Malheur Experiment Station Information for Sustainable Agriculture

Processing Quality of New Potato Cultivars Following Prolonged Storage

Glenn E. Vogt

J.R. Simplot Co., Caldwell, ID and

Eric P. Eldredge and Clinton C. Shock

Malheur Experiment Station

Oregon State University

Ontario, OR 2002

Introduction

The competitive position of Treasure Valley potato production and processing depends on production efficiency at every level. The competitive position could be improved through the identification and adoption of potato cultivars with higher yields and better processing attributes than 'Russet Burbank'. Substantial research efforts are made each year to find better cultivars, and the best of these cultivars are entered into the "Western Region Early- and Late-harvest Potato Variety Trials". These trials evaluate yield, grade, and processing quality, but they do not test cultivar processing quality after long-term storage.

Regardless of 'Russet Burbank' shortcomings, 'Russet Burbank' tubers are particularly appropriate for long-term storage and processing out of storage. These trials were conducted to evaluate Western Regional cultivar performance for processing after long-term storage.

Materials and Methods

The details of the Western Region Early- and Late-harvest Potato Variety Trials in 1999, 2000, and 2001 have been reported previously (Eldredge et al. 2000, 2002; Shock et al. 2001). Cultivars were evaluated for yield, grade, and processing quality after harvest.

At the time of grading, a sample of 20 tubers from each cultivar and each replicate were sent to long-term storage at 50°F. Tubers were stored for 4-8 months, then they were evaluated for solids, dextrose, and sucrose. The tubers from the early-harvest trial in 1999 were stored for 4 months, the tubers from the late-harvest trial in 2000 were stored for 7 months, and the tubers from both the early- and late-harvest trials in 2001 were stored for 8 months.

Tuber solids were determined using the weight in air vs. weight in water method. Dextrose and sucrose were determined using a model 2700 YSI Industrial Sugar Analyzer (Yellow Springs Instrument Co., Yellow Springs, OH) using the method of Sowokinos and Preston (1988). Fried strips were evaluated for USDA fry color by comparison against the USDA's color (USDA 1972). Dextrose and sucrose are reported in percent fresh weight.

"Sugar-ends" were defined as fried tuber strips with USDA color number 3 to 4 on two or more sides, with the color extending at least 1/4 inch down from the end of the strip but no more than one-half the length of the strip. A "sugar-end" strip would not have shriveled or shrunken tissue at the dark end of the strip. "Dark-ends" were defined with the same characteristics as sugar-ends, but as also having shriveled or shrunken tissue at the end of the fried strip, resulting from collapsed cells.

Treatment differences were compared using analysis of variance and protected least significant differences at the 5 percent probability level (LSD (0.05)). Direct comparisons of tuber quality at harvest with tuber quality after long-term storage were not possible due to the different laboratory methods used in the two sets of tests.

Results and Discussion

While all of the cultivars in the Western Regional Early- and Late-processing Trials are supposed to be processing types, 'Russet Norkotah' is known only as a fresh market cultivar. In the present trials, 'Russet Norkotah' has been used as a check variety, especially in comparison to the Norkotah clones 'TXNS102' and 'TXNS296'. 'Russet Norkotah' and the Norkotah clones had relatively low solids and high dark-ends and sugar-ends compared to most of the cultivars tested (Tables 1-5). The relatively poor processing performance of these cultivars was expected.

Cultivar type had a significant effect on every potato variable reported from these trials, except the percent of USDA number 3 fry color strips.

Solids

Averaged over four trials, tuber solids after 4-8 months of storage ranged from 21.2 percent for 'Russet Norkotah' to 26.4 percent for 'AC87079-3' (Table 5). 'Russet Burbank' at 22.6 percent was among the lowest quarter of the cultivars. Tuber solids were strongly influenced by year. This is to be expected, since potatoes grown in years with substantial heat stress tend to produce lower solids. There were no significant interaction effects of cultivar by year and no significant effects of early vs. late harvest date on tuber solids.

