Crisp Colour Research Articles

Acrylamide in potato crisps prepared from 20 UK-grown varieties: Effects of variety and tuber storage time

Twenty varieties of field-grown potato were stored for 2months and 6months at 8°C. Mean acrylamide contents in crisps prepared from all varieties at both storage times ranged from 131μg/kg in Verdi to 5360μg/kg in Pentland Dell. In contrast to previous studies, the longer storage period did not affect acrylamide formation significantly for most varieties, the exceptions being Innovator, where acrylamide formation increased, and Saturna, where it decreased. Four of the five varieties designated as suitable for crisping produced crisps with acrylamide levels below the European Commission indicative value of 1000μg/kg (Saturna, Lady Rosetta, Lady Claire, and Verdi); the exception was Hermes. Two varieties more often used for French fries, Markies and Fontane, also produced crisps with less than 1000μg/kg acrylamide. Correlations between acrylamide, its precursors and crisp colour are described, and the implications of the results for production of potato crisps are discussed.

Effect of CIPC on Sprout Inhibition and Processing Quality of Potatoes Stored Under Traditional Storage Systems in India

Indigenous non-refrigerated methods like heaps and pits are used in India for short-term storage of potatoes (Solanum tuberosum L.) to avoid distress sale. Storing untreated potatoes generally results in high losses from sprouting, moisture loss and rotting. To reduce storage losses by inhibition of sprouting and to determine the suitability of stored potatoes for processing into crisps, a single spray application of a commercial formulation of 3-chlorophenyl carbamate (CIPC or chlorpropham) 50% a.i., (Oorja, United Phosphorus Limited, Mumbai, India) of CIPC (or chlorpropham) was tested on potatoes during storage from March to June under two traditional storage methods [heap (17–33 °C, 58–92% relative humidity (RH)) and pit (17–27 °C, 72–95% RH)] in 2 years [2005 up to 90 days of storage (DOS) and 2006 up to 105 DOS], using four cultivars and two rates of CIPC application (20 and 30 mg a.i. kg−1 tubers). The two rates of application were comparably effective in reducing weight losses, sprouting and sprout growth in stored tubers, and the effect was more pronounced in pit storage than in heap storage. By contrast to untreated tubers, CIPC-treated potatoes remained turgid under the two storage methods and fetched market prices comparable to those for cold-stored (2–4 °C) potatoes after 105 days of storage. Reducing sugar concentrations in treated potatoes decreased during storage especially in 2006 when the initial reducing sugar concentration was higher than in 2005. Crisp colour improved only in 2005 after 90 DOS, but it deteriorated in 2006 during storage up to 105 DOS. Sucrose concentration increased tremendously during storage in 2 years. Only one cultivar (Kufri Chipsona-1) with low initial reducing sugar concentration and less sucrose accumulation during storage could produce acceptable colour crisps after storage in both years. The remaining three cultivars—with high initial reducing sugar concentration—were suitable for processing after storage in heap and pit in 2005, but not in 2006. Stored potatoes were safe for human consumption as the CIPC residue concentrations were far below the permissible level of 10 mg kg−1 as prescribed by the European Union. Single spray application of CIPC (20 mg kg−1 treatment) can effectively reduce storage losses in potatoes stored in traditional non-refrigerated methods of heap and pit and extend the storage life by 90 to 105 days.

Influence of Source and Time of Potassium Application on Potato Growth, Yield, Economics and Crisp Quality

