Bruise damage susceptibility of pomegranates and impacts on fruit quality

Hussein, Zaharan (2019-02)

Thesis (PhDFoodSc)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The consumption of pomegranate (Punica granatum, L) fruit is attributed to its health and nutritional benefits, which are linked with reported high antioxidant capacity, antimutagenic, anti-inflammatory, anti-atherosclerotic and anti-hypertension activities. Postharvest handling of pomegranate fruit takes a couple of weeks (5 – 8) and includes a series of operations from harvest to export (i.e. harvesting, sorting, packing/repacking and transportation). In the course of these operations, there are various situations where pomegranate fruit are subjected to multiple modest drop impacts that predispose the fruit to varying levels of excessive external forces resulting in bruise damage. Impacts may occur as the result of sudden fall of fruit onto other fruit, parts of the tree, harvesting bucket and bin, or any other uncushioned surfaces in the course of loading and offloading. The presence of a bruise on pomegranate fruit causes produce quality deterioration that contributes to downgrading, rejection of produce and ultimately, to postharvest losses. It is therefore important to understand the mechanism of bruising and how to minimise it. The overall aim of this research was to investigate the bruise damage susceptibility of selected pomegranate fruit cultivars, to ascertain the effects of bruising and storage duration on fruit quality attributes and finally, to explore the feasibility of non-destructive measurements to detect and characterise bruise damage. The studies reported in Chapter 4 investigated the susceptibility of three pomegranate fruit cultivars (‘Acco’, ‘Herskawitz’ and ‘Wonderful’) to impact bruising. The impact threshold required to bruise pomegranate fruit was investigated for each cultivar with a view to identify the cultivar that is most susceptible to bruising. The probability of bruise occurrence (PBO) was determined from the population of selected fruit impacted at minimal drop heights (0.10, 0.15, 0.20 m). At the drop impact of 0.10 m, results showed that ‘Wonderful’ had the lowest impact threshold, with a PBO value of 0.44 and an impact energy of 371.87 mJ, whereas neither ‘Acco’ nor ‘Herskawitz’ showed any signs of bruising. At the drop impact height of 0.15 m the highest bruise occurrence was seen in ‘Wonderful’ (PBO = 1; 692.98 mJ), followed by ‘Acco’ (PBO = 0.75; 406.26 mJ) and ‘Herskawitz’ (PBO = 0.5; 511.57 mJ). These results showed that ‘Wonderful’ fruit had a higher susceptibility to bruising compared to the other investigated cultivars, and therefore needs to be handled with extra care during harvest and postharvest handling. Furthermore, the study investigated the effect of cold (5 ºC) and ambient (20 ºC) storage temperatures on bruise damage susceptibility. Fruit were dropped at higher drop impact levels (0.2, 0.4 and 0.6 m), stored for a period of 10 d at either 5 ºC or 20 ºC, during which the physiological responses including weight loss and respiration rate were evaluated. Bruise size were determined in terms of bruise volume (BV) and bruise area (BA), while bruise susceptibility was calculated as the BV per unit of impact energy. The results revealed that bruise size and bruise susceptibility at higher drop heights (0.2, 0.4 and 0.6 m) were cultivar dependent and in the order of ‘Wonderful’ > ‘Herskawitz’ > ‘Acco’. The bruise size of cold (5 ºC) conditioned pomegranate fruit was significantly higher than that of fruit conditioned at an ambient (20 ºC) temperature. Further results showed that drop impact bruising had a larger effect on the fruit physiological response (respiration rate and weight loss) for bruised fruit in comparison to non-bruised fruit. Fruit impacted at higher drop impact levels (0.4 or 0.6 m) exhibited two to three-fold higher respiration rate than fruit bruised at a lower impact level (0.2 m) or nonbruised fruit. Respiration rate and weight loss increased with prolonged storage duration and at an ambient temperature, both in bruised and non-bruised fruit. Further study to evaluate the feasibility of X-ray micro-computed tomography (X-ray µCT) in detection and characterization of bruise damage on pomegranate fruit is reported in Chapter 5. Pomegranate fruit bruised by dropping at 0.6 m was scanned with X-ray