By Olaniyi Amos Fawole

311 Pages·2013·3 MB·English

Maturity Indexing, Pharmacological Properties and
Postharvest Performance of Pomegranate Fruit Grown in
South Africa

By
Olaniyi Amos Fawole
Dissertation presented for the degree of Doctor of Philosophy (Agric) in the
Faculty of AgriScience at Stellenbosch University

Promoter: Prof. U.L. Opara Postharvest Technology Research Laboratory
South African Research Chair in Postharvest

Technology, Department of Horticultural

Science
Stellenbosch University

DECEMBER 2013
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DECLARATION

By submitting this dissertation electronically, I declare that the entirety of the work contained
therein is my own original work, and that I have not previously in its entirety or in part submitted
it for obtaining any qualification.

Signature: Date: 19: 07: 2013

Copyright © 2013 Stellenbosch University
All rights reserved
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SUMMARY

The development and application of science-based tools for determining optimum fruit
maturity and postharvest handling protocols to maintain quality and reduce losses during
postharvest handling and marketing is essential to maintain the competitiveness of the emerging
pomegranate industry in South Africa. Currently, there are no quality standards for the South
African pomegranate industry, neither is there a general consensus on the optimal harvest
maturity indices for fruit cultivars. These information are important to ensure the delivery of
good quality fruit to consumers, particularly for long supply chains. The overall aims of this
study were (a) to develop science-based management tools for determining optimum maturity
indices and storage performance of pomegranate fruit cultivars grown in South Africa, and (b) to
characterise the physico-chemical and pharmacological properties of selected cultivars relevant
to postharvest handling and industrial applications.
In Section II, seasonal studies on pomegranate („Baghwa‟ and „Ruby‟) fruit growth and
the evolution of maturity indices during development were conducted. Significant increases in
total soluble solids (TSS), sugars (glucose and fructose) and anthocyanin composition, coupled
with significant decline in titratable acidity (TA), organic acids and total phenolics (TP) occurred
with advancing fruit maturity. Fruit at advanced maturity stages were characterized by intense
pigmentation of peel and aril, which coincided with maximum accumulation of anthocyanins.
Among all the major maturity indices investigated, TSS, BrimA and anthocyanins did not show
significant (p<0.05) seasonal variability, and strong correlations were found among the indices.
In combination, these indices accounted for fruit juice sugar content, acidity and colour and
could serve as reliable markers to determine optimal maturity for both pomegranate cultivars.
The studies in Section III focused on characterization of postharvest quality including
nutritional, medicinal and antioxidant properties of fruit parts. Quality attributes of eight
commercial cultivars were analysed by cluster analysis, which enabled the cultivars to be
separated into two clusters (cluster 1 = „Ruby‟, „Arakta‟ and „Ganesh‟; cluster 2 = „Bhagwa‟,
„Acco‟ and „Herskawitz‟) and two ungrouped cultivars („Molla de Elche‟ and „Wonderful‟)
based on important quality attributes (size, texture, colour, soluble solids, acidity, juiciness and
phenolics). Furthermore, pomegranate fruit peel extracts were studied to highlight their potential
for value-adding in pharmaceutical and other industrial applications. The results showed that
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fruit peels of the investigated cultivars possess strong antibacterial, antioxidant and anti-
tyrosinase activities, and hence could be exploited as potential sources of natural antimicrobial
and antioxidant agents, as well as a potential tyrosinase inhibitor.
The research reported in Section IV investigated the effects of harvest maturity and
storage conditions on postharvest quality and nutritional value of „Bhagwa‟ and „Ruby‟ cultivars.
Fruit harvested at commercial maturity were stored at 5±0.3°C, 7±0.5°C and 10±0.4°C with
92±3% RH and at room temperature (20±2.2°C, 65±5.5% RH) for 16 weeks. Fruit physiological
responses and quality were affected by storage condition, with the maximum levels of respiration
occurring at higher temperature and extended storage duration. Fruit colour and antioxidant
capacity varied slightly among storage temperatures, with total soluble solids and titratable
acidity decreasing gradually over time at different temperatures. Considering that fruit stored at
5°C and 92% RH had significantly reduced weight loss, low incidence of physiological disorders
and best results in maintaining flavour attributes (TSS and TA, TSS:TA ratio), the investigated
cultivars may be stored at 5°C and >92% RH for 8 - 12 weeks.
In paper 9 (Section IV), the research investigated the relationships between instrumental
and sensory measurements of pomegranate fruit at different harvest maturities during storage and
shelf life. Mature „Bhagwa‟ fruit harvested at different times could not be discriminated by
sensory attributes assessed by a trained panel. However, TSS (R2 = 0.677) and juice content
(R2 = 0.512) were the two most decisive quality attributes at shelf life related to harvest maturity
status. For „Ruby‟, however, a combination of instrumental and sensory attributes appeared to be
influential in discriminating mature fruit harvested at different times, with TSS:TA ratio being
the most decisive (R2 = 0.654) in distinguishing different fruit harvests, followed by sweet taste
(R2 = 0.474) and hue angle (R2 = 0.431). The results showed that to ensure the best post-storage
quality of „Bhagwa‟, the optimum harvest maturity was between 167 - 175 DAFB (H2 and H3)
when fruit reached maximum TSS level (>16°Brix; H3) and juice content (>65 mL/100 g aril;
H2). However, for „Ruby‟, this study indicated that the optimum harvest date was at 143 DAFB
(H2) when TSS:TA ratio was >55, which coincided with significantly higher sensory rating for
sweet taste after shelf life of fruit at H2 than H1 and H3, respectively.
The results from this thesis provide new understanding and better insights on fruit
characteristics of major pomegranate cultivars grown in South Africa. Overall, the study
provides new knowledge on science-based tools for assessing fruit readiness for harvest as well
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as storage conditions to maintain fruit postharvest quality and reduce losses. It also provides
scientific information on phytochemical contents and antioxidant compounds in fruit to promote
value-adding of pomegranate as a good raw material with potential applications in health food
products and other industrial applications such as pharmaceuticals and cosmetics.
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OPSOMMING

