Food Chemistry 127 (2011) 1114–1118
Contents lists available at ScienceDirect
Food Chemistry journal homepage: www.elsevier.com/locate/foodchem
Ascorbic acid enrichment of whole potato tuber by vacuum-impregnation K. Hironaka a,⇑, M. Kikuchi a, H. Koaze a, T. Sato a, M. Kojima a, K. Yamamoto a, K. Yasuda a, M. Mori b, S. Tsuda b a b
Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan National Agriculture and Food Research Organization for Hokkaido Region in Japan, Memuro 082-0071, Japan
a r t i c l e
i n f o
Article history: Received 3 March 2010 Received in revised form 6 January 2011 Accepted 25 January 2011 Available online 1 February 2011 Keywords: Whole potato Vacuum impregnation Ascorbic acid Steam-cooking Storage
a b s t r a c t The aim of this study was to evaluate the use of vacuum-impregnation (VI) for enriching the ascorbic acid content of whole potatoes. Whole potatoes were immersed in a 10% ascorbic acid (AA) solution. A vacuum pressure of 70 cm Hg was applied for 0–60 min, following atmospheric pressure restoration for 3 h, while samples remained in the VI solution. AA concentrations of potatoes were measured using HPLC. The effects of cooking and storage time in subsets of the fortified samples were also evaluated. Results indicated that the AA concentration of whole potatoes increased with vacuum time (max 150 mg/ 100 g fr. wt.). In addition, a steam-cooking study showed that 100 g of the 25 min steam-cooked VI potatoes could provide adults with 90–100% of the recommended daily allowance of AA (100 mg). The storage study showed that VI whole potatoes had a relatively high AA concentration (50 mg/100 g fr. wt.), even at 14 days of storage at 4 °C. This study indicated that VI treatment of whole potatoes was useful for enriching the AA content. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Increased consumer interests in the health benefits of foods have led to significant development of nutraceuticals and functional foods (Zhao & Xieb, 2004). The global functional food market is estimated to be 47.6 billion US$, the United States being the largest market segment, followed by Europe and Japan (Sloan, 2002). Lastly, the range of functional foods that have potential health benefits has grown tremendously. Examples include baby foods, bakery goods and cereals, confectionery, dairy foods, ready meals, snacks, soft drinks, such as energy and sport drinks, meat products and spreads. These functional foods are associated with various types of benefit, and involve vitamin and mineral fortification, cholesterol reduction, antioxidants, phytochemicals, dietary fibre, herbs and botanicals, and probiotics, prebiotics and symbiotics (Alzamora et al., 2005). Potato (Solanum tuberosum L.) is one of the world’s most important crops, ranking fifth in terms of human consumption and fourth in worldwide production (Burgos, Auqui, Amoros, Salas, & Bonierbale, 2009). Beyond supplying energy and good quality protein, potato is also an important source of vitamins and minerals. However, its value within the human diet – particularly as a source of vitamin C – is often underestimated or ignored (Dale, Griffiths, & Todd, 2003). Potatoes have relatively high ascorbic acid (AA) contents. AA is an essential component of most living tissues. The ⇑ Corresponding author. Tel.: +81 155 49 5572; fax: +81 155 49 5577. E-mail address: [email protected] (K. Hironaka). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.01.111
metabolic role of AA is related to an oxidation and reduction reaction in which AA is reversibly oxidised to dehydroascorbic acid. AA promotes the hydroxylation reaction in a number of biosynthetic pathways (Barnes & Kodieck, 1972; Levine, 1986). Hydroxylation is required to stabilise the triple helical conformation of collagen. Compromised collagen production, associated with AA deficiency, results in impaired wound healing (Bird, Schwartz, & Peterkofsky, 1986). Moreover, AA plays an important role in protection against oxidative stress as an antioxidant. AA is an important scavenger of free radical species, such as reactive oxygen species that can cause tissue damage resulting from lipid peroxidation, DNA breakage or base alterations, and may contribute to degenerative diseases, such as heart disease or cancer (Bates, 1997). Due to its participation in the oxidation of transition metal ions, AA also plays an important role in enhancing the bioavailability of non-haem ion (Teucher, Olivares, & Cori, 2004). The Food and Agriculture Organization (FAO) indicated that the recommended nutrient intake of vitamin C ranges from 25 to 45 mg/day, depending on age. However, based on available biochemical, clinical and epidemiological studies, the current recommended daily allowance (RDA) for AA is suggested to be 100 mg/day for adults to achieve cellular saturation and reduce risk of heart disease, stroke and cancer, in healthy individuals (Naidu, 2003). Vacuum-impregnation (VI) treatment is effective in preventing discoloration of fruit pieces by enzymatic and oxidative browning, without using antioxidants, via removal of oxygen from the pores (Alzamora et al., 2000; Barbosa-Canovas & Vega-Mercado, 1996). Another important factor contributing to quality improvement is
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
that functional food ingredients, such as firming agents, antioxidants and antimicrobial ingredients, penetrate into the pore structure of the product to effectively improve quality and extend shelflife. For example, sucrose impregnated into the pores of cut pears, was found to protect natural tissue structure, thus improving texture quality and lowering drip loss in subsequent drying, canning or freezing processes by limiting collapse and cellular disruption (Bolin & Huxsoll, 1993). In addition, Xie and Zhao (2003a, 2003b) studied calcium and zinc fortification of fruits using VI processing of high-fructose-corn-syrup solution containing calcium and/or zinc in fresh-cut apples, strawberry slices and whole Marionberry. Results showed that 15–20% DRI of calcium, and above 40% DRI of zinc, could be fortified in 200 g of fresh-cut apples, and about 11% and 23% DRI of calcium and zinc can be obtained in 200 g of berries, respectively, without affecting the physicochemical properties of the fruits. However, no studies exist on VI treatment for potato tuber. Fito and Pastor (1994) point out that intercellular space is important for sample behaviour during VI processing because it determines the volume that can be occupied by the external liquid in the product tissue. However, the intercellular air space of potato is very small (1%) compared with that of apple (25%), peach (15%) and mushroom (37–45%) (Alzamora et al., 2005). In addition, potatoes have a thick periderm, impermeable to water and gases (Peterson, Barker, & Howarth, 1985). Thus, we first evaluated the VI possibility of whole potato, using red ink. Next, we tried to evaluate the effect of vacuum time on the AA content of VI potatoes. Finally, effects of steam-cooking and storage, at 4 °C, on AA content were also evaluated.
2. Materials and methods 2.1. Materials Tubers for processing (Toyoshiro) and fresh-consumption (Irish Cobbler) cultivars were harvested in September, late 2007, and then tubers of approximately 150 g were selected.