µCT. The results showed that two-dimensional CT images of fruit scanned at 0 h (immediately after drop impact), 48 h, 3 d and 5 d after impact bruising showed no evidence of bruise damage. Changes in bruise-damaged tissue as characterised by a darker appearance were observed in pomegranate fruit scanned after 7 d of impact bruising. Furthermore, visual assessment of two-dimensional X-ray µCT images were buttressed by the results of quantitative µCT data analysis. The latter demonstrated that bruised pomegranate fruit can be visualised and differentiated from 7 d after impact bruising with lower grey values (18000 - 30000) compared with non-bruised fruit (26000 - 34000). The image analysis and quantitative µCT data obtained in this study confirmed that X-ray µCT is not a suitable non-destructive method to detect and characterise fresh bruises (immediately bruised) on pomegranate fruit. Studies to explore alternative non-invasive techniques, such as a hyperspectral imaging system for early detection of fresh bruises on pomegranate fruit, are warranted. Chapter 6 focused on evaluating the physical, biochemical and microstructural changes of impact-bruise damaged pomegranate fruit. The results showed that there were significant changes in colour (browning), peel electrolyte leakage (PEL), polyphenol oxidase (PPO) enzyme activity and accumulation of reaction oxygen species (ROS) measured in pomegranate fruit peel with increasing drop impact bruising. The combination of time and temperature (in which fruit was incubated) significantly (p < 0.05) contributed to changes in PEL, PPO enzyme activity and fruit browning. Cellular microstructural differences between control and bruised fruit tissues were visible in scanning electron microscope images after 4 and 48 h of drop impact. These findings provided evidence that the loss of membrane integrity of pomegranate fruit skin cells are caused by impact bruising. Chapter 7 covered the study on bruise damage of pomegranate during long-term cold storage, focusing on susceptibility to bruising and changes in textural properties of fruit. Fruit from cold (5 ºC) storage were impact bruised from different drop heights (0.2, 0.4 and 0.6 m). The bruise volume and bruise area of pomegranate fruit increased with increasing drop impact heights and storage duration for the first two months of storage, and then decreased in the last month of storage. Similarly, the results of textural properties showed that increase both in puncture resistance, cutting and compression strength were dependent on impact bruising and storage duration. These results have demonstrated that bruise damage would result in significant changes in fruit textural attributes with concomitant low consumer appeal. Studies in Chapter 8 investigated the effects of bruising and long-term cold (5 ºC) storage on the physiological response, physico-chemical quality attributes, textural properties and antioxidant content of pomegranate fruit. Respiration rate and weight loss of whole fruit were both influenced by increasing drop impact bruising and storage duration. Furthermore, there were increases in chemical quality attributes (total soluble solids, titratable acidity, Brix-to-acid ratio and BrimA), and antioxidant content of bruised pomegranate fruit during long-term storage. This was partly attributed to the concentration effect due to an increased moisture loss from bruise damaged fruit. Results on changes in aril colour and texture were dependent on both bruising and storage duration (p < 0.05). Overall, this research represents a pilot study aimed at providing scientific insights to broaden the understanding of pomegranate fruit susceptibility to bruising during postharvest handling and its impacts on fruit quality. The findings in this dissertation have established that bruise susceptibility of pomegranate fruit is dependent on the level of drop impact, cultivar, storage temperature and duration. Furthermore, this study showed that bruising, storage conditions and duration play a crucial role on physiological responses (i.e. respiration rate and weight loss), textural properties and chemical quality attributes of the fruit. From a practical point of view, the study has revealed that, bruise damage affects the sensory appeal of pomegranate fruit during storage, which could result in downgrading of fruit market value or complete fruit loss.

