Characterisation of "glassiness" in commercially processed french fried potatoes
Date
2005-03
Authors
Sadie, Louise
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The relationship between the “glassiness” defect in frozen French fries and the
moisture, starch and reducing sugar content of the affected potato tuber was
investigated. The effect of soil water quality, cultivar, soil depth, storage
duration, specific gravity and blanching conditions during French fry production
on the occurrence of “glassiness” was determined. Fourier transform near
infrared (FT-NIR) spectroscopy was used to identify possible classifications of
defected tubers.
No significant difference occurred between the moisture (p=0.10, trial 1
and p=0.15, trial 2), starch (p=0.76, trial 1 and p=0.70, trial 2) or reducing sugar
(p=0.05, trial 1 and p=0.51, trial 2) content of potato sample with and without the
“glassiness” defect. Samples of the cultivar Herta (Her) showed the lowest
occurrence of the defect (23%, trial 1 and 0%, trial 2), while the cultivar
Columbus (Col) showed the highest occurrence (70%, trial 1 and 84%, trial 2).
The soil water quality prevailing in the area of cultivation contributed to the
amount of “glassiness” occurring in the samples of the cultivar Col. Col obtained
from the Parys area (electrical capacity (EC) = 145 mS.m-1) showed a 21%
occurrence of “glassiness”. Col obtained from the Uitvlug (EC = 57 mS.m-1) and
Zandrug (EC = 25 mS.m-1) areas showed a 91% occurrence of the defect. All
samples cultivated in the Parys area during trial 1 showed a significantly lower
occurrence of “glassiness” (p=0.01) than samples obtained from the areas
Uitvlug and Zandrug. During trial 2 all samples obtained from the Thaaibos area
(EC = 82 mS.m-1) showed a lower occurrence of the defect than samples
obtained from the area Witklip (EC = 178 mS.m-1) although this difference was
not statistically significant (p=0.06). Soil depth, specific gravity and storage
duration did not contribute to a significant difference in the occurrence of
“glassiness” between samples.
Modified blanching conditions of 62ºC for 25 min instead of 80ºC for 20
min during frozen French fry processing had a reducing effect on the occurrence
of the defect in the cultivars Fianna (Fia) (p=0.06), Pentland Dell (Pen) (p=0.05) and Col (p<0.01). The modified blanching conditions improved the texture
uniformity in the French fry strip, reducing oil absorption during frying and
prevented fry strips from breaking during subsequent processing steps.
FT-NIR calibration models could not be successfully developed for the
prediction of the moisture, starch and reducing sugar content in a potato sample.
Principal component analysis (PCA) indicated no classification between potato
samples affected by the “glassiness” defect and samples without the defect. The
calibration models for moisture, starch and reducing sugar content yielded a
standard error of prediction (SEP) of 1.62%, 2.28% and 0.07%, respectively.
The respective correlation coefficients of these calibration models were 0.46,
0.42 and 0.41.
The “glassiness” defect was most prominent in the cultivar Col. The
occurrence of the defect was reduced and French fry quality improved by
adjusting blanching parameters to 25 min at 62ºC. FT-NIR spectroscopy is not
recommended for screening of potato quality prior to processing.
Description
Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2005.
Keywords
Dissertations -- Food science, Theses -- Food science, Potato products -- Testing, French fries -- Testing, Fourier transform infrared spectroscopy