Field studies were conducted at the Central Potato Research Institute Campus, Modipuram (India), during two seasons (2003–2004 and 2004–2005), with two processing cultivars (cvs Kufri Chipsona-1 and Kufri Chipsona-2) and nine combinations of potassium source (K-chloride, K-sulphate and K-nitrate) and time of K application (basal dressing, split application and split application + foliar spray) to investigate their effect on tuber yield and processing attributes for crisp production under subtropical conditions. Yearly variations were observed for most of the variables studied. Between cultivars, the tuber and biomass yield was higher in cv. Kufri Chipsona-1, whereas specific gravity, tuber dry-matter percentage and crisp recovery were higher in cv. Kufri Chipsona-2. Stem number, plant height and compound leaf number were not influenced by sources of K fertilizer or application time. Processing-grade tuber yield, total tuber yield and biomass yield were statistically similar for K-chloride and K-sulphate and lower for K-nitrate. K sources affected both specific gravity and tuber dry-matter percentage significantly; K-sulphate and K-nitrate gave significantly higher values than K-chloride. The application time had no significant effect on processing grade and total tuber yield or on tuber specific gravity and dry-matter percentage. Values for crisp colour and reducing sugars were within the acceptable range for all treatments. Crisp yields were calculated to be highest and oil percentage of the crisps to be lowest when K-sulphate was applied as K fertilizer. Net income and benefit:cost ratio were highest for K-chloride followed by K-sulphate and lowest for K-nitrate. The study suggests that for crisping potatoes, K-sulphate is more suited than K-chloride, as it not only increased tuber dry-matter percentage and crisp yield, but also decreased crisp oil percentage.

IDENTIFICATION OF PRE-HARVEST BIOMARKERS IN POTATOES FOR IMPROVEMENT OF POST-HARVEST MANAGEMENT OF FRY COLOUR

Potatoes (Solanum tuberosum) for processing of crisps and french fries have special quality demands compared to ware potatoes. A low amount of reducing sugars in the tubers is necessary to prevent the non-enzymatic Maillard reaction between sugars and free amino acids during frying. The Maillard reaction is responsible for development of undesirable dark coloured compounds with bitter taste. Moreover, it was recently discovered that intermediates in the Maillard reaction were responsible for the formation of the potential carcinogenic compound acrylamide. Large variation in suitability of potatoes for processing is often seen. Potatoes of the same cultivar from one field/lot may accumulate sugars much faster during storage than potatoes from another field/lot. Reliable biomarkers for long-term storability must be identified to improve the management of potatoes going into storage. A three-year study with the potato crisp cultivar 'Saturna' was conducted. Development in crisp colour during storage was evaluated in relation to different vine killing dates during final growth and to the variation observed between commercial fields. Samples were also taken weekly during final growth in order to characterize the physiological tuber maturity at harvest. The results showed that high benefits might be obtained at the potato processing companies if potatoes could be handled at harvest according to year specific development in fry colour during storage. Management of potatoes at harvest according to field specific development in fry colour during storage within a year showed less potential for benefits. Nitrogen status of the crop in the final part of growth period and rate of leaf senescence were identified as promising markers for fry colour of 'Saturna' during storage, while pre-harvest measurements of sugar content in the tubers were useless.

Tuber components affecting acrylamide formation and colour in fried potato: variation by variety, year, storage temperature and storage time

AbstractVariation in asparagine and glucose contents, identified as precursors for acrylamide development in model experiments, has been studied in eight potato clones during long‐term storage at 3 and 10 °C. In addition, glutamine, fructose and sucrose contents were determined and the role of all five substances in colour formation in fried potato products was assessed. Large genotype differences were found in all characteristics, and the ranking order was almost the same for different years and storage times. Breeding for potatoes with low asparagine levels as well as low reducing sugar levels might be another way, in addition to altering processing parameters, to keep the acrylamide level low in fried products. Storage per se at low temperature did not result in higher asparagine levels. The risk that elevated reducing sugar levels during low‐temperature storage might lead to increased acrylamide levels needs further investigation. The determined tuber components accounted for only 11–60 per cent of the total variation in fry colour after storage at 3 °C. It is suggested that screening based on crisp colour in November, perhaps complemented with a few later controls on interesting clones, could be useful for sorting out clones with good crisping abilities during the rest of the low‐temperature storage season. Copyright © 2004 Society of Chemical Industry

Effects of nitrogen fertiliser on potato (Solanum tuberosum L., cv. Russet Burbank) in Tasmania. 1. Yield and quality

