Influence of harvest date on nitrate contents of three potato varieties for off-season production

The influence of potato variety and harvest date was investigated on tuber nitrate content for off-season production in three varieties: Arinda (mid-early), Spunta (mid-late) and Mondial (late). Samples of tubers were harvested at 90, 105 and 120 days after planting in winter–spring crop and at 80, 95 and 110 days after planting in summer–autumn crop. Tuber nitrate content was determined by ion selective electrode (ISE) method. Investigated varieties differed in nitrate content. In both off-season crops, the highest quantities of nitrate were contained in the late Mondial, with respect to the middle early Arinda variety and Spunta. After a delay of the harvest date, nitrate contents in the investigated tuber samples significantly decreased in winter–spring crop, whereas they increased in summer–autumn crop in the three varieties, but to the greatest extent in the case of late Mondial variety. Regardless of variety and harvest time, the content of nitrate in tubers was within the guidelines proposed by some European countries.     

The influence of genotype on the effects of impact damage and light exposure on the accumulation of glycoalkaloids in potato tubers

The experiment was carried out in 1999 with 24 Polish and 23 West European cultivars of potato tubers. The tubers were analysed for TGA content after 3 months of dark storage conditions in store-house (8 degrees C). 20 tubers of every cultivar were damaged and placed for a week to dark and under 15 W fluorescent lamps--13 mumol m-2 sec(-1)--equivalent to light in supermarkets. Glycoalkaloids content was determined with Bergers (1980) method. Tubers which had been damaged and exposed for a week to fluorescent light had two fold higher levels of TGA, than undamaged tubers stored at dark. It was found that content of glycoalkaloids in potato tubers and the increase of TGA content due to damage and light exposure depended on genotype. It was higher in varieties with higher level of these compounds, for example: Peppo, Albatros, Columbus and Santana (above 200 mg/kg fresh weight)--tab. I. The smaller increase occurred in tubers of varieties with low content of TGA: Polish--Irga, Grot, Baszta, Tokaj and West European--Satina, Ditta Gloria, Victoria--tab. I, II. Therefore it is important to breed new cultivars with low content of TGA.     

Nutritional composition of freshly harvested and stored Latvian potato (Solanum tuberosum L.) varieties depending on traditional cooking methods

The information about nutritional composition of potatoes at both the ingredient and recipe levels in the Food Composition Data Base (FCDB) of Latvia is insufficient. Therefore, the aim of this research was to determine the nutritional composition and energy content of potatoes prepared by traditional cooking methods before and after storage. Five Latvian potato varieties were selected: Lenora, Brasla, Imanta, Zile and Madara. A two-year research was conducted during two periods: just after harvesting (2007, 2008) and after six months of storage (2008, 2009). The following cooking methods were used: shallow frying (150 ± 5 °C); deep-fat frying (180 ± 5 °C) and roasting (210 ± 5 °C). The weight of the potatoes was recorded before and after frying along with the time and temperature during frying. Chemical analyses were performed to determine the content of reducing sugars, starch, fructose, glucose, sucrose, fibre, fat, protein, moisture, vitamin C and amino acids. The content of the analyzed nutrients differed significantly between both potato varieties and applied cooking methods: differences between potato varieties and cooking methods were found for vitamin C, moisture, reducing sugars, fructose, glucose, sucrose, amino acids, essential amino acids, and energy content, whereas significant differences in starch, fibre, fat and protein content were found between cooking methods.     

Oxalate Content of Raw and Cooked Oca (Oxalis tuberosa)

Oca (Oxalis tuberosa Mol.) or New Zealand yam, in common with other members of this genus, contains oxalate, an antinutritive factor. Twelve South American and two New Zealand cultivars of oca were analysed for the total oxalate contents of tubers. Total oxalate levels ranged from 80 to 194 mg/100 g wet matter (WM). As these tubers are normally cooked before consumption, the oxalate levels were measured after they had been cooked by three conventional cooking methods. Oxalate levels ranged from 77 to 220 mg/100 g WM for boiled and steamed tubers, while the levels of oxalate found in baked tubers were significantly increased when compared to the raw tubers. The oxalate content of the baked tubers ranged from 164 to 335 mg/100 g WM. Total calcium content of the raw tubers ranged from 7.5 to 15.5 mg/100 g WM; cooking had little effect on the calcium content. Among cultivars mean oxalate/calcium ratio of the raw, boiled and steamed tubers ranged from 2.5 to 9.9. Baked tubers had a significantly increased oxalate/calcium ratio (mean for all cultivars 9.5).     