2.2. VI treatment of red ink Red ink (Kokuyo, IP-540r) was distilled 300 times using ionexchanged water. Whole potatoes (Irish Cobbler) were immersed in the red ink solution that was placed inside a desiccator at room temperature. A vacuum pump (Model PD-102, Yamato, Japan) was connected to the desiccator, and a vacuum pressure of 9.33 kPa was applied to the system for 60 min, then atmospheric pressure restoration for 3 h. The whole potatoes were cut transversely or longitudinally after vacuum or restoration. Then, cut sections were photographed by a digital camera (Model Finepix F31, Fuji, Japan).
1115
2.4. Cooking VI potatoes were placed in a stainless steam cooker, which was covered with a lid and steamed over boiling water at atmospheric pressure until easily penetrated with a fork (25 min) (Faller & Fialho, 2009; Weaver, Timm, & Ng, 1983). 2.5. Storage Potatoes for domestic consumption are stored at 5 °C or so to avoid serious sprout growth (Burton, van Es, & Hartmans, 1991). VI potatoes (Toyoshiro variety) were also stored at 4 °C and 90% relative humidity for up to 2 weeks. The ascorbic acid contents of the samples were measured at 3, 7 and 14 days. 2.6. Ascorbic acid determination Potato tubers were washed, peeled and diced into approximately 5 mm cubes. The concentration of ascorbic acid (AA) was determined using the HPLC technique, reported by Sapers, Douglas, Ziolowski, Miller, and Hicks (1990) with slight modification. Potato tissues (10 g) were blended with a solution containing 10 ml of 2.5% metaphosphoric acid and 20 ml of acetonitrile: 0.05 M KH2PO4 (75:25). The homogenate was filtered and then passed through a C18 Sep-Pak cartridge (Waters Associates, Milford, MA) and filtered through a 0.45 l HPLC disk (Paul Corp., Japan). The filtrate was injected into the HPLC system, equipped with a pump (Model L-6320, HITACHI), column oven (Model L-7300, HITACHI) and UV detector (Model L-7400, HITACHI) set at 254 nm wavelength. The detector signal was recorded on a recorder (Model D-7500, HITACHI). The chromatographic column was a 7.8 300 mm i.d. Gelpack C18 (GL-C610H-S, HITACHI). A 0.3% metaphosphoric acid solution was used as mobile phase. An AA standard curve was prepared, using solutions containing 25, 50, 75, and 100 lg/ml. The standard solution was injected into the HPLC system and the corresponding peak area was obtained (Diamante, Ishibashi, & Hironaka, 2002). 2.7. Statistical analyses All analyses were performed six times, and results were averaged to obtain mean values. Duncan’s multiple range test of SPSS (1992) was used to determine differences between means of vacuum time, cooking treatment or storage time. 3. Results and discussion
2.3. VI treatment of ascorbic acid
Fig. 1 shows the impregnation of red ink into a potato without a vacuum. No impregnations occurred in the potato during immersion. Thus, immersion treatment alone could not cause impregnation into the potato. Fig. 2 shows the impregnation during restoration. Potatoes, just after the vacuum treatment, had no impregnations into the potato, but those after 3 h of restoration had impregnation. Therefore, Figs. 1 and 2 indicate that the
VI treatment of whole potatoes (Toyoshiro and Irish Cobbler) was carried out in a 10% ascorbic acid solution. A mass ratio, of the solution to potato, of 3% w/w was used to ensure adequate immersion and minimise the dilution effect on the concentration of VI solution (Sormani, Maffi, Bertolo, & Torreggiani, 1999). A vacuum pressure of 9.33 kPa was applied to the system for 0–60 min, and atmospheric pressure restoration for 3 h. Whole potatoes were drained, rinsed with distilled water to remove the attached solution, and gently blotted with tissue papers. Ascorbic acid contents of impregnated and untreated (fresh as control) potatoes were analysed immediately.
Fig. 1. Immersion of whole potato tuber (Toyoshiro variety) in a red ink solution without vacuum.
1116
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
Fig. 2. Impregnation of red ink into whole potato tuber (Toyoshiro variety) by restoration.
impregnation into a potato tuber requires both vacuum and restoration treatments. Fig. 3 shows photographs of the impregnation potato of 1 h vacuum plus 3 h restoration treatment, and the 4 h immersion potato. This Figure indicates that the impregnation occurred almost at the central pith and the areas between the vascular ring and the periderm. Concerning the pith and vascular ring of potato, Artschwager (1924) reported that the pith forms the narrow central core of the tuber, but is continuous with eyes by means of lateral branches, and the vascular ring (as it appears to the naked eye) constitutes a narrow band of tissue that contains the xylem and the secondary phloem. While potatoes have a thick periderm to prevent rapid water loss from the thin-walled parenchyma of the tuber (Peterson et al., 1985), they have 74–141 lenticels per tuber (Wigginton, 1973). Lenticels provide permeable regions (Cutter, 1991). For example, Burton (1965) found an O2 permeability value of 2.5 mm3 cm 2 h 1 kPa 1for mature tubers. When a potato is immersed in a physiologically active compound (PAC)-concentrated solution under vacuum conditions, air might be extracted from the eyes and lenticels and then, when atmospheric pressure is restored, the impregnation penetrates the intercellular spaces of porous tissues through the eyes and lenticels by capillary action and by the pressure gradients (i.e., the hydrodynamic mechanism) that are imposed on the system, helping incorporation of PACs (Fito, 1994). So, the strong impregnation of red ink in the tuber was found at the central pith and the areas between the vascular ring and the periderm, as shown in Fig. 3. As shown in Fig. 4, the AA content of VI potato (Toyoshiro) increased with vacuum time. The 60 min VI potato had a 21 times higher (p < 0.05) AA content than had raw potatoes. In addition, VI potatoes (per 100 g), beyond 30 min of vacuum time, had an AA content in excess of the FAO value (45 mg/day). One hundred grammes of sixty min VI treatment-potatoes, in particular, had a 150 mg AA content. In Europe, daily potato uptake per capita, in 2005, was 260 g, followed by North America (160 g) (Keijbets, 2008). Thus, in these areas, daily potato consumptions of VI potatoes can exceed RDA value (100 mg/day) (Naidu, 2003).
Fig. 3. Impregnation of red ink into whole potato tuber (Toyoshiro variety) by restoration.
