Ascorbic Acid and Dehydroascorbic Acid Content of Tropical Root Crops from the South Pacific

The total vitamin C content (ascorbic acid (AA) plus dehydroascorbic acid (DAA) was estimated by HPLC for sweet potato (Ipomoea batatas), taro (Colocasia esculenta), giant taro (Alocasia macrorrhiza), giant swamp taro (Cyrtosperma chamissonis), taro (Xanthosoma spp.), yam (Dioscorea alata), yam (D. esculenta), cassava (Manihot esculenta) and mean values were 23.6, 15.1, 16.9, 15.7, 13.6, 27.5, 20.3, and 14.9 mg/100g fresh weight, respectively. Standard titrimetric and colorimetric methods gave results only for AA which were generally comparable with HPLC. Drying at 40°C caused loss of AA which was not quantitatively converted into DAA. Storage of sweet potato at 25°C and 15°C for 28 days reduced the total vitamin C content by 17% and 15%, respectively; there was no significant decrease at 0°C. Cooking reduced the levels of AA and DAA by up to 70%.     

Thiamin, Riboflavin, and Nicotinic Acid Contents of Tropical Root Crops from the South Pacific

The thiamin, riboflavin, and nicotinic acid contents of sweet potato (Ipomea batatas, taro (Colocasia esculenta), giant taro (Alocasia macrorrhiza), giant swamp taro (Cyrtosperma chamissonis), taro (Xan-thosoma spp), yam (Dioscorea alata and D. esculenta) were determined for fresh and 40°C dried material obtained from six South Pacific countries. Losses on drying at 40°C for 2-3 days were 10-15% for the three vitamins. Sweet potato contained the largest amount of thiamin (40-120 μg/100g fresh weight) and along with Colocasia esculenta and Xanthosoma spp. the largest amounts of nicotinic acid. The root crops provided inadequate amounts of thiamin, riboflavin, and nicotinic acid with values ranging from 12-123, 12-59 and 220-1310 Hg/100g fresh weight, respectively. Losses on cooking were about the same for all vitamins and root crops, with about a 20% loss on boiling (water retained) or baking and about a 40% loss on boiling (water discarded).     

Trypsin inhibitor activity in vegetative tissue of sweet potato plants and its response to heat treatment

Trypsin inhibitor activity (TIA) and crude protein content of seven genotypes of sweet potato were investigated. There was considerable genotypic variation in TIA, with a four‐ to fivefold range in roots and a threefold range in stems. The mean TIA in stems at harvest time was 36% of that in roots, whilst the mean TIA in leaves was only 17% of that in roots. The TIA level in roots was correlated with that in stems (r = 0.83, p = 0.02) and leaves (r = 0.70, p = 0.08). In most genotypes the TIA level in vine‐tips was low during the early growth stage, increased from day 30 to day 110 after transplanting, then remained constant in subsequent growth stages. However, in genotype Guang 70‐9, vine‐tips had a high level of TIA at all growth stages. Sweet potato green tissue contained three‐ to fivefold more crude protein than roots. No correlation between TIA and crude protein in sweet potato roots was found across genotypes, but TIA was significantly correlated with crude protein content (r = 0.73, p = 0.06) in sweet potato vine‐tips. Moist heat treatment (MHT) was found to be effective in eliminating TIA in sweet potato. Most TIA in sweet potato green tissue and roots was eliminated by MHT at ≥80 °C, but heat stability was dependent on genotype. Guang 70‐9 had relatively highly heat‐stable trypsin inhibitor. The results suggested that screening for genotypes with high protein content and low TIA and use of an appropriate processing method could improve the utilisation of sweet potato for both human food and animal feed. © 2001 Society of Chemical Industry     

Composition and availability of soluble and insoluble oxalates in raw and cooked taro (Colocasia esculenta var. Schott) leaves

Taro (Colocasia esculenta var. Schott) is a major staple food crop in parts of Asia and the Pacific Islands and is grown as a minor crop in New Zealand. Soluble, insoluble and total oxalate content of young and older leaves were determined by HPLC following hot water (80 °C) and hot (80 °C) acid (0.2 mol/L HCL) extractions. Young taro leaves contained 589 ± 35.8 mg total oxalates/100 g fresh weight (FW) while older taro leaves contained (443 ± 15.0 mg total oxalates/100 g FW). Soluble oxalates were 74% of the total oxalate content of the young and old leaves.     