Cooking dependent loss of metabolites in potato breeding lines and their wild and landrace relatives

Elucidating and improving the nutritional value of staple crops is an important focus in breeding programs. Hence, wild and cultivated potatoes have been metabolite profiled to assess metabolic plasticity present in potato tubers and changes that occur in these after cooking. The present data highlighted metabolic similarities of certain wild species to breeding lines, indicating preference during domestication. In the case of potato, the cooking process has to be taken into consideration for the assessment of nutritional quality. The degree of nutritional change during cooking depends on several factors including cooking method, stability of metabolites with nutritional properties and chemotype of the varietal matrix. The differences between raw and boiled tubers were similar within each germplasm group. No notable distinctions of total phenolic levels could be observed within germplasm groups, whereas total carotenoids and glycoalkaloids were significantly decreased. Genotypes/cultivars with notable changes upon cooking distinguished them within their genotype group.     

Phenolic ripeness assessment of grape skin by texture analysis

The elaboration of high quality red wines requires the assessment of grape phenolic maturity by the determination of phenolic compound concentration and their extractability during winemaking process. The main aim of this work was to ascertain whether simple texture parameters, like the grape skin hardness and thickness, account for phenolic maturity of berry skin. Furthermore, the function of these grape mechanical properties in the differentiation of 13 grapevine varieties from Galicia (northwest of Spain) was studied during both 2005 and 2006 vintages. An Universal Testing Machine TAxT2i Texture Analyzer was used to carry out the texture test. Total anthocyanin concentration varied from 191 to 2660 mg kg⁻¹ fresh berry weight, while extractable anthocyanin concentration ranged from 116 to 1453 mg kg⁻¹ fresh berry weight, respectively, found in Merenzao and Loureira Tinta varieties. A significant regression was found between anthocyanin extractability, berry skin break force and thickness. Berry skin break force and energy represent meaningful variables for varietal characterization and differentiation. The toughest berry skin corresponded to the Sousón variety, while Mouratón cultivar indeed was the weakest berry skin.     

Glycoalkaloids in potatoes: Content of glycoalkaloids in potatoes for consumption

Potatoes contain glycoalkaloids in varying levels depending upon variety, treatment and so on. Glycoalkaloids are potentially toxic at the natural levels in potatoes, and Nordic assessments recommend that the safety levels of total glycoalkaloids (TGA) in new potato varieties should not exceed 100 mg/kg. Thus the aim of this study was to make a survey of the distribution and contents of TGA in potatoes on the Danish market, including many different and relevant varieties during a 6-year period. A total of 386 samples of potato tubers were analysed for α-solanine and α-chaconine by extraction with acetic acid and determination by RP-HPLC with UV-detection at 202 nm. The results not only confirmed that contents above 100 mg TGA/kg in potato tubers frequently occurred in some years, but also showed the possibility of finding lower contents in the same varieties other years. This led to the cautious conclusion that by careful selection of varieties and environmental conditions, generally providing consumers with potatoes containing less than 100 mg TGA/kg would be possible.     

The glycaemic index of potatoes: the effect of variety, cooking method and maturity.

OBJECTIVE: The aim of this study was to determine the impact of variety, cooking method and maturity on the GI of potatoes, it was hypothesised that new potatoes may have a relatively lower GI. DESIGN AND SUBJECTS: Ten healthy volunteers were recruited as subjects through advertising on the campus of the University of Sydney. Equal (50 g) carbohydrate portions of eight potato meals (three varieties, four cooking methods, two states of maturity) and two reference white bread meals were fed in random order to each of the subjects over a period of 10 weeks. Capillary blood samples were taken in the fasting state and then at 15, 30, 45, 60, 90 and 120 min from the start of each meal. Samples were analysed for plasma glucose concentrations and incremental areas under plasma glucose curves were calculated. The GI of the potato was calculated as the AUC of the potato expressed as a percentage of the individual's average AUC of the white bread. This was then multiplied by 0.7 to index the GI to glucose as the reference food. RESULTS: GI values (mean +/- s.e.m.) ranged from 65+/-9 (canned new potatoes) to 10+/-15 (boiled Desiree potatoes), glucose = 100. No significant difference was found among the three varieties of potato tested (P = 0.38) or among the four different cooking methods (P = 0.55). The GI values of the canned new potato and boiled Desiree potato were significantly different (P = 0.047). The average size of the tuber was found to correlate with the GI (r = 0.83, P<0.05). CONCLUSIONS: Potatoes, regardless of variety, cooking method and maturity, have exceptionally high GI values. New potatoes have relatively lower GI values which is attributed to differences in starch structure.     