Die ontwikkeling en toepassing van wetenskapgegronde instrumente vir die bepaling
van optimale vrugrypheid en naoes-hanteringsprotokolle om gedurende die naoes-hantering en
-bemarking van vrugte gehalte te behou en verliese te verminder, is noodsaaklik om die
mededingendheid van die ontluikende granaatbedryf in Suid-Afrika te verseker. Tans is daar
nie enige gehaltestandaarde vir die Suid-Afrikaanse granaatbedryf óf algemene
eenstemmigheid oor die optimale oesrypheidsaanwysers vir vrugtekultivars nie. Hierdie
inligting is belangrik om die naoes-lewering van uithalervrugte aan verbruikers te verseker,
veral vir lang verskaffingskettings. Die oorkoepelende doelwitte van hierdie studie was (a) om
wetenskapgegronde bestuursinstrumente te ontwikkel vir die vasstelling van optimale
rypheidsaanwysers en bergingsprestasie van granaatkultivars wat in Suid-Afrika verbou word,
en (b) om die fisiko-chemiese eienskappe en farmakologiese kenmerke van gekose kultivars te
tipeer.
In deel II is seisoenale studies oor granaatgroei en die ontwikkeling van rypheidsaanwysers
gedurende groei onderneem. Namate vrugte ryp geword het, is beduidende toenames in totale
oplosbare vaste stowwe (TSS), suikers (glukose en fruktose) en antosianien-samestelling
opgemerk, sowel as ‟n beduidende afname in titreerbare suur (TA), organiese suur en totale fenol
(TP). Vrugte in gevorderde stadia van rypheid is gekenmerk deur intense pigmentasie van die skil
en aril, wat met maksimum opbou van antosianien verband gehou het. Van ál die belangrike
rypheidsaanwysers wat ondersoek is, het TSS, BrimA en antosianien onbeduidende (p<0.05)
seisoenale veranderlikheid getoon, en is sterk verbande tussen die aanwysers opgemerk.
Gesamentlik sou die aanwysers kon rekenskap gee van sapsuikerinhoud, -suurgehalte én -kleur, en
sou dit dus as betroubare rypheidsmerkers kon dien om optimale rypheid vir albei granaatkultivars
te bepaal.
Die studies in deel III het gekonsentreer op die tipering van die naoes-kenmerke, onder
meer die voedings-, medisinale en antioksidant-kenmerke van vrugtedele. Kenmerke van agt
kommersiële kultivars is deur middel van groepsontleding bestudeer, waarvolgens die kultivars
op grond van belangrike kenmerke (grootte, tekstuur, kleur, oplosbare vaste stowwe, suurgehalte,
sappigheid en fenol) in twee groepe (groep 1 = „Ruby‟, „Arakta‟ en „Ganesh‟; groep 2 =
„Bhagwa‟, „Acco‟ en „Herskawitz‟) en twee niegegroepeerde kultivars („Molla de Elche‟ en
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„Wonderful‟) ingedeel is. Ten einde die toegevoegde waarde van granaatskille vir farmaseutiese
en kosmetiese doeleindes te bevorder, is skilekstrakte ook bestudeer. Die resultate toon dat die
vrugteskille van die bestudeerde kultivars oor sterk antibakteriese, antioksidant- en anti-
tirosinase-eienskappe beskik. Daarom kan die skil van die granaatkultivars as moontlike bron
van natuurlike antimikrobiese en antioksidant-agense sowel as ‟n moontlike tirosinase-inhibitor
ontgin word.
Die navorsing in deel IV het ondersoek ingestel na die uitwerking van oesrypheid en
