Effect of temperature on lipid‐derived volatile compounds in boiled potato during storage

BACKGROUND: The aroma of boiled potatoes is greatly appreciated by consumers. Although it is formed by 150 volatile compounds, only a few seem to actually contribute to the characteristic aroma. In addition, potatoes have to be stored at a low temperature after harvest to guarantee a year‐round supply. However, even at low temperatures, tuber volatile composition is modified during storage. The aim of the present study was to investigate the effect of storage temperature on boiled potato volatile constituents, mainly focused on lipid‐derived components, by considering different varieties stored at 4 °C and 8 °C. RESULTS: It was found that fewer lipid‐derived components were obtained when the potato tubers were stored at 4 °C rather than 8 °C. Specifically, the amounts of 2,4‐decadienal isomers and hexanal increased with the storage time, particularly at 8 °C. Similarly, pentanal and nonanal, which are autoxidation products, occurred to a greater extent at higher temperatures. In contrast, the levels of sugar‐derived compounds, in general, increased during storage at 4 °C rather than 8 °C as a result of higher content of sugars at low temperature. CONCLUSION: The effect of storage temperature on lipid‐derived volatile components in boiled potato appears to depend on the variety studied. Generally speaking, lower temperatures during storage promote sugar content and, as a consequence, sugar‐derived products. At the same time, lower temperatures result in less lipid oxidation and, therefore, a fewer lipid‐derived compounds. Copyright © 2009 Society of Chemical Industry     

Effect of cross‐linking on some properties of potato (Solanum tuberosum L.) starches

Starches separated from different potato cultivars were modified using two different cross‐linking agents: epichlorohydrin (EPI) and phosphoryl chloride (POCl₃) at different concentrations (1.0 and 2.0 g kg^?1 POCl₃; 2.5, 5.0 and 10 g kg^?1 EPI). Differential scanning calorimetry, rheological and retrogradation measurements were performed to characterise the influence of cross‐linking on the properties of potato starches. Cross‐linking considerably reduced swelling power, solubility, water‐binding capacity and paste clarity. The decrease became greater as the reagent concentration increased. The starches treated with 1.0 g kg^?1 POCl₃ exhibited exceptionally higher swelling power than their counterpart native starches. Neither cross‐linking agent caused any change in morphology of the starch granules. Studies on the phase transitions associated with the gelatinisation showed significantly higher values for the onset temperature (T_o), peak temperature (T_p), conclusion temperature (T_c) and enthalpy of gelatinisation (ΔH_gel) for the cross‐linked starches than the native starches. Starches treated with both the reagents showed lower peak storage modulus (G′) and loss modulus (G″) than their native counterparts. The tendency of the starch pastes towards retrogradation increased considerably with increases in storage duration. However, the starches treated with 1 g kg^?1 POCl₃ exhibited much lower syneresis than the other cross‐linked starches. Copyright © 2006 Society of Chemical Industry     

Effect of production site and storage on antioxidant levels in specialty potato (Solanum tuberosum L.) tubers

BACKGROUND: The potato can make a significant contribution of antioxidants to the human diet. In this study, antioxidant levels in tubers of 14 specialty potato clones grown at four production sites (two conventional, two organic), both fresh and stored, were examined across 2 years. RESULTS: Antioxidant activity of fresh tubers at all locations was higher in 2006 than in 2005. Cooler late‐season temperatures in 2006 may have been responsible for the increased levels of antioxidants. Stored tubers had higher levels of antioxidant activity than fresh tubers, with a larger storage effect in 2005, when antioxidant levels in fresh tubers were lower. There was no consistent effect of production system (organic versus conventional) on antioxidant activity in tubers. CONCLUSION: For the specialty potato clones we evaluated, antioxidant levels were generally highest in potatoes grown in high‐yielding production environments, and they increased during storage. Therefore, potatoes with high nutritional value, in terms of antioxidant activity, can be produced using conventional production and storage systems. Copyright © 2008 Society of Chemical Industry     