Effect of the variety and size of fresh and frozen brussels sprouts on the vitamin C level

The content of vitamin C was determined in the following varieties of Brussels sprouts: Maczuga, Citadel F1, Lancelot F1 and Valiant F1 with diameter 15, 20, 25, 30 and 35 mm. The raw vegetable, the blanched raw sprouts, frozen sprouts immediately after freezing and after 2, 4 and 6 months of frozen storage, and sprouts kept frozen for 6 months and boiled then. The content of vitamin C in the raw vegetable, in the frozen semiproduct, and in the product ready for consumption depended on the variety and on the size of the vegetable, and with rising size the content of vitamin C was decreasing. Immediately after harvesting the sprouts contained from 109 to 198 mg of vitamin C in 100 g of fresh mass. Higher levels of vitamin C were present in heterotic varieties, lower in the stabilized variety Maczuga. Depending on the variety blanching led to a decrease of vitamin C content by 15 to 27%, freezing reduced it by 1% to 8%, during 6 months of storage of frozen vegetables this reduction was 14 to 32%, and boiling of frozen sprouts decreased it by another 30-39%. Consequently, the final product contained from 33% to 48% of vitamin C amount in the raw vegetable, which was, on the average, 73 mg/100 g of fresh mass in the Citadel variety, 60 mg in the Valiant variety, 59 mg in the Lancelot variety, and 52 mg in the Maczuga variety. The boiled sprouts of 15 mm diameter contained, on average, 59% vitamin C more than the sprouts with 35 mm diameter.     

Testing of folate conjugase from chicken pancreas vs. commercial enzyme and studying the effect of cooking on folate retention in Thai foods

Crude enzyme from chicken pancreas as a source of folate conjugase was prepared in a lyophilised form. Homogeneity, stability and activities were checked against a commercial enzyme. Subsequently, the prepared crude enzyme was used to investigate the process of folate extraction in various food matrices and study the effect of cooking on folate retention in several Thai foods. The lyophilised enzyme was homogeneous and contained 4 μg endogenous folate per g of prepared lyophilised crude enzyme. The stability of the lyophilised enzyme and the diluted enzyme, kept at 4 °C, was at least 12 months and 3 days, respectively. The activity of the prepared lyophilised folate conjugase, used at the level of 20 mg/g sample, was evaluated by a microbiological assay of total folate in brown rice, egg, whole milk powder, soybeans and asparagus. It showed comparable results to that of the commercial enzyme. Single-enzyme treatment (folate conjugase alone) was sufficient for the determination of folate content in brown rice, soybeans and asparagus. However, for egg and whole milk powder, it was necessary to apply tri-enzyme treatment as this showed a significantly higher level (at P < 0.05) of total folate than that obtained using only single- or di-enzyme (protease + folate conjugase) treatments. Among the representative foods studied, the levels of total folate ranked in order of concentration, were soybeans > egg > asparagus > brown rice > steamed-mackerel (common form sold) (305, 117, 95, 41 and 24 μg/100 g wet weight basis, respectively). After cooking, the true retention of total folate in the cooked foods ranged from 60% in brown rice (cooked in an electric rice cooker) up to 82% in boiled asparagus. On a wet weight basis, the total folate content in boiled soybeans, boiled asparagus, boiled egg, fried mackerel and cooked brown rice was 100, 84, 72, 22 and 12 μg/100 g, respectively. One boiled egg (50 g) contributes 36 μg folate, which is equal to 18% of the Thai Recommended Daily Intake (RDI), and thus it can be considered as a good source of folate based on one serving size. A serving of boiled soybeans (70 g) or boiled asparagus (80 g) is an excellent source of folate, each contributing about 35% of the Thai RDI.     

Determination of Myo-inositol and d-chiro-inositol in black rice bran by capillary electrophoresis with electrochemical detection

A high-performance capillary electrophoresis (CE) method with electrochemical detection (ED) is developed for simultaneous determination of myo-inositol and d-chiro-inositol in black rice bran in this work. A 140 μm diameter copper-disk electrode operated in a wall-jet configuration, which exhibited good response at +0.65 V (relative to the saturated calomel electrode (SCE)) for the two analytes in 50 mm sodium hydroxide solution, was used as working electrode. The optimum conditions for determination was optimized with regard to the potential applied to the working electrode, concentration of the running buffer, separation voltage and injection time. The analytes were separated within 20 min. Excellent linearity was obtained in the concentration range from 1.0×10⁻⁶ to 1.0×10⁻⁴ g/ml for both analytes. The detection limit (S/N=3) was 5.3×10⁻⁷ and 7.3×10⁻⁷ g/ml for myo-inositol and d-chiro-inositol, respectively. The work provides a useful method for the analysis of myo-inositol and d-chiro-inositol in black rice bran.     