Determination of oxalates in Japanese taro corms using an in vitro digestion assay

An in vitro assay was used to extract gastric soluble and intestinal soluble oxalates from the corms of four different Japanese taro (Colocasia esculenta (L.) var. Schott) cultivars (Akame, Ishikawa-wase, Yamato-wase and an unnamed cultivar). The oxalate contents were measured in the raw tissue and after boiling and baking the corms.     

Determination of sugars in tropical root crops using 13C N.m.r. spectroscopy: Comparison with the h.p.l.c. method

The ¹³C nuclear magnetic resonance (n.m.r.) spectrum of sugars normally present in foods, viz. glucose, fructose, sucrose, maltose and raffinose contains resonances that are diagnostic of each sugar. The quantity of each sugar is determined by measurement of the ratios of the peak heights of the sugar resonances compared with peak height of an internal standard, present at constant concentration in all solutions. A linear calibration relationship between the peak height ratio and concentration is established for single resonances of glucose and fructose and for two resonances of each of sucrose, maltose and raffinose. Samples of sweet potato and taro flour dried at 40°C, were blended with 80% ethanol, the sugars were extracted and analysed by ¹³C n.m.r. and h.p.l.c. Both methods gave similar results and have similar degrees of reproducibility. The n.m.r. method is useful for quantitation of sugars and identification of other molecules extracted from the food, but requires more material than does h.p.l.c. Drying at 40°C causes a decrease in sucrose content and increases in glucose, fructose and maltose which partly compensate for the loss in sucrose. There is considerable variability of the sugar content between different sweet potato tubers and between different taro corms of the same cultivar as well as across different cultivars. For sweet potato the total sugar content is 0.6-3.6% fresh weight, with considerably more sucrose present than glucose, fructose and maltose. With taro total sugar content is 0.2-0.8% fresh weight. Raffinose is present in one sample only.     

Effects of micronization on the physico‐chemical properties of peels of three root and tuber crops

BACKGROUND: The aim of this study was to investigate the effect of micronization on the physicochemical properties of the peels of root and tuber crops, including yam (Dioscorea alata L.), taro (Colocasia esculenta L.) and sweet potato (Ipomea batatas L.). Two continuous milling sections, including hammer milling and ball milling, were applied to three samples to obtain micro‐sized particles of root and tuber peels. The micronization by ball‐milling treatment for 10 h was carried out to investigate the distribution of particle sizes and the changes in physiochemical properties. RESULTS: The results indicate that the peels of three crops appeared to be significantly decreased in particle size after 10 h of ball‐milling treatment. Moreover, the ball‐milling treatments resulted in the redistribution of fiber components from insoluble fiber to soluble fiber. The micronization treatments decreased the bulk density but increased the solubility and water‐holding capacities of the micronized peels. CONCLUSION: Our findings suggested that micronization treatments can improve functional properties of the fiber components of micronized peels, which provide a good source of dietary fiber in food applications. Copyright © 2010 Society of Chemical Industry     

Taro Colocasia esculenta (L.) Schott Amylopectin Structure and Its Effect on Starch Functional Properties

Flour extracted from small‐, medium‐, and large‐corm taro Colocasia esculenta (L.) Schott cultivated in central Thailand had similar proximate composition, comparable calcium oxalate and amylose content, but different starch granule size and average chain length of amylopectin. Starch from the larger corm taro had a smaller average granule size and a lower average amylopectin chain length (CL_avg), a lower average external chain length (ECL_avg), and a lower average internal chain length (ICL_avg) when compared to that from the smaller corm taro. The solubility of taro starch was inversely proportional to CL_avg, ECL_avg, and ICL_avg. Starch having a shorter CL_avg, ECL_avg, and ICL_avg had a higher peak viscosity and breakdown. The onset (T_o), peak (T_p), and conclusion temperatures (T_c) of starch gelatinization and the extent of starch paste retrogradation did not correlate with the amylopectin structure.     

