The effect of temperature, moisture content and pH during solid-state fermentation (SSF) of MD2 pineapple peel withRhizopus oryzae(MUCL 28168) was evaluated on the release of bioactive compounds with antioxidant capacity. Applying a central composite design, it was found that temperature had a significant effect (p < 0.05) on the total phenolic content and DPPH antioxidant activity while for the ABTS radical elimination activity, the factor that presented a significant effect was the pH (p < 0.05); as this factor increases, the antioxidant activity enhances. The optimal conditions for fermentation process were 80% of moisture content, pH 5.5, temperature 37.3 °C and 24 h of process to maximize phenolic content and antioxidant activity. Gallic acid, chlorogenic acid, caffeic acid and cinnamic acid were identified in the extracts by HPLC analysis. These results permit to conclude that SSF of pineapple peel is an effective bioprocess for the release of phenolic compounds with antioxidant activity.Graphical abstract

Antioxidant phenolic compounds were extracted from fermented samples of Golden pineapple peels via an ultrasound method. The fermentation conditions to maximize the production of phenolic content and antioxidant activity were previously determined (pH: 5.5, T: 37.3 °C and 85% moisture content). A central composite design with 20 treatments was applied to evaluate the effect of the ethanol concentration, time, and temperature on the production of phenolic compounds and antioxidant activity of the extracts. The statistical analysis showed that the optimal conditions to produce extracts with high phenolic content and antioxidant activity were: 62 °C, 30 min and 58% ethanol. We obtained 866.26 mg gallic acid equivalents (GAE)/g d.m in total phenolic content and for antioxidant activity expressed as percentage inhibition, 80.06 ± 1.02% for ABTS and 63.53 ± 2.02% for DPPH, respectively. The bioactive compound profile in the extracts was identified and quantified using ultra-high performance liquid chromatography (UHPLC), this method showed the presence of rosmarinic acid, caffeic acid, vanillic acid, p-coumaric acid, ferulic acid, quercetin-3 glucoside, rutine, quercetin, kaempherol-3 glucoside and gallic acid, demonstrating the great potential of these by-products to obtain components that can benefit the consumer’s health.

Recent research has highlighted the effectiveness of starter inocula in fermentation processes. In this sense, this study examines the use of an inoculum composed of coffee pulp, mucilage broth, and microorganisms such as Saccharomyces cerevisiae, L. delbrueckii ssp. bulgaricus, and S. thermophilus in fermenting Castillo variety coffee. An inoculum was prepared, measuring variables such as the pH, acidity, °Brix, lactic acid bacteria, and yeast viability. Following optimization, the inoculum was evaluated in a fermentation process, evaluating the pH, °Brix, acidity, microbiological analysis, ochratoxin A, and cup quality post-drying and roasting. The findings demonstrated a significant reduction in the pH from 4.47 to 4.05 and in the °Brix from 15.8 to 8.45, indicating efficient organic acid production and sugar degradation. Acidity levels increased from 20.02 mg/g to 42.69 mg/g, while microbial viabilities remained above 10⁷ CFUs/g, suggesting effective biomass production. The process effectively reduced the microbial load without detecting ochratoxin A. Sensory evaluations confirmed the enhanced cup quality, validating the positive impact of inoculum use in coffee fermentation. The results support the use of coffee pulp and mucilage broth as effective substrates for the growth of the evaluated microorganisms, and the application of starter cultures containing lactic acid bacteria and yeast can elevate the coffee to a specialty grade.

Utilizing coffee by-products in the fermentation process of coffee offers a sustainable strategy by repurposing agricultural waste and enhancing product quality. This study evaluates the effect of applying a starter culture, derived from coffee residues, on the dynamics of reducing and total sugars during coffee fermentation, as well as the composition of aromatic compounds, organic acids, and the sensory profile of coffee inoculated with yeast (Saccharomyces cerevisiae) and lactic acid bacteria (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus), in comparison to a spontaneously fermented sample. Volatile compounds were identified and quantified using dynamic headspace gas chromatography-mass spectrometry (HS/GC-MS), with predominant detection of 2-furancarboxaldehyde, 5-methyl; 2-furanmethanol; and furfural—compounds associated with caramel, nut, and sweet aromas from the roasting process. A reduction in sugars (glucose, fructose, and sucrose) occurred over the 36 h fermentation period. Lactic acid (2.79 g/L) was the predominant organic acid, followed by acetic acid (0.69 g/L). The application of the inoculum improved the sensory quality of the coffee, achieving a score of 86.6 in evaluations by Q-graders, compared to 84 for the control sample. Additionally, descriptors such as red apple, honey, and citrus were prominent, contributing to a uniform and balanced flavor profile. These findings indicate that controlled fermentation with starter cultures derived from coffee by-products enhances sustainability in coffee production. It achieves this by supporting a circular economy, reducing reliance on chemical additives, and improving product quality. This approach aligns with sustainable development goals by promoting environmental stewardship, economic viability, and social well-being within the coffee industry.

Phenolic compounds that are present in pineapple by-products offer many health benefits to the consumer; however, they are unstable to many environmental factors. For this reason, encapsulation is ideal for preserving their beneficial effects. In this work, extracts were obtained by the combined method of solid-state fermentation with Rhizopus oryzae and ultrasound. After this process, the encapsulation process was performed by ionotropic gelation using corn starch, sodium alginate, and Weissella confusa exopolysaccharide as wall material. The encapsulates produced presented a moisture content between 7.10 and 10.45% (w.b), a solubility of 53.06 ± 0.54%, and a wettability of 31.46 ± 2.02 s. The total phenolic content (TPC), antioxidant capacity of DPPH, and ABTS of the encapsulates were also determined, finding 232.55 ± 2.07 mg GAE/g d.m for TPC, 45.64 ± 0.9 µm Trolox/mg GAE for DPPH, and 51.69 ± 1.08 µm Trolox/mg GAE for ABTS. Additionally, ultrahigh performance liquid chromatography (UHPLC) analysis allowed us to identify and quantify six bioactive compounds: rosmarinic acid, caffeic acid, p-coumaric acid, ferulic acid, gallic acid, and quercetin. According to the above, using ionotropic gelation, it was possible to obtain microencapsulates containing bioactive compounds from pineapple peel extracts, which may have applications in the development of functional foods.