Feasibility of closed ventilation and automatic ventilation for sea freight of Proteaceae cut flower stems

Thesis (MScAgric)--Stellenbosch University, 2018.

ENGLISH ABSTRACT: Global trends aimed at advancing sea freight technology and reducing carbon emissions have led to the invention of automated reefer technologies. This development brings the challenge of having to determine product physiological limits that are vital for the implementation of automatic ventilation technology on South African produced Proteaceae cut flower stems. A study was conducted to determine the respiration rates, lower O2 limits and CO2 toxicity tolerance limits of Proteaceae cut stems in order to assess the feasibility of using automatic ventilation (AV+) vs. conventional fixed open-air exchange (AirEx) ventilation shipping of Proteaceae cut stems. In a closed ventilation system (representing unvented conditions as is possible with AV+ technology) which contained a mixed load of Proteaceae products in 45-55 % free air, it was observed that the O2 level fell to approximately 8.5 % whilst the CO2 level rose to about 10 %, when a HarvestWatch™ dynamic controlled atmosphere (DCA) system was used for gas sampling. Using a handheld gas analyser as an alternative sampling method revealed that under these conditions O2 levels fell below 2 %, and CO2 levels rose to above 17 %. Although the O2 dropped considerably, it was still above the Lower Oxygen Limit (LOL), which ranged from 0.09-0.33 % O2, 0.08-0.41 % O2 and 0.08-0.48 % O2 for Leucadendron, Leucospermum and Protea products respectively. At 5 ℃, the respiration rates were between 15.11-48.07 mL CO2.kg-1.h-1 for Leucadendron, 19.06-45.44 mL CO2.kg-1.h-1 for Leucospermum and 10.76-27.24 mL CO2.kg-1.h-1 for Protea. Closed ventilation, low O2 and high CO2 atmospheres generally resulted in mass loss that was lower than or comparable to AirEx. The inflorescence and leaf colour changes in Proteaceae products stored in closed ventilation, low O2 and high CO2 treatments were commercially not significant. There were no signs of low O2 and/or high CO2 damage on the stems stored under closed ventilation. The inflorescence and leaf visual quality of Proteaceae products stored in closed ventilation was generally better than that of stems stored in AirEx. Leucadendron, Leucospermum and Protea stems stored in high CO2 treatments had comparable or better quality than stems stored in AirEx. However, exposure to 15 % CO2 for 21 d reduced longevity of some products. In Leucadendron, the response to AirEx, DCA and 2 % O2 on flower head visual quality was variable and the treatments were equally effective in maintaining leaf visual quality. Flower and leaf visual quality and longevity was comparable between the AirEx and low O2 treatments in Leucospermum and Protea. Monosaccharides plus oligosaccharides were the most abundant sugars, followed by polysaccharides, and starch was the least abundant in Leucadendron, Leucospermum and Protea stems. Differences in polysaccharide and starch content were minor, between AirEx and low O2 treatments, also between AirEx and high CO2 treatments. Lipid peroxidation was comparable between AirEx and high CO2 atmospheres. The AirEx, DCA and 2 % O2 treatments had an insignificant effect on total phenolic content of products. Further research is recommended under commercial conditions in AV+ type reefers, where automatic ventilation should be set to maintain a minimum of 2 % O2 and maximum of 15 % CO2 concentration during long-term sea freight shipping of Proteaceae cut flowers to ensure optimum product quality throughout the cold chain for an extended vase life.