bergingsomstandighede op die naoes-gehalte en -voedingswaarde van die kultivars „Bhagwa‟ en
„Ruby‟. Vrugte wat op kommersiële rypheid geoes is, is vir 16 weke by 5±0.3 °C, 7±0.5 °C en
10±0.4 °C met 92±3% RH, sowel as by kamertemperatuur (20±2.2 °C, 65±5.5% RH) geberg.
Die bergingsomstandighede het die fisiologiese reaksies en gehalte van die vrugte beïnvloed:
Maksimum vlakke van respirasie het teen hoër temperature en met verlengde berging
voorgekom. Die kleur en antioksidantvermoë van die vrugte het effens tussen
bergingstemperature verskil, en totale oplosbare vaste stowwe en titreerbare suur het mettertyd
geleidelik by verskillende temperature afgeneem. Gedagtig daaraan dat die vrugte wat teen 5 °C
en 92% RH geberg is beduidend minder gewigsverlies, ‟n lae voorkoms van fisiologiese
afwykings en die beste resultate in blywende geurkenmerke (TSS en TA, TSS:TA-verhouding)
getoon het, kan die bestudeerde kultivars vir 8 tot 12 weke teen 5 °C en >92% RH geberg word
(navorsingstuk 8).
In navorsingstuk 9 (deel IV) is daar ondersoek ingestel na die verhouding tussen
instrument- en sintuiglike metings van granate in verskillende stadia van oesrypheid gedurende
berging en raklewe. Geen verskil in sintuiglike kenmerke kon bespeur word by ryp „Bhagwa‟-
vrugte wat op verskillende tye geoes is nie. Tog was TSS (R2 = 0.677) en sapinhoud (R2 = 0.512)
die twee bepalendste gehaltekenmerke wat betref oesrypheidstatus gedurende raklewe. By
„Ruby‟ kon ‟n kombinasie van instrument- en sintuiglike kenmerke egter wél tussen stadia van
oesrypheid onderskei, met die TSS:TA-verhouding die bepalendste (R2 = 0.654) in die
onderskeid tussen verskillende vrugteoeste, gevolg deur ‟n soet smaak (R2 = 0.474) en
skakeringshoek (R2 = 0.431). Die resultate toon dat die beste nabergingsgehalte vir „Bhagwa‟
verkry word by ‟n optimale oesrypheid van 167–175 DAFB (H2 en H3), wanneer vrugte die
maksimum TSS-vlak (>16°Brix; H3) en sapinhoud (>65 mL/100 g aril; H2) bereik het. Vir
„Ruby‟ dui hierdie studie op ‟n optimale oesdatum van 143 DAFB (H2) met ‟n TSS:TA-
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verhouding van >55, wat verband gehou het met ‟n beduidend hoër telling vir soet smaak by H2
eerder as by H1 en H3 ná raklewe.
Die resultate van hierdie tesis bied ‟n beter begrip van, en insig in, die vrugtekenmerke van
granaatkultivars wat in Suid-Afrika verbou word. Oor die algemeen bied die studie wetenskaplike
inligting om moontlik die toegevoegde waarde van granate as ‟n goeie bron van minerale elemente
sowel as farmaseutiese, kosmetiese en antioksidant-verbindings te bevorder. Dit bied ook kennis
oor die ontwikkeling van wetenskapgegronde instrumente vir die vasstelling van optimale
vrugrypheid en naoes-hanteringsprotokolle om gedurende die naoes-hantering en -bemarking van
granate vruggehalte te behou en verliese te verminder.
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PUBLICATIONS AND CONFERENCE PRESENTATIONS
FROM THIS THESIS
Published/submitted articles

