Comparison of Different Hydrocolloids on the Novel Development of Muffins from “Purple Yam” (Dioscorea alata) Flour in Sensory, Textural, and Nutritional Aspects

Hydrocolloids can act as gluten substitutes to form the structural equivalents of the gluten network in gluten-free bakery products. “Purple yam” (Dioscorea alata) is one of the underutilized yams in Sri Lanka with high nutritional potential. The overall objective of this study was to develop gluten-free muffins using “Purple yam” (Dioscorea alata) flour with hydrocolloids (pectin, xanthan gum, and guar gum) and investigate the nutritional composition and selected properties of the muffins. The texture profiles of gluten-free muffins were analyzed through the following parameters: hardness, adhesiveness, cohesiveness, etc. The chromameter values were obtained and sensory evaluations for gluten-free muffins were carried out. The highest moisture content was recorded in pectin-incorporated muffins ( 17.70 ± 0.50 % ). The protein content of all three types of muffins was around 5%. The highest fat content was recorded in pectin-incorporated muffins ( 19.26 ± 0.51 % ). The ash content of all three types of muffins was around 2%. Potassium was the most predominant element found in each muffin. The hardness of guar gum-incorporated muffin ( 6379.3 ± 135.9 g ) was greater than that of the pectin-incorporated one ( 6082.3 ± 23.4 g ). Xanthan gum-incorporated muffins had significantly decreased cohesiveness ( 0.19 ± 0.04 ). The highest springiness was obtained in pectin-incorporated muffin ( 37.13 ± 1.61 mm ). The descending order of the chewiness of muffin is pectin − added > xanthan gum − added > guar gum − added sample. According to the sensory evaluation, pectin-incorporated muffin was the best as it had obtained the highest sum of ranks for appearance, color, taste, after taste, and overall acceptability.

Antioxidative Characteristics and Sensory Acceptability of Bread Substituted with Purple Yam (Dioscorea alata L.)

In this study, plain bread was made by substituting wheat flour with purple yam flour (Dioscorea alata, L). The addition of 0, 10, 15, 20, and 30% purple yam flour aims to increase the functional value of plain bread as a source of natural antioxidants. The bread produced with two baking temperatures (170°C and 180°C) was tested for anthocyanin levels, total phenol, antioxidant activity (DPPH free radical scavenging), volume expansion, color, and preference test. The results showed that the temperatures of the bread baking did not affect anthocyanin levels, total phenol, antioxidant activity, volume expansion, and bread color ( p > 0.05 ). The substitution of purple yam flour had a significant effect on anthocyanin levels, total phenol, antioxidant activity, volume, and bread color ( p < 0.05 ). The levels of anthocyanins, total phenol, antioxidant activity, and darker color increased with the addition of purple yam flower whereas the rate of expansion reduced. However, the addition of purple yam flour did not affect the level of preference for the bread produced. Purple yam flour can be added to the manufacture of bread made from wheat flour as much as 30% with a baking temperature of 180°C. The resulting bread contained total anthocyanins 54.62 mg/100 g db, total phenol 391.14 mg EAG/100 g db, antioxidant activity 48.53% and volume expansion 64.85%, color L ∗ = 53.06 , a ∗ = 6.52 , b ∗ = 13.32 , C = 14.87 , H = 64.06 , and sensory score = 3.24 (preferred).

Dioscorea alata as Alternative Culture Media for Fungal Cultivation and Biomass Production

Dioscorea alata (purple yam) is a tuber crop that contains plenty of nutrients. It is widely cultivated in Thailand, but it is underutilized. In this study, the suitability of purple yam to replace potato dextrose media for fungal growth was investigated. Mushrooms and molds were grown on purple yam dextrose agar (PYDA), whereas yeasts were cultured in purple yam dextrose broth (PYDB). Response surface methodology (RSM) with Box-Behnken design (BBD) was used to optimize the culture conditions for Saccharomyces cerevisiae biomass production. The growth profile of S. cerevisiae in PYDB under optimized culture conditions was also studied. All test mushrooms and molds recorded the highest colony diameter and mycelial dry weight on PYDA containing 40% purple yam. Similar to mushrooms and molds, yeasts in PYDB with 40% purple yam showed the highest number of cells. The growth of fungi on purple yam dextrose media was significantly higher than those on potato dextrose media under standard conditions. The optimal conditions from the RSM results for the biomass production of S. cerevisiae in PYDB were purple yam concentration of 49.61%, dextrose concentration of 4.87%, pH value of 5.74, and inoculum size of 7.00%. The biomass of S. cerevisiae in PYDB under the optimal conditions obtained from the results of the optimization by RSM was thirty times higher than S. cerevisiae biomass in potato dextrose broth under standard conditions. Our results suggest that purple yam could be an alternative to potato dextrose media for fungal cultivation.

Effect of steam-cooking on (poly)phenolic compounds in purple yam and purple sweet potato tubers

This study investigated the influences of steam-cooking on (poly)phenolic compounds and colors in purple yam (Dioscorea alata L.) and purple sweet potato (Ipomoea batatas) tubers cooked at the household level. Steam-cooking did not significantly change the contents of total phenolic compounds, flavonoids, anthocyanins and antioxidant capacity measured by ABTS radical scavenging assay in purple yam (P≥0.05), but lowered the antioxidant capacity measured by Crocin assay (P<0.05). The liquid chromatograph– mass spectrometer–Ion Trap–Time of Flight (LCMS-IT-TOF) indicated the degradation of high MW alatanin B to lower MW alatanins due to the loss of glucose units. Purple sweet potato, however, responded to steam-cooking differently from purple yam (P<0.05). Steam-cooking drastically increased total phenolic compounds, flavonoids, anthocyanins, antioxidant capacities, and retained the vivid reddish-purple color of cooked purple sweet potato (P<0.05). The stability of polyphenolic compounds in starchy tubers against steam-cooking at the household level was, in part, due to the different contents of indigenous phenolic compounds in the raw tubers.