Resistance to airflow, cooling characteristics and quality of pomegranate fruit inside ventilated packaging

Thesis (MScFoodSc)--Stellenbosch University, 2015.

ENGLISH ABSTRACT: Ventilated packaging has found wide scale industry applications in fresh fruit handling and cooling operations. Given variations in fruit physical and thermal properties, optimal package design for a particular product and supply chain requires a multi-parameter approach incorporating cooling, mechanical and economic performance, as well as resource utilisation efficiency. A wide range of ventilated package designs are used in postharvest handling and marketing of fresh fruit, and several studies have investigated the cooling performance of fruit such as apples, citrus and table grapes; however, very little is known about the performance of pomegranate ventilated packaging. Therefore, the overall aim of this study was to evaluate the cold chain performance of some of frequently used ventilated cartons and internal packages (liners) during forced-air cooling (FAC) and cold storage in the South African pomegranate industry, in terms of resistance to airflow (RTA), cooling characteristics, energy efficiency and fruit quality. The two studied carton designs, CT1 and CT2 had 5.4% difference in total ventilation. CT2 had relatively higher ventilation in both length and width directions (8.82% and 6.67%, respectively) compared to CT1 (6.52% and 2.86%). In a stack of cartons packed with fresh pomegranate fruit (cv. Wonderful), this resulted into a generally faster fruit cooling rate (29.19%) in CT2. However, the obstruction of vent-holes in the lengthwise orientation of the stack of CT2 resulted in over 50% higher RTA compared to CT1. The results also showed that packaging fruit inside a liner offered up to 50% greater RTA than fruit packaging with no liner. Consequently, the use of liners also delayed fruit cooling and increased energy consumption, with seven-eighths cooling times close to 3 times those of fruit inside packaging with no liner. Packaging fruit with liner required about 3.9 and 8.7 times more energy to cool fruit in CT1 and CT2, respectively, compared with no-liner. Fruit in carton stacks also exhibited a heterogeneous cooling pattern, with fruit in the upstream position to incoming air cooling about 36% faster compared to fruit at back stack position. During FAC of fruit over a period of 11.6 and 4.5 hours in liner and no liner, respectively, the use of humidification to maintain 95±1% relative humidity (RH) minimised weight loss by about 13.63% compared to precooling fruit inside cold room at 90±1% RH. Fruit packaged without liners also lost about 17.39% more weight during precooling compared to fruit packaged with liners. Fruit in liners and without liners which took longer to cool to set temperature (7oC) lost more weight than fruit that got to set storage temperature faster. A further study into the effects of RH on pomegranate fruit quality during ambient (20oC) storage showed that storing fruit under high RH (95%) minimised weight loss, maintained fruit colour, firmness and physicochemical quality attributes. Storing fruit under low RH (65%) led to excessive weight loss up to 29.13±1.49% after 30 days (compared to 5.78±0.44% at 95% RH), thereby resulting into an estimated financial loss of ZAR7.78 kg-1 and ZAR1.54 kg-1 at low and high RH storage conditions, respectively. The onset of visible signs of shrivels occurred when fruit weight loss reached about 5.16%. Linear regression equations developed to estimate weight loss in pomegranates during ambient storage gave a high goodness-of-fit (R2) of 0.9931 and 0.9368 for low and high RH environments, respectively. This research has provided an insight into the effects of packaging design used in the pomegranate industry on cooling performance and impacts on fruit quality. Although the use of internal packaging (liners) minimised fruit weight loss, it increased RTA, precooling time, energy consumption and cooling costs. Cold room humidification offered potential remedy to the problem of high moisture loss of pomegranates. Further studies are warranted to optimise the vent design of pomegranate packaging, including the use of perforated liners, to improve cooling performance cost-effectively without compromising structural/mechanical performance in the cold chain.