AFRIKAANSE OPSOMMING: Die verbruik van granate (Punica granatum, L) word toegeskryf aan gesondheids- en voedingsvoordele wat verband hou met berigte hoë antioksidant kapasiteit, anti-mutageniese, anti-inflammatoriese, anti-aterosklerotiese en anti-hipertensie aktiwiteite. Na-oes hantering van granate duur 5 – 8 weke en sluit 'n reeks praktyke in van oes tot verskeping (o.a. oes, sortering, verpakking/herverpakking en vervoer). Gedurende hierdie praktyke is granate onderhewig aan vele gematigde val-impakte wat ‘n reeks eksterne kragte op die vrug uitoefen en kneusing veroorsaak. Hierdie impakte gebeur wanneer vrugte skielik op ander vrugte, dele van die boom, in die oes-krat en pallet, of enige ander onbedekte oppervlakke tydens die laai en aflaai proses val. Kneusing verlaag die gehalte van granaat vrugte, wat bydra tot afgradering, verwerping en uiteindelik na na-oesverliese. Dit is dus belangrik om die meganisme van kneusing te verstaan en hoe om dit te verminder. Die oorhoofse doelwit van hierdie navorsing was om die kneusingsvatbaarheid van gekeurde granaat kultivars te ondersoek, om die effek van kneusing en bergingsduur op kwaliteitskenmerke van die vrugte te bepaal, en ten slotte om die uitvoerbaarheid van nie-vernietigende metings te ondersoek om kneusingskade vroegtydig te identifiseer en te kenmerk. Die studie in Hoofstuk 4 het die vatbaarheid van drie granaat kultivars (‘Acco’, ‘Herskawitz’ en ‘Wonderful’) vir kneus-impak ondersoek. Die impak-drempel wat nodig is om granate te kneus, is ondersoek vir elke kultivar met die oog op die identifisering van die kultivar wat die mees vatbaarste is vir kneusing. Die waarskynlikheid van kneusing (PBO) is vasgestel vanuit die populasie van geselekteerde vrugte wat by ‘n minimale valhoogte (0.10, 0.15, 0.20 m) geaffekteer is. By die valhoogte van 0.10 m het 'Wonderful' die laagste impakdrempel gehad, met 'n PBO-waarde van 0.44 en 'n impak-energie waarde van 371.87 mJ, terwyl 'Acco' en 'Herskawitz' geen kneusings vertoon het nie. By die val-impak hoogte van 0.15 m is die hoogste kneus-waarskynlikheid in ‘Wonderful’ (PBO = 1; 692.98 mJ) gevind, gevolg deur 'Acco' (PBO = 0.75; 406.26 mJ) en ‘Herskawitz’ (PBO = 0.5; 511.57 mJ). Hierdie resultate het getoon dat ‘Wonderful’ granate ‘n hoër vatbaarheid vir kneusing gehad het in vergelyking met ‘Acco’ en ‘Herskawitz’. Daarom moet ‘Wonderful’ granate met ekstra sorg hanteer word tydens oes- en na-oes hanteringspraktyke. Verder het die studie die effek van koue (5 ºC) en omringende (20 ºC) bergingstemperature op kneusingsvatbaarheid bestudeer. Vrugte is by hoër val-impakhoogtes (0.2, 0.4 en 0.6 m) laat val, gestoor vir ‘n periode van 10 d by 5 ºC of 20 ºC, waartydens die fisiologiese reaksie, insluitend gewigsverlies en respirasietempo, geëvalueer is. Kneusgrootte is vasgestel in terme van kneusvolume (BV) en kneusoppervlakte (BA), terwyl kneusingsvatbaarheid bereken is as die BV per eenheid impak-energie. Die resultate het getoon dat die kneusgrootte en die kneusingsvatbaarheid van granate by hoër valhoogtes (0.2, 0.4 en 0.6 m) van die kultivar afhang in die volgorde: ‘Wonderful’ > ‘Herskawitz’ > ‘Acco’. Die kneusgrootte van verkoelde (5 ºC) granate was aansienlik hoër as dié wat by ‘n omringende temperatuur (20 ºC) geberg was. Verdere resultate het getoon dat val-impak kneusing ‘n groter effek op die fisiologiese reaksie (respirasietempo en gewigsverlies) van gekneusde vrugte in vergelyking met nie-gekneusde vrugte gehad het. Vrugte wat geraak is by hoër val-impakhoogtes (0.4 of 0.6 m) het twee tot drie keer die respirasietempo getoon van vrugte wat teen ‘n laer impakhoogte (0.2 m) of glad nie gekneus was nie. Respirasietempo en gewigsverlies het toegeneem met bergingsduur en by omringde temperatuur, in beide gekneusde en niegekneusde vrugte. Hoofstuk 5 evalueer die uitvoerbaarheid van mikrofokus X-straal rekenaartomografie (X-straal μCT) in die opsporing en karakterisering van kneusingskade in granate. Granate is gekneus deur die vrugte teen ‘n valhoogte van 0.6 m te laat val, voor dit met X-straal μCT geskandeer is. Die tweedimensionele CT-beelde kon nie enige kneusingskade vind in vrugte wat geskandeer is by 0 h (direk na die val-impak), 48 h, 3 d en 5 d. Veranderinge in die