Effect of short-term storage on phenolic content,o-diphenolase and peroxidase activities of cut yam tubers (Dioscorea sp)

The effect of short-term storage on the protein, phosphorus and phenolic content as well as peroxidase and o-diphenolase activities of cut, harvested Jamaican yam (Dioscorea sp) tubers (D rotundata. D alata and D cayenensis) was studied. There was an initial increase in the total phenolic content up to the third week of storage followed by a gradual decrease to the sixth week. Phenolic content was found to be highest in D cayenensis followed by D rotundata and D alata. The activities of peroxidase (EC 1. 11. 1. 7) and o-diphenolase (EC 1. 10.3.1) increased steadily up to the third week of storage and thereafter decreased to the fifth week. The intensity and rapidity of browning in tubers when cut, correlated very closely with the tuber o-diphenolase and phenolic content levels while the onset of rotting correlated with the peroxidase activity levels in the species studied.     

Biochemical composition and storage of Jamaican yams (Dioscorea sp)

Dioscorea yam tubers of 11 cultivars from five common species grown in Jamaica were analysed for the following: protein content, total phenolics, vitamin C, total lipids, fatty acid composition and activity of the polyphenol oxidase enzyme. The results show that the yams grown in Jamaica are of good nutritional value with considerable amounts of protein, vitamin C, low lipids with only one cultivar ‘renta yam’ (D alata) possessing high levels of phenolic compounds. The fatty acids present in the total lipid extracts show that yam tubers generally possess high levels of saturated fatty acids mainly palmitic acid. However, the species D alata (cv white yam) and the species D trifida (cv yampie) have high levels of the unsaturated fatty acid, linolenic. All the polyphenol oxidases from the 11 cultivars show activities towards the diphenol substrates, catechol and DL-DOPA (DL-3,4-dihydroxyphenylalanine). However, no oxidation was observed with L-tyrosine, a monophenol substrate. All cultivars studied were found to have different lengths of dormancy which varied with storage conditions. When the harvested tubers were washed, sunned and stored at 20?C in a dark cupboard, it was possible to extend their lengths of dormancy by a further 11 weeks.     

Physicochemical changes occurring during post-harvest hardening of trifoliate yam (Dioscorea dumetorum) tubers

Processing of Dioscorea dumetorum tubers into flour could be a means of adding a longer-term value to this tropical plant with a high nutritional potential but which presents a post-harvest hardening problem. This study was carried out in order to investigate the effect of storage under prevailing tropical ambient conditions (19–28 °C, RH 60–85%) for 56 days on the physicochemical characteristics of flours produced from hardened tubers. With the exception of bulk density, the results showed that all the physicochemical properties measured (water absorption capacity, oil absorption capacity, water solubility index, hydrophilic–lipophilic index, swelling capacity and least gelatinising concentration) were significantly influenced by tuber storage time (P<0.05). In general, the physicochemical indices increased with storage in at least two phases, from days 2 to 21 and from days 28 to 56. Since sprouting of most tubers was observed after 28 days of storage, the results suggest that post-harvest hardening and sprouting influence the above-mentioned indices of flours produced from D. dumetorum tubers.     

穿龙薯蓣微晶纤维素的制备及其理化性质研究

以提取皂苷后的穿龙薯蓣残渣为原料,分离纯化得到纤维素,经过水解制得微晶纤维素(MCC)。用化学方法测定样品中MCC的含量及其聚合度,并采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)表征所制备的MCC的理化性质。实验结果表明:利用穿龙薯蓣残渣制得的样品中MCC为 91.7%、聚合度为164、结晶度为 77.1%、平均颗粒大小为 23.21 nm,这些参数与台湾明台101QD型MCC对照品的测试结果相符合。     

Genetic diversity of organoleptic properties in water yam (Dioscorea alata L)