Fig. 4. Effect of vacuum time on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Toyoshiro variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
The AA content of the Irish Cobbler also increased with vacuum time (Fig. 5). The 60 min VI potato had a nine times higher (p < 0.05) AA content than had raw potatoes. Moreover, VI potatoes (per 100 g), beyond 30 min of vacuum time, had AA contents higher than the FAO value (45 mg/day). Especially, 60 min VI potatoes (100 g) had AA contents higher than the RDA value (100 mg/day) (Naidu, 2003). Concerning the vacuum time of VI treatment for vegetables and fruits, Gras, Vidal, Betoret, Chiralt, and Fito (2003) used a pressure of 50 mbar and a vacuum time of 10 min for impregnation of calcium to cylindrically cut eggplants and carrots. Guillemin, Degraeve, Noel, and Saurel (2008) performed a sodium chloride and/or sodium alginate VI treatment under 0.05 bar for 2 min, for apple cubes, in order to improve the firmness. Sapers Garzarella, and Pilizota (1990) used a 2 min vacuum time, at 169–980 mbar pressures, for NaCl VI treatment of diced or strip potatoes. However, compared with the above studies, a long vacuum time was needed for whole potatoes in the present study (Fig. 1). This long time for VI treatment may be due to the thick periderm of whole potatoes which is less permeable to water and gas (Peterson et al., 1985). Fig. 6 shows the decrease in AA content of VI potatoes (Toyoshiro) by steam-cooking. As shown in this Figure, steam-cooking Toyoshiro
Fig. 5. Effect of vacuum time on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Irish Cobbler variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
Fig. 6. Effect of steam-cooking on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Toyoshiro variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h; steam-cooking temperature and time, 100 °C, 25 min. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
potatoes resulted in a 42% decrease in AA content. However, VIcooked potatoes had 22 times higher (p < 0.05) AA contents than had un-VI-cooked potatoes. In addition, VI-cooked potatoes of 100 g had a 90 mg AA content, which is over twice the FAO value (45 mg/day) (Naidu, 2003). For the Irish Cobbler (Fig. 7), the AA content of VI-cooked potatoes decreased by 33%. However, VI-cooked potatoes had eight times higher (p < 0.05) AA contents than had un-VI-cooked potatoes. Moreover, VI-cooked potatoes of 100 g had a 100 mg AA content, which is over twice the FAO value (45 mg/day) (Naidu, 2003). Concerning cooking loss of AA of potatoes, Burton (1989) reported a 10–15% AA loss for unpeeled-steamed potatoes. In the present study, an AA loss of over 33% was found in VI-cooked potatoes. As for calcium distribution in tissues of calcium VI-treated apple cylinders, Gras et al. (2003) reported that calcium incorporation mainly occurred in the intercellular spaces. Thus, AA also may be located in intercellular spaces in the present study. Peterson et al. (1985) indicated that the lenticels of potatoes allow excess water loss from the internal tissues of the tuber. Therefore, the large loss of AA content in the present study might be due to loss through the lenticels from the intercellular spaces. Further study is therefore needed on AA distribution in the tissues of VI potatoes. AA content of VI potatoes decreased with storage time (Fig. 8). With respect to the decrease in AA content of stored potatoes, Shekhar, Iritani, and Arteca (1978) reported that tubers stored at
1117
Fig. 8. Change in AA content of VI whole potato tuber (Irish Cobbler variety) during storage at 5 °C: VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
5.5 °C showed a marked reduction in ascorbic acid levels. Also, during storage at 10 °C, there was a sharp initial decline in AA levels (Augustin et al., 1978; Keijbets, 1984) in tubers having a high concentration; for example, some immature tubers showed the most marked decrease. Such losses amount to 33% over 3–4 weeks at 10 °C for the mature King Edward potato, compared to 10% loss for mature crops (Burton, 1989). Also, VI potatoes with a high AA content may result in the marked loss observed in the present study. While VI potatoes had a decrease in AA content during storage, they had an AA content 10 times higher (p < 0.05) than un-VI potatoes. In addition, VI potatoes (per 100 g) had a high AA content, in excess of the FAO value (45 mg/day) (Naidu, 2003), even after 14 storage days. When these potatoes are cooked, AA contents might decrease by 40%. However, the daily uptake of VI potatoes of 200 g exceeds at least the FAO value. VI of food matrices with adequate solutions/suspensions of physiologically active compounds has been claimed as a useful way to obtain this kind of product, without destroying the initial food matrix, but only occupying its initial porous fraction (intercellular spaces) with a liquid phase (Fito et al., 2001). Thus, the liquid release from potato tubers by VI treatments might be small. However, further studies will be needed on actual nutritive losses by VI treatments (e.g. sugars, phenols). Finally, this study indicates that VI treatment of whole potatoes was useful for enriching the AA content of cooked or stored potatoes. The daily uptake of 200 g of VI potatoes by this method will be good for health because it exceeds the FAO value. 4. Conclusion The results from this study indicate that the VI treatment increased the AA content of whole potatoes ten times (150 mg/100 g fr. wt.). In addition, 100 g of the 25 min steam-cooked VI potatoes could provide adults with 90–100% of the recommended daily allowance of AA (100 mg). Moreover, the VI potatoes had a relatively high AA concentration (50 mg/100 g fr. wt.), even at 14 days of storage at 4 °C. This study indicated that VI treatment of whole potatoes was useful for enriching the AA content.
Fig. 7. Effect of steam-cooking on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Irish Cobbler variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h; steam-cooking temperature and time, 100 °C, 25 min. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
References Alzamora, S. M., Salvatori, D., Tapia, M. S., Lo´pez-Malo, A., Welti-Chanes, J., & Fito, P. (2005). Novel functional foods from vegetable matrices impregnated with biologically active compounds. Journal of Food Engineering, 67, 205–214.
