| dc.description.abstract | The studies presented here were conducted to
determine the storage and processing characteristics
of three established Kenyan varieties of potato
(Solanum tuberosum). They included the red-skinned
Kerr's Pink and Desiree, and the white-skinned Kenya
Baraka varieties, and were grown under similar cultural
conditions at the National Potato Research Station
(NPRS), Tigoni. Tests were carried out over a period
of three growing seasons, starting in 1980/81.
Quality aspects of raw potatoes including specific
gravity and sugar content were determined at different
times of harvest and during storage. In addition,
potatoes were processed into crisps and flakes, whereupon,
quality of finished products was analysed using
standard procedures.
Storage characteristics of ware potato tubers
of the three varieties were determined during holding
at ambient temperature for 16 weeks. The tubers were
stored in a chamber which was built inside a naturally
ventilated potato seed store and which, too, utilized
outside air for ventilation.
Treating potato tubers with propham (IPC) at the
rate of 2g per kilogramme, significantly reduced weight
losses in all varieties compared with the untreated
control tubers. Treated and untreated Desiree tubers
showed excellent keeping characteristics throughout
Pink, while keeping satisfactorily for 12 weeks, had
high weight losses after 14 weeks. Those of Kenya
Baraka had a short shelf-life of only 8 weeks, after
which they lost their marketable and processing value
due to excessive dehydration.
Potatoes of all varieties had low sugar content
during storage. In addition, the specific gravity was
found to increase with time in storage. Conversely,
levels of reducing sugars and sucrose generally declined
with time in storage. Whereas no effect of chemical
sprout suppressant was observed on either specific
gravity or reducing sugar content, the untreated control
tubers of all varieties had slightly higher content
of sucrose than the treated samples following a 16 weeks'
storage period at ambient temperature. These observations
appear to be of significance in relation to short
term storage of potatoes for the processing industry in
Kenya's high-altitude potato growing areas, where storage
IS based mainly on natural ventilation of store houses
or buildings.
The processing performance of Kerr's Pink, Desiree
and Kenya Baraka potato varieties for manufacture of
potato crisps was determined at different harvest times
(75, 90, 105, 120 and 135 days after planting) during
a typical short growing season (1980/81) and in a long
wet one (1981) t and after storage at various temperatures
(soc, 120C and ambient).
Potato crisps were analysed subjectively for colour
using the PC/SFA colour chart, and for appearance and
flavour by a sensory panel. The data indicated low
variability in crisp quality among the varieties tested.
High quality crisps were made from potatoes of all varieties
and harvest times in the 1980/81 growing season.
Lower processing performance was, however, 'observed from
potatoes of all varieties at the initial harvest date
during the 1981 growing season, following which, crisp
quality progressively improved with later harvests. Lower
initialcrisp quality was attributed to the cool, wet
weather conditions of 1981 growing season which delayed
maturation and produced immature tubers having exceptionally
high content of reducing sugars. Also, potato
tubers of the 1981 growing season had low specific
gravity and produced crisps of lower yield than those
from the high specific gravity tubers of the relatively
drier 1980/81 growing season.
Differences in processing performance after storage
were pronounced due to the effect of temperature
conditions. Although all varieties gave acceptable
crisps when processed immediately after harvest or
after storage at 12°C, crisp quality rapidly deteriorated
upon storage at 5°C for 8 weeks. Reconditioning
the tubers at 18°C (controlled) or ambient temperature
(14.5 - l6.8oC at night) improved crisp quality. Whereas
reconditioning at 18°C produced acceptable crisp
c)lour in three weeks, longer periods of up to 8 weeks
were required to adequately recondition tubers at
ambient temperature. However, such long periods at
ambient temperature result in profuse sprouting and
high dehydration losses. Therefore, the ambient temperature
regimes were considered insufficient for reconditioning
purposes.
Storage of mature potatoes for periods up to 14
weeks at ambient temperature .gave crisps of satisfactory
quality for all varieties. However, potatoes of
Kenya Baraka from earlier harvested tubers in 1980/81
tended to accumulate reducing sugars during storage,
and produced dark crisps on processing. Also, since
,no chemical sprout suppressants were applied on potatoes
used for the crisp tests, many tubers from all
varieties were sprouted and dehydrated, particularly
after 8 weeks of storage.
In a separate processing trial, potatoes of Kerr's
Pink, Desiree and Kenya Baraka were used for manufacture
of potato flakes. The flakes were prepared using a
single drum drier. Quality of finished flakes was
tested by sensory and physico-chemical methods.
Flakes of acceptable colour, flavour and textural
quality were made from all varieties. No variety was
rated superior in all quality aspects tested. | |