Dextrose and Sucrose

Averaged over four trials, dextrose after 4-8 months of storage ranged from 0.46 percent for 'A9014-2' to 1.31 percent for 'A8893-1'. 'Russet Burbank' averaged 0.85 percent. Dextrose varied greatly between years, probably a reflection of all the environmental differences experienced by the tubers during tuber growth, maturation, harvest, and storage. There were no significant interaction effects of cultivar by year and no significant effects of early vs. late harvest date on dextrose.

After 4 to 8 months of storage, sucrose ranged from 0.10 percent for Russet Burbank to 0.196 percent for A8893-1. Cultivars interacted with year to produce different sucrose levels, while the effects of year or early or late harvest were not significant.

Distribution of USDA Fry Color

After 4-8 months of storage, the distribution of USDA fry colors was very different between cultivars. The line 'A9014-2' had 90.9 percent fried strips of USDA color 0 or lighter while 'A8893-1' had only 22.7 percent in the same category. 'Russet Burbank' performance was intermediate with 45.5 percent fried strips of USDA color 0 or lighter.

Dark-ends and Sugar-ends

Averaged over four trials, after 4-8 months of storage, 'Russet Burbank' had more dark-ends than any of the other cultivars (26.9 percent) and significantly more sugar-ends (15.8 percent) than any of the other cultivars except 'Russet Norkotah' (13.5 percent) and 'TXNS102' (11.5 percent). The problems of dark-ends and sugar-ends in 'Russet Burbank' do not appear to be related to its average fry color, average percent sucrose, or average percent dextrose. Rather it is a problem of the poor distribution of the reducing sugars (measured here as dextrose) and resultant dark fry color down the length of the fried tuber strip.

References

Eldredge, E.P., and C.C. Shock. 2000. Potato variety trials at Ontario. Oregon State University Agricultural Experiment Station, Special Report 1015:134-140.

Eldredge, E.P., C.C. Shock, and L.D. Saunders. 2002.Potato Variety Trials 2001. Oregon State University Agricultural Experiment Station, Special Report 1038:178-189.

Shock, C.C., E.P. Eldredge, and L.D. Saunders. 2001. Potato variety trials 2000. Oregon State University Agricultural Experiment Station, Special Report 1029:135-145.

Sowokinos, J.R., and D.A. Preston. 1988. Maintenance of potato processing quality by chemical maturity monitoring (CMM). Minnesota Agricultural Experiment Station Bulletin 586-1988.

USDA. 1972. USDA's color standard for frozen French-fried potatoes. Third edition. Munsell Color Co., Baltimore, MD.

Table 1. Potato tuber processing quality for the 1999 Western Regional Late-harvest Processing Trial after 4 months of storage. Malheur Experiment Station, Oregon State University, Ontario, OR.

Table 2. Potato tuber processing quality for the 2000 Western Regional Early-harvest Processing Trial after 7 months of storage. Malheur Experiment Station, Oregon State University, Ontario, OR.

				Distribution of strips by USDA fry color						Appearance of fried strips
Cultivar	Solids	Dextrose	Sucrose	0	1	2	3	4		Dark-ends	Sugar-ends
	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - % - - - - - --- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Russet Burbank	22.37	1.02	0.082	41.7	45.0	13.3	0.0	0.0		25.0	13.3
Ranger Russet	24.03	1.67	0.057	78.8	12.5	6.3	1.3	1.3		3.8	6.3
Russet Norkotah	20.70	1.03	0.071	35.0	16.0	40.5	6.0	3.0		8.5	8.0
Shepody	21.73	1.12	0.066	81.8	16.8	0.0	0.0	1.5		0.0	1.5
A8792-1	24.43	3.64	0.133	20.5	30.5	33.3	14.0	1.5		1.5	5.3
A8893-1	21.93	2.59	0.135	13.3	21.7	36.7	18.3	10.0		1.7	5.0
A9014-2	24.70	1.18	0.027	73.5	21.0	5.5	0.0	0.0		0.0	0.0
A9045-7	23.63	1.68	0.080	28.8	48.8	18.8	3.8	0.0		1.3	0.0
AC87079-3	25.63	1.76	0.082	28.8	36.3	26.3	5.0	3.8		6.3	2.5
AC87138-4	22.00	2.29	0.100	17.5	33.3	34.0	15.3	0.0		1.5	8.0
AC89536-5	24.75	2.06	0.176	28.8	17.8	33.0	9.0	11.5		0.0	0.0
ATX9202-3RU	22.95	1.33	0.031	70.0	7.5	16.3	5.0	1.3		1.3	1.3
TXNS102	22.10	1.27	0.122	8.3	36.7	31.3	10.7	13.0		13.7	12.0
TXNS296	22.28	1.10	0.106	6.3	45.0	27.5	16.3	5.0		18.8	23.8
Mean	23.09	1.69	0.090	38.1	27.8	23.0	7.5	3.7		5.9	6.2
LSD(0.05) Cultivar	2.20	0.70	0.055	35.9	NS	23.1	NS	NS		8.0	6.6