Effects of gibberellic acid and chlorocholine chloride on tuberisation and growth of potato (Solanum tuberosum L)

Treatment of potato plants with gibberellic acid (GA₃) enhanced both shoot and stolon growth and dry weight but delayed tuber initiation and decreased tuber yield. Conversely, treatment with chlorocholine chloride (CCC) growth retardant reduced shoot and stolon growth and dry weight but promoted tuberisation. Chlorophyll a and b contents were both increased appreciably with CCC. In the tubers, CCC increased starch content by 11% compared to untreated control, whereas GA₃ decreased starch content by about 13%. A very high reducing sugar content in the stem of GA₃-treated crop indicated active hydrolysis of sucrose coming from the leaves, leading to its reduced supply to the tubers because of further possible sucrose hydrolysis while passing through the long stolons. However, in the CCC treated crop, the higher chlorophyll content of the leaves with reduced stolon length will promote efficient sucrose supply to the tubers. © 1998 Society of Chemical Industry.     

Photo-induced changes in the total chlorogenic acid content of potato (Solanum tuberosum) Tubers

The exposure of potato tubers to light resulted in a significant cultivar-dependent increase in chlorogenic acid content. The magnitude of the observed increase resulting from 48 h light exposure was significantly correlated with the initial chlorogenic acid content of the tubers and also with the previously reported photo-induced increases in total glycoalkaloids. Time-course studies indicated that the greatest rate of increase occurred between 8 and 16 h continual exposure. Prolonged storage under light revealed that chlorogenic acid values in some cultivars reached a maximum value after 48 h, whilst in others these continued to increase almost linearly until the end of the experiment 5 days later.     

Textural and pasting properties of potatoes (Solanum tuberosum L.) as affected by storage temperature

Fresh tubers from five potato (Solanum tuberosum L.) cultivars were stored at different temperatures (4, 8, 12, 16 and 20 °C) and 80–90% relative humidity for 18 weeks after harvest to examine the effect of storage temperature on their textural and pasting properties. Texture profile analysis was performed on raw and cooked potatoes using an Instron universal testing machine to measure textural parameters such as fracturability, hardness, cohesiveness, adhesiveness and springiness. Both raw and cooked potato tubers showed a considerable reduction in all textural parameters upon storage, irrespective of the storage temperature employed. Raw potatoes showed a decrease in fracturability and hardness with increasing storage temperature, whereas their cooked counterparts showed the opposite trend. The extent of change in the textural properties of both raw and cooked potatoes also varied among the different cultivars. Fresh and stored tubers from all cultivars were freeze‐dried, ground into flours and analysed for amylose content and pasting properties. The amylose content of flours prepared from potatoes stored at 4 and 8 °C was observed to be considerably lower than that of flours prepared from potatoes stored at 16 and 20 °C. Pasting characteristics such as peak viscosity, setback and final viscosity increased with increasing storage temperature, while the reverse was observed for pasting temperature, when studied using a rapid visco analyser. Breakdown in viscosity of the flour pastes from all cultivars was considerably reduced during storage, irrespective of the storage temperature employed. Copyright © 2006 Society of Chemical Industry     

Physico‐chemical and sensory attributes in conjunction with multivariate analysis of two potato (Solanum tuberosum L.) cultivars after 90 days of storage: an exploratory authentication study

Two cultivars of potato (Spunta and Agria), were studied in terms of their physico‐chemical and sensory characteristics. These cultivars were cultivated in three geographical regions of Greece (Macedonia, North Greece; Thessaly, Central Greece; Peloponnese, South Greece) and were stored for 90 days after harvesting. The physico‐chemical characteristics of the tubers determined, were pH, total acidity, firmness, dry matter and content in Ν, in Κ, P, Cu, Mn, Zn and Fe. The sensory characteristics measured for raw tubers of potato after storage, were skin colour, skin brightness, internal colour, surface roughness, odour intensity, moistness, surface wrinkling and stains while the sensory characteristics measured for the boiled tubers of potato were odour intensity, moistness, special taste, sweet taste, aftertaste persistence, metal taste, pastiness, mastication, flavour intensity, elasticity and overall acceptability. The application of multivariate analysis (principal component analysis, cluster analysis and discriminant analysis), revealed a variety of relations between the various parameters and resulted in satisfactory grouping either per geographical region or per cultivar.     

