After-cooking Darkening Research Articles

Potato quality XXV. Specific gravity and after-cooking darkening of Katahdin potatoes as influenced by fertilizers

The effect of two sources and three levels of potash and two levels of phosphorus, at a constant rate of application of nitrogen, on specific gravity and after-cooking darkening of Katahdin potatoes was studied.

Potato quality XVIII : The distribution of radioiron in the potato tuber and its significance in after-cooking darkening

Radiotracer techniques were used to study the distribution of iron in intact potato tuber sections. Autoradiographs of longitudinal tuber sections show that iron is particularly concentrated at the stem end of the tuber just below the periderm. Accumulation of radioiron in other tissues, i.e. internal phloem and vascular ring, is shown by autoradiographs of tuber cross-sections. Radioiron was also found to be concentrated in meristematic areas, especially at lateral buds. A parallel is noted between areas of iron accumulation and areas in the tuber reported to be associated with after-cooking darkening. The distribution of iron is probably more important than previously realized in determining the distribution of after-cooking darkening in individual potato tubers.

Potato quality XV. Improving texture and measuring textural changes in potato flakes

Mealiness or consistency is the most important textural factor in certain forms of processed potatoes. An objective method of measuring this has been shown using a modified L.E.E.-Kramer shear press. Addition of sodium acid pyrophosphate at various locations in the processing line will increase mealiness and prevent discoloration from after-cooking darkening. To substantiate textural changes, objective methods were used and the influence of moisture and flake ratio in the reconstituted products was shown. Microscopic examinations showed that SAPP-treated cells when ruptured did not lose their contents. As the ratio of water to flakes is increased the shear force is decreased. The temperature of the water also creates shear force differences, although the general slope of the curves are similar. Phosphorus concentrations in potato flakes are shown for various treatments with and without SAPP. Both ortho and pyro forms were analyzed and all treatments showed increased phosphorus concentrations. Total iron content was similar in all treatments but color scores were higher in the SAPP-treated samples.

Potato quality XIII. Preventing after-cooking discoloration in oil blanched French fries

Treatment of slices with a 2% solution of Na2H2P2O7 in the blancher will prevent after-cooking darkening in par-fried French-fries. The Na2H2P2O7 seems to act as a sequestering agent in complexing the ferrous iron in a colorless form. The texture of the finished product is improved and uniform quality control of color is made possible. Sodium acid pyrophosphate does not increase the free fatty acids of the frying media and the increase in the per cent of P2O5 in the treated product is negligible. Frozen French-fries held at O F. that are discolored can be transformed into a creamy white product by dipping them for two minutes in a 2% solution of Na2H2P2O7 at 40 F. The pyrophosphate does not cause the detrimental effects on texture that some acids, sequestering, and chelating agents cause in the finished product.

Alaska 114. A tough-skinned main crop potato

Alaska 114 is a medium vine type potato producing a very uniform size and shape tuber. It has a tough skin, yields well, stores well, has good culinary qualities and exhibits significantly less after-cooking darkening than Green Mountain.Phytophthora infestons has not been observed on potatoes in Alaska since this variety has been under test so its susceptibility to late blight is not known.

After-cooking darkening in oil-blanched French-fried potatoes

A lot of potatoes grown in New Brunswick, Canada, in 1957 contained on the average slightly more iron,o-dihydroxyphenyl compounds, and tannins than did a lot grown in Idaho in the same year, but the differences were not important. The measurements were made on potato pulp from composite samples. Oil-blanched French-fried potatoes (a partially cooked product) prepared from the New Brunswick tubers showed dark grey spots, and those prepared from the Idaho tubers did not. Since the pigment appeared in localized portions of the product, it is suggested that the distribution and not necessarily the amount of chromogenic materials in the tubers, is important. Blanching in 1 per cent citric acid or 0.1 per cent disodium ethylenediaminetetraacetate during preparation prevented discoloration in the finished product.

Potato quality IX. Use of sequestering agents in preventing after-cooking darkening in pre-peeled potatoes

A 60 second dip in a mixture of 1 per cent sodium bisulfite and 1 per cent sequestering agent (the di sodium or tetra sodium salt of ethylenediamine tetraacetic acid) effectively prevented after-cooking darkening of pre-peeled potatoes when there was a time lag of 24 hours or more between time of treatment and time of cooking.

Potato quality viii. effect of foliar applications of sequestering and chelating agents on after-cooking darkening.

Several sequestering and chelating agents were sprayed on potato plants in the field. Observations and Hunter Color Difference Meter readings of boiled potatoes from these treatments indicate that several of these agents prevent or reduce after-cooking darkening. This probably results from the iron in the tubers being sequestered or chelated so that it is held in a non-ionizable form and cannot take part in a reaction with o-diphenols and therefore, prevents the normal formation of the dark colored pigment, a ferric-o-diphenol compound.