Phenolic acids in potatoes,vegetables, and some of their products

The aim of this study was to determine the distribution and contents of soluble and total phenolic acids in a wide range of vegetables consumed in Finland. The determinations were performed from the pooled samples (14 potato and 45 other vegetable samples). Soluble phenolic acids were extracted with methanolic acetic acid and a tentative quantification was performed by HPLC. The contents of total phenolic acids were determined by HPLC after alkaline and acid hydrolyses. Chlorogenic acid derivatives were the most dominant soluble phenolic acids, while caffeic acid was the most dominant phenolic acid aglycone in the samples studied. Highest contents of soluble phenolic acids were found in raw and cooked potato peels: 23–45 mg/100 g fresh weight calculated as aglycones. In addition, pot-grown lettuces, Chinese cabbage, broccoli, carrot, aubergine, Jerusalem artichoke, peanut and most of the boiled and peeled potato tubers contained more than 5 mg/100 g of soluble phenolic acids calculated as aglycones. Among the best vegetable sources of total phenolic acids were potatoes, with contents varying from 7.9 mg/100 g (cooked and peeled Rosamunda variety) to 52 mg/100 g (cooked peel of Van Gogh variety), and red cabbage, carrot, aubergine, Jerusalem artichoke, broccoli, pot-grown lettuce, spinach, radish and red beet, with contents from 11 mg/100 g (spinach) to 52 mg/100 g (pot-grown lettuce Lollo Rosso). Variation in the phenolic acid contents of the vegetables was either moderate or considerable and needs further research.     

Determination of anthocyanins from acerola (Malpighia emarginata DC.) and açai (Euterpe oleracea Mart.) by HPLC–PDA–MS/MS

The anthocyanins from acerola and açai, two tropical fruits known for their bioactive compounds, were studied. Two varieties of acerola in natura and one brand of frozen pulp of açai were analyzed by high-performance liquid chromatography connected to photodiode array and mass spectrometry detectors (HPLC–PDA–MS/MS). The açai pulp presented 282–303 mg/100 g of total anthocyanin, with predominance of cyanidin 3-glucoside and cyanidin 3-rutinoside, in average proportions of 13% and 87%, respectively. The composition of the two acerola varieties (Waldy Cati 30 and Olivier) were similar, being cyanidin 3-rhamnoside (76–78%) the major anthocyanin, followed by pelargonidin 3-rhamnoside (12–15%). The acerola Waldy variety showed total anthocyanin content of 6.5–7.6 mg/100 g, while 7.9–8.4 mg/100 g were found in the Olivier variety, for fruits harvested in 2003 and 2004. No statistical differences were found between varieties and harvests for the total anthocyanin content in acerola fruits.     

Compositional characteristics of commercial beetroot products and beetroot juice prepared from seven beetroot varieties grown in Upper Austria

Beta vulgaris L. (beetroot) contains high amounts of biologically active substances including betalains and inorganic nitrate. We determined the amounts of various compounds (minerals, betalains, oxalic acid, phenolic acids, and sugars) in juice prepared from seven different beetroot varieties cultivated in Upper Austria. Large differences were found between the varieties for some substances (such as nitrate), whereas others showed only minor variation (certain minerals and sugars). The total betalain content was found to range between 0.8 and 1.3 g/L fresh juice (about 60% betacyanins and 40% betaxanthins) that accounted for 70–100% of the total phenolics content. Other detected phenolics were hydroxycinnamic acids, which accounted for up to 2.6% of total phenolics. Nitrate content varied 10-fold between single varieties. Sugar composition was similar in all varieties with an average total content of about 7.7%, consisting of 95% sucrose. Only minor differences in the concentration of oxalic acid (0.3–0.5 g/L fresh juice) were found between the varieties. In addition, 16 commercial juices and four powders were analyzed for their nitrate contents, as its metabolic product nitric oxide has been reported to provide cardiovascular benefits. Large variations of the nitrate levels, ranging from 0.01 to 2.4 g/L, were found.     