Phenolic compounds in potato (Solanum tuberosum L.) peel and their health-promoting activities

Potato peel (PP), a by-product of food processing industry, comprising 6–10% of tuber is mostly considered as a waste. Potato peel waste (PPW) can be utilised as a natural source of antioxidants that otherwise may create disposal-related problems leading to environmental pollution. Valorisation of PPW is a fascinating area of research and is in the interest of potato-based food processing industry. PP contains phenolic compounds (mainly chlorogenic, caffeic and ferulic acids), that are known for bioactivities. Phenolic acids from PP can be efficiently recovered by improving the efficiency of extraction methods. Phenolics extracted from PPW have an immense potential for utilisation as sources of antioxidant and functional components in food. PP extract (PPE) has been evaluated for protective (antioxidant, antidiabetic, hepatoprotective and antibacterial properties) effects and can be projected as a potential source of phenolic compounds beneficial for human health.     

Changes in anthocyanin,flavonoid and phenolic acid concentrations during development and storage of coloured potato (Solanum tuberosum L) tubers

Changes in the anthocyanin concentration of coloured potato tubers have been investigated in cultivars with coloured skin and coloured or white flesh. The biosynthesis of anthocyanins coincided with tuber initiation in cultivars with intensely coloured mature tubers and, after a slight increase as the smaller tubers increased in size, anthocyanin concentrations remained relatively constant. Thus, because tubers were increasing in weight, anthocyanin was being synthesised to maintain a more or less constant concentration. In cultivars with less coloured tubers, the developing tubers remained white for a longer time, with anthocyanin concentrations increasing gradually up to a maximum at a certain tuber weight depending on the cultivar. The concentration of flavonoids was lower than that of anthocyanins but followed a similar pattern. Phenolic acid levels were about twice those of the anthocyanins and reached their maximum at a slightly lower tuber weight than anthocyanins and flavonoids. During cold storage (4°C) the anthocyanin concentration in coloured tubers increased, whereas tubers stored at higher temperatures did not show this increase. The increased colour in cold‐stored tubers is discussed in terms of its relationship to ‘cold sweetening’ and the increased concentration of sugars in cold‐stored tubers. The distribution of anthocyanins altered during tuber development and also during cold storage. In very small developing tubers the anthocyanins appeared first at the stem end of the tuber whilst the bud end remained white. As the anthocyanin concentration increased during tuber development, it increased over the whole tuber, but the concentration at the stem end was always higher than that at the bud end, until the tuber reached maturity, when the concentration became approximately equal at both ends. After cold storage, tubers had a higher concentration of anthocyanin in the bud end than the stem end; the opposite to that found in developing tubers. © 1999 Society of Chemical Industry     

Light‐induced glycoalkaloid accumulation of potato tubers (Solanum tuberosum L)

The total glycoalkaloid concentration of non‐sprouted potato tubers, cvs Marfona, Fianna, Maris Piper, Kestrel and Golden Wonder, was measured following 15 days of continuous illumination (250 µmol m⁻² s⁻¹ photosynthetically active radiation) using high‐performance liquid chromatography. Comparisons were made of the influence of four sources of illumination: fluorescent tube‐type warm white, high‐pressure sodium, high‐pressure mercury types MB/U and MBFR/U. Irrespective of cultivar, glycoalkaloid concentrations of tubers placed in the dark remained relatively constant from day 0 to day 15 and did not exceed food safety values of 200 mg kg⁻¹ FW. A highly significant cultivar, light and cultivar × light (P < 0.01) interaction was recorded. Cultivar Kestrel was shown to be light‐sensitive with high rates of glycoalkaloid accumulation irrespective of light source, and cv Maris Piper was demonstrated to be light‐insensitive. In the majority of cultivars tested, maximal rates of glycoalkaloid accumulation were recorded following exposure of tubers to sodium or fluorescent light, and minimal rates of accumulation were recorded following exposure of tubers to mercury (MB/U and MBFR/U) illumination. In virtually all cases glycoalkaloid concentrations steadily increased with time during light exposure with no indication of cessation. In some instances the α‐chaconine/α‐solanine ratio decreased over 15 days of illumination (P < 0.05), indicating enhanced α‐solanine synthesis over that of α‐chaconine. The implications of these results in terms of consumer safety are discussed. © 1999 Society of Chemical Industry     

