Pigmented rice varieties are abundant in phenolic compounds. Antioxidant activity and bioaccessibility of phenolic compounds are modified in the gastrointestinal tract. After in vitro simulated digestion, changes in antioxidant activity and bioaccessibility of phenolic compounds (phenolic acids, flavonoids, and anthocyanins) in purple rice brans (Hom Nil and Riceberry) were compared with undigested crude extracts. The digestion method was conducted following the INFOGEST protocol. Antioxidant activity was determined using the ferric-reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity assays. The bioaccessibility index (BI) was calculated from the ratio of digested to undigested soluble phenolic content. Overall results showed that the in vitro simulated digested rice brans had lower antioxidant activity and lower total phenolic, flavonoid, and anthocyanin contents. However, the concentration of sinapic acid was stable, while other phenolic acids (gallic, protocatechuic, vanillic, ρ-coumaric, and ferulic acids) degraded after the oral, gastric, and intestinal phases. The BI of sinapic, gallic, vanillic, and ferulic acids remained stable, and the BI of quercetin was resistant to digestion. Conversely, anthocyanins degraded during the intestinal phase. In conclusion, selective phenolic compounds are lost along the gastrointestinal tract, suggesting that controlled food delivery is of further interest.

Tropical fruit peels, frequently discarded during agricultural and food processing, represent an underutilized source of natural antioxidants and bioactive compounds. This study aimed to valorize tropical fruit peels, namely mango, banana, dragon fruit, pineapple, and papaya, by transforming them into functional food ingredients. Ethanol-based ultrasound-assisted extraction was applied to enhance the bioactive compounds and their antioxidant potentials. The variation in physicochemical characteristics, bioactive components, and antioxidant capacity of various fruit peel powders was investigated. 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric-reducing antioxidant power (FRAP), and total antioxidant capacity assays were used to evaluate the antioxidant activities. The qualitative method was used for the phytochemical screening. Additionally, reverse-phase high-performance liquid chromatography (RP-HPLC) analysis reveals their phenolic compositions. Then, the selected high-potential components were used to incorporate into biscuits. The digestion method was conducted following the INFOGEST protocol. Comparing all tested powders, the mango peel powder (MPP) had the highest total phenolic content (TPC) with 69.81 mg GAE g−1 and the highest antioxidant activity, which corresponded with the presence of gallic acid (13.95 mg g⁻¹), chlorogenic acid (9.62 mg g⁻¹), and quercetin (11.59 mg g⁻¹). The incorporation of MPP (5–15%) into biscuits improved nutritional composition and antioxidant potential while maintaining acceptable sensory characteristics at lower inclusion levels. Simulated in vitro digestion confirmed the retention and bioaccessibility of phenolics and flavonoids, indicating their functional relevance. This study addresses a gap in bioaccessibility and sensory acceptability of tropical fruit peel–fortified functional foods. This valorization framework also adopts circular economy principles, using residual biomass for composting. The findings demonstrate a green, scalable approach to transform fruit peel waste into health-promoting, functional ingredients aligned with sustainable food production.

Oxidative stress and inflammation are critical factors in hypertension and type 2 diabetes mellitus (T2DM). Kombucha, a fermented tea beverage, is enriched with bioactive compounds during fermentation. This study evaluated the antihypertensive, antihyperglycemic, antioxidant, and anti-inflammatory activities of kombucha made from mulberry leaf green tea (MLGT) and black tea (MLBT) during in vitro digestion. The bioaccessibility of 1-deoxynojirimycin (DNJ), γ-aminobutyric acid (GABA), phenolics, and flavonoids was assessed through simulated oral, gastric, and intestinal phases. MLGT kombucha exhibited higher initial antioxidant activity, while MLBT showed greater compound stability and ACE inhibitory activity during digestion. Notably, α-glucosidase inhibition declined significantly in the intestinal phase, in parallel with reduced DNJ and flavonoid content. Strong correlations were observed between specific phenolic acids and bioactivity profiles, highlighting ρ-coumaric and sinapic acids in ACE inhibition and DNJ in antiglycemic activity. These findings demonstrate the functional potential of mulberry leaf kombucha as a beverage to support metabolic health, pending confirmation through in vivo studies.

Food processing, including drying and cooking, generally influences the physical and chemical qualities of food products. The present study assessed the changes in oxalate contents of two rice paddy herbs (phak-kha-yaeng in Thai), Limnophila aromatica (phak-kha-yaeng khao) and Limnophila geoffrayi (phak-kha-yaeng daeng), as affected by different drying methods, namely hot-air, freeze and vacuum drying. The entire, soluble and insoluble oxalate contents of the cooked samples were also evaluated. Dried samples showed a significant increase in soluble oxalate content compared to fresh samples except for hot-air dried phak-kha-yaeng daeng, while entire and insoluble oxalate contents in dried samples were significantly decreased. Levels of soluble oxalates which were 30% in fresh phak-kha-yaeng khao and 46% in fresh phak-kha-yaeng daeng can be significantly reduced after cooking by boiling. In addition, the cooking of both the hot-air dried phak-kha-yaeng samples also showed greater losses in oxalates than those of other samples studied. Hot-air drying should be considered as a suitable drying method for phak-kha-yaeng with respect to reducing its oxalates. The present study has provided useful information for the drying of vegetables or plant foods to reduce the risk of consuming plant foods which contain high levels of oxalates.