Protein, iron, zinc and calcium concentrations of potatoes following traditional processing as “chuño”

Samples from unprocessed and processed cooked tubers of the nine most abundant potato cultivars used to prepare the traditional freeze-dried food product, “chuño” in the central highlands of Peru were prepared and analyzed for their protein and mineral concentrations. The protein, iron, zinc and calcium concentration of cooked chuño of the nine cultivars evaluated ranged from 0.49 to 1.15 g, from 0.29 to 0.65 mg, from 0.04 to 0.14 mg and from 18.9 to 31.0 mg per 100 g on a fresh weight basis, respectively. Potatoes processed as chuño have a lower concentration of protein and zinc than unprocessed tubers, and a higher content of calcium, while iron concentration may be expected not to be subjected to changes. Water used in preparing the chuño is suggested to be the cause for an increased calcium concentration in the final product, as the water used had higher calcium content before (1.35 mequiv./l) than after (0.84 mequiv./l) use in the preparation. Thus, water seems to be source of the increased calcium concentration.     

Potential Contribution of Mangoes to Reduction of Vitamin A Deficiency in Kenya

The β-carotene content of fresh and dried mangoes commonly consumed in Kenya was evaluated and converted to retinol equivalent (RE). Mango fruits of varieties Ngowe, Apple, and Tommy Atkins were harvested at mature green, partially ripe, and ripe stages and their β-carotene content analyzed. The stability of β-carotene in sun dried mangoes was also studied over 6 months under usual marketing conditions used in Kenya. The effect of using simple pretreatment methods prior to drying of mango slices on retention of β-carotene was as well evaluated. In amounts acceptable to children and women, fresh and dried mangoes can supply 50% or more of the daily required retinol equivalent for children and women. Stage of ripeness, variety, postharvest holding temperature, method of drying, and storage time of dried mango slices affected β-carotene content and consequently vitamin A value of the fruits. Apple variety grown in Machakos had the highest β-carotene. It exceeded the daily RE requirements by 11.8% and 21.5% for women and children respectively. Fresh or dried mangoes are a significant provitamin A source and should be included in food-based approaches aiming to reduce vitamin A deficiency.     

Potential contribution of mangoes to reduction of vitamin A deficiency in Kenya

The β-carotene content of fresh and dried mangoes commonly consumed in Kenya was evaluated and converted to retinol equivalent (RE). Mango fruits of varieties Ngowe, Apple, and Tommy Atkins were harvested at mature green, partially ripe, and ripe stages and their β-carotene content analyzed. The stability of β-carotene in sun dried mangoes was also studied over 6 months under usual marketing conditions used in Kenya. The effect of using simple pretreatment methods prior to drying of mango slices on retention of β-carotene was as well evaluated. In amounts acceptable to children and women, fresh and dried mangoes can supply 50% or more of the daily required retinol equivalent for children and women. Stage of ripeness, variety, postharvest holding temperature, method of drying, and storage time of dried mango slices affected β-carotene content and consequently vitamin A value of the fruits. Apple variety grown in Machakos had the highest β-carotene. It exceeded the daily RE requirements by 11.8% and 21.5% for women and children respectively. Fresh or dried mangoes are a significant provitamin A source and should be included in food-based approaches aiming to reduce vitamin A deficiency.     

Cellular transport of lutein is greater from uncooked rather than cooked spinach irrespective of whether it is fresh,frozen, or canned

Lutein, a carotenoid found in significant levels in spinach, has attracted a great deal of attention owing to its reported function as a shield against the photooxidative effects of blue light. Therefore, the rationale of this study was to examine the effects of various processing and cooking methods on lutein bioavailability from spinach (Spinacia oleracea) using an in vitro digestion procedure coupled with the use of a human intestinal Caco-2 cell model. Fresh, frozen, and canned spinach were analyzed uncooked and after boiling or microwave cooking. Lutein content from the uncooked and cooked digested food (digestate) and appropriate micelles was determined. Micellarized lutein from the spinach samples was adjusted to 0.1 μmol/L and added to Caco-2 cells. Cellular uptake and secretion (cellular transport) of lutein were determined. Our results showed that digestate obtained from uncooked canned spinach had greater lutein content (P < .05) than uncooked fresh or frozen spinach. Microwave cooking, but not boiling, significantly lowered the lutein content of canned spinach digestate and micelles compared with their uncooked counterparts. Interestingly, there were no differences in the micellarization of lutein between the cooking and processing methods. Cellular transport of lutein was greater from uncooked spinach micelles compared with boiled or microwave-cooked spinach. To conclude, although the lutein content of digesta and micelles may have been modified, its micellarization was not significantly affected by any of the cooking or processing methods tested. In general, cellular transport of lutein was greatest in uncooked spinach irrespective of whether the spinach was fresh, frozen, or canned.