Processing of pigmented‐flesh potatoes (Solanum tuberosum L.) on the retention of bioactive compounds

Retention of bioactive compounds in white‐ (WFP), yellow‐ (YFP), red‐ (RFP) and purple (PFP)‐fleshed potatoes after drum‐drying (DD) and Refractance Window? drying (RW) was compared with freeze‐drying (FD). Processing, generally, did not influence total phenolics. Total carotenoid was high in YFP, but decreased with DD. Both DD and RW decreased lutein concentration in YFP. The RFP and PFP had the highest total anthocyanin, and their concentrations were decreased by DD. RW decreased total anthocyanin in PFP only. Total antioxidant activity in WFP was higher with DD but lower with RW. In contrast, DD and RW drying had no significant effect on total antioxidants in YFP, RFP and PFP. Therefore, drying generally decreased antioxidants, with FD and RW retaining the highest concentration of bioactive compounds.     

Microstructural,cooking and textural characteristics of potato (Solanum tuberosum L) tubers in relation to physicochemical and functional properties of their flours

Potato tubers from six different cultivars were freeze‐dried, ground into flour and analyzed for thermal, pasting and textural characteristics (using differential scanning calorimetry, Rapid Visco analyzer and Instron universal testing machine, respectively) to study the relationship between flour characteristics and cooked potato mealiness. The potatoes with higher sensory mealiness scores resulted in flours having lower transition and pasting temperatures, higher amylose content, setback, peak and final viscosity. The flour gels from the mealier potatoes also exhibited higher values of textural parameters such as hardness, cohesiveness, chewiness and springiness. The microstructure of the tuber parenchyma (studied using scanning electron microscopy), cooking and sensory characteristics of potatoes were found to be related to the pasting and textural characteristics of their flours. Potato cultivars with lower mealiness scores, loosely packed cell arrangement, with comparatively large‐size cells and thinner cell walls showed lower values of textural parameters for both raw and cooked potatoes. This information may prove useful for the selection of potato cultivars with desirable textural and flour‐making properties for specific end‐uses. Copyright © 2005 Society of Chemical Industry     

The chip‐processing potential of four potato (Solanum tuberosum L.) cultivars in response to long‐term cold storage and reconditioning

BACKGROUND: The reconditioning potential of four potato cultivars (Diamant, Hermes, Lady Rosetta and Spunta) was evaluated in three years of crop production. After 30, 60, 120 and 150 days of storage at 4.5 °C, cultivars were reconditioned at 16 °C for 0, 15 and 30 days before being evaluated for sprout growth, tuber fresh weight loss (FWL), sucrose content, reducing sugar (RS) content (sum of glucose and fructose contents) and chip fry colour (FCL). RESULTS: Reconditioning induced rapid sprouting and pronounced FWL after 120 days of storage. Storage (30–150 days) was not critical to FCL and RS but affected sucrose levels. All cultivars showed an improvement in FCL and a reduction in RS and sucrose after reconditioning. The increment in FCL improvement and RS and sucrose depletion was greater between days 0 and 15 of reconditioning than between days 15 and 30 of reconditioning. Year contribution was significant to FCL and RS but not to sucrose variance. Acceptable FCL was attained after 15 days of reconditioning of Hermes and after 30 days for Lady Rosetta, while Diamant and Spunta remained substandard. RS levels in response to reconditioning were lowest in Hermes and Lady Rosetta. CONCLUSION: FCL conformed to tuber RS accumulation profiles. Cultivar RS ranking following reconditioning remained unaltered from year to year throughout storage. RS and FCL during the first 30 days of cold storage may be a reliable comparative index of reconditioning potential, as high‐RS‐accumulating and poor‐chipping cultivars exhibit inadequate response to reconditioning. Tuber sucrose appeared of little significance as an index of the reconditioning ability of cultivars. Copyright © 2009 Society of Chemical Industry     