PRODUCTION AND CHARACTERISTICS OF TRADITIONAL ALCOHOLIC BEVERAGE MADE WITH SWEET POTATO AS THE SACCHARIFYING AGENT

Efforts were made to reproduce the traditional Japanese alcoholic beverage, miki using cooked rice and mashed raw sweet potato tubers as the saccharifying agent. The resulting miki-like alcoholic beverage contained 5–6% ethanol (v/v); it had a pleasant aroma but a sour taste with faint bitterness. With increased amounts of raw sweet potato added to the initial mash, the concentrations of higher alcohols, esters and bitter compounds in the miki increased. Oligosaccharides, including maltotetraose and maltopentaose, were detected in the miki made with higher concentrations of raw sweet potato mash. Miki, a previously uncharacterized, traditional, Japanese alcoholic beverage was therefore produced without the enzymic activities of germinating seeds, such as malt, or a fungal starter, such as koji .     

Effects of heat treatment on the quality and storage life of sweet potato

The effects of heat treatment (50 °C) on the sprouting inhibition and spoilage of sweet potato roots (curing temperature: 29 °C) stored in wrapper‐type cold store (WTCS) were determined during year‐long storage. The quality attributes of sweet potato were also evaluated. The results indicated that hot water treatment significantly inhibited sprouting and decay of sweet potato for the storage period. It also showed that there were no significant differences in starch properties in terms of pasting properties, enthalpy and temperatures onset (T_O), peak (T_P) and endset (T_E) of gelatinisation of sweet potato starches among all the treatments, especially between heat‐treated and without‐heat‐treated samples. Also, hot water treatment did not have any significant impact on the internal components' quality of the roots: less than 4% of the year‐long stored roots were discarded due to spoilage. Heat treatment supplied a lethal dose of heat to surface pathogens and cauterised the eyes without damaging the nutritional and processing qualities of sweet potato. The success of storage experiments in prolonging sweet potato stored in WTCS by heat treatment was obtained from the effective control of weight loss, sprouting and decay without influence on quality characteristics. This new technique opens a new avenue to prolonging the storage life of sweet potato with good quality and minimal loss. Copyright © 2006 Society of Chemical Industry     

Food group meat panel symposium annual discussion meeting—new developments in meat

An HPLC method was developed for the analysis of α-carotene, β-carotene, retinol and vitamin D2. Sweet potato Ipomoea batatas, taro Colocasia esculenta, taro Xanthosoma sagittifolium, giant taro Alocasia macrorrhiza, giant swamp taro Cyrtosperma chamissonis, yam Dioscorea alata and yam D esculenta contained no appreciable amounts of α-carotene, retinol or vitamin D2 and the amounts of β-carotene were equivalent to 0-300 μg kg-1 retinol in the fresh samples. This small amount, compared with the WHO/FAO adult RDA of 750 μg day-1, and the virtual absence of vitamin A related eye diseases in the South Pacific region, demonstrates the adequacy of greens and fiuits, and fish coastal areas, in meeting the vitamin A requirement.     

Effect of heat treatment on quality, thermal and pasting properties of sweet potato starch during yearlong storage

BACKGROUND: Proper postharvest handling and storage of sweet potato is an important link in the chain from producer to consumer or manufacturing industry. Heat treatments have been used as a non‐chemical means to modify the postharvest quality and reduce pathogen levels and disease development of a wide variety of horticultural products. The objective of this study was to investigate the effects of hot water treatment (HWT) on the quality, gelatinisation enthalpy and pasting properties of sweet potato starch during long‐term storage. The weight loss, sprouting, spoilage and sugar content of sweet potato were also determined. RESULTS: HWT significantly inhibited the sprouting and decay of sweet potato during the storage period. There were no significant differences (P < 0.05) in the pasting properties and onset (T_O), peak (T_P) and endset (T_E) temperatures of gelatinisation of sweet potato starch among all treatments, especially between heat‐treated and non‐heat‐treated samples. HWT also had no significant impact on the quality of the internal components of the roots. Less than 4% of the yearlong‐stored roots were discarded owing to spoilage. HWT supplied a lethal dose of heat to surface pathogens and black spot without damaging the nutritional and processing qualities of sweet potato. CONCLUSION: HWT was an effective method to reduce root sprouting and deterioration without significant impact on the quality of the internal components of sweet potato. This novel technique will open a new avenue to extend the storage life of sweet potato with good quality and minimal waste. Copyright © 2011 Society of Chemical Industry     