1. Fawole, O.A., Opara, U.L. 2013. Harvest discrimination of pomegranate fruit:
postharvest quality changes and relationships between instrumental and sensory
attributes during shelf life. Journal of Food Science, 78, S1264–S1272. IF: 1.66
2. Fawole, O.A., Opara, U.L., 2013. Developmental changes in maturity indices of
pomegranate fruit: A descriptive review. Scientia Horticulturae, 159, 152–161. IF:
1.53(ranked 12th of ScienceDirect TOP25 Hottest Articles; July - September 2013)
3. Fawole, O.A., Opara, U.L., 2013. Fruit growth dynamics, respiration rate and
physico-textural properties during pomegranate development and ripening. Scientia
Horticulturae, 157, 90 – 98. IF: 1.53
4. Fawole, O.A., Opara, U.L., 2013. Effects of maturity status on biochemical
concentration, polyphenol composition and antioxidant capacity of pomegranate fruit
arils (cv. 'Bhagwa'). South African Journal of Botany, 85, 23 – 31. IF: 1.66
5. Fawole, O.A., Opara, U.L., 2013. Changes in physical properties, chemical and
elemental composition and antioxidant capacity of pomegranate (cv. „Ruby‟) fruit at
five maturity stages. Scientia Horticulturae, 150, 37 – 46. IF: 1.53 (ranked 13th of
ScienceDirect TOP25 Hottest Articles; April - June 2013)
6. Fawole, O.A., Opara, U.L., 2013. Effects of storage temperature and duration on
physiological responses of pomegranate fruit. Industrial Crops and Products,
47, 300 – 309. IF: 2.47
7. Fawole, O.A., Opara, U.L., 2013. Seasonal variation in chemical composition, aroma
volatiles and antioxidant capacity of pomegranate during fruit development. African
Journal of Biotechnology, 12, 4006 – 4019. IF: 0.50
8. Fawole, O.A., Makunga, N.P., Opara, U.L., 2012. Antibacterial, antioxidant and
tyrosinase-inhibition activities of pomegranate fruit peel methanolic extract. BMC
Complementary and Alternative Medicine, 12, 200: 1-11. IF: 2.24 (qualified as
“highly assessed”)
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9. Fawole, O.A., Opara, U.L., 2012. Composition of trace and major minerals in
different parts of pomegranate (Punica granatum) fruit cultivars. British Food
Journal, 114, 1518 – 1532. IF: 0.70
10. Fawole, O.A., Opara, U.L., Theron, K.I., 2012. Chemical and phytochemical
properties and antioxidant activities of three pomegranate cultivars grown in South
Africa. Food Bioprocess and Technology, 5, 2934 – 2940. IF: 4.12
11. Fawole, O.A., Opara, U.L. Physico-mechanical, phyto-chemical, and free radical
scavenging properties and volatile compounds in eight pomegranate cultivars and
classification by principal component and cluster analyses. British Food Journal, 116
(In press). IF: 0.70
12. Fawole, O.A., Opara, U.L. Instrumental and sensory measurements to determine

harvest index of pomegranate fruit in consideration of long supply chains. Postharvest
Biology and Technology (under review). IF: 2.41

List of conference presentations

1. Fawole, O.A., Opara, U.L., 2012. Harvest maturity discrimination of pomegranate fruit
(cv. „Bhagwa‟) by instrumental and sensory measurements during storage and shelf life
conditions (oral). Presented at 7th International CIGR Technical Symposium. “Innovating
the Food Value Chain” Stellenbosch, South Africa, November 25-29.

2. Fawole, O.A., Opara, U.L., 2012. Seasonal variation in physicochemical properties and
antioxidant capacity of pomegranate fruits (cv. „Ruby‟) during maturation (oral).
Presented at 7th International CIGR Technical Symposium. “Innovating the Food Value
Chain” Stellenbosch, South Africa, November 25-29.

3. Fawole, O.A., Makunga, N.P., Opara, U.L., 2012. Investigation of antibacterial,
antioxidant and tyrosinase-inhibition activities of South African grown pomegranate fruit
peel extract (poster). Presented at 7th International CIGR Technical Symposium.
“Innovating the Food Value Chain” Stellenbosch, South Africa, November 25-29.