beskadigde weefsel van geskandeerde granate kon slegs 7 d na die kneus-impak gekenmerk word deur 'n donkerder area. Die visuele beoordeling van tweedimensionele X-straal μCT beelde is verder versterk deur kwantitatiewe μCT data-analise. Laasgenoemde het getoon dat gekneusde granate gevisualiseer en gedifferensieer kan word vanaf 7 d na kneus-impak met laer grys waardes (18000 - 30000) in vergelyking met nie-gekneusde vrugte (26000 - 34000). Die beeldanalise en kwantitatiewe μCT-data wat in hierdie studie verkry is, het bevestig dat X-straal μCT nie ‘n geskikte nie-vernietigende metode is om vars kneusing (wat onmiddellik gekneus is) in granate op te spoor en te karakteriseer nie. Studies om alternatiewe nieindringende tegnieke te ondersoek, soos ‘n hiperspektrale beelding stelsel, vir vroeë opsporing van vars kneusing in granate is geregverdig. Hoofstuk 6 het gefokus op die evaluering van die fisiese, biochemiese en mikrostruktuur veranderinge van kneus-impak beskadigde granate. Die resultate het getoon dat daar met ‘n toenemende val impak kneusing aansienlike veranderinge in kleur (verbruining) skilelektroliet lekkasie (PEL), polifenool oksidase (PPO) ensiem aktiwiteit en ophoping van reaktiewe-suurstofspesies (ROS) in die granaatskil was. Die kombinasie van tyd en temperatuur (waarby die vrugte geïnkubeer was) het beduidend (p < 0.05) bygedra tot veranderinge in PEL, PPO ensiem aktiwiteit en verbruining. Sellulêre mikrostruktuur verskille tussen die kontrole en gekneusde vrugteweefsels was na 4 en 48 uur van die valimpak sigbaar in skanderingselektronmikroskoop beelde. Hierdie bevindinge lewer bewyse dat die verlies van sellulêre membraan-integriteit in granaatskille veroorsaak word deur kneus-impak. Hoofstuk 7 bestudeer die skade aan granate tydens langtermyn verkoeling, met die klem op vatbaarheid van kneusing en veranderinge in tekstuureienskappe van die vrugte. Vrugte wat by koue (5 ºC) temperatuur geberg is, is by verskillende valhoogtes (0.2, 0.4 en 0.6 m) laat val. Die kneusvolume en kneusoppervlakte van granate het toegeneem met toenemende val-impak hoogte en bergingsduur vir die eerste twee maande, waarna dit afgeneem het in die laaste maand van opberging. Die tekstuureienskappe resultate toon verder, dat die verhoging in beide die punthoudingsweerstand en die sny- en druksterkte, afhangend is van die kneusimpak en bergingsduur. Hierdie resultate dui aan dat kneusingskade tot beduidende veranderinge in tekstuureienskappe van granate lei, wat moontlik met ‘n lae verbruikersappèlle gepaardgaan. Hoofstuk 8 ondersoek die effekte van kneusing en langtermyn koue (5 ºC) berging op die fisiologiese reaksie, fisiese-chemiese kwaliteitseienskappe, teksturele eienskappe en antiooksidant-inhoud van granate. Respirasietempo en gewigsverlies van heel vrugte is albei beïnvloed deur toenemende val-impak kneusing en bergingsduur. Verder was daar ‘n toename in chemiese kwaliteitseienskappe (totale oplosbare vastestowwe, titreerbare sure, Brix-tot-suur verhouding en BrimA), en anti-oksidant-inhoud van gekneusde granate tydens langtermyn opberging. Dit is deels toegeskryf aan die konsentrasie-effek as gevolg van ‘n verhoogde vogverlies van kneus beskadigde vrugte. Die veranderinge in ariel kleur en tekstuur het van beide kneusing en bergingsduur (p < 0.05) afgehang. Oor die algemeen verteenwoordig hierdie navorsing ‘n loodsstudie wat daarop gemik is om wetenskaplike insigte te verskaf om die begrip van kneusingsvatbaarheid in granate tydens na-oes hantering, sowel as die impak daarvan op vrug kwaliteit te verbreed. Die bevindinge in hierdie proefskrif het vasgestel dat vatbaarheid vir kneusingskade in granate afhangend is van val-impak hoogte, kultivar, bergingstemperatuur en -duur. Verder het hierdie studie getoon dat kneusing, bergingstoestande en -duur ‘n deurslaggewende rol op fisiologiese reaksie (o.a. respirasie tempo en gewigsverlies), tekstuureienskappe en chemiese kwaliteitseienskappe van die vrug speel. Uit ‘n praktiese oogpunt het die studie gewys dat kneusingskade die sintuiglike aanloklikheid van granate tydens berging beïnvloed, wat verder tot die afgradering van vrug markwaarde of algehele vrugte verlies kan lei.

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