Résumé
Aim: In several countries, lactofermented sweet potatoes are part of the traditional meal. However, a gap of knowledge was identified to increase sweet potato’s value chain and to develop food products of good nutritional quality. To proceed to lactofermentation, the use of amylolytic strains can increase the digestibility of sweet potato starch, while that of bacteria producing exopolysaccharides can improve the rheological properties and organoleptic quality of food. Hence, the objective was to isolate LAB with targeted properties to ferment sweet potatoes and to design functional foods from them.Method:Sweet potatoes cultivars were obtained from Vatel BRC (Biological Resource Collection, France). LAB were isolated and identified from sweet potatoes. The isolates plus 16 other LAB strains were then characterized with micro-tests of sweet potato fermentation. Amylolytic activity was screened with Bacillus subtilis used at positive control.Results:More than 80% of LAB isolates were identified as Leuconostoc mesenteroides. The strains all formed colonies on sweet potato plates and acidified the medium, but with variable growth and acidification levels. After 7 days, fermented sweet potato purée odor varied from unpleasant to pleasant, depending on the isolate, with five isolates among 29 leaded to pleasant smell. EPS production on sucrose MRS was detected for 10 L. mesenteroides isolates and 14 strains from the collection belonging to Leuconostoc and Weissella species. On sweet potato medium, only 6 sweet potato isolates and 11 strains from the collection were able to produce EPS. Moreover, mucoid appearance of the colony depended on the strain. Finally, no amylolytic activity was detected for any of the 13 isolates and only one strain from the collection hydrolyzed starch. Conclusion:On the basis of their ability to lacto-ferment sweet potato purée (growth and acidification capacity), to produce EPS and to degrade starch, one L. mesenteroides sweet potato isolate and two collection strains of the species Leuconostoc mesenteroides and Weissella cibaria were selected. They will be used to ferment sweet potato roots from different cultivars, in combination with different cooking methods. The process applied to sweet potato is expected to impact their composition, nutrient bioavailability and glycemic index.