Recommended daily fiber intake (25-38g) is often unmet due to modern diets heavy in processed foods. A link exists between diabetes and obesity, and a decline in dietary fiber and phenolic intake. Dietary phenolics (DPs) are associated with a lower risk of hyperglycemia and improved glucose homeostasis. Dietary fiber (DF) plays a crucial role in transporting DPs through the gastrointestinal tract, leading to the production of beneficial metabolites and an antioxidant environment in the colon. Agri-industrial residues, rich in DF and DPs, have shown positive effects on endothelial function, relevant to obesity, diabetes, and metabolic syndrome. Fruit and vegetable pomace, a byproduct of juice production, is a valuable source of DF and DPs, depleted of easily available sugars. A recently developed technology for producing pomace flour from minimally processed pomace offers good stability during storage. Previous studies have shown that apple and beetroot pomace flour (APF and BPF) supplementation reduces glycemia, improves glucose tolerance, and decreases body weight gain in mice. APF and BPF, as gluten-free flours, can be incorporated into various food products. This study aimed to develop innovative jelly candies incorporating APF and BPF into different matrices (agar, pectin, gelatin) to create a healthier, functional treat while maintaining sensory appeal and texture, potentially offering a lower glycemic index than conventional products.

Existing research highlights the health benefits of dietary fiber and polyphenols, particularly in mitigating the risks associated with obesity and diabetes. Studies have demonstrated the positive effects of increased fiber and phenolic intake on glucose homeostasis and overall metabolic health. The role of dietary fiber in the transport and bioavailability of polyphenols has also been established. Several studies have explored the use of fruit and vegetable pomaces as sources of functional ingredients, but much less research is on the specific incorporation of pomace flour into confectionery products. Previous work has focused on incorporating other natural antioxidant sources such as pomegranate juice, rosemary, and propolis into jelly candies to boost their health benefits; however, limited work has focused on integrating whole pomace flour. This study addresses this gap, exploring the impact of apple and beetroot pomace flour on the nutritional profile, sensory attributes, and glycemic response of jelly candies.

Apple and beetroot pomace (AP and BP) were obtained from fruit processing plants. The wet pomace was industrially dried (under 55°C) and ground into flour (APF and BPF). A randomized experimental design used three gelling agents (agar, pectin, gelatin), two pomace flours (APF and BPF), and sucrose as a sweetener. Nine batches were produced, including three controls without flour addition. Proximate composition (moisture, protein, fat, carbohydrates, fiber), total and soluble fiber, cellulose, fructans, total polyphenolics (TPC), total flavonoids (TFC), betacyanins (Bc), betaxanthins (Bx), and antioxidant activity (DPPH and FRAP assays) were determined in fresh and nine-month-stored samples, after in vitro digestion following the INFOGEST protocol. Sensory analysis (appearance, texture, odor, taste) by a trained panel evaluated fresh and nine-month-stored samples. Texture analysis (hardness, springiness, cohesiveness) was conducted using a texture analyzer. In vivo glycemic index (GI) and glycemic load (GL) studies involved 10 non-diabetic adults consuming 25g of pectin-based jelly candies (control and enriched) followed by blood glucose measurements for 120 minutes to assess postprandial glucose response. Data analysis utilized t-tests and ANOVA with Tukey's HSD post-hoc test (p<0.05).

Both APF and BPF showed high dietary fiber content (Table 1). Jelly candies with APF and BPF had higher DF content (>3g/100g) and significantly lower carbohydrate-to-fiber ratios compared to controls (Figure 1, Table 2), although not reaching the recommended <10:1 ratio. In vitro digestion revealed significantly higher TPC, TFC, and antioxidant activity (DPPH and FRAP) in APF/BPF-enriched jellies compared to controls (Table 3). These bioactives showed good retention after nine months of storage (Figure 2, Table 3). Betacyanin and betaxanthin content also exhibited good retention (Table 4). Sensory analysis showed that APF/BPF-enriched jellies were sensory acceptable with pectin-based jellies receiving the highest scores (Table 5). Texture analysis indicated that APF and BPF affected texture, with pectin-based jellies exhibiting higher hardness (Table 6). In vivo studies revealed significantly lower postprandial glucose levels, area under the curve (AUC), and glycemic index (<55) for pectin jellies with APF/BPF compared to the control (Figure 3). These were categorized as low-GI foods.

This study successfully demonstrated the potential of APF and BPF to enhance the nutritional and functional properties of jelly candies. The use of whole pomace flour, rather than extracts, maximizes the retention of bioactives and simplifies the manufacturing process. The significant reduction in carbohydrate-to-fiber ratio, the high levels of polyphenols and betalains with good retention during storage, and the demonstrably lower glycemic response in vivo all support this. The results align with previous research showing the anti-obesity and anti-diabetic potential of dietary fiber and polyphenols. The findings contribute to the growing body of research on upcycling agricultural waste into value-added functional foods. Consumer acceptance is crucial in the food industry, and the sensory analysis confirms the acceptability of the developed jelly candies.

This research provides a novel approach to creating functional jelly candies by incorporating apple and beetroot pomace flour. The enhanced nutritional profile, including increased dietary fiber and bioactive compounds with good storage stability, along with the reduced glycemic response, makes these candies a healthier alternative. Future research could focus on replacing sucrose with alternative sweeteners to further enhance the health benefits and explore additional pomace sources and formulations.

The in vivo study involved a relatively small sample size (n=10). The study primarily focused on pectin-based jellies due to their superior sensory properties in the initial screening; therefore, generalizations to other gelling agents may be limited. Further research with larger sample sizes and a broader range of gelling agents is warranted to confirm these findings.