A Frontier Review of Nutraceutical Chinese Yam

Yams are the edible subterranean rhizomes, or tubers, of plants from the genus Dioscorea. There are approximately 600 species of yam plants in the world, with more than 90 of these growing in East Asia. One particular species, Dioscorea opposita Thunb., is highly praised as "the Chinese yam". This distinction arises from millennia of storied history, both as a nutritional food source and as a principal ingredient in traditional Chinese medicine. Among the many cultivars of Dioscorea opposita Thunb., Huai Shanyao has been widely regarded as the best. This review surveyed the historical background, physiochemical composition, applications as food and medicine, and research prospects for the Chinese yam. Modern science is finally beginning to confirm the remarkable health benefits of this yam plant, long-known to the Chinese people. Chinese yam promises anti-diabetic, anti-oxidative, anti-inflammatory, immunomodulatory, anti-hyperlipidemic, anti-hypertensive, anti-cancer, and combination treatment applications, both as a functional food and as medicine.

Impact of Sulfur Fumigation on the Chemistry of Dioscoreae Rhizoma (Chinese Yam)

Dioscoreae Rhizoma (Chinese yam; derived from the rhizome of Dioscorea opposita Thunb.) (DR), commonly consumed as a food or supplement, is often sulfur-fumigated during post-harvest handling, but it remains largely unknown if and how sulfur fumigation impacts the chemistry of DR. In this study, we report the impact of sulfur fumigation on the chemical profile of DR and then the molecular and cellular mechanisms potentially involved in the chemical variations induced by sulfur fumigation. The results show that sulfur fumigation significantly and specifically changed the small metabolites (molecular weight lower than 1000 Da) and polysaccharides of DR at both qualitative and quantitative levels. Multifaceted molecular and cellular mechanisms involving chemical transformations (e.g., acidic hydrolysis, sulfonation, and esterification) and histological damage were found to be responsible for the chemical variations in sulfur-fumigated DR (S-DR). The research outcomes provide a chemical basis for further comprehensive and in-depth safety and functional evaluations of sulfur-fumigated DR.

Optimization of Microwave Coupled Hot Air Drying for Chinese Yam Using Response Surface Methodology

The effect of microwave coupled hot air drying on rehydration ratio (RR) and total sugar content (TSC) of Chinese yam was investigated. Single factor test and response surface methodology were used for process parameter optimization with hot air temperature, hot air velocity, slice thickness, and microwave power density as variables and RR and TSC of dried products as responses. The effect of variables on RR followed the order: slice thickness > hot air temperature > microwave power density > hot air velocity. The effect of variables on TSC followed the order: slice thickness > microwave power density > hot air velocity > hot air temperature. The optimized process parameters were hot air velocity of 2.5 m/s, hot air temperature of 61.7 °C, slice thickness of 8.5 mm, and microwave power density of 5.9 W/g. Under the optimal conditions, the predicted values of RR and TSC were 1.90 g/g and 5.74 g/100 g, respectively, which is very close to corresponding actual values (1.83 g/g and 5.72 g/100 g). The desirability of 0.913 further validated the effectiveness of the model. The findings from this work may apply to other agricultural products.

Freeze-drying changes the structure and digestibility of B-polymorphic starches

Starch granules both isolated from plants and used in foods or other products have typically been dried. Common food laboratory and industry practices include oven (heat), freeze, and ethanol (solvent-exchange) drying. Starch granules isolated from maize (A-type polymorph) and potato (B-type polymorph) were used to understand the effects of different dehydration methods on starch structure and in vitro digestion kinetics. Oven and ethanol drying do not significantly affect the digestion properties of starches compared with their counterparts that have never been dried. However, freeze-drying results in a significant increase in the digestion rate of potato starch but not maize starch. The structural and conformational changes of starch granules after drying were investigated at various length scales using scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction, FTIR spectroscopy, and NMR spectroscopy. Freeze-drying not only disrupts the surface morphology of potato starch granules (B-type polymorph), but also degrades both short- and long-range molecular order of the amylopectin, each of which can cause an increase in the digestion rate. In contrast to A-polymorphic starches, B-polymorphic starches are more disrupted by freeze-drying, with reductions of both short- and long-range molecular order. We propose that the low temperatures involved in freeze-drying compared with oven drying result in greater chain rigidity and lead to structural disorganization during water removal at both nanometer and micrometer length scales in B-type polymorphic starch granules, because of the different distribution of water within crystallites and the lack of pores and channels compared with A-type polymorphic starch granules.