Thesis (MScEng) -- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The grape juice concentrate (GJC) plant of the KWV at Robertson spent
significant amounts of money on the decolourisation of grape juice
concentrate. A chemically activated powdered activated carbon (PAC)
purchased from Norit, namely CA1, was used as decolourisation product.
Apart from the expenses involved, it contributed largely to the solid waste
produced at this plant. A way was sought to minimise or prevent GJC
discolourisation (and possibly solid waste) without increasing operating
expenses.
Browning reactions in GJC are as old as the product itself. Numerous
researchers have studied the origins of these reactions, the reactants and
products involved, as well as the reaction kinetics of these reactions. From
the work of these researchers four possible browning reaction pathways
were identified, namely:
• enzymatic oxidative browning,
• non-enzymatic oxidative browning,
• non-enzymatic browning (the Maillard reaction), and
• caramelisation.
It was also identified that 5-hydroxymethylfurfural (HMF) are indicative of
the browning potential of GJC. A method to analyse for HMF
(quantitative and qualitative) was develop for the purposes of this study,
namely positive electron-spray ionisation preceded by high-pressure liquid
chromatography (HPLC) and followed by dual mass spectrometry. This
method showed good repeatability and was used to analyse all samples
generated during this study. It was confirmed that the manufacturing process at this plant favours nonenzymatic
browning reactions, since mild heat treatment deactivates
enzymes. Further investigation indicated that the overruling browning
reaction on this plant was non-enzymatic oxidative browning. It was
shown that neither the presence, nor the absence of protein had any effect
on the rate of formation of HMF. It was, however, confirmed that HMF
formation could be attributed to high temperatures and prolonged exposure
to these temperatures.
Other adsorption products were evaluated against the then current PAC
(CA1), namely a steam activated PAC supplied by Norit, SA4, and a
polymeric adsorbent, Polyclar V (polyvinylpolypyrrolidone/PVPP). Both
SA4 and PVPP indicated superior HMF adsorption capacities. Replacing
CA1 with SA4 could result in operating expenses savings and possible
solid waste reduction. However, PVPP were too expensive to be
considered an economically viable replacement for CA1.
Improved concentration technologies such as reverse osmosis (RO)
membrane concentration followed by centrifugal evaporation (CE) or twostage
CE should be considered as possible replacement for the existing
concentration technology (multi-stage falling film evaporator). This
should decrease heat treatment/exposure by more than 90% and thus
reduce browning significantly. An added advantage could be the reduction
of solid waste, since less (if not no) decolourisation will be required.
Alternatively, juice should be stored with added sulphur dioxide (SO2),
since it was shown that this juice contained much lower HMF
concentrations than diluted concentrate (stored for the same time). This
should reduce heat exposure by up to 50% and thus minimise browning
reactions. / AFRIKAANSE OPSOMMING: Die druiwesapkonsentraat (DSK) aanleg van die KWV in Robertson het
jaarliks aansienlike bedrae geld spandeer tydens die ontkleuringsproses van
DSK. ‘n Chemies geaktiveerde verpoeierde koolstof (GVK) verkrygbaar
van Norit, naamlik CA1, is gebruik as ontkleuringsproduk. Buiten die
kostes verbonde aan hierdie produk het dit ook grootliks bygedra tot
soliede afval by hierdie aanleg. Oplossings is gesoek om die
verbruining/ontkleuring van DSK (en dalk ook soliede afval) te verminder
(of selfs te voorkom) sonder om bedryfskostes te verhoog.
Verbruiningsreaksies in DSK bestaan al so lank soos DSK self. Verskeie
navorsers het die oorsake, reaktante, produkte en reaksiekinetika van
hierdie reaksies oor die jare heen bestudeer. Uit die werk van sommige
van hierdie navorsers kon vier moontlike verbruiningsreaksieroetes
geïdentifiseer word, naamlik:
• ensiematiese oksidatiewe verbruining,
• nie-ensiematiese oksidatiewe verbruining,
• nie-ensiematiese verbruining (die Maillard-reaksie), en
• karamelisering.
Daar was verder geïdentifiseer dat 5-hidroksiemetielfurfuraal (HMF)
aanduidend is van die verbruiningspotensiaal van DSK. ‘n Analitiese
metode (kwalitatief en kwantitatief) om vir HMF te analiseer is vir die doel
van hierdie studie ontwikkel, naamlik positiewe elektronsproei ionisasie,
voorafgegaan deur hoëdruk vloeistof chromatografie en gevolg deur
dubbele massa spektrometrie. Hierdie analitiese metode het goeie
herhaalbaarheid getoon en was deurgaans gebruik om monsters te analiseer
gedurende hierdie studie. Dit was bevestig dat die vervaardigingsproses by hierdie aanleg nieensiematiese
verbruiningsreaksies begunstig, aangesien geredelike
hittebehandeling ensieme deaktiveer. Verdere navorsing het getoon dat die
oorheersende verbruiningsreaksies by hierdie aanleg nie-ensiematiese
oksidatief van aard is. Resultate het getoon dat proteinstabiliteit geen
invloed op die vormingstempo van HMF het nie. Dit was egter bevestig
dat vorming van HMF direk verband hou met hoë temperature en lang
blootstellingsperiodes aan hierdie temperature.
Ander adsorpsieprodukte was vergelyk met die huidige GVK (CA1),
naamlik ‘n stoom geaktiveerde verpoeierde koolstof (Norit se SA4) en ‘n
polimeriese adsorbant, Polyclar V (polivinielpolipirrolidoon/PVPP). Beide
SA4 en PVPP het CA1 oortref wat betref HMF adsorpsie. Moontlike
bedryfskostebesparings (en soliede afval verminderings) potensiaal bestaan
indien CA1 vervang word met SA4. Die teenoorgestelde is egter waar vir
PVPP wat bedryfskoste aangaan.
Instede van die huidige verdampinstegnologie, naamlik vallendefilmverdamping,
hoort verbeterde konsentrasietegnologieë soos tru-osmose
membraankonsentrasie gevolg deur sentrifugale verdamping, of,
alternatiewelik, twee-stadium sentrifugale verdamping, orrweeg te word.
Op hierdie wyse behoort hittebehandeling (en dus verbruining) met sowat
90% verminder te word. ‘n Moonlike addisionele voordeel is die
vermindering van soliede afval aangesien minder ontkleuring nodig sal
wees.
Indien die verbeterde tegnologieë te duur is moet daar gekyk word daarna
om die ongekonsentreerde sap met addisionele swaweldioksied (SO2) te
stoor, aangesien veel laer HMF konsentrasies in sulke sap waargeneem is
as in verdunde direkte konsentraat wat vir dieselfde typerk gestoor is. Hittebehandeling sal op hierdie wyse met tot 50% verminder word (en dus
verbruining ook).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16381 |
| Date | 12 1900 |
| Creators | Loedolff, Matthys Johannes |
| Contributors | Lorenzen, L., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvii, 151 leaves : ill. |
| Rights | University of Stellenbosch |
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