Moisture loss studies in nectarine (Prunus persica var. necterina)

Chigwaya, Kenias (2016-12)

Thesis (MScAgric)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Moisture loss studies in nectarines (Prunus persica var. nectarina) Moisture loss during long term storage is one of the main post-harvest problems in nectarines. The long handling chain to which fruit are exposed to, from harvest until the end of shelf-life, exposes fruit to moisture loss. Moisture loss occurs as a result of the vapour pressure deficit (VPD) between the fruit and surrounding atmosphere. In addition to causing loss of saleable weight, moisture loss also results in fruit having a shrivelled appearance. Moisture is lost from fruit through various openings in the fruit peel such as micro-cracks and lenticels. In this study we investigated the effect of fruit to fruit variation, harvest date, tree and orchard effects and cultivar differences on the variation in water vapour permeance (P’H2O) of three nectarine cultivars namely ‘Alpine’, ‘Summer Bright’ and ‘August Red’. The study showed that large fruit to fruit differences were the main contributor (>45%) to the variation in P’H2O, followed by harvest date (>35%), cultivar differences (>7%) and orchard effects (>3%) whilst tree effects did not contribute to P’H2O. Generally, the P’H2O of all three cultivars increased steadily as the harvest date approached and continued to increase post-harvest, but P’H2O at optimum harvest was not closely correlated to their susceptibility to shrivel. In addition, ‘August Red’ nectarines were exposed to different handling chains from harvest until the end of shelf-life to determine the VPD at different stages in the handling chain in order to establish the point which is most effective in reducing moisture loss and shrivel. The results indicated that none of the proposed handling chains performed better than the current standard handling protocol in reducing moisture loss and shrivel. This protocol stipulates that nectarines should be harvested during the cooler time of the day and field heat should be removed as soon as possible after harvesting. Furthermore, the handling protocol requires that nectarines should be packed within 12 hours of arrival at the pack-house. Several researchers have reported that silicon containing fertilizers improve fruit quality and we therefore also investigated whether pre-harvest applications of potassium silicate (K2SiO3) can reduce post-harvest moisture loss, shrivel and split pit in ‘Southern Glo’ nectarines. The results showed that both soil and foliar K2SiO3 applications were not effective in reducing post-harvest moisture loss, shrivel or the incidence of split pit in ‘Southern Glo’ nectarines. For future studies, it is recommended to increase the frequency of K2SiO3 applications. The study also looked at the effectiveness of different packaging films in reducing moisture loss and shrivel in ‘August Red’ and ‘Alpine’ nectarines. Failure to package fruit optimally may result in weight loss, shrivel, decay and the incidence of internal defects such as woolliness, pulpiness and over-ripeness. The results showed that the use of Xtend® and high density poly-ethylene (HDPE) bags significantly reduced moisture loss and shrivel in nectarines in both pulp trays and plastic punnets. The standard nectarine HDPE wrappers resulted in significantly higher percentage mass loss as well as shrivel incidence in ‘Alpine’ nectarines. It is therefore important to reduce moisture loss at harvest by following the standard handling protocol and by packing fruit optimally.

AFRIKAANS OPSOMMING: Studies oor vogverlies in nektarienvrugte (Prunus persica var. nectarina) Vogverlies tydens langtermynopberging is een van die hoof na-oes probleme wat nektariens ervaar. Vrugte word aan ʼn lang hanteringsketting blootgestel vanaf oes tot die einde van raklewe en dit lei tot vogverlies. Vogverlies vind plaas as gevolg van die water dampdruk tekort (WDDT) tussen die vrug en die omringende atmosfeer. Buiten dat dit die verkoopbare gewig van vrugte verminder, sal vogverlies ook daartoe lei dat vrugte ʼn verrimpelde voorkoms het. Vog gaan verlore uit die vrug deur verskeie openinge in die skil byvoorbeeld mikrokrakies en lentiselle. In hierdie studie het ons die effek van vrug tot vrug variasie, oesdatum, boom- en boord effekte en kultivarverskille op vogdeurlaatbaarheid (P’H2O) van drie nektarienkultivars, naamlik ‘Alpine’, ‘Summer Bright’ en ‘August Red’ ondersoek. Die studie het getoon dat vrug tot vrug variasie die hoof bydrae (>45%) tot verskille in P’H2O gemaak het, gevolg deur oesdatum (>35%), kultivar verskille (>7%) en boord effekte (>3%) terwyl boom effekte geen bydrae gelewer het tot P’H2O nie. Oor die algemeen het die P’H2O van al drie kultivars geleidelik gestyg soos die optimum oesdatum nader gekom het en het verder gestyg na die optimum oesdatum. Die P’H2O tydens optimum oes was egter nie goed gekorreleer met die kultivar se geneigdheid om te verrimpel nie. Verder is ‘August Red’ nektariens blootgestel aan verskillende hanteringsprotokolle vanaf oes tot na raklewe om die WDDT te bepaal tydens verskillende tydstippe in die hanteringsketting om te bepaal tydens watter periode die WDDT die beste gereduseer kon word om sodoende vogverlies en verrimpeling te verminder. Nie een van die voorgestelde hanteringskettings het beter presteer om vogverlies en verrimpeling te verminder as die standaard, aanbevole hanteringsketting nie. Hierdie protokol stipuleer dat nektariens gedurende die koeler tyd van die dag geoes moet word en dat veldhitte so vinnig moontlik na oes verwyder moet word. Verder vereis die protokol dat nektariens binne 12 uur na aankoms by die pakhuis verpak moet word. Verskeie navorsers het aangedui dat silikonbevattende kunsmisstowwe vrugkwaliteit kan verbeter. Ons het dus ondersoek of voor-oes toedienings van kaliumsilikaat (K2SiO3) na-oes vogverlies, verrimpeling en gebreekte pitte in ‘Southern Glo’ nektariens kan verminder. Beide grond- en blaartoedienings vanK2SiO3 was oneffektief om na-oes vogverlies, verrimpeling en gebreekte pitte in ‘Southern Glo’ nektariens te verminder. In toekomstige studies moet die frekwensie van K2SiO3 toedienings dalk verhoog word. Hierdie studie het ook die effektiwiteit van verskillende verpakkingsmateriale om vogverlies en verrimpeling te verminder op ‘August Red’ en ‘Alpine’ nektariens ondersoek. Wanneer vrugte nie optimaal verpak word nie kan massaverlies, verrimpeling, verrotting en interne kwaliteitsverliese soos voosheid, pulpagtigheid en oorrypheid voorkom. Resultate het daarop gedui dat die gebruik van Xtend® en hoë digtheid poli-etileen (HDPE) sakke vogverlies en verrimpeling betekenisvol kan verminder in nektariens in beide pulprakkies en plastiek houers. Die standaard nektarien HDPE “wrappers” het tot betekenisvol meer massa verlies en die voorkoms van verrimpeling gelei in ‘Alpine’ nektariens. Dit is dus belangrik om vogverlies naoes te verminder deur die standaard hanteringsprotokol te volg en nektariens optimaal te verpak.

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