1118
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
Alzamora, S. M., Tapia, M. S., Leunda, A., Guerrero, S. N., Rojas, A. M., Gerschenson, L. N., et al. (2000). Minimal preservation of fruits: A cited project. In J. E. Lozano, C. Anon, E. Parada-Arias, & G. V. Barbosa-Canovas (Eds.), Trends in Food Engineering (pp. 205–225). Pennsylvania, USA: Technomic Publishing. Artschwager, E. (1924). Studies on the potato tuber. Journal of Agricultural Research, 27, 809–835. Augustin, J., Johnson, S. R., Teitzel, C., Toma, R. B., Shaw, R. L., True, R. H., et al. (1978). Vitamin composition of freshly harvested and stored potatoes. Journal of Food Science, 43, 1566–1574. Barbosa-Canovas, G. V., & Vega-Mercado, H. (1996). Osmotic dehydration of foods (pp. 265–288). Florence, Italy: International Thomson. Barnes, M. J., & Kodieck, K. (1972). Biological hydroxylations and ascorbic acid with special regard for collagen metabolism. Vitamins and Hormones, 30, 1–43. Bates, C. (1997). Bioavailability of vitamin C. European Journal of Clinical Nutrition, 51(Suppl. 1), S28–S33. Bird, T. A., Schwartz, N. B., & Peterkofsky, B. (1986). Mechanism for the decreased biosynthesis of cartilage proteoglycan in the scorbutic guinea pig. The Journal of Biological Chemistry, 261, 11166–11172. Bolin, H. R., & Huxsoll, C. C. (1993). Partial drying of cut pears to improve freeze– thaw texture. Journal of Food Science, 58, 357–360. Burgos, G., Auqui, S., Amoros, W., Salas, E., & Bonierbale, M. (2009). Ascorbic acid concentration of native Andean potato varieties as affected by environment, cooking and storage. Journal of Food Composition and Analysis, 22, 533–538. Burton, W. G. (1965). The permeability to oxygen of the periderm of the potato tuber. Journal of Experimental Botany, 16, 16–23. Burton, W. G. (1989). The Potato (pp. 447–449) (3rd ed.). London, UK: Longman. Burton, W. G., van Es & Hartmans, K. J. (1991). The physics and physiology of storage. In P. Harris (Ed.), Potato Crop (pp. 610) (2nd ed.). London, UK: Chapman & Hall. Cutter, E. G. (1991). Structure and development of the potato plant. In P. Harris (Ed.), Potato Crop (pp. 111) (2nd ed.). London, UK: Chapman & Hall. Dale, M. F., Griffiths, W., & Todd, D. (2003). Effects of genotype, environment, and postharvest storage on the total ascorbate content of potato (Solanum tuberosum) tubers. Journal of Agriculture and Food Chemistry, 51, 244–248. Diamante, L. M., Ishibashi, K., & Hironaka, K. (2002). Effect of temperature and water activity on quality deterioration and shelf life of dried mangoes. Annals of Tropical Research, 24, 60–81. Faller, A. L. K., & Fialho, E. (2009). The antioxidant capacity and polyphenol content of organic and conventional retail vegetables after domestic cooking. Food Research International, 42, 210–215. Fito, P. (1994). Modelling of vacuum osmotic dehydration of foods. Journal of Food Engineering, 23, 313–328. Fito, P., Chiralt, A., Betoret, N., Gras, M., Chafer, M., Martinez-Monzo, J., et al. (2001). Vacuum impregnation and osmotic dehydration in matrix engineering: Application in functional fresh food development. Journal of Food Engineering, 49, 175–183. Fito, P., & Pastor, R. (1994). Non-diffusional mechanisms occurring during vacuum osmotic dehydration. Journal of Food Engineering, 21, 513–519. Gras, M. L., Vidal, D., Betoret, N., Chiralt, A., & Fito, P. (2003). Calcium fortification of vegetables by vacuum impregnation interactions with cellular matrix. Journal of Food Engineering, 56, 279–284.
Guillemin, A., Degraeve, P., Noel, C., & Saurel, R. (2008). Influence of impregnation solution viscosity and osmolarity on solute uptake during vacuum impregnation of apple cubes (var Granny Smith). Journal of Food Engineering, 86, 475–483. Keijbets, M. J. H. (1984). Vitamin C during long-term storage of potatoes. Abst. 9th Triennial EAPR Conference (pp. 390–391). Keijbets, M. J. H. (2008). Potato processing for the consumer: Developments and future challenges. Potato Research, 51, 271–281. Levine, M. (1986). New concepts in the biology and biochemistry of ascorbic acid. The New England Journal of Medicine, 314, 892–902. Naidu, K. A. (2003). Vitamin C in human health and disease is still a mystery? An overview. Nutrition Journal, 2, 7–16. Peterson, R. L., Barker, W. G., & Howarth, M. J. (1985). Development and structure of tubers. In P. H. Li (Ed.), Potato Physiology (pp. 133). London, UK: Academic Press. Sapers, G. M., Garzarella, L., & Pilizota, V. (1990). Application of browning inhibitors to cut apple and potato by vacuum and pressure infiltration. Journal of Food Science, 55, 1049–1053. Sapers, G. M., Douglas, F. W., Ziolowski, M. A., Miller, R. L., & Hicks, K. B. (1990). Determination of ascorbic acid, dehydroascorbic acid and acid-2-phosphate: Infiltrated apple and potato tissue by high-performance liquid chromatography. Journal of Chromatography, 503, 431–436. Shekhar, V. C., Iritani, M., & Arteca, R. (1978). Changes in ascorbic acid content during growth and short-term storage of potato tubers (Solanum Tuberosum L.). American Potato Journal, 55, 663–670. Sloan, E. (2002). The top 10 functional food trends: The next generation. Food Technology, 56, 32–57. Sormani, A., Maffi, D., Bertolo, G., & Torreggiani, D. (1999). Textural and structural changes of dehydrofreeze-thawed strawberry slices: Effects of different dehydration pretreatments. Food Science and Technology International, 5, 479–485. SPSS (1992). SPSS for Windows Base System User’s Guide Release 5.0 (pp. 269–270). Chicago, USA: SPSS Inc.. Teucher, B., Olivares, M., & Cori, H. (2004). Enhancers of iron absorption: Ascorbic acid and other organic acids. International Journal for Vitamin and Nutrition Research, 76, 403–419. Weaver, M. L., Timm, H., & Ng, H. (1983). Changes in nutritional composition of Russet Burbank potatoes by different processing methods. American Potato Journal, 60, 735–744. Wigginton, M. J. (1973). Diffusion of oxygen through lenticels in potato tuber. Potato Research, 16, 85–87. Xie, J., & Zhao, Y. (2003a). Improvement of physicochemical and nutritional qualities of frozen Marionberry by vacuum impregnation pretreatment with cryoprotectants and minerals. Journal of Horticultural Science and Biotechnology, 78, 248–253. Xie, J., & Zhao, Y. (2003b). Nutritional enrichment of fresh apple (Royal Gala) by vacuum impregnation. International Journal of Food Science and Nutrition, 54, 387–398. Zhao, Y., & Xieb, J. (2004). Practical applications of vacuum impregnation in fruit and vegetable processing. Trends in Food Science and Technology, 15, 434–451.