Improving the food quality of yams (Dioscorea spp) is an ongoing challenge to yam breeders and researchers. Forty accessions of D alata were evaluated for the suitability of their tubers for the preparation of two dominant food forms (boiled and pounded) as part of an effort to identify potential parents for use in genetic improvement. Trained panellists were presented with randomised, replicated and coded samples of boiled yam tuber pieces and asked to rate them for mealiness, colour, wetness, softness and taste. The sensory attributes considered for pounded yam (dough from boiled and pounded tubers) were consistency, colour, sheen, smoothness, stickiness, elasticity and hardness. Ratings were based on hedonic scales. Cluster analysis revealed groupings of accessions into eight and nine similarity clusters for boiled yam and pounded yam respectively. The mean scores for general preference were regressed on individual attribute scores. Mealiness, colour and taste were important in the general preference for boiled yam. Consistency, colour and stickiness determined the general preference for pounded yam. Of the accessions, 67% were identified as being suitable for preparation as a boiled vegetable, while 55% were assessed to be good for pounded yam, based on the respective quality attributes evaluated. © 2003 Society of Chemical Industry     

山药多糖研究进展

山药是药食兼用植物,山药多糖被认为是山药中重要的活性物质。综述山药多糖的提取分离工艺、纯化方法,化学结构分析和生理活性研究的现状,为未来研究山药多糖的新提取工艺,探讨构效关系,作用机制提供参考。     

三种山药药理活性成分及其矿物元素分析

为比较不同种类山药的活性成分,本项研究选取三个市售山药品种进行分析检测。分别测定了乡山野淮、铁棍山药、参薯三种山药中的总皂苷含量和总多糖含量,并利用电感耦合等离子体发射光谱法（ICP-OES）对这三种山药中的9种矿物元素进行了测定。测量结果显示,山药总皂苷含量在0.01%⁰.05%之间,由高到低依次为乡山野淮、铁棍山药、参薯;总多糖含量在1.14%³.82%之间,由高到低依次为参薯、铁棍山药、乡山野淮。铁棍山药的硒含量为205.0μg/kg,参薯和乡山野淮的锌元素含量为3.9 mg/kg和4.1 mg/kg,均高于全国代表值。综合比较可得,乡山野淮皂苷含量高,参薯多糖含量高,而铁棍山药综合了二者的优点且微量元素尤其是硒丰富,品质优异突出。由此可以根据不同目的进行开发利用。      

Characterization of new starches separated from different Chinese yam (Dioscorea opposita Thunb.) cultivars

The starches separated from four different Dioscorea opposita Thunb. cultivars were investigated for morphological, thermal, crystal, and physicochemical properties, such as amylose content, swelling power, solubility and water-binding capacity properties. Amylose content of D. oppositastarches from different cultivars ranged from 20.74% to 25.94%. The shape of starch granules separated from different D. opposita Thunb. cultivars varied from round to oval or elliptic. The mean particle diameter of starches ranged from 23.39 to 26.87 μm. The transition temperatures (T_o, T_p and T_c) and enthalpy of gelatinization (ΔH_gel) were determined using differential scanning calorimetry (DSC). T_o, T_p and T_c varied from 73.6 to 74.8, 78.8 to 81.0, and 83.3 to 87.2 °C, respectively. D. opposita cv. Jinchengerhao starch showed the highest ΔH_gel values (12.48 J/g) while D. opposita cv. Baiyu starch showed the lowest values (8.413 J/g). The crystal type of starches separated from different D. opposita cultivars was a typical C_B-type pattern. The degrees of crystallinity of the four D. opposita cultivars starches were about 50.52%, 32.99%, 33.57% and 36.16%, respectively.     

半纤维素辅助提取黄姜色素的研究

通过单因素及正交试验研究了半纤维素酶对黄姜色素提取的影响。酶法提取的最佳工艺条件为:酶加量为7.0 mg/gp、H 4.3、酶处理时间4.0 h、酶处理温度45℃。     

盾叶薯蓣糖化液发酵生产2,3-丁二醇

利用克雷伯氏杆菌以盾叶薯蓣糖化液为底物发酵生产2,3-丁二醇(2,3-BD),考察了2,3-BD浓度、生产强度、有机酸生成及代谢流量分布情况. 结果表明,盾叶薯蓣中的有机酸成分能促进三羧酸循环途径和乙酸途径的代谢流,减弱琥珀酸途径的代谢流,从而提高2,3-BD的浓度. 以盾叶薯蓣糖化液为底物,采用批式流加方式,补加固体葡萄糖,发酵56 h,发酵液中2,3-BD最终浓度达到80.20 g/L,乙偶姻与2,3-BD浓度之和最终达到86.19 g/L,生产强度达到1.54 g/(L×h),比单独以葡萄糖为底物时分别提高了8.50%, 7.38%和7.69%.