Composition and bioavailability of oxalates in baked taro (Colocasia esculenta var. Schott) leaves eaten with cows milk and cows milk and coconut milk

Taro leaves are an important food in the Pacific Islands but the overall oxalate composition and its nutritional effect has not been investigated. The oxalate contents of taro leaves were determined using chemical and in vitro extraction methods. Maori‐type taro leaves contained 524.2 ± 21.3 mg total oxalates 100 g^?1 fresh weight (FW) and 241.1 ± 20.9 mg soluble oxalates 100 g^?1 FW while the Japanese‐type leaves contained 525.6 ± 19.9 mg total oxalates 100 g^?1 FW and 330.4 ± 28.3 mg soluble oxalates 100 g^?1 FW. Maori‐type taro leaves contained 416.4 ± 1.5 mg gastric soluble oxalates 100 g^?1 FW and 212.4 ± 34.8 mg intestinal soluble oxalates 100 g^?1 FW while the Japanese‐type leaves contained 433.3 ± 9.7 mg gastric soluble oxalates 100 g^?1 FW and 224.2 ± 38.7 mg intestinal soluble oxalates 100 g^?1 FW). Human feeding experiments were conducted to determine the availability of the oxalates in the baked leaves following additions of cows milk and coconut milk. The consumption of a test meal of baked taro leaves resulted in a significant increase (P < 0.001) in the output of urinary oxalate in the following 6 h when compared to the output of oxalate during a reference collection. When the leaves were baked with cows milk or cows milk and coconut milk combined and consumed there was a small non‐significant reduction in urinary oxalate output which suggests that less soluble oxalate was absorbed from these mixtures.     

Added Value Improvement of Taro and Sweet Potato Commodities by Doing Snack Processing Activity

Tubers processing is one of efforts to support program on food diversification utilizing local foods. Introduction of processing technology of taro and sweet potato tubers to be flour and snack products (stick and chip) was done to disseminate the technology in farmer level in order to improve the commodities’ added value and later could improve farmer's welfare. The introduction was done in “Mekar Sari” women group in Bali on June up to December 2013. The result showed that women group can prepare good quality products by themselves. With R/C ratio is more than one, food processing activities are feasible to be done. By selling flour, prospective revenue accepted was IDR 85,125 or 3.4 times higher than selling fresh tubers and even could become IDR 191,906 or 7.7 times higher if they processed at least one of snack products (stick).     

Physicochemical properties and in vitro digestibility of flours and starches from taro cultivated in different regions of Thailand

This research aimed to study physicochemical properties and in vitro digestibility of flours and starches from taro cultivated in different regions of Thailand, that is, Kanchanaburi (KB), Chiang Mai (CM), Phetchaburi (PB) and Saraburi (SB). Taro starches were extracted from taro flours using either water or alkaline extraction. The taro flours had significantly (P ≤ 0.05) larger particle size, higher pasting and gelatinisation temperatures, and resistant starch content but lower total starch content, whiteness (L* value), paste viscosities and clarity than their corresponding extracted starches. All the taro starches exhibited polygonal and irregular granules and gave A-type X-ray diffraction pattern. The alkaline-extracted taro starches had significantly (P ≤ 0.05) higher extraction yield, total starch content, L* value, pasting and gelatinisation temperatures, and paste clarity but lower granular size, amylose content, resistant starch content, paste viscosities and relative crystallinity than their water-extracted counterparts.     

