No abstract

Yam is a root and tuber climbing plant and main calorie source in some tropical regions of Africa. In this study, properties of fermented (brown) yam flour (FYF) and unfermented (white) yam flour (UYF) were compared with refined wheat flour (RWF). The yam flours were lower in protein (3.3%–5.9%), arabinoxylans (0.93%–1.40%), phytic acid (0.17–0.53 mg/g), phenolic acids (0.57–2.28 mg FAE/g), amylose (17.3%–22.6%), and fat (0.2%–0.4%) but higher in potassium 119–845 mg/100 g), ash (1.70%–2.21%), total starch (73.8%–74.2%) and fiber contents (6.8%–7.0%). All the samples exhibited high (>90) estimated glycemic index (eGI) values. However, FYF and UFY had significantly (p < 0.05) lower eGI than RWF. Thermal studies showed that FYF and UYF required more energy for gelatinization than RWF. Compared to RWF, FYF swelled more rapidly and retrograded faster. FYF had significantly (p < 0.05) higher gel firmness than RWF and UYF. Overall, the flours exhibited different characteristics which will impact functional and nutritional properties. Practical applications Yam is a staple crop grown in tropical and subtropical Africa, the Caribbean, South Pacific, and Asia. Increased utilization of local staple crops in production of composite flours or in food products can increase economic gain for farmers and local economies. The study of the functional characteristics of the yam flours would allow for the development of tailor‐made composite flours for production of many unique food products. These yam flours may also be of use in formulation of gluten‐free products, especially products such as cakes and pastry that don't require high gluten strength.

Mixtures of refined wheat flour (RWF) with flours from different sources could impact the functional qualities and shelf life of wheat-based products. Storage stability is one of the most critical factors for tortilla quality. Tortillas made from yam (Dioscorea sp.) wheat composite flours were characterized. RWF was substituted with 5%, 10%, 15%, and 20% of fermented yam flour-brown (FYF) and unfermented yam flour-white (UYF). Farinograph water absorptions of UYF-composite flours (65.5% -77.1%) were significantly (P < 0.05) higher than FYF-composite flour absorptions (60.5% -61.5%). During storage, moisture contents of composite flour tortillas increased while the RWF-tortilla decreased. Tortilla from FYF-composite flour exhibited greater strength (3.1 N at day zero on average) compared to UYF-composite tortillas (2.1 N at day zero on average), while UYF-composite flour tortillas had good extensibility and rollability properties. The properties and composition type and ratios of flour blends affected tortilla quality during the storage period. The substitution of RWF with 15% or 20% UYF would be more suitable for making tortilla with improved properties compared to that of FYF.