Thirteen field trials were conducted on ferrosols and tenosols in Tasmania to assess the response of potatoes (Solanum tuberosum L., cv. Russet Burbank) to basal (up to 250 kg/ha) and topdressed (up to 100 kg/ha) nitrogen fertiliser. Economic yield responses to basal nitrogen were obtained at 9 sites. Topdressing did not increase yield compared with equivalent rates of basal nitrogen, and often failed to compensate for a lack of nitrogen applied at planting. This lack of response may reflect the inability of the potato crop to make use of nitrogen applied during tuber bulking. Nitrogen fertiliser decreased tuber specific gravity at several sites. The effects of nitrogen on misshapen tubers, bruising susceptibility, crisp colour and hollow heart were inconsistent and often of no practical importance. However, at 2 sites, nitrogen fertiliser increased yields of misshapen tubers at the expense of processing tuber yields. At 1 of these sites, nitrogen topdressing decreased the yield of misshapen tubers. Otherwise, topdressing had similar effects on tuber quality to those of basal nitrogen. Growers should fertilise with nitrogen to optimise their yields. Optimum rates were greater in paddocks that had been continuously cropped for more than 10 years (average rate 193 kg/ha), than in those that had been in pasture (average rate 48 kg/ha).

The effect of controlled atmosphere storage at 4°C on crisp colour and on sprout growth, rotting and weight loss of potato tubers

After three weeks curing at 10°C, potato tubers cv. Record were stored at 4°C under different controlled atmospheres (CA) for six months to study the effect on crisp fry colour, sprout growth and rotting. Combinations of low levels of CO2 (0.7–1.8%) and low levels of O2 (2.1–3.9%) gave a significantly lighter crisp colour, low sprout growth and fewer rotted tubers compared with 0.9% CO2 and 21.0% O2. Tubers stored in these conditions. showed a significantly higher weight loss and shrinkage after reconditioning. High CO2: low O2 combinations during storage completely inhibited sprout growth and caused the darkest crisp colour, but after reconditioning tubers gave the same level of sprouting and crisps as light as the other CA combinations. Furthermore these combinations, especially CO2 at 10 or 15%, increased the onset of rotting. Also our results showed that at low concentrations of CO2 (0.7–1.6%), and low O2 (2–2.4%) there was an increase in tuber rotting.

Influence of stem canker (Rhizoctonia solani Kühn) on tuber yield, tuber size, reducing sugars and crisp colour in cv. Record

In eight experiments in 4 years, inoculating seed tubers withR. solani caused stem canker and in seven experiments decreased the total yield and the yield of tubers 40–70 mm. Yields of larger tubers were usually increased. In most experiments inoculating increased the reducing sugar content of the tubers and darkened the colour of crisps, but did not consistently affect the amounts of sucrose. Treating soil with aldicarb or oxamyl before planting also slightly increased the total reducing sugars.

Effects of nitrogen, phosphorus, and potassium on yield, specific gravity, crisp colour, and tuber chemical composition of potato (Solanum tuberosum L.) cv. Kennebec

