MINERAL COMPOSITION OF CEREAL BARS WITH ADDED DRIED VINIFERA GRAPE SKINS

Enhancing the mineral content of foods is an important strategy to improve nutritional quality. Grape skins, a by-product of the wine industry, are naturally rich in potassium and low in sodium, making them a promising ingredient to increase potassium levels and reduce sodium in cereal-based products. This study evaluated sodium (Na) and potassium (K) levels in cereal bars enriched with dried wine grape skins to assess their mineral contribution and potential as a value-added food ingredient. Four formulations were developed: a control (CCB), without the addition of grape skins; a 10% white grape skin (WCB); another with 10% red grape skin (RCB); and a mixed 5% of both (MCB). The white (WGS) and red (RGS) grape skins, derived from the Verdelho and Castelão cultivars, respectively, were also characterized separately. Both skins were obtained through mechanical pressing, without undergoing fermentation, and were dehydrated prior to incorporation into the cereal bars. The samples were mineralized in acidic solution using a microwave digestion system and analyzed by atomic absorption spectrometry. The results revealed significant variations, with a notably high potassium content in the formulations containing grape skins, especially in WCB (516.29 mg/100g), followed by MCB (472.98 mg/100g) and RCB (409.02 mg/100g). The control sample (CCB), although free of skins, showed 377.53 mg/100g, a value attributed to the presence of naturally potassium-rich ingredients such as oats, chia, flaxseed, sunflower seeds, and puffed rice. When analyzed separately, the pomaces also stood out, particularly WGS (1482.62 mg/100g) compared to RGS (966.48 mg/100g), a result explained by the inherently mineral-rich composition of grape skins, especially the white variety, and the concentration effect of dehydration. Regarding sodium, CCB exhibited the highest content (10.42 mg/100g), while the other formulations ranged between 7.30 and 8.48 mg/100g. No detectable sodium was found in either WGS or RGS, which explains the lower sodium concentrations in the bars containing skins. These findings reflect plant physiology, as plants tend to accumulate potassium in their metabolism, unlike sodium, which is more prevalent in industrialized foods and scarce in natural or minimally processed ingredients. The addition of grape skins resulted in a significant increase in potassium content, particularly in the WCB formulation, and a reduction in sodium levels, reinforcing the more balanced nutritional profile of these samples. Thus, the incorporation of grape pomace proves to be a viable strategy for enhancing the nutritional and functional value of the product.