Variations in the nutritional profile and colour parameters of sweet potato varieties with different flesh colours: Effects of cropping system, mulching and growing season

The study investigated the effects of cropping system (CS), mulching (M) and year (Y) on the nutritional profile and colour parameters of four sweet potato varieties, namely Purple Speclet, Martina, Janja and Lučka. The results showed that the variations were mainly due to the genetic makeup of the varieties, with Purple Speclet having the highest dry matter, protein, vitamin C content, total phenolic content, antioxidant potential and total soluble solids. Lučka had the highest total sugar content, while Martina and Janja only stood out in terms of glucose content. The nutritional parameters correlated strongly with the colour parameters, suggesting that colour could be a useful indicator for predicting the nutritional quality of sweet potatoes. Nutritional parameters such as total phenolic content (TPC), vitamin C, antioxidant activity (AOP) and dry matter (DM) were significantly influenced by growing season, cropping system and mulching. The growing season had the greatest influence on TPC, vitamin C, AOP and DM. Mulching had the highest impact on DM, glucose content and vitamin C, while the cropping system had the highest impact on vitamin C, AOP and protein content. In particular, organic farming without PE mulching during the growing season resulted in higher levels of vitamin C, TPC and AOP, especially in relatively less favourable weather conditions. However, when PE mulch was used, there was a significant decrease in TPC and AOP. In contrast, no significant environmental influence was observed for the colour parameters, evidently differentiated in the purple-fleshed genotype with respect to the others, indicating that they are predominantly under strong genetic control. The results could help to introduce nutrient-rich sweet potato varieties into sustainable cropping systems and promote the production of sweet potatoes in Europe, particularly the Slovenian varieties Lučka, Martina and Janja, which have not been widely cultivated to date.