Five field experiments were conducted over 3 years in the Mt Lofty Ranges (4 sites) and the Upper South East (1 site) to examine the significance of main effects and interactions between nitrogen (N, up to 360 kg N/ha), phosphorus (P, up to 320 kg P/ha), and potassium (K, up to 480 kg K/ha) on total yield, yield of 80-350 g size grade, specific gravity, crisp colour, and chemical composition of tubers of potato cv. Kennebec. There were significant (P<0.05) main effects of increasing rates of applied N on total tuber yield and yield of 80-350 g tubers at 2 of the 5 experimental sites; the effect of applied P was significant at 3 sites, and applied K also at 3 sites. Application of N, P, and K increased total tuber yield by 13-432%, 19-145%, and 19-89%, respectively, at responsive sites. Increases in the yield of 80-350 g tubers were similar to those for total yield. There were significant first-order interactions (N x K, N x P, K x P) at 2 sites. The interactions were (i) response to the application of 1 nutrient limited by suboptimal rates of another; and (ii) yield depression, due to high rates of 1 or more nutrients. Nitrogen and P increased specific gravity at only 1 of the sites where they were applied. Potassium increased specific gravity at 1 site but decreased it at another. There were significant N x K, N x P, and K x P interactions at 2 sites. Vascular ring colour index (CI) and medulla CI were significantly (P<0.05) affected by rates of applied N, P, and K at 1, 3, and 4 experimental sites, respectively. Application of K (up to 480 kg K/ha) decreased vascular ring CI and medulla CI. Application of P increased the colour indices; for example, increasing the rate of P from nil to 160 kg/ha increased mean (� s.e.) vascular ring CI from 51 � 18 to 117 � 17. No interactions between N, P, and K in their effects on medulla CI were significant. For vascular ring CI, significant first-order interactions (K x N, K x P) were observed at 2 sites, at which application of N and P at nil K significantly increased vascular ring CI. At 240 or 480 kg K/ha, there was no change. Significant (P<0.001) curvilinear relationships were found between specific gravity and the concentrations of N, P, and K in the stem-end region of tubers; the coefficients of determination (r2) were 0.27, 0.62, and 0.76, respectively. For the combined medulla CI and vascular ring CI data, the corresponding values were 0.19 (P<0.001), 0.29 (P<0.001), and 0.05 (n.s.), respectively.

Estimating potato crisp colour variability using image analysis and a quick visual method

Image analysis gave better precision than colorimetry in measuring the darkening caused by excess free sugar during crisping of potatoes. The image analyser was used to measure individual crisp Average Optical Density (AOD) values in order to examine the variability of AOD within and between tubers. It is unnecessary to measure more than one crisp per tuber when assessing breeding lines, although two crisps per tuber are recommended for quality control. Crisps from at least ten tubers should be measured. A ‘Quick Crisp’ method, in which single crisps from each of four tubers are judged against standard samples, is reported. Regression of results from this method on crisp reflectance percentage (Agtron score) gaveR 2 of 0.967. However, the observer tended to overestimate at low values and underestimate at high values. Over several trials, the crossover point varied from 15 to 50 Agtron score units. Measurement of crisp colour variability for improving selection, management and purchasing decisions is discussed.

Potassium nutrition of Kennebec and Russet Burbank potatoes in Tasmania: effect of soil and fertiliser potassium on yield, petiole and tuber potassium concentrations, and tuber quality

The response of potato (Solanum tuberosum L.) cultivars Russet Burbank and Kennebec to soil and fertiliser potassium (K) was studied on basaltic krasnozems of north-west Tasmania. Yield increases in response to fertiliser K were recorded at sites with up to 300-400 mg/kg of bicarbonate extractable soil K. The close correlation between relative yield and soil K indicated that soil K can reliably predict fertiliser requirements. Petiole K concentrations at early tuber set increased with fertiliser K at responsive sites; maximum yields were achieved with 12-14% petiole K for Kennebec and 11-13% for Russet Burbank. Petiole K concentrations provide an excellent indication of the K status of a growing crop. Tuber K concentrations increased with both soil and fertiliser K, and yields of 50-80 t/ha removed 180-380 kg K/ha in the tubers. At severely deficient sites specific gravity and crisp colour increased with low rates of fertiliser K, but the general trend was for fertiliser K to reduce specific gravity and crisp colour. Bruising susceptibility decreased with fertiliser K at some sites but the physiological disorder, 'hollow heart', was not influenced by fertiliser K. There were consistent differences between the 2 cultivars. Russet Burbank required higher soil K, had lower petiole and tuber K concentrations and removed less K in the marketable tubers.

