Ultrafiltration (UF), using Romicon pilot-scale hollow-fiber
cartridges (Model HFXS-MK11) in the batch mode, was investigated
as a possible procedure for clarifying, stabilizing and preserving
White Riesling (WR) and Thompson Seedless (ThS) grape juice. The
effect of UF processing of SO₂-treated or untreated juice, of process
temperature and membrane molecular weight cut-off (MMWCO) on
UF juice composition and quality, was determined. "Sparkling
clear" pale light-colored UF permeates were obtained and subjected
to storage stability trials at different temperatures. Juice
parameters evaluated included proteins, phenolics, polyphenol oxidase
(PPO), microorganisms, browning, haze and sensory properties.
UF at elevated temperatures of up to 50°C, compared to lower
temperatures, had the advantage of increased rate of filtration
with decreases in browning or haze of clarified permeates and of
markedly reduced microbial loads. UF of SO₂-treated juices (13-
20 ppm free) had several advantages including further reduction
in browning, haze, and microbial load, and complete inhibition of
PPO activity.
More proteins (34% - 92%) than phenolics (2% - 27%) were retained
by UF membranes. However, more proteins and less phenolics
were retained in SO₂-treated than untreated juices. Increasing
MMWCO from 10,000 to 100,000 had no effect on the retention of
browning, haze, or microorganisms but decreased the retention of
proteins from 58 percent to 34 percent in SO₂-treated WR juice.
A MMWCO of 50,000 or less retained essentially all PPO.
ThS juice browned more than WR during juice preparation and
UF processing, yet its clarified permeates were lighter. It contained
less phenolics, more proteins and more PPO activity, and
higher percentages of its proteins and phenolics were retained by
UF membranes.
UF juices processed with or without low concentrations of SO₂
(13-20 ppm free) could be stored for at least one year at 1°C
without fermentation spoilage. At 21°C only the treated juices
could be stored for this long, untreated juices fermenting within
one week. At 1°C, there was no increase in browning, but a gradual
increase in haze upon storage, the latter being greater in untreated
juices. At 21°C, browning increased gradually, resulting
in pale golden juices but haze formation was markedly less than in
juices stored at 1°C. Similar but accelerated changes occurred
with storage at 38°C. The above changes correlated with the disappearance
of free SO₂.
Although juices were preserved for up to one year, "absolute
juice sterility" was never obtained. Leakages around the cartridge
gaskets, rather than failure of membranes, was believed to be
responsible.
Sensory analysis detected no significant differences (p = 0.05)
in color, aroma and taste between juices processed with SO at 30°C
and 50°C. Juices processed without SO₂ were not significantly
different in color, but demonstrated small differences (p = 0.05)
in aroma and taste. The SO₂-treated and untreated juices at both
processing temperatures, as well as treated juices stored at
21°C and 1°C for twelve months, were significantly different
(p = 0.01) in color, aroma and taste. Although these juices
had different flavor "characters," only small or no significant
differences (p = 0.05) in desirability were detected.
It is concluded that good quality clarified grape juice
but of different flavor "character" can be produced by UF, either
in the presence or absence of SO₂. Both juice "styles" (± SO₂)
may find preferred use, but juices processed with SO₂ have the
advantage of ambient storage, retaining good quality after one
year at 21°C. Recommended optimum processing conditions are
50°C, in the presence of minimal amounts of SO₂ (13-20 ppm free),
using membrane molecular weight cut-off of 30-50,000. However,
application of the process to "cold-sterilization" of grape juice
requires further evaluation. / Graduation date: 1983
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27474 |
| Date | 03 December 1982 |
| Creators | Fombin, Joseph Forchap |
| Contributors | Heatherbell, D. A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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