Contents lists available at ScienceDirect
Food Chemistry journal homepage: www.elsevier.com/locate/foodchem
Ascorbic acid enrichment of whole potato tuber by vacuum-impregnation K. Hironaka a,⇑, M. Kikuchi a, H. Koaze a, T. Sato a, M. Kojima a, K. Yamamoto a, K. Yasuda a, M. Mori b, S. Tsuda b a b
Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan National Agriculture and Food Research Organization for Hokkaido Region in Japan, Memuro 082-0071, Japan
a r t i c l e
i n f o
Article history: Received 3 March 2010 Received in revised form 6 January 2011 Accepted 25 January 2011 Available online 1 February 2011 Keywords: Whole potato Vacuum impregnation Ascorbic acid Steam-cooking Storage
a b s t r a c t The aim of this study was to evaluate the use of vacuum-impregnation (VI) for enriching the ascorbic acid content of whole potatoes. Whole potatoes were immersed in a 10% ascorbic acid (AA) solution. A vacuum pressure of 70 cm Hg was applied for 0–60 min, following atmospheric pressure restoration for 3 h, while samples remained in the VI solution. AA concentrations of potatoes were measured using HPLC. The effects of cooking and storage time in subsets of the fortified samples were also evaluated. Results indicated that the AA concentration of whole potatoes increased with vacuum time (max 150 mg/ 100 g fr. wt.). In addition, a steam-cooking study showed that 100 g of the 25 min steam-cooked VI potatoes could provide adults with 90–100% of the recommended daily allowance of AA (100 mg). The storage study showed that VI whole potatoes had a relatively high AA concentration (50 mg/100 g fr. wt.), even at 14 days of storage at 4 °C. This study indicated that VI treatment of whole potatoes was useful for enriching the AA content. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Increased consumer interests in the health benefits of foods have led to significant development of nutraceuticals and functional foods (Zhao & Xieb, 2004). The global functional food market is estimated to be 47.6 billion US$, the United States being the largest market segment, followed by Europe and Japan (Sloan, 2002). Lastly, the range of functional foods that have potential health benefits has grown tremendously. Examples include baby foods, bakery goods and cereals, confectionery, dairy foods, ready meals, snacks, soft drinks, such as energy and sport drinks, meat products and spreads. These functional foods are associated with various types of benefit, and involve vitamin and mineral fortification, cholesterol reduction, antioxidants, phytochemicals, dietary fibre, herbs and botanicals, and probiotics, prebiotics and symbiotics (Alzamora et al., 2005). Potato (Solanum tuberosum L.) is one of the world’s most important crops, ranking fifth in terms of human consumption and fourth in worldwide production (Burgos, Auqui, Amoros, Salas, & Bonierbale, 2009). Beyond supplying energy and good quality protein, potato is also an important source of vitamins and minerals. However, its value within the human diet – particularly as a source of vitamin C – is often underestimated or ignored (Dale, Griffiths, & Todd, 2003). Potatoes have relatively high ascorbic acid (AA) contents. AA is an essential component of most living tissues. The ⇑ Corresponding author. Tel.: +81 155 49 5572; fax: +81 155 49 5577. E-mail address: [email protected] (K. Hironaka). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.01.111
metabolic role of AA is related to an oxidation and reduction reaction in which AA is reversibly oxidised to dehydroascorbic acid. AA promotes the hydroxylation reaction in a number of biosynthetic pathways (Barnes & Kodieck, 1972; Levine, 1986). Hydroxylation is required to stabilise the triple helical conformation of collagen. Compromised collagen production, associated with AA deficiency, results in impaired wound healing (Bird, Schwartz, & Peterkofsky, 1986). Moreover, AA plays an important role in protection against oxidative stress as an antioxidant. AA is an important scavenger of free radical species, such as reactive oxygen species that can cause tissue damage resulting from lipid peroxidation, DNA breakage or base alterations, and may contribute to degenerative diseases, such as heart disease or cancer (Bates, 1997). Due to its participation in the oxidation of transition metal ions, AA also plays an important role in enhancing the bioavailability of non-haem ion (Teucher, Olivares, & Cori, 2004). The Food and Agriculture Organization (FAO) indicated that the recommended nutrient intake of vitamin C ranges from 25 to 45 mg/day, depending on age. However, based on available biochemical, clinical and epidemiological studies, the current recommended daily allowance (RDA) for AA is suggested to be 100 mg/day for adults to achieve cellular saturation and reduce risk of heart disease, stroke and cancer, in healthy individuals (Naidu, 2003). Vacuum-impregnation (VI) treatment is effective in preventing discoloration of fruit pieces by enzymatic and oxidative browning, without using antioxidants, via removal of oxygen from the pores (Alzamora et al., 2000; Barbosa-Canovas & Vega-Mercado, 1996). Another important factor contributing to quality improvement is
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
that functional food ingredients, such as firming agents, antioxidants and antimicrobial ingredients, penetrate into the pore structure of the product to effectively improve quality and extend shelflife. For example, sucrose impregnated into the pores of cut pears, was found to protect natural tissue structure, thus improving texture quality and lowering drip loss in subsequent drying, canning or freezing processes by limiting collapse and cellular disruption (Bolin & Huxsoll, 1993). In addition, Xie and Zhao (2003a, 2003b) studied calcium and zinc fortification of fruits using VI processing of high-fructose-corn-syrup solution containing calcium and/or zinc in fresh-cut apples, strawberry slices and whole Marionberry. Results showed that 15–20% DRI of calcium, and above 40% DRI of zinc, could be fortified in 200 g of fresh-cut apples, and about 11% and 23% DRI of calcium and zinc can be obtained in 200 g of berries, respectively, without affecting the physicochemical properties of the fruits. However, no studies exist on VI treatment for potato tuber. Fito and Pastor (1994) point out that intercellular space is important for sample behaviour during VI processing because it determines the volume that can be occupied by the external liquid in the product tissue. However, the intercellular air space of potato is very small (1%) compared with that of apple (25%), peach (15%) and mushroom (37–45%) (Alzamora et al., 2005). In addition, potatoes have a thick periderm, impermeable to water and gases (Peterson, Barker, & Howarth, 1985). Thus, we first evaluated the VI possibility of whole potato, using red ink. Next, we tried to evaluate the effect of vacuum time on the AA content of VI potatoes. Finally, effects of steam-cooking and storage, at 4 °C, on AA content were also evaluated.
2. Materials and methods 2.1. Materials Tubers for processing (Toyoshiro) and fresh-consumption (Irish Cobbler) cultivars were harvested in September, late 2007, and then tubers of approximately 150 g were selected.