The incorporation of sweet potato application in the preparation of a rice beverage

Summary To increase the industrial applications of sweet potato, a rice beverage was prepared by adding barley sprouts, sweet potato, or a mixture of barley sprouts and sweet potato (1:1). Amylases from barley sprouts and sweet potatoes had a similar hydrolysis pattern to β‐amylase. Heat stability of this enzyme in sweet potato was higher than that in barley. Reducing sugar content in the mixture of barley sprouts and sweet potato was higher than in either barley sprouts or sweet potato alone. After the preparation of the rice beverage, the maltose content of the mixture with barley sprouts, either barley sprouts and sweet potato, or sweet potato was 37.2, 44.1 and 40.3 mg mL^?1 after 6 h, respectively. The amylase activity in the mixture with barley sprouts and sweet potato decreased more than that of the mixture with only sweet potato. The use of sweet potato resulted in an increase of sweetness, flavour and improved preference in rice beverage.     

芋头淀粉的分离和纯化

用重结晶法可以得到纯度较高的芋头直链淀粉和支链淀粉。直、支链淀粉的蓝值分别是1 1 8和 0 2 0 ,λmax分别为 61 4nm和 5 87nm ,芋头淀粉中直链淀粉含量为 1 4 7%。高效液相色谱表明 ,芋头支链淀粉的分子质量具有较宽的分布 ;重均聚合度 ,大米支链淀粉 >芋头直链淀粉 >大米直链淀粉 >芋头支链淀粉 ;分散度 ,芋头支链淀粉 >芋头直链淀粉 >大米直链淀粉 >大米支链淀粉 ;芋头支链淀粉中 ,长支链所占比例 >短支链 ;分散度 ,长支链 >短支链。     

不同芋头品种真空微波干燥品质变化的比较

分析8个不同芋头品种真空微波干燥前后营养成分的变化,比较不同芋头品种生产的芋头脆片色泽、硬度、脆度、膨化率、微观结构和感官品质等品质变化。结果表明:新鲜芋头含水量高达61.33~82.94%,奉化芋头含量最高;淀粉含量范围为15.87~30.25%,香沙芋含量最高;荔浦芋中的蔗糖最高,约为2.6 g/100 g,红香芋中的可溶性蛋白为1455 mg/100 g,明显高于其他品种。芋头片干燥后营养成分中除了蔗糖,其他含量均减少,且减少量差异显著,淀粉含量减少最多。不同品种的芋头真空微波干燥后品质差异明显,其中,荔浦芋、龙香芋、奉化芋头、槟榔芋和香沙芋亮度大、色差小,产品色泽保持良好;龙香芋和乌骨芋外形膨化且内部多孔状结构明显,硬度适中、酥脆性好;龙香芋、奉化芋头和乌骨芋的色泽、形态、口感、风味综合评分高,可接受程度明显高于其他芋头品种。     

A comparison of the hydrolysis of sweet potato starch with β-amylase and infrared radiation allows prediction of reducing sugar production

The apparent reaction rate constants (k) of the reaction that generates reducing sugar (presented as mg maltose equivalents) from raw sweet potato starch by using β‐amylase were determined by varying enzyme concentration, starch concentration and pH. The Arrhenius plot of the k‐value reached a peak at approximately 86 °C; the activation energy and frequency factor were also determined. Moreover, the amount of reducing sugar produced in sweet potato heated by infrared irradiation was estimated by using the values of k and the kinetic parameters. The calculated amounts of reducing sugar produced generally agreed with the experimental values. These results indicate that the amount of reducing sugar produced in heat‐treated sweet potato can be predicted by the methodology described in this study.     

抗坏血酸与壳聚糖处理对鲜切香芋贮藏效果的研究

以湖南香芋头为试材,研究不同浓度抗坏血酸与壳聚糖处理对鲜切香芋的贮藏效果及生理生化变化的影响。结果表明,在15℃贮藏温度下,与对照相比,0、1.0、5.0、10.0g/L 抗坏血酸(VC)分别与15.0g/L 壳聚糖配合处理较好地保持了鲜切香芋的外观和营养,减少鲜切香芋的失重率和褐变度,并抑制多酚氧化酶(PPO)、过氧化物酶(POD)和淀粉酶的活性。其中,5.0g/L 抗坏血酸与壳聚糖配合处理的保鲜效果最明显。