Alternative postharvest technologies for the maintenance of ‘Parthenon’ broccoli quality during export and domestic marketing.

Thesis (PhDAgric)--Stellenbosch University, 2022.

ENGLISH ABSTRACT: Broccoli is prized for its nutritional quality. The green colour and a compact head symbolise freshness. Export and domestic marketing of broccoli is limited by its high perishability. The aim of this study was to investigate the use of two 1-methylcyclopropene (1-MCP) application methods in combination with packing to maximise broccoli storage life under different temperature regimes typically found in the export and domestic handling chains. Under simulation of domestic handling chains, optimal temperature storage (0 °C) of broccoli (cv. Parthenon) in combination with 1-MCP and packaging [Xtend™ modified atmosphere packaging (MAP) or macro-perforated high-density polyethylene (HDPE) liners] resulted in a maximum storage duration of 30 days. In a second season, optimal temperature storage with MAP (RipeLock™) allowed for 42 days storage. Storage at suboptimal temperatures (viz. 7.5 °C or 12 °C), in mixed loads with ethylene is, however, common during domestic handling. Under such environments 1-MCP prevented broccoli (cv. Parthenon) yellowing that occurred with increasing storage temperature from 0 °C-7.5 °C and 7.5 °C-12 °C. Furthermore, 1-MCP alone or in the presence of ethylene extended shelf-life of broccoli (cv. Parthenon) compared to controls, at both temperatures. This research showed how an in-box treatment system of 1-MCP can be used as a viable alternative to the traditional, bulk, in-room application method, having a similar effect in reducing yellowing compared to controls. Sensory quality of broccoli was maintained in MAP (RipeLock™) at 0 °C and 7.5 °C. At 12 °C, where sensory quality was the poorest, 1-MCP reduced the perception of ‘sulphur odour’ compared to untreated and ethylene exposed broccoli. Dimethyl trisulphide (DMTS), an off-odour related volatile, was the most abundant volatile measured at all storage temperatures. The oxidative state of broccoli increased with an increase in storage temperature from 0 °C to 7.5 °C to 12 °C. Ascorbic acid and glutathione were oxidized with an increase in storge temperature. Glutathione, however, had a consistently higher percentage oxidation compared to ascorbic acid. Under simulated export conditions, broccoli was stored at 0 °C in various MAP types with or without 1-MCP. 1-MCP was either applied in-room before packaging or in-box during packaging. Results showed that extended storage without packaging is not recommended due to excessive weight loss. Across two seasons variations in shelf-life were noted. In the first season, a maximum storage duration of 25 days was realised with broccoli stored in Xtend™, or a generic HDPE MAP film with 1-MCP. In the second season, the maximum storage duration was 35 days, irrespective of MAP type or 1-MCP treatment. Here, the limiting factor for shelf-life was sensory quality. At optimal temperature volatiles related to off-odour were negligible, indicating that sensory deterioration was not related to fermentation in the MAP environment. In the second season it was reported that if good quality broccoli is stored at 0 °C, RipeLock™ or Xtend™ MAP in combination with 1-MCP should yield no benefit over untreated broccoli in non-specific, generic liners bags (15 μm HDPE).

AFRIKAANSE OPSOMMING: Broccoli word hoog op prys gestel vir sy voedingsgehalte, of te wel voedingswaarde. Die groen kleur en kopverdigting simboliseer varsheid. Die hoë bederfbaarheidsvlak beperk egter die uitvoer en kleinhandel bemarkingsgeleenthede van broccoli. Die doel van hierdie studie was om die gebruik van twee 1-metielsiklopropeen (1-MCP) toedieningsmetodes in kombinasie met verskeie verpakkingstipes te ondersoek om sodoende die opbergingslewe van broccoli te maksimeer ten bate van binnelandse en uitvoer bemarking. Vir plaaslike bemarking by optimale temperatuuropberging (0°C) van 'Parthenon' broccoli is 'n maksimum opbergingsduur van 30 dae bereik met 1-MCP in kombinasie met verpakking [Xtend™ gemodifiseerde atmosfeer verpakking (MAV) of makro-geperforeerde hoë digtheid poli-etileen (HDPE) voerings]. In 'n tweede seisoen het optimale temperatuuropberging met MAV (RipeLock™) toegelaat vir 42 dae opberging. Opberging by suboptimale temperature (nl. 7.5 °C of 12 °C), in gemengde vragte met etileen is egter algemeen in die plaaslike hanteringskettings. Onder sulke omgewings het 1-MCP vergeling verhoed wat gesien was met verhoogde opbergingstemperatuur tussen 0 °C-7.5 °C en 7.5 °C-12 °C. Verder het 1-MCP alleen of in die teenwoordigheid van etileen die raklewe van 'Parthenon' broccoli verleng in vergelyking met kontroles, by beide temperature. Hierdie navorsing het getoon hoe 'n nuwe, in-sak behandelingstelsel van 1-MCP gebruik kan word as 'n lewensvatbare alternatief teenoor die tradisionele, grootmaat, in-kamer toedieningsmetode, wat ‘n soortgelyke effek het in die vermindering van vergeling in vergelyking met kontroles. Goeie sensoriese kwaliteit van broccoli het behoue gebly in MAV (RipeLock™) by 0 °C en 7.5 °C. By 12 °C, waar sensoriese kwaliteit die swakste was, het 1-MCP die persepsie van 'swawel reuk' verminder in vergelyking met onbehandelde en etileen blootgestelde broccoli. Dimetieltrisulfied (DMTS), 'n slegte reukverwante vlugtige stof, was die volopste vlugtige stof gemeet by alle bergingstemperature. Die oksidatiewe toestand van broccoli het toegeneem met 'n toename in opbergingstemperatuur van 0 °C tot 7.5 °C, en van 7.5 °C tot 12 °C. Askorbiensuur was egter in die meer gereduseerde vorm in vergelyking met glutatioon, wat tipies meer geoksideer was. Broccoli is gestoor vir gesimuleerde uitvoer (0 °C), in verskeie MAV tipes in kombinasie met 1-MCP, as 'n tradisionele kamer behandeling voor verpakking of ‘n in-sak toediening tydens verpakking. Resultate het getoon dat langdurige berging sonder verpakking nie aanbeveel word nie as gevolg van oormatige vogverlies. Oor twee seisoene is variasie in rakleeftyd opgemerk. In die eerste seisoen is ʼn maksimum opbergingsduur van 25 dae gerealiseer met broccoli wat gestoor was in Xtend™, of in die generiese HDPE MAV film met 1-MCP. In die tweede seisoen was die maksimum opbergingsduur 35 dae, ongeag van die MAV-tipe of 1-MCP-behandeling. Hier was die beperkende faktor vir raklewe, sensoriese kwaliteit. By optimale temperatuur was vlugtige stowwe wat verband hou met afreuk egter weglaatbaar, wat aandui dat sensoriese agteruitgang nie verband hou met fermentasie in die MAV omgewing nie. In die tweede seisoen is gerapporteer dat indien hoë kwaliteit broccoli by 0°C gestoor word, gespesialiseerde MAV in kombinasie met 1-MCP geen voordeel behoort te lewer bo die onbehandelde broccoli opgeberg in nie-spesifieke, generiese MAV sakke (15 μm HDPE) nie.

Doctoral