Effect of nitrogen on the size, specific gravity, crisp colour and reducing sugar concentration of potato tubers (Solanum tuberosum L.) cv. Kennebec

Four field experiments were conducted over 2 years on coarse grain siliceous sands in the Mt Lofty Ranges (3 sites) and Lower South East (1 site) to examine the effect of different rates of applied nitrogen (up to 320 kg N/ha) on the size, specific gravity, crisp colour and reducing sugar concentration of potato tubers of the cv. Kennebec. As the rate of applied nitrogen (N) was increased, there was a significant (P<0.05) increase in the yield of 80-350 and >350 g tubers. Rate of applied N did not significantly affect the yield of <80 g tubers. Highest yields of >350 g (large) tubers occurred at N rates in the range 160-320 kg N/ha. In contrast, the yield of 80-350 g tubers (preferred size for crisping), for the 80-120 kg N/ha sates, was not significantly different from the maximum yield of 80-350 g tubers for each site. At all sites, total tuber yields for the 80-120 kg N/ha rates were not significantly different from maximum yields. The effect of applied N on specific gravity (SG) was significant; the magnitude of the effect varied between sites. For the pooled data from all sites, correlation between SG and nitrate-N concentration in the petioles of youngest fully expanded leaves (P-YFEL) were not significant, however, there were significant correlations between the reduction in SG and petiole nitrate-N concentration. When tlie lengths of the largest tubers were <2 mm. 25 mm and 50 mm, reductions in SG of less than 0.0025 occurred when the P-YFEL nitrate-N concentrations were 1.70-2.50%, 0.70-2.00% and 0.25-1.25%, respectively. Tuber SG increased slightly after storage for 2 and 4 months but the changes were not related to the rate of applied N. There were no consistent trends between sites in vascular ring colour index (CI) and medulla CI, determined after 0, 2 and 4 months storage, as the rate of applied N increased. However, significant (P<0.05) changes in vascular ring and medulla CI did occur during storage, with significant reductions in medulla CI for 3 of the 4 sites. For all sites, vascular ring CI was highest after 2 months storage. Reducing sugar concentration of tubers was significantly affected by the rate of applied N at 2 sites. Tubers from all sites also showed significant changes in seducing sugar concentration during storage. Maximum reducing sugar concentrations (up to 0.23% fresh weight) occurred after 2 months storage. Coefficients of determination (r2 ) for the relationships between reducing sugar concentration and vascular ring and medulla CI were in the range 0.001-0.37. Based on data for 3 of the 4 sites, mean weight loss for tubers after 4 months storage was 6.6% and weight loss was not affected by the rate of applied N. Based on our data for the cv. Kennebec grown on siliceous sands, we suggest growers should use N fertiliser rates which are just sufficient to ensure that N is not limiting yield. This practice should result in acceptable tuber size, SG and crisp colour, even after the tubers have been stored for up to 4 months.

Comparison of 10 clones of the potato cultivar, Kennebec

Nine clones of Solanum tuberosum L. cv. Kennebec from sources in Victoria, South Australia and Tasmania, and the commercially grown clone, clone 1, which was imported from Vancouver, were multiplied from pathogen-tested seed and compared in 3 Victorian potato districts during 2 seasons. Haulm appearance of the 10 clones was similar. Tubers of clones 2 and 9 had a more desirable elliptical shape with shallow eyes than clones 1, 7, 8, 11 and 13. Clone 7 produced significantly (P<0.05) less total yield than the highest yielding clone at 3 sites. Compared with the other clones, clones 2 and 7 yielded significantly (P<0.05) less oversize (>450 g) and medium (100-450 g) tubers and significantly (P<0.05) higher yields of small (<100 g) tubers at several sites. Clone 1 produced a much higher proportion (5.7%) of total yield as oversize tubers than clones 2 (1.6%) and 7 (0.8%). Clones 2 and 7 produced a significantly higher (P<.05) number of tubers per plant than all other clones at the 3 sites. Averaged over these 3 sites, clones 2 (and 7) produced 6.2 (6.8) tubers per plant and the other clones were in the range 4.5-5.0. No consistent differences in specific gravity or crisp colour were observed between the clones. Clone 2 was selected as being best suited for the crisp processing industry because of its even shape, high number of tubers per plant and low yield of oversize tubers, while maintaining high yields and good specific gravity and crisp colour. Our results show that differences exist in total and size grade yield and tuber number and appearance between clones of a cultivar. They further highlight the importance of selection work to maintain desirable characteristics of established cultivars and to remove mutants with undesirable characteristics.