelings met fisiese behandelings soos plastiek verpakking en waslaag toepassing gefokus word ten einde voordeel te trek uit die hekkie effek. Daarbenewens kan’n kombinasie van die FLU en PUT ondersoek word, om voordeel te trek uit die volle potensiaal van die twee chemiese behandelings.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101413
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