AFRIKAANSE OPSOMMING: Geventileerde verpakking het 'n wye skaal bedryfstoepassing in vars vrugte behandeling en verkoelings bedrywighede gevind. Sekere variasies in fisiese en termiese vrug eienskappe, optimale verpakkings ontwerpe vir 'n spesifieke produk en voorsieningsketting vereis 'n multi-parameter benadering wat insluit verkoeling, meganiese en ekonomiese prestasie, sowel as hulpbronbenutting doeltreffendheid.‘n Groot verskeidenheid van geventileerde verpakkings ontwerpe word gebruik in na-oes behandeling en bemarking van vars vrugte. Verskillende studies het die verkoelings uitwerking op vrugte soos appels, sitrus en tafeldruiwe ondersoek; Daar is egter baie min bekend oor die prestasie van granate in geventileerde verpakking. Die oorkoepelende doel van hierdie studie was om die verkoelings prestasie van sommige van die dikwels gebruikte geventileerde kartonne en interne pakkette tydens geforseerde lugverkoeling (GL) en koue storing in die Suid-Afrikaanse granaat bedryf te evalueer in terme van lugvloei weerstand (LW), verkoelings eienskappe, energie-doeltreffendheid en die kwaliteit van vrugte. Die twee bestudeerde verpakkings ontwerpe, CT1 en CT2 het met 5.4% verskil in die totale ventilasie. CT2 het relatief hoër ventilasie in beide die lengte en breedte rigtings (8.82% en 6.67 % onderskeidelik) getoon in vergelyking met CT1 (6.52% en 2.86%). In 'n stapel van kartonne met vars granate (cv.Wonderful), was die verkoeling vinniger (29.19 %) met die CT2 verpakking. Die obstruksie van ventilasie openinge in die lengte van die stapel van die CT2 verpakking het gelei tot meer as 50% hoër LW in vergelyking met CT1 verpakking. Resultate het ook getoon dat die vrugte verpak in 'n sak, meer as 50% groter as LW vrugte verpakking is sonder ‘n sak. Die gevolg was dat die gebruik van sakke ook verkoeling van die vrugte vertraag en energieverbruik verhoog met sewe-agstes verkoelingtyd; omtrent 3 keer die van vrugte binnekant verpakking met geen sak. Verpakte vrugte in ‘n sak vereis omtrent 3.9 en 8.7 keer meer energie om vrugte af te koel in CT1 en CT2, onderskeidelik, in vergelyking met die sonder sakke. Vrugte in karton stapels toon ook 'n heterogene verkoelings patroon, met vrugte in die stroomop posisie van inkomende verkoeling sowat 36% vinniger in vergelyking met vrugte aan die agterste stapel posisie. Gedurende GL van vrugte oor 'n tydperk van 11.6 en 4.5 ure met of sonder sakke, onderskeidelik, het die gebruik van bevogtiging om 95±1% relatiewe humiditeit (RH) te behou, gewigsverlies met sowat 13.63% geminimaliseer in vergelyking met vooraf verkoelde vrugte binnekant ‘n koelkamer by 90±1% RH. Vrugte sonder sakke verloor ook oor die 17.39% meer gewig tydens vooraf verkoeling in vergelyking met vrugte verpak in sakke. Vrugte in en of sonder sakke neem langer om af te koel na voorgeskrewe temperature (7°C) verloor meer gewig as vrugte wat vinniger in opgestelde koel stoorgeriewe blootgestel word. 'n Verdere ondersoek na die uitwerking van RH op die vrugte kwaliteit van granate onder omringende (20°C) berging toestande, het getoon dat die vrugte onder hoë RH (95%) lei tot minimale gewigsverlies, behou vrugte kleur, fermheid en fisio-chemiese kwaliteite. Vrugte gestoor onder lae RH (65 %) het gelei tot oormatige gewigsverlies tot 29.13±1.49% na 30 dae (in vergelyking met 5.78±0.44% op 95% RH) en sodoende tot 'n geskatte finansiële verlies van ZAR7.78 kg-1 en ZAR1.54 kg-1 teen 'n lae en hoë RH bergingstoestande, onderskeidelik. Die aanvang van sigbare tekens van “shrivels” het plaasgevind toe vrugte gewigsverlies van omtrent 5.16% bereik het. Lineêre regressievergelykings was ontwikkel om te skat wat gewigsverlies in granate tydens berging was; gevolglik was hoë passingstoets (R2) van 0.9931 en 0.9368 vir lae en hoë RH omgewings. Hierdie navorsing het 'n insig verskaf in die uitwerking van verpakkings ontwerpe wat gebruik word in die granaatbedryf op verkoelings prestasie en die impak op vrugkwaliteit. Hoewel die gebruik van interne verpakking (sakke) die vrugte gewigsverlies geminimaliseer het, het dit LW verhoog, voorafverkoelings tyd verleng en energie verbruik en verkoeling koste opgestoot. Koelkamer bevogtiging het moontlike oplossings vir die probleem van hoë vog verlies van granate gebied. Verdere studies is gewaarborg om die ventileringsontwerp van granaat verpakking te optimaliseer, asook die gebruik van geperforeerde sakke, om verkoelings prestasie kostedoeltreffend sonder om strukturele/meganiese prestasie prys te gee in die verkoelingsproses.

Masters