The effect of prior storage on the potential of potato tubers (Solanum tuberosum L) to accumulate glycoalkaloids and chlorophylls during light exposure,including artificial neural network modelling

Potato tubers of four varieties (Brodick, King Edward, Pentland Dell and Record) were stored under commercial conditions and exposed to light for up to 10 days after 0, 10, 20 and 30 weeks. These were analysed for photosynthetic pigment and glycoalkaloid content. There was no significant alteration in either tuber chlorophyll or glycoalkaloid content during dark storage. All four varieties greened in response to light exposure, but only three exhibited a significant increase in glycoalkaloid concentrations during this exposure. Storage duration did not significantly affect pigment accumulation. However, there was a marked effect of storage on the extent of glycoalkaloid accumulation. Tubers of all four varieties stored for more than 10 weeks did not accumulate glycoalkaloids to the same extent as fresh tubers. Indeed, Brodick and Record did not accumulate any glycoalkaloids in response to light after 30 weeks of storage. A number of artificial neural network models of the results were produced. These accurately modelled cultivars individually, but a model encompassing all the data was not successful at predicting cultivar differences. © 1999 Society of Chemical Industry     

Effects of time/temperature treatments on potato (Solanum tuberosum) starch: a comparison of isolated starch and starch in situ

Previously, time/temperature treatments of starch have been performed mainly on starch/water systems. In this study the same time/temperature treatments were applied to starch/water systems and to potato starch in situ. Two potato varieties (Solanum tuberosum cultivars Asterix and Bintje) were used. The effect of time/temperature treatments on gelatinisation behaviour was evaluated using differential scanning calorimetry (DSC). A blanching process was simulated by heating samples to 74 °C and then cooling them to 6 °C. A DSC scan showed that starch was completely gelatinised after this treatment. Retrogradation of amylopectin increased during storage at 6 °C from 0 to 24 h after blanching. Annealing of starch, with the aim of altering cooking properties, was performed by heating samples to temperatures below the gelatinisation onset temperature. Treating samples at 50 °C for 24 h caused a shift in gelatinisation onset temperature of 11–12 °C for isolated starch and 7–11 °C for in situ samples. The extent of the annealing effect depended on the difference between onset and annealing temperatures, and prolonged treatment time increased the effect. Starch/water systems and tissue samples behaved similarly when exposed to time/temperature treatments. The most apparent difference was the shift of gelatinisation to higher temperatures in tissue samples. Copyright © 2003 Society of Chemical Industry     

Effect of environmental stress during tuber development on accumulation of glycoalkaloids in potato (Solanum tuberosum L)

The effects of low temperature and of combined stresses, cool temperature and waterlogging and also warm temperature and drought, on potato tuber glycoalkaloid levels were investigated, with emphasis on comparison of tubers of similar size. The early maturing cultivars Home Guard, Rocket and British Queen were grown under favourable controlled environment conditions (18/14 °C day/night temperature, 14 h photoperiod) until the imposition of treatments after the start of tuber initiation. Transfer to low temperature (12/9 °C) did not increase total glycoalkaloid concentration in any of the three cultivars. However, waterlogging at 12/9 °C increased total glycoalkaloid concentration during the later stages of development of British Queen. Drought stress at 24/18 °C also increased total glycoalkaloid concentration in British Queen, although the response varied between individual tubers of similar size. Total glycoalkaloid concentrations in tubers of Rocket were not affected by the combined stress treatments, and any effects on Home Guard were very much less than on British Queen. © 1999 Society of Chemical Industry