AFRIKAANSE OPSOMMING: Internasionale tendense gemik op die bevordering van seevragbehoueringstegnologie asook om koolstofvrystelling te beperk het gelei tot die vooruitgang van automatiese reefer tegnologie. Hierdie ontwikkeling bied die uitdaging om die fisiologiese beperkings van snyblomprodukte vas te stel wat krities is vir die implementering van automatiese ventilasie (AV+) tegnologie op Suid-Afrikaans geproduseerde Proteaceae snyblom stele. ʼn Studie is uitgevoer om die respirasietempos, laer O2 limiete (LOL) asook CO2 toksiteitstoleransie limiete van Proteaceae snyblomstele te bepaal om sodoende die toepaslikheid van die gebruik van automatiese ventilation (AV+) teenoor die konvensionele vaste oop-lug stelsel (AirEx) ventilasie te evalueer. In ʼn geslote sisteem (wat nie-geventileerde toestande soos moontlik met AV+ tegnologie voorstel) met ʼn gemengde vrag van Proteaceae produkte in 45-55 % vry lug, is waargeneem dat die O2 vlakke tot ongeveer 8.5 % gedaal het, terwyl die CO2 vlakke tot net bokant 10 % gestyg het, wanneer ‘n HarvestWatch™ dynamiesbeheerde atmosfeerstelsel (DCA) gebruik was om gasse te monitor. Wanneer ‘n draagbare gas analiseerder as ʼn alternatiewe moniteringsmetode gebruik is, is waargneem dat met hierdie metode O2 vlakke tot onder 2 % geval het, terwyl die CO2 vlakke tot bokant 17 % gestyg het. Alhoewel die O2 aansienklik geval het, was dit steeds bokant die LOL wat gewissel het vanaf 0.09-0.33 % O2, 0.08-0.41 % O2 en 0.08-0.48 % O2 vir Leucadendron, Leucospermum en Protea produkte onderskeidelik. By 5 ℃ is respirasie waardes van tussen 15.11-48.07 mL CO2.kg-1.h-1 vir Leucadendron, 19.06-45.44 mL CO2.kg-1.h-1 vir Leucospermum and 10.76 27.24 mL CO2.kg-1.h-1 vir Protea aangeteken. Geslote ventilasie, lae O2 en hoë CO2 atmosfeer het oor die algemeen laer of soortgelyke massa verlies getoon as waargeneem met AirEx. Die bloeiwyse en loof kleurveranderings van Proteaceae produkte wat in geslote ventilasie, lae O2 en hoë CO2 behandelings gestoor is, was nie kommersieël betekenisvol verskillend van mekaar nie. Daar was geen teken van lae O2 en/of hoë CO2 skade aan stele gestoor in geslote ventilasie nie. Die bloeiwyse en loof visuele kwaliteit van Proteaceae produkte gestoor in geslote ventilasie was oor die algemeen beter as dié van stele wat in AirEx gestoor is. Leucadendron, Leucospermum en Protea stele onder hoë CO2 behandeling het vergelykbare of beter kwaliteit getoon as stele gestoor AirEx. Blootstelling aan 15 % CO2 vir 21 d het egter die langslewendheid van sommige produkte negatief beïnvloed. In Leucadendron, was die impak van AirEx, DCA en 2 % O2 op die bloeiwyse se visuale kwaliteit variërend, maar meestal was behandelings ewe effektief om blaarkwaliteit te handhaaf. Blom- en blaar visuele kwaliteit en langslewendheid was vergelykbaar tussen die AirEx en lae O2 behandelings in Leucospermum en Protea. Monosakkariede asook oligosakkariede was die mees verteenwoordigende suikers, gevolg deur polisakkariede, met stysel in die laagste hoeveelheid waargeneem in Leucadendron, Leucospermum en Protea stele. Verskille in polisakkariede en stysel inhoud was weglaatbaar tussen AirEx en lae O2 behandelings, asook tussen AirEx en hoë CO2 behandelings. Lipied peroksidase was vergelykbaar tussen produkte blootgestel aan AirEx en hoë CO2 atmosfeer. Die AirEx, DCA en 2 % O2 behandelings het ‘n nie-betekenisvolle effek op die totale fenoliese inhoud van die produkte gehad. Verdere studies word aanbeveel onder kommersiële toestande in AV+ tipe reefers waar automatiese ventilasie gestel word om ‘n minimum van 2 % O2 en ‘n maksimum van 15% CO2 konsentrasie te handhaaf binne vragbehouering gedurende lang-termyn seevrag verskeping van Proteaceae snyblom stele om optimale produk kwaliteit te verseker regdeur die koue ketting vir met ʼn verlengde vaaslewe.