2.2. VI treatment of red ink Red ink (Kokuyo, IP-540r) was distilled 300 times using ionexchanged water. Whole potatoes (Irish Cobbler) were immersed in the red ink solution that was placed inside a desiccator at room temperature. A vacuum pump (Model PD-102, Yamato, Japan) was connected to the desiccator, and a vacuum pressure of 9.33 kPa was applied to the system for 60 min, then atmospheric pressure restoration for 3 h. The whole potatoes were cut transversely or longitudinally after vacuum or restoration. Then, cut sections were photographed by a digital camera (Model Finepix F31, Fuji, Japan).
1115
2.4. Cooking VI potatoes were placed in a stainless steam cooker, which was covered with a lid and steamed over boiling water at atmospheric pressure until easily penetrated with a fork (25 min) (Faller & Fialho, 2009; Weaver, Timm, & Ng, 1983). 2.5. Storage Potatoes for domestic consumption are stored at 5 °C or so to avoid serious sprout growth (Burton, van Es, & Hartmans, 1991). VI potatoes (Toyoshiro variety) were also stored at 4 °C and 90% relative humidity for up to 2 weeks. The ascorbic acid contents of the samples were measured at 3, 7 and 14 days. 2.6. Ascorbic acid determination Potato tubers were washed, peeled and diced into approximately 5 mm cubes. The concentration of ascorbic acid (AA) was determined using the HPLC technique, reported by Sapers, Douglas, Ziolowski, Miller, and Hicks (1990) with slight modification. Potato tissues (10 g) were blended with a solution containing 10 ml of 2.5% metaphosphoric acid and 20 ml of acetonitrile: 0.05 M KH2PO4 (75:25). The homogenate was filtered and then passed through a C18 Sep-Pak cartridge (Waters Associates, Milford, MA) and filtered through a 0.45 l HPLC disk (Paul Corp., Japan). The filtrate was injected into the HPLC system, equipped with a pump (Model L-6320, HITACHI), column oven (Model L-7300, HITACHI) and UV detector (Model L-7400, HITACHI) set at 254 nm wavelength. The detector signal was recorded on a recorder (Model D-7500, HITACHI). The chromatographic column was a 7.8 300 mm i.d. Gelpack C18 (GL-C610H-S, HITACHI). A 0.3% metaphosphoric acid solution was used as mobile phase. An AA standard curve was prepared, using solutions containing 25, 50, 75, and 100 lg/ml. The standard solution was injected into the HPLC system and the corresponding peak area was obtained (Diamante, Ishibashi, & Hironaka, 2002). 2.7. Statistical analyses All analyses were performed six times, and results were averaged to obtain mean values. Duncan’s multiple range test of SPSS (1992) was used to determine differences between means of vacuum time, cooking treatment or storage time. 3. Results and discussion
2.3. VI treatment of ascorbic acid
Fig. 1 shows the impregnation of red ink into a potato without a vacuum. No impregnations occurred in the potato during immersion. Thus, immersion treatment alone could not cause impregnation into the potato. Fig. 2 shows the impregnation during restoration. Potatoes, just after the vacuum treatment, had no impregnations into the potato, but those after 3 h of restoration had impregnation. Therefore, Figs. 1 and 2 indicate that the
VI treatment of whole potatoes (Toyoshiro and Irish Cobbler) was carried out in a 10% ascorbic acid solution. A mass ratio, of the solution to potato, of 3% w/w was used to ensure adequate immersion and minimise the dilution effect on the concentration of VI solution (Sormani, Maffi, Bertolo, & Torreggiani, 1999). A vacuum pressure of 9.33 kPa was applied to the system for 0–60 min, and atmospheric pressure restoration for 3 h. Whole potatoes were drained, rinsed with distilled water to remove the attached solution, and gently blotted with tissue papers. Ascorbic acid contents of impregnated and untreated (fresh as control) potatoes were analysed immediately.
Fig. 1. Immersion of whole potato tuber (Toyoshiro variety) in a red ink solution without vacuum.
1116
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
Fig. 2. Impregnation of red ink into whole potato tuber (Toyoshiro variety) by restoration.
impregnation into a potato tuber requires both vacuum and restoration treatments. Fig. 3 shows photographs of the impregnation potato of 1 h vacuum plus 3 h restoration treatment, and the 4 h immersion potato. This Figure indicates that the impregnation occurred almost at the central pith and the areas between the vascular ring and the periderm. Concerning the pith and vascular ring of potato, Artschwager (1924) reported that the pith forms the narrow central core of the tuber, but is continuous with eyes by means of lateral branches, and the vascular ring (as it appears to the naked eye) constitutes a narrow band of tissue that contains the xylem and the secondary phloem. While potatoes have a thick periderm to prevent rapid water loss from the thin-walled parenchyma of the tuber (Peterson et al., 1985), they have 74–141 lenticels per tuber (Wigginton, 1973). Lenticels provide permeable regions (Cutter, 1991). For example, Burton (1965) found an O2 permeability value of 2.5 mm3 cm 2 h 1 kPa 1for mature tubers. When a potato is immersed in a physiologically active compound (PAC)-concentrated solution under vacuum conditions, air might be extracted from the eyes and lenticels and then, when atmospheric pressure is restored, the impregnation penetrates the intercellular spaces of porous tissues through the eyes and lenticels by capillary action and by the pressure gradients (i.e., the hydrodynamic mechanism) that are imposed on the system, helping incorporation of PACs (Fito, 1994). So, the strong impregnation of red ink in the tuber was found at the central pith and the areas between the vascular ring and the periderm, as shown in Fig. 3. As shown in Fig. 4, the AA content of VI potato (Toyoshiro) increased with vacuum time. The 60 min VI potato had a 21 times higher (p < 0.05) AA content than had raw potatoes. In addition, VI potatoes (per 100 g), beyond 30 min of vacuum time, had an AA content in excess of the FAO value (45 mg/day). One hundred grammes of sixty min VI treatment-potatoes, in particular, had a 150 mg AA content. In Europe, daily potato uptake per capita, in 2005, was 260 g, followed by North America (160 g) (Keijbets, 2008). Thus, in these areas, daily potato consumptions of VI potatoes can exceed RDA value (100 mg/day) (Naidu, 2003).
Fig. 3. Impregnation of red ink into whole potato tuber (Toyoshiro variety) by restoration.
Fig. 4. Effect of vacuum time on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Toyoshiro variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
The AA content of the Irish Cobbler also increased with vacuum time (Fig. 5). The 60 min VI potato had a nine times higher (p < 0.05) AA content than had raw potatoes. Moreover, VI potatoes (per 100 g), beyond 30 min of vacuum time, had AA contents higher than the FAO value (45 mg/day). Especially, 60 min VI potatoes (100 g) had AA contents higher than the RDA value (100 mg/day) (Naidu, 2003). Concerning the vacuum time of VI treatment for vegetables and fruits, Gras, Vidal, Betoret, Chiralt, and Fito (2003) used a pressure of 50 mbar and a vacuum time of 10 min for impregnation of calcium to cylindrically cut eggplants and carrots. Guillemin, Degraeve, Noel, and Saurel (2008) performed a sodium chloride and/or sodium alginate VI treatment under 0.05 bar for 2 min, for apple cubes, in order to improve the firmness. Sapers Garzarella, and Pilizota (1990) used a 2 min vacuum time, at 169–980 mbar pressures, for NaCl VI treatment of diced or strip potatoes. However, compared with the above studies, a long vacuum time was needed for whole potatoes in the present study (Fig. 1). This long time for VI treatment may be due to the thick periderm of whole potatoes which is less permeable to water and gas (Peterson et al., 1985). Fig. 6 shows the decrease in AA content of VI potatoes (Toyoshiro) by steam-cooking. As shown in this Figure, steam-cooking Toyoshiro
Fig. 5. Effect of vacuum time on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Irish Cobbler variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
Fig. 6. Effect of steam-cooking on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Toyoshiro variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h; steam-cooking temperature and time, 100 °C, 25 min. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
potatoes resulted in a 42% decrease in AA content. However, VIcooked potatoes had 22 times higher (p < 0.05) AA contents than had un-VI-cooked potatoes. In addition, VI-cooked potatoes of 100 g had a 90 mg AA content, which is over twice the FAO value (45 mg/day) (Naidu, 2003). For the Irish Cobbler (Fig. 7), the AA content of VI-cooked potatoes decreased by 33%. However, VI-cooked potatoes had eight times higher (p < 0.05) AA contents than had un-VI-cooked potatoes. Moreover, VI-cooked potatoes of 100 g had a 100 mg AA content, which is over twice the FAO value (45 mg/day) (Naidu, 2003). Concerning cooking loss of AA of potatoes, Burton (1989) reported a 10–15% AA loss for unpeeled-steamed potatoes. In the present study, an AA loss of over 33% was found in VI-cooked potatoes. As for calcium distribution in tissues of calcium VI-treated apple cylinders, Gras et al. (2003) reported that calcium incorporation mainly occurred in the intercellular spaces. Thus, AA also may be located in intercellular spaces in the present study. Peterson et al. (1985) indicated that the lenticels of potatoes allow excess water loss from the internal tissues of the tuber. Therefore, the large loss of AA content in the present study might be due to loss through the lenticels from the intercellular spaces. Further study is therefore needed on AA distribution in the tissues of VI potatoes. AA content of VI potatoes decreased with storage time (Fig. 8). With respect to the decrease in AA content of stored potatoes, Shekhar, Iritani, and Arteca (1978) reported that tubers stored at
1117
Fig. 8. Change in AA content of VI whole potato tuber (Irish Cobbler variety) during storage at 5 °C: VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
5.5 °C showed a marked reduction in ascorbic acid levels. Also, during storage at 10 °C, there was a sharp initial decline in AA levels (Augustin et al., 1978; Keijbets, 1984) in tubers having a high concentration; for example, some immature tubers showed the most marked decrease. Such losses amount to 33% over 3–4 weeks at 10 °C for the mature King Edward potato, compared to 10% loss for mature crops (Burton, 1989). Also, VI potatoes with a high AA content may result in the marked loss observed in the present study. While VI potatoes had a decrease in AA content during storage, they had an AA content 10 times higher (p < 0.05) than un-VI potatoes. In addition, VI potatoes (per 100 g) had a high AA content, in excess of the FAO value (45 mg/day) (Naidu, 2003), even after 14 storage days. When these potatoes are cooked, AA contents might decrease by 40%. However, the daily uptake of VI potatoes of 200 g exceeds at least the FAO value. VI of food matrices with adequate solutions/suspensions of physiologically active compounds has been claimed as a useful way to obtain this kind of product, without destroying the initial food matrix, but only occupying its initial porous fraction (intercellular spaces) with a liquid phase (Fito et al., 2001). Thus, the liquid release from potato tubers by VI treatments might be small. However, further studies will be needed on actual nutritive losses by VI treatments (e.g. sugars, phenols). Finally, this study indicates that VI treatment of whole potatoes was useful for enriching the AA content of cooked or stored potatoes. The daily uptake of 200 g of VI potatoes by this method will be good for health because it exceeds the FAO value. 4. Conclusion The results from this study indicate that the VI treatment increased the AA content of whole potatoes ten times (150 mg/100 g fr. wt.). In addition, 100 g of the 25 min steam-cooked VI potatoes could provide adults with 90–100% of the recommended daily allowance of AA (100 mg). Moreover, the VI potatoes had a relatively high AA concentration (50 mg/100 g fr. wt.), even at 14 days of storage at 4 °C. This study indicated that VI treatment of whole potatoes was useful for enriching the AA content.
Fig. 7. Effect of steam-cooking on ascorbic acid (AA) content of vacuum impregnation (VI) whole potato tuber (Irish Cobbler variety): VI solution, 10% AA; vacuum pressure, 70 cm Hg; restoration time, 3 h; steam-cooking temperature and time, 100 °C, 25 min. Values are the means ± SD (n = 6). Different letters show significant differences at 0.05 probability.
References Alzamora, S. M., Salvatori, D., Tapia, M. S., Lo´pez-Malo, A., Welti-Chanes, J., & Fito, P. (2005). Novel functional foods from vegetable matrices impregnated with biologically active compounds. Journal of Food Engineering, 67, 205–214.
1118
K. Hironaka et al. / Food Chemistry 127 (2011) 1114–1118
Alzamora, S. M., Tapia, M. S., Leunda, A., Guerrero, S. N., Rojas, A. M., Gerschenson, L. N., et al. (2000). Minimal preservation of fruits: A cited project. In J. E. Lozano, C. Anon, E. Parada-Arias, & G. V. Barbosa-Canovas (Eds.), Trends in Food Engineering (pp. 205–225). Pennsylvania, USA: Technomic Publishing. Artschwager, E. (1924). Studies on the potato tuber. Journal of Agricultural Research, 27, 809–835. Augustin, J., Johnson, S. R., Teitzel, C., Toma, R. B., Shaw, R. L., True, R. H., et al. (1978). Vitamin composition of freshly harvested and stored potatoes. Journal of Food Science, 43, 1566–1574. Barbosa-Canovas, G. V., & Vega-Mercado, H. (1996). Osmotic dehydration of foods (pp. 265–288). Florence, Italy: International Thomson. Barnes, M. J., & Kodieck, K. (1972). Biological hydroxylations and ascorbic acid with special regard for collagen metabolism. Vitamins and Hormones, 30, 1–43. Bates, C. (1997). Bioavailability of vitamin C. European Journal of Clinical Nutrition, 51(Suppl. 1), S28–S33. Bird, T. A., Schwartz, N. B., & Peterkofsky, B. (1986). Mechanism for the decreased biosynthesis of cartilage proteoglycan in the scorbutic guinea pig. The Journal of Biological Chemistry, 261, 11166–11172. Bolin, H. R., & Huxsoll, C. C. (1993). Partial drying of cut pears to improve freeze– thaw texture. Journal of Food Science, 58, 357–360. Burgos, G., Auqui, S., Amoros, W., Salas, E., & Bonierbale, M. (2009). Ascorbic acid concentration of native Andean potato varieties as affected by environment, cooking and storage. Journal of Food Composition and Analysis, 22, 533–538. Burton, W. G. (1965). The permeability to oxygen of the periderm of the potato tuber. Journal of Experimental Botany, 16, 16–23. Burton, W. G. (1989). The Potato (pp. 447–449) (3rd ed.). London, UK: Longman. Burton, W. G., van Es & Hartmans, K. J. (1991). The physics and physiology of storage. In P. Harris (Ed.), Potato Crop (pp. 610) (2nd ed.). London, UK: Chapman & Hall. Cutter, E. G. (1991). Structure and development of the potato plant. In P. Harris (Ed.), Potato Crop (pp. 111) (2nd ed.). London, UK: Chapman & Hall. Dale, M. F., Griffiths, W., & Todd, D. (2003). Effects of genotype, environment, and postharvest storage on the total ascorbate content of potato (Solanum tuberosum) tubers. Journal of Agriculture and Food Chemistry, 51, 244–248. Diamante, L. M., Ishibashi, K., & Hironaka, K. (2002). Effect of temperature and water activity on quality deterioration and shelf life of dried mangoes. Annals of Tropical Research, 24, 60–81. Faller, A. L. K., & Fialho, E. (2009). The antioxidant capacity and polyphenol content of organic and conventional retail vegetables after domestic cooking. Food Research International, 42, 210–215. Fito, P. (1994). Modelling of vacuum osmotic dehydration of foods. Journal of Food Engineering, 23, 313–328. Fito, P., Chiralt, A., Betoret, N., Gras, M., Chafer, M., Martinez-Monzo, J., et al. (2001). Vacuum impregnation and osmotic dehydration in matrix engineering: Application in functional fresh food development. Journal of Food Engineering, 49, 175–183. Fito, P., & Pastor, R. (1994). Non-diffusional mechanisms occurring during vacuum osmotic dehydration. Journal of Food Engineering, 21, 513–519. Gras, M. L., Vidal, D., Betoret, N., Chiralt, A., & Fito, P. (2003). Calcium fortification of vegetables by vacuum impregnation interactions with cellular matrix. Journal of Food Engineering, 56, 279–284.
Guillemin, A., Degraeve, P., Noel, C., & Saurel, R. (2008). Influence of impregnation solution viscosity and osmolarity on solute uptake during vacuum impregnation of apple cubes (var Granny Smith). Journal of Food Engineering, 86, 475–483. Keijbets, M. J. H. (1984). Vitamin C during long-term storage of potatoes. Abst. 9th Triennial EAPR Conference (pp. 390–391). Keijbets, M. J. H. (2008). Potato processing for the consumer: Developments and future challenges. Potato Research, 51, 271–281. Levine, M. (1986). New concepts in the biology and biochemistry of ascorbic acid. The New England Journal of Medicine, 314, 892–902. Naidu, K. A. (2003). Vitamin C in human health and disease is still a mystery? An overview. Nutrition Journal, 2, 7–16. Peterson, R. L., Barker, W. G., & Howarth, M. J. (1985). Development and structure of tubers. In P. H. Li (Ed.), Potato Physiology (pp. 133). London, UK: Academic Press. Sapers, G. M., Garzarella, L., & Pilizota, V. (1990). Application of browning inhibitors to cut apple and potato by vacuum and pressure infiltration. Journal of Food Science, 55, 1049–1053. Sapers, G. M., Douglas, F. W., Ziolowski, M. A., Miller, R. L., & Hicks, K. B. (1990). Determination of ascorbic acid, dehydroascorbic acid and acid-2-phosphate: Infiltrated apple and potato tissue by high-performance liquid chromatography. Journal of Chromatography, 503, 431–436. Shekhar, V. C., Iritani, M., & Arteca, R. (1978). Changes in ascorbic acid content during growth and short-term storage of potato tubers (Solanum Tuberosum L.). American Potato Journal, 55, 663–670. Sloan, E. (2002). The top 10 functional food trends: The next generation. Food Technology, 56, 32–57. Sormani, A., Maffi, D., Bertolo, G., & Torreggiani, D. (1999). Textural and structural changes of dehydrofreeze-thawed strawberry slices: Effects of different dehydration pretreatments. Food Science and Technology International, 5, 479–485. SPSS (1992). SPSS for Windows Base System User’s Guide Release 5.0 (pp. 269–270). Chicago, USA: SPSS Inc.. Teucher, B., Olivares, M., & Cori, H. (2004). Enhancers of iron absorption: Ascorbic acid and other organic acids. International Journal for Vitamin and Nutrition Research, 76, 403–419. Weaver, M. L., Timm, H., & Ng, H. (1983). Changes in nutritional composition of Russet Burbank potatoes by different processing methods. American Potato Journal, 60, 735–744. Wigginton, M. J. (1973). Diffusion of oxygen through lenticels in potato tuber. Potato Research, 16, 85–87. Xie, J., & Zhao, Y. (2003a). Improvement of physicochemical and nutritional qualities of frozen Marionberry by vacuum impregnation pretreatment with cryoprotectants and minerals. Journal of Horticultural Science and Biotechnology, 78, 248–253. Xie, J., & Zhao, Y. (2003b). Nutritional enrichment of fresh apple (Royal Gala) by vacuum impregnation. International Journal of Food Science and Nutrition, 54, 387–398. Zhao, Y., & Xieb, J. (2004). Practical applications of vacuum impregnation in fruit and vegetable processing. Trends in Food Science and Technology, 15, 434–451.