Table 3. Potato tuber processing quality for the 2001 Western Regional Early-harvest Processing Trial after 8 months of storage. Malheur Experiment Station, Oregon State University, Ontario, OR.

Table 4. Potato tuber processing quality for the 2001 Western Regional Late-harvest Processing Trial after 8 months of storage. Malheur Experiment Station, Oregon State University, Ontario, OR.

				Distribution of strips by USDA fry color						Appearance of fried strips
Cultivar	Solids	Dextrose	Sucrose	0	1	2	3	4		Dark-ends	Sugar-ends
	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - % - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Russet Burbank	22.98	0.61	0.106	53.8	43.8	2.5	0.0	0.0		21.3	15.0
Ranger Russet	24.08	0.34	0.148	63.5	31.5	5.0	0.0	0.0		1.3	7.7
Russet Norkotah	21.43	0.46	0.200	36.3	36.3	18.8	8.8	0.0		8.8	16.3
Shepody	24.70	0.23	0.137	76.3	12.5	11.3	0.0	0.0		0.0	1.3
A8893-1	23.90	0.95	0.278	20.0	37.5	31.3	7.5	3.8		0.0	1.3
A9014-2	25.83	0.13	0.154	98.8	1.3	0.0	0.0	0.0		0.0	0.0
A9045-7	26.48	0.51	0.229	46.3	23.8	25.0	5.0	0.0		0.0	0.0
A90586-11	25.00	1.01	0.243	25.0	11.3	37.5	25.0	1.3		0.0	0.0
AC87079-3	26.75	0.40	0.207	39.0	48.4	11.5	1.3	0.0		3.8	3.8
AC87138-4	25.10	0.22	0.226	70.0	27.5	2.5	0.0	0.0		1.3	3.8
AC89536-5	25.20	0.83	0.188	26.3	37.5	23.8	11.3	1.3		0.0	0.0
AC91014-2	26.15	0.29	0.260	62.1	20.4	12.5	5.0	0.0		0.0	0.0
AO92017-6	25.65	0.14	0.155	90.0	10.0	0.0	0.0	0.0		0.0	1.3
ATX9202-3RU	24.60	0.23	0.174	77.5	13.8	7.5	1.3	0.0		6.3	5.0
Stampede Russet	22.53	0.76	0.222	50.0	16.3	15.0	7.5	11.3		1.3	7.5
TXNS102	21.55	1.17	0.150	61.3	30.0	7.5	1.3	0.0		20.0	11.3
TXNS296	22.75	0.44	0.194	55.0	33.8	11.3	0.0	0.0		3.8	2.5
Mean	24.39	0.51	0.192	55.9	25.6	13.1	4.3	1.0		4.0	4.5
LSD(0.05) Cultivar	2.04	0.61	0.072	39.9	24.9	19.4	12.8	NS		9.1	6.9

Table 5. Potato tuber processing quality for 13 varieties in the 1999, 2000, and 2001 Western Regional Harvest Processing Trial after long-term storage. Malheur Experiment Station, Oregon State University, Ontario, OR.

*4-trial average.
^†3-trial average.

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