The functional dessert: Purple yam jam starch digestibility and prebiotic potential

• Purple yam jam has nondigestible oligosaccharides and resistant starches. • Lipid-amylose complex and retrograded starches comprised nondigestible portion. • Purple yam jam is among the foods with low glycemic index. • Purple yam jam enhances growth patterns of the probiotic Lacticaseibacillus casei. Purple yam jam (PYJ) is a dessert made from purple yam ( Dioscorea alata L.) tuber evaluated for its starch fractions. An in vitro gastrointestinal digestibility test parallel with an in vitro fermentation by a probiotic bacterium on undigested jam-supplemented medium were conducted. The estimated glycemic index (eGI) was determined due to the utilization of starch and sugar as ingredients and subsequently, the prebiotic potential of the nondigestible portion was tested. The PYJ has 31.09 % rapidly digestible starch, 26.30 % slowly digestible starch, and 42.61 % resistant starch (RS). It has a hydrolysis index of 24.17 and an estimated glycemic index of 53.00. The formulated purple yam jam is therefore classified as among the low eGI foods category (eGI < 56.00). The probiotic bacteria Lacticaseibacillus casei exhibited better growth characteristics in medium supplemented with undigested jam portion than in medium with inulin as sole carbon source. L. casei has better growth characteristics in jam-supplemented medium based on growth rate (0.08 h −1 in jam-supplemented medium versus 0.06 h −1 in inulin medium) and doubling time (8.64 h in jam-supplemented medium versus 11.29 h in inulin medium). The prebiotic activity score of undigested purple yam jam is 0.77 which qualifies the dessert to be included in prebiotic foods having the ability to enhance the growth of beneficial bacteria while suppressing the growth of potentially pathogenic enteric bacteria. It was concluded that purple yam jam is a functional food with